GB2398970A

GB2398970A - Time clock synchronisation between a base station and wireless mobile transceivers

Info

Publication number: GB2398970A
Application number: GB0304622A
Authority: GB
Inventors: Benny Christensen; Soren Sorensen
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2003-02-28
Filing date: 2003-02-28
Publication date: 2004-09-01
Anticipated expiration: 2023-02-28
Also published as: GB2398970B; GB0304622D0

Abstract

A wireless communications network, comprises a plurality of mobile stations, each include a time clock and a processor, the network generates and sends synchronisation messages indicating the time, upon receipt of the message, the processor uses it to adjust the mobile stations' time clock. The time reference for the message may be obtained from an external source such as a global positioning system, GPS. The message may be a SDS type. The mobile station may conform to the TETRA specification.

Description

COMMUNICATION SYSTEMS AND APPARATUS AND METHODS FOR USE

THEREIN

Field of the Invention

This invention relates to communication systems and apparatus and methods for use therein. In particular, the invention relates to signalling message scheduling in a wireless communication system. The invention is applicable to, but not limited to, signalling message scheduling in a radio communication system supporting packet data communication, e.g. a TETRA (Terrestrial Trunked Radio) network.

Background of the Invention

Wireless communication systems, for example cellular telephony or private mobile radio communication systems, typically provide for radio telecommunication links to be arranged between a system infrastructure including a plurality of base transceiver stations (BTSs) and a plurality of subscriber units or terminals, often termed mobile stations (MSs).

An example of a zone/cell-based wireless communication system is a TETRA (Terrestrial Trunked Radio) system, which is a system operating according to TETRA standards or protocols as defined by the European Telecommunications Standards Institute (ETSI). A primary focus for TETRA equipment is use by the emergency services, as TETRA provides dispatch and control services. The system infrastructure in a TETRA À t #he 44..

À À À t À system is generally referred to as a switching and management infrastructure (SWMI), which substantially contains all of the communication elements apart from the MSS. This includes base transceiver stations (BTSs) connected to a conventional public-switched telephone network (PSTN) through base station controllers (BSCs) and mobile switching centres (MSCs) . The communication network may provide radio communication between the infrastructure and MSs (or between MSS via the infrastructure) of information in any of the known forms in which such communications are possible. In particular, information may represent speech, sound, data, picture or video information. Data information is usually digital information representing written words, numbers etc. i.e. the type of user information processed in a personal computer. In addition, signalling messages are communicated. These are messages relating to the communication system itself, e.g. to control the manner in which user information is communicated in compliance with the selected industry protocol such as TETRA. Different channels may be used for communication of the different forms of information including a control channel for control information.

Summary of the invention

According to the present invention in a first aspect there is provided a wireless communication system including a plurality of mobile stations and system infrastructure for transmitting wireless communications l :: '. e:: to and receiving wireless communications from the mobile stations, each of the mobile stations including a time clock, and wherein the system infrastructure includes means for generating and sending to the mobile stations synchronization messages indicating the current time and each of the mobile stations includes a processor operable upon receipt of one of the synchronization messages to adjust its time clock.

The time synchronization messages may be generated and routed within the infrastructure by a processor and may be transmitted to the mobile stations by a base transceiver, e.g. included in a base transceiver station, also operable to receive inward communications by the infrastructure. The messages may conveniently comprise signals sent on a control communication channel, i.e. a channel dedicated to the communication of control signals. The messages may be sent as SDS (short data service) messages (do these have to be via a data channel?) The time synchronization messages may be generated by reference to a clock of the infrastructure or by reference to an external clock, e.g. the sychronisation clock of the Global Positioning System (GPS) by having one or more GPS receivers incorporated in the infrastructure, e.g. in each of a plurality of BTSs.

The time synchronization messages may be sent periodically, e.g. once per day, by the infrastructure as a broadcast message, e.g. from each of a plurality of BTSs. Alternatively, the messages may be sent in ce. it: '. .: ee.e.: response to a request signal sent by a mobile station, e.g. when a user has selected an optional control function provided by the MS requesting time re-set. The signal may be sent by SDS from the MS.

