GB2440578A

GB2440578A - Method and system for wireless communication

Info

Publication number: GB2440578A
Application number: GB0615117A
Authority: GB
Inventors: Shaobo Sun
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2006-07-31
Filing date: 2006-07-31
Publication date: 2008-02-06
Anticipated expiration: 2026-07-31
Also published as: GB2440578B; GB0615117D0; EP2055119A4; WO2008016772A3; WO2008016772A2; EP2055119A2

Abstract

A method (400) operates in a wireless communication system including at least one base station (101) and a plurality of user terminals (105, 107, 109). The method includes the base station (i) selecting one of a plurality of available response procedures by which user terminals should send in response to a first message to be broadcast by the base station a second message to the base station; and (ii) sending a broadcast wireless signal including the first message to user terminals; and a plurality of the user terminals sending to the base station, in response to receiving the first message, a wireless signal including the second message by the response procedure selected by the base station. Also described is a system (100), a base station (101) and a user terminal (105, 200).

Description

1 2440578 TITLE: METHOD AND SYSTEM FOR WIRELESS COMMUNICATION

FIELD OF THE INVENTION

The present invention relates to a method and a system for wireless communication.

BACKGROUND OF THE INVENTION

Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio communication links to be arranged within the system between a plurality of user terminals. Such user terminals may be mobile and may therefore be known as mobile stations', NSs' . At least one user terminal, e.g. used in conjunction with mobile stations, may be a fixed terminal, e.g. a control terminal. Such a system typically includes a system infrastructure which generally includes a network of various fixed installations such as base stations, BSs', which are in direct radio communication with user terminals. Each of the ESs operating in the system may have one or more transceivers which may for example serve user terminals in a given local region or area, known as a cell' or site', by radio communication. Such a system is known as a cellular system. The user terminals which are in direct communication with a particular BS are said to be served by the BS, and all radio communications to and from each user terminal within the system are made via its serving BS. Cells of neighbouring BSs in a cellular system are often overlapping. Signals sent from user terminals to their serving BS are known as uplink' signals. Signals sent from a BS to user terminals are known as downlink' signals. Uplink and downiLink signals may be sent on different channels, e.g. with different carrier frequencies. A wireless communication system which is a cellular system may also be a trunked system in which radio channels of the system are shared between user terminals for different communications, and each channel is assigned for a particular communication for a temporary period only. The allocation of channel resources is managed by at least one system controller which may be incorporated in a BS.

Wireless communication systems typically operate according to a set of industry standard procedures or protocols known collectively as a standard' . An example of such a standard for mobile communications is the TETRA (TErrestrial Trunked Radio) standard which has been defined by the European Telecommunications Standards Institute (ETSI) . A system which operates according to the TETRA standard is known as a TETRA system. TETRA systems are primarily designed for application by professional radio users such as the emergency and security services. Other systems designed for application by such professional radio users include APCO 25 systems which operate in accordance with the APCO Project 25 standard defined by the Association of Public-Safety Communications Officials international, Inc. In wireless communication systems such as TETRA systems, communications may be sent on different channel types according to the type of signalling to be sent.

For example, control signals for system synchronisation and control are sent on a control channel. Signals to communicate user speech and data are sent respectively on a voice channel and a data channel. User speech and data is known collectively as user traffic information.

In some circumstances, it is necessary for a BS to send the same message to all, or a large number of, user terminals, e.g. MSs, currently being served by the BS in a given cell. In some wireless communication systems, broadcast communications are used to send such messages.

This allows saving of downlink channel resources. For some downlink broadcast messages it may be necessary for user terminals receiving the message to send an acknowledgement in response. For example, all of the user terminals, e.g. MSs, may be required to take an action instructed by the BS. For example, where a temporary loss of service by the BS has occurred, such an action may be a demand for all user terminals registered with the BS before the loss of service to re-register. The acknowledgement required by a user terminal may be to indicate that the terminal is ready to take the action or has initiated the action. The acknowledgement response message needs to be only a short standard data message.

In some systems, such as TETRA systems, acknowledgement messages sent in response to broadcast messages are sent using a random access procedure. For example, the system may be a TDMA (Time Divided Multiple Access) system in which communications are synchronised to be in a continuous timing structure which consists of time slots, frames and multiframes. In a TETRA system four slots make up a frame and eighteen frames make up a multiframe (one second) . In such a timing structure, some designated slots are available on a control channel for random access opportunities for MSs to send messages to the infrastructure. The MSs needing to send a message make random attempts as selected by an algorithm run in the MS to access the control channel to send the message.

