FR2823054A1 - Mobile assisted handover system searches partial cell data speeds allocation - Google Patents

Abstract

A mobile assisted handover identification system sends a partial cell description comprising an ordered list of frequencies to a mobile phone which starts a search for cell with the best radio signal level and selects that itself or another cell chosen by the network on the basis of results sent from the mobile.

Description

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METHOD FOR IDENTIFYING A CELL IN A CELL SYSTEM
OF MOBILE RADIOCOMMUNICATIONS
The present invention relates generally to mobile radio systems.

 In general, these systems have a cellular architecture, and techniques are provided for making it possible to change cells during communication, such as for example the so-called handover techniques (or hanover) or the so-called reselection techniques. cell.

 Briefly, it is recalled that the handover techniques or hanover are used for circuit mode services and require a reservation of resources in advance before asking the mobile station to connect to the new cell. A technique conventionally used is the technique of inter-cellular transfer assisted by the mobile (or MAHO, for "Mobile Assisted Hand-Over" in English), according to which a mobile station performs radio measurements on cells close to its server cell and reports the results of these radio measurements to the network, in order to facilitate the handover decision by the latter.

 Briefly, it is recalled that cell re-selection techniques are used for packet mode services, and do not require a reservation of resources in advance, the mobile station making a request for such a reservation when it accesses the re-selected cell. A distinction is generally made between several cell reselection control modes: a cell reselection mode controlled by the mobile station: in this case the mobile station itself decides on a cell reselection, on the basis of radio measurement results that '' it performs on neighboring cells, a cell reselection mode controlled by the network: in this case, a cell reselection is decided by the network, on the basis of measurement results transmitted to it by the mobile station, then ordered by the network at the mobile station.

 The identity of the neighboring cells on which measurements are to be made is generally indicated by the network to the mobile stations, generally according to a mode of transmission by diffusion. The identity of the reselected cell (in the

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 network controlled cell reselection mode) is indicated by the network to the mobile station, usually in a dedicated signaling message. Thus, in these systems, and in particular for the reasons thus recalled, the network may need to communicate to mobile stations the identity of certain cells. It is then necessary to be able to identify each cell.

 A cell is generally identified by means of a set of radio parameters which characterize it, this set of parameters also being called cell description.

For example, the 3GPP TS 04.60 standard relating to the GSM / GPRS system specifies that the Packet Cell Change Order message (transmitted by the network to the mobile station and containing the identity of the reselected cell) contains the following parameters making it possible to identify a reselected cell of GSM / GPRS type:
ARFCN BS) C.

 Briefly, we recall that in a GSM / GPRS type system, or more generally in a system implementing a multiple access technique of FDMA (for Frequency Division Multiple Access) and / or TDMA (for Time Division Multiple Access in English), a cell is identified mainly by a beacon frequency (also called BCCH frequency) which is indicated by the ARFCN (Absolute Radio Frequency Channel Number) parameter. In particular, the beacon frequency carries channels (such as broadcast channels and common control channels) necessary to allow access to the network by mobile stations, and it is also on the beacon frequency that radio measurements are carried out. previously mentioned. In order to allow mobile stations to distinguish cells to which the same beacon frequency could possibly be allocated (in particular in the case of short re-use distance of these beacon frequencies), the BSIC (Base Station Identity Code) parameter is also used , different BSICs are thus allocated to cells using the same beacon frequency.

 Furthermore, in these systems, technological developments have led to distinguishing between so-called second generation or 2G radio access technologies, in particular of the GSM / GPRS (Global System for Mobile communication / General) type.

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Packet Radio Servi. ce ), et des technologies dites de troisième génération, ou 3G, notamment de type UMTS ( Universal Mobile Telecommunication System ). Dans le cas de l'UMTS, on distingue par ailleurs deux modes possibles : FDD ( Frequency Domain Duplex ) et TDD ( Time Domain Duplex ).