A further alternative is for the infrastructure to send the synchronization message to the MS whenever a certain event occurs, or certain events occur, requiring communication between the infrastructure and the MS. For example, the message may be sent as a response to the MS requesting registration on the system, in addition to providing a registration approval message in a known way. This may allow the MS clock to be synchronized for example when the MS makes registration for the first time. Subsequent synchronization messages may be sent in response to receipt of updated location signals from the MS, e.g. when the MS sends signals indicating roaming or handover from site to site (BTS to BTS). In order to minimise the amount of extra signalling from the infrastructure in the form of the synchronization messages, the infrastructure may include a memory which records when such a message has been sent to each given MS and ensures that only one such message is sent in a given period, e.g. per day. For MSs that do not undergo roaming or handover within a given time period, the synchronization message may be sent to the MS whenever communication between the MS and the infrastructure takes place periodically, e.g. every hour, to update the current location record in the infrastructure of the MS.

In all cases, the synchronization message when received by the MS may be interpreted by a processor ce. be: .e Id: c e: À . . within the MS as a synchronization message and may be applied by the processor to adjust the clock of the MS in a known manner. The time, adjusted in this manner, may be displayed to the user on an electro-optical display of the MS operatively connected to the clock or a processor connected to the clock in a known manner.

In accordance with a second aspect of the present invention, there is provided a method of synchronizing in a wireless communication system including a plurality of mobile stations and system infrastructure for transmitting wireless communications to and receiving wireless communications from the mobile stations, each of the mobile stations including a time clock, the method including generating and sending to one or more of the mobile stations a synchronization message indicating the current time and in the receiving mobile station employing the received synchronization message to adjust the time clock of the mobile station.

In accordance with a third aspect of the present invention, there is provided a processor operable as the infrastructure processor in the system according to the first aspect.

In accordance with a fourth aspect of the present invention, there is provided a mobile station operable ct. l. .e t: :. le e: À as the mobile station in the system according to the first aspect.

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

Brief Description of the accompanying drawings

FIG. 1 is a timing diagram of a known scheduling operation used in a TETRA communication system.

FIG. 2 is a schematic block diagram of a bunked radio communication system that can be adapted to support the various inventive concepts of an embodiment of the present invention; and FIG. 3 is a timing diagram of a scheduling operation in accordance with an embodiment of the present invention.

Description of embodiments of the invention

Referring to FIG. 1, there is shown schematically a mobile radio communication system l operating in accordance with TETRA standard protocols. The system l comprises a SwMI lO and a plurality of MSs, two of which, MSs l9 and 20, are shown. The MSs l9, 20 in the system l can communicate directly with the SwMI lO and with each other via the SwMI 10 in a bunked mode of operation (TMO) . The MSs 19, 20 may also be able to communicate directly with each other in a direct mode of operation (DMO) . # À À À À À . À À À . . . À À . Communications in the TOO are sent to and received from the MSs 19, 20 by a BTS 14 and the control of such communications is by a processor 16. The BTS 14 and the processor 16 are sub-systems within the SwMI 10.

Communications from the MSS 19 or 20 can also be sent via the BTS 14 to a MSC (master switch controller) 15 also incorporated in the SwMI 10. The MSC 15 is linked by a direct link (call control connection) 17 to a PSTN (public service telephone network) 12.

The BTS 14 routes calls to the processor 16 or to the MSC 15 depending on whether the call is directed to another MS in the system 1 or to a target terminal (not shown) to be reached via the PSTN 12. The SwMI 10 incorporates a MS register 18 operably coupled to the processor 16. The register 18 maintains records of information about the MSs in the system 1. In particular, the register 18 maintains a record of the identity and location of the MSs. The identity is determined for example by the MS fixed ID address number which can initially be used to contact each MS by the SwMI. For a TETRA terminal, this is the so called ITSI (individual TETRA subscriber identity). The register 18 may be associated with a visited location register forming part of the processor 16 which gathers information relating to the location of the current cell or system which can serve the MS in question. Thus, in the embodiment shown in Figure 1, the visited location register is aware that the MS 20 is currently being served by the SwMI 10.

The location information may be provided to the visited location register of the processor 16 in a known manner.

