FR2871979A1 - Network e.g. global system for mobile communication network, searching process, involves selecting acceptable cell to pass emergency call from stored list by searching frequency corresponding to lowest number of successful connections - Google Patents

Abstract

The process involves storing a list of carrier frequencies in a terminal over a network (22), and counting number of successful and non successful connections. A proper cell is selected from the list by searching a frequency corresponding to a greatest number of successful connections. An acceptable cell is chosen to pass an emergency call from the list by searching frequency corresponding to the lowest number of the connections. An independent claim is also included for a universal mobile telecommunication system terminal having a unit for classifying scrambling codes of a stored list.

Description

METHOD OF ACCELERATING THE SEARCH OF A NETWORK OF

  TELECOMMUNICATION BY A MOBILE TERMINAL

TECHNICAL AREA

  The invention is in the field of telecommunications and relates more specifically to a method of accelerating the search for a network by a mobile terminal.

  The invention also relates to a multimode mobile communication terminal 10 comprising means for implementing the method.

STATE OF THE PRIOR ART

  When a mobile terminal is turned back on after an extinction, and when a user of a mobile terminal moves to geographical areas covered by separate Public Land Mobile Network (PLMN) networks, with each loss of coverage on the current network, the mobile terminal must search for a new network offering the best conditions of communication.

  This new network can be chosen according to the automatic or manual mode. In automatic mode, a search order is given to the terminal. This order can be given periodically or can be generated punctually each time the terminal loses network coverage. The terminal then searches the networks present in the environment. Then, through the SIM (Subscriber Identity Module) card, the operator gives the selection priority to one of the networks found.

  In manual mode, the user selects a network from a list of available networks in the environment.

  When a network is selected, the terminal tries to register. In case of failure, the terminal tries to register on another network. If successful, the terminal can obtain services from this network.

  After registration, the terminal can get

  from the cell on which he is encamped with information about his radio environment. This information is carried by the control channel BCCH (for Broadcast Control Channel) and include in particular the frequency band used in the PLMN, a list of frequencies of neighboring cells (ARFCN, for Absolute Radio Frequency Number), the list of beacon frequencies neighboring cells BA list for the GSM system (GSM for Global System For mobile), and the list of frequencies carrying 3GCellReselection-list neighbor 3G cell scrambling codes for the UMTS system.

  In the remainder of this description, H-PLMN (for Home PLMN) denotes the mobile network where the subscription information of the user is stored (GSM or UMTS for example), V-PLMN (for Visited PLMN) the current mobile network where the mobile accesses its services but which is not its HPLMN, RPLMN (for Registered PLMN) the network in which the mobile terminal is registered or last successfully registered and RAT (for Radio Access Technology) radio access technology implemented in an H-PLMN or a V-PLMN.

  The 3GPP standard (for Third Generation Partnership Group) defines the cell selection procedure in a GSM or UMTS network by the following steps: When the mobile is switched on, the physical layer L1, AS (for Access Stratum) performs the following tasks : A) - If the R-PLMN is such that RAT = GSM, a search for a suitable cell with PLMN = R-PLMN is carried out among: - the frequency of the last cell and / or, - all the frequencies of the last BA LIST 15 and / or - the frequency range of the last BA Range and / or - all the frequencies supported by the mobile.

  B) - The physical layer informs the L3 layer (Non AS) of the search result that is, that a suitable cell is found and that its PLMN = R-PLMN or no R-PLMN cell PLMN is not found.

  C) - If the R-PLMN is such that RAT = UTRA, a search for a suitable cell with PLMN = R-PLMN is carried out among: - the frequency and the scrambling code of the last cell and / or, - all the frequencies of the last FDDFrequencylist and / or,

_ _

  the frequency range of the last FDDfrequencyrange and / or all the frequencies supported by the mobile.

  D) - The physical layer informs the L3 layer (Non AS) of the search result, that is, a suitable cell is found and its PLMN = R-PLMN, or no R-PLMN cell, or PLMN is not found.

  E) - After reception of the message by L3: - In the event of a failure to search for the R-PLMN, L3 requests a search for PLMN giving the priority of RAT (RAT = GSM or RAT = UTRA).

  - If successful, the registration procedure

on the R-PLMN is enabled.

  F) - If L1 receives a PLMN search request, L1 performs a complete search for all suitable cells and their PLMNs. L3 then starts the registration on the highest priority PLMN found.

