Cell selection method in a cellular radio mobile network system

The present invention relates generally the cellular mobile radio that is to say, the cellular radio networks mobile and mobile stations intended to be used in such networks.

The present invention relates more particularly the cell selection when accessing a station movable to such a network, for communication.

It is known to carry out a selection cell, to a network access, by the mobile station itself, the corresponding algorithm used in the mobile station being also called selection algorithm cell.

Specifically, the network broadcasts in the cell waitress, on a particular channel called beacon channel, of information needed to implement such a algorithm, especially those containing information a neighbor cell list to listen for the mobile station to determine which of these neighboring cells or of the serving cell, the received signal level on the path tag is the most favorable. The cell thus determined is, subject to certain other criteria are satisfied, the selected cell for network access. In addition, the commissioning of the mobile station, no serving cell that has been selected, the station mobile explores the set of beacon channels, and determines the server cell using the same criteria.

For a more complete description of the systems Cellular mobile radio such as including GSM (for 'Global System for Mobile communications "in English), reference may be made by example in the book of M. Mouly and MB PAUTHET, entitled "The GSM System for Mobile Communications "(Palaiseau, France, 1992 ISBN: 2-9507190-07-7).

The present invention relates more particularly even cell selection during network access for communication in a cellular network mobile radio having different types of cells in which different types of services are available.

An example of such a network is constituted by a network in which are introduced gradually in a existing infrastructure, corresponding to such a system a second generation system (especially GSM above system), new radio access means this infrastructure, corresponding to a system such as a third generation system (in particular the system UMTS for "Universal Mobile Telecommunication System" English) for the progressive introduction of new services, particularly transmission services high-speed data.

Such a system thus comprises cells or resources under which such new services available, namely UMTS cells, or GSM cells / UMTS (that is to say cells having a channel common tag for GSM radio access means and means of UMTS radio access), and cells in which said new services are not available, namely GSM cells.

In such a system, the possibility exists that selected cell according to the selection algorithm cell mentioned above is a GSM cell, while service required for a given why communication the mobile station accesses the network, require UMTS or GSM / UMTS cell, or conversely the cell selected is a UMTS cell or GSM / UMTS that then service required to satisfy a GSM cell, so the radio resource allocation in a network is not in any case optimized based services required by users.

Another example of such a network is a network in which are introduced into an existing infrastructure corresponding to a given system, for example the system GSM, and in a given geographic area, means additional radio access, dedicated to a group particular user, and allowing these users for additional services this geographical area.

In such a system, are also getting a selected cell according to the selection algorithm cell mentioned above is a cell into which said additional services are not available in particularly in the case where an authorized user to benefit from such additional services is in limit the geographical area, in which case neither the user or the provider of these services are not satisfied.

So the problem is usually made in a cellular mobile radio system comprising different cell types in which different Service types are available, the cell selected for network access is not necessarily to a better cell in terms of services.

It is also known, in a cellular network mobile radio such as in particular the network GSM, perform, during communication, a selection cell to determine a better cell to which transfer the communication, the procedure corresponding being also known in English as the "Handover". It is also known to perform Such a cell selection by the network, based on measurement results that it receives from the mobile station. More Specifically, the selected cell is the first in a list of candidate cells called cells (classified some order of preference according to said results measurement) to which a transfer is possible, that is to say in particular in which resources are available for the call.

Are also known, in a cellular network mobile radio such as the GSM network, said the concept of English "directed retry", that a call transfer (or "handover" in English) a cell initially selected for access to the network to better selected cell subsequently, may be necessary to reflect the that the cell selection is performed so different in both cases, as has been recalled, and thereby can lead to select different cells.

It may further be mentioned WO97 / 44922, describing a cellular radio system mobile having different types of cells, which are available different types of services multimedia, and wherein the selection of a better cell to which to transfer an ongoing call is performed on the measurement results as a basis for Candidate cells, availability of resources these candidate cells, and the type of service required. This document does not address the cell selection when access to the network for communication. In addition, This document describes a mobile station equipped with means to him to implement such a selection of better cell to which transfer calls In progress. If such cell selection was set deals with the mobile station for the cell selection when access to the network for communication, it would include the drawback of requiring many signaling exchanges between mobile station and network for its implementation, resulting in a high consumption of radio resources for such trade, and thus increased the overall level of interference in the network. The current invention also aims to avoid these drawbacks.

The invention has particular object of allow access by a mobile station to a network cellular mobile radio with different cell types in which different Service types are available, avoiding various drawbacks mentioned in the foregoing.

The present invention thus provides a process for cell selection when accessing from a mobile station in a cellular mobile radio network for a communication, said method being essentially characterized in that, said network having different cell types in which different types of services are available, comprises the following steps:<ul><li>cell selection by said mobile station, in for access to the network,</li><li>network access in the cell so selected, corresponding to a given cell type,</li><li>depending on the required type of service for that communication, decision to transfer or not this communication to a cell of another type constituting a best cell in terms of services.</li></ul>

In other words, and with reference to said concept in English "directed retry", the invention may be considered introducing a new application of such a concept, wherein a transfer is performed communication (or "handover" in English) of a cell selected initially for access to the network to a another cell constituting a better cell in terms on duty.

Another object of the present invention consists in a cellular mobile radio network, peremttant to implement such a method (this invention advantageously requires no modification mobile stations to enable its implementation).

Other objects and features of the present invention appear on reading the description Next an embodiment when taken in conjunction with the accompanying drawings, in which:<ul><li>Figure 1 is a diagram showing a example of system to which the present invention is applicable,</li><li>Figure 2 is a diagram intended to illustrate the different steps of an exemplary method according the invention,</li><li>Figures 3 and 4 are diagrams for illustrate an example of means to provide a network which the present invention is applicable to allow using the method of the invention.</li></ul>

A cellular mobile radio system essentially comprises, as shown in Figure 1:<ul><li>a set of base stations (BTS for "Base Transceiver Station "in English), such as those noted BTS0, BTS1, BTS2, and BTS3 BTS4, each of these stations base being, in the example shown, assigned to a cell (Denoted respectively C0, C1, C2, C3, and C4), and these base stations being connected, via a radio interface, with mobile stations, such as MS0, MS1, MS2, MS3, MS4,</li><li>a set of base station controllers (or BSC for "Base Station Controller" in English), such as those rated BSC1 and BSC2, each BSC controlling of viewpoint of radio resource management, a subset cell, the base station controller BSC1 controlling in the example illustrated the cells C0, C1 and C2, and the base station controller controlling BSC2 in this example the cells C3 and C4,</li><li>a plurality of mobile switching centers, also called MSC (for "Mobile Switching Center" in English), only one of which, noted MSC1, is shown in FIG, each MSC being, a non-illustrated manner Specifically, in connection with external networks such that include PSTN (for "Public Switched Telephone Network ") or ISDN (for" Integrated Services Digital Network "), and controlling, from the perspective of the communications management, a subset controllers base stations, the mobile switching center MSC1 controlling in the example illustrated controllers BSC1 and BSC2 base stations.</li></ul>

The assembly formed by the BTS and BSC, also called BSS (For "base station subsystem" in English), which is was called above the means of access to the radio network.

As an example to which the present invention is applicable radio access means formed elements BTS3, BTS4 and BSC2 are new means of access Radio, corresponding to the UMTS system, introduced in existing infrastructure corresponding to the GSM system already having its own radio access means formed BTS0 elements, BTS1, BTS2 and BSC1. Cells such as C0, C1 and C2 then constitute a first type of cells, matching GSM cells, and cells such as C3 and C4 constitute a second cell type, corresponding to UMTS or GSM / UMTS cells. stations mobile considered are also mobile stations dual mode capable of communicating on one or the other of radio interfaces corresponding to these different means radio access.

Figure 2 illustrates the different stages of a exemplary method of the present invention.

The following steps are illustrated in Figure 2:<ul><li>cell selection by a mobile station to of network access, for example the following algorithm cell selection mentioned above (step 1, denoted "Cell Selection")</li><li>network access for a given call, in the cell so selected, corresponding to a given type cell (step 2, denoted by "Access") </li><li>phase of establishing communication (step 21, rated "Establishing communication"), including its turn off the signaling exchange steps necessary for that establishment of communication (such as Steps 22 and 23 marked "Display"), a step decision to transfer or not this communication to a cell of another type constituting a better cell in terms of service (step 3 rated "Transfer?")</li><li>communications phase in the cell and selected (step 24, noted "Communication"), or at least beginning of the communication phase, one or more Transfer can indeed be carried out thereafter, the During this communication.</li></ul>

In cases where a transfer is not decided in step 3, the cell thus selected remains that initially selected for network access.

In cases where a transfer is decided in step 3, the following steps are performed to determine to which cells said other type of communication is to be transferred, these steps may be similar to those usually employed to select a better cell to which transfer calls current, except that they do not apply here at cells of any type, but said cells Another type:<ul><li>a step in which it is determined whether Candidate cells may be said other type determined (step 4, denoted "cell (s) candidate (s)?")</li><li>a step in which it is determined whether a transfer to one or other of these candidate cells, considered in a certain order of preference is possible, that is to say it is not a cell rejected (5 step denoted "cell (s) candidate (s) rejected (s)? ").</li></ul>

In the case where such a non-rejected candidate cell is determined, a transfer to this cell is controlled (Step 6 denoted "Transfer").

