WO2004043015A1

WO2004043015A1 - Proximity detector

Info

Publication number: WO2004043015A1
Application number: PCT/GB2003/004789
Authority: WO
Inventors: Michael Hugh Burchett; Jonathan Randall Garnsworthy; William Alan Jacks; Mario Del Mistro
Original assignee: Cambridge Consultants Limited
Priority date: 2002-11-05
Filing date: 2003-11-05
Publication date: 2004-05-21
Also published as: GB0225790D0; AU2003276472A1

Abstract

A wireless communication system comprises a base station (1) that can communicate with one or more mobile devices (2, 3, 4, 5) for example cellular telephones, computers etc. within the vicinity of the base station by radio. The base station attempts to connect to a mobile device within its vicinity at at least two predetermined signal power levels. The base station may then determine the proximity of each of the mobile devices based on the signal power level at which the connection attempt is successful. The system enables the proximity of mobile devices to be determined without modification of the devices and with reduced interference from other equipment in the vicinity.

Description

PROXIMITY DETECTOR

This invention relates to wireless communication systems, and especially, although not exclusively, to communication systems based on so-called "piconets", that is to say networks comprising two or more devices that are separated by relatively short distances.

One such network has recently been developed in order to enable personal mobile devices such as cellular telephones, and computers, e.g. laptop and notepad computers, to communicate with a base station by radio. Such a network has the advantage that devices may be connected to the base station and/or other devices, and may then function without the necessity to provide cabling between them.

Such distances may, for example be up to 100 metres, but will often be considerably shorter, for example up to 10 metres or even less, for example up to 3 metres or even less than 1 metre depending on the particular application. Thus, for example, it has been proposed to employ this form of system for communication between cellular telephones or computers and peripheral components simply by placing them next to one another.

A wireless communication system that may be employed for this purpose is a two-way communication system in which a device, for example the base station, will communicate with one or a number of other device at any one time, and which is secure so that other devices cannot listen to communications between the devices. One form of system that has received considerable attention is a wireless communication system in which data packets are transmitted between devices at low power, for example -30 dB to 20 dBm. The radio uses frequency hopping to spread the energy across the spectrum, for example employing 79hops in a pseudo random pattern, each displaced by l Hz between 2.402 GHz and 2.480GHz. This form of communication system is governed by the specification of the Bluetooth System, and is known under the trademark "Bluetooth". In this system, the base station will initially and periodically send an enquiry in order to determine what mobile devices are within the range of the base station, and make an initial connection to the devices in what is called "page" mode in which it sends a page instruction and waits for a response. The base station will then communicate with the devices, or a number of them depending on their responses, at a lower power level. During the initial enquiry which can take 1 to 2 seconds, the base station determines the Bluetooth ID. and clock offset of the mobile device, that is to say when the mobile device is in page scan mode. The base station will then note the clock of set of each mobile device within its vicinity in order to communicate with them.

Although this system will function satisfactorily to allow communication between the base station and the mobile devices, the system gives no information as to the proximity of the device(s) to the base station other than to ascertain whether or not the devices are within range of the base station.

One system that could determine the proximity of a device to the base station is that employing a received signal strength indicator (RSSI) in which the mobile devices determine their distance from the base station from the received signal power of the base station. This system, however, has the disadvantage that any other transmitters such as other mobile devices within the vicinity will give a false reading for the position of the mobile device. The RSSI system measures the power received after the signal and interferers have been mixed with one generated by a local oscillator, with the result that there is no selectivity between any other interferer or signal in the same bandwidth. One consequence of this is that if the mobile device is located behind a relatively powerful transmitter (not necessarily one employing the same transmission protocol) , it can be difficult to track the mobile device.

Another system that may be employed to provide an indication of the location of the mobile device employs a measurement of the phase difference between the signal as transmitted and as received. Such a system can be very accurate in resolving and tracking different devices, but will require modltlcations to both the hardware of the mobile devices and to the software employed in the devices, in particular to the operating system software.

