GB2388749A

GB2388749A - Method and system for determining velocity of a mobile radiotelecommunications device including determining frequency difference due to doppler shift

Info

Publication number: GB2388749A
Application number: GB0211428A
Authority: GB
Inventors: Richard Ormson
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2002-05-17
Filing date: 2002-05-17
Publication date: 2003-11-19
Anticipated expiration: 2022-05-17
Also published as: GB2388749B; GB0211428D0

Abstract

The invention provides for a method, and related system (10), of determining the velocity of movement of a mobile radio communications device (12) arranged for receiving signals from a plurality of base-stations (14, 16, 18), including the step of determining the frequency difference between a reference clock signal of the mobile radio communications device and the said signals received from the said plurality of base-stations (14, 16, 18), which said frequency difference arises due to doppler shift due to the movement of the mobile radio communications device relative to the base-stations (14, 16, 18). The invention also relates to a method of controlling the frequency of repeated operational functions within a mobile radio communications device, wherein the said frequency is controlled responsive to measurement of the velocity of movement of the device.

Description

238874 9

METHOD AND SYSTEM FOR DETEMINING

MOVEMENT CHARACTERISTICS OF A MOBILE RADIO

TELECOMMUNICATIONS DEVICE

5 The present invention relates to a method, and related system, for À determining movement characteristics of a mobile radio telecommunications device. Also, the present invention relates to a method, and related system, for 10 controlling the frequency of repeated operational functions within a mobile radio communications device.

With the increasing popularity use of mobile radio telecommunication devices, such as cellular telephones, additional requirements have arisen with 15 regard to special aspects of the use of such devices.

In particular, it has become increasingly important to identify the location at which such a mobile device is located when in use and this can prove particularly important, for example, in emergency situations. There is a 20 variety of known arrangements for determining the device location. The two most common are the GPS system which employs signals from a constellation of satellites, and the EOTD system which uses signals from the mobile network itself.

25 Yet further, it can prove advantageous to identify characteristics of the L actual movement of the mobile device.

One manner of determining the velocity of a moving mobile device would be to take two separate locational measurements of the moving device, 30 determine the distance between the two locations and the time period between the measurements. However, such an arrangement is far from ideal since it is not until the second measurement is taken that an indication of the velocity

can be obtained. Thus, any such measurement is, by its very nature, a measurement of the previous velocity of the handset, which, for operational purposes, might no longer be accurate and relevant.

5 It would therefore prove advantageous to provide a method and system for determining characteristics of movement of a mobile telecommunications device in a more instantaneous manner.

According to one aspect of the present invention there is provided a 10 method of determining the speed of movement of a mobile radio communications device arranged for receiving signals from a plurality of base stations, including the step of determining the frequency difference between a reference clock signal of the device and the said signals received from the base-stations, which said frequency difference arises due to doppler shift in 15 the received signals.

in determining the speed of movement of the mobile device in this ' manner, it is possible to obtain a relatively instantaneous indication of the I speed of movement and, from this, if required, the velocity of movement of the 20 mobile device in real time.

Operational requirements and characteristics of the device, and the communication system in general, can vary dependent upon, for example, the velocity at which the mobile device is moving as now appreciated in 25 accordance with an aspect of the present invention. i As should be appreciated, in cellular communication systems, a number of operations within the cellular phone are generally performed on a periodic: basis and the frequency with which such operations are repeated is generally 30 fixed. This can prove to be inefficient and in particular represents a potential waste of power insofar as at least some such repeated operations are in fact only necessary or useful in certain circumstances. Such circumstances

( typically relate to spatial characteristics of the cellular phone and, in particular, characteristics of movement thereof. An example of such an operation comprises neighbour cell measurements in which the information derived in accordance with the repeated operation is only useful in the event of a 5 handover to a neighbouring cell or for reselection. Another such operation includes locational measurements where the operation need only be repeated if the location of the cellular phone has changed since the previous locational reading. 10 Through the accurate measurement of the speed of movement of the mobile device, the present invention can provide a useful reference against which the frequency of such repeated operation can be controlled and varied so as, for example, to improve efficiency of operation and introduce power savings. It is also noted that data concerning the speed and direction of movement of a mobile communications device can prove useful in applications relating to location-based services such as the provision of real time directions etc. The present invention again provides for a relatively simple, and accurate, 20 real time measurement of the speed and/or velocity for use in the provision of such services.

The present invention is also particularly advantageous in that it can be implemented by means of currently existing mobile radio communications 25 device hardware and network maps. In particular, the frequency difference determined in accordance with the present invention comprises, in many instances, one of the parameters determined by a Digital Signal Processor commonly employed within a cellular phone for decoding procedures. In this manner no additional processing is required in order to identify the frequency 30 difference required by one aspect of the method of the present invention.

( In a particular embodiment, the reference clock signal of the handset is locked to a signal from a base-station, which can comprise a base- station of a serving cell of a cellular system.

5 Further, the said plurality of base-stations can include a plurality of neighbouring cells in addition to the serving cell.

The said frequency difference can be determined by means of a Digital Signal Processor of the said device.

Preferably, the invention provides for a method of determining the velocity of movement of a handset and which includes the step of determining the differential Doppler shift in a manner as defined above.

15 In particular, the invention involves the step of solving simultaneous equations including values of relative speed of the handset in predetermined directions. The said predetermined directions can comprise orthogonal directions. 20 Known mobile radio communications devices can be arranged to provide repeated operational functions but the manner in which the frequency of the said repeated functions is controlled is disadvantageously limited.

Advantageously, the invention can provide for a method of controlling 25 the operation of a mobile radio communications device, including the step of varying the frequency of repeated operational functions within the device in response to a determination of a characteristic of movement of the device in a manner as defined above.

30 According to another aspect of the present invention there is provided a method of controlling the operation of a mobile radio communications device which includes repeated operational functions, including the step of

determining the velocity of movement of the device and varying the frequency of the said repeated functions responsive to the said measured velocity.

This aspect is particularly advantageous in that the said frequency can 5 be controlled and varied irrespective of the direction of movement of the device relative to the base-station and, if required, taking the actual direction of movement into account. Other systems, for example monitoring changes in the received signal strengths, only allow motion towards or away from the serving base-station to be calculated. In the case of certain 10 operations, such as location measurements, this information is insufficient to allow the measurement frequency to be safely altered.

The method therefore allows for a more detailed and accurate measurement of the movement characteristics of the device so that the said 15 frequency of operation can be controlled and varied in a manner which is accurately responsive to the state of motion of the device relative to, for example, a base station and neighbouring stations.

Preferably this further aspect of the present invention is arranged to 20 determine the velocity of movement of the device in a manner as outlined above. Of course, the invention also provides for a mobile radio communications device arranged to provide repeated operational functions 25 and having means for varying the frequency of the said repeated operational functions responsive to a measurement of the velocity of movement of the said device. According to yet another aspect of the present invention there is 30 provided a mobile radio communications system including means for determining the speed of movement of a mobile radio communications device thereof, the system comprising a plurality of base-stations with which the said

device is arranged to communicate, and including means for determining the frequency difference between a reference clock signal of the device and the said signals received from the said plurality of base-stations; which said frequency difference arises from a doppler shift in the received signals.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: Fig 1 is a schematic plan view of a cellular communications system 10 within which a cellular phone handset is located and moving; and Fig. 2 is a block diagram of a mobile radio communications device embodying the present invention.

Fig. 1 illustrates a cellular communications system 10 for allowing 15 communication via a mobile cellular handset 12 and, as illustrated, the handset 12 is located in the vicinity of three base-stations 14, 16 and 18, each associated with a respective one of three adjacent cells (not shown) of the cellular communications system 10.

20 As illustrated in the drawing, the base-station 14 is taken to be the base-station of the serving cell for the handset 12 and so the basestations 16, 18 comprise base-stations of neighbouring cells. Although the base-station 14 is in communication with the handset 12 for the transmission and receipt of communication signals, the handset 12 nevertheless is arranged also to 25 receive signals and data from the neighbouring cell base-stations 16, 18 such as neighbour cell measurements for use in a subsequent handover to one of those neighbouring cells.

When in communication with the base-station 14 of the serving cell, the 30 local clock signal generated at the handset 12 has its frequency locked to a frequency derived from a signal received from the base- station 14 of the serving cell by way of the air interface between the base-station 14 and

handset 12. When the handset 12 is in motion the signals actually received at the handset 12 from the base-station 14 experience a doppler shift. The signals are shifted by an amount proportional to the handset's radial motion towards, or away from, the base-station 14. Since, as mentioned above, the 5 local reference clock of the handset 12 is locked to the actual signal as received from, rather than as originally transmitted by, the base-station 14, the local clock signal in the handset 12 inherits this offset such that the clock signal of the handset 12 contains an element of doppler shift error when compared with the actual network clock frequency of the signal as transmitted 10 from the base-station 14.

As mentioned, during operation, the handset 12 is also required to decode signals from the base-stations 16, 18 of the neighbouring cells. Since these base-stations 16, 18 of the neighbouring cells are at mutually different 15 locations, and at locations different from that of the basestation 14 of the serving cell, the signals received from the basestations 16, 18 at the handset 12 will likewise exhibit a doppler shift. However this shift is different from that experienced in relation to the signals received from serving cell and as inherited in the reference clock signal generated in the handset 12. Thus, 20 since the local clock at the handset 12 is already locked to the Doppler shifted signal received from the base-station 14, a further element of frequency error will be experienced when decoding the signals from the base-stations 16, 18 of the neighbouring cells and this error represents the difference between the serving cell and neighbouring cell doppler shifts.

In accordance with the present invention, it is a requirement that this observed frequency difference between the doppler shifted serving-cell signal and the doppler shifted neighbouring-cell signals be identified and subsequently used in determining the speed and velocity of movement of the 30 handset 12. Advantageously, this frequency difference value generally comprises one of the parameters commonly determined by a handset's Digital Signal Processor as part of the handset's standard decoding procedure. In

this case, there will be no need for an additional processing overhead in the handset 12 in adopting an arrangement according to the present invention.

However, in order to extract useful information from the measured 5 offsets signalling to or from the network is required. In the former case the signalling carries the observed frequency difference to the network and the calculation is performed in the network, in the latter the signalling carries additional information to the handset and the handset performs the calculation.

Thus there will be an additional signalling requirement but it is considered that 10 such an additional requirement has little, if any, detrimental affect in the overall operation of the handset 12. In the case where the handset performs the velocity calculation there will also be a small additional processing; requirement. Again, it is not expected that this would have any detrimental affect in the overall operation of the handset 12.

Once having determined the speed of movement of the handset 12 on the basis of the above-mentioned differential doppler offsets, the velocity of the handset 12 can be calculated once the base-station and handset locations are determined. The base-station locations are in any case known and the 20 handset location can be identified by any one of the currently known locating systems, such as GPS or EOTD.

Having identified the location of the handset 12, and from the predetermined knowledge of the locations of the base-stations 14, 16, 18, 25 calculations can readily be performed to identify the bearings from the various base-stations 14, 16, 18, to the handset 12.

In the example as illustrated, the handset 12 is located in accordance with a north-east grid system 20 and the bearings of the handset from each of 30 the base-stations 14, 16 and 18 relative to a true north direction are indicated by angles X, Y. Z. I

( As will be appreciated below, the velocity of the handset 12, as indicated by arrow 22, has components in each of the directions of the three base-stations 14, 16, 18 as indicated by arrows 24, 26, 28.

5 For the cell associated with the base-station 14 and which comprises the serving cell, the speed, i.e. magnitude of the velocity, corresponding to i each of the reported differential doppler measurements corresponds to: IV,6llV,41 and IV,8llV,4 where V,4 iS the component of the velocity of handset 12 in the direction of base-station 14, V,6 is the component of the velocity of the handset 12 in the direction of base- station 16 and V'8 is the component of the velocity of the handset in the direction of the base-station 18.

15! From reference to Fig. 1, and in particular the coordinate angles X, Y and Z. it will be appreciated that, through the use of trigonometric expressions and the resolving of the velocity 22 of the handset 12 into relative values in a northerly and an easterly direction that: I V(north) l = IV,41 sin X = IV,61 sin Y = IVY sin Z 1 V(east) 1 IVY cos X - |V'6| cos Y = |Vl8l cos Z From these expressions, it will be appreciated that it is possible to derive the 25 following four simultaneous equations: v, 6lilv,41 = IV(north)lsin Y i IV(north)lsin X lv,8lilv,41 = IV(north)lsin Z IV(north)lsin X 30 and |V,6|i|V,4|=|V(east)|cos Y i|V(east)|cos X

|V,8|i|V14|=|V(east)|cos Y |V(east)tcos X As will be appreciated, these four simultaneous equations present four unknown values, i.e. V(north), V(east) and the two + or - sign options and so 5 can be solved by conventional methods; the values of the speed such as IV,6lilV,I and IV1BIilV141 having been determined, as noted above, from the doppler offset frequency differences.

The solution to the four above-mentioned differential equations provides 10 values for the speed of the handset resolved into north, and east, directions i.e. the values IV(nodh)l and IV(east)l. Having determined these two relative speed values, the correct direction in which these values apply is determined by considering both the sign of the IV,6llV,41 and IV,sItlV,41 values previously measured and also the sign of the + orvariables determined during the 15 solution of the above-mentioned simultaneous equations. This gives velocities in the north and east axes. Combining these velocities in the usual vector manner give the handset velocity 22.

From the above-mentioned processing, it will be appreciated that the 20 present invention is particularly advantageous since, in identifying differential doppler data with regard to two neighbouring cells, sufficient information is obtained to ascertain the actual velocity of the handset 12 almost instantaneously at any required moment in time.

25 Confirmation of the values of any of the variables determined in accordance with the above calculations can be achieved through employing signals from the base-stations of yet further neighbouring cells.

Likewise, it should be appreciated that the above-mentioned processing 30 and calculations and determination of the velocity of the handset could actually be performed in the handset itself if the processing overhead is not considered

( restrictively disadvantageous and assuming the network will allow for the broadcasting of locational information to the handset.

Turning now to Fig. 2, there is illustrated a mobile radio communications 5 device 12 arranged to operate according to an aspect of the present invention in which the frequency of repeated operational functions is to be varied responsive to measurement of the velocity of movement of the device.

The device comprises a handset 12 having an antennae 30 by means of which 10 signals are transmitted from, and received by, the handset 12 via a transceiver arrangement comprising a transmitter 32 and receiver 34 which arrangement 32, 34 is, in turn, connected to a modem 35. A central controller unit 38 of the handset 12 feeds un-modulated signals to, and receives demodulated signals from, the modem unit 36.

Also illustrated for completeness are the handset's speaker 40, microphone 42 and keypad 44 all of which are connected to the central controller 38.

20 In addition to controlling the actual communication between the handset and a base station (not shown in Fig. 2), the controller unit 38 is also responsive for controlling network-related operations, such as neighbour cell measurements and location measurements, and which operations are repeated on a periodic basis.

The frequency with which such periodic operations are repeated can have a marked effect on power requirement of the handset and thus on battery lifetime, overall efficiency and the size of the handset.

30 Also shown in schematic form within Fig. 2 is the handset's Digital Signal Processor (DSP) 46 which, as part of its usual decode procedure, is arranged to determine the difference in frequency, the doppler shift, between

( the local handset clock as locked to the serving cell, and signals received from neighbouring cells.

The controller 38 is, according to an aspect of the present invention, 5 arranged to control the frequency of the aforementioned repeated operations in response to the velocity of movement of the handset 12 as such data, i.e. having elements of speed and direction, can be usefully employed in accurately determining whether or not one or more of the periodic operations actually needs repeating at all or whether, for example, its frequency of 10 repetition should be increased or reduced. This can serve to improve the efficiency with which power from the handset's battery is employed.

This aspect of the present invention can advantageously make use of the Doppler frequency shift signals determined in the DSP 46 to determine the 15 handset velocity as noted in relation to Fig. 1. The velocity value can be determined onboard the handset 12, or remotely within the network, but the key feature is that a control element is provided within the handset for controlling the frequency of repetition of the periodic operations responsive to a determined value of handset velocity.

Claims

! Claims

1. A method of determining the velocity of movement of a mobile radio communications device arranged for receiving signals from a : 5 plurality of base-stations, including the step of determining the frequency difference between a reference clock signal of the device; and the said signals received from the said plurality of base-stations, which said frequency difference arises due to Doppler shift due in the received signals.

2. A method as claimed in Claim 1, wherein the said reference clock signal is locked to a signal from a base-station.

3. A method as claimed in Claim 2, wherein the reference clock signal 15 is locked to a signal from a serving cell of a cellular system.

4. A method as claimed in Claim 3, wherein the said plurality of base stations includes a plurality of neighbouring cells in addition to the serving cell.

5. A method as claimed in any one or more of Claims 14, wherein the said plurality of base-stations comprises at least two base-stations.

6 A method as claimed in any one of Claims 1-5, wherein the said 25 frequency difference is determined by means of a Digital Signal Processor of the said device.

7. A method as claimed in Claim 6, wherein the said Digital Signal Processor comprises a Digital Signal Processor arranged for 30 decoding processing within the handset.

8. A method as claimed in any one of Claims 1-7, wherein the value of frequency difference determined is transmitted from the handset for subsequent determination of the said velocity of movement remote from the device.

9. A method as claimed in any one or more of Claims 1-7, wherein the said frequency difference measured is retained for determination of the said velocity of movement at the said device.

10 10. A method as claimed in any one or more of Claims 1 to 9, and including the further steps of determining the locations of the said basestations and the location of the device.

A method as claimed in Claim 10 and including the step of solving 15 simultaneous equations including values of relative speed of the handset in predetermined directions.

12. A method as claimed in Claim 11, wherein the said predetermined directions comprise orthogonal directions.

13. A method of controlling the operation of a mobile radio communications device, including the step of varying the frequency of repeated operational functions within the device in response to a determination of a characteristic of movement of the device as 25 claimed in any one or more of Claims 1-12.

14. A mobile radio communications system including means for determining the velocity of movement of a mobile radio communications device thereof, that system comprising a plurality of 30 base-stations with which the said device is arranged to communicate, and including means for determining the frequency difference between a reference clock signal of the device and the

! said signals received from the said plurality of base-stations, which said frequency difference arises from a doppler shift in the received signals. 5

15 A system as claimed in Claim 14 and arranged with means for operation in accordance with the method as claimed in any one or more of Claims 2-13.

16. A method of controlling the operation of a mobile radio 10 communications device which includes repeated operational functions, including the step of determining the velocity of movement of the said device and varying the frequency of the said repeated functions responsive to the said measured velocity.

15

17. A method as claimed in Claim 16, and including a step of determining the velocity of movement of the device in accordance with the method of Claim 10.

18. A mobile radio communications device arranged to provide repeated 20 operational functions and including means for varying the frequency of the said repeated operational functions responsive to the velocity of movement of the said device.

19. A method of determining the speed of movement of a mobile radio 25 communications device, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.

20. A mobile radio communications system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying 30 drawings.