GB2316835A

GB2316835A - Synchronisation of electronic apparatus

Info

Publication number: GB2316835A
Application number: GB9617800A
Authority: GB
Inventors: Idris John Mark Rees; Chris Seymour
Original assignee: Motorola Ltd
Current assignee: Motorola Solutions UK Ltd
Priority date: 1996-08-24
Filing date: 1996-08-24
Publication date: 1998-03-04
Also published as: GB9617800D0

Abstract

A frame counter synchronisation pulse generator 11, for use in a digital cellular radio communication system, consists of a CPU 12, to which an accurately timed pulse train and time data signals, extracted from GPS satellite signals by GPS receiver 13, are applied, the pulses also being applied to a synchronisation pulse gate 14. CPU 12 is programmed with a predefined time zero, from which all base stations are deemed to have started to function, and calculates, from the time data, which of the pulses of the pulse train is an integral number of pulse periods from the reference time zero and also corresponds to an integral number of signal frames of a base station with which the frame counter synchronisation pulse generator 11 is associated. The pulse generator may be used to synchronise the internal clocks and oscillators of base stations associated with a cellular system.

Description

Synchronisation of Electronic Apparatus.

Field of the Invention The present invention relates to the synchronisation of the actions of electronic apparatus, and more particularly to the synchronisation of dispersed equipment such base transceiver stations forming part of digital cellular radio communication systems.

Background of the Invention Digital cellular radio communication systems include groups of transceiver stations each of which forms a base station of a respective cell of the cellular communication system. The base transceiver station of each cell is linked to a control centre called a base switching centre. The base switching centre of one group of cells is linked to those of other groups of cells to contribute the cellular radio communication system. For the successful operation of such a system it is necessary to operate the internal circuitry of at least the base transceiver stations of a group of cells in as near a state of synchronisation as possible.

In the United Kingdom, at least, it is the current practice in cellular radio communications systems to lock the internal circuitry of each base transceiver station to a reference 2.048 MHz signal derived from the telephone network. However, this means that the long term accuracy of the operation of the base transceiver stations and their internal clock circuits can only be as good as the stability of the reference system used by the telephone network.

In digital cellular radio communication systems conforming to the recommendations of a body known as the Groupe System Mobile (A Ga,M system) operations take place in binary groups, or frames, which last for approximately 4.62 ms. Advantages can accrue from ensuring that the clocks of base transceiver stations in a group of cells, at least, have their internal systems synchronised perfectly. For example, it has been proposed that if the frames of all the base transceiver stations in a group of cells of the system, at least can be synchronised to within one bit of a frame, then faster handover of a mobile station from one base transceiver station to another as the mobile station moves around with the area covered by the system can occur. In practice, locking the internal clocks of the base transceiver stations to the telephone system base 2.048 MHz data link does not allow the required accuracy of synchronisation between base transceiver stations to be achieved.

Each base transceiver station in the system is equipped with a means for measuring the time taken for signals to propagate between it and its respective base switching centre. It has been proposed that as the total delay is known, half of this would represent the time taken for a signal to propagate in one direction and this could be used to send a frame reset pulse to the base transceiver stations linked to the base switching centre.

However, again this is not satisfactory. Firstly, the signal transmission times in each direction are not necessarily the same and, secondly, the relevant part of the GSM specification (GM03) allows the signal transmission time to vary by approximately plus or minus forty bits over a twenty four hour period. As eight bits of this variation, or wander, equals one frame bit, during a twenty four hour period any given base transceiver station can move five frame bits out of its original relationship with its neighbouring base transceiver stations.

Summat of the Invention The present invention provides an apparatus for facilitating the synchronisation of items of electronic equipment and to provide an improved method of synchronising the internal clocks and frequencies of a plurality of base transceiver stations included in a cellular radio communication system.

According to the invention in one aspect, there is provided an apparatus for producing a train of control pulses at regular intervals, comprising means for receiving a sequence of accurately timed reference signal pulses, means for receiving time data signals, means for combining the time data signals with the reference signals to produce a reference time zero, and means for producing the said train of control pulses at regular intervals, each of the said intervals being equal to that occupied by a predetermined integral number of the reference signal pulses.

The position locating system known as GPs makes use of a series of accurately timed location signals which are transmitted by an array of geostationary satellites, the location signals being peculiar to each satellite and indicative of its location. Preferably, the present invention is adapted to utilise the location signals transmitted by a GPS satellite.

According to the invention in a second aspect, there is provided a method of synchronising the actions of a plurality of dispersed items of electronic equipment, comprising the operations of receiving at each item of electronic equipment from a reference source a reference signal including a series of accurately timed pulses and time data signals, deriving a reference time zero from the time data signals and producing control pulses at regular intervals from the reference time zero which are an integral number of the said accurately timed pulses in the reference signal.

The dispersed items of electronic equipment may be radio transceiver stations forming part of a cellular radio communication system and the reference signals may be location signals transmitted from a GPS satellite.

Specifically, the radio transceiver stations may be base stations forming part of a digital cellular radio communication system and there is included the operations of receiving at each of the transceiver stations location signals from a geostationary satellite, extracting therefrom a train of accurately timed reference pulses and time data signals, synchronising an oscillator in the transceiver station with the reference pulses, deriving a reference time zero from the time data signals and producing a series of synchronisation pulses at intervals which are both an integral number of digital signal frame periods transmitted by the transceiver station and an integral number of the reference pulses from the reference time zero.

When the radio transceiver stations are base transceiver stations of a digital cellular radio communication system operating in accordance with GSM specifications in which a single signal frame takes 60/13 s a suitable repetition interval for the signal frame counter synchronisation pulses is every three seconds from the reference time zero.

Brief Description of the Drawings The invention will now be described, by way of example, with reference to the accompanying drawings in which; FIG. 1 is a block circuit diagram of a pulse generator embodying the invention, and FIG. 2 is a block circuit diagram of a system embodying the invention for controlling the action of a base transceiver station forming part of a digital cellular radio communication system.

Description of a Preferred Embodiment Referring to FIG. 1, a frame counter synchronisation pulse generator 11 for use in a digital cellular radio communication system consists of a central processing unit 12 to which a series of accurately timed regular pulses is applied together with time data signals. Both the train of pulses and the time data signals are derived from location signals transmitted by a GPS satellite, not shown, and received by a receiver and decoder 13. The train of pulses derived from the location signals also are applied to a synchronisation pulse gate 14. The central processing unit 12 is programmed with an arbitrarily chosen time zero from which all the base transceiver stations in the cellular radio communication system are deemed to have started to function and calculates from the satellite time data signals which of the pulses of the train of regular pulses is an integral number of pulse periods from the reference time zero and also corresponds to an integral number of signal frames of a base transceiver station (not shown) with which the frame counter synchronisation pulse generator 11 is associated. For a GSM based cellular radio communication system, a frame period is 4.62 msecs. Hence a suitable frame counter synchronising pulse interval is three seconds, and at this interval the central processing unit causes the gate 14 to pass one of the pulses of the regular train of pulses derived from the satellite location signal.

Referring to FIG. 2, which illustrates the application of the invention to the control of a base transceiver station 21 as referred to above, the one second pulse signals and time data signals from a GPS satellite 22 are received, decoded and applied to the frame synchronisation pulse generator II as described above. The output pulses from the frame synchronisation pulse generator 11 are applied to a frame counter 23 in the base transceiver station 21 and lock its action to the one second pulse signals derived from the location signals from the satellite 22. These pulses also are applied to an internal oscillator 24 in the base transceiver station 21 and lock it to the one second pulses derived from the location signals transmitted by the satellite 22. As is normal practice, the base transceiver station is linked to a base switching centre (not shown in the FIG. 2) via a telephone 2.048 MHz data link.

Claims

Claims:

1. An apparatus for producing a train of control pulses at regular intervals, comprising means for receiving a sequence of accurately timed reference signal pulses means for receiving time data signals, means for combining the time data signals with the reference signals to produce a reference time zero, and means for producing the said train of control pulses at regular intervals, each of the said intervals being equal to that occupied by a predetermined integral number of the reference signal pulses.

2. An apparatus according to claim 1 adapted to receive location signals from a geostationary satellite and derive the sequence of accurately timed reference signal pulses and time data signals therefrom.

3. An apparatus according to claim 1 or claim 2 for use in a base transceiver station forming part of a digital cellular radio communication system wherein the said train of control pulses has a repetition interval which is equal to an integral number of frame intervals of a frame counter included in the base transceiver station.

4. An apparatus according to claim 3 wherein each frame interval is 60/13 msecs long and the train of control pulses is adapted to synchronise the frame counter with the accurately timed reference pulses at intervals of three seconds from the reference time zero.

5. A method of synchronising the actions of a plurality of dispersed items of electronic equipment, comprising the operations of receiving at each item of electronic equipment from a reference source a reference signal including a series of accurately timed pulses and time data signals, deriving a reference time zero from the time data signals and producing control pulses at regular intervals from the reference time zero which are an integral number of the said accurately timed in the reference signal.

6. A method according to claim 5 wherein the dispersed items of electronic equipment are transceiver stations forming part of a digital cellular radio communication system and there is included the operations of receiving at each of the transceiver stations location signals from a geostationary satellite, extracting therefrom a train of accurately timed reference pulses and time data signals, synchronising an oscillator in the transceiver station with the reference pulses, deriving a reference time zero from the time data signals and producing a series of synchronization pulses at intervals which are both an integral number of digital signal from periods transmitted by the transceiver station and an integral number of the reference pulses from the reference time zero.

7. A method according to claim 6 wherein the synchronization pulses are applied to a signal frame counter to synchronize its action with the reference pulses.

8. A method according to claim 6 wherein each signal frame has a duration of 60/13 msec and the synchronization pulses are applied to the signal frame counter at intervals of 3 secs.

9. An apparatus for producing a train of control pulses substantially as herein before described and with reference to FIG. 1 of the accompanying drawings.

10. A method for synchronising the actions of a plurality of dispersed items of electronic equipment substantially as herein before described and with reference to FIG. 1 and FIG. 2 of the accompanying drawings.