Yet another system that may be employed is a "time of flight" system that uses the time delay between transmission of a signal by the base station and receipt of the returning signal from the mobile device in order to determine its distance from the base station. Such systems may also be very accurate in determining position, but are greatly influenced by the time taken for the signal to be processed by the mobile device between receipt and transmission of the reply. The processing time delay is significantly greater than the time taken for the signal to be transmitted between the base station and the mobile device, and the time latency within the device will vary from system to system. In addition there is no common clock in the system which introduces additional errors.

According to one aspect, the present invention provides a wireless communication system which comprises a base station that can communicate with one or more mobile devices within the vicinity of the base station by radio; wherein the base station is operative to attempt to connect to a mobile device within its vicinity at at least two predetermined signal power levels. The base station may then determine the proximity of the or at least one mobile device based on the signal level at which the connection attempt is successful.

The system according to the present invention has the advantage that it may be employed to determine the proximity of one or more mobile devices without the necessity to modify any of them, so that the position of standard or "off the shelf" devices may be determined. In addition, where a number of mobile devices are in the vicinity of the base station, the proximity of any device may be determined irrespective of the other devices, and irrespective of any other potentially interfering equipment.

The base station may attempt to connect to the mobile device at the lower or lowest predetermined signal power level and then increase the signal power level before attempting to connect to the device again, or it may attempt to connect to the mobile device at a relatively high signal power level and decrease the signal power level before attempting to connect to the mobile device again.

The base station may attempt to connect to the mobile device at a different signal power level by altering the power level of the transmit signal or by altering the power level of the received signal. For example, if the power level of the received signal is altered, an attenuator may be located in the signal receive path between the antenna and the signal decoding circuitry of the base station. The received signal power level as measured by the decoding circuitry will thus be subjected to attenuation during transmission to and from the mobile device as well as attenuation in the signal receive path of the base station. If the connection attempt is unsuccessful, the attenuation in the signal receive path can be reduced accordingly. Such a system may be employed in a number of areas, and especially where dedicated mobile devices are employed. However some commercial mobile or remote devices may employ automatic power adjusting in order to increase their battery life which may produce false proximity measurements. In such areas it is preferred for the transmit signal to be altered. This may be achieved in any of a number of ways, for example by locating a variable attenuator in the signal transmit path between the coding circuitry and the antenna. It is possible for an attenuator to be located in both the signal transmit and receive path of the base station.

It is possible according to the broadest aspect of the invention for the base station to transmit to the mobile devices at a number of different signal strengths in order to connect or attempt to connect to the devices, so that the base station can determine whether any device is in any of a number of different distance ranges therefrom by assessing the lowest signal strength at which a connection attempt is successful. However, for many applications, this is not necessary, and it is sufficient for the base station to know only whether a mobile device is "near" or "far" from the base station. In such a case, the base station may be arranged so that it can send data to, and receive data from, only the mobile device, or only those mobile devices, to which it could form a successful connection at the said lower predetermined signal power level. Thus, such a base station can distinguish between mobile devices that are "close", that is to say sufficiently close to enable communication at the predetermined signal power level, and those mobile devices that are "far" or "distant" but within the vicinity of the base station, that is to say, those mobile devices that are recognised on an initial enquiry by the base station. Other devices that do not respond to the enquiry are not within the vicinity of the base station.

In some systems, for example where standard mobile devices such as cellar telephones or computers are employed, the initial enquiry scan from the base station will attempt to connect to any mobile device. However, in other systems, for example systems that incorporate dedicated mobile devices, the base station may include a list of compatible mobile devices and their I.Ds so that the initial enquiry scan will attempt to connect only to those mobile devices recognised by the base statio .

It is possible for the physical geometry and signal strength of the base station to be such that only a single mobile device can communicate with the base station at the lowest signal power level. Such a system has the advantage that it can, for example, detect the mobile device that is at the head of a queue in order to allow transfer of data for example at a point of sale.

Although the term "base station" has been used in order to distinguish the station from mobile devices that may enter and leave the vicinity of the base station, this is not intended to imply that the base station is physically fixed in one position. It could, in certain circumstances move, for example it could be portable, so that it is the proximity of the movable devices with respect to the base station rather than with respect to any geographical position that is important. What is important is that the base station is a unit that locates or measures the proximity of a mobile device. In some systems such as the Bluetooth system the base station will initiate communication, for example on a master/slave basis.