Packet Radio Servi. ce), and so-called third generation technologies, or 3G, in particular of the UMTS (Universal Mobile Telecommunication System) type. In the case of UMTS, there are also two possible modes: FDD (Frequency Domain Duplex) and TDD (Time Domain Duplex).

 The description of a cell differs according to the type of radio access technology used in this cell.

For example, the 3GPP TS 04.60 standard relating to the GSM / GPRS system envisages the case of mobile stations known as multi-RAT (multi-Radio Access Technologies) and specifies that the message Packet Cell Change Order contains, for the case of reselected cell of type UMTS / FDD for example, the following parameters to identify this cell:
FDD-ARFCN - SCRAMBLING CODE.

 Briefly, it is recalled that, for example in a UMTS / FDD type system, or more generally in a system implementing a multiple access technique of CDMA type (for Code Division Multiple Access in English), the frequency used can be the same in the different cells of the system. However, it is also possible to allocate different frequencies (in particular to allow an increase in capacity and / or a reduction in interference in the system). The frequency used in a cell is then identified using the FDD-ARFCN (FDD-Abso! Ute Radio Frequency Channel Number) parameter. In addition, a cell is mainly identified by a scrambling code (or scrambling code in English) specific to this cell, and indicated by means of the SCRAMBLING-CODE parameter. Scrambling concerns all the channels transmitted in the downstream direction with the exception of certain so-called synchronization channels.

In particular, knowledge of the scrambling code is necessary to be able to receive channels such as in particular broadcast channels and common control channels, necessary to allow access to the network by mobile stations, and specific channels (such as in particular a pilot channel) used by mobile stations to carry out the radio measurements mentioned above.

 Furthermore, such systems generally include a plurality of networks, or PLMNs (for Public Land Mobile Network in English) whose coverage areas may or may not overlap, and which are operated independently of the

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 each other by different operators. This allows in particular to extend the geographic coverage and / or the services offered.

 Insofar as this is authorized by roaming agreements between operators of these different networks, provision can then be made for a network to be able to indicate to mobile stations the identity of cells belonging to a neighboring network. . It is then necessary that this network has access to the description of cells of this neighboring network.

 However, for a given network, the cell description is generally defined (or redefined in the case of reconfiguration of this network) by so-called operation and maintenance means (or O & M, for Operation & Maintenance in English) to this network. Coordination between operating and maintenance means relating to the different networks considered is then necessary, which increases the burden of these operating and maintenance means, in a way that could be deemed unacceptable by certain operators. This load is particularly increased in the case of different radio access technologies in these networks (or at least in certain cells of these networks).

 The object of the present invention is in particular to avoid such disadvantages as far as possible.

 A subject of the present invention is thus a method for identifying a cell in a cellular mobile radio communication system, this method being essentially characterized in that it comprises the following steps: a network called server network communicates to at least one mobile station l identity of at least one cell of at least one network called neighboring network, said identity being indicated by means of a partial description of this cell, your mobile station performs a cell search, based on said partial description.

 According to another characteristic, said neighboring network using a 3G radio access technology, and the frequencies allocated to the operator of this neighboring network for this radio access technology forming a set of N frequencies:

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ladite description partielle comporte une liste de n fréquences (avec 1 n < N) appartenant audit ensemble de N fréquences et incluant la fréquence utilisée dans la cellule à identifier, ladite recherche de cellule comporte une recherche de la meilleure, suivant un critère prédéterminé, de différentes cellules pouvant être décrites au moyen de ladite description partielle.

said partial description comprises a list of n frequencies (with 1 n <N) belonging to said set of N frequencies and including the frequency used in the cell to be identified, said cell search comprises a search for the best, according to a predetermined criterion, of different cells which can be described by means of said partial description.

 According to another characteristic, the frequencies of said list are ordered according to a decreasing probability of use in the cell to be identified.

 According to another characteristic, said neighboring network using 2G type radio access technology, and the frequencies allocated to the operator of this neighboring network for this radio access technology forming a set of M frequency bands: said partial description includes a list of m (with 1 m M) frequency bands belonging to said set of M frequency bands and including the frequency band used in the cell to be identified, - said cell search includes a search for the best, according to a criterion predetermined, of different cells which can be described by means of said partial description.

 According to another characteristic, the frequency bands of said list are ordered according to a decreasing probability of use in the cell to be identified.

 According to another characteristic, said predetermined criterion includes a radio criterion.

 According to another characteristic, said radio criterion is a criterion of best level of received signal.

 According to another characteristic, said partial description is supplied to the server network by means of operation and maintenance of this network, cooperating for this purpose with means of operation and maintenance of the neighboring network.

 According to another characteristic, a cell to be identified is a cell whose reselection is ordered by the server network to a mobile station.

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 According to another characteristic, a cell to be identified is a neighboring cell, on which radio measurements are to be carried out by a mobile station.

 Another object of the present invention is a mobile radio communication system comprising means for implementing such a method.

 Another object of the present invention is a mobile radio network equipment comprising means for implementing such a method.

 Another object of the present invention is operation and maintenance equipment for a mobile radio network, comprising means for implementing such a method.

 Another object of the present invention is a mobile station comprising means for implementing such a method.

 Other objects and characteristics of the present invention will appear on reading the following description of exemplary embodiments.

 The object of the invention is therefore in particular to minimize the interPLMN coordination necessary for the operation and maintenance functions in a mobile radiocommunication system.

 The invention is applicable to any type of radio access technology. We first consider, by way of example, the case of 3G type radio access technology. An example of application is the reselection of inter-PLMN cell, controlled by a 2G type network, to a 3G type network.

 As observed by the applicant, we can take advantage of the fact that the frequencies allocated to a 3G operator are few in number (for example 1 to 4 frequencies allocated per operator) and should not change very often, to simplify coordination inter-PLMN linked to the definition and updating of the parameters allowing to describe the cells of such a network.

 Thus, the invention suggests using a partial description, in this case a list of n frequencies (with 1 nN) belonging to the set of N frequencies allocated to the 3G operator, and including the frequency used in the cell. to identify (or reselected cell in the application example cited above).

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 A mobile station receiving such a partial description then performs a cell search. In particular, the mobile station can carry out a search for the best (according to a predetermined criterion) of the different cells which can be described by means of this partial description. Such a predetermined criterion may in particular include a radio criterion (in particular a criterion of best level of received signal).

 The higher the number of frequencies in the list, the more the said functions relating to inter-PLMN coordination are reduced, but the longer the cell station search time can be. Conversely, the lower the number of frequencies in the list, the more these functions relating to interPLMN coordination are increased, but the shorter the cell station search time can be. A compromise can be sought if necessary.

 To reduce the cell search time, the list can also be ordered, so that the first frequency in the list corresponds to the most likely frequency used in the cell to be identified.

 The list can also be reduced to a single frequency (the one used in the cell to be identified).

 In the case of 3G radio access technology of the UMTS / FDD type, these frequencies are identified by means of the parameter called FDD-ARFCN.

 In this case, the partial description is a description limited to frequency parameters, and not comprising a scrambling code (the latter parameter being liable to change relatively more often than these frequency parameters).

 In the application example considered at cell reselection, this list of frequencies, or partial description, is transmitted in the Packet Cell Change Order message. The coding of the information contained in this message then allows this message to contain such a list of frequencies and authorizes the absence of a scrambling code.

 A mobile station receiving such a partial description can then determine a better cell for the first of the frequencies in the list, then for the following frequencies if they exist.

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(ou Scrambling Code Group en anglais) transmise sur le canal Secondary SCH , un groupe de codes d'embrouillage comportant en l'occurrence plusieurs codes d'embrouillage possibles, essai de chacun de ces codes d'embrouillage, puis sélection de celui de ces codes d'embrouillage pour lequel le niveau de signal reçu est le plus élevé (le canal utilisé pour de telles mesures de niveau de signal reçu étant en l'occurrence le canal CPICH ( Common Pilot Channel ). To determine a better cell for one of the frequencies in the list, the mobile station can for example perform the following operations (for example in the case of radio access technology of UMTS / FDD type): acquisition of frequency synchronization, on the frequency considered, time synchronization acquisition (in this case by means of the Primary SCH and Secondary SCH synchronization channels, these synchronization channels being in this case transmitted without scrambling), - decoding of the so-called code group information muddle

(or Scrambling Code Group in English) transmitted on the Secondary SCH channel, a group of scrambling codes comprising in this case several possible scrambling codes, testing each of these scrambling codes, then selecting the one of these scrambling codes for which the received signal level is the highest (the channel used for such received signal level measurements being in this case the CPICH (Common Pilot Channel) channel.

 Such operations are of the same type as those carried out initially by a mobile station, when it is switched on, to select an appropriate cell, listening to which the mobile station can be put. However, they are carried out here in a different context, since it is not here an initial cell selection made when the mobile station is started, but operations carried out subsequently, while the mobile station is already in operation. relationship with the network, and that the network then indicates to the mobile station the identity of a cell, in this case by means of such a partial description. Furthermore, in the case of initial cell selection by the mobile station, the mobile station initially has no description (even partial) of the cell. In addition, the goal here is different, since this allows, as already indicated, to reduce the inter-PLMN coordination necessary for the operation and maintenance functions.

 Thus, in the case of cell reselection to a 3G type network (in particular of UMTS type) the mobile station can receive a partial description of target cell, this partial description comprising a frequency (also called

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fréquence UTRAN, où UTRAN est utilisé pour UMTS Terrestriat Radio Access Network ) ou une liste de fréquences UTRAN.

UTRAN frequency, where UTRAN is used for UMTS Terrestriat Radio Access Network) or a list of UTRAN frequencies.

 If the mobile station receives only one frequency, it chooses the best of the cells corresponding to this frequency.

 If the mobile station receives more than one frequency, it repeats the process for each frequency in the list, in descending order if these frequencies have been ordered so that the first of the frequencies in the list is most likely.

 Furthermore, for the UMTS system, a TDD type cell can also be described using the same type of partial description as an FDD type cell. In the case of 3G radio access technology of UMTS / TDD type, these frequencies are identified by means of the parameter called TDD-ARFCN.

 Furthermore, the present invention applies equally well to the case of 2G type radio access technology. An example of application is the reselection of inter-PLMN cell, controlled by a 3G type network, to a 2G type network.

 As the applicant observed, one can take advantage of the small number of frequency bands allocated to a 2G operator, and of the fact that these frequency bands should not change very often, in order to simplify the inter-PLMN coordination linked to defining and updating the parameters enabling the cells of such a network to be described.

 Thus, the invention suggests using a partial description, in this case a list of m frequency bands (with 1 m <M) belonging to the set of M frequency bands allocated to the operator 2G, and including the frequency band used in the cell to be identified (or reselected cell in the application example mentioned above).

 A mobile station receiving such a partial description then performs a cell search. In particular, the mobile station can carry out a search for the best (according to a predetermined criterion) of the cells which can be described by means of this partial description. Such a predetermined criterion may in particular include a radio criterion (in particular a criterion of best level of received signal).

 The higher the number of frequency bands in the list, the more the said functions relating to inter-PLMN coordination are reduced, but the longer the cell station search time can be. Conversely, the lower the number of frequency bands in the list, the more these functions relating to the

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 inter-PLMN coordination are increased, but the shorter the cell station search time can be. A compromise can be sought if necessary.

 To reduce the cell search time, the list can also be ordered, so that the first frequency band in the list corresponds to the most likely frequency used in the cell to be identified.

 The list can also be reduced to a single frequency band (the one used in the cell to be identified).

 In the case of 2G radio access technology of the GSM / GPRS type, these frequency bands can for example be identified by means of two values of the ARFCN parameter, one corresponding to a lower bound of an interval and the other to an upper bound of the interval.

 In the application example considered for cell reselection, this list of frequency bands, or partial description, is transmitted in the Packet Cell Change Order message. The coding of the information contained in this message then allows this message to contain such a list of frequency bands, instead of the parameters currently specified.

 A mobile station receiving such a partial description can then determine a better cell for the first of the frequency bands in the list, then for the following frequency bands if they exist.

 In the case of radio access technology of type 2G (for example of GSM / GPRS type), the operations to be carried out can also be of the same type as those carried out by a mobile station for an initial cell search, as indicated above for the case of 3G type radio access technology (for example of UMTS type).

 The invention is applicable to any case where a network called the server network must communicate to at least one mobile station the identity of at least one cell of at least one other network called the neighboring network. Server and neighbor networks may or may not use the same radio access technology. The radio access technology may be arbitrary, and the reason for the communication of the cell identity may be arbitrary (in particular it may be a reselection of cell ordered by the network).

 The present invention also relates, in addition to such a method, to a mobile radiocommunication system, as well as a network of

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 mobile radio communications or a mobile radio network entity or equipment, an operation and maintenance equipment for a mobile radio communication system, and a mobile station, comprising means for implementing such a method.

 The particular production of such means does not present any particular difficulty for the skilled person, such means do not need to be described here in more detail than what has been done previously, by their function.

Claims (14)

 CLAIMS 1. Method for identifying a cell in a cellular mobile radio communication system, this method being characterized in that it comprises the following steps: a network called server network communicates to at least one mobile station the identity of at least a cell of at least one network called neighboring network, said identity being indicated by means of a partial description of this cell, - the mobile station performs a cell search, based on said partial description.  2. Method according to claim 1, characterized in that said neighboring network using a 3G type radio access technology, and the frequencies allocated to the operator of this neighboring network for this radio access technology forming a set of N frequencies: - said partial description includes a list of n frequencies (with 1 n <N) belonging to said set of N frequencies and including the frequency used in the cell to be identified, - said cell search includes a search for the best, according to a predetermined criterion, of different cells which can be described by means of said description partial.  3. Method according to claim 2, characterized in that the frequencies of said list are ordered according to a decreasing probability of use in the cell to be identified.  4. Method according to claim 1, characterized in that said neighboring network using a 2G type radio access technology, and the frequencies allocated to the operator of this neighboring network for this radio access technology forming a set of M frequency bands: said partial description includes a list of m (with 1 m M) frequency bands belonging to said set of M frequency bands and including the frequency band used in the cell to be identified, - said cell search includes a search the best, according to a predetermined criterion, of different cells which can be described by means of said partial description. <Desc / Clms Page number 13>  5. Method according to claim 4, characterized in that the frequency bands of said list are ordered according to a decreasing probability of use in the cell to be identified.  6. Method according to one of claims 2 to 5, characterized in that said predetermined criterion includes a radio criterion.  7. Method according to claim 6, characterized in that said radio criterion is a criterion of best level of received signal.  8. Method according to one of claims 1 to 7, characterized in that said partial description is provided to the server network by means of operation and maintenance of this network, cooperating for this purpose with means of operation and maintenance of the neighboring network.  9. Method according to one of claims 1 to 8, characterized in that a cell to be identified is a cell whose reselection is ordered by the server network to a mobile station.  10. Method according to one of claims 1 to 9, characterized in that a cell to be identified is a neighboring cell, on which radio measurements are to be carried out by a mobile station.  11. Mobile radio communication system comprising means for implementing a method according to one of claims 1 to 10.  12. Mobile radio network equipment comprising means for implementing a method according to one of claims 1 to 10.  13. Operation and maintenance equipment for a mobile radio network, comprising means for implementing a method according to one of claims 1 to 10.  14. Mobile station comprising means for implementing a method according to one of claims 1 to 10.