  G) - If no correct PLMN is found, the mobile will camp on any PLMN in limited service (emergency calls only).

  When the terminal goes out: If RAT = GSM, according to what is used on ignition, the mobile memorizes: - the frequency of the last cell and / or, - all the frequencies of the last BA LIST and / or - the frequency range of the last BA Range and / or - all the frequencies supported by the mobile.

  If RAT = UTRA, according to what is used on ignition, the mobile can memorize: - the frequency of the last cell and / or, all the frequencies of the last FDD Frequency list and / or, the frequency range the last FDD frequency range and / or - all the frequencies supported by the mobile.

  Figure 1 schematically illustrates a PLMN search and cell selection procedure according to the prior art. In this figure, the physical layer L1, AS (for Access Stratum) carries the reference 2 and the L3 network layer, NAS (for Non Access Stratum) carries the reference 4.

  After switching on the terminal or after a loss of network coverage, the network layer 4 sends the physical layer 2 a request "PLMN Search REQ" to search for a PLMN (arrow 5). Upon receipt of this request, the terminal performs a search on all the frequencies supported by the mobile (step 6). At the conclusion of this search, the physical layer 2 sends to the network layer 4 (arrow 7) the parameters identifying a certain number of cells satisfying pre-defined reception quality criteria and the identifiers of the PLMNs to which these cells belong.

  In step 8, the network layer 4 selects a non-forbidden PLMN according to predefined criteria and sends the physical layer 2 a search request for a cell in this PLMN (arrow 10).

  In step 12, the physical layer 2 again conducts a cell search among all the frequencies supported by the mobile, and sends (arrow 14) the result of the search to the network layer 4.

  In step 16, the network layer 4 performs a test to determine if the found cell is suitable.

  If so, the network layer 4 sends (arrow 20) to the network 22 an update REQ LU request to update the location of the terminal in the network.

  Step 21 is to check whether the update of the terminal location is successful or not. If yes, the network 22 sends an acknowledgment of receipt to the network layer 4 (arrow 24).

  If the found cell is not suitable, the network layer 4 performs a cell search among the cells providing emergency services (step 24).

  If the updating of the location of the terminal is successful, the network 22 sends to the network layer 4 (arrow 24) an acknowledgment, and the terminal camps (step 30) on the selected cell.

  If the update of the location of the terminal fails, for example if the PLMN is prohibited or the PLMN area in which the terminal is prohibited, the network informs the network layer 4 (arrow 32) which stores the identifier PLMN in the SIM card of the terminal.

  The duration of the search in a GSM network is typically 30s for all the frequencies 5 supported by a mobile.

  A problem arises from the fact that a search failure of R-PLMN results in the duration of this procedure being greater than 35 seconds in the actual communication conditions. In addition, the introduction of GSM / UMTS dual-mode terminals will increase this time to values that are too high.

  The object of the invention is to accelerate the search phase of a new network ignition, when the terminal is located in a geographical area covered by a telecommunications network VPLMN, and in case of loss of network coverage.

  DISCLOSURE OF THE INVENTION The invention advocates a method for reducing the search time of PLMN and cell selection.

  For this purpose, the method according to the invention applies both to a GSM network (based on the TDMA) and to a UMTS network (based on the CDMA) and comprises the following steps: - memorize in the terminal a list carrier frequencies previously used to access the network; for each carrier frequency, count the number of successful connections and the number of unsuccessful connections; - classifying the frequencies of said list in descending order according to the number of successful connections - select a suitable cell from the stored list by seeking firstly the carrier frequencies corresponding to the largest number of successful connections, - select an acceptable cell to be able to making emergency calls from the stored list by first seeking the carrier frequencies corresponding to the lowest number of successful connections.

  According to a further characteristic of the invention, for each carrier frequency, the number of successful connections is updated dynamically with each cell search.

  In an alternative embodiment of the invention, the list of carrier frequencies comprises a first group comprising a reduced number of frequencies corresponding to the greatest number of successful connections, and a second group of carrier frequencies broadcast by the network.

  In a second variant embodiment, said list of carrier frequencies comprises a first group comprising a reduced number of carrier frequencies corresponding to the largest number of successful connections, and a second group of carrier frequencies previously stored in the terminal and associated with transmission networks. specific telecommunication.