Use of a random access procedure for sending of messages by MSs is suitable when the number of MSs involved is not great. However, if a large number of MSs, say more than 100, need to send a message by the random access procedure, a high level of collision may be expected between the random access attempts of different MSs. This may be unsatisfactory if the infrastructure needs to receive all acknowledgement messages within a short period of time, e.g. about 2 seconds.

SU}ARY OF THE INVENTION According to the present invention in a first aspect there is provided a method of operation in a wireless communication system, the method being as defined in claim 1 of the accompanying claims.

According to the present invention in a second aspect there is provided a wireless communication system, the system being as defined in claim 14 of the accompanying claims.

According to the present invention in a third aspect there is provided a base station for use in a wireless communication system, the base station being as defined in claim 17 of the accompanying claims.

According to the present invention in a fourth aspect there is provided a user terminal for use in a wireless communication system, the user terminal being as defined in claim 18 of the accompanying claims. The user terminal may be a mobile station.

Further features of the invention are as defined in the accompanying dependent claims and in the embodiments of the invention to be described.

Embodiments of the present 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 block schematic diagram of a layout of a wireless communication system which may be adapted to operate in accordance with an embodiment of the invention.

FIG. 2 is a block schematic diagram of a layout of a mobile station in the system of FIG. 1.

FIG. 3 is a block schematic diagram of a layout of a base station in the system of FIG. 1.

FIG. 4 is a flow chart of a method embodying the invention which may be used in the system of FIG. 1.

FIG. 5 is a flow chart of an alternative method embodying the invention which may be used in the system of FIG. 1.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In accordance with embodiments of the invention there is provided a method of operation in a wireless communication system including at least one base station and a plurality of user terminals operable to communicate with the base station by wireless communication. The method includes the base station (i) selecting one of a plurality of available response procedures by which user terminals should send in response to a first message broadcast by the base station a second message to the base station; and (ii) sending a broadcast wireless signal including the first message to user terminals; and a plurality of the user terminals sending, in response to receiving the first message, to the base station a wireless signal including the second message by the response procedure selected by the base station.

The base station may select the response procedure from a random access procedure and a reserved access procedure in which the signal including the second message from each responding user terminal is sent in an allocated uplink channel resource.

The base station may indicate a response procedure to be used by user terminals to send the second message by data included in an indication field of the first message. For example, the indication field may include at least one variable digit added by the base station and understood by the user terminals to indicate the selected response procedure.

Alternatively, user terminals may determine the required procedure by deduction. For example, user terminals may determine whether to use the random access procedure or the reserved access procedure to send the second message by detecting whether a separate notification message indicating allocation of an uplink channel resource has been received.

The base station may select the response procedure according to current operational conditions in the system.

The second message may be a message required in response to any of the instructions broadcast by a base station as in the prior art. The second message may simply be an acknowledgment by the user terminal of the instruction by the base station. Some further action by the user terminal as instructed by the base station may follow the second message. Thus, the response message may for example be one of the following known responses: (1) an acknowledgement of a request by the base station that the user terminal be re-registered for service by the base station, e.g. after a breakdown in service by the base station; (2) a confirmation that the user terminal is ready to receive a group call; the group call may be requested from a system control terminal.

The system in which the method embodying the invention is applied may comprise a mobile communication system such as a TETRA system or an APCO 25 system referred to earlier, or a GSM (Global System for Mobile communications) system. The user terminals may comprise mobile stations. Alternatively, the system may comprise a WLAN (wireless local area network), e.g. in accordance with a WLAN standard defined by the IEEE (Institute of Electrical and Electronic Engineers), e.g. the IEEE 802.11 standard.

FIG. 1 shows an illustrative communication system which may be adapted in accordance with an embodiment of the invention. It will be apparent to those skilled in the art that the system 100 and the components which are to be described as operating therein may take a number of forms well known to those skilled in the art. Thus, the layout of the system 100, and of its operational components to be described should be regarded as illustrative rather than limiting. The system 100 of FIG. 1 will be described as an illustrative mobile communication system such as a TETRA system.

