GB2421873A - Method of Requesting for and Allocation of channels in a Mobile Communications System. - Google Patents

Abstract

A mobile station (101) which is operable in a trunked radio communication system (100) to communicate with other terminals (104, 105) via an infrastructure (103) on a channel allocated by the infrastructure, the channel allocation being made by the mobile station sending a channel allocation request signal to the infrastructure and the infrastructure allocating an available channel and notifying the mobile station of the channel availability, the channel allocation also being removable by the infrastructure if no traffic communication on the allocated channel has been detected before expiry of a hang time, wherein the mobile station (101) is operable (i) to detect that a channel on which that mobile station requested to make or continue a call has been removed by an infrastructure channel controller owing to a delay in the request reaching the controller; and in response (ii) automatically to generate and send another call set-up request signal to the infrastructure. Also described is a system and a method in which the mobile station operates.

Description

TITLE: MOBILE STATION, METHOD AND SYSTEM FOR USE IN

MOBILE COMMUNICATIONS

FIELD OF THE INVENTION

The present invention relates to a mobile station, method and system for use in mobile communications. In particular, it relates to trunked systems including push-to-talk terminals for use in communications, particularly speech communications, and channel use in such systems.

BACKGROUND OF THE INVENTION

A cellular or trunked communication system is one in which mobile or portable user terminals, such as mobile telephones, portable radios or radios on vehicles, herein collectively referred to as mobile stations', can communicate via a network infrastructure which generally includes fixed installations including a plurality of fixed base stations (base transceiver stations) and various sub-systems for management and control of the system including the base stations. Each base station has one or more transceivers which serve mobile stations in a given region or area known as a cell' or site' by radio communication. The cells of neighbouring base stations are often overlapping.

In trunked radio communication systems, there is a set of radio traffic channels that can be used for communications between system users who generally are operating mobile stations. There are not enough channels for each user to have his/her own dedicated traffic channel, so the channels are effectively kept in a pool, or trunked, and are allocated by the system infrastructure to users on a request-by-request basis.

Generally, when the pool of traffic channels has been emptied then new call requests will have to wait until another current call ends so that a traffic channel becomes available for a new call. There are different algorithms that can be employed by the system infrastructure in order to try to give each user a reasonable access to the shared traffic channel resources. Message trunking' is one such algorithm.

Basically, in message trunking, the radio traffic channel allocated for a particular call remains allocated after someone has stopped speaking, so that if a person needs to reply to a message then the traffic channel will be immediately available. In contrast, if the traffic channel is deallocated when the talker finishes speaking then another call request may obtain use of this free (available) traffic channel; when the person attempts to reply in this case then no channels will be available and the reply will encounter a delay.

This latter mode of operation is called transmission trunking'.

For message trunking, the traffic channel is kept active by a system controller (usually a programmed processor in the system infrastructure) for a period that is termed a hang time' . The hang time runs from when the previous speaker in the call finished speaking.

If no-one replies before the hang time expires then the traffic channel will be de-allocated by the system controller.

In a push-to-talk communication system, a voice communication call is initiated by a user by operation of a push-to-talk switch, or PTT', included on or in the user's communication terminal, e.g. mobile station.

At the start of a new call, the first PTT operation by the user who is the call initiator causes the call to be established and the traffic channel to be assigned (connection to be established) by the part of the infrastructure serving that user's mobile station. In message trunked systems, as noted earlier, the traffic channel is kept active after the call initiator has finished speaking. Therefore subsequent PTT operations in such a system merely request for the user to have permission to speak; the traffic channel, i. e. call connection, is still active from the original call set- up.

Where the mobile stations taking part in a call are located in the same region and are served by a single cell or site of the infrastructure, the infrastructure is likely to detect any request sent from a mobile station to continue a conversation before the hang time expires. This is because the link from the mobile stations to the infrastructure channel controller is a short delay link, e.g. a link which experiences a delay of less than 5Oms. However, where one of the mobile stations has migrated to a cell or site which is distant from that in which other mobile stations are located, there may be a significant delay in the link between the infrastructure channel allocation controller and the migrated mobile station. For example, a long delay may be experienced when the link includes a satellite communication link, a dial-up link or an internet link, e.g. involving an IP packet congestion. For example, the delay may be 300ms or more. This link delay adds to the inherent delay of operation at the mobile station and within the infrastructure. In some cases, the delay may cause the hang time to expire before a request to start or continue a call by the migrated mobile station has been granted. In this case, the channel is cleared and a new call has to be set up. This requires re-entry of the data relating to the participants in the call as well as fresh operation of the PTT. This requirement to re- establish a call can be an annoying additional user procedure or even a serious delaying factor in an emergency situation.