A clock 21 is operably coupled to the processor 16 and the BTS 14. The clock 21 provides timing control for the system 1. Although the clock 21 is shown within the SwMI I: À À À À 4 À 10, it could alternatively be external to the SwMI 10, e.g. in a GPS to which the SwMI 10 may be operably coupled by one or more GPS receivers (not shown).

Operation of the SwMI 10 to generate and send time synchronization messages to one of the MSS, say the MS 19, is as follows. The processor 16 determines that a time synchronization message has to be sent to the MS 19. This occurs because the processor 16 detects a signal from the MS 19 requesting such a message. Alternatively, such a message may be generated in one of the alternative ways described earlier, e.g. after a pre-determined period has elapsed since the last such message was sent to the MS 19 or the processor 16 has detected that the MS 19 has sent an update location signal or is roaming or performing a handover procedure is making some other system communication with the processor 16. The processor 16 notes the precise current time from the clock 21 and compiles an SDS message including this time information. The SDS sends the message on the main TETRA control channel by addressing the message to the ITSI of the MS 19. The use of the message by the MS 19 is described later.

Referring now to FIG. 2, a block diagram of the MS 19 adapted to operate using an embodiment of the present invention is shown. The MS 19 may be suitable for operating in a TMO or DMO depending on the mode selected. Operation of functions within the MS 19 are controlled by a controller 30, which generally comprises a suitably programmed digital signal processor. The controller 30 may also controls the information flow and operational state of processors within the MS 19.

Information relevant to operation of the MS 19 is stored in a memory 34 associated with the controller 30.

r' lt: t' 'I: 1 À À For example, layer 2 ID address information to be used in communications sent by the MS 19 is stored in the memory 34. A clock 32 is operably coupled to the controller 30.

The MS 19 has a receiver chain and a transmitter chain and includes an antenna 42 coupled to a duplex filter or circulator 44 that provides isolation between receiver and transmitter chains within the MS 19. The receiver chain includes a receiver front-end circuit 46 (effectively providing reception, filtering and intermediate or base band frequency conversion of incoming communications). The front-end circuit 46 receives radio communications from another terminal, such as another MS, e.g. the MS 20 (FIG.

1). The front-end circuit 46 is serially coupled to a signal processor (generally realised by a digital signal processor, DSP) 48a coupled to the controller 30. The signal processor 48a performs signal demodulation, error correction and formatting, and recovers end-to-end encrypted information from the received signal.

A signal representing the information recovered by the signal processor 48a is serially coupled to a baseband processing device 50a, which takes the information received from the processor 48a and formats it in a suitable manner to send to an output device 51 such as a speaker.

Data relating to operation of the MS 19 including information about functions selectable by a user is displayed on an electro-optical display 33 operably coupled in a known manner to the controller 30 which supplies information for display.

The functions of the controller 30, the signal processor 48a and the baseband processor 50a although shown as separate in FIG. 2 may be implemented within the same physical microprocessor device. À .

À À . . À À . À . . À . . . À À . . The transmitter chain of the MS 19 essentially includes an input device 60, such as a microphone, coupled in series through a baseband processor sob, a signal processor 48b, transmitter/modulation circuitry 62 and a power amplifier 64. The processor 48b, transmitter/modulation circuitry 62 and the power amplifier 64 are operationally responsive to the controller 30. An output from the power amplifier 64 is supplied to the duplex filter or circulator 44, as known in the art. The transmit chain in the MS 19 takes the baseband signal from input device 60 and delivers it to the signal processor 48b where it is encoded for transmission by the transmit/modulation circuitry 62 and power amplifier 64.

The signal processor 48b in the transmit chain may be implemented in a device distinct from the processor 48a in the receiver chain. Alternatively, a single processor 48 may be used to implement processing of both transmit and receive signals, as shown in FIG. 2. Similarly, the baseband processor 50a and the baseband processor 50b may be separate devices or may be combined in a single device as shown in FIG. 2.

Of course, the various components within the MS 19 can be realised in discrete or integrated component form, with an ultimate structure therefore being a suitable design selection from these forms.