The system 100 shown in FIG. 1 includes a BS (base station) 101 operably connected to a system infrastructure 103. The BS 101 has radio links with a plurality of user terminals in a service cell or site defined by the position of the ES 101. The user terminals may include MSs (mobile stations) and may include at least one fixed terminal, e.g. used by a dispatcher or other operator sending and receiving operational control messages. Three of many possible MSs are shown, namely MSs 105, 107 and 109 having radio links 111, 113 and 115 respectively with the BS 101. The BS 101 thereby serves MSs including the NSs 105, 107 and 109 with radio communications to and from other MSs either served by the BS 101 or by other BSs (not shown) of the system 100 operably linked to the BS 101 or in other systems (not shown) operably linked to the system 100.

The system infrastructure 103 includes known sub-systems (not shown) required for operation of the system 100. Such sub-systems may include for example sub-systems providing authentication, routing, MS registration and location, system management and other operational functions within the system 100. The system infrastructure 103 may include also other BSs (not shown) providing cells serving other MSs.

FIG. 2 shows an illustrative layout 200 of operational components in each MS of the system 100, including the MSs 105, 107 and 109. A controller 201 controls functional operations of the MS. A processor 202 operably connected to the controller 201 processes information sent to and from the MS. The controller 201 and the processor 202 are operably connected to a timer 205 which provides operational synchronisation and timing and to a memory 206 which stores data and programs needed in operation by the controller 201 and the processor 202.

The processor 202, which may for example comprise a digital processor, is operably connected to an RF transceiver 203 which transmits and receives RF signals including signals carrying information sent to and from the MS. The signals are delivered over the air to and from an antenna 217 connected to the RF transceiver 203.

When the RF transceiver 203 via the antenna 217 receives an RF signal including information representing communicated speech, the processor 202 extracts the speech information and delivers a signal including the extracted speech information to an audio output 210 which comprises a transducer such as a speaker which converts the signal to audio form to reconstruct the communicated speech for a user of the MS having the layout 200. The MS having the layout 200 also includes an audio input 211 which comprises a transducer such as a microphone which converts speech of the user into the form of an electrical signal and delivers the signal to the processor 202 which processes the signal into a form suitable for inclusion in an RF signal for transmission by the transceiver 203 via the antenna 217.

When the RF transceiver 203 receives via the antenna 217 a signal representing communicated (non-speech) data, e.g. alphanumeric characters representing words or numerals or picture or video information, the processor 202 extracts information relating to the corriniunicated data and delivers a signal including the extracted data to a data output 212. The data output may for example comprise a connection to an external data processing terminal (not shown), e.g. a personal computer.

A data input 213 provides an input signal from a user including data to be communicated. The data input 213 may for example comprise a connection to a data source, e.g. a personal computer (not shown) . The signal provided by the data input 213 is delivered to the processor 202 which processes information included in the signal into a form suitable for inclusion in an RF signal to be transmitted by the RF transceiver 203 via the antenna 217.

The MS having the layout 200 includes a user interface 214, e.g. a keypad and control buttons, which allows a user to enter instructions and data into the MS. The user interface 214 is operably connected to the controller 201 to receive signals representing instructions entered by a user at the user interface 214. The user interface 214 is also operably connected to the processor 202 to enable a signal representing data entered by the user at the user interface 214 to be delivered to the processor 202. The processor 202 processes data included in the signal into a form suitable for inclusion in an RF signal to be transmitted by the RF transceiver 203 via the antenna 217.

The MS having the layout 200 may optionally include a known GPS (Global Positioning System) receiver 215 which receives signals from GPS satellites and computes the current location of the MS from such signals in a known manner. The GPS receiver 215 is operably coupled to the processor 202 and may deliver current location information obtained by the receiver 215 to the processor 202 for storage in the memory 206.

The MS having the layout 200 includes an electro-optical display 209 operable to display information to a user in a known manner. The display 209 is driven by a display driver 207 under control of the controller 201.

The MS includes a battery 216 which provides a source of electrical energy for all active components of the MS.

FIG. 3 shows an illustrative layout 300 of operational components in the BS 101. A similar layout may be used in any other ESs (not shown) of the system 100. A controller 301 controls functional operations of the BS 101. A processor 302, e.g. a digital processor, operably connected to the controller 301 processes information sent in RE signals to and from the BS 101.

The controller 301 and the processor 302 are operably connected to a timer 305 which provides operational synchronisation and timing and to a memory 306 which stores data and programs needed in operation by the controller 301 and the processor 302.

