Method and device for communication on a network

0001The present invention concerns a method and device for communicating on a network. It applies in particular to local wireless networks with centralised architecture, for which each communication is organised between a so-called base communication station, also referred to as the "fixed part", and a mobile communication station, also referred to as the "portable part".

0002An example of such a communication network is given by the telephones using the European DECT standard (initials of the English words "Digital Enhanced Cordless Telecommunication").

0003In such a local network, a base station supplies a synchronisation signal to all the mobile stations in the network. The set of stations (the base station and one or more mobile stations) which thus synchronise themselves with each other, constitutes a cell.

0004The communication capacity of a cell is fixed by the DECT standard. When this capacity becomes too low, it is known that a base station can be added, manually, so that a second cell is added to the first. However, in this case, the stations in different cells cannot communication with each other and the cells are fixed.

0005According to the DECT standard, a cell cannot automatically break itself down into several cells in order to increase the total communication capacity of all the stations.

0006When two mobile stations have to communicate with each other, they must each communicate with a base station, which doubles the passband requirement for the communication concerned.

0007The present invention sets out to remedy these drawbacks.

0008To this end, the present invention aims to allow the automatic breakdown of a cell into several cells by providing, on the one hand, that at least one mobile station is capable of functioning as a base station and on the other hand providing mechanisms enabling the initial base station to control the constitution of the new cell.

0009Thus, according to a first aspect, the present invention relates to a method of communication between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control signal then functioning in "mobile station" mode, characterised in that it includes, for at least one communication between two communication stations functioning in mobile station mode, in connection with a first base station: <ul id="ul0001" list-style="dash" compact="compact"><li>an operation of determining a second station, during which a communication station functioning in mobile station mode able to function in base station mode is determined,</li><li>a switching request operation during which a message representing a request to switch into base station mode is sent to the second station determined during the determination operation.</li></ul>

0010By virtue of these provisions, for the communication, a new base station will be sought. It should be noted here that the new base station can be one of the stations which is to communicate or a third station which has the capability of functioning as a base station.

0011According to particular characteristics, the second communication station performs, following reception of said message: <ul id="ul0002" list-style="dash" compact="compact"><li>an operation of determining agreement, or not, to function in base station mode, and</li><li>an operation of replying to the base station, during which the communication station transmits a message representing agreement, or not, to function in base station mode.</li></ul>

0012By virtue of these provisions, the communication station envisaged as the future base station can itself determine whether it accepts this role. Thus, when the initial base station is too partially or badly informed of the actual capability of the second communication station of operating in base station mode for the communication, an error can be avoided since it is the best informed communication station, the one which is intended to be the future base station, which finally decides.

0013According to particular characteristics, when at least one of the communication stations intended to communicate with each other is capable of functioning in base station mode, during the operation of determining the second station, one of the communication stations intended to communicate with each other and capable of functioning in base station mode is determined as the second station.

0014By virtue of these provisions, the cell can consist solely of two stations which are to communicate with each other, which simplifies the functioning of the network and makes it possible for the entire passband of the new cell to serve, without having to duplicate the transmitted information, as is the case when a communication between two mobile stations passes through a base station.

0015According to particular characteristics, when, following the switching request operation, the second station has switched into base station mode, said second station performs an operation of switching into mobile station mode, when the communication is terminated.

0016By virtue of these provisions, as soon as the communication is terminated, the cell in which this communication took place merges into the cell from which it came. Different mobile stations can then once again communicate with each other.

0017According to particular characteristics, when the passband necessary for a communication between two communication stations functioning in mobile station mode in connection with a first base station is greater than a predetermined value, there are performed, for said communication: <ul id="ul0003" list-style="dash" compact="compact"><li>the operation of determining a second station, and</li><li>the switching request operation.</li></ul>

0018According to other particular characteristics, when the passband necessary for a communication between two communication stations functioning in mobile station mode in connection with a first base station is not available for the first base station, there are performed, for said communication: <ul id="ul0004" list-style="dash" compact="compact"><li>the operation of determining a second station, and</li><li>the switching request operation.</li></ul>

0019By virtue of each of these provisions, the decision to create a new cell is dependant upon a passband criterion and resolves any passband problem which could arise for the communication itself or for a future communication request.

0020According to a second aspect, the present invention relates to a device for communication between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control signal then functioning in "mobile station" mode, characterised in that it has a processing means adapted, for at least one communication between two communication stations functioning in mobile station mode, in connection with a first base station: <ul id="ul0005" list-style="dash" compact="compact"><li>to determine a second communication station functioning in mobile station mode able to function in base station mode, and</li><li>to send, to the second station, a message requesting switching into base station mode.</li></ul>

0021The invention also relates to a network, a computer, a camera, a facsimile machine, a photographic apparatus, a television receiver, a printer, a scanner and an audio/video player, characterised in that they have a device as briefly disclosed above.

0022The invention also relates to: <ul id="ul0006" list-style="dash" compact="compact"><li>a means of storing information which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above, and</li><li>a means of storing information which is removable, partially or totally, and which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above.</li></ul>

0023The preferential or particular characteristics, and the advantages, of said device, said computer, said camera, said facsimile machine, said photographic apparatus, said television receiver, said printer, said scanner, said audio/video player and said information storage means being identical to those of the method as briefly disclosed above, these advantages are not repeated here.

0024When a station has the capability of behaving either as a base station or as a mobile station, this capability remains an exclusive item of information of said communication station, which prevents its use by the network.

0025The present invention sets out to remedy these drawbacks.

0026To this end, the present invention relates, according to a third aspect, to a method of communicating between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control signal functioning in "mobile station" mode, characterised in that it includes, performed by at least one communication station capable of functioning according to each of the modes, base station and mobile station, and of switch between these two functioning modes: <ul id="ul0007" list-style="dash" compact="compact"><li>an operation of determining the presence of a station functioning in base station mode, and</li><li>when, during the presence determination operation, it is determined that a station is functioning in base station mode, an operation of putting into communication with said base station and an operation of transmitting, to said base station, an item of information representing a capability of switching from one operating mode to another.</li></ul>

0027Thus the information concerning the capability of the mobile stations in a cell to become a base station can be used by a base station for: <ul id="ul0008" list-style="dash" compact="compact"><li>requesting such a mobile station to become a base station, when the covering base station is going to become inactive,</li><li>requesting such a mobile station to become a secondary base station in order to assist the initial base station to guarantee all the necessary communications internal to the cell.</li></ul>

0028More generally, the invention makes it possible to dynamically modify the configuration of the network and of its cell or cells.

0029According to particular characteristics, during the transmission operation: <ul id="ul0009" list-style="dash" compact="compact"><li>said item of information represents a capability of switching automatically between the two communication modes,</li><li>said information represents a capability of switching manually between the two communication modes,</li><li>said information includes an item of information representing a message specific to the initial proprietor of the communication system,</li><li>said information includes an item of information representing a memory capacity of said station,</li><li>said information includes an item of information representing a degree of filling of the memory of said station,</li><li>said information includes an item of information representing a processing capacity of a microprocessor of said station, and/or</li><li>said information includes an item of information representing a maximum data rate.</li></ul>

0030By virtue of each of these provisions, the knowledge of the capability of the communication station which supplies this information is precise.

0031According to a fourth aspect, the present invention relates to a device for communicating between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control station then functioning in "mobile station" mode, characterised in that it has a processing means adapted: <ul id="ul0010" list-style="dash" compact="compact"><li>to function according to each of the modes, base station and mobile station,</li><li>to switch between these two functioning modes,</li><li>to determine the possible presence of a station functioning in mobile station mode, and</li><li>when it has determined that a station is functioning in base station mode, to get into communication with said base station and to transmit to it an item of information representing a capability of switching from one functioning mode to another.</li></ul>

0032The invention also relates to a network, a computer, a camera, a facsimile machine, a photographic apparatus, a television receiver, a printer, a scanner and an audio/video player, characterised in that they have a device as briefly disclosed above.

0033The invention also relates to: <ul id="ul0011" list-style="dash" compact="compact"><li>a means of storing information which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above, and</li><li>a means of storing information which is removable, partially or totally, and which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above.</li></ul>

0034The preferential or particular characteristics, and the advantages, of said device, said computer, said camera, said facsimile machine, said photographic apparatus, said television receiver, said printer, said scanner, said audio/video player and said information storage means being identical to those of the method as briefly disclosed above, these advantages are not repeated here.

0035In a local wireless network with centralised architecture, for example of the type using the DECT standard, a base station can be switched off or switched automatically into mobile station mode, and a mobile station having the capability of becoming a base station may have to request going into base station mode in place of the current base station.

0036The document US-A-5 691 980 discloses how a master node of a network can detect an excessively low battery level and choose a new master node amongst slave nodes. It chooses the slave node having the best battery level. According to this document, it is the initial master node which determines its replacement. This document does not make it possible to take into account a system comprising heterogeneous portable terminals, as in a DECT network. In addition, according to this document, a slave node cannot take the initiative in becoming a master node.

0037The present invention sets out to remedy these drawbacks.

0038To this end, the present invention relates, according a fifth aspect, to a method of communicating between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode, and the stations not supplying a control signal then functioning in "mobile station" mode, characterised in that it includes: <ul id="ul0012" list-style="dash" compact="compact"><li>a request operation during which a first communication station transmits to a second communication station a message representing a request to change station functioning in base station mode.</li></ul>

0039By virtue of these provisions, a communication station functioning as a base station or a communication station functioning at a mobile station can require a change in organisation of the cell in order to improve its functioning or in order themselves to change functioning mode. The network can thus be reconfigured dynamically, taking into account various constraints, and optimise its functioning.

0040According to particular characteristics, during said request operation, the change request message includes an item of information representing the identity of a mobile station envisaged as a new base station.

0041By virtue of these provisions, the first station which requires the change in base station can determine and transmit the identity of the station envisaged as the new base station.

0042According to particular characteristics, the first communication station is the communication station functioning in base station mode, prior to the request operation.

0043According to other particular characteristics, the second communication station is a communication station envisaged for functioning in base station mode following a request operation.

0044By virtue of these provisions, the two partners in the communication are the two communication stations which envisage exchanging their role in the cell. This simplifies communication and avoids interfering with the other communication stations.

0045According to particular characteristics, the request operation is performed by the communication station functioning in base station mode prior to the request operation and the second communication station performs, following the reception of the message representing a request to change station functioning in base station mode: <ul id="ul0013" list-style="dash" compact="compact"><li>an operation of determining agreement, or not, to function in base station mode, and</li><li>an operation of response to the base station, during which the second communication station transmits a message representing the agreement or not to function in base station mode.</li></ul>

0046By virtue of these provisions, it is the station envisaged as the future base station which determines whether or not it accepts this role. Thus, if the initial base station is only partially informed of the actual capability of the mobile station of taking the role of base station, it cannot impose this change in role on the second communication station.

0047According to particular characteristics, when a communication station operating in base station mode is switched off, it performs said request operation.

0048By virtue of these provisions, the communication station which is operating in base station mode causes another communication station to start to function in base station mode before stopping its own functioning.

0049According to particular characteristics, the first communication station is a communication station envisaged for functioning in base station mode following the request operation.

0050According to other particular characteristics, the second communication station is the communication station functioning in base station mode prior to the request operation.

0051By virtue of these provisions, the two partners in the communication are the two communication stations which envisage exchanging their role in the cell. This simplifies communication and avoids interfering with the other communication stations.

0052According to particular characteristics, in the absence of a response on the part of a second communication station, the first station considers that the envisaged change in base station has failed.

0053By virtue of these provisions, the method of the invention functions both with devices according to the present invention and with devices known in the state of the art prior to the present invention.

0054According to particular characteristics, following the request operation, performed by the first communication station: <ul id="ul0014" list-style="dash" compact="compact"><li>an operation of determining acceptance of change in station functioning in base station mode, and</li><li>when it is determined that the envisaged change is not accepted, a new request operation during which a new message representing a request to change base station is addressed to another communication station.</li></ul>

0055By virtue of these provisions, the station which requires a change in base station may make several successive attempts to achieve this objective.

0056According to particular characteristics, each request operation includes an operation of selecting the station for which there is intended the message requesting a change in station functioning in base station mode.

0057According to other particular characteristics: <ul id="ul0015" list-style="dash" compact="compact"><li>the selection operation includes an operation of reading a destination station identity in a list of communication stations,</li><li>the selection operation includes an operation of determining the mobile station having better capabilities of becoming the new base station, and/or</li><li>the selection operation includes an operation of determining a mobile station having a need to transmit.</li></ul>

0058By virtue of each of these provisions, the stations which are envisaged for functioning in base station mode can, in a preferential order which depends on the characteristics of the selection operation, be the destination of messages representing a request to change station functioning in base station mode.

0059According to particular characteristics, the communication method as briefly disclosed above includes, performed by a communication station operating in mobile station mode: <ul id="ul0016" list-style="dash" compact="compact"><li>an operation of determining capability of functioning in base station mode, and</li><li>said request operation, during which said request message represents the capability of the first station of functioning in base station mode.</li></ul>

0060By virtue of these provisions, a communication station which operates in mobile station functioning mode can determine that it is effective for it to take the role of a base station.