SUMMARY OF THE INVENTION

According to the present invention in a first aspect there is provided a mobile station according to claim 1 of the accompanying claims.

According to the present invention in a second aspect there is provided a communication system according to claim 6 of the accompanying claims.

According to the present invention in a third aspect there is provided a method according to claim 9 of the accompanying claims.

Further features of the invention are disclosed in the accompanying dependent claims and in the embodiments of the invention described later.

Where a mobile station has requested to set up or to continue a call and there has been a delay in the request reaching the infrastructure (e.g. a channel allocation controller) which has caused a hang time to expire before the request has been granted, the mobile station receives a message from the infrastructure (e.g. channel allocation controller) that the call set up request has not been successful or, where the request was to continue a call, that the call has been dropped (lost) because the channel has been de-allocated. By the invention, the mobile station automatically generates and sends a further call set-up request. Thus, the new call set-up request may beneficially be made without further user input. This avoids undesirable further delays caused by user involvement in re-establishing the call.

The mobile station according to the invention may operate in a TETRA or other trunked communication system. In a TETRA system, a call set-up request is of standard format referred to as U-setup' and the grant message by the infrastructure is of standard format referred to as Dsetup' . Thus, the new call set-up request generated and sent automatically is of the U- setup' format where the mobile station operates in a TETRA system.

Where a mobile station operates to send an automatic request for a further call set-up, the request does not necessarily go to the infrastructure channel allocation controller to which the delayed request was sent. For example, where the mobile station is registered for service with a local network site, the channel set-up may be managed by another infrastructure channel controller in the local network site. This avoids infrastructure delay in re-establishing the call.

Furthermore, the infrastructure channel controller(s) may detect that a call has been dropped owing to the length of delay in a communication link and may adjust the hang time which operates in the new call to a longer, more convenient value.

In this specification a call' is a communication

between two radio communication terminals. The communication may be to transfer speech information or data (text) or picture or video information or a combination of these types of information. As will be apparent to those skilled in the art, various call types are possible. Where the call comprises speech communication the call could be a group call or a private (individual or point to point') call. Where the call comprises a data communication the call could be to transfer packet data or circuit mode data.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an arrangement of operational units within a trunked mobile communications system embodying the invention.

FIG. 2 is a schematic diagram showing in more detail a controller included in the system of FIG. 1.

DESCRIPTION OF E!.ffiODIMENTS OF THE INVENTION

FIG. 1 is a block diagram showing a TETRA communication system 100 including MSs (mobile stations) 101, 104 and 105 and two networks 102, 103. The MS 101 is currently served by the network 102 and the MSs 104 and 105 are currently served by the network 103 distant from the network 102. The networks 102 and 103 are linked via a long delay link 106 which may be formed for example by one or more of a radio or microwave link, a wired cable link, a link via the internet or a satellite communication link.

The network 102 includes as one of its main components (together with other components) a BTS (base station) 107 which includes one or more transceivers providing radio communication with the MS 101 when the MS 101 is within range of the BTS 107. The network 102 also includes a router 108 for routing communications into and out of the network 102 and within the network 102, an authentication processor 109 which carries out authentication functions of the network 102 and a channel allocation processor 110. The channel allocation processor operates in conjunction with a hang timer 111.

The network 103 includes as one of its main components (together with other components) a BTS 112 which includes one or more transceivers providing radio communication with the MSs 104 and 105 when the MSs 104 and 105 are within range of the base station 112. The network 103 also includes a router 114 for routing communications into and out of the network 103 and within the network 103, an authentication processor 114 which carries out authentication functions of the network 103 and a channel allocation processor 115 which operates in conjunction with a hang timer 116.

RF communications between the network 102 and MSs served by the network 102 are sent and received via the BTS 107 and are routed within or into and out of the network 102 by the router 109. Similarly, RF communications between the network 103 and mobile stations served by the network are sent and received via the BTS 112 and are routed within or into and out of the network 103 by the router 114.

FIG. 2 shows an arrangement 200 of the main functional components of the mobile station 101. This is illustrative of the mobile stations operating in the system 100 shown on FIG. 1, including the MSs 104 and 105.

The arrangement 200 includes an antenna 202 coupled to a circulator 204 (or switch or duplex filter) providing isolation between transmitter and receiver chains of the MS 101. Incoming radio signals picked up by the antenna 202 are passed via the circulator 204 to a receiver chain which includes a receiver front-end 206 which comprises circuitry which provides reception, filtering and down-conversion to base-band frequency signals. The receiver front-end 206 is serially coupled to a signal processor 208 which extracts information from a base-band signal recovered from the receiver front-end 206. The signal processor 208 operates under control of a controller 214 which generally controls all functional operations in the mobile station arrangement 100. The controller 214 is a programmed digital signal microprocessor. Output information from the signal processor 208 is provided to a user at a user interface output 210 which may for example comprise a speaker and/or a visual display, depending on the type of information (e.g. speech, data, picture, video etc) to be output.

A RSSI (received signal strength indicator) 212 is also connected to the receiver front-end 206. The RSSI 212 measures the strength (energy) of a received signal in a known manner and provides an input to the controller 214 giving information on the RSSI of a currently received signal.

Coupled to the controller 214 is a memory 216 which stores data and programs needed for use by the controller 214. A timer 218 is coupled to the controller 214 to control timing of operations within the arrangement 200.

The arrangement 200 includes a transmitter chain which includes a user input 220 such as a microphone, keypad, camera etc. The user input 220 provides input information or data to be communicated from a user and is connected in turn to a transmitter/modulator 222 and a power amplifier (PA) 224, both of which are under the control of the controller 214. An output from the power amplifier 224 is provided as an output signal for radio transmission by the antenna 202 and is provided to the antenna 202 via the circulator 204.

The arrangement 200 also includes a PTT (Push To Talk switch) 230. The PTT 230 includes a user operated device connected to a microswitch. When the device is operated by a user the microswitch is closed causing a signal to be sent to the controller 214. The controller 214 recognises the signal as a request for the user to set-up or have control of a current communication channel to send a communication via that channel. The controller 214 forwards a signal based on this request to the BTS 107 of the network 102.

The user operated device of the PTT 230 may be the button of a conventional mechanical switch.

Alternatively, the PTT 230 could be any of the PTTs known in the art including software switches or buttons operated by click of a mouse or voice activated switches.

Thus, all RF signals received by the MS 101 (generally from the BTS 107) at the antenna 202 are passed via the circulator 204 to the receiver front-end 206, are extracted by the signal processor 208 and passed to the controller 214. Any received information to be saved is stored in the memory 216. All signals for use in system control sent by the MS 101 are sent in baseband digital form from the controller 214 to the transmitter/modulator 222 from which they are passed in RF form via the power amplifier 224 and circulator 204 to be sent over the air by the antenna 202. All user information communications are sent from the transmitter/modulator 222, via the PA 224 and circulator 204 to the antenna 202 from which they are sent over the air.

In operation of the system 100, each MS is initially registered with a network that is to be its serving network. For example the MS 101 registers with the network 102. Mutual authentication between the MS 11 -101 and the network 102 is established by a series of communications in accordance with the TETRA standard sent between the controller 214 of the MS 101 and the authentication processor 109. Similarly, mutual authentication between the MS 104 and the network 103 and between the MS 105 and the network 103 is established by a series of communications in accordance with the TETRA standard sent between the respective controllers 214 of the MS5 104 and 105 and the authentication processor 113. Where the network with which an MS is registering for service is not the home network of the MS but is a visited' network, e.g. where network 103 rather than the network 102 is the home network of the MS 101, the authentication procedure also involves an exchange of information between the visited network and the MS's home network in accordance with the TETRA standard.