The processor 302 is operably connected to a plurality of RE transceivers two of which are shown, namely an RE transceiver 303 and an RF transceiver 307.

Each of the RE transceivers 303 and 307 transmits and receives RE signals including signals carrying information sent to and from user terminals including MSs served by the BS 101. The signals are delivered over the air to and from an antenna 304 connected to the RE transceiver 303 and to and from an antenna 308 connected to the RE transceiver 307.

When the RF transceiver 303 receives via the antenna 304 an RE signal including information representing communicated speech or data, the signal is passed to the processor 302. Similarly, when the RF transceiver 307 receives via the antenna 308 an RF signal including information representing communicated speech or data, the signal is passed to the processor 302. The processor 302 converts each signal including communicated information from the transceiver 303 or the transceiver 304 into an electronic signal including communicated information. The communicated information includes system control information and user communicated information for onward delivery. Where the communicated information comprises system control information the electronic signal produced by the processor 302 is passed to the controller 301. Where the electronic signal produced by the processor 302 comprises user communicated information for onward delivery it is delivered to a router 312 which routes the electronic signal toward its destination, e.g. via the system infrastructure 103. Similarly, each incoming electronic signal received from the infrastructure 103 whIch includes communicated user information, i.e. to be sent to one of the user terminals including MSs served by the BS 101, is routed by the router 312 to the processor 302. The processor 302 processes the electronic signal into a form suitable for inclusion in an RF signal for transmission by the transceiver 303 via the antenna 304 or for transmission by the transceiver 307 via the antenna 308.

The processor 302 also prepares and receives system control messages received from the controller 301.

A base radio controller 313 is operably connected to the controller 313. The base radio controller 313 controls allocation of radio channels for signals sent to and from user terminals including MSs served by the BS 101. A site controller 315 is operably connected to the controller 301. The site controller 315 controls operations within the site or cell covered by the BS 101, other than channel allocations controlled by the base radio controller 313.

The BS 101 includes a power supply 311, e.g. from the main (mains) electricity supply, which provides a source of electrical energy for all active components of the ES 101.

In the following description, the expressions

Layer 2' and Layer 3' are used. Layer 2' and Layer 3' refer to Layers 2 and 3 respectively of the OSI (Open Systems Interconnection) well known protocol stack as adopted by the ISO (International Standards Organisation) . This protocol stack is used in the telecommunications industry to indicate different layers or levels of functions relating to communications between units. Layer 2 refers generally to data link functions and Layer 3 refers generally to network functions. In TETRA systems referred to earlier, Layer 2 is sub-divided into a Medium Access Control (MAC) sub-layer and a Logical Link Control (LLC) sub-layer, and Layer 3 is called a Mobile/Base Link Control Entity (MLE) FIG. 4 is a flow chart of an illustrative method of operation embodying the invention employed in the system 100. The method 400 begins in a step 401 in which the ES 101 prepares to send a broadcast message to user terminals which are MSs which it serves. The message may be one that is to be directed to all MSs served by the BS 101 or to MSs which are in at least one particular class or group of MSs included in the MSs served by the BS 101. For example, the particular class or group may be that of MSs which have been designated to undertake a particular operation via the system 100. In a step 403, the BS 101 decides whether a response is required from MSs when they receive the broadcast message. If the ES 101 produces a NO' decision in step 403 indicating that no response is required from MSs receiving the broadcast message, a step 405 follows. If the ES 101 alternatively produces a YES' decision in step 403 indicating that a response is required from MSs receiving the broadcast message, a step 413 follows.

Where step 405 follows the production of a NO' decision in step 403, the BS 101 sends in step 405 the broadcast message with no response indication. This may include no indication that any response is to be sent by MSs receiving the broadcast message or it may include a particular indication portion included in the broadcast message to indicate to receiving MSs that they are not to respond. Where no indication is included, the message may be sent in a Layer 2 downlink signal. In a step 407 which follows step 405, all MSs served by the BS 101 receive the message broadcast in step 405. In an optional step 409, MSs decide whether the received message applies to them. If the message is directed to all MSs served by the ES 101, no limitation will be placed on the receiving MSs to which the broadcast message applies. Thus, each receiving MS will recognise no limitation and decide that the message applies to that MS. If the broadcast message is directed to at least one particular class or group of MSs, but not all NSs, served by the BS 101, the at least one class or group is identified in the broadcast message. Each receiving MS determines if it is in the identified class or group. This determination may be done by the controller 201 of the MS by reference to the memory 206 of the MS which may store details of the classes and groups to which the MS belongs. If the controller 201 determines that it is in the identified class or group, it decides that the message applies to that MS. All MSs that decide in step 409 that the message applies to them follow in a step 411 any instruction given in the broadcast message.