  In a third variant embodiment, said list of carrier frequencies is subdivided into a first sub-list comprising carrier frequencies associated with authorized telecommunications networks and a second sub-list comprising carrier frequencies associated with telecommunication networks or communication zones. unauthorized location.

  When implemented in a WCDMA telecommunication network such as UMTS, according to a variant of the invention, the method according to the invention comprises the following steps: storing in the terminal a list of scrambling codes corresponding to each a cell in which the mobile terminal has previously accessed a service; - for each scrambling code, count the number of successful connections and the number of unsuccessful connections; classifying the scrambling codes of said list by decreasing numbers of successful connections; selecting a suitable cell from the stored list by first searching for the cells corresponding to the scrambling code having the largest number of successful connections.

  The invention can be implemented by a GSM mobile terminal comprising: means for generating a list of carrier frequencies previously used to access the network; means for counting, for each carrier frequency, the number of successful connections and the number of unsuccessful connections; means for classifying the frequencies of said list in descending order of the number of successful connections; means for selecting a suitable cell from the stored list by first seeking the carrier frequencies corresponding to the greatest number of successful connections.

  The invention may be implemented by a UMTS mobile terminal comprising: means for generating a list of scrambling codes each corresponding to a cell in which the mobile terminal has previously accessed a service; means for counting, for each scrambling code, the number of successful connections and the number of unsuccessful connections; means for classifying the scrambling codes of said list in descending order of the number of successful connections; means for selecting a suitable cell from the stored list by first searching for the cells corresponding to the scrambling code having the largest number of successful connections.

11 BRIEF DESCRIPTION OF THE DRAWINGS

  Other characteristics and advantages of the invention will emerge from the description which follows, taken by way of non-limiting example, with reference to the appended figures in which: FIG. 1 previously described schematically illustrates the network search procedure and FIG. 2 schematically illustrates the network search and cell selection procedure according to the invention; FIG. 3 represents a general flowchart illustrating the creation of carrier frequency lists according to FIG. method of the invention.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS In the remainder of the description, identical references will denote the steps and the elements common to the figures of the prior art and to the figures illustrating the invention.

  The steps of the method according to the invention will now be described with reference to FIG.

  After switching on the terminal or after a loss of network coverage, the network layer 4 sends the physical layer 2 a request "PLMN Search REQ" to search for a PLMN (arrow 5). Unlike the method of the prior art, upon receiving this request, the terminal performs a carrier frequency search in a memory of the mobile terminal comprising a list of frequencies previously used to access the network (step 40). The frequencies of said list are ranked in descending order of the number of successful connections. The cell selection procedure is performed by first searching for the carrier frequencies corresponding to the greatest number of successful connections.

  At the end of this search, the physical layer 2 sends (arrow 7) to the network layer 4 the parameters identifying a list of suitable cells and the identifiers of the PLMNs to which these cells belong.

  In step 8, the network layer 4 selects a non-forbidden PLMN based on predefined criteria and sends the physical layer 2 (Arrow 10) a search request for a cell in this PLMN.

  In step 42, the physical layer 2 performs a cell selection from the restricted list of suitable frequencies corresponding to the largest number of successful connections. This search is done in descending order of the number of successful connections.

  The physical layer 2 sends (arrow 44) then the result of the search to the network layer 4.

  In step 16, network layer 4 performs a test to determine if the found cell is suitable.

  If so, the network layer 4 sends (arrow 20) to the network 22 an update REQ LU request to update the location of the terminal in the network.

  Step 21 is to check whether the update of the terminal location is successful or not. If yes, the network 22 sends an acknowledgment of receipt to the network layer 4 (arrow 24).

  If the found cell is not suitable, the network layer 4 performs a cell search among the cells providing emergency services (step 24). This search is performed primarily in the previously stored restricted list of frequencies for which the number of successful connections is the lowest. This search is performed in descending order of this number.

  In step 48, the network layer 4 updates the frequency list stored in the terminal, and in step 30 the terminal camps on the selected suitable cell.

  If the update of the location of the terminal fails, for example if the PLMN is prohibited or the PLMN area in which the terminal is prohibited, the network informs the network layer 4 (arrow 32). In step 33, the network layer 4 stores the identifier of the PLMN in the SIM card of the terminal.

  In step 50, the network layer 4 updates the frequency list stored in the terminal and performs a cell search providing emergency services (step 52). This search is performed primarily in the previously stored restricted list of frequencies for which the number of successful connections is highest.

  The steps of creating the frequency lists according to the invention will now be described with reference to FIG.

  A counter Fid_REG_k of the number of successful or failed connections is associated with each carrier frequency Fid_k used to access the network. Following a re-ignition of the terminal or a loss of the connection, the counter REG REG k is initialized in step 60.

  In step 62, the network 22 checks whether the connection with a frequency Fid k is successful or not.

  If yes, the counter REG REG k is incremented in step 64.

  Otherwise, the counter REG REG k is decremented in step 66.

  The frequencies Fid for which the value of the counter Fid_REG_k is the highest will be considered as those with which the probability of succeeding the connection to the network is greatest.

  These frequencies will be searched first. On the other hand, the frequencies for which the value of the counter Fid_REG_k is the smallest (in negative value) will be considered as those with which the probability of succeeding the connection to the network is greatest. These frequencies will be sought primarily for emergency services.

  Steps 68 to 70 are tests for respectively limiting the number of successful registrations to a maximum value "MAX allowed" and the number of registrations failed to a maximum value "MIN allowed".

  If Fid_REG_k is greater than "MAX allowed", the counter is not incremented. Its value is set in step 72 to "MAX allowed".

  If FidREGk is less than "MAX allowed", the sensor is incremented in step 76.

  Similarly, if the REG REG k is less than "MIN allowed", the sensor value is set (step 74) to "MIN allowed". Otherwise, the counter is incremented in step 76.

Claims (9)

  A method of accelerating the selection by a mobile communication terminal of a telecommunication network, characterized in that it comprises the following steps: storing in the terminal a list of carrier frequencies previously used to access the network; for each carrier frequency, count the number of successful connections and the number of unsuccessful connections; - classifying the frequencies of said list in descending order of the number of successful connections; select a suitable cell from the stored list by first seeking the carrier frequencies corresponding to the greatest number of successful connections, - select an acceptable cell to be able to make emergency calls from the stored list by seeking priority carrier frequencies corresponding to the lowest number of successful connections.   2. Method according to claim 1, characterized in that, for each carrier frequency, the number of successful connections is updated dynamically for each cell search.   3. Method according to claim 1, characterized in that said list of carrier frequencies comprises a first group comprising a reduced number of carrier frequencies corresponding to the most successful connections, and a second group of carrier frequencies broadcast by the network.   4. Method according to claim 2, characterized in that said list of carrier frequencies comprises a first group comprising a reduced number of carrier frequencies corresponding to the most successful connections, and a second group of carrier frequencies previously stored in the terminal and associated with specific telecommunication networks.   5. Method according to claim 1, characterized in that said list of carrier frequencies is subdivided into a first sub-list comprising carrier frequencies associated with authorized telecommunications networks and a second sub-list comprising carrier frequencies associated with telecommunication networks. not allowed.   6. Method according to claim 1, characterized in that said telecommunication network is a network based on the principle of CDMA.   7. The method of claim 6, characterized in that it comprises the following steps: - store in the terminal a list of scrambling codes each corresponding to a cell in which the mobile terminal has previously accessed a service; - for each scrambling code, count the number of successful connections and the number of 5 unsuccessful connections; classifying the scrambling codes of said list in descending order of the number of successful connections; select a suitable cell from the stored list by first searching the cells corresponding to the scrambling code having a greater number of successful connections.   8. Mobile terminal characterized in that it comprises: - means for generating a list of carrier frequencies previously used to access the network; means for counting, for each carrier frequency, the number of successful connections and the number of unsuccessful connections; means for classifying the frequencies of said list in descending order of the number of successful connections; means for searching for a suitable cell from the memorized list by first seeking the carrier frequencies corresponding to the greatest number of successful connections; means for searching for an acceptable cell from the stored list by first seeking the corresponding carrier frequencies; scrambling code having a greater number of unsuccessful connections.   A UMTS terminal characterized in that it comprises: means for generating a list of scrambling codes each corresponding to a cell in which the mobile terminal has previously accessed a service; means for counting, for each scrambling code, the number of successful connections and the number of unsuccessful connections; means for classifying the scrambling codes of said list in descending order of the number of successful connections; means for searching for a suitable cell from the stored list by first searching for the cells corresponding to the scrambling code having a greater number of successful connections.   means for searching for an acceptable cell from the stored list by first searching for the cells corresponding to the scrambling code having a greater number of unsuccessful connections.