GB2387509A

GB2387509A - Mobile communications device and synchronisation method for multi-system access

Info

Publication number: GB2387509A
Application number: GB0208494A
Authority: GB
Inventors: Tony Banks; Richard Ormson; Nik Bowdler
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2002-04-12
Filing date: 2002-04-12
Publication date: 2003-10-15
Anticipated expiration: 2022-04-12
Also published as: GB2387509B; GB0208494D0

Abstract

The present invention provides for a mobile radio communications device, and related method, in which a first crystal oscillator is arranged for providing a first master clock frequency for a time base of a first communications system and a second crystal oscillator is arranged for providing a second master clock frequency for a time base of a second communications system. The time bases are calibrated by counting signals from each oscillator within a certain time period, and determining a ratio of the master clock frequencies based on the ratio of the signal counts. The first and second communications systems may be UMTS and GSM systems.

Description

MOBILE RADIO COMMUNICATIONS DEVICE

AND METHOD OF OPERATION

The present invention relates to a mobile communications 5 device, and related method of operation and, in particular, to a mobile phone and related method of operation.

Mobile phones comprise a master clock circuit for generating a relatively high frequency clock signal which forms part of the 10 timebase circuitry within the mobile phone. The timebase generated within the mobile phone is intended to be synchronized with a timebase of a base station with which the mobile phone communicates in accordance with a particular communication system such as, for example, the Global System 15 for Mobile Communication (GSM). Such synchronization is usually achieved by use of an automatic frequency control (AFC) mechanism which operates by comparing the frequency of certain signals received from the base station with the frequency of the local clock and then adjusting the local 20 clock to remove the observed frequency difference.

A plurality of mobile communication systems available have been developed which require different master clocks and timebases for their operation.

A mobile phone offering access to two or more such systems would therefore be advantageous since the same mobile phone handset could then be used with a selected one of the different communication systems supported. This choice of 30 system for the same mobile phone would therefore lead to a greater geographical coverage for one and the same mobile phone since different communication systems commonly exhibit different geographical boundaries. This geographical limit commonly occurs at international boundaries and also occurs as 35 a consequence of the time taken to achieve full coverage of a new network technology. Such a dual mode mobile phone would therefore be particularly attractive to users who travel overseas and also to the early users of new technology

communications systems.

In order to achieve such interoperability between two respective communications systems, a mobile phone will require 5 at least two master clock circuits serving to track the timebases and air interfaces of the respective communication systems. In order to be practically viable, such dual-mode interoperability should allow for ready switching from one communication system to the other and, in particular, allow 10 for the calibrating of the at least two master clock frequencies with respect to each other so as to allow for an accurate and quick transition between the two communication systems. 15 The present invention seeks to provide for a mobile radio communications device, and related method, which allow for interoperability between two communication systems requiring different timebases in a simple, reliable and cost effective manner. According to one aspect of the present invention, there is provided a mobile radio communications device having a first crystal oscillator for providing a first master clock frequency for a timebase of a first communication system, a 25 second crystal oscillator for providing a second master clock frequency for a timebase for a second communication system, calibrating means for calibrating the timebases of the two said systems and comprising a first counting means arranged to be clocked by the first master clock frequency, a second 30 counting means arranged to be clocked by the second master clock frequency, means for determining the count of each of the first and second counting means for a simultaneous calibration time period, and means arranged to determine the ratio of the first master clock frequency to the second master 35 clock frequency on the basis of the ratio of the said counts by the first and second counting means.

The present invention is advantageous in that it can be

- achieved by means of a circuit architecture consistent with that used in current single mode mobile phones.

As will be appreciated, the present invention therefore 5 advantageously employs at least two separate crystal oscillators for providing the respective master clock signals which are employed in generating the at least two timebases for the at least two respective communication systems.

( Advantageously, protocol stack and hardware can be adapted unchanged from single mode mobile devices. Appropriate control of the respective crystals can thus be achieved without requiring any specific multiplexing arrangements.

Also the power consumption can be limited through the 15 temporary shutting-down of elements such as the oscillator, the digital/analogue conversion circuitry and the Application Specific Integrate Circuits (ASICS) which are not required when the handset is communicating by the other of, for example, two communication systems.

The invention as defined above is particularly advantageous in that it can serve to address the potential problem of drift between the timebases and thereby allow for accurate synchronization and interoperability between the two 2s communication systems.