In the case where such a candidate cell, or Such a non-rejected candidate cell, can not be found, a transfer can be attempted later to preferably within certain time limits (Steps 7 and 8 marked "Time?"). If no transfer to best cell in terms of service is definitely possible, communication is left in the cell initially selected for network access. The network may then provide, for example in the case considered here a mixed GSM / UMTS, a lower quality of service, including a data transmission service to more low flow, or any replacement service up is a next transfer to a better cell terms of service is possible, according to the movements of the user and the radio conditions change and traffic within the network during this communication.

It should be noted that according to another example cells defined as candidate cells could be cells of any type, and cells candidates to which transfer is attempted only said other type of cells.

In the example illustrated in Figure 1, if the cells C0, C1 and C2 are GSM cells, access to network by a mobile station MS0 such as for example, corresponding to a communication, for example a data transmission broadband service available in a UMTS cell or GSM / UMTS such that cells C3 and C4 for example, can be performed in the manner next:<ul><li>selecting a GSM cell, for example the cell C0, by the mobile station MS0, </li><li>network access and cell C0 selected,</li><li>depending on transmitted signaling data by the mobile station during the establishment phase of the communication, decision of transfer to a UMTS cell or GSM / UMTS; In the example shown, it will be for example of cell C3.</li></ul>

Figures 3 and 4 are diagrams to illustrate an example of means to be provided in the network, respectively, in the MSC and BSC entities, to use a method according to the invention.

As illustrated in Figure 3, an MSC receives a mobile station MS when accessing the network and the phase establishment of a communication:<ul><li>the INF1 identifying information the user,</li><li>INF2 of information to identify the type of service required for the call concerned.</li></ul>

MSC also receives such a database that in particular the HLR database (for "Home Location Register "in English), in response to INF1 information, INF3 information identifying the services the user is allowed to use, and possibly geographical restrictions for such use.

MSC illustrated in Figure 3 further comprises rated M means for determining, from information INF 2 and INF 3, the INF4 information indicating the type of cell constituting a better cell in terms of service for this user and this communication.

For example, in the case considered here of a mixed GSM / UMTS, and as already indicated above, a such a best cell in terms of services may, in If the requested service is a streaming service broadband data available only in a UMTS or GSM / UMTS cell, be such a UMTS cell or GSM / UMTS, or, otherwise, be a GSM cell.

As illustrated in Figure 4 means designated M ' are provided in the BSC entity, to:<ul><li>firstly decide whether a transfer or not to performed to a better cell in terms of service, this decision being taken on the basis of:<ul><li>the selected cell type for access to network, represented by a INF5 information that can be provided by the BSC considered (that is to say, the BSC controlling the current serving cell, that is to say in this case the selected cell for network access)</li><li>the type of cell constituting a better cell in terms of service, represented by the INF4 information</li></ul></li><li>on the other hand, in the case where it is decided that such transfer should actually be done, select that of the cells to which the transfer is make this selection being made on the basis of:<ul><li>information such as INF6 corresponding to measurement results provided by the mobile station MS,</li><li>Information on the availability of resources in the considered candidate cells, such as INF7 information provided by management means radio resources within BSC considered (in the case Transfer said internal or intra-BSC), or such as INF8 information provided by the MSC that controls the BSC (In the case of transfer said external or inter-BSC),</li></ul></li><li>information about the type of cell constituting a better cell in terms of service, such as information INF4.</li></ul>

The means M 'operate essentially the method described above, for, based on information such as INF4 INF8 to determine whether a transfer to best cell in terms of service is to be performed, and if so select the one of the cells to which this transfer is to be performed, the cell thus selected being indicated by information such as INF9 transmitted to the mobile station MS.

The particular embodiment of the means M and M ' so as to operate the assembly according to the method describes, does not represent any particular problem for the skilled, requires no description specific. In addition, the distribution of different functions between MSC and BSC entities can be other than that envisaged above by way of example.

In addition, the transmission of information such as INF1 to INF9, within the network, can be achieved according to known communication protocols within of such a network, that do not require to be described again right here.

The example describes particular allows optimizing resource allocation radio within the network, based on the services required by the users. .

The invention is not limited in this example application, if the selected cell initially for access to the network is a GSM cell and where a transfer is then performed to a UMTS cell or GSM / UMTS. It can also be used in the case where the cell selected initially for access to the network, is a UMTS or GSM / UMTS cell and where a transfer is then made to a GSM cell (if permitted for the requested service), thereby enabling to further optimize radio resource allocation within the network.

Furthermore, as already indicated, the invention is not limited to the application example described corresponding to a mixed GSM / UMTS.