0061According to particular characteristics, on reception of said request message, the second station performs: <ul id="ul0017" list-style="dash" compact="compact"><li>an operation of comparing capability of functioning in base station mode, during which it determines whether or not the first station has a better capability than the second station of functioning in base station mode, and,</li><li>in the affirmative, an operation of transmitting, to the first communication station, a message representing an acceptance of change in communication station functioning in base station mode.</li></ul>

0062By virtue of these provisions, the second communication station determines whether it accepts the change in base station requested.

0063According to a sixth aspect, the present invention relates to a device for communicating between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the station not supplying a control signal then functioning in "mobile station" mode, characterised in that it has, in a first communication station, a processing means adapted to transmit, to a second communication station, a request message representing a request to change station functioning in base station mode.

0064The invention also relates to a network, a computer, a camera, a facsimile machine, a photographic apparatus, a television receiver, a printer, a scanner and an audio/video player, characterised in that they have a device as briefly disclosed above.

0065The invention also relates to: <ul id="ul0018" list-style="dash" compact="compact"><li>a means of storing information which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above, and</li><li>a means of storing information which is removable, partially or totally, and which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above.</li></ul>

0066The preferential or particular characteristics, and the advantages, of said device, said computer, said camera, said facsimile machine, said photographic apparatus, said television receiver, said printer, said scanner, said audio/video player and said information storage means being identical to those of the method as briefly disclosed above, these advantages are not repeated here.

0067The document US-A-5 691 980 discloses how a master node in the network can detect an excessively low battery level and choose a new master node amongst slave nodes. It chooses the slave node having the best battery level. According to this document, it is the initial master node which determines its replacement. This document does not make it possible to take into account a system comprising heterogeneous portable terminals, as in a DECT network. In addition, according to this document, a slave node cannot take the initiative in becoming a master node.

0068When the base station is no longer in a position to correctly fulfil this role or when the quality of the transmission is not sufficient, no prior art is known which allows automatic switching of a mobile station into a base station.

0069To this end, according to a seventh aspect, the present invention relates to a method of communication between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control signal then functioning in "mobile station" mode, characterised in that it includes, performed by a station functioning in base station mode: <ul id="ul0019" list-style="dash" compact="compact"><li>an operation of determining the capability of said station functioning in base station mode of continuing this role, and</li><li>when, during the capability determination operation, it is determined that said capability is reduced, a request operation during which a first communication station transmits, to a second communication station, a message representing a request to change station functioning in base station mode.</li></ul>

0070By virtue of these provisions, the cell can reconfigure itself automatically when the base station leaves the cell or when a mobile station which could have better capabilities of functioning as a base station than a current base station enters the cell.

0071According to particular characteristics, during said request operation, the change request message includes an item of information representing the identity of a mobile station envisaged as a new base station.

0072By virtue of these provisions, the first station, which requires the change of base station, can determine and transmit the identity of the station envisaged as a new base station.

0073According to particular characteristics, the first communication station is the communication station functioning in base station mode, prior to the request operation.

0074According to other particular characteristics, the second communication station is a communication station envisaged for functioning in base station mode following the request operation.

0075By virtue of these provisions, the two partners in the communication are the two communication stations which envisage exchanging their role in the cell. This simplifies communication and avoids disturbing the other communication stations.

0076According to particular characteristics, the request operation is performed by the communication station functioning in base station mode prior to the request operation and the second communication station performs, following the reception of the message representing a request to change station functioning in base station mode: <ul id="ul0020" list-style="dash" compact="compact"><li>an operation of determining agreement, or not, to function in base station mode, and</li><li>an operation of response to the base station, during which the second communication station transmits a message representing the agreement or not to function in base station mode.</li></ul>

0077By virtue of these provisions, it is the station envisaged as the future base station which determines whether or not it accepts this role. Thus, if the initial base station is only partially informed of the actual capability of the mobile station of taking the role of base station, it cannot impose this change in role on the second communication station.

0078According to particular characteristics, the communication station operating in base station mode determines said capability as a function of the quantity of energy which it has available.

0079According to other particular characteristics, said communication station functioning in base station mode performs an operation switching into mobile station mode when the quantity of energy which it has available is less than a predetermined value.

0080By virtue of these provisions it reduces its energy consumption by changing from a base station functioning mode, which entails a high energy consumption, to a mobile station functioning mode for which the energy is principally consumed during communication.

0081According to other particular characteristics, the communication station operating in base station mode determines said capability according to the quality of transmission between it and mobile stations.

0082By virtue of these provisions, when the initial base station moves away from the other communication stations in the cell, and more generally when it no longer provides sufficient transmission quality, another communication station is called onto take the role of base station.

0083According to particular characteristics, the first communication station is the communication station functioning prior to the base station mode request operation.

0084According to other particular characteristics, the second communication station is a communication station envisaged for functioning in base station mode following the request operation.

0085By virtue of these provisions, the two partners in the communication are the two communication stations which envisage exchanging their role in the cell. This simplifies communication and avoids disturbing the other communication station.

0086According to particular characteristics, in the absence of a response on the part of a second communication station, the first station considers that the envisaged change in base station has failed.

0087By virtue of these provisions, the method of the invention functions both with devices according to the present invention and with devices known in the state of the art prior to the present invention.

0088According to particular characteristics, following the request operation, performed by the first communication station: <ul id="ul0021" list-style="dash" compact="compact"><li>an operation of determining acceptance of change in station functioning in base station mode, and</li></ul>    when it is determined that the envisaged change is not accepted, a new request operation during which a new message representing a request to change base station is addressed to another communication station.

0089By virtue of these provisions, the station which requires a change in base station can make several successive attempts to achieve this objective.

0090According to particular characteristics, each request operation includes an operation of selecting a station for which there is intended the message requesting a change in station functioning in base station mode.

0091According to other particular characteristics: <ul id="ul0022" list-style="dash" compact="compact"><li>the selection operation includes an operation of reading a destination station identity from a list of communication stations,</li><li>the selection operation includes an operation of determining the mobile station having better capabilities of becoming the new base station,</li><li>the selection operation includes an operation of determining a mobile station having a requirement to transmit,</li><li>the selection operation includes an operation of determining a mobile station which has already operated in base station mode.</li></ul>

0092By virtue of each of these provisions, the stations which are envisaged for functioning in base station mode can, in a preferential order which depends on the characteristics of the selection operation, be destinations for the messages representing a request to change station functioning in base station mode.

0093According to an eighth aspect, the present invention relates to a device for communication between communication stations adapted to communicate with each other when at least one of said communication stations supplies a control signal, said station then functioning in "base station" mode and the stations not supplying a control signal then functioning in "mobile station" mode, characterised in that it has a processing means adapted: <ul id="ul0023" list-style="dash" compact="compact"><li>to determine the capability of a communication station functioning in base station mode of continuing this role, and</li><li>when it has determined that the said capability is reduced, to cause a first communication station to transmit to a second communication station a message representing a request to change station functioning in base station mode.</li></ul>

0094The invention also relates to a network, a computer, a camera, a facsimile machine, a photographic apparatus, a television receiver, a printer, a scanner and an audio/video player, characterised in that they have a device as briefly disclosed above.

0095The invention also relates to: <ul id="ul0024" list-style="dash" compact="compact"><li>an information storage means which can be read by a computer or a microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above, and</li><li>an information storage means which is partially or totally removable and can be read by a computer or microprocessor storing instructions of a computer program characterised in that it implements the method of the invention as briefly disclosed above.</li></ul>

0096Other advantages, aims and characteristics of the present invention will emerge from the following description, given with reference to the accompanying drawings, in which: <ul id="ul0025" list-style="dash" compact="compact"><li>Figure 1 depicts, schematically, an operating flow diagram of a mobile station, with a view to its insertion in a network, in accordance with the prior art,</li><li>Figure 2 depicts schematically a network including communication devices according to the second, fourth, sixth and eighth aspects of the present invention, adapted to implement the communication method of the first, third, fifth and seventh aspects of the present invention,</li><li>Figure 3A depicts schematically the architecture of an electronic circuit incorporated in a communication device according to the second, fourth and sixth aspects of the present invention,</li><li>Figure 3B depicts schematically the architecture of an electronic circuit incorporated in a communication device according to the eighth aspect of the present invention,</li><li>Figure 4 depicts schematically an operating flow diagram of a communication device according to the second, fourth, sixth and eighth aspects of the present invention, with a view to its insertion in a network,</li><li>Figure 5 details part of the flow diagram illustrated in Figure 4,</li><li>Figure 6A depicts schematically the organisation of information sent by a communication device according to the second, fourth and sixth aspects of the present invention, with a view to informing a base station of the capabilities of this device related to functioning in base station mode,</li><li>Figure 6B depicts schematically the organisation of information sent by a communication device according to the eighth aspect of the present invention, with a view to informing a base station of the capabilities of this device related to functioning in base station mode,</li><li>Figures 7, 8A and 8B depict schematically exchanges of information occurring between communication devices according to the second, fourth, sixth and eighth aspects of the present invention, when a mobile station joins or leaves a cell,</li><li>Figures 9, 10, 11 and 12 depict schematically operating flow diagrams of communication devices according to the second, fourth, sixth and eighth aspects of the present invention, with a view to a change in base station,</li><li>Figure 13 is a schematic time representation of the messages exchanged between communication devices in accordance with the flow diagrams in Figures 9 to 12,</li><li>Figures 14A and 14B depict schematically the organisation of information sent by communication devices according to the second, fourth, sixth and eighth aspects of the present invention, with a view to collecting information concerning the capability of mobile stations of functioning in base station mode,</li><li>Figures 15 and 16 depict schematically messages exchanged between communication devices according to the second, fourth, sixth and eighth aspects of the present invention, with a view to collecting information concerning the capability of mobile stations of functioning in base station mode,</li><li>Figure 17 depicts schematically a physical frame structure known in the state of the art,</li><li>Figure 18A depicts schematically a communication internal to a cell according to the state of the art,</li><li>Figures 18B and 18C depict schematically a cell split implemented by the device which is the object of the second, fourth, sixth and eighth aspects of the present invention,</li><li>Figures 19 and 20 depict schematically operating flow diagrams of communication devices according to the second, fourth, sixth and eighth aspects of the present invention, with a view to splitting the cell during an internal communication,</li><li>Figures 21A, 21B and 22 depict schematically information exchanges occurring between communication devices according to the second, fourth, sixth and eighth aspects of the present invention, with a view to splitting the cell during an internal communication,</li><li>Figure 23 depicts schematically a flow diagram of classification of mobile stations as a function of criteria defining their capability of functioning as a base station,</li><li>Figure 24 depicts schematically a flow diagram implemented by a communication station functioning initially as a mobile station, with a view to communication, in the absence of a base station,</li><li>Figure 25 depicts schematically a flow diagram implemented by a communication station functioning initially as a mobile station, on reception of a message requesting a change in base station in accordance with the message illustrated in Figure 6B,</li><li>Figure 26 depicts schematically a flow diagram implemented by a communication station connected to an external network,</li><li>Figure 27 depicts schematically a flow diagram implemented by a communication station functioning initially as a base station, when its capability of pursuing this functioning mode decreases,</li><li>Figure 28 depicts schematically a flow diagram implemented by a communication station functioning initially in mobile station mode, on reception of a message requesting a change in base station,</li><li>Figure 29 depicts schematically a flow diagram implemented by a communication station, functioning in base station mode, in order to determine a radio transmission quality, and</li><li>Figure 30 depicts schematically a flow diagram implemented by a communication station functioning initially in mobile station mode, but having already functioned in base station mode, when its capabilities of functioning in base station mode have been restored.</li></ul>

0097In the description which follows, the term "communication device" designates a communication station able to behave, in a communication network, as a base station or as a mobile station, in accordance on the one hand with the DECT standard and on the other hand with the different functioning modes described in relation to the accompanying drawings.

0098Figure 1 describes the procedure of locking a mobile station onto a signal transmitted by a base station, as known in the prior art.

0099When a mobile station is powered up, it goes into an internal initialisation state 101. Next, during an operation 102, the mobile station goes into reception mode on the next channel (there are ten of them) in the frequency band allocated for communications in accordance with the DECT standard (that is to say 1880 to 1900 MHz), seeking a signal transmitted by a base station which is suitable to it. When operation 102 is first iterated, it is the first channel which is chosen. When, before performing operation 102, the last channel is considered, it is the first channel which is chosen, during operation 102.

0100Next, during a test 103, the mobile station listens out on the radio channel under consideration, for a predetermined period, in order to detect a synchronisation pulse coming from a base station. The mobile station thus determines whether or not a base station is using the channel under consideration for sending a synchronisation signal.

0101When the result of test 103 is negative, during a test 104, the mobile station determines whether or not the channel under consideration is the last one. When the result of test 104 is negative, operation 102 is reiterated. When the result of test 104 is positive, during an operation 105, the mobile station goes into standby mode and then, during an operation 107, it waits for a predetermined period <i>T0</i> (which can be a decreasing function of the energy resources of the mobile station), before reiterating operation 102.

0102When the result of test 103 is positive, during a test 108, the mobile station determines whether or not it has a right of access to the base station which sends the synchronisation signal.

