A method for acquiring system information by a mobile station

0001The present invention generally relates to mobile communication systems.

0002Detailed descriptions of mobile communication systems can be found in the litterature, in particular in Technical Specifications published by standardisation bodies such as in particular 3GPP (3^rd Generation Partnership Project).

0003It is simply recalled that the general architecture of a mobile communication system essentially comprises, as illustrated in <figref idref="f0001">figure 1</figref> : <ul id="ul0001" list-style="dash" compact="compact"><li>a Radio Access Network 1, or RAN,</li><li>a Core Network 4, or CN.</li></ul>

0004The RAN comprises network elements such as base stations 2 and base station controllers 3. The RAN is in relation, on the one hand with mobile stations 5, via an interface 6, and on the other hand with the CN via an interface 7. The CN is in relation with external networks (not illustrated specifically). Within the RAN, the base stations communicate with the base station controllers via an interface 8.

0005In systems of UMTS type, the RAN is called UTRAN (UMTS Terrestrial Radio Access Network), the base stations are called Node B, the base station controllers are called RNC (Radio Network Controller), and the mobile stations are called UE (User Equipment). The interface 6 is called Uu interface, the interface 7 is called lu interface, the interface 8 is called lub interface, and an interface 9 between RNCs, called lur interface, is also introduced. The interface 6 is also called radio interface, and the interfaces 7, 8, 9, are also called terrestrial interfaces.

0006Now, there is an evolution of RAN (for example UTRAN) architecture towards an architecture called E-RAN (for example E-UTRAN). This evolution is also called Long Term Evolution. For example, the E-UTRAN comprises network elements such as base stations. The base stations are called e-Node B. The interface between e-Node Bs is called X2 and the interface between one e-Node B and the CN (or Access Gateway) is called S1.

0007In the following, UTRAN will more particularly be considered, as an example of RAN to which the present invention applies; however it should be understood that the present invention is not limited to this particular example.

0008UTRAN performs a number of functions, including RRC (Radio Resource Control) functions, as specified in particular in 3GPP TS 25.331.

0009Broadcasting of system information from UTRAN to UEs in a cell is specified in 3GPP TS 25.331. It is also disclosed in <nplcit id="ncit0001" npl-type="b"><text>H. KAARANEN ET AL: "UMTS Networks, Architecture, Mobility and Services" 2001, JOHN WILEY &amp; SONS, LTD</text></nplcit>, XP002418774. The system information elements are broadcast in System Information Blocks SIBs (SiBs currently specified being called SIB 1, ... SIB 18). A SIB groups together system information elements of the some nature. Different SIBs may have different characteristics, regarding their repetition rate and the requirements on UEs to re-read the SIBs. The system information is organised as a tree. A Master Information Block (MIB) gives references and scheduling information to a number of SIBs in a cell. The SIBs contain the actual system information.

0010<patcit id="pcit0001" dnum="WO02056616A"><text>WO 02/056616</text></patcit> discloses a method that provides for operating a wireless communication system having packet data capabilities, and includes steps of: (a) sending a message from a mobile station to a network on a same physical channel that is used to transmit packet data, the message specifying individual ones of packet system information (PSI) messages that are required for reception by the mobile station; and (b) in response to receiving the message, transmitting only the specified individual ones of the PSI messages from the network to the mobile stations over the same physical channel used to transmit the packet data.

0011<patcit id="pcit0002" dnum="EP1686827A"><text>EP-A-1 686 827</text></patcit> discloses A method and apparatus is provided for signaling network sharing information about neighbor cells in an NS system where a RAN is shared among a plurality of CN operators. In the signaling method, it is determined whether each of neighbor cells of a current cell in which a UE is located, is shared by a CN operator other than a CN operatar controlling the neighbor cell. System information without network sharing information is generated if at least one of the neighbor cells is shared by a CN operator other than a CN operator controlling the neighbor cell. System information including the network sharing information is generated if none of the neighbor cells are shared by any CN operator other than CN operators controlling the neighbor cells. The system information is then broadcast to the UE from the current cell.

