GB2409950A

GB2409950A - Updating location data of a mobile device using previous location and velocity of the device

Info

Publication number: GB2409950A
Application number: GB0400261A
Authority: GB
Inventors: Richard Ormson
Original assignee: NEC Technologies UK Ltd
Current assignee: NEC Technologies UK Ltd
Priority date: 2004-01-07
Filing date: 2004-01-07
Publication date: 2005-07-13
Anticipated expiration: 2024-01-07
Also published as: GB2409950B; GB0400261D0

Abstract

A method and apparatus are provided for determining the location of a mobile communication device. The location is derived using a location deriving system. The velocity is then derived, preferably using a Doppler shift measured on signals included in the system in which the mobile device operates. A new location is then derived from the original location and the velocity signal. By reducing the amount of location readings taken, battery power is conserved.

Description

POWER SAVING MOBILE COMMUNICATION DEVICES

This invention relates to a method and apparatus for a power saving in a mobile communication device.

In modern mobile communication devices, such as mobile telephones and the like, location based services are becoming more and more important. In order to use location based services, a communication device must be able to determine its location in some way either internally or from external signals and be able to offer a user of the device services which are based on the last established location.

A number of different ways have been proposed for measuring the location of a device. The most popular of which are the Global Positioning System (GPS) which uses satellite signals to determine location, and Enhanced Offset Time Differential (EOTD). These techniques are very different but have the common factor that in order to perform a location measurement a significant amount of power is consumed.

so A number of location based services when running give directions to a user to find a particular location and track their route to that location thereby ensuring that the directions are properly followed. In order to do this, the device's location has to be measured on a frequent basis. If the measurement consumes a significant amount of power then in a battery operated device, the battery life will be shortened.

In our earlier British patent application no. GB-A-2388749 a method and apparatus are described for so establishing the velocity of a handset using measurements that the handset performs as part of a neighbouring cell monitoring procedure. In this earlier application the velocity of movement of a mobile communications device was determined by measuring the frequency difference between a reference clock signal on the mobile device and the frequency corresponding signals received from a plurality of base stations in a cellular communications network.

The frequency difference arises due to Doppler shift due to movement of mobile radio communications device and thus this can be used to derive the velocity of a moving mobile communication device.

lo A number of other techniques are known for measuring handset velocity and these will be familiar to those skilled in the art.

The technique described in GB-A-2388749 is a differential Doppler technique to give the velocity of the handset.

This differential Doppler technique uses measurements that are performed as part of the handsets obligations under transmission standards. These measurements are regularly scheduled as laid down by the appropriate standards.

Thus, new measurements of velocity of the handset can be so derived without having to perform any operations besides those already required for normal operation.

We have appreciated that these velocity signals which can be derived from signals received as part of the operational standards and are part of the requirement for handsets can be used in applications where location based tracking services are provided.

A preferred embodiment of the invention will now be described in detail by reference to the accompanying drawing in which: so Figure 1 shows a flow diagram showing how an embodiment of the invention operates.

At 2, the location of the communication device or handset is returned using a known technique such as GPS or EOTD.

This gives a current location for the handset.

From this handset location, a handset velocity can be derived using the differential Doppler technique of GB-A-2388749 at 4. The system then waits for a predetermined time x at 6 before a new handset location is determined at 8 from the old location in combination with a velocity multiplied by the time x to give the change in location. The sum of these two gives the new location.

The current location is then set to the new location at 10 and can be used at 12 in a tracking application or any other application requiring the location of the device.

The current location is then referred back to a decision box 14 which determines whether or not it is time to make a new location fix. If it is, the process returns to step 2 where a current location is determined again. If it is not time to perform a new (location measurement) a new handset velocity is obtained at 4 and the process repeated, through to block 10 again.

In the process of deriving a new handset location from the measured current location and a location difference based on velocity and time gives a predicted position for the handset. There may be errors in this. However, provided the time between new absolute location determinations is not excessive, errors should be small and will be corrected when a new current location is determined. The length of time between direct location measurements as checked at 14 will be a trade off between ensuring a So reasonable accuracy for the predicted position and a reasonable saving in battery power by reducing the number of times that the handset location is determined. r - 4 -

The differential Doppler technique as discussed above uses measurements that are performed as part of a handsets obligations under a number of different transmission standards. The time delay x is introduced to allow time s for a new set of measurements to be gathered. The measurements required by the standards are cyclic in nature and hence there is a finite time between updates.

There is little point in calculating a new velocity and new location if the measurement data has not been updated, lo so period x is set to be at least the measurement interval. As the calculations require a certain amount of processor time, they incur a certain power consumption.

As usual, we wish to minimise power consumption, so we do not continuously update. It may be desirable to set x to a longer interval than the measurement period in certain implementations, but generally the savings are minimal beyond this point.

It appears that the time between direct measurements of the handset location are a function of the accuracy and magnitude of velocity measurement and also the accuracy required by the application in use at box 12. The less accuracy required, the longer the interval can be. The better the accuracy required by the application, the shorter the interval can be. The exact relationship preferably needs to be established individually for each cellular technology and wave band, and for each application.

It can therefore be seen that the applicants have appreciated that use of the differential Doppler technique so which operates on existing parts of received transmission standards enables the frequency with which actual location of a mobile communication device has to be determined to be reduced. Thus, the power consumption in a mobile device is reduced. - 5 -

Claims

Claims 1. A method for determining the location of a mobile communication

device comprising the steps of: determining the location using a location deriving system; determining the velocity of the device; deriving a new location from the original location and the velocity; wherein the step of deriving the velocity of the lo device is performed using signals available in the communication system in which the device is operating.
2. A method according to claim 1 in which the device operates in a cellular system having a plurality of base stations and the velocity of the device is derived from a Doppler shift in signals received from base stations due to movement of the device.
3. A method according to claim 2 in which the Doppler shift is derived from a comparison of frequencies of signals received from base stations and the frequency of a reference clock provided on the device.
4. A method according to claims 1, 2 and 3 in which the location is repeatedly derived using the location deriving system after a predetermined period of time.
5. A method according to any preceding claim including the step of providing location data repeatedly to a tracking application which requires regularly updated location data.
6. Apparatus for determining the location of a mobile communication device comprising: so a location deriving means; means for determining the velocity of the device; means for deriving a new location from the original location and the velocity; wherein the means for determining the velocity uses signals available in the communication system in which the device is operating to derive the velocity.
7. Apparatus according to claim 6 in which the device operates in a cellular system having a plurality of base stations and the means for deriving the velocity measures a Doppler shift in signals received from base stations due lo to movement of the device.
8. Apparatus according to claim 7 in which the Doppler shift is derived from a comparison of frequencies of signals received from base stations and the frequency of the reference clock provided on the device.
9. Apparatus according to claim 6, 7 or 8 in which the location deriving system repeatedly derives the location after a predetermined period of time.
10. Apparatus according to any of claims 6 to 9 including means to repeatedly provide location data to a tracking so application which requires regularly updated location data.
11. Determining the location of a mobile communication device substantially as herein described.
12. Apparatus for determining the location of a mobile communication device substantially as herein described.