The present invention is not restricted to those systems that only include a single base station. More than one base station may be employed to increase the system capacity by networking for example where a large number of mobile devices may be present, or to improve tracking of the mobile devices over large areas. One base station may handle the initial enquiries while another handles subsequent communications, or all base stations may handle enquiries and communications. In other systems both these arrangements may be employed.

Usually the base station will communicate with only a single mobile device at any one time, although it is possible for it to connect to a number of devices simultaneously if desired.

The system is described herein with reference to the Bluetooth protocol, but it will be appreciated that the system is applicable to a variety of alternative transmit/receive wireless protocols.

The system and method according to the invention may be implemented by means of software that is incorporated in, or capable of being loaded in, a programmable computer that is associated with radio transmitting and receiving equipment. Thus, according to another aspect, the invention provides a carrier which carries a computer program, comprising processor implementable instructions for generating, by means of a programmable computer and associated wireless transmitting and receiving equipment, a system according to the invention or to perform a method according to the invention.

One form of system according to the present invention will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of the location methodology of the system according to the invention;

Figure 2 is a schematic representation of the system indicating information held by the base station; and

Figure 3 is a block diagram showing a radio transceiver module of the base station of the system according to the invention. Referring to the accompanying drawings, Figures 1 and 2 show schematically a wireless communication system and location methodology for a piconet in which a single base station 1 can communicate with a number of mobile devices 2, 3, 4, 5. The mobile devices may be any form of electronic equipment, for example "off the shelf" equipment such as cellular telephones, portable computers, identity cards for secure entry systems, cards for allowing funds transfer or the like. Alternatively the devices may be dedicated devices based on proprietory designs. The' system operates on the "Bluetooth" protocol as described in the Bluetooth specification in which the base station 1 communicates with a number of mobile devices using a full duplex spread spectrum frequency hopping protocol at frequencies between 2.402 and 2.480 GHz. Initially the base station transmits an enquiry call 6 with a relatively high signal strength, which may be higher than the signal strengths used for subsequent connection attempts, in order to ascertain what compatible mobile devices are in the vicinity of the base station. This enquiry will take from 1 to 2 seconds for each mobile device 2-5 in the vicinity of the base station 1, during which time the base station will ascertain what its clock offset is. Information 8 regarding the clock offset and the information 9 regarding the identification of the mobile device is recorded by the base station 1 and will enable the base station to communicate with any mobile device at a subsequent time without going through the 1-2 second long enquiry call. Such calls will continue to be made periodically in order to determine which new mobile devices have entered the vicinity of the base station and which have left.

Once the base station has ascertained which mobile devices are in its vicinity, it attempts to connect to each device in turn (step 10 ) at a predetermined low signal strength. The particular signal strength will depend on the application of the system, and the number of mobile devices that may be connected to the base station at any one time etc. If the connection is successful (step 12) the base station determines that the particular mobile device 2 only requires a low (1) signal strength to form a connection and so is in a near zone in which it is relatively close to the base station. The information 11 regarding the signal strength is stored in memory. The base station 1 may then attempt to connect to other mobile devices in turn (steps 12, 14) until it has attempted connection to all the mobile devices in its vicinity and thus knows which mobile devices are in the near zone. The base station then attempts to connect to the mobile devices 3, 4 that it was unable to connect to at the first, low signal strength now employing a higher signal strength (H), in order to determine which mobile devices are within the vicinity of the base station but in a "far zone" that is relatively distant from the base station (step 16). If the base station is unable to connect to a mobile device at the second, higher, signal strength it determines that the mobile device is "out of range". At the end of this process, the base station has a listing in memory of all the mobile devices in its vicinity, and, together with other information on the mobile devices, has recorded their proximity in terms of the signal strength required to make a connection. The base station can then transfer data with that mobile device or those mobile devices that are within the near zone.

The particular order in which the base station conducts these operations may be varied depending on the circumstances. For example, it may not be necessary to attempt to connect to all the mobile devices at low signal strength before attempting to connect to them at the higher signal strength, especially if the design of the system is such that only one mobile device can be in the near zone of the base station at any one time. In such a case it may be appropriate to transfer data to whichever mobile device has been found to be in the near zone before attempting to connect to other mobile devices at a higher signal strength. Alternatively, the base station may attempt to connect to a mobile device within its vicinity at a low signal strength and then to increase the signal strength if the attempt fails, before moving to the next device.