0012<patcit id="pcit0003" dnum="WO0072609A"><text>WO 00/72609 A</text></patcit> discloses that in a cellular telecommunications system or network, tags are associated with one or more system control parameters. For example, a given tag value may be indicative of particular values for one or more system information parameters. In each cell, a base station (BS) transmits or braodcasts currently valid tag values. System information blocks including the system information parameters themselves (which correspond to particular tag(s)) are also broadcast by base stations. A mobile station receiving a valid tag value from a base station determines whether or not it has to read system information block(s) corresponding to that tag depending upon whether the base station has already stored or cached such block(s) corresponding to the tag value. As will be appreciated by those skilled in the art, different embodiments of the instant invention may result in the mobile station not having to re-read identical system information each time it changes cells, or while moving in the same cell. This may conserve radio resources and reduce battery consumption, thereby improving standby time of the mobile station.

0013<patcit id="pcit0004" dnum="EP1032236A"><text>EP-A-1 032 236</text></patcit> discloses that in order to control traffic congestion in a cellular satellite telecommunications network, user terminals are grouped together in different predetermined access classes which can be controlled individually in order to restrict access to the network. Cell broadcast messages are transmitted from SAN 1 via satellite 3a to user terminals UTI in a particular cell to provide coorse access class data corresponding to sub-groups of a plurality of the individual access classes permitted or denied access to the network. This coarse data is supplied in response to a predicted call traffic demand produced by a traffic planning model, exceeding the capacity of the network. Additionally, if the demand exceeds the levels predicted by the traffic planning model due to an unpredicted demand, fine access class information is transmitted to control the individual access classes in the sub-groups. The fine access class information, when it is transmitted is detected at a higher rate than the coarse access class information.

0014<patcit id="pcit0005" dnum="US6874113B2"><text>US-B2-6 874 113</text></patcit> disclosss a method for processing a received communication which includes periodic transmissions of a set of information segments. A first transmission of the set of information segments is received and processed to identify each of the segments asvolid or invalid. The valid segments of the first set are then stored. Where all segments of the set are not stored, subsequent transmissions of the set of information segments are received and only those segments not previously stored are processed to identify each such segment as valid or invalid. The valid segments so identified are then stored. Subsequent transmissions are repeatedly received unless all segments of the set have been stored.

0015A problem with such broadcasting of system information is the time it takes for a mobile station to acquire system information. This has a significant impact on the delays as perceived by the user, such as in particular the delays at call establishment, or cell reselection, or call re-establishment. Furthermore, the amount of system information is increasing, due in particular to technology evolutions, such as for example current deployment of new radio access technologies and/or current evolutions of Radio Access Network architecture, thereby still increasing such delays. This negatively affects user experience, Another problem is that such broadcasting of system information requires significant bandwidth, which does not correspond to efficient bandwidth use. Another problem is that such broadcasting of system information lacks flexibility, in particular the broadcast information cannot be optimised or adapted to each situation.

0016It is an object of the present invention to solve part or all of such problems and/or to avoid part or all of such drawbacks.

0017These and other objects are achieved, in one aspect of the present invention, by a method for acquiring system information by a mobile station in a mobile radiocommunication system, comprising a step of: <ul id="ul0002" list-style="dash" compact="compact"><li>acquiring part of said system information on or after access to the network for establishing or re-establishing a radio connection.</li></ul>

0018In another aspect, part of system information which can be acquired on or after said access includes non access related system information.

0019In another aspect, said method comprises a step of: <ul id="ul0003" list-style="dash" compact="compact"><li>acquiring part of said system information before said access,</li></ul>

0020In another aspect, part of system informations which should be acquired before said access includes access -related system information.

0021In another aspect, said method comprises the steps of: <ul id="ul0004" list-style="dash" compact="compact"><li>the mobile station sending at least one request to the network for acquiring system information on or after said access,</li><li>the network sending system information, upon reception of said request.</li></ul>

0022In another aspect, said access corresponds to initial access.

0023In another aspect, said method comprises a step of: <ul id="ul0005" list-style="dash" compact="compact"><li>the network indicating which system information should be acquired before access, and/or which system information can be acquired on or after access.</li></ul>

0024In another aspect, said system information includes neighbour cell information, and said method comprises a step of: <ul id="ul0006" list-style="dash" compact="compact"><li>the network indicating which neighbour cell information should be acquired before access, and/or which neighbour cell information can be acquired on or after access.</li></ul>

0025In another aspect, different types of neighbour cell information include intra-frequency cell information, inter-frequency cell information, and inter-radio access technology cell information, and said method comprises a step of: <ul id="ul0007" list-style="dash" compact="compact"><li>the network indicating neighbour cell information type or types which should be acquired before access, and/or neighbour cell information type or types which can be acquired on or after access.</li></ul>

0026In another aspect, said method comprises a step of: <ul id="ul0008" list-style="dash" compact="compact"><li>the network providing said indication in broadcast system information.</li></ul>

0027In another aspect, said method comprises a step of: <ul id="ul0009" list-style="dash" compact="compact"><li>the network providing said indication in a Master Information Block.</li></ul>

0028In another aspect, said method comprises a step of: <ul id="ul0010" list-style="dash" compact="compact"><li>the network providing said indication in a System Information Block to be read by mobile stations before access.</li></ul>

0029In another aspect, said method comprises a step of: <ul id="ul0011" list-style="dash" compact="compact"><li>the mobile station sending said request in at least one message sent according to Radio Resource Control protocol.</li></ul>

0030In another aspect, said method comprises a step of: <ul id="ul0012" list-style="dash" compact="compact"><li>the mobile station sending said request in at least one message chosen in a group comprising:</li></ul><ul id="ul0013" list-style="dash" compact="compact"><li>Cell Update message,</li><li>Cell Update Complete message,</li><li>RRC Connection Request message,</li><li>RRC Connection Set-up complete message,</li><li>Measurement Report message,</li><li>UTRAN Mobility Information Confirm message,</li><li>Uplink Direct Transfer message,</li><li>Physical Channel Reconfiguration Complete message,</li><li>Dedicated message indicating a System Information Request.</li></ul>

0031In another aspect, said method comprises a step of: <ul id="ul0014" list-style="dash" compact="compact"><li>the network sending system information which can be acquired on or after access, in a dedicated channel.</li></ul>

0032In another aspect, said method comprises a step of: <ul id="ul0015" list-style="dash" compact="compact"><li>the network sending system information which can be acquired on or after access, in at least one message sent according to Radio Resource Control protocol.</li></ul>

0033In another aspect, said method comprises a step of: <ul id="ul0016" list-style="dash" compact="compact"><li>the network sending system information which can be acquired on or after access, in at least one message chosen in a group comprising:</li></ul><ul id="ul0017" list-style="dash" compact="compact"><li>Cell Update Confirm message,</li><li>RRC Connection Set-up message,</li><li>UTRAN Mobility Information message,</li><li>Measurement Control message,</li><li>Downlink Direct Transfer message.</li></ul>

0034In another aspect, said method comprises a step of: <ul id="ul0018" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of mobile station or user requirements and/or system requirements.</li></ul>

0035In another aspect, said method comprises a step of: <ul id="ul0019" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of radio access capabilities of said mobile station.</li></ul>

0036In another aspect, said method comprises a step of: <ul id="ul0020" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of the on-going services or Quality of Service for the user.</li></ul>

0037In another aspect, said method comprises a step of: <ul id="ul0021" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of information received from said mobile station.</li></ul>

0038In another aspect, said method comprises a step of: <ul id="ul0022" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of information received from said mobile station in a request for acquiring system information on or after access.</li></ul>

0039In another aspect, said method comprises a step of: <ul id="ul0023" list-style="dash" compact="compact"><li>the mobile station sending to the network information enabling the network to adapt system information which can be acquired on or after access.</li></ul>

0040In another aspect, said method comprises a step of: <ul id="ul0024" list-style="dash" compact="compact"><li>the mobile station sending to the network information enabling the network to adapt system information which can be acquired on or after access, in a request for acquiring system information on or after access.</li></ul>

0041In another aspect, said method comprises a step of: <ul id="ul0025" list-style="dash" compact="compact"><li>the network adapting system information which can be acquired on or after access, as a function of system load.</li></ul>

0042In another aspect, adapted system information comprises neighbour cell information.

0043In another aspect, said method comprises a step of: <ul id="ul0026" list-style="dash" compact="compact"><li>the mobile station acquiring system information which should be acquired before access, from system information broadcast by said network.</li></ul>

0044In another aspect, said method comprises a step of: <ul id="ul0027" list-style="dash" compact="compact"><li>the mobile station acquiring system information which can be acquired on or after access, from system information broadcast by said network.</li></ul>

0045These and other objects are achieved, in another aspect of the present invention, by a mobile station comprising means for performing a method according to the present invention.

0046These and other objects are achieved, in another aspect of the present invention, by a network entity, such as in particular Radio Network Controller (RNC) for UTRAN, comprising means for performing a method according to the present invention.

0047These and other objects of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings: <ul id="ul0028" list-style="dash" compact="compact"><li><figref idref="f0001">figure 1</figref> is intended to recall the architecture of a mobile communication system such as for example UMTS, and of a Radio Access Network such as for example UTRAN,</li><li><figref idref="f0002 f0003">figures 2 to 6</figref> are intended to illustrate examples of a method according to the present invention.</li></ul>

0048By way of example, UTRAN will more particularly be considered in the following description, as an example of RAN to which the present invention applies; however it should be understood that the present invention is not limited to this particular example.

0049The present invention may also be explained as follows, to simplify based on examples. In particular, the example of initial access for establishing (or re-establishing) a radio connection will be more particularly considered in the following; however it should be understood that the present invention is not limited to this example, and could be used in other examples such as access for establishing a radio connection in case of cell reselection for example.

0050Since new radio access technologies are being deployed, in one UTRAN cell, the number of neighbouring cells is increasing. Therefore system information corresponding to neighbour cell information ( such as in particular in SIB 11) are increasing. If all the information would have to be read before the UE initial access, this initial access could be delayed, thus impacting the call set-up delay and affecting the user experience.

0051In one aspect, the present invention in particular recognizes that it would be beneficial to acquire part of system information on or after access, contrary to the prior art where all system information are acquired before access. This would enable to avoid such drawbacks.

0052In <figref idref="f0002">figure 2</figref>, a step of access by the mobile station to the network for establishing or re-establishing a radio connection is noted S1, and a step of acquiring system information on or after access is noted S2.

0053In another aspect, the present invention also recognizes that it would be beneficial to specify several system information categories, ones which should be read for initial access , and others which can be read later, in further step(s), by the UE.

0054In <figref idref="f0002">figure 3</figref>, a step of access by the mobile station to the network for establishing or re-establishing a radio connection is noted S1, a step of acquiring system information which should be read before access is noted S3, and a step of acquiring system information which can be acquired on or after access is noted S2.

0055In particular, system information which should be read before access may include access - related system information, and system information which can be read on or after access may include non access - related system information.

0056Access - related information may for example include information that are necessary for performing radio resource management and/or control procedures before establishment of a RRC connection (i.e. in idle mode). Non access - related information may for example include information that are necessary for performing radio resource management and/or control procedures on or after establishment of a RRC connection (i.e. in connected mode).

0057In another aspect, the present invention also recognizes that, since, after the initial access, a UE may have a connection with the radio access network (UTRAN, or E-UTRAN...), the second step and subsequent system information acquisitions may be performed "on demand", thus allowing the radio access network to provide the UE with the needed system information, and only the ones which are needed, which saves downlink bandwidth and decrease the relevant information acquisition time.

0058Therefore, at call establishment or re-establishment, the UE should not waste time acquiring all system information, but should only acquire those which are useful for initial access. And remaining sets of SIBs would rather be acquired later, when the UE is in connected mode (for example in Cell_DCH state).

0059For instance, at RLC unrecoverable error, the UE may need to reselect another cell: then, it is useful for the UE to have acquired all the neighbourhood configuration sent in SIB 11 and SIB 12. Moreover a UE involved in location services, may need on assistance data information contained in SIB 15 and SIB 16.

0060In such examples, SIB 11, 12, 15 and 16 contain much information, and the UE would benefit to request the UTRAN to transmit system information, in connected mode (for example during Cell_DCH state), if they have not been acquired before the initial access.

0061The present invention also proposes to define several categories of system information in the UE, or in the radio access network or both. Access category (or access related) system information defines the information which should be acquired by the UE before initial access.

0062In another aspect, the present invention also proposes that several categories can be used among the system information describing the neighborhood. The neighborhood in particular includes different cells of same technology, or different cells of different frequencies or bands, or different technologies.

0063The UE can acquire the part of the neighborhood which is needed before initial access (this part may be null).