0103To this end, when the result of test 103 is positive, the mobile station can obtain the information broadcast by the base station, every multi-frame (each multi-frame being composed of sixteen frames with a duration of ten milliseconds). Amongst the information broadcast by the base station, there is notably the so-called "ARI" parameter (initials of the words "Access Rights Identity") which defines the access rights to the base station under consideration. Each mobile station having at least one identity referred to as "PARK" (initials of the words "Portable Access Rights Key"), it is the correspondence between at least one of the "PARK" identities and the "ARI" parameter which is tested during test 108.

0104When the result of test 108 is negative, test 104 is performed. When the result of test 108 is positive, during an operation 109, the mobile station locks onto the base station which is sending the synchronisation signal detected on the channel under consideration.

0105At the end of operation 109, the mobile station can obtain the information broadcast by the base station whose ARI parameter corresponds with at least one of its "PARK" identities.

0106The mobile station can then initiate or accept a connection by means of the base station onto which the mobile station is locked. The mobile station can then communicate with the other mobile stations which are also locked onto the same base station and with the base station itself, in particular when the latter supplies an access point to another network, for example by telephone.

0107It should be noted here that, if there is no base station which is sending a synchronisation signal, no communication is possible between the mobile stations, in accordance with the prior art.

0108Figure 2 depicts, in one and the same local area 200, different communication devices in accordance with the present invention: <ul id="ul0026" list-style="dash" compact="compact"><li>the communication devices 202 and 203 are telephones of a known type, complying, for example, with the DECT GAP standard (initials of the words "Generic Access Profile") and which is dedicated to portable telephone voice transmission,</li><li>the communication devices 201, 204 and 205 are multimedia terminals able to behave, in the cell 200, as a base station or as a mobile station.</li></ul>

0109In the embodiment described and depicted, the communication devices 201, 204 and 205 support the DECT GAP standard, and comply with the type "A" data profile, relating to data transfers up to a rate of 24 kilobits per second. The communication device 201 also complies with the type "AB" data profile, relating to the transfer of data up to a rate of 552 kilobits per second, but can switch into base station mode only following a manual operation by the user.

0110Each device according to the present invention, 201, 204 and 205, operates, by default, in accordance with the description of Figure 1, that is to say, at the time of initialisation, it goes into mobile station functioning mode.

0111In Figure 3A, it can be seen that each communication device according to the second, fourth and sixth aspects of the present invention, 201, 204 or 205, has, connected together by a bus 301: <ul id="ul0027" list-style="dash" compact="compact"><li>a controller 306,</li><li>a DECT base band unit 302,</li><li>a DECT radio unit 303, itself connected in addition to a sending/receiving antenna 307,</li><li>a random access memory 304,</li><li>a read-only memory 305,</li><li>a keyboard 307,</li><li>a display 308,</li><li>an energy level controller 309, itself connected in addition to an electrical power supply 310 (battery, accumulator or mains), and</li><li>an input/output interface 311.</li></ul>

0112The controllers 306 and 309 and the DECT base band unit 302 consist in fact of a processor and an operating program stored in the read-only memory 305.

0113The DECT base band unit 302 is of a known type and is adapted to exploit all the capabilities of the DECT standard known up to the time of the present invention.

0114The controller 306 is adapted to implement the method of the invention and in particular the flow diagrams illustrated in the figures. The energy level controller 309 is intended to evaluate the available energy level, in a known fashion, in order to determine timing values (see below).

0115The random access memory 304 stores, in registers which, for convenience, each bear the same name as the data which they contain: <ul id="ul0028" list-style="dash" compact="compact"><li>temporary variables <i>l</i> and <i>k</i>,</li><li>a variable "<i>MO</i>" representing the current operating mode, mobile station or base station,</li><li>a variable "<i>MD</i>" representing the random access memory available,</li><li>a variable <i>"CMD"</i> representing a value coefficient for the available memory which takes one of three values "0", "1" or "2" depending on whether the memory area available has a capacity less than two predetermined values <i>MD_N1</i> and <i>MD_N2</i>, is between the two predetermined values or is greater than the two predetermined values,</li><li>a memory area <i>"Tx/Rx"</i> reserved for the reception or transmission of data,</li><li>a table <i>"Table_SM"</i> containing a list of the identities of the mobile stations (including the devices according to the present invention) declared to the base station, and the information associated with these mobile stations,</li><li>a list "<i>List_SM_auto</i>" containing a list of the identities of the devices according to the present invention, that is to say those able to change operational mode automatically (for example stations 204 and 205),</li><li>a list <i>"List_SM_manuaf"</i> containing a list of the identities of the mobile stations able to change operational mode, through the intervention of their user (for example station 201), and</li><li>a list <i>"List_SM_direct"</i> containing a list of the identities of the mobile stations able to communicate directly with each other, without a base station.</li></ul>

0116The read-only memory 305 stores, in registers which, for convenience, each bear the same name as the data which they contain: <ul id="ul0029" list-style="dash" compact="compact"><li>an item of information <i>"CM"</i> on the memory capacity of the device,</li><li>an item of information <i>"CP"</i> on the capacity of the processor of the device,</li><li>an indicator "<i>IP</i>' representing profiles of the DECT standard supported by the device (in fact by its DECT base band unit 302),</li><li>an item of information <i>"TS"</i> representing the types of time intervals (referred to as "slots" in the remainder of the description and, in particular, in Figure 17, a term in accordance with the usage of persons skilled in the art of communications) which are DECT supported (single, double or half-slot),</li><li>an item of information <i>"DM"</i> representing a maximum data rate supported by the device (for example between 24 and 552 kilobits per second),</li><li>the memory area capacity values <i>MD_N1</i> and <i>MD_N2,</i></li><li>an item of information representing its identity,</li><li>a coefficient <i>"CPR"</i> representing the number of DECT profiles supported,</li><li>an item of information <i>"CO"</i> representing the operational capability of the device. This information can take the following values: <ul id="ul0030" list-style="none" compact="compact"><li>. "<i>SB</i>": the device can operate only in base station mode,</li><li>. "SM": the device can operate only in mobile station mode,</li><li>. "<i>SB/SM_manual</i>": the device can change operating mode through the intervention of its user,</li><li>. "<i>SB/SM_auto</i>": the device can automatically change operating mode,</li><li>. "<i>SM/SM_direct</i>": the device can communicate directly with another mobile whose information <i>"CO"</i> takes the value <i>"SM/SM_direct"</i> and</li></ul></li><li>an item of information "BA" representing the automatic or manual switching capability from a base station functioning mode to a mobile station functioning mode and vice versa (<i>"BA"</i> being equal to <i>"true",</i> when this capability exists, and <i>"false"</i> otherwise).</li></ul>

0117The read-only memory 305 constitutes a means of storing information which can be read by a computer or a microprocessor, storing instructions of a computer program characterised in that it implements the method of the invention. According to a variant, the read-only memory 305 is removable, partially or totally, and has for example a magnetic strip, a flash memory, a diskette or a fixed-memory compact disc (CD-ROM).

0118In Figure 3B, it can be seen that each communication device according to the eighth aspect of the present invention, 201, 204 or 205, has, connected together by a bus 301: <ul id="ul0031" list-style="dash" compact="compact"><li>a controller 306,</li><li>a DECT base band unit 302,</li><li>a radio unit 303, itself connected in addition to a sending/receiving antenna 307,</li><li>a random access memory 304,</li><li>a read-only memory 305,</li><li>a keyboard 307,</li><li>a display 308,</li><li>an energy level controller 309, itself connected in addition to an electrical power supply 310 (battery, accumulator or mains),</li><li>an input/output interface 311, and</li><li>a communication quality controller 312.</li></ul>

0119The controllers 306 and 309 and the DECT base band unit 302 consist in fact of a processor and an operating program stored in the read-only memory 305.

0120The DECT base band unit 302 is of a known type and is adapted to exploit all the capabilities of the DECT standard known up to the time of the present invention.

0121The controller 306 is adapted to implement the method of the invention and, in particular, the flow diagrams illustrated in the figures. The energy level controller 309 is intended: <ul id="ul0032" list-style="dash" compact="compact"><li>to recognise the type of electrical power supply (mains or battery), in a known fashion, and to evaluate the energy level available for the communication device, in order to determine:</li><li>time delay values (see below), and</li><li>an ability to become a base station or to remain so.</li></ul>

0122The communication quality controller 312 is adapted to evaluate the quality of the radio signal and to supply a value <i>QR</i> representing this quality.

0123The random access memory 304 stores, in registers which, for convenience, each bear the same name as the data which they contain: <ul id="ul0033" list-style="dash" compact="compact"><li>temporary variables <i>I</i> and <i>k</i>,</li><li>a value <i>"QR"</i> representing the quality of the radio signal measured by the controller 312,</li><li>a value <i>"NB"</i> representing an available energy quantity,</li><li>a value <i>"DB"</i> representing the past functioning of the station, in base station mode,</li><li>a variable <i>"MO"</i> representing the current operating mode, mobile station or base station,</li><li>a variable <i>"MD"</i> representing the random access memory available,</li><li>a variable <i>"CMD"</i> representing a value coefficient for the available memory which takes one of three values "0", "1" or "2" depending on whether the memory area available has a capability less than two predetermined values <i>MD_N1</i> and <i>MD_N2</i>, is between the two predetermined values or is greater than the two predetermined values,</li><li>a memory area <i>"Tx/Rx"</i> reserved for the reception or transmission of data,</li><li>a table <i>"Table_SM"</i> containing a list of the identities of the mobile stations (including the devices according to the present invention) declared to the base station, and the information associated with these mobile stations,</li><li>a list "<i>List_SM_auto</i>" containing a list of the identities of the devices according to the present invention, that is to say those able to change operational mode automatically (for example stations 204 and 205),</li><li>a list <i>"List_SM_manual"</i> containing a list of the identities of the mobile stations able to change operational mode, through the intervention of their user (for example station 201), and</li><li>a list <i>"List_SM_direct"</i> containing a list of the identities of the mobile stations able to communicate directly with each other, without a base station.</li></ul>

0124The read-only memory 305 stores, in registers which, for convenience, each bear the same name as the data which they contain: <ul id="ul0034" list-style="dash" compact="compact"><li>an item of information <i>"CM"</i> on the memory capacity of the device,</li><li>an item of information <i>"CP"</i> on the capacity of the processor of the device,</li><li>a minimum communication quality value <i>QR_min,</i></li><li>a maximum communication quality value <i>QR_max,</i></li><li>a minimum available energy quantity value <i>NB_min,</i></li><li>a maximum available energy quantity value <i>NB_max,</i></li><li>an indicator "<i>IP</i>" representing the profiles of the DECT standard supported by the device (in fact by its DECT base band unit 302),</li><li>an energy coefficient <i>"CE"</i> which represents the energy source of the station under consideration, according to three values: <i>"CE_HIGH",</i> equal to "2", for a printer, copier, facsimile machine or office computer, and more generally for any equipment which is generally connected to the mains or which has a means of detecting connection to the mains which indicates that the station is connected to the mains, <i>"CE_MID",</i> equal to "1", for a portable computer and more generally for a communication station which can operate either on the mains or on a battery, and <i>"CE_LOW",</i> equal to "0", for a pocket organiser or portable telephone, and more generally for a communication station which operates almost exclusively on a battery,</li><li>a fixity coefficient <i>"CF"</i> which represents the normal mobility of the station under consideration, according to three values: <i>"CF_HIGH",</i> equal to "2", for a printer, copier, facsimile machine or office computer, and more generally for any equipment which generally fixed, <i>"CF_MID",</i> equal to "1", for a portable computer and more generally for a communication station which can be moved but which is generally not in movement during its operation, and <i>"CF_LOW",</i> equal to "0", for a pocket organiser or portable telephone, and more generally for a communication station which may be in movement during its use,</li><li>an item of network interface information <i>"IR"</i> which represents the types of network which can be accessed by the station, equal to "0" when no other network can be accessed and being non-nil when another network can be accessed, the positions of the bits equalling "1" in the binary representation of <i>"IR"</i> indicating which types of network can be accessed: <ul id="ul0035" list-style="none" compact="compact"><li>xxxx xxx1 PSTN (Public Switched Telephone Network)</li><li>xxxx xx1x ISDN (Integrated Service Digital Network)</li><li>xxxx x1xx LAN (Local Area Network)</li><li>xxxx 1xxx ATM (Asynchronous Transfer Mode),</li></ul></li><li>a network interface coefficient <i>"CIR"</i> which represents the number of external networks accessible,</li><li>an item of information <i>"TS"</i> representing the types of time intervals (referred to as "slots" in the remainder of the description and, in particular, in Figure 17, a term in accordance with the usage of persons skilled in the art of communications) which are DECT supported (single, double or half-slot),</li><li>an item of information <i>"DM"</i> representing a maximum data rate supported by the device (for example between 24 and 552 kilobits per second),</li><li>the memory area capacity values <i>MD_N1</i> and <i>MD_N2,</i></li><li>an item of information representing its identity,</li><li>a coefficient <i>"CPR"</i> representing the number of DECT profiles supported,</li><li>an item of information "<i>CO</i>" representing the operational capability of the device. This information can take the following values: <ul id="ul0036" list-style="none" compact="compact"><li>. "<i>SB</i>": the device can operate only in base station mode,</li><li>. "SM": the device can operate only in mobile station mode,</li><li>. "<i>SB/SM_manual</i>": the device can change operating mode through the intervention of its user,</li><li>. "<i>SB/SM_auto</i>": the device can automatically change operating mode,</li><li>. "<i>SM/SM_direct</i>": the device can communicate directly with another mobile whose information "<i>CO</i>" takes the value <i>"SM/SM_direct"</i> and</li></ul></li><li>an item of information "BA" representing the automatic or manual switching capability from a base station functioning mode to a mobile station functioning mode and vice versa (<i>"BA"</i> being equal to <i>"true",</i> when this capability exists, and <i>"false"</i> otherwise).</li></ul>

0125The read-only memory 305 constitutes a means of storing information which can be read by a computer or a microprocessor, storing instructions of a computer program characterised in that it implements the method of the invention. According to a variant, the read-only memory 305 is removable, partially or totally, and has for example a magnetic strip, a flash memory, a diskette or a fixed-memory compact disc (CD-ROM).

0126The procedure followed by the controller 306 for determining the operating mode (base station or mobile station) is detailed in Figure 4. When a communication device according to the present invention is powered up, it goes into an internal initialisation state 401. Next, during an operation 402, the communication device goes into reception mode on the next channel of the frequency band allocated for communications in accordance with the DECT standard, as disclosed with regard to operation 102 (Figure 1).

0127Next, during a test 403, the communication device listens to the radio channel under consideration, for a predetermined period, in order to detect a synchronisation pulse coming from a base station (including the case of another communication device behaving as a base station). The communication device thus determines whether or not a base station is using the channel under consideration for sending a synchronisation signal.

0128When the result of test 403 is negative, during a test 404, the communication device determines whether or not the channel under consideration is the last. When the result of test 404 is negative, operation 402 is reiterated.

0129When the result of test 403 is positive, during a test 405, the communication device determines whether or not it has a right of access to the base station which is sending the synchronisation signal, as described with regard to operation 108 (Figure 1).

0130When the result of test 405 is negative, the communication device performs test 404. When the result of test 405 is positive, during an operation 406, identical to operation 109 (Figure 1), the communication device locks onto the base station which is sending the synchronisation signal detected on the channel under consideration.

0131At the end of operation 406, the communication device can obtain the information broadcast by the base station whose ARI parameter corresponds with at least one of its "PARK" identities. The communication device can also initiate or accept a connection by means of the base station onto which the device is locked. The communication device can then communicate on the one hand with the other mobile stations and the communication devices according to the present invention which behave as a mobile station, and which are also locked onto the same base station, and on the other hand with the base station itself or with the communication device which is behaving as a base station.

0132When the result of test 404 is positive, during an operation 407, the controller 306 of the communication device causes this communication device to switch into base station mode.

0133In this base station functioning mode, it sends, at regular time slots, with a duration less than the predetermined duration of test 403, a synchronisation signal, on one of the DECT channels. The duration of the regular time slot is, according to the DECT standard, 160 milliseconds.

0134Next, the communication device allows a time <i>T1</i> to pass (for example one minute), operation 408, whilst continuing its functioning as a base station, before performing a test 409, during which it determines whether mobile stations are synchronised with it (see detail of test 409 in Figure 5).

0135When the result of test 409 is negative, during an operation 411, the controller 306 causes the functioning mode to switch into mobile station mode, and then the communication device allows a predetermined time <i>T2</i> to pass (for example as a decreasing function of the available energy evaluated by the energy level controller 309), operation 412, before renewing operation 402.

0136When the result of test 409 is positive, during an operation 413, the communication device allows a predetermined time <i>T3</i> to pass (for example as an increasing function of the available energy evaluated by the energy level controller 309), whilst continuing its functioning in base station mode, before performing a test 414, during which the communication device determines whether or not at least one communication with a mobile station is active. When the result of test 414 is positive, it is reiterated. When the result of test 414 is negative, during an operation 415, the controller 306 causes the communication device to switch from base station mode to mobile station mode. Next, the communication device reiterates operation 402.

0137It will be understood that, in accordance with the flow diagram of Figure 4, two operating criteria are used: <ul id="ul0037" list-style="dash" compact="compact"><li>when, in mobile station functioning mode, the communication device detects no base station, it goes into base station functioning mode, and</li><li>when, in base station functioning mode, the communication device detects no mobile station, it goes into mobile station functioning mode.</li></ul>

0138In addition, when, in base station functioning mode, the communication device does not detect any communication with a mobile station, it goes into mobile station functioning mode. The purpose of the latter arrangements is to cause the base station to return to mobile station mode before once again seeking whether another base station can be detected.

0139In order to detect the presence of mobile stations (including the case of communication devices according to the present invention which behave as a mobile station), the case is chosen, with regard to Figure 5, in which each communication device able to function in base station mode is informed of the identity of each communication device and of each mobile station able to communicate with it.

0140In this case, the communication device first of all performs a test 501 (Figure 5), during which the controller 306 determines whether or not the list of mobile stations able to communicate with the communication device is empty. When the result of test 501 is positive, the result of test 409 is negative, operation 502. When the result of test 501 is negative, during an operation 503, a temporary variable <i>I,</i> which serves as an indicator on said list, is initialised to the value "0". Then, during an operation 504, the communication device sends, to the network, a message requesting an answer to the device identified by the <i>l</i>^th identifier of the list. Then the communication device allows a predetermined time <i>T4</i> to pass, operation 505, before performing a test 506, during which it determines whether or not an answer message has been sent by a communication device. When the result of test 506 is positive, during a test 507, the device determines whether the identity of the device which sent the answer message corresponds to the identity of the device which was called during operation 504. When the result of test 507 is positive, the result of test 409 is positive, operation 510. When the result of test 507 is negative, or when the result of test 506 is negative, during an operation 508, the value of the variable <i>I</i> is incremented.

0141Next, during a test 509, the communication device determines whether or not the value of the variable <i>I</i> is less than or equal to the size of the list. When the result of test 509 is positive, operation 504 is reiterated. When the result of test 509 is negative, the result of test 409 is negative, operation 502.

0142As a variant, in order to detect the presence of mobile stations, the following procedure is used: when a mobile station detects a base station and locks onto this base station, the mobile station sends to the base station a message representing its identity and its capabilities (see below). The base station can then update a list of mobiles present in the cell. Conversely, when a mobile station leaves the cell (that is to say the area of coverage of the base station) or before switching off, it sends to the base station a message indicating that it is terminating its access rights.

0143It should be noted here that the procedure of detecting that a mobile station is leaving its cell is known from the prior art, by analysing the signal reception power.

0144Figure 6A depicts the structure of information concerning the operational mode capability of a station in the network, according to the first to sixth aspects of the present invention. This information can be transmitted in DECT protocol messages using a field reserved for the transfer of non-standardised information, referred to in the standard as <i>"escape-to-proprietary".</i> According to the invention, the non-standardised information is used solely in the following messages in the standard: <ul id="ul0038" list-style="dash" compact="compact"><li><i>"access-rights-request",</i> and</li><li><i>"locate-request",</i> which includes an attachment request.</li></ul>

0145The first octet 601 of the field described in Figure 6A indicates that the information elements which follow are non-standardised information to be sent within a DECT protocol message. The second octet 602 contains the information octet number to be transmitted. The third octet 603 indicates that the octets 604 and 605 contain an EMC (<i>"Equipment Manufacturer Code"</i>) parameter, which serves to identify the manufacturer using this proprietary information. Thus, if an item of equipment whose EMC parameter is different from that indicated by the octets 604 and 605, it does not process the information which follows.

0146Naturally, if the present invention were to be the subject of standardisation between different manufacturers, octets 601, 604 and 605 would no longer be used in the same way.

0147Octet 606 represents the operational capability <i>CO</i> (identical to its value, in the embodiment described and depicted) of the device which acts as a mobile station. The following octets, 607 to 611, whose number is equal to the number of information octets to be transmitted (number represented by octet 602) minus four, serve to transmit more precise information on the capabilities of the device of operating as a base station. For example, the following parameters can be transmitted: <ul id="ul0039" list-style="dash" compact="compact"><li>memory capacity of the device (octet 607),</li><li>degree of filling of the memory of the device (octet 608),</li><li>power, speed of the processor of the device (octet 609), and</li><li>maximum rate supported by the device (octet 610),</li></ul>

0148The position bit 8 (on the left) of the information octets 607 to 610 takes one of the values: <ul id="ul0040" list-style="dash" compact="compact"><li>"1", when the information element is transmitted in this message, or</li><li>"0" when the value of the following bits of the octet has no meaning (the information element is not transmitted in the message).</li></ul>

0149Figure 6B depicts the structure of information concerning the operational mode capability of a station in the network, according to the seventh and eighth aspects of the present invention. This information can be transmitted in DECT protocol messages using a field reserved for the transfer of non-standardised information, referred to in the standard as <i>"escape-to-proprietary"</i>. According to the invention, the non-standardised information is used solely in the following messages in the standard: <ul id="ul0041" list-style="dash" compact="compact"><li><i>"access-rights-request",</i> and</li><li><i>"locate-request",</i> which means "request for location" and which includes an attachment request.</li></ul>

0150The first octet 701 of the field described in Figure 6B indicates that the information elements which follow are non-standardised information to be sent within a DECT protocol message. The second octet 702 contains the information octet number to be transmitted. The third octet 703 indicates that the octets 704 and 705 contain an EMC (<i>"Equipment Manufacturer Code"</i>) parameter, which serves to identify the manufacturer using this proprietary information. Thus, if an item of equipment whose EMC parameter is different from that indicated by the octets 704 and 705, it does not process the information which follows.

0151Naturally, if the present invention were to be the subject of standardisation between different manufacturers, octets 701, 704 and 705 would no longer be used in the same way.

0152Octet 706 represents the operational capability CO (identical to its value, in the embodiment described and depicted) of the device which acts as a mobile station. The following octets, 707 to 711, whose number is equal to the number of information octets to be transmitted (number represented by octet 702) minus four, serve to transmit more precise information on the capabilities of the device for operating as a base station. For example, the following parameters can be transmitted: <ul id="ul0042" list-style="dash" compact="compact"><li>memory capacity of the device (octet 707),</li><li>degree of filling of the memory of the device (octet 708),</li><li>power, speed of the processor of the device (octet 709), and</li><li>maximum rate supported by the device (octet 710),</li><li>fixity coefficient <i>"CF"</i> (octet 712),</li><li>energy coefficient <i>"CE"</i> (octet 713),</li><li>network interface <i>"IR"</i> (octet 714).</li></ul>

0153The position bit 8 (on the left) of the information octets 707 to 710 takes one of the values: <ul id="ul0043" list-style="dash" compact="compact"><li>"1", when the information element is transmitted in this message, or</li><li>"0" when the value of the following bits of the octet has no meaning (the information element is not transmitted in the message).</li></ul>

0154Figure 7 describes how a mobile station obtains rights of access to a base station and how it terminates its rights of access. The access rights procedure enables a base station and a mobile station to exchange their respective identities and information concerning the capabilities of the mobile station. The mobile station initiates the procedure by sending, to the base station, a message <i>"access_rights_request"</i> which contains notably the capabilities of the mobile station in the field <i>"terminal capability"</i>. In this field, according to the invention, use is made of the profile indicator parameter (<i>"profile indicator"</i>) and slot type parameter (<i>"slot type capability"</i>) (see below).

0155The additional information necessary for the functioning of the device according to the present invention is transmitted in the field <i>"escape to proprietary"</i> of the message <i>"access_rights_request"</i> (Figures 6A and 6B).

0156When a base station receives a message <i>"access_rights_request",</i> if the mobile station is authorised to access the resources of the base station, the latter returns a message <i>"access_rights_accept",</i> and adds, in the table of the declared mobile stations, the information concerning the mobile station which sent the message <i>"access_rights_request"</i>.

0157According to the first to sixth aspects of the present invention, the information thus collected is stored in the <i>table_SM</i>, of the random access memory 304, organised in the following fashion: <ul id="ul0044" list-style="none" compact="compact"><li>No Identity CO CM RM CP IP TS DM ...</li><li>1</li><li>2</li><li>...</li></ul>

0158When a mobile station is added to the <i>table_SM</i>, the following information concerning it are stored therein: <ul id="ul0045" list-style="dash" compact="compact"><li>its mobile identity,</li><li>its operational capability (CO),</li><li>its memory capacity (<i>CM</i>),</li><li>the degree of filling of its memory (<i>RM</i>),</li><li>its processor capacity (<i>CP</i>),</li><li>its profile indicator (<i>IP</i>),</li><li>its slot type capability (<i>TS</i>),</li><li>its maximum throughput (<i>DM</i>), and possibly other information characterising it.</li></ul>

0159The parameters <i>IP</i> and <i>TS</i> are read in the field <i>"Terminal Capability"</i> of the message <i>"access_rights_request",</i> whilst the parameters <i>CO</i>, <i>CM, RM, CP</i> and <i>DM</i> are read in the field <i>"escape to proprietary"</i> described in Figure 6A. When a mobile station wishes to terminate its access rights to a base station, it sends a message 803 <i>"access_rights_terminate_request".</i> The base station then erases the information concerning this mobile station in its <i>table_SM</i> and returns a message <i>"access_rights_terminate_accept"</i> 804. The mobile station can then no longer use the resources of the base station.