Where step 413 follows the production of a YES' decision in step 403, the BS 101, e.g. by the site controller 315, analyses current operational conditions to determine what response procedure should be used by MSs receiving the broadcast message that need to respond to it. The current operational conditions may include any one or more of the following: (i) a number of user terminals, e.g. MSs, currently being served by the ES 101; (ii) a number of user terminals, e.g. MSs, that need to respond to the broadcast message; (iii) a speed of response to the broadcast message required from user terminals, e.g. MSs; (iv) a current level of activity on at least one uplink control channel.

In a step 415, the ES 101 selects by reference to the current operational conditions a first response procedure or a second response procedure. The first response procedure comprises each receiving MS that has to respond to the broadcast message sending a response message using a known random access procedure. The second response procedure comprises each receiving MS that has to respond to the broadcast message sending a response message by a reserved access procedure.

Where in step 415 the BS 101 selects the first response procedure, indicated by a 1' in FIG. 4, a step 417 follows. In step 417, the ES 101 sends the broadcast message with a random access indication. The broadcast message may be included in a Layer 3 downlink signal.

The broadcast message includes an indication, understood by the receiving MSs, that the receiving MS is to send any response message required from that MS by the random access procedure, which may be a procedure known per se.

In an optional step 421, similar to step 409, the receiving MSs decide whether the received message applies to them. If the receiving MSs decide that the received message applies to them, the MSs (i) send a response message, which may be included in a Layer 2 uplink signal, in a step 423 using the random access procedure in a known manner; and (ii) follow, in a step 425, any instruction (in addition to the instruction to send a response message) given in the broadcast message, e.g. an instruction to re-register with the base station.

Where in step 415 the BS 101 selects the second response procedure, indicated by a 2' in FIG. 4, a step 427 and a step 429 follow in parallel. In step 427, the BS 101 sends the broadcast message, which may be included in a Layer 3 downlink signal, including an indication, understood by the receiving MSs, that the receiving MS is to send any response message required from that MS by the reserved access procedure, which may be a procedure known per Se. In a step 431 which follows step 427, MSs receive the message broadcast in step 427.

In an optional step 433, similar to step 409, the MSs which have received the broadcast message in step 431 decide whether the broadcast message applies to them.

MSs that decide that the broadcast message applies to them prepare to receive (in a step 435) a further message which is a notification message regarding channel resource allocated by the ES 101.

In step 429 the BS 101, e.g. the base radio controller 313, allocates reserved access channel resource for a separate response from each MS that has to respond to the message broadcast in step 427. In step 435, which follows steps 427 to 433, the BS 101 sends to each appropriate MS a notification message indicating the reserved access channel resource which has been made available for that MS to send its own separate response to the message broadcast in step 427. The notification message may be sent on a downiLink control channel included in a Layer 2 downlink signal. The notification message may comprise a PDU (protocol data units) message in a standard format understood by the receiving MS.

Typically, the allocated resource indicated will be a forthcoming time slot or half a time slot on an uplink control channel. In response to receiving the notification message in step 435, appropriate MSs send in a step 437 a response message in the channel resource allocated as specified in the notification message received in step 435. The response message sent in step 437 may be a PDU message in standard format understood by the BS 101. The response message may be included in a Layer 2 uplink signal in a known manner. Finally, in a step 439, each appropriate MS follows any instruction (in addition to the instruction to send a response) given in the broadcast message sent in step 427.

In the method 400, the indication of a requirement for a response to a broadcast message, and the type of response required, may be included inan additional data field employed in the broadcast message. For example, the broadcast message may comprise a PDU (protocol data unit) message including an unused or added data field containing an added digit understood by the receiving MS indicating the selected response procedure to be

followed. For example, in an added field 0' may

indicate a random access procedure response and 1' may indicate a reserved access procedure response.

Alternatively, a two bit indication selected from 00', 01', 10' and 11' may be used to indicate which of more than two possibilities has been selected for the response procedure.

In the method 400, where the reserved access procedure is indicated in the broadcast message, the base radio controller 313 may be notified of the need to allocate channel resources. This may take place before, during or after sending of the broadcast message, preferably before sending. The base radio controller 313 may obtain details of MSs currently served by the ES 101 from the site controller 315. The base radio controller 313 or the site controller 315 may obtain details of MSs which are members of at least one group to which the broadcast message is to be directed from a database of MS details, e.g. a home location register, e.g. included in the system infrastructure 103.

The delay between the ES 101 sending the broadcast message in step 427 and the BS 101 sending the channel resource notification message in step 435 may be selected so that there is a high probability that each receiving MS will be ready to use the allocated channel resource in time but without the delay being an unduly long delay. The delay selected by the BS 101, e.g. by the controller 301, may be dynamically adjusted depending on operational conditions.

FIG. 5 is a flow chart of an alternative method 500 embodying the invention which may be used in the system of FIG. 1. The method 500 includes step 413 which is the same as the step 413 of the method 400 shown in FIG. 4. The method 500 includes steps which follow step 413 which are alternative to the steps which follow step 413 in the method 400. In the method 500, following the ES 101 selecting a random access procedure in step 413, the ES 101 sends in a step 501 a broadcast message to MSs including a particular instruction to MSs. The broadcast message may be included in a Layer 3 signal. It includes an indication that a response message is required from each MS to which the instruction applies. The broadcast message does not include any indication of what kind of response procedure is to be used by responding MSs to send the response message. The broadcast message is received by MSs in a step 503. The MSs that receive the broadcast message in step 503 decide in an optional step 505 whether the broadcast message applies to them.

MSs that decide in step 505 that they have to send a response message next decide the procedure by which they should send the required response message. Since there is no indication in the broadcast message received of the required response procedure, MSs decide whether a reserved access response or a random access response is required by using a deduction process as follows. In a step 507, the MSs look for a notification message indicating that a reserved access channel resource has been granted. The MSs may be programmed to wait for a given period of time to see whether such a notification message is received. Such a notification message if received may be received in Layer 2 signalling from the BS 101. However, since the BS 101 has selected in step 413 random access for the response procedure, no notification is detected by the MSs in a step 509. Thus, the NSs thereby deduce that the random access procedure has to be used to send the response message. In a step 511, the MSs use the random access procedure in a known manner to send the required response message to the BS 101.

In the method 500, following the BS 101 selecting a reserved access procedure in step 413, the BS 101 allocates, e.g. by the base radio controller 313, in a step 513, the required channel resources for the response messages. In a step 515, the BS 101 notifies each of the MSs that have to send a required response message a notification message indicating the channel resource allocated. As noted earlier, such a notification may be sent in Layer 2 signalling. In parallel with step 513, the BS 101 sends in a step 517 a broadcast message which is the same as that sent in step 501. Steps 519, 521 and 523 follow which are the same as steps 503 to 507 respectively. In a step 525 which follows step 523 and step 515, the MSs that are to send a response message detect the notification message sent in step 515. The MSs thereby deduce that they are to use the reserved access procedure to send the required response message. Finally, in a step 527, the MSs use the reserved access procedure in a known manner to send the required response message. The response message sent in this way may be included in a Layer 2 uplink control channel signal in a known manner. In particular, each MS uses the allocated channel resource indicated in the notification message sent in step 515 and detected in step 525.

The method 500 is particularly suited to a TETRA communication system. In the step 413 the ES 101 may produce an internal message known as a MLE-UNITDATA Request Primitive' PDU (Protocol Data Unit) message in accordance with the TETRA standard. Such a message results in a required downlink broadcast message being sent in step 519. It also informs the BS's Layer 2 services, e.g. as provided by the base radio controller 313, that the message is being broadcast to a group of MSs. In accordance with embodiments of the invention, the same internal message may additionally include one or more further indications to the ES's Layer 2 services, e.g. provided by the base radio controller 313, as follows: (1) that a response message is required from MSs in response to the broadcast message; (ii) the procedure which has been selected for the response messages to be sent by MSs; (iii) the amount of resources, e.g. the number of channel slots or half slots, that need to be reserved for the response messages.

At least one of these indications in (i) and (ii) may be provided by at least one indication digit included as an additional data field in the internal message. The indication in (iii) may be a digital number, included as an additional data field in the internal message, equal to the amount of resources required to be allocated.

