Method for Avoiding Interruptions of Push To

(19) &

(11) EP 1 795 021 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.: of the grant of the patent: H04W 4/10 (2009.01) 11.11.2009 Bulletin 2009/46 (86) International application number: (21) Application number: 04787270.0 PCT/EP2004/052390

(22) Date of filing: 30.09.2004 (87) International publication number: WO 2006/037372 (13.04.2006 Gazette 2006/15)

(54) METHOD FOR AVOIDING INTERRUPTIONS OF PUSH TO TALK SERVICES VERFAHREN ZUR VERMEIDUNG VON UNTERBRECHUNGEN VON PUSH-TO-TALK-DIENSTEN PROCEDE POUR EVITER LES INTERRUPTIONS DE SERVICES "PUSH TO TALK"

(84) Designated Contracting States: • CERWALL, Patrik AT BE BG CH CY CZ DE DK EE ES FI FR GB GR S-125 25 Älvsjö (SE) HU IE IT LI LU MC NL PL PT RO SE SI SK TR • BLADSJÖ, David S-125 25 Älvsjö (SE) (43) Date of publication of application: 13.06.2007 Bulletin 2007/24 (74) Representative: Sjöberg, Mats Hakan Ericsson AB (73) Proprietor: Telefonaktiebolaget LM Ericsson Patent Unit IP Networks (publ) Box 1505 164 83 Stockholm (SE) 125 25 Älvsjö (SE)

(72) Inventors: (56) References cited: • LARSSON, Anders EP-A- 1 081 969 WO-A-99/65266 S-125 25 Älvsjö (SE) WO-A-2004/075581 GB-A- 2 330 484

Note: Within nine months of the publication of the mention of the grant of the European patent in the European Patent Bulletin, any person may give notice to the European Patent Office of opposition to that patent, in accordance with the Implementing Regulations. Notice of opposition shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 795 021 B1

Printed by Jouve, 75001 PARIS (FR) 1 EP 1 795 021 B1 2

Description mented is neither talking nor sending non-transparent data ensuring that the other party is having comfort noise Field of the Invention being generated in its receiver and, thus, will not hear any audible effect of the handover. [0001] The present invention relates to a method and 5 [0006] As already mentioned above, walkie-talkie type apparatus for avoiding interruptions of so-called push to services are ideal for communicating brief messages be- talk over cellular services. More particularly, the invention tween two or a relatively small number of users. A talk relates to avoiding interruptions which arise due to the session is likely to consist of a small number of talk bursts cell re-selection of mobile stations between radio base sent in both directions. Given the brief nature of the talk stations of the radio access network. 10 sessions, it is desirable to minimise service interruptions which might arise due to operator network performance Background to the Invention issues. [0007] Considering now the provision of GPRS packet [0002] Walkie-talkie type services have long proved switched access in GSM networks, this makes use the popular amongst users who wish to communicate brief 15 GSM cell-based radio access network architecture which messages quickly between one another. Conventionally, is illustrated in Figure 1. Within each cell 1, a Base Trans- such services have been provided by two-way portable ceiver Station (BTS) 2 provides the interface between a radios which utilise a dedicated part of the radio spec- mobile station and the radio access network 3. In order trum, but which only allow users to communicate with a to maintain high quality communication links with mobile small group of pre-selected users who utilise similar ter- 20 stations 4 as mobile stations approach and cross cell minals and who are within range of the relatively short boundaries, a cell re-selection mechanism is provided operating range of the radios. More recently, services for transferring mobile stations from one BTS to another. have been introduced into the United States which piggy- Cell re-selection may also occur for other reasons, for back on the existing cellular telephone infrastructure. example to avoid network congestion. BTSs are grouped However, these services have been proprietary in nature 25 into sets, with each set being controlled by a Base Station and have not allowed users to communicate between Controller (BSC) 5. The combination of a BSC and the different operator networks. associated BTSs controlled by that BSC is referred to as [0003] In an attempt to broaden the use of walkie-talkie a Base Station System (BSS). The radio access network type services, an industry grouping known as the Open 3 is coupled to a GPRS core network 6 which includes Mobile Alliance (www.openmobilealliance.org) has been 30 Serving GPRS Support Nodes (SGSNs) 7 and a Gate- established with the aim of standardising suitable proto- way SPRS Support Nodes (GGSNs) 8 which facilitate cols which will allow inter-network operability for Warlike- packet switched access to other networks, for example Talkie services offered over cellular networks. The serv- the Internet. As with the cells, the BSCs are arranged in ice established by the various standards is known as a hierarchical architecture, with groups of BSCs being Push to talk Over cellular (PoC). PoC proposes that as- 35 served by a common SGSN. sociated speech data will be transported over a packet [0008] GSM specifies extremely sophisticated mech- switched access network. In the case of GSM and UMTS, anisms for ensuring that circuit switched voice calls (as this will be the general packet radio service (GPRS) ac- opposed to packet switched data sessions) are trans- cess network. In other network architectures, analogous ferred smoothly during a cell re-selection. Indeed, users packet switched access networks will be utilised for trans- 40 are normally unaware that a cell re-selection has oc- porting talk data. Push to Talk services may also be of- curred. The mechanisms for performing cell re-selection fered over circuit switched access networks, although over GPRS sessions are not so sophisticated. As cur- this is not the preferred option. rently specified, cell re-selection of a GPRS session may [0004] In the UK Patent Application GB 2330484 is dis- result in a significant interruption in the transfer of talk closed a radio communication system having a plurality 45 bursts associated with a PoC service. This applies in re- of base stations wherein a mobile station communicating spect of cell re-selections for any of the parties involved to a first base station initiates handoff to a second base in a PoC session, not just the currently talking party. With station during periods of communication inactivity. The current implementations of GPRS, cell re-selection is a system is arranged such that the remote communication decision left to the mobile stations, and a cell re-selection unit initiates the communication hand-over during peri- 50 (assuming that the old and the new BTS are served by ods of inactivity of the communication between the first the same BSC) can result in an interruption in the delivery remote unit and the first base station. of data of around 2 to 3 seconds. Whilst the most recent [0005] In the international application WO 99/65266 is GPRS specification sets out an improved, network con- disclosed a system for elimination of audible effects of trolled cell re-selection procedure, the interruption is still handover. In the international application, once it is de- 55 on the order of 700ms. The probability of such a cell re- termined by the system that a handover of a mobile needs selection occurring during a PoC session is quite high. to be performed, that handover is delayed until the party In the case of a cell re-selection between BTSs served on the link on which discontinuous transmission is imple- by different BSCs, the interruption is likely to be even

2 3 EP 1 795 021 B1 4 greater, on the order of 4 to 5 seconds, although such [0014] The term "push to talk" service is used here to cell re-selections will happen only infrequently. In certain identify services of a walkie-talkie nature. These are serv- rare cases, a BTS cell re-selection will not only result in ices which allow two or more users to be connected to- a change in serving BSC, but will also result in a change gether extremely quickly for the exchange of talk bursts. in the Serving GPRS Support Node (SGSN) within the 5 Push to Talk service differ from conventional voice calls GPRS network. This can lead to a service interruption in that these services allow only one person to talk at a on the order of 10 to 15 seconds. given time. In order to talk, users must have control of [0009] Such delays are likely to be annoying to users the "floor". Control is typically achieved by one user re- and may have a serious detrimental effect on the per- leasing a talk button to release floor control, and another ceived quality of the service and therefore on the levels 10 user pressing a talk button to assume floor control. of user satisfaction. While the problem may be mitigated [0015] Preferably, talk bursts are transported between by setting the pre-buffering (downloading before starting the mobile stations and the radio access network over a playback) in the receiving mobile station long enough to packet switched service. In the case of UMTS and GSM, be able to cope with cell re-selections without interrup- this service may be the General Packet Radio Service. tion, this is not desirable as latency is the top-prioritised 15 [0016] Preferably, said step of determining when a cell characteristic for the PoC service, and the longer the pre- re-selection for the mobile station is appropriate is carried buffering, the higher the latency. out within the radio access network. In the case of a GSM/ GPRS access network, this is carried out at the serving Summary of the Invention Base Station Controller. The determination is made 20 based upon measurement received from the mobile sta- [0010] The inventors of the present invention have rec- tion. More preferably, cell re-selection is controlled by ognised that, in a typical PoC session, significant periods the NC2 procedure. The step of delaying the cell re-se- of silence can be expected to occur between talk bursts. lection procedure is implemented using the NC2 proce- Indeed, periods of silence between switches from one dure. user having control of the floor to another having control 25 [0017] Preferably, said step of determining whether or are unavoidable. For example, a PoC session may last not the mobile station is involved in a push to talk service for a total of forty seconds. Within this forty second ses- comprises inspecting, at the Base Station Controller, the sion, four talk bursts may be exchanged between users, Quality of Service profile for the ongoing packet switched each talk burst averaging seven seconds in duration. In- (GPRS) session. terleaved between the four talk bursts are three silent 30 [0018] Preferably, the method comprises sending a periods, each lasting for perhaps four seconds (the time cell re-selection request to the mobile station from the taken to transfer control, plus "thinking" time for the user radio access network following the end of a current talk to whom floor control is handed). These silent periods burst. (extended if necessary) can be advantageously used to [0019] In certain embodiments of the invention, the perform cell re-selection without resulting in any per- 35 method may comprise overriding said delay to instruct ceived delay in talk playback to the participating users. immediate cell re-selection in the event that the radio link [0011] The invention is of course applicable to push to quality of the ongoing session falls below an acceptable talk services, other than PoC, which utilise cellular net- quality threshold. This threshold may be defined in terms works to transport associated talk data. of: carrier to interference ration C/I, Bit Error Rate BER, [0012] It is an object of the present invention to reduce 40 or cell throughput. In other embodiments, the delay may or eliminate delays in talk playback associated with push be overridden if the ongoing talk burst continues beyond to talk services utilising cellular telecommunications net- some defined timer value. This value may be: predefined works as the traffic transport mechanism. based upon expected behaviour, an adaptively calculat- [0013] According to a first aspect of the present inven- ed valued based on the ongoing speech burst, a value tion there is provided a method of controlling the cell re- 45 computed on the basis of the previous behaviour of the selection of a mobile station between cells of a cellular- mobile station, a value computed on previous behaviour based radio access network, the method comprising the of mobile stations handled by the radio access network. steps of: [0020] According to a second aspect of the present invention there is provided a method of operating a base determining when a cell re-selection for the mobile 50 station controller of a cellular-based radio access net- station is appropriate; work, the method comprising: determining whether or not the mobile station is involved in a push to talk service comprising a series determining when a cell re-selection for the mobile of talk bursts; and station is appropriate; if the mobile station is involved in a push to talk serv- 55 determining whether or not the mobile station is in- ice, delaying the cell re-selection until such time as volved in a push to talk service comprising a series a period of silence between talk bursts occurs. of talk bursts; and if the mobile station is involved in a push to talk serv-

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ice, delaying the instructing of a cell re-selection until the cell re-selection procedures are set out in TS 05.08, such time as a period of silence between talk bursts "Technical Specification Group GSM/EDGE Radio Ac- occurs. cess Network subsystem link control (Release 1999). In particular, Chapter 10.1.4 of that TS defines a number [0021] According to a third aspect of the present in- 5 of procedures for controlling the cell re-selection behav- vention there is provided a method of operating a mobile iour of mobile stations. The currently implemented pro- station for use with a cellular-based radio access net- cedure is "NC0". This leaves cell re-selection decisions work, the method comprising: to the mobile stations themselves, the decisions being made based upon measurements made by the mobile determining when a cell re-selection for the mobile 10 stations (e.g. signal strength, etc). station is appropriate; [0025] An improved cell re-selection control procedure determining whether or not the mobile station is in- known as "NC2" will be implemented within the Packet volved in a push to talk service comprising a series Control Unit (PCU) entity at the BSC. NC2 requires that of talk bursts; and mobile stations periodically send measurement reports if the mobile station is involved in a push to talk serv- 15 to the network identifying the quality of radio links avail- ice, delaying the instructing of a cell re-selection until able between the mobile stations and those BTSs with such time as a period of silence between talk bursts which they are able to communicate (i.e. which are in occurs. range). On the basis of these measurements, the serving BSC, which is responsible for a number of BTSs, identi- Brief Description of the Drawings 20 fies the BTS to which the mobile station should be attached. In the event that a BTS is identified which is not [0022] the BTS with which the mobile station is currently communicating, NC2 requires the BSC to send a cell re-se- Figure 1 illustrates schematically a GSM/GPRS net- lection command to the mobile station. It will be appre- work; 25 ciated that the "new" BTS may be a BTS controlled by Figure 2 illustrates the nature of a Push to talk Over that same BSC or by another BSC. In addition, the new Cellular session including speech bursts utilising the BTS may be associated with a different SGSN. When current NC0 or NC2 procedure; the mobile station receives the relocate command, it se- Figure 3 illustrates the nature of a Push to talk Over lects the cell according to the cell description included in Cellular session including speech bursts utilising a 30 the cell re-selection command. Although NC2 does pro- modified NC2 procedure; and vide for a mobile station to autonomously re-select a cell, Figure 4 illustrates signalling in the network of Figure this is only possible following a downlink signal failure or 1 between a mobile station and the radio access net- a random access failure. work which is associated with a cell re-selection pro- [0026] NC2 requires that a mobile station act immedi- cedure. 35 ately upon receipt of a cell re-selection command. In the normal course of events, only a few seconds is likely to Brief Description of Certain Embodiments elapse between the BSC determining that a cell re-selection is required, and the cell re-selection actually oc- [0023] Push to talk Over Cellular (PoC) is a proposal curring. Whilst NC2 provides adequate mechanisms for which is to be implemented on GSM/GPRS networks and 40 ensuring that no data is lost during the cell re-selection, which makes use of the IP Multimedia Subsystem (IMS) and that the new BTS picks up where the old BTS standardised by the 3rd Generation Partnership Project stopped, it does not completely avoid the introduction of to facilitate the introduction of advanced data services delays in the sending of data from the new BTS. Of into cellular networks, and in particular of real-time mul- course, in the scenario where data is being downloaded timedia services. The IMS relies upon the Session Initi- 45 to a mobile station, e.g. from a web server, relatively small ation Protocol (SIP) which has been defined by the In- delays are likely to go unnoticed by users and will cer- ternet Engineering Task Force (IETF) for the setting up tainly not seriously affect the performance level per- and control of multimedia IP-based sessions. A PoC ceived by the users. However, in the case of real time server is located within the IMS or is attached thereto, voice data such as is associated with a PoC service, such and implements the functionality for setting up and con- 50 interruptions are likely to prove extremely annoying to trolling PoC sessions. users. [0024] With reference to Figure 1, radio access serv- [0027] Figure 2 illustrates the nature of a typical PoC ices are provided to users by way of a cellular architec- session assuming implementation of the NC0 or NC2 (as ture. Within each cell, mobile stations communicate over- currently proposed) cell re-selection control procedures. the-air with a Base Transceiver Station (BTS). Several 55 In the illustrated example, a mobile station referred to as cells (and associated BTSs) are controlled by a Base the "A-party" transmits two short talk bursts separated Station Controller (BSC). The concept of BTS cell re- by some period of silence. With this talk burst is being selection has been outlined above. In the case of GPRS, sent over the A-Party’s radio access network, it is as-

4 7 EP 1 795 021 B1 8 sumed that a cell re-selection occurs for the mobile sta- [0032] A key element in implementing the procedure tion of the A-party. The receiving mobile station belonging detailed here is the detection of the end of a speech burst to the B-party will receive all of the talk burst. However, associated with a PoC session. One or a combination of an interruption is likely to occur in the middle of the play- criteria can be used for this purpose. These include: back due to the cell re-selection. Considering now the 5 second short talk burst, it is assumed that a cell re-se- 1. An uplink or downlink speech burst is considered lection occurs for the mobile station of the B-party during ended when the associated (uplink or downlink) playback of the transmitted speech burst (the B-party’s Temporary Block Flow (TBF) is released. The TBF mobile station may be attached to the same radio access is the connection used by the two Radio Resource network as the A-party’s terminal, or to a different access 10 entities to support the unidirectional transfer of Log- network). Again, whilst all of the transmitted talk burst is ical Link Control Protocol Data Units on packet data played back to the B-party, a short interruption occurs physical channels. A TBF is temporary and is main- corresponding to the cell re-selection of the B-party’s mo- tained only for the duration of the data transfer. TBF bile station. As well as being annoying to the receiver, release happens a configurable time, set by BSS the interruption in the talk burst may seriously affect the 15 timers, after the last packet is sent or received. intelligibility of the played back speech. 2. A new timer is introduced for this purpose and [0028] To address this problem, the currently pro- which is reset after each packet. A speech burst is posed NC2 procedure is modified to allow the introduc- considered ended if the timer expires before a further tion of a mechanism which causes cell re-selection to be packet is received. The same or different timers delayed until a period of silence arises in a PoC service. 20 could be used for the uplink and downlink directions. This firstly requires some means for detecting that a 3. A downlink speech burst is considered ended im- GPRS session for which a cell re-selection is required, mediately when the downlink buffer in the BSS is is detected as relating to a PoC service. Fortuitously, empty. certain current PCU implementations already make pro- 4. An uplink speech burst is considered ended when vision for such detection, see 3GPP TS 23.107, "Tech- 25 an uplink CV equals 0. (CV is a countdown value nical Specification Group Services and System Aspects; sent by the mobile station to the BSS.) Quality of Service (QoS) concept and architecture", (Re- lease 1999). In these implementations, the BSS inspects [0033] The invention takes advantage of the fact that, the QoS profile for the ongoing GPRS session, and if the in a cellular network architecture, the cells are overlap- mobile station uses QoS Streaming with a certain QoS 30 ping. At times of cell re-selection, the radio conditions profile, the BSS knows that the ongoing media stream is are still sufficiently good in the "old" cell for transferring a PoC type of media flow. A PoC tag is set accordingly. data even if cell re-selection is postponed for a few sec- [0029] The NC2 procedure (as currently defined) is onds. Since the speech bursts associated with the PoC modified in order to delay instructing a mobile station to service are typically quite short, the speech burst will perform a cell re-selection if the PoC tag is set, until such 35 have time to finish before the radio conditions deteriorate time as any current talk burst, in either the uplink or the significantly. As a result, interruptions may be eliminated downlink direction, has ended. Once a talk burst has end- altogether. However, in certain situations a talk burst ed, the cell re-selection procedure can commence. If this might continue for a relatively long period whilst the mo- procedure has not completed prior to receipt of a new bile station is moving at high speed across a cell bound- talk burst from a third party mobile, i.e. in the downlink 40 ary. In such a scenario, the service may deteriorate rel- direction, the talk burst is buffered at the BSC until such atively quickly, and it may be necessary to force the cell time as the cell re-selection has been completed. In the re-selection to occur even though the talk burst has not uplink direction, the mobile station will not be able to take yet finished. Different "fallback" decision criteria may be control of the floor until the cell re-selection has been defined to cover this eventuality. These include postpon- completed. Indeed, these are the normal procedures for 45 ing cell re-selection until: handling a new talk burst during a cell-reselection procedure. • Either a current speech burst ends or a maximum [0030] This is illustrated schematically in Figure 3 configurable timer expires. where, again, a cell re-selection of the A-party’s mobile • Either the current speech burst ends or an adaptive station occurs during a first talk burst and a cell re-selec- 50 time, calculated based upon the ongoing speech tion of the B-party’s mobile station occurs during a second burst, expires. talk burst. The solution is clearly applicable in both the • Either the current speech burst ends or an adaptive uplink and downlink directions, and is also applicable to time, calculated for the particular mobile station, ex- intra-BSC cell reselection, inter-BSC cell reselection, and pires. inter-SGSN cell reselection. 55 • Either the current speech burst ends or an adaptive [0031] Figure 4 is a flow diagram illustrating the sig- time, calculated on the BSS level, expires. nalling between the mobile station and the BSC, via the • Either the current speech burst ends or radio condi- BTS, associated with a cell re-selection procedure. tions in the old cell drop below a certain carrier to

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interference ration (C/I). for the mobile station is appropriate is carried out at • Either the speech burst ends or radio conditions in the serving Base Station Controller based upon the old cell results in a certain measurement received from the mobile station. • Bit Error Rate. • Either the speech burst ends or throughput in the old 5 4. A method according to claim 3, wherein cell re-se- cell drops below a certain limit. lection is controlled by a NC2 procedure and the step of delaying the cell re-selection procedure is imple- [0034] Different decision criteria may be applied for dif- mented using the NC2 procedure. ferent cell reselection types, i.e. for intra-BSC cell reselection, inter-BSC cell reselection, and inter-SGSN cell 10 5. A method according to any one of the preceding reselection. claims and comprising sending a cell re-selection [0035] It will be appreciated by the person of skill in request to the mobile station from the radio access the art that various modifications to the above embodi- network following the end of a current talk burst. ments may be made without departing from the scope of the attached claims. For example, it is possible to signal 15 6. A method according to any one of the preceding the cell re-selection immediately to the mobile station, claims and comprising overriding said delay to in- and then implement the delay at the mobile station. The struct immediate cell re-selection in the event that mobile station would know if it is involved in a PoC ses- the radio link quality of the ongoing session falls be- sion. However, this solution may have disadvantages as low an acceptable quality threshold. it would create type approval issues for the mobile station, 20 within the current 3GPP specifications. Of course the 7. A method according to claim 7, said threshold being 3GPP standard could be changed to allow such behav- defined in terms of: carrier to interference ration C/I, iour, but currently the lower-layers are very separate from Bit Error Rate BER, or cell throughput. the application layers. A further disadvantage with a mobile station based solution would be that it would only 25 8. A method according to any one of claims 1 to 6 and work for those particular mobile stations that choose to comprising overriding said delay to instruct immedi- implement the solution, while a network based solution ate cell re-selection in the event that the ongoing talk would work for all NC2 capable mobile stations. burst continues beyond some defined timer value.

30 9. A method according to claim 9, wherein said timer Claims value is: predefined based upon expected behaviour; an adaptively calculated valued based on the 1. A method of controlling the cell re-selection of a mo- ongoing speech burst; a value computed on the ba- bile station (4) between cells (1) of a cellular-based sis of the previous behaviour of the mobile station; radio access network (3), the method comprising the 35 or a value computed on previous behaviour of mobile steps of: stations handled by the radio access network.

determining, within the radio access network, 10. A method according to claim 1, which method is ap- when a cell re-selection for the mobile station is plied for operating a base station controller (BSC) of appropriate; characterized by 40 the cellular-based radio access network (3). determining whether or not the mobile station is involved in a packet switched push to talk serv- 11. A method according to claim 1, which method is ap- ice comprising a series of talk bursts, by inspect- plied for operating a mobile station (MS) for use with ing, at the Base Station Controller (5), a Quality the cellular-based radio access network (3). of Service profile for the ongoing packet 45 switched session; and if the mobile station is involved in a push to talk Patentansprüche service, delaying the cell re-selection until such time as a period of silence between talk bursts 1. Verfahren eines Steuerns der Zellenneuauswahl ei- occurs. 50 ner Mobilstation (4) zwischen Zellen (1) eines zellular-basierten Funkzugangsnetzwerkes (3), wobei 2. A method according to claim 1, wherein the packet das Verfahren die Schritte umfasst: switched service is the General Packet Radio Serv- ice. Bestimmen innerhalb des Funkzugangsnetz- 55 werkes, wenn eine Zellenneuauswahl für die 3. A method according to any of claims 1 or 2, wherein Mobilstation geeignet ist; gekennzeichnet the radio access network is a GSM/GPRS network, durch and said step of determining when a cell re-selection Bestimmen, ob die Mobilstation an einem Pa-

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ketvermittelten Drücken-um-zu-Sprechen- Wert berechnet auf der Basis des vorangehenden Dienst mit einer Serie von Gesprächs-Bursts be- Verhaltens der Mobilstation; oder ein Wert berech- teiligt ist oder nicht, durch Untersuchen an der net auf vorangehendem Verhalten von Mobilstatio- Basisstationssteuergerät (Base Station Control- nen, die von dem Funkzugangsnetzwerk behandelt ler) (5) eines Dienstqualitätsprofils für die an- 5 werden. dauernde Paket-vermittelte Sitzung; und falls die Mobilstation an einem Drücken-um-zu- 10. Verfahren nach Anspruch 1, wobei das Verfahren Sprechen-Dienst beteiligt ist, Verzögern der Zel- zum Betreiben eines Basisstationssteuergerätes lenneuauswahl bis zu einer derartigen Zeit, (BSC) des zellular-basierten Funkzugangsnetzwer- wenn ein Ruhezeitraum zwischen Gesprächs- 10 kes (3) angewendet wird. Bursts auftritt. 11. Verfahren nach Anspruch 1, wobei das Verfahren 2. Verfahren nach Anspruch 1, wobei der Paket-ver- zum Betreiben einer Mobilstation (MS) zur Verwen- mittelte Dienst der General Packet Radio Service dung mit dem zellular-basierten Funkzugangsnetz- (Allgemeinpaketfunkdienst) ist. 15 werkes (3) angewendet wird.

3. Verfahren nach Anspruch 1 oder 2, wobei das Funk- zugangnetzwerk ein GSM/GPRS-Netzwerk ist und Revendications der Schritt eines Bestimmens, wenn eine Zellenneu- auswahl für die Mobilstation geeignet ist, an dem 20 1. Procédé de commande de la re-sélection de cellule bedienenden Basisstationsteuergerät basierend auf d’un poste mobile (4) entre des cellules (1) d’un ré- einer Messung durchgeführt wird, die von der Mo- seau d’accès radio cellulaire (3), le procédé compre- bilstation empfangen wird. nant les étampes :

4. Verfahren nach Anspruch 3, wobei eine Zellenneu- 25 de détermination, à l’intérieur du réseau d’accès auswahl durch ein NC2-Verfahren gesteuert wird radio, d’un moment où une re-sélection de cel- und der Schritt eines Verzögerns des Zellenneuaus- lule pour le poste mobile est appropriée ; wahlverfahrens unter Verwendung des NC2-Verfah- caractérisé : rens implementiert ist. par la détermination de ce que le poste mobile 30 est ou non impliqué dans un service à comman- 5. Verfahren nach einem der vorangehenden Ansprü- de d’alternat à commutation de paquets com- che und mit Senden einer Zellenneuauswahlanfrage prenant une série de salves de parole, en exa- zu der Mobilstation von dem Funkzugangsnetzwerk minant, au niveau du régisseur (5) de station de folgend dem Ende eines gegenwärtigen Gesprächs- base, un profil de qualité de service pour la ses- Bursts. 35 sion en cours de commutation de paquets ; et si le poste mobile est impliqué dans un service 6. Verfahren nach einem der vorangehenden Ansprü- à commande d’alternat, par le retard de la re- che und mit einem Aufheben der Verzögerung, um sélection de cellule jusqu’à ce que se produise eine Zwischenzellenneuauswahl in dem Fall anzu- un moment comme une période de silence entre weisen, dass die Funkverbindungsqualität der an- 40 salves de parole. dauernden Sitzung unter eine akzeptierbare Quali- tätsschwelle fällt. 2. Procédé selon la revendication 1, dans lequel le service à commutation de paquets est le service général 7. Verfahren nach Anspruch 6, wobei die Schwelle de- de radiocommunication par paquets (GPRS pour finiert ist in Form: einer Träger-zu-Interferenz-Zutei- 45 "General Packet Radio Service"). lung C/I, einer Bitfehlerrate BER oder eines Zellen- durchsatzes. 3. Procédé selon l’une quelconque des revendications 1 ou 2, dans lequel le réseau d’accès radio est un 8. Verfahren nach einem der Ansprüche 1 bis 6 und réseau du système global pour les communications mit einem Aufheben der Verzögerung, um eine Zwi- 50 mobiles (GSM pour "Global System for Mobile com- schenzellenneuauswahl in dem anzuweisen, dass munications")/GPRS, et dans lequel ladite étape de der andauernde Gesprächs-Burst sich über einen détermination du moment où une re-sélection de cel- definierten Zeitgeberwert fortsetzt. lule pour le poste mobile est appropriée s’effectue au niveau du régisseur de station de base en service 9. Verfahren nach Anspruch 8, wobei der Zeitgeber- 55 en se basant sur une mesure reçue du poste mobile. wert ist: vordefiniert basierend auf erwartetem Ver- halten; ein adaptiv berechneter bewerteter basie- 4. Procédé selon la revendication 3, dans lequel la re- rend auf dem andauernden Gesprächs-Burst; ein sélection de cellule est commandée par une procé-

7 13 EP 1 795 021 B1 14

dure NC2 et dans lequel l’étape de retardement de la procédure de re-sélection de cellule est mise en oeuvre en utilisant la procédure NC2.

5. Procédé selon l’une quelconque des revendications 5 précédentes et comprenant l’envoi, par le réseau d’accès radio au poste mobile, d’une demande de re-sélection de cellule à la suite de la fin d’une salve de parole en cours. 10 6. Procédé selon l’une quelconque des revendications précédentes et comprenant le fait d’ignorer ledit retard pour ordonner la re-sélection immédiate de cellule dans le cas où la qualité de liaison radio de la session en cours tombe au-dessous d’un seuil de 15 qualité acceptable.

7. Procédé selon la revendication 6, ledit seuil étant défini à partir d’un rapport porteuse sur brouillage (C/I pour "Carrier to Interference"), d’un taux d’er- 20 reurs sur les bits (BER pour "Bit Error Rate"), ou d’une capacité de cellule.

8. Procédé selon l’une quelconque des revendications 1 à 6 et comprenant le fait d’ignorer ledit retard pour 25 ordonner une re-sélection immédiate de cellule dans le cas où la salve de parole en cours se poursuit au- delà d’une certaine valeur définie de temporisateur.

9. Procédé selon la revendication 8, dans lequel ladite 30 valeur de temporisateur est : prédéfinie en se basant sur un comportement escompté ; une valeur calcu- lée de façon adaptative en se basant sur la salve de parole en cours ; une valeur calculée sur la base du comportement antérieur du poste mobile, ou une va- 35 leur calculée sur le comportement antérieur des pos- tes mobiles traités par le réseau d’accès radio.

10. Procédé selon la revendication 1, dans lequel le pro- cédé est appliqué pour mettre en oeuvre un régis- 40 seur de station de base (BSC pour "Base Station Controller") du réseau d’accès radio cellulaire (3).

11. Procédé selon la revendication 1, dans lequel le pro- cédé est appliqué pour mettre en oeuvre un poste 45 mobile (MS pour "Mobile Station") pour utilisation avec le réseau d’accès radio cellulaire (3).

8 EP 1 795 021 B1

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11 EP 1 795 021 B1

REFERENCES CITED IN THE DESCRIPTION

This list of references cited by the applicant is for the reader’s convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description

• GB 2330484 A [0004] • WO 9965266 A [0005]