0160According to the seventh and eighth aspects of the present invention, the information thus collected is stored in the <i>table_SM</i>, of the random access memory 304, organised in the following fashion: <ul id="ul0046" list-style="none" compact="compact"><li>No Identity CO CM RM CP IP TS DM CE CF IR</li><li>1</li><li>2</li><li>...</li></ul>

0161When a mobile station is added to the <i>table_SM</i>, the following information concerning it are stored therein: <ul id="ul0047" list-style="dash" compact="compact"><li>its mobile identity,</li><li>its operational capability (CO),</li><li>its memory capacity (<i>CM</i>),</li><li>the degree of filling of its memory (<i>RM</i>),</li><li>its processor capacity (<i>CP</i>),</li><li>its profile indicator (<i>IP</i>),</li><li>its slot type capability (<i>TS</i>),</li><li>its maximum throughput (<i>DM</i>),</li><li>its energy coefficient (<i>CE</i>),</li><li>its fixity coefficient (<i>CF</i>),</li><li>its network interface information (<i>IR</i>),</li></ul>    and, optionally, other information characterising it.

0162The parameters <i>IP</i> and <i>TS</i> are read in the field <i>"Terminal Capability"</i> of the message <i>"access_rights_request",</i> whilst the parameters <i>CO</i>, <i>CM, RM, CP, DM, CF, CE</i> and <i>IR</i> are read in the field <i>"escape to proprietary"</i> described in Figure 6B. When a mobile station wishes to terminate its access rights to a base station, it sends a message 803 <i>"access_rights_terminate_request".</i> The base station then erases the information concerning this mobile station in its <i>table_SM</i> and returns a message <i>"access_rights_terminate_accept"</i> 804. The mobile station can then no longer use the resources of the base station.

0163Figure 8A illustrates how a mobile station attaches itself to or detaches itself from a base station. When a mobile station enters the cell of a base station over which the mobile station has obtained access rights, it must initiate a procedure of attachment to the base station. By this procedure, the mobile station indicates to the base station that it is ready to receive calls. To attach itself, the mobile station sends to the base station a message <i>"Locate_request"</i> 811 which contains information concerning notably the identity and capabilities of the communication station and the possibility of sending non-standardised information. With the message <i>"Locate_request"</i> 811, it is possible to transfer to the base station the same information as with the message <i>"access_rights_request".</i> If a mobile station has important changes to its parameters (for example memory space still available) compared with the time of the access right procedure, it can use the field <i>"escape to proprietary"</i> as defined in Figures 6A and 6B, to inform the base station thereof.

0164When a base station receives a message <i>"Locate_request"</i> 811, it verifies that the mobile station is identified in its <i>"table_SM"</i> and, in the affirmative, returns a message <i>"Locate_accept"</i> 812. The base station then uses the information contained in its <i>"table_SM",</i> the table of the declared mobile stations, in order to insert the mobile station under consideration in the appropriate list, <i>List_SM_auto,</i> if its operational capability <i>CO</i> is equal to <i>SB/SM_auto, List_SM_manual</i> if its operational capability <i>CO</i> is equal to <i>SB/SM_manual</i> or <i>List_SM_direct</i> if its operational capability is equal to <i>SM/SM_direct.</i>

0165The reverse procedure to attachment is detachment. When a mobile station leaves the cell or is switched off, it sends a message <i>"detach"</i> 813 to the base station, which then withdraws the mobile station from the list corresponding to its operational capability.

0166However, the detachment procedure may not always be initiated by the mobile station which leaves the cell (because of breakdown or excessive speed for example). The last part, in Figure 8B, illustrates how the base station can periodically check on the validity of the information which it is keeping in the list stored in its random access memory 304.

0167The base station then periodically sends a request for a procedure of updating its location (or its attachment), by means of a message <i>"MM_info_suggest"</i> 821, whose field <i>"info_type"</i> is equal to <i>"locate_suggest".</i> The procedure of updating the location of a mobile station is identical to the attachment procedure, the messages 822 and 823 being respectively identical to the messages 811 and 812.

0168By virtue of the provisions illustrated in Figures 7, 8A and 8B, the list <i>list_SM_auto</i> contains all the mobile stations present in the cell and having the capability of switching automatically between base station mode and mobile station mode.

0169As explained with regard to Figure 23, the <i>list_SM_auto is</i> classified according to the decreasing capability of the mobile stations of becoming a base station: the first element in the list concerns the mobile station which has the best capability of becoming a base station. In order to classify this list, after each attachment, detachment or updating procedure, the base station takes into account all the parameters stored in the <i>table_SM_auto (CM, RM, CP, IP, TS, DM,</i> ... according to the first to sixth aspects of the invention; <i>CM, RM, CP, IP, TS, DM, CF, CE, IR</i>, ... according to the seventh and eighth aspects of the invention).

0170The <i>list_SM_manual</i> is sorted in the same way as the <i>list_SM_auto.</i> These lists can be used in the following situations: <ul id="ul0048" list-style="dash" compact="compact"><li>the base station becomes inactive following a powering down or a switching into mobile station mode and it seeks a replacement base station amongst the mobile stations having a capability of becoming a base station,</li><li>the base station is excessively used (memory full, number of simultaneous communications greater than a predetermined value) and it seeks a second base station for taking over some of the traffic.</li></ul>

0171The base station then chooses the first mobile station in the <i>list_SM_auto.</i> If the <i>list_SM_auto</i> is empty, or if none of the stations in the list <i>list_SM_auto is</i> suitable, the base station can have recourse to the first mobile station represented in the <i>list_SM_manual.</i> It must then transmit a message which triggers the display or sending of a signal to the mobile station chosen in order to warn the user that a change of functioning mode at the mobile station under consideration is required.

0172The base station uses the <i>list_SM_direct</i> so that the communications internal to the cell each involving at least one station represented in this list are directly organised by this station.

0173Figures 9 and 10 illustrate how a base station in activity (referred to as "initial") finds a replacement base station (referred to as "final"), for example when the initial base station can no longer fulfil its role as base station (switching off or automatic or manual switching to mobile station mode).

0174The procedure described in Figure 9 can be implemented only when there is no active connection. In addition, any new connection request is refused during this procedure.

0175As illustrated in Figure 9, the initial base station commences with a test 902 during which it determines whether or not another base station is present (as illustrated in Figure 1). When the result of the test 902 is positive, the procedure is complete, with success, since the mobile stations which communicate with the initial base station will be able to replace the latter for their communications and the initial base station changes functioning mode and becomes a mobile station, operation 912.

0176When the result of test 902 is negative, during a test 903, the initial base station determines whether or not the <i>list_SM_auto</i> is empty. When the result of test 903 is positive, the procedure is ended, having failed, since no mobile station can take the role of base station. The user is then informed that, if the base station ceases its activity, all the communications will be suspended, operation 913.

0177When the result of test 903 is negative, during an operation 904, the variable <i>I</i> is initialised to the value "0". Then, during an operation 905, the initial base station sends a message <i>"new_base_request"</i> to the <i>l</i>^th mobile station in the <i>list_SM_auto.</i> During operation 905, the initial base station waits for a sufficient period of time to enable a mobile station in accordance with the device which is the object of the present invention to reply, before performing a test 906. Next, during this test 906, the initial base station determines whether or not it has received, from the mobile station under consideration, a message <i>"new_base_accept".</i>

0178When the result of test 906 is positive, during an operation 907, the information stored in the table <i>table_SM</i>, and in the lists <i>list_SM_auto, list_SM_manual</i> and <i>list_SM_direct,</i> are transferred into the random access memory of the mobile station under consideration. Next, during a test 908, the initial base station determines whether or not it has received, from the mobile station under consideration, a data transfer acknowledgement message. When the result of test 908 is negative, it is reiterated. When the result of test 908 is positive, the initial base station changes operating mode, operation 912, and the base station change operation is ended, on the initial base station side, with success.

0179When the result of test 906 is negative, the initial base station considers that the allocation of the base station role has been refused by the <i>l</i>^th station in the list <i>list_SM_auto.</i> Then, during an operation 910, the value of the variable <i>I</i> is incremented by 1. Then, during a test 911, the initial base station determines whether or not the value of the variable <i>I</i> is greater than or equal to the number of mobile stations represented in the <i>list_SM_auto.</i>

0180When the result of test 911 is negative, operation 905 is reiterated. When the result of test 911 is positive, the base station change procedure is ended, having failed, and the user is warned that the cessation of the activity of the initial base station will cause the suspension of all the communications, operation 913.

0181According to a variant, not shown, when, during test 911, it is determined that the list <i>list_SM_auto</i> has been entirely run through, the operations and tests 905 to 912 are reiterated, running through the list <i>list_SM_manual.</i> Operation 912 is then performed only after the mobile station which sent the message <i>"new-base-accept"</i> (test 906) has sent a message confirming change in functioning mode.

0182When the procedure has been ended with success, by the detection of another base station during test 902 or by the acknowledgement of an information transfer by a mobile station during a test 908, the base station has thus changed operating mode and has become a mobile station, unless the procedure illustrated in Figure 9 has been brought about by a switching off of the initial base station, in which case the latter ceases its activity.

0183Figure 10 illustrates the procedure of changing base station on the part of a mobile station, when, during a test 1001, it determines that a message <i>"new_base_request"</i> has been received from the base station and is intended for the mobile station under consideration. Next, during a test 1002, the mobile station determines whether or not its operating capability <i>CO</i> has one of the values <i>SB/SM_auto</i> or <i>SB/SM_manual,</i> determining whether or not the value of the information <i>"BA"</i> is <i>"true".</i> When the result of test 1002 is negative, during an operation 1004, a message <i>"new_base_reject"</i> is sent by the mobile station under consideration to the base station in order to indicate to it that the allocation of the base station role has been refused. Then the procedure is ended, without the mobile station having switched into base station functioning mode.

0184When the result of test 1002 is positive, during a test 1003, the mobile station determines whether its available memory capacity <i>MD</i> is strictly less than the value <i>MD_N1</i> stored in the read-only memory 305. This value <i>MD_N1</i> corresponds in fact to a minimum available memory capacity for taking the base station role.

0185When the result of test 1003 is positive, operation 1004 is performed. When the result of test 1003 is negative, during an operation 1005, the mobile station sends a message accepting the role of base station <i>"new_base_accept",</i> to the initial base station. Then, during a test 1006, the mobile station determines whether it has received, from the initial base station, the necessary information for taking the base station role, that is to say all the information stored in the lists <i>list_SM_auto, list_SM_manual</i> and <i>list_SM_direct,</i> and in the table <i>table_SM.</i>

0186When the result of test 1006 is negative, it is reiterated. When the result of test 1006 is positive, during an operation 1007, the mobile station sends, to the base station, an acknowledgement of receipt of the information. Then, during an operation 1008, the mobile station changes functioning mode and becomes a base station. The procedure is then ended.

0187Where the mobile station has an operating code value <i>SB/SM_manual,</i> the test 1003 is supplemented by: <ul id="ul0049" list-style="dash" compact="compact"><li>a triggering of a warning signal intended to warn the user that he must manually switch the operating mode of the communication station concerned,</li><li>a wait for a sufficient period for the user to have the time to effect the manual switching, and</li><li>a test of change of operating mode by the user (not shown) and, where the user has not effected the change in operating mode during a predetermined period which follows the test 1003, operation 1004 is performed.</li></ul>

0188It will be noted that, in accordance with the functioning mode illustrated in Figures 9 and 10, the initial base station uses static criteria, that is to say which do not immediately change value according to the change in the network or mobile stations, in order to choose a replacement base station, whilst the mobile station envisaged as the future base station can accept or refuse the role of new base station, using dynamic criteria, that is to say taking into account immediately any change in the state of the mobile station which would prevent its activity as a base station.

0189Figures 11 and 12 illustrate how, at the initiative of a station which is initially a mobile station, a change in base station can be effected. For example, when such a mobile station has locked onto the initial base station, following its being powered up, and when this mobile station is a candidate for being a base station (for example because it supports all the variants and the most extensive modes of the DECT standard), a test 1101 is positive. Otherwise, this procedure is ended. When the result of test 1101 is positive, during an operation 1102, the mobile station listens to the channel known, in the DECT standard, under the name of "Q". On this channel, in fact, the initial base station regularly broadcasts information which may be useful to mobile stations and, in particular, information concerning the DECT profiles which it supports.

0190Next, during a test 1103, the mobile station determines whether or not it has better capabilities of being a base station than the initial base station. When the result of test 1103 is negative, the procedure is ended. When the result of test 1103 is positive, during an operation 1104, the mobile station sends a message <i>"chg_base_request",</i> which means change in base required, to the initial base station, and then allows a sufficient period to pass for the base station to be able, if it is in accordance with the communication device of the present invention, to send a message in answer.

0191Then, during a test 1105, the mobile station determines whether or not it has received, in return, from the base station, a message <i>"chg_base_accept",</i> which means acceptance of change in base. When the result of test 1105 is negative, the mobile station considers that it has received a refusal to change base on the part of the initial base station, and the base change procedure is ended.