Suppose that the MS5 101, 104 and 105 are registered with their current serving networks and that the MS 104 is to set up a group communication with the MS 105 and the MS 101 and possibly a number of other registered MS5 (not shown) . A call set up request is established by the user of the MS 104 by entering the details of the called MSs 101 and 105, e.g. by providing a group identifier code which identifies a particular group to which the MS5 104, 101 and 105 belong, and by pressing a button or key to operate the PTT 230. This action causes the MS 104 to send a radio signal to the BTS 112. The BTS 112 interprets the signal as a call set up request and passes the signal to the channel allocation processor 115. The processor 115 in response checks the validity of the request and then makes a communication channel available by a known allocation procedure and establishes a link between the MSs 101, 104 and 105 which are to communicate. The MS 104 (or alternatively the BTS 112) detects when the user finishes speaking and passes a corresponding signal to the channel allocation processor 115.

The input signals referred to above are applied to the channel allocation processor 115 which incorporates a memory 21. The processor 115 extracts information from the input signal it obtains when the call is being established, such as the identity of the requesting user or user terminal and the call type being requested. The processor 115 issues in response a signal indicating that the call set request is granted. This is passed back to the requesting MS 104 via the base station 112.

The processor 115 also issues an instruction signal causing the BTS 112 to provide a link between the MSs 104 and 105 and the BTS 112 on a suitable channel. The processor 115 also sends a message to the corresponding processor 110 of the network 102 to set up a corresponding link between the MS 101 and the BTS 107, the link extending also between the network 102 and the network 103.

When the processor 115 receives a signal to indicate that the user of the MS 104 has finished communicating (e.g. speaking) the processor 115 starts the hang timer 116 running. The processor 115 determines and sets a hang time to be observed by the hang timer 116. If a signal requesting continuation of the call is sent by one of the other MSs, e.g. MS 105, by operation of the PTT 230 of the relevant MS. it is directed to the processor 115 which allocated the channel being used. If the continuation request is received in time and is granted, an output signal is sent from the processor 115 via the BTS 112 to the requesting MS indicating that the requested continuation is granted. For example, if the request is from the MS 105, there is only a short link from the MS 105 to the processor 115 and the receipt of the request signal and issue of a grant signal by the processor 115 takes place with little delay. A detector incorporated within the processor 115 watches for output signals from the processor 115 to indicate that a call continuation request has been granted. The detector also watches for expiry of the hang time running in the hang timer 116. If, as described above, a call continuation request is made and granted before expiry of the hang time, this is detected by the detector of the processor and an output signal is sent from the processor 115 to the hang timer to clear the hang timer 116.

However, in the case where the MS 101 requests continuation of the call initiated by the MS 104, there is a long delay between the hang timer 116 starting running and the issue of the continuation grant signal by the processor 115. Thus the detector of the processor 115 detects expiry of the hang time running in the hang timer 116 before such a call continuation request is granted. The detector issues an expiry indication and the processor 115 thereby issues a channel clear down signal causing the communication channel currently used for the call to be cleared down and to be available to another call.

Thus, where the user of the MS 101 wishes to continue the call but has lost the channel allocation owing to the link delay that has occurred, a new call set up has to be initiated by the MS 101. In the prior art this new call set up was required to be done by entry of the details of the other MSs in the call and by operation of the PTT 230 of the MS 101.

However, in accordance with an embodiment of the invention, the controller 214 detects that the channel has been lost because of the link delay which has occurred and automatically initiates a new call set up procedure. For this new call, a call set up request is generated automatically by the controller 214 by retrieving from the memory information about the dropped call, e.g. the identities of participant MSs in the call. This action causes the MS 101 to send a radio signal to the BTS 107 of the network 102. The BTS 107 interprets the signal as a call set up request and passes the signal to the channel allocation processor 110 of the network 102. The processor 110 in response checks the validity of the request and then makes a communication channel available by a known allocation procedure and establishes a link between the MSs 101, 104 and 105 which are to communicate. The MS 101 (or alternatively the base station 107) detects when the user finishes speaking and passes a corresponding signal to the channel allocation processor 110 and communication proceeds in a manner similar to that as described earlier for the call requested by the MS 104.

The allocation processor 115 and/or the allocation processor 110 may detect that a call has been dropped by the delay in a link between networks 102, 103 serving the participating MSs in the call and may in response that a new call set up has been requested between the same MSs. In this case, the processor 115 and/or the processor 110 may set a longer hang time to run in the hang timer 116 and/or 110 as described in Applicant's copending UK Patent Application Number GB 0425145.0. The hang time may be reduced again to a regular value when a call between the participants has finished.

Claims (16)

1. A mobile station which is operable in a trunked radio communication system to communicate with other terminals via an infrastructure on a channel allocated by the infrastructure, the channel allocation being made by the mobile station sending a channel allocation request signal to the infrastructure and the infrastructure allocating an available channel and notifying the mobile station of the channel availability, the channel allocation also being removable by the infrastructure if no request for traffic communication on the allocated channel has been detected before expiry of a hang time, wherein the mobile station is operable (i) to detect that a channel on which that mobile station requested to make or continue a call has been removed by a channel allocation processor of the infrastructure owing to a delay in the request reaching the controller; and in response (ii) automatically to generate and send another call setup request signal to the infrastructure.

2. A mobile station according to claim 1 which includes a receiver for receiving a signal from an infrastructure transmitter indicating that a channel has been removed and a controller for generating a new call setup request signal and a transmitter for sending the new call set-up request to an infrastructure receiver.

3. A mobile station which includes a user operable PTT (push to talk) switch to request an initial call set-up or call continuation.

4. A mobile station according to any one of the preceding claims which is operable to measure a delay between sending a call set-up or continuation request signal and receiving a signal in reply from an infrastructure channel controller and to detect that the delay has caused channel removal by the channel controller.

5. A mobile station according to any one preceding claims which is operable in accordance with TETRA standard procedures.

6. A mobile communication system including a system infrastructure and a plurality of mobile stations wherein the mobile stations are operable to communicate with one another via the infrastructure on a channel allocated by the infrastructure, the infrastructure including a channel allocation controller operable to allocate and maintain a channel for a given call by receipt of a request from a mobile station to set-up or continue a call on the channel, the channel allocation controller also being operable to remove the channel from the call if no traffic communication on the allocated channel has been detected before expiry of a hang time, wherein at least one of the mobile stations is operable (i) to detect that a channel on which that mobile station requested to make or continue a call has been removed by the channel allocation controller owing to a delay in the request reaching the controller; and in response (ii) automatically to generate and send another call set-up request signal to the infrastructure.

7. A system according to claim 6 which includes a further channel operation controller and in operation the further set-up request signal is sent to the further channel allocation controller.

8. A system according to claim 6 or claim 7 which is operable in accordance with TETRA standard procedures.

9. A method of operation in a mobile communication system including a system infrastructure and a plurality of mobile stations wherein the mobile stations are operable to communicate with one another via the infrastructure on a channel allocated by the infrastructure, the method including: a mobile station sending a request signal to a channel allocation controller to set-up or continue a call on a channel allocated by the controller, the channel allocation controller allocating or maintaining a channel by receipt of the request signal from the mobile station, removing the allocated channel from the call by the channel allocation controller if no traffic communication on the allocated channel is detected before expiry of a hang time, at least one of the mobile stations further carrying out the steps of (i) detecting that a channel on which that mobile station requested to make or continue a call has been removed by the channel allocation controller owing to a delay in the request signal reaching the controller; and in response (ii) automatically generating and sending another call set-up request signal to the infrastructure.

10. A method according to claim 9 which includes the mobile station sending the further set-up request signal to a further channel allocation controller of the infrastructure.

11. A method according to claim 9 or claim 10 wherein the channel allocation controller operates in a message trunked mode.

12. A method according to any one of claims 9 to 11 wherein the infrastructure detects that a call has been dropped owing to a link delay and adjusts a hang time value in response.

13. A method according to any one of claims 9 to 12, which operates in accordance with TETRA standard procedures.

14. A mobile station according to any one of claims 1 to 5 and substantially as described herein with reference to the accompanying drawings.

15. A system according to any one of claims 6 to 8 and substantially as described herein with reference to the accompanying drawings.

16. A method according to any one of claims 9 to 13 and substantially as described herein with reference to the accompanying drawings.