Yet further, the present invention can allow for the calibration of one master clock against the other even in situations where both clock signals might be subject to 30 problems such as independent frequency control, potential drift and thermal fluctuation.

In one particular embodiment, one communication system comprises the Global System for Mobile Communication (GSM), 35 and the other communication system comprises the Universal Mobile Telecommunication System (UMTS). In this manner, the said first counting means is clocked by the GSM system clock and the second counting

Radio Access (UTRA) system clock.

Advantageously, the respective counting means are arranged to be started simultaneously and, in particular, by a software 5 command. The counting means is then arranged to run for a pre-specified calibration time period, which calibration period is defined in terms of the number of counts of one or other of the counters or by the number of clock cycles of the controlling CPU.

The two counting means can therefore be arranged to be controlled to be stopped simultaneously and, the respective count results can then be read by the Central Processor Unit (CPU) of the mobile phone.

As will be appreciated, the ratio of the UTRA clock frequency to the GSM clock frequency will be equal to the ratio of the count result of the first counting means to the count result of the said second counting means.

The ready determination of this ratio, and comparison of this ratio to the fixed ratio which would be seen if both clocks were totally accurate, allows for ease of compensation of any drift between the timebases of the respective systems such 2s that the operation of the phone in accordance with the two systems can be quickly and accurately synchronized. For example if the observed ratio is found to differ from the ideal ratio by + lppm, then the timebase corresponding to the second clock would need to be retarded by 1 period every 1 30 million periods. Taking the specific example of the GSM timebase, this would mean a retardation of 1 bit count every 3.69 seconds. Either the first or second timebase can be adjusted in this manner. The correct timebase to amend is the one for the radio access system that is not currently in a 35 logical connection to a cellular network.

The counting means employed depend UpOD the accuracy required.

For example, for a O.lppm accuracy, 20 million counts would be

l s required and this would require two 25 bit counters. However, it is envisaged that it would only be necessary to achieve an accuracy within the timebase to l bit. Thus in accordance with the GSM system this would equate to 48 counts of the s l3MHz clock. On this basis, for a gap of 2 seconds between GSM operations, it would be desirable to achieve accuracy to 48 counts in 26 million which is approximately 2ppm and so a somewhat smaller counter than that noted above would therefore be required.

According to another aspect of the present invention there is provided a method of controlling a timebase within a mobile radio communications device comprising the steps of providing a first master clock signal of a first frequency for a 15 timebase of a first communication system, providing a second master clock signal of a second frequency for a timebase of a second communication system, simultaneously counting the respective clock signals for a predetermined time period, and determining the ratio of the first clock frequency to the 20 second clock frequency on the basis of the ratio of the respective counts so as to allow for compensation of drift between the two timebases and so allow for synchronization therebetween. 2s The invention is described further hereinafter, by way of example only, with reference to the accompanying drawing which comprises a schematic block diagram illustrating one embodiment of the present invention.

In the drawing there is illustrated the basic circuit architecture lo within a mobile phone handset and which is arranged according to an embodiment of the present invention.

3s As will be appreciated, the handset comprises a dual-mode handset having circuitry 12 for use when the handset is to communication by way of, for example, UMTS, and duplicated circuitry 14 arranged for u

communicate by way of the GSM telecommunications system.

The handset comprises a common Central Processing Unit (CPU) 16 arranged for controlling both the UMTS circuitry 12 and the 5 GSM circuitry 14 and the counter circuits discussed further below. The UMTS circuitry comprises a Digital Signal Processor (DSP) 18 connected to an automatic frequency control and 10 digital/analog convertor element 12 which is in turn connected to an oscillator 22 arranged to provide the UTRA system master clock for forming the timebase of the mobile phone when synchronization is required with the corresponding timebase within a basestation of the UMTS system. An output from the lS oscillator 22 is feed into a clock signal counting module 24 as will be described further below. The GSM circuitry likewise comprises a Digital Signal Processor (DSP) 26 feeding into an automatic frequency control and digital/analogue convertor 28 which is in turn connected to control the GSM 20 system oscillator 30. As with the UTRA system oscillator 22, the GSM system oscillator 30 delivers an output signal that is monitored by the counter module 24.

The counter module 24 contains a first counter 32, a second 2s counter 34 and a control register 36 for receiving control signals from the CPU 16 by way of common bus 38 and which serves to provide counter enable/disable signals for each of the counters 32, 34 so as to initiate, and then interrupt operation of the counters.

The first counter 32 is arranged to receive an output from the UTRA oscillator 22, whereas the second counter 34 is arranged to receive an output from the GSM oscillator 30.

35 Each of the respective counters 32, 34 therefore serves to count clock signals delivered from each of the respective oscillators 22, 30 associated with the respective UMTS and GSM timebases within the mobile phone.

As mentioned, the control register 36 is arranged, under control from the CPU 16 to provide a counter enable signal simultaneously so that each of the counters 32, 34 commences s its count of the respect clock signals from the clock signals provided by the respective oscillators 22, 30 simultaneously.

The CPU 16 control of this operation allows for the counters 32, 34 to run for a predetermined period wherein, at the lo completion of which period, the counters are arranged to be disabled simultaneously.

The count measured in each counter 32, 34 is then delivered by output lines 40, 42, and the common bus 38 to the CPU 16.

The CPU 16 is then arranged to read the two count values and, on the basis of the ratio therebetween, calculate the ratio of the UTRA clock frequency to the GSM clock frequency.

20 This ratio is then compared with the ideal ratio and an offset in ppm obtained. This offset is advantageously employed to compensate for any drift between the timebases of the UMTS and GSM systems so as to synchronize the respective UMTS and GSM operations and therefore allow for ease of interoperability 25 between the two systems.

Claims

1. A mobile radio communications device having a first crystal oscillator for providing a first master clock 5 frequency for a timebase of a first communication system, a second crystal oscillator for providing a second master clock frequency for a timebase for a second communication system, calibrating means for calibrating the timebases of the two said systems and comprising a first counting means arranged to lo be clocked by the first master clock frequency, a second counting means arranged to be clocked by the second master clock frequency, means for determining the count of each of the first and second counting means for a simultaneous calibration time period, and means arranged to determine the 15 ratio of the first master clock frequency to the second master clock frequency on the basis of the ratio of the said counts by the first and second counting means.

2. A device as claimed in Claim 1, wherein the first and

20 second counting means are arranged to be enabled and disabled simultaneously by a common control signal.

3. A device as claimed in Claim 2, wherein the common control signal comprises a software command.

2s

4. A device as claimed in any one of Claims 1, 2 or 3, having a processing unit also arranged to receive count results from the first and second counting means.

30

5. A device as claimed in Claim 4, wherein the processing unit is arranged to calculate the ratio of the said count re. It.c;

6. A method of controlling a timebase within a mobile radio 35 communications device comprising the steps of providing a first master clock signal of a first frequency for a timebase of a first communication system, providing a second master clock signal of a second frequency for a time-base of a second

communication system, simultaneously counting the respective clock signals for a predetermined time period, and determining the ratio of the first clock frequency to the second clock frequency on the basis of the ratio of the respective counts s so as to allow for compensation of drift between the two timebases and so allow for synchronization therebetween.

7. A method as claimed in Claim 6, and including the step of enabling and disabling the counting means simultaneously by 10 way of a software control signal.

8. A mobile radio communications device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.

N - Szo :,-= 11':510=

Application No: GB 0208494.5 Examiner: David McWhirter Claims searched: 17 Date of search: 26 November 2002 Patents Act 1977 Search Report under Section 17 Databases searched: UK Patent Office collections, including GB, EP, WO & US patent specifications, in:

UK C1 (Ed.T): H4L (LRAD, LRPMG, LRPTA, LRPTE, LRPTG, LRPTK, LRPMW LDSS, LEP)

Int C1 (Ed.7): H04B 7/212, 7/26, H04Q 7/32, 7/38 Other Online EPODOC, WPI, PAJ Documents considered to be relevant: Category Identity of document and relevant passage Relevant to clanns A WO 01/67788 A2 (QUALCOMM)

X Document indicating lack of novelty or inventive step A Document indicating technological background and/or state of the art.

Y Document indicating lack of inventive step if combined P Document published on or after the declared prioritydate but before the with one or more other documents of same category. filing date of this invention.

E Patent document published on or after, but with pnority date eaHier & Member of the same patent family than, the filing date of this application.

An Executive Agency of dle Department of Trade and Industry