0192When the result of test 1105 is positive, the operations 1106, 1107 and 1108 are respectively identical to operations 1006, 1007 and 1008. Then the base station change procedure is ended.

0193On the initial base station side, when, during a test 1201, it determines that it has received a message <i>"chg_base_request",</i> from a mobile station which is locked, it performs a test 1202 during which it determines whether or not, both at the same time, the information <i>"BA"</i> representing its communication capability is equal to "true" and its operating mode <i>MO</i> corresponds to that of a base station.

0194When the result of test 1202 is negative, during an operation 1203, the initial base station sends, to the mobile station under consideration, a message <i>"chg_base_reject".</i> Then the procedure is ended. When the result of test 1202 is positive, during an operation 1204, the initial base station sends, to the mobile station under consideration, a message <i>"chg_base_accept".</i> Then, during a test 1205, the initial base station determines whether or not there is an active connection.

0195When the result of test 1205 is positive, it is reiterated. When the result of test 1205 is negative, during an operation 1206, the base station sends, to the mobile station under consideration, the information stored in the table <i>table_SM,</i> and in the lists <i>list_SM_auto, list_SM_manual</i> and <i>list_SM_direct.</i>

0196Next, during a test 1207, the initial base station determines whether or not it has received, from the mobile station under consideration, a message acknowledging the data transfer. When the result of test 1207 is negative, it is reiterated. When the result of test 1207 is positive, during an operation 1208, the initial base station changes operating mode and starts to function in mobile station mode, and the operation of changing base station is ended with success.

0197Figure 13 depicts: <ul id="ul0050" list-style="dash" compact="compact"><li>in the form of messages 1301 to 1304, the messages exchanged between the initial base station, on the left, and the mobile station which will become a base station, on the right, in the context of the procedure illustrated in Figures 9 and 10, and</li><li>in the form of messages 1305 and 1306, the messages exchanged between a mobile station, on the left, and the base station, in the context of the procedure illustrated in Figures 11 and 12.</li></ul>

0198In order to collect information concerning the capability of the mobile stations present in the network of operating in base station mode, the base station according to the present invention uses a message of the broadcast type illustrated in Figure 14A. The base station thus interrogates all the mobile stations in order to obtain the following information: <ul id="ul0051" list-style="dash" compact="compact"><li>a list of the mobile stations which can switch automatically into base station mode,</li><li>this same list sorted according to one or more parameters chosen by the base station,</li><li>the identity of the mobile station which has the best overall capability of operating in base station mode, at a given instant,</li><li>the identity of the mobile station which has the best capability of operating in base station mode, according to one or more criteria fixed by the base station.</li></ul>

0199A first type of message 1401 (in Figure 14A) is a request from the base station broadcast to all the mobile stations, which includes the following fields: <ul id="ul0052" list-style="dash" compact="compact"><li>a message code field 1402 <i>"broadcast_SB_req",</i> which means approximately "request broadcast by the base",</li><li>a type field 1403 <i>CT,</i> defining the type of request concerned,</li><li>a length field 1404 <i>CL,</i> which defines the number of parameters in the request, and</li><li>parameter fields 1405 <i>CP(0)</i> to 1406 <i>CP(CL-1),</i> which contain the criteria with respect to which the answer is awaited.</li></ul>

0200The type field 1403 <i>CT</i> and length field 1404 <i>CL</i> can take different values, making it possible to specify to the different mobile stations how to respond to the request and according to which criteria, the latter being specified by the fields 1405 to 1406.

0201When the information transmitted in the field 1403 <i>CT</i> is equal to "0", each mobile station must without delay send its capability of acting as a base station and, if the value contained in the field 1404 <i>CL</i> is non-nil, each mobile station must return the value of the parameters specified in the request.

0202When the information transmitted in the field 1403 <i>CT</i> is equal to "1", each mobile station must send its capability of acting as a base station after a period whose value represents the value of the capability of the mobile station of becoming a base station, and, if the value contained in the field 1404 <i>CL</i> is non-nil, each mobile station must return the value of the parameters specified in the request.

0203The measurement of the capability of the mobile station of becoming a base station is determined in accordance with the answer time described below.

0204According to the first to sixth aspects of the invention, the parameters represented by the fields 1405 to 1406 include: <ul id="ul0053" list-style="dash" compact="compact"><li>the operational capability <i>CO,</i></li><li>the available memory capacity,</li><li>the DECT profiles supported,</li><li>the DECT slot type supported (single, double or half-slot), and</li><li>the computing capacity of the central unit.</li></ul>

0205According to the seventh and eighth aspects of the invention, the parameters represented by the fields 1405 to 1406 include: <ul id="ul0054" list-style="dash" compact="compact"><li>the operational capability <i>CO,</i></li><li>the available memory capacity <i>CM,</i></li><li>its energy coefficient <i>CE,</i></li><li>its fixity coefficient <i>CF,</i></li><li>its network interface information <i>IR,</i></li><li>the DECT profiles supported,</li><li>the DECT slot type supported (single, double or half-slot), and</li><li>the computing capacity of the central unit.</li></ul>

0206The message 1411 <i>"broadcast_SB_ans"</i> (in Figure 14B), which means approximately "answer to the message broadcast by the base station", concerns the answer of the different mobile stations to the base station. This message 1411 is sent using the oriented connection mode. It includes the following fields: <ul id="ul0055" list-style="dash" compact="compact"><li>a message code field 1412,</li><li>an identity field 1413, in which the mobile station specifies its identity,</li><li>an answer field 1414 <i>CR,</i> stating the answer of the mobile station,</li><li>a length field 1415 <i>CL',</i> representing the number of data in the answer,</li><li>data fields 1416 to 1417, containing the data required by the base station.</li></ul>

0207The answer field 1414 <i>CR</i> can take the following values: <ul id="ul0056" list-style="dash" compact="compact"><li><i>"accept"</i> ("acceptance"), meaning that the communication station has the capability of acting as a base station, the data fields, if the field <i>length</i> 1415 indicates a non-nil length, then give information concerning the parameters required by the base station,</li><li><i>"reject"</i> ("refusal"), meaning that, momentarily, the mobile station cannot act as a base station or does not have information relating to the parameters required by the base station. The data fields, if the field <i>length</i> 1415 indicates a non-nil length, can then give an explanation for the rejection.</li></ul>

0208An absence of answer to the message 1401, on the part of a mobile station, is considered to be an answer whose answer field <i>CR</i> would be <i>"reject",</i> when a predetermined period of time has elapsed.

0209By default, if in the message 1401 the operational capability is not required, only the mobile stations having the capability of switching automatically from one functioning mode to another can respond by means of a message 1411.

0210Figure 15 represents an exchange of messages between the base station and each mobile station having the capability of becoming a base station. The message 1401 is broadcast by the base station at regular time slots, for example every minute.

0211In Figure 15, the message 1401A is a message 1401 of the type without delay (<i>CT</i>=0) and the length field <i>CL</i> is also equal to "0". Each of the mobile stations according to the present invention then answers by return (that is to say without waiting), in the form of messages 1411A, 1411B or 1411C. In the example described the mobile stations 204, 205 and 201 answer, the first two with an answer field <i>CR</i> of the <i>"accept"</i> type and the last with an answer field <i>CR</i> of the <i>"reject"</i> type.

0212In order to determine the answer field, each mobile station according to the present invention determines whether or not its operating code is one of the codes <i>"SB/SM_auto"</i> or <i>"SB/SM_manual",</i> and, in the affirmative, whether its available memory capacity is greater than the predetermined value <i>MD_N1.</i>

0213In Figure 16, the broadcast message 1401B is a message 1401 of the type with delay (<i>CT</i>=1) and with parameters (<i>CL</i>=1), the only parameter adopted being the operational capability. The mobile stations which have a capability of functioning as a base station answer whilst waiting for a period of time which is a function of the value of their operational capability: the first mobile stations which answer have an operational capability equal to <i>"SB/SM_auto"</i> (message 1411D and 1411E), whilst the last mobile station which responds has an operational capability equal to <i>"SB/SM_manual"</i> (message 1411F).

0214In general terms, in the embodiment of the first to sixth aspects of the present invention, the period of waiting before the answer is determined as from the instant of receiving the message 1401B. This period takes the value:<maths id="math0001" num=""><math display="block"><mrow><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">answer</mtext></mrow></msub><mtext> = </mtext><msub><mrow><mtext mathvariant="italic">CCO.t</mtext></mrow><mrow><mtext mathvariant="italic">CO</mtext></mrow></msub><mtext> + </mtext><msub><mrow><mtext mathvariant="italic">CPR.t</mtext></mrow><mrow><mtext mathvariant="italic">CPR</mtext></mrow></msub><mtext> + </mtext><msub><mrow><mtext mathvariant="italic">CMD.t</mtext></mrow><mrow><mtext mathvariant="italic">CMD</mtext></mrow></msub><mtext>,</mtext></mrow></math><img file="EP0984652A2_D0001.tif" /></maths>    a formula in which: <ul id="ul0057" list-style="dash" compact="compact"><li><i>CCO</i> is the operational capability coefficient (which is equal to "0" if the operational capability is <i>"SB/SM_auto",</i> "5" if the operational capability is <i>"SB/SM_manual",</i> "5" if the operational capability is <i>"SM/SM_direct"</i> and infinity if the operational capability is equal to <i>"SM"</i>),</li><li><i>CPR</i> is the supported profiles coefficient (which is equal to "0" if the profiles supported are B, MMAP and GAP, "1" if the profiles supported are A and GAP and "2" if the only profile supported is GAP),</li><li><i>CMD</i> is the available memory coefficient,</li><li><i>t</i>_<i>CCO</i> is the period allocated to the operational capability coefficient,</li><li><i>t</i>_<i>CPR</i> is the period allocated to the supported profile coefficient,</li><li><i>t</i>_<i>CMD</i> is the period allocated to the available memory coefficient.</li></ul>

0215For example the above three periods are equal to 10 milliseconds (the period of a DECT frame for the answer period always to be a multiple of the period of a DECT frame).

0216In general terms, in the embodiment of the seventh and eighth aspects of the present invention, the period of waiting before the answer is determined as from the instant of receiving the message 1401B. This period takes the value:<maths id="math0002" num=""><math display="block"><mrow><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">answer</mtext></mrow></msub><mtext> = </mtext><msub><mrow><mtext mathvariant="italic">CCO.t</mtext></mrow><mrow><mtext mathvariant="italic">CO</mtext></mrow></msub><mtext> + </mtext><msub><mrow><mtext mathvariant="italic">CPR.t</mtext></mrow><mrow><mtext mathvariant="italic">CPR</mtext></mrow></msub><mtext> + </mtext><msub><mrow><mtext mathvariant="italic">CND.t</mtext></mrow><mrow><mtext mathvariant="italic">CMD</mtext></mrow></msub><mtext> + </mtext><msub><mrow><mtext mathvariant="italic">CE.t</mtext></mrow><mrow><mtext mathvariant="italic">CE</mtext></mrow></msub><msub><mrow><mtext mathvariant="italic"> + CF.t</mtext></mrow><mrow><mtext mathvariant="italic">CF</mtext></mrow></msub><msub><mrow><mtext mathvariant="italic"> + CIR.t</mtext></mrow><mrow><mtext mathvariant="italic">CIR</mtext></mrow></msub><mtext mathvariant="italic">,</mtext></mrow></math><img file="EP0984652A2_D0002.tif" /></maths>    a formula in which: <ul id="ul0058" list-style="dash" compact="compact"><li><i>CCO</i> is the operational capability coefficient (which is equal to "0" if the operational capability is <i>"SB/SM_auto",</i> "5" if the operational capability is <i>"SB/SM_manual",</i> "5" if the operational capability is <i>"SM/SM_direct"</i> and infinity if the operational capability is equal to <i>"SM"</i>),</li><li><i>CPR</i> is the supported profiles coefficient (which is equal to "0" if the profiles supported are B, MMAP and GAP, "1" if the profiles supported are A and GAP and "2" if the only profile supported is GAP),</li><li><i>CMD</i> is the available memory coefficient,</li><li><i>t</i>_<i>CCO</i> is the period allocated to the operational capability coefficient,</li><li><i>t</i>_<i>CPR</i> is the period allocated to the supported profile coefficient,</li><li><i>t</i>_<i>CMD</i> is the period allocated to the available memory coefficient,</li><li><i>t</i>_<i>CE</i> is the period allocated to the energy coefficient,</li><li><i>t</i>_<i>CF</i> is the period allocated to the fixity coefficient,</li><li><i>t</i>_<i>CIR</i> is the period allocated to the network interface coefficient.</li></ul>

0217For example the above six periods are equal to 10 milliseconds (the period of a DECT frame for which the answer period is always a multiple of the period of a DECT frame).

0218In Figure 16, the formula for calculating the answer time is limited to<maths id="math0003" num=""><math display="block"><mrow><msub><mrow><mtext mathvariant="italic">T</mtext></mrow><mrow><mtext mathvariant="italic">answer</mtext></mrow></msub><mtext> = </mtext><msub><mrow><mtext mathvariant="italic">CCO.t</mtext></mrow><mrow><mtext mathvariant="italic">CO</mtext></mrow></msub><mtext mathvariant="italic">,</mtext></mrow></math><img file="EP0984652A2_D0003.tif" /></maths>    since the only parameter represented in the message 1601 is the operational capability parameter.