Only a single base station 1 is shown in Figure 2, but a number of such stations may be connected in a network if desired.

Figure 3 shows schematically the design of the radio transceiver module of the base station employed in the invention. The radio transceiver module includes a module interface 20 connected to a standard Bluetooth chip which itself is connected to a flash EEPROM 24. The chip 22 is connected to the transmit/receive switch which itself is connected to a bandpass filter 28 and antenna 30.

The radio transceiver module is modified according to the invention by inclusion of a variable attenuator 32 to allow attenuation of the transmitted signal. Only the transmit path is attenuated. As the receive path is not attenuated, the receiver sensitivity is not degraded and the proximity detector's operation is not affected by the power control algorithm in the detected "Bluetooth" equipment. The base station's power control algorithm is disabled, and the attenuator 32 setting is controlled by using three of the general purpose input/output (GPIO) lines 34 from the chip. Most such chips have eight or more GPIO lines. The power transmitted is set by the external attenuator 32 setting and the chip 22 internal PA setting. A typical operation is to switch between two transmit power settings, thereby distinguishing between the near and the far zones .

Claims

Claims :

1. A wireless communication system which comprises a base station that can communicate with one or more mobile devices within the vicinity of the base station by radio, wherein the base station is operative to attempt to connect to a mobile device within its vicinity at at least two different predetermined signal power levels, and to determine the proximity of the or at least one mobile device based on the signal level at which the connection attempt is successful.

2. A system as claimed in claim 1, wherein the base station is operative to send data to and/or receive data from the mobile device or mobile devices to which it could connect at the lower or lowest predetermined signal power level .

3. A system as claimed in claim 1 or claim 2, which is such that the base station can communicate with only one mobile device at the lower or lowest predetermined signal power level.

4. A system as claimed in any one of claims 1 to 3, wherein the base station is operative to attempt to connect to a mobile device at one of two signal power levels.

5. A system as claimed in any one of claims 1 to 4, wherein the base station is operative to retain information on each mobile device in its vicinity.

6. A system as claimed in claim 5, wherein the information comprises the relative signal strength at which an attempt to connect was successful.

7. A system as claimed in any one of claims 1 to 5, wherein the base station is operative to alter the transmit signal power level in order to connect or attempt to connect to a mobile device.

8. A system as claimed in claim 7, wherein the base station includes a variable attenuator to attenuate the signal power level.

9. A system as claimed in any one of claims 1 to 8, wherein the signal path in the receive direction in the base station is not attenuated.

10. A system as claimed in any one of claims 1 to 9, in which an enquiry is transmitted in order to determine what mobile devices are in the vicinity of the base station.

11. A system as claimed in claim 10, wherein the base station is operative to transmit the enquiry on a periodic basis.

12. A system as claimed in claim 10, wherein an additional station is operative to transmit the enquiry.

13. A system as claimed in claim 10, which includes a plurality of base stations.

14. A system as claimed in any one of claims 10 to 13, wherein the base station is operative to communicate with the or each mobile device by hopping between a plurality of channels .

15. A system as claimed in claim 14, wherein the base station is operative to retain the clock offset of the or each mobile device during periods in which the base station and the mobile device are not communicating.

16. A system as claimed in claim 15, wherein the clock offset of the or each mobile device is determined by a response of the or each mobile device to the enquiry.

17. A system as claimed in any one of claims 1 to 16, wherein one or more mobile devices are in the vicinity of the base station.

18. A system as claimed in any one of claims 1 to 17, Wherein the base station is operative to attempt to connect to a mobile device at the lower or lowest signal power level and then to attempt to connect to the mobile device at a higher signal power level.

19. A method of communicating with one or more mobile devices within the vicinity of a base station, wherein the base station connects or attempts to connect to a mobile device within its vicinity at at. least two different predetermined signal power levels, and determines the proximity of the or at least one mobile device based on the signal level at which the connection attempt is successful.

20. A carrier which carries a computer program comprising processor implementable instructions for generating, by means of a programmable computer and associated radio transmitting and receiