WO2000035231A1 - Systeme de radiocommunications - Google Patents

Systeme de radiocommunications Download PDF

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Publication number
WO2000035231A1
WO2000035231A1 PCT/GB1999/004121 GB9904121W WO0035231A1 WO 2000035231 A1 WO2000035231 A1 WO 2000035231A1 GB 9904121 W GB9904121 W GB 9904121W WO 0035231 A1 WO0035231 A1 WO 0035231A1
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WO
WIPO (PCT)
Prior art keywords
duplex
call
full
stations
group
Prior art date
Application number
PCT/GB1999/004121
Other languages
English (en)
Inventor
Alister John Bailey
Original Assignee
Simoco International Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Simoco International Limited filed Critical Simoco International Limited
Priority to AU16677/00A priority Critical patent/AU1667700A/en
Publication of WO2000035231A1 publication Critical patent/WO2000035231A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks
    • H04W84/08—Trunked mobile radio systems

Definitions

  • the present invention relates to a radio communication system such as a private mobile radio (PMR) system, and in particular to such a system in which a conversation between two parties can be broadcast simultaneously to other users of the system.
  • PMR private mobile radio
  • Many users of private mobile radio systems make extensive use of half -duplex (i.e. in which there is voice transmission in both directions, but in only one direction at any one time) group call arrangements to enable all members of a group of users to listen in to communications from other members of the group.
  • half -duplex i.e. in which there is voice transmission in both directions, but in only one direction at any one time
  • group call arrangements to enable all members of a group of users to listen in to communications from other members of the group.
  • the UK police operate "all-informed" groups by using such half -duplex group-call functions.
  • each party in the group will typically have a half -duplex connection to the fixed radio network (such that they can only transmit to or receive from the fixed network at any given time, and select which they want to do usually by pressing their push-to-talk (PTT) button) . Only one party in the group can talk at any given time, and the remaining members of the call group all listen in on their respective radio channel.
  • PTT push-to-talk
  • Newly proposed trunked mobile radio communications systems such as the Terrestrial Trunked Radio (TETRA) system have provision for full-duplex calling (i.e. in which there is voice transmission in both directions simultaneously) , as do cellular mobile telephone systems.
  • TETRA Terrestrial Trunked Radio
  • a mobile radio station can simultaneously both transmit a signal to and receive a signal from the other party.
  • Each party would therefore typically communicate over two separate radio channels simultaneously (one in each transmission direction) .
  • Such full-duplex communication is inherently a one-to-one teleservice between individuals, rather than groups .
  • a method of establishing a call between a group of call terminating stations of a mobile radio communications system, where at least some of the stations in the group are mobile radio stations comprising: setting up a full-duplex connection between at least two stations in the group; and retransmitting the speech transmitted over the full-duplex connection to one or more mobile stations in the group not linked by the full-duplex connection via a half-duplex radio connection or a simplex radio connection; whereby the users of the one or more other mobile stations can listen to the speech transmitted over the full-duplex connection.
  • a mobile radio communications system comprising: a group of call terminating stations all capable of communication with each other, at least some of the stations in the group being mobile radio stations; means for establishing a full-duplex connection between at least two stations of the group; means for substantially simultaneously establishing half-duplex radio connections and/or simplex radio connections to one or more mobile stations in the group not linked by the full-duplex connection; and means for substantially simultaneously transmitting over said half-duplex connections and/or simplex connections to the other mobile stations in the group the speech transmitted over said full -duplex connection.
  • the speech signals transmitted over a full-duplex connection between at least two stations of the communication system are retransmitted or broadcast to other mobile radio stations in a group of the system via half-duplex or simplex radio connections.
  • This allows the members of the communication system group to listen to the full- duplex conversation between members of the user group, but without the need to establish full-duplex radio connections to all the mobile stations in the group.
  • the Applicants have recognised that while users may wish to still retain all informed groups together with full- duplex connections, in many cases the users wish only for other members of the group to listen in to such a conversation, rather than for all members of the group to participate in the conversation simultaneously.
  • the present invention meets many users' requirements, while using radio channel capacity relatively efficiently.
  • the call terminating stations in the group of stations may be any station of the communications system at which a call terminates (i.e. a subscriber party of the communications system, as distinct from intermediate stations of the communications system such as base stations or sites of a fixed radio communications network) .
  • the group stations could include a fixed line station such as a user of the public switched telephone network (PSTN) or a despatcher having a hard wired connection to the communication system.
  • PSTN public switched telephone network
  • the group of call terminating stations will include plural mobile radio stations which are in radio communication with the rest of the system.
  • the group of call terminating stations between which the call is established will typically be a predetermined such group, with its own particular group identity, although this is not necessary. It could alternatively, for example, comprise such a predetermined call group of the radio system and another call terminating station of the system, such as might be the case when a dispatcher wishes to call a call group of mobile stations. In this case, the full-duplex connection would typically be between the other call terminating station and at least one call terminating station of the predetermined call group. As a further alternative, the group of call terminating stations to which the call is established could, for example, be defined dynamically in use. The full-duplex connection between the group stations can be established as desired, and can conveniently be done in the standard manner for the communication system in question.
  • the full duplex connection could alternatively be between two mobile stations of the system (in which case the full-duplex connection could be between the mobile stations directly or via a fixed radio communication system network) .
  • PSTN public switched telephone network
  • the Applicants have recognised that there may well be situations where it is desired to have a full duplex call between two mobile stations broadcast to a half-duplex group, rather than simply having a stand-alone half duplex group call. This could be the case, for example, where the mobile station call originators expect to have a full duplex call but it is still desired to have an "all-informed" group.
  • the full-duplex connection could be between two call-terminating stations in the same cell (served by the same base station) , or, more typically, they will be in different cells and served by different base sites or stations.
  • a full duplex connection may be established between more than two stations of the group, if desired, but this would require more radio resource and increase the signalling complexity. Thus preferably it is between two stations only.
  • the half-duplex and simplex connections to the mobile radio stations in the group can also be established in any suitable way known in the art. They are preferably only attempted to be established once the full-duplex connection has been established. Most preferably, half duplex connections are used to connect to the mobile radio stations in the group not party to the full duplex connection, since that permits those mobile stations to transmit as well as receive signals whilst participating in the call.
  • the half-duplex group connection set-up process preferably comprises paging the other, and preferably each of the other, mobile stations in the group with an instruction to establish the half-duplex connection so that they can receive the call.
  • the set-up process can ask for an acknowledgement from each called party or station before the group call transmission is begun, but preferably no acknowledgements from the receiving group stations are required, as this permits the call to be set up more quickly.
  • the page to the other mobile group members is preferably periodically repeated while the call is taking place to allow any group mobile stations that missed the initial page to join the call subsequently.
  • the radio communications system includes a fixed radio network (which can comprise radio base stations or sites, switching and system management infrastructure, and connections to external networks such as the PSTN, etc, as is known in the art) via which the half-duplex or simplex radio connections to the other mobile radio stations are established, all the mobile stations party to the half-duplex or simplex connections served by the same base station of the fixed radio network preferably receive the retransmitted full duplex speech signals broadcast by the base station on the same radio channel or channels, as this uses radio channel capacity more efficiently.
  • a fixed radio network which can comprise radio base stations or sites, switching and system management infrastructure, and connections to external networks such as the PSTN, etc, as is known in the art
  • the half-duplex mobile station can conveniently listen to the downlink signal of the full duplex call, if appropriate.
  • non-mobile, hard-wired call terminating stations in the group are to listen in to the full- duplex connection they can do so as desired, e.g. via a full duplex connection (which a line will provide) or via a suitably arranged "pseudo half duplex" connection which mimics a half-duplex radio connection over a hard- wired connection, as is known in the art.
  • a particularly preferred way of implementing the present invention in mobile radio communications systems which support both full-duplex and half-duplex services is to set up the call of the present invention using a full-duplex call set-up process and a half-duplex or simplex group call set-up process, with the half-duplex or simplex group call comprising a re-broadcasting of the full-duplex call.
  • Most preferably the arrangement would use the standard full-duplex call set-up and the standard half-duplex or simplex group call set-up process of or defined for the radio system in question.
  • a normal full-duplex call would be set-up between two stations in the group, and a separate, normal, half-duplex or simplex group call setup to all the other group stations.
  • the half-duplex or simplex group call would be a normal one, except that it would be a re-broadcasting of the complete (i.e. both sides of the) full-duplex call.
  • the present invention effectively uses existing services provided by the radio system but in a new manner and combination to provide a new call arrangement that the Applicants have recognised will be advantageous in some circumstances .
  • a method of providing a group call in a mobile radio communications system comprising: setting up a full-duplex call between two call terminating stations of the mobile radio communications system; and setting up a half-duplex group call or a simplex group call to a group of call terminating stations of the mobile radio communications system; wherein said group call comprises a retransmission of speech signals from said full-duplex call.
  • a mobile radio communications system comprising: plural call terminating stations all capable of communication with each other; means for setting up a full-duplex call between two call terminating stations of the mobile radio communications system; and means for setting up a half-duplex group call or a simplex group call to a group of call terminating stations of the mobile radio communications system, which group call comprises a retransmission of speech signals from said full-duplex call.
  • This arrangement preferably uses a modified call request from the user initiating the call which would cause a full-duplex call to be set-up between two stations together with half-duplex or simplex group call connections to the other group stations (which would carry both sides of the full-duplex conversation) .
  • the call could be implemented as a special service with its own dedicated service identifiers.
  • the call request preferably specifies the group of stations to be called (which could have an identifying label) and the station to be called in full-duplex.
  • a call terminating station of a mobile radio communications system comprising means for making a call request to the system, which call request includes the identification of another call terminating station of the system with which a full- duplex call is to be established, and the identification of a predetermined group of call terminating stations of the system with which a half-duplex group call or a simplex group call is substantially simultaneously to be established.
  • the speech signals of the full-duplex connection are broadcast to remaining group stations via the half-duplex or simplex connections set up. This speech should be played back by the remaining group stations to their users as a single conversation.
  • both (or all) the full duplex speech signals should be mixed before they are played to a listener. This mixing can be done where desired, such as at each receiving station individually (such that each receiving station would receive both halves (or all parts) of the full duplex conversation and then combine them into a single speech signal before playing them) .
  • both halves (or all parts) of the full duplex conversation are combined or mixed before transmission to the receiving remaining group stations, e.g. in the fixed radio network infrastructure, such that the receiving stations only receive a single speech signal which they can then play to their user.
  • the speech mixing itself can be performed as desired and in any manner known in the art. It could, for example, be performed in the analogue or digital domains.
  • the mixing could be voice activated as is known in the art.
  • the group call of the present invention can be terminated as desired. For example, it could be terminated when, or a predetermined period of time after, one or preferably both parties to the full duplex connection have released or cleared the full duplex call.
  • a listening group member i.e. one of the remaining stations in the group party to the half-duplex connection
  • a listening group member can request to join the full- duplex call or that the full-duplex call be moved to itself (for example in a mobile radio system by pressing their push-to-talk button) .
  • Such requests could be permitted to be made whilst the full-duplex call is ongoing, and/or, for example, during a predetermined time period after one of the original full duplex parties releases the call (thus allowing the call to be picked up by another group member, if desired) .
  • the full duplex callers can be alerted to the desire of another group station to interrupt their call by means of an appropriate indication from their stations such as an audible tone.
  • the requesting station could be included directly in the full-duplex conversation with the two users presently in full-duplex communication by establishing full-duplex connections between all three parties.
  • the new interrupting group member replaces one of the parties to the original full- duplex conversation, such that, in effect, the previous full-duplex call is terminated and a new full-duplex call is established between the new interrupting group members and the remaining original full-duplex party. This saves radio channel resource, and maintains resource allocation in a trunked system whilst still giving the illusion that all members of the group are party to a multi-way full-duplex group call.
  • the dropping of one of the pre-existing full-duplex connections may be delayed until one of the stations attached via that link has stopped speaking or relinquished the connection (for example by releasing his push-to-talk button (PTT) in a private mobile radio system), i.e. until there is no signal from that station.
  • PTT push-to-talk button
  • one of the pre-existing full-duplex connections could be dropped substantially immediately a request is made.
  • the stations party to the half-duplex connection i.e. the remaining group members
  • the stations party to the half-duplex connection are preferably therefore able to make different priority requests to participate in the full-duplex call.
  • a first such request could be a low-priority interrupt (call pre-emption) in response to which the system endeavours to connect the interrupting party to the full-duplex call when possible.
  • a group member could indicate their wish to interrupt by attempting to call one or other or both (e.g. if only equipped for half-duplex) of the stations in the full- duplex conversation, and on call-release by one of the full-duplex users (e.g. releasing PTT) take over.
  • a second such request could be a higher priority request which forces the communication system to provide the new group member with a full-duplex connection substantially as soon as possible (i.e. to force one of the two stations to move from the full-duplex connection substantially immediately) .
  • a group member could call one or both of the stations in the full- duplex conversation with a higher priority status set such that one or other of them is forced to relinquish their connection as soon as possible in favour of a full-duplex connection with the calling group station.
  • the pre-existing full-duplex connection to be replaced is preferably selected by using one or more, preferably predetermined, arbitration criteria. For example, it could be determined by which user invoked the original call (such that, e.g. the original call initiator is retained under all circumstances) , by which original user was the last party to speak, by which party released their channel first, in accordance with a predetermined priority list (e.g. such that the connection with lowest priority is terminated) or a combination of such factors. In the penultimate case it may be further arranged that the station making the call request will not be allowed access if it has a lower priority than the two pre-existing parties to the full- duplex call, or such that it gets access anyway in place of the current party having the lowest priority.
  • predetermined, arbitration criteria For example, it could be determined by which user invoked the original call (such that, e.g. the original call initiator is retained under all circumstances) , by which original user was the last party to speak, by which party released their channel first, in accordance
  • arbitration criteria could also be used to determine which of a plurality of group members who seek to interrupt the full-duplex call simultaneously becomes a party to the full-duplex call. It could also be arranged such that not all stations in the group have the facility to interrupt the full-duplex call.
  • the arrangement is such that a new speaker has a minimum call duration as a party to the full-duplex call before he is able to be replaced by another group member.
  • a group call set up in accordance with the present invention can be restricted to a single cell or base station of a mobile radio communications system, or may extend over one or more cells of the mobile radio communications system, such that one or more base sites are involved in setting up and handling the call.
  • a radio communications station for use in a mobile radio communication system which includes a plurality of mobile stations, the communications station comprising: means for establishing full-duplex radio communication between the station and a first mobile radio station of the radio communications system; means for establishing half-duplex radio communication or simplex radio communication between the station and one or more other mobile stations of the radio communication system; and means for transmitting both the speech signal transmitted to and the speech signal received from the first mobile station substantially simultaneously to said other mobile stations of the radio communication system via said half-duplex or simplex radio communication connection or connections.
  • This radio communications station would typically be a fixed base station of the radio communication system, but this is not essential. It could also comprise a suitably equipped mobile station, such as a mobile radio or phone (whether vehicle mounted or portable) .
  • the communications station of this aspect of the present invention preferably further includes means for mixing the speech signals received and transmitted over the full duplex connection to form a single speech signal which is then transmitted over the half-duplex connections .
  • the call set up process of the present invention can include a step of checking initially if radio or other resource and/or call participants necessary for the call is available, and if it is not blocking the call and so informing the call originator. Otherwise, the call set up process would then proceed as described above.
  • the methods in accordance with the present invention may be implemented at least partially using software e.g. computer programs. It will thus be seen that when viewed from further aspects the present invention provides computer software specifically adapted to carry out the methods hereinabove described when installed on data processing means, and a computer program element comprising computer software code portions for performing the methods hereinabove described when the program element is run on a computer.
  • the invention also extends to a computer software carrier comprising such software which when used to operate a radio system or a radio communications station comprising a digital computer causes in conjunction with said computer said system or station to carry out the steps of the method of the present invention.
  • a computer software carrier could be a physical storage medium such as a ROM chip, CD ROM or disk, or could be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite or the like.
  • FIG. 1 shows a block schematic diagram of a mobile radio communications system in accordance with the present invention
  • Figure 2 shows the system of Figure 1 configured in a different manner
  • Figure 3 shows schematically the setting up of a group call in accordance with the present invention in a time division multiple access (TDMA) mobile radio system.
  • TDMA time division multiple access
  • FIG 1 shows a Trunked Private Mobile Radio (PMR) system including a fixed radio network which includes base stations PS1, PS2 and PS3 linked by fixed connections such as, for example, land line or microwave connections. (although three base stations are shown in the Figures, it will be understood that the radio system may comprise only one or any number of such stations.) Seven mobile stations SSI - SS7 are shown in radio communication with the base stations. In the arrangement shown in Figure 1 a group call in accordance with the present invention has been set up. In this call, mobile stations SS2 and SS7 are having the full-duplex call, and all the remaining mobile stations are listening in over half-duplex connections.
  • PMR Trunked Private Mobile Radio
  • mobile station SS2 has, as shown, a full-duplex connection to base station PS1 and mobile station SS7 has a full-duplex connection to base station PS3, such that mobile stations SS2 and SS7 have effectively a full duplex connection (via the fixed radio network) to each other.
  • mobile station SSI has a half-duplex connection to base station PS1
  • mobile station SS3 and mobile station SS4 have a half-duplex connection with base station PS2
  • mobile station SS5 and mobile station SS6 have a half-duplex connection with base station PS3.
  • the radio system operates to rebroadcast the speech signals from mobile stations SS2 and SS7 over the half- duplex radio connections to the remaining mobile stations in the group, so that those mobile stations can listen in to the full duplex call and hear both sides of the conversation, i.e. hear both call terminating stations, mobile station SS2 and mobile station SS7.
  • the speech signals can be transmitted on two half-duplex channels to each mobile station (i.e. with each channel carrying the signal received from mobile station SS2 and mobile station SS7, respectively), where they are then mixed.
  • the fixed radio network can mix the speech signals which are then transmitted as a single half-duplex channel to each receiving mobile station.
  • the mobile stations having half-duplex connections to the same base station can listen and receive on separate channels, but preferably they will, as would normally be the case, receive, i.e. listen to, the same channel (i.e. effectively share the same channel) as this saves radio resource.
  • the communication system is illustrated as having only mobile stations as call terminating stations, it could also include other such stations such as a standard telephone user connected to the PSTN or a dispatcher connected by wire to the mobile radio system. The means by which such users are connected to a mobile radio system are well known. These other stations could be party to the full-duplex call or the half duplex group broadcast, in the same way as the mobile stations.
  • Figure 3 is a chart whose X-axis is time which shows the sequence of events necessary to set up the group call shown in Figure 1 in a TDMA (time division multiple access) radio system such as the TETRA system. It should be noted that the invention can be implemented in systems other than TETRA.
  • the four lines of time slots in Figure 3 relate to the transmission activity of mobile station SS2 , the fixed radio network (in this case base stations PS1, PS2 and PS3 - it is assumed in this example that these three base stations are synchronised, but this is, as is known in the art, not essential), mobile station SS7 and the collective group (GRP) respectively (comprising in this example mobile stations SSI, SS3-SS6) .
  • the fixed radio network in this case base stations PS1, PS2 and PS3 - it is assumed in this example that these three base stations are synchronised, but this is, as is known in the art, not essential
  • GRP collective group
  • Mobile station SS2 makes a random access to base station PS1 (i.e. the fixed radio network) on a control or signalling channel (e.g. TETRA Main Control Channel (MCCH) ) as soon as feasible at time T2 to request that the call be set up.
  • the signal sent by mobile station SS2 comprises a call setup request that identifies the request as relating to a duplex call with mobile station SS7 and a group call with the appropriate fully informed group. It could, for example, be the combination of the usual system duplex call and group call signalling. Alternatively a separate signalling message for the group calls of the present invention could be provided.
  • base station PS1 acknowledges the request to mobile station SS2 and issues a page (via other base stations if necessary and in this case via base station PS3) to mobile station SS7 to indicate that mobile station SS7 is being called. Mobile station SS7 then indicates to its user that they are being called.
  • the mobile stations SS2 and SS7 can, if necessary, linearise their transmitters (e.g. using transmissions on the common linearisation channel in TETRA) . (This step is only necessary in TETRA where the Main Control Channel is not on the same frequency as the allocated traffic channel.)
  • mobile station SS2 and mobile station SS7 confirm their presence on the traffic channel.
  • a dummy burst may be transmitted at time T10 by the base station to mobile stations SS2 , SS7 (at time TlOa) and to the group (at time TlOb) until speech transmission begins.
  • the two mobile stations SS2 , SS7 having the full duplex link transmit to one another and at T12 the base station (s) transmit both sides of the call to the reminder of the group over the half -duplex connections established.
  • Mobile station SS3 would first transmit a call pre-emption request to the radio communications system. A request to relinquish its full-duplex status is then, for example, sent by the fixed radio network to mobile station SS7. When the user of mobile station SS7 releases the call (e.g. by releasing their PTT or pressing their "on-hook” button) , call transfer proceeds and mobile station SS3 is allocated the duplex channel that was previously allocated to mobile station SS7.
  • Mobile station SS3 now has a full- duplex link with base station PS2 and mobile station SS7 now has a half-duplex link with base station PS3 (it shares a channel with mobile station SS6) .
  • the other connections are the same as shown in Figure 1.
  • mobile stations SS2 and SS3 now have the full-duplex call, with the other stations listening in.
  • the mobile station that wishes to take part in the call may issue a priority call pre-emption request which the communication system tries to satisfy substantially immediately by forcing one of SS2 and SS7 from the full- duplex call. It may be desired not to provide all of the mobile stations with this facility. Indeed a number of priority requests relating to different levels of urgency may be provided if desired and allocated to all of the mobile stations. Instead they could be allocated only to certain mobile stations, for example according to the seniority of the user of the station within the organisation that uses the mobile radio system.
  • the call can be cleared and terminating as desired, e.g. by the full -duplex connected stations indicating their desire to clear the call to the radio system infrastructure and the radio system infrastructure then instructing all stations to clear the call, or by the radio system infrastructure instructing all stations to clear the call upon expiry of a call timer associated with the call .
  • the present invention can be arranged to operate on any mobile radio system that provides a full duplex service and group addressing functions, such as a suitable private mobile radio system or cellular mobile phone system.
  • the invention is not restricted to a digital TDMA system as described here but may be implemented with any digital system and/or with an analogue system that provides addressing.

Abstract

L'invention porte sur un système privé interconnecté de communications radio téléphoniques (PMR) comprenant un réseau radio fixe de stations de base (PS1, PS2, PS3) relies par des lignes terrestres ou hertziennes, et un réseau de stations mobiles (SS1 - SS7). On peut établir (via le réseau radio fixe) une communication de groupe en duplex intégral entre les deux stations (SS2 et SS7), alors que toutes les autres stations mobiles, reliées en semi-duplex, peuvent être à l'écoute. Le susdit système fonctionne en rediffusant sur les liaisons en semi-duplex les signaux vocaux des stations mobiles (SS2 et SS7) aux autres stations mobiles du groupe qui peuvent ainsi écouter les conversations combinées de la liaison en duplex intégral.
PCT/GB1999/004121 1998-12-08 1999-12-08 Systeme de radiocommunications WO2000035231A1 (fr)

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Application Number Priority Date Filing Date Title
AU16677/00A AU1667700A (en) 1998-12-08 1999-12-08 Radio communication system

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9826986.3 1998-12-08
GBGB9826986.3A GB9826986D0 (en) 1998-12-08 1998-12-08 Radio communication system

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Publication number Priority date Publication date Assignee Title
EP1569474A1 (fr) 2004-02-27 2005-08-31 Research In Motion Limited Messagerie de demande pour un canal de transmission dans des systèmes de communication vocaux semi duplex
EP1976312A2 (fr) 2004-02-27 2008-10-01 Research In Motion Limited Procédé, dispositif et système pour la messagerie de requête de canal de transmission pour systèmes de communication vocaux en semi-duplex
EP1976312A3 (fr) * 2004-02-27 2008-10-15 Research In Motion Limited Procédé, dispositif et système pour la messagerie de requête de canal de transmission pour systèmes de communication vocaux en semi-duplex
US7933620B2 (en) 2004-02-27 2011-04-26 Research In Motion Limited Transmit channel request messaging for half-duplex voice communications systems
GB2416273A (en) * 2004-07-14 2006-01-18 Motorola Inc Simultaneous call processing for two calls transmitting on the same communication channel
EP1701562A1 (fr) * 2005-03-09 2006-09-13 Vodafone Holding GmbH Procédé et système pour optimiser la capacité d'un système de communication mobile

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AU1667700A (en) 2000-06-26
GB2344726A (en) 2000-06-14
GB2344726B (en) 2001-07-18
GB9929053D0 (en) 2000-02-02

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