0064In another aspect, the present invention also proposes that the radio access network can indicate, for each part of the neighborhood, whether the UE should acquire it or if the UE can acquire it in a further step.

0065Such indication can be transmitted by the radio access network, for example in a Master Information Block, or in a system information block which shall be read by the UE before initial access.

0066Once initial access has been performed, the UE may acquire the remaining system information (either in one step or in several steps).

0067The UE may receive the remaining system information on a broadcast channel, or on a dedicated channel, e.g. a signaling radio bearer.

0068The present invention also proposes that when the information is received in connected mode (for example on a dedicated channel), the UE may request the needed system information to the radio access network.

0069In <figref idref="f0002">figure 4</figref>, a step of sending such request for acquiring system information is noted S4, and a step of sending system information to the mobile station upon such request is noted S5.

0070In an example, in order to allow the UE read part of System Information and acquire the remaining SIBs once the initial access has been performed, it is proposed to add signalling so that the UE may request some SIBs to be transmitted on DCCH once the UE is in Cell_DCH.

0071Such system information request would allow to speed up the initial call set-up, and re-entering of service after RLC unrecoverable errors. It contains the SIBs which are needed by the UE, and which have not been decoded so far.

0072The UE request of system information may be sent, for instance, in the Cell Update message, in the Cell Update Complete message, in the RRC Connection Request message, in a Measurement Report message, or in the UTRAN Mobility Information Confirm message, or piggy backed in the Uplink Direct Transfer message, or sent in a Physical Channel Reconfiguration Complete message, or in a dedicated message indicating a System Information Request.

0073The example of sending a request in the Cell Update message is illustrated in <figref idref="f0003">figure 5</figref> where it is noted "Cell Update with SI request".

0074On receipt of this request, the radio access network should send to the UE the relevant system information.

0075This may be transmitted for example in the Cell Update Confirm message, or RRC Connection Set-up message, or UTRAN Mobility Information message, or in a Measurement Control message, or piggy backed in the downlink Direct Transfer message, or sent in the existing System Information Blocks: the different categories of neighbor cells and parameters could be split among new system information, or among existing system information with new instances.

0076The example of sending system information in the Cell Update Confirm message is illustrated in <figref idref="f0003">figure 5</figref> where it is noted "Cell Update Confirm with SI".

0077In an example, on receipt of a request, the radio access network should send to the UE the relevant system information on DCCH once the UE is in Cell_DCH. Since DCCH may be carried on HS-DSCH, missing information may be transmitted very efficiently from UTRAN to the UE.

0078In other words, in the considered examples, due in particular to the extension of content of system information, it is therefore proposed to add signalling in 3GPP TS 25.331 in order to allow the UE to explicitly request for some System Information Blocks and to allow the UTRAN to send SIBs on DCCH.

0079In another aspect, the present invention also proposes that the UTRAN can benefit from information it already handles in order to optimize the System information sent in a dedicated mode to the UE.

0080In particular, the UTRAN may use the radio access capabilities of the UE in order to send information about the relevant neighborhood, for instance a UE supporting E-UTRA should be provided with information about E-UTRA neighboring cells.

0081The UTRAN may also base the information on the system load: for instance very loaded neighbor cells/frequencies/bands/technologies could be removed from the list of neighboring cells/frequencies/bands/technologies.

0082The UTRAN may also base the information on services: for instance some cells/frequencies/bands/technologies could be favoured (or forbidden) in the list of neighboring cells/frequencies/bands/technologies, if the user has activated a certain QoS.

0083In <figref idref="f0003">figure 6</figref>, such a step of adapting or optimising system information which can be acquired after access, as a function of mobile station or user requirements and/or system requirements, is noted S7, and a step of sending such adapted or optimised system information is noted S8. In addition, a step of sending to the network information enabling such adaptation or optimisation, in particular in a request for acquiring further system information, is noted S6.

0084The present invention also has for its object a mobile station, as well as a network entity (such as in particular Radio Network Controller (RNC) for UTRAN), comprising means for performing a method according to the present invention, according to any of the above described aspects, taken individually or in combination.

0085The detailed implementation of the above-mentioned means does not raise any special problem for a person skilled in the art, and therefore such means do not need to be more fully disclosed than has been made above, by their function, for a person skilled in the art.