0219Figure 17 shows that the messages are transmitted according to a predetermined timing. Each communication cycle 1701, 1702 or 1703 lasts 10 milliseconds and is divided into twelve equal time slots. For a communication, one or more time slots for each cycle are allocated in a fixed manner.

0220Figure 18A depicts the state of the art for establishing a connection internal to a cell. Figure 18A shows the route of an internal communication between a mobile station 1802 and a mobile station 1803. This communication passes through a base station 1801. The information which pass at time <i>t</i> over the link between the mobile station 1802 and the base station 1801 next passes over the link between the base station 1801 and the mobile station 1803. There is therefore a duplication of the information and a dual occupation of the communication medium of the cell for two transmissions of the same information.

0221This dual occupation of the communication medium is not critical when the information transmitted is voice information. In the case of a data communication, the duplication of the links, of the information and of the occupation of the communication medium may saturate the cell and block a request for connection to the outside of the cell.

0222In Figures 18B and 18C, the functioning of the device which is the object of the present invention can be seen, a functioning intended to avoid such a duplication.

0223In this functioning: <ul id="ul0059" list-style="dash" compact="compact"><li>when at least one of the mobile stations which is to communicate, referenced 1805 and 1806, is capable of functioning in base station mode, or when the mobile stations 1805 and 1806 are both capable of communicating direct, the cell is organised so that communication between the two mobile stations is direct, without passing through another station,</li><li>and, in the contrary case, a mobile station 1810 capable of functioning as a base station takes this role vis-à-vis the two mobile stations 1805 and 1806 which are to communicate and constitutes with them a new cell, in order to release the initial base station 1804 from the traffic concerning communication between the mobile stations 1805 and 1806.</li></ul>

0224Figure 19 shows, in the form of a flow diagram, how the creation of a new cell is implemented or the mobile stations are put in direct communication.

0225When, during an operation 1901, the base station 1804 receives a call request internal to the cell, from a mobile station 1806 and intended for a mobile station 1805, it performs a test 1902 during which it determines: <ul id="ul0060" list-style="dash" compact="compact"><li>whether the connection requested requires a number of slots greater than a predetermined value (for example four slots, a value beyond which the communication is necessarily other than a voice communication), or</li><li>whether the number of slots necessary is greater than the number of slots available.</li></ul>

0226When the result of test 1902 is negative, during an operation 1903, the connection between the mobile stations 1805 and 1806 is established by means of the base station, in a fashion known in the state of the art prior to the present invention.

0227When the result of test 1902 is positive, during a test 1904, the base station determines whether or not at least one of the mobile stations 1805 or 1806 has a current connection.

0228When the result of test 1904 is positive, operation 1903 is performed. When the result of test 1904 is negative, during a test 1905, the base station determines whether or not the mobile stations 1805 and 1806 are both in the list <i>SM_direct</i>. When the result of test 1905 is positive, during an operation 1906, the base station sends, to each of the mobile stations 1805 and 1806, a message <i>"switch-mode-request"</i> in order to indicate to them to switch into direct communication mode, and to indicate to them the identity of the mobile station which constitutes their interlocutor (see Figure 21B).

0229In the event of failure of the implementation of the direct communication between the mobile stations 1805 and 1806 (for example if one of the mobile stations rejects the switching into direct communication mode), a test 1907 is performed (see below).

0230In the event of success in putting the mobile stations 1805 and 1806 in direct communication, at the end of their direct communication, the two mobile stations synchronise themselves once again with the base station 1804.

0231When the result of test 1905 is negative, during a test 1907, the base station 1804 determines whether or not the mobile station 1805 is in the <i>list_SM_auto.</i> When the result of test 1907 is positive, during an operation 1908, the base station 1804 sends to the mobile station 1805 a message <i>"switch-mode-request"</i> 2101 (Figure 21A) in order to indicate to it that it should switch into base station mode and sends it the identity of the mobile station 1806 so that the mobile station 1805 allocates access rights to it.

0232In addition, on reception of a message <i>"switch-mode-accept"</i> 2102 from the mobile station 1805, the base station 1804 sends to the mobile station 1806 a message <i>"switch-base-request"</i> 2103 containing the identity of the base station 1805, in order to indicate to the mobile station 1806 that it should synchronise itself with the new base station 1805 (see Figure 21A).

0233In the event of failure of the switching of the mobile station 1805 into base station mode (for example if it rejects the switching), a test 1909 is performed (see below).

0234When the result of test 1907 is negative, during a test 1909, the base station 1804 determines whether or not the mobile station 1806 is in the <i>list_SM_auto.</i> When the result of test 1909 is positive, during an operation 1910, the base station 1804 sends to the mobile station 1806 a message <i>"switch-mode-request"</i> 2101 in order to indicate to it that it should switch into base station mode and sends it the identity of the mobile station 1805 so that the mobile station 1806 allocates access rights to it.

0235In addition, on reception of a message <i>"switch-mode-accept"</i> 2102 from the mobile station 1806, the base station 1804 sends to the mobile station 1805 a message <i>"switch-base-request"</i> 2103 containing the identity of the base station 1806, in order to indicate to the mobile station 1805 that it should synchronise itself with the new base station 1806.

0236It will be seen, with regard to Figure 21A, that, for the one of the mobile stations which switches into base station mode, as soon as the data communication 2104 between the stations 1805 and 1806 is ended, it returns to mobile station mode after having sent a message <i>"switch-base-request"</i> 2105 to the mobile station with which it was communicating data. The mobile station which receives this message 2105 then synchronises itself once again with the base station 1804.

0237In the event of failure of the switching of the mobile station 1806 into base station mode (for example if it rejects the switching), an operation 1911 is performed (see below).

0238When the result of test 1909 is negative, during an operation 1911 (Figure 20), the base station determines whether or not the number of slots which remain available is strictly less than the number of slots necessary for the requested communication.

0239When the result of test 1911 is negative, operation 1903 is performed. When the result of test 1911 is positive, during an operation 1912, the temporary variable k is initialised to the value "0". Then, during a test 1913, the base station determines whether or not the value of the variable k is strictly less than the size of the list <i>list_SM_auto.</i> When the result of test 1913 is negative, operation 1903 is performed. It should be noted here that the performance of operation 1903 does not guarantee the setting up of the communication, rejection procedures being provided, in accordance with the known state of the art. When the result of test 1913 is positive, during a test 1914, the base station determines whether or not the <i>k</i>^th station in the list <i>list_SM_auto</i> has a current connection.

0240When the result of test 1914 is positive, during an operation 1915, the value of the variable <i>k</i> is incremented by 1. Then test 1913 is reiterated. When the result of test 1914 is negative, during an operation 1916, the base station 1804 sends, to the mobile station identified at the <i>k</i>^th position in the list <i>list_SM_auto,</i> here the mobile station 1810, a message <i>"switch-mode-request",</i> and then, if the mobile station under consideration 1810 agrees to take the role of the new base station, the initial base station 1804 sends, to each of the mobile stations 1805 and 1806, a message <i>"switch-base-request",</i> indicating the identity of the new base station 1810 so that each of the mobile stations 1805 and 1806 synchronises itself with the new base station 1810 (see Figure 22).

0241At the end of the communication between the mobile stations 1805 and 1806, the new base station 1810 once again switches into mobile station functioning mode.

0242If, on reception of the message <i>"switch-mode-request",</i> the mobile station 1810 refuses to change communication mode, by sending a message <i>"switch-mode-reject",</i> or by not responding to the message <i>"switch-mode-request",</i> operation 1915 is performed by the base station 1804.

0243According to a variant, not shown, when the result of test 1913 is negative, the part of the flow diagram illustrated in Figures 19 and 20, starting from test 1907, is once again implemented, but considering the list <i>"list_SM_manual"</i> in place of the list <i>"list_SM_auto".</i>

0244In Figure 21A it can be seen that, for the mobile station 1805 to switch into base station mode and for the mobile station 1806 to attach itself to the base station 1805, the initial base station 1804 sends first of all, to the mobile station 1805, a message <i>"switch-mode-request"</i> 2101 and awaits in return a message <i>"switch-mode-accept"</i> 2102. Then the initial base station 1804 sends, to the mobile station 1806, a message <i>"switch-base-request"</i> 2103, and awaits in return a message <i>"switch-base-accept"</i> 2106.

0245When the communication between the stations 1805 and 1806 is ended, the message <i>"switch-base-request"</i> 2105 is followed in return by a message <i>"switch-base-accept"</i> 2107.

0246In Figure 21B it can be seen that, to establish direct communication between the mobile stations 1805 and 1806, during operation 1906, the base station 1804 first of all sends, to one of the mobile stations involved in the communication to be set up (for example the station 1805), a message 2111 <i>"switch-mode-request",</i> indicating the requested communication mode (direct communication mode) and indicating the identity of the other mobile station. On reception of a message <i>"switch-mode-accept"</i> 2112 from the mobile station (station 1805 in our example) for which the message <i>"switch-mode-request"</i> 2111 was intended, the base station 1804 sends, to the other mobile station involved in the communication (station 1806 in our example), a message <i>"switch-mode-request"</i> 2113 indicating the requested communication mode (direct communication mode) and indicating the identity of the other mobile station. On reception of a message <i>"switch-mode-accept"</i> 2114 from the mobile station (station 1806 in our example) for which the message <i>"switch-mode-request"</i> 2113 was intended, the two mobile stations switch into direct communication mode. At the end of the communication, the station 1805 sends, to the station 1806, a message <i>"switch-mode-request"</i> 2116 and receives in return a message <i>"switch-mode-accept"</i> 2117, and the two stations 1805 and 1806 then switch into mobile station mode.

0247In Figure 22, it can be seen that, to establish a communication between the mobile stations 1805 and 1806 by means of a new base station 1810, during operation 1916, the base station 1804 first of all sends, to the mobile station 1810, a message <i>"switch-mode-request"</i> 2201 indicating the required communication mode, base station mode, and the two mobile stations 1805 and 1806 to which access rights are to be opened. On reception, from the mobile station 1810, of a message <i>"switch-mode-accept"</i> 2202, the base station 1804 sends, to the mobile station 1806, a message <i>"switch-base-request"</i> 2203.

0248On reception of a message <i>"switch-base-accept"</i> 2208 in return, the base station 1804 sends, to the mobile station 1805, a message <i>"switch-base-request"</i> 2204. Each of the messages 2203 and 2204 indicates, to each of the mobile stations, that the new base station which concerns them is station 1810.

0249After the mobile station 1805 has sent a message <i>"switch-base-accept"</i> 2209 to the base station 1804, mobile stations 1805 and 1806 attach themselves to the new base station 1810.

0250By means of communications 2205 and 2206, the mobile stations 1806 and 1805 then communicate data to each other, through the new base station 1810. At the end of the communication of the data, the new base station 1810 sends, to the mobile station 1806, a message <i>"switch-base-request"</i> 2207 and, to the mobile station 1805, a message <i>"switch-base-request"</i> 2208, indicating to each of the mobile stations that the new base station is the station 1804.

0251On reception, in return, of messages <i>"switch-base-accept"</i> 2210 and 2211, from the mobile stations 1805 and 1806, the base station 1810 switches into mobile station mode.

0252Figure 23 describes a flow diagram for classifying mobile stations having a capability of switching automatically into base station mode, as a function of criteria defining this capability of becoming a base station.

0253Naturally, a similar procedure can be followed to classify the list of mobile stations having a capability of switching manually into base station mode.

0254The procedure illustrated in Figure 23 is executed by a base station when a new mobile station (hereinafter designated SMk) joins itself to a cell and sends a message illustrated in Figures 6A and 6B.

0255When this event occurs, during an operation 3201, the controller 306 of the base station effects an initialisation of the temporary variable <i>I</i> to the value "0". Then, during a test 3202, the controller 306 determines whether or not the value of the temporary variable <i>I</i> is greater than or equal to the size of the list <i>list_SM_auto.</i> When the result of test 3202 is positive, during an operation 3207, the identity of the mobile station SMk is inserted at position <i>I</i> in the list <i>list_SM_auto,</i> and the classification procedure is terminated.

0256When the result of test 3202 is negative, during a test 3203, the controller 306 determines whether or not the maximum transmission rate of the station SMk is strictly greater than the maximum rate of the <i>l</i>^th station of the list <i>list_SM_auto.</i>

0257When the result of test 3203 is positive, operation 3207 is performed. When the result of test 3203 is negative, during a test 3204, the controller 306 determines whether or not the maximum transmission rate of the station SMk is strictly less than the maximum rate of the <i>l</i>^th station in the list <i>list_SM_auto.</i>

0258When the result of test 3204 is positive, during an operation 3208, the value of the temporary variable <i>I</i> is incremented by 1 and test 3202 is reiterated. When the result of test 3204 is negative, during a test 3205, the controller 306 determines whether or not the memory capacity of the station SMk is strictly greater than the memory capacity of the <i>l</i>^th station in the list <i>list_SM_auto.</i>

0259When the result of test 3205 is positive, operation 3207 is performed. When the result of test 3205 is negative, during a test 3206, the controller 306 determines whether or not the memory capacity of the station SMk is strictly less than the memory capacity of the <i>l</i>^th station in the list <i>list_SM_auto.</i>

0260When the result of test 3206 is positive, operation 3208 is performed. When the result of test 3206 is negative, a new parameter for the capability of becoming a base station is considered and tests similar to tests 3203 and 3204, or 3205 and 3206, are performed, considering this new parameter in place of the maximum transmission rate (tests 3203 and 3204) or memory capacity (tests 3205 and 3206). Naturally, the parameters tested are tested in decreasing order of importance. When the last parameter has been considered with once again a negative result for the two tests concerning it, operation 3207 is performed.