In an embodiment of the invention, the MS 19 receives a time synchronization message from the processor 16 via the BTS 14. The message after receipt and demodulation by the front-end circuitry 46 is passed to the controller 30 which interprets the message as a synchronization update and sends a control signal to the clock 65 adjusting the current time, as indicated in the received message, at the r À 1, À C À clock 65 of the MS 19. The adjusted current time may also be displayed on the display 33.

In the embodiment in which the user may initiate adjustment of the clock 65 of the MS 19, the user may select a Clock reset' function displayed on the display by

Claims

le cl: et' 'l: :: :e.e:: e' : : À . Claims 1. A wireless communication

system including a plurality of mobile stations and system infrastructure for transmitting wireless communications to and receiving wireless communications from the mobile stations, each of the mobile stations including a time clock, and wherein the system infrastructure includes means for generating and sending to the mobile stations synchronization messages indicating the current time and each of the mobile stations includes a processor operable upon receipt of one of the synchronization messages to adjust its time clock.
2. A system according to claim 1 and wherein the infrastructure includes one or more processors operable to generate and route the synchronization messages.
3. A system according to claim 1 or claim 2 and wherein the infrastructure includes one or more base transceivers operable to send communications including the synchronization messages to mobile stations served by the at least one base transceiver and also operable to receive inward communications from mobile stations by the infrastructure.
4. A system according to claim 1, claim 2 or claim 3 and wherein the synchronization messages comprise signals sent on a control communication channel.
5. A system according to any one of the preceding claims wherein the synchronization messages are sent as SDS (short data service) messages.
6. A system according to any one of the preceding claims and wherein the infrastructure includes a clock operably connected to the processor.

The Id: 't I: :e '. c:
7. A system according to any one of the preceding claims 1 to 6 wherein the time synchronisation messages are generated by the processor of the infrastructure by reference to a clock external to the system.
8. A system according to claim 7 wherein the time synchronisation messages are generated by the processor of the infrastructure by reference to signals received by a Global Positioning System (GPS) receiver.
9. A system according to claim 8 wherein the infrastructure includes one or more base stations each having an associated GPS receiver for receiving GPS synchronisation signals.
10. A system according to any one of the preceding claims wherein the infrastructure is operable to generate the time synchronisation messages periodically and to send the messages periodically as broadcast messages.
11. A system according to any one of the preceding claims wherein the infrastructure is operable to generate and send the time synchronisation messages in response to request signals received from mobile stations.
12. A system according to any one of the preceding claims wherein the infrastructure is operable to generate and send a time synchronisation message to a mobile station whenever an event occurs which requires communication between the infrastructure and the mobile station.
13. A system according to claim 12 wherein the infrastructure is operable to generate and send a time synchronisation message to a mobile station in response 4 C ', * to the mobile station requesting registration on the system.
14. A system according to claim 13 wherein the infrastructure is operable to generate and send a time synchronization message to a mobile station when the mobile station makes registration for the first time but not when subsequent registrations are made.
15. A system according to any one of claims 12 to 14 wherein the infrastructure is operable to generate and send a time synchronization message to a mobile station in response to receipt of an updated location or cell service, roaming or handover signal from the mobile station.
16. A system according to claim 15 wherein the infrastructure includes a memory operable to record when such time synchronization message has been sent to each given mobile station and is operable by reference to the memory to ensure that only one such message is sent to each given mobile station in a given period.
17. A system according to any one of the preceding claims wherein each of the mobile stations includes a processor operatively coupled to its clock and operable to interpret a time synchronization message when received by the mobile station and to adjust the clock.
18. A system according to claim 17 wherein each of the mobile stations includes an electro-optical display operatively coupled to its processor operable to display the adjusted time.
19. A system according to claim 1 and substantially as described herein with reference to the accompanying drawings.

tI. e': st' tt: a À v À À . , t 1, ,
20. A method synchronizing in a wireless communication system including a plurality of mobile stations and system infrastructure for transmitting wireless communications to and receiving wireless communications from the mobile stations, each of the mobile stations including a time clock, the method including generating and sending to one or more of the mobile stations a synchronization message indicating the current time and in the receiving mobile station employing the received synchronization message to adjust the time clock of the mobile station.
21. A processor operable as an infrastructure processor included in the system according to claim 2.
22. A mobile station operable as the mobile station in the system according to claim 1.