In response to receiving the internal message, the Layer 2 services of the BS 101, e.g. as provided by the base radio controller 313, may make available the necessary channel resources in a known manner and notify the MSs of the resources in a known manner in step 515.

In addition, the BS 101 may prepare for receipt of the response messages sent by MS5 in step 529.

In the methods 400 and 500 (as in the prior art)

each response message received by the ES 101 from MSs that have responded to the broadcast message, may be passed to other sub-systems of the system 100, e.g. in the system infrastructure 103. For example, information obtained from the response messages may need to be recorded in a system database such as a home location register.

The methods 400 and 500 embodying the invention beneficially allows the ES 101 to select a response procedure, to be used by user terminals including MSs in response to a broadcast message, which suits the current operational conditions. In particular, where a large population of MSs are currently being served by the ES 101 and have to respond to the broadcast message, it can be favourable to use the reserved access procedure, rather than the random access procedure used when there is smaller population of MSs, since the reserved access procedure can consume less channel resource and can be conducted more efficiently in large population conditions.

Although the present invention has been described in terms of the embodiments described above, especially with reference to the accompanying drawings, it is not intended to be limited to the specific form described in such embodiments. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the terms comprising' or including' do not exclude the presence of other integers or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor.

Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.

Claims

CLAIMS

1. A method of operation in a wireless communication system including at least one base station and a plurality of user terminals operable to communicate with the base station by wireless communication, the method including the base station (i) selecting one of a plurality of available response procedures by which user terminals should send in response to a first message broadcast by the base station a second message to the base station; and (ii) sending a broadcast wireless signal including the first message to user terminals; and a plurality of the user terminals sending, in response to receiving the first message, to the base station a wireless signal including the second message by the response procedure selected by the base station.

2. A method according to claim 1 wherein the base station selects the response procedure according to current operational conditions in the system.

3. A method according to claim 2 wherein the base station selects the response procedure according to a number of user terminals being served by the base station.

4. A method according to claim 2 or claim 3 wherein the base station selects the response procedure according to a number of user terminals that need to respond to the first message.

5. A method according to any one of the preceding claims 2 to 4 wherein the base station selects the response procedure according to a speed of response required from user terminals to the first message.

6. A method according to any one of the preceding claims 2 to 5 wherein the base station selects the response procedure according to a current level of activity on an uplink control channel.

7. A method according to any one of the preceding claims wherein the base station selects the response procedure from (i) a random access procedure; and (ii) a reserved access procedure in which the signal including the second message from each responding user terminal is sent in an allocated uplink channel resource.

8. A method according to claim 7 wherein when the base station selects the reserved access procedure for the response procedure, it sends to each user terminal which needs to send the second message in response to receiving the first message a separate notification message indicating an uplink channel resource which the user terminal has to use to send the second message and each of those user terminals sends its second message in a signal which uses the indicated uplink channel resource.

9. A method according to any one of the preceding claims wherein at least one of the first message and the second message comprises a Protocol Data Unit (PDU) short data message sent on a control channel.

10. A method according to any one of the preceding claims wherein the first message is sent in a Layer 3 downlink signal and the second message is sent in a Layer 2 uplink signal.

11. A method according to any one of the preceding claims wherein the base station indicates a response procedure to be used by user terminals to send the second message by data in an indication field of the first message.

12. A method according to any one of claims 8 to 11 wherein user terminals determine whether to use the random access procedure or the reserved access procedure to send the second message by detecting whether the separate notification message indicating an uplink channel resource has been received.

13. A method according to any one of the preceding claims wherein when the base station selects a reserved access procedure for user terminals to send the wireless signal including the second message it generates an internal message including an indication of the amount of channels resources required for the user terminals to send the wireless signal.

14. A wireless communication system including at least one base station and a plurality of user terminals operable to communicate with the base station by wireless communication, wherein the system is operable to use the method according to any one of the preceding claims.

15. A system according to claim 14 which comprises a mobile communication system which is a TETRA system, an APCO 25 system or a GSM system.

16. A system according to claim 14 which comprises a WLAN (wireless local area network) in accordance with an IEEE standard.

17. A base station operable as the at least one base station in the system according to claim 14, claim 15 or claim 16.

18. A user terminal operable as at least one of the user terminals in the system according to claim 14, claim 15 or claim 16.

19. A user terminal according to claim 18 which comprises a mobile station.

20. A method according to any one of the preceding claims 1 to 13 and substantially as described herein with reference to the accompanying drawings.