0261It will now be described how, when a station has determined that it has better capabilities of being a base station than the current station, it sends to it a message <i>"chg-base-request",</i> which includes information representing its fixity coefficient <i>CF</i>, its energy coefficient <i>CE</i> and its network interface coefficient <i>CIR</i>.

0262On reception of this message the initial base station then successively compares these coefficients, in decreasing order of their importance (the communication coefficient is of greater importance than the fixity coefficient, itself of greater importance than the energy coefficient): for each coefficient successively processed: <ul id="ul0061" list-style="dash" compact="compact"><li>if the initial base station has a better coefficient than the mobile station, it rejects the change in base, by means of a message <i>"chg-base-reject",</i></li><li>if the initial base station has a lesser coefficient than the mobile station, it accepts the change in base, by means of a message <i>"chg-base-accept",</i> and</li><li>in the latter case (equality for the coefficient under consideration) it goes to the following coefficient.</li></ul>

0263When all the coefficients have been processed, the base station returns an acceptance of change in base, in the form of a message <i>"chg-base-accept".</i>

0264For implementing this procedure, the mobile station follows the flow diagram illustrated in Figure 11, only operation 1104 being modified in order to transmit, in the message <i>"chg-base-request",</i> information representing the coefficients <i>CF, CE</i> and <i>CIR</i>.

0265The base station then performs the operations illustrated in Figure 25. First of all, during an operation 2501, the base station receives a message <i>"chg-base-request".</i> Next, during a test 2502, the base station determines whether or not its operating mode is the base station mode (<i>MO</i> = <i>SB</i>) and at the same time it has the capability of changing functioning mode (<i>BA =</i> true). When the result of test 2502 is negative, the controller 306 of the base station performs an operation 2505, during which it sends a message <i>"chg-base-reject"</i> to the mobile station which sent the message <i>"chg-base-request".</i> The procedure is then ended (on a failure).

0266When the result of test 2502 is positive, during a test 2503, the controller 306 determines whether or not the coefficient <i>CIR</i> received is nil. When the result of test 2503 is positive, during a test 2512, the controller 306 determines whether or not the coefficient <i>CIR</i> stored in the read-only memory 305 is nil. When the result of test 2512 is negative, operation 2505 is performed. When the result of test 2512 is positive, during a test 2504, the controller 306 determines whether or not the coefficient <i>CF</i> received is less than or equal to the coefficient <i>CF</i> stored in the read-only memory 305 and at the same time the coefficient <i>CE</i> received is less than or equal to the coefficient <i>CE</i> stored in the read-only memory 305.

0267When the result of test 2504 is positive, operation 2505 is performed. When the result of test 2504 is negative, an operation 2507, described below, is performed.

0268When the result of test 2503 is negative, during a test 2506, the controller 306 determines whether or not the coefficient <i>CIR</i> received is different from the coefficient <i>CIR</i> stored in the read-only memory and at the same time the coefficient <i>CIR</i> stored in the read-only memory is different from "2".

0269When the result of test 2506 is negative, test 2504 is performed. When the result of test 2506 is positive, during operation 2507, the initial base station sends, to the mobile station which sent the message <i>"chg-base-request",</i> a message <i>"chg-base-accept".</i> Next, during a test 2508, the controller 306 determines whether or not the coefficient <i>CIR</i> stored in the read-only memory is nil.

0270When the result of test 2508 is negative, the procedure is completed and the initial base station remains in base station mode. When the result of test 2508 is positive, during a test 2509, the controller 306 determines whether or not a connection is active. When the result of test 2509 is positive, it is reiterated. When the result of test 2509 is negative, during an operation 2510, the initial base station switches into mobile station mode.

0271Where the communication station is combined with an access to an external network, the device illustrated in Figure 3B also has: <ul id="ul0062" list-style="dash" compact="compact"><li>an external communication means 314 accessing an external line 315 of an external network, and</li><li>a line controller 313.</li></ul>

0272The line controller 313 is adapted to detect the taking of the external line 315 by the external communication means 314.

0273In this case, it functions by implementing the flow diagram illustrated in Figure 26. It will be seen there that initially such a device functions in base station mode, operation 2601. It then performs a test 2602, during which it determines whether or not the external line is taken, using the line controller 313.

0274When the result of test 2602 is negative, it is reiterated. When the result of test 2602 is positive, during a test 2603, it determines whether or not access to the external line is effected by a mobile station. When the result of test 2603 is positive, test 2602 is reiterated. When the result of test 2603 is negative, during an operation 2604, the controller 306 causes the operating mode to switch into mobile station mode. Then, during a test 2605, the controller 306 determines whether or not the external line is busy, using the line controller 313. When the result of test 2605 is negative, it is reiterated. When the result of test 2605 is positive, during an operation 2606, the operating mode is switched into base station mode.

0275The procedure followed by the base station for requesting a new base station when its communication quality is too low, is illustrated in Figure 27.

0276The station under consideration operating in base station mode, operation 2301, its controller 306 performs a test 2302 during which it determines whether or not: <ul id="ul0063" list-style="dash" compact="compact"><li>the quantity of energy <i>NB</i> available is less than the quantity <i>NB_min,</i> or</li><li>the quality of the radio signal <i>QR</i> is less than the value <i>QR_min.</i></li></ul>

0277When the result of test 2302 is negative, during an operation 2310, the controller 306 waits for a time <i>T7,</i> and then the test 2302 is reiterated. When the result of test 2302 is positive, during an operation 2303, the controller 306 performs a procedure of seeking a new base station.

0278Following the operation 2303, during a test 2304, the controller 306 determines whether or not a new base station has been found. When the result of test 2304 is positive, during an operation 2305, the value <i>DB</i> is set to the value "1" and then, during an operation 2306, the operating mode of the base station under consideration is switched into mobile station mode.

0279When the result of test 2304 is negative, during a test 2307, the controller 306 determines whether or not the quantity of available energy <i>NB</i> is less than the value <i>NB_min.</i>

0280When the result of test 2307 is positive, operation 2306 is performed. When the result of test 2307 is negative, during an operation 2309, the central unit waits for a time <i>T8,</i> and then test 2302 is reiterated.

0281Naturally, the procedure illustrated in Figure 27 can be followed only when no connection is active. Otherwise it is necessary to add a connection deactivation operation, before operation 2306.

0282For a mobile station (see Figure 28), when it receives a message <i>"new-base-request"</i> which designates it, operation 2801, its controller 306 performs first of all a test 2802, during which it determines whether or not on the one hand the quantity of energy <i>NB</i> available is greater than the quantity <i>NB_max</i> and on the other hand, at the same time, the quality of the radio signal <i>QR</i> is higher than the value <i>QR_max.</i>

0283When the result of test 2802 is negative, during an operation 2807, the controller 306 sends a message <i>"new-base-reject"</i> to the base station, and thus ends the procedure of changing its operating mode. When the result of test 2802 is positive, during an operation 2803, the central unit 306 sends, to the base station, a message <i>"new-base-accept".</i>

0284Following operation 2803, the controller 306 determines, during a test 2804, whether or not it has received the information necessary for its functioning in base station mode.

0285When the result of test 2804 is negative, it is reiterated. When the result of test 2804 is positive, during an operation 2805, the controller 306 of the mobile station under consideration sends an acknowledgement message <i>"ack"</i> to the initial base station. Then, during an operation 2806, the controller 306 switches into base station operating mode. The procedure of switching operating mode because of failure of the initial base station is then ended.

0286In order to evaluate the communication quality, a first method consists of determining a transmission error rate.

0287A second method is illustrated in Figure 29. It is intended to be executed at regular time slots. First of all, during an operation 2901, the controller 306 of the base station effects an initialisation of the variables which are used in the flow diagram of Figure 29. Next, during operation 2902, the controller 306 causes a message <i>"signal-strength-request"</i> to be broadcast to all the mobile stations in the cell.

0288Each mobile station then returns a message representing the power of the message <i>"signal-strength-request"</i> which it has received (see in this regard, in the DECT standard, the use of the primitive <i>"PL_ME_SIG_STR_req"</i>).

0289So that all the answers have the time to reach it, the base station waits for a time <i>T9,</i> operation 2903, before performing an operation 2904, during which the variable <i>QR</i> is determined as being the mean of the values of the answers obtained during operation 2903.

0290Figure 30 illustrates a procedure followed by a mobile station which has previously been a base station and which has recovered the capabilities of functioning correctly in base station mode.

0291This station being in mobile station operating mode, operation 3101, its controller 306 performs a test 3102, during which it determines whether or not, all at the same time: <ul id="ul0064" list-style="dash" compact="compact"><li>the quantity of energy <i>NB</i> available is greater than the quantity <i>NB_max,</i></li><li>the quality of the radio signal <i>QR</i> is higher than the value <i>QR_max,</i> and</li><li>the value of the variable <i>DB</i> is equal to "1".</li></ul>

0292When the result of test 3102 is negative, the controller 306 performs an operation 3110, during which it waits for a time <i>T10.</i> Then it reiterates test 3102.

0293When the result of test 3102 is positive, during an operation 3103, the controller 306 gives the value "0" to the variable <i>DB.</i> Then, during an operation 3104, the controller 306 listens out on the channel Q. Next, during a test 3105, the controller 306 determines whether its capabilities of being a base station are better than those of the base station currently active.

0294When the result of test 3105 is negative, the procedure is ended (by a failure). When the result of test 3105 is positive, during an operation 3106, the controller 306 sends a message <i>"chg-base-request"</i> to the active base station. During operation 3106, the mobile station under consideration waits for a sufficient period to enable a communication station according to the present invention and functioning in base station mode to answer, before performing a test 3107.

0295Then, during test 3107, the controller 306 determines whether or not it has received a message <i>"chg-base-accept"</i> from the active base station. When the result of test 3107 is negative, the controller 306 considers that the request to change base station has failed and the procedure is ended (on a failure). When the result of test 3107 is positive, during operation 3108, the controller 306 switches the operating mode into base station mode. Then the procedure is ended (with success).

0296Figure 24 shows a second functioning mode of a communication device according to the eighth aspect of the present invention. When such a communication device has not detected any base station (in accordance with the prior art or after having performed all the operations and tests illustrated in Figure 4, including one of operations 411 or 415, but without reproducing operation 402), and it has an information transmission to effect, it takes the role of base station throughout the transmission.

0297To this end, during an operation 2401, the station under consideration determines that it has an information transmission to effect. It then reproduces operations 401 to 403 in Figure 4, and <ul id="ul0065" list-style="dash" compact="compact"><li>if a base station which provides it with a right of access is detected, it locks onto this base station, but</li><li>if no base station is detected, it performs operation 2402 during which the controller 306 causes the operating mode of the device to switch into base station mode.</li></ul>

0298Next, during an operation 2403, the device waits for a predetermined period <i>T5</i>, whilst regularly transmitting synchronisation signals. This period is intended to leave time for the mobile station with which the device wishes to communicate to lock onto it. Then, during an operation 2404, the device transmits an identification request to the mobile station with which it wishes to communicate. Next, during an operation 2405, it allows a predetermined period <i>T6</i> to pass, which must be sufficient for the mobile station called to be able to respond.

0299Then, during a test 2406, the device determines whether or not it has received, from at least one mobile station, an answer to the identification request. When the result of test 2406 is negative, during an operation 2410, the controller 306 causes the functioning mode of the device to switch into mobile station mode. When the result of test 2406 is positive, during a test 2407, the device determines whether or not the identity of one of the mobile stations corresponds to the identity of the station with which it must communicate.

0300When the result of test 2407 is negative, the operation 2410 is performed. When the result of test 2407 is positive, during an operation 2408, the transmission which the device is to make is effected. Then, at the end of the transmission, during an operation 2409, the transmission is ended. Finally, operation 2410 is performed.

0301According to a first variant, all the communication requests issuing from the other mobile stations are refused, the base station testing the identity of each mobile station requesting communication and accepting only the communications coming from the mobile station with which it has communicated during operation 2408 and which are intended for it. According to this first variant, the other mobile stations therefore do not then benefit from the capability of the device of changing operating mode.

0302According to a second variant, if, whilst the device is acting as a base station, a mobile station locks onto it and attempts to establish a communication, the device behaves as a base station, until the attempt is abandoned or, if the attempt succeeds, until the end of the communication, or else until another base station substitutes itself for it (see Figures 9 to 13). To implement this second variant, after the operation 2409 and before performing operation 2410, the controller 306 of the communication station determines, during a test (not shown), whether or not a connection with it is active, and in the affirmative reiterates this test, at regular time slots. If this test determines that no connection is active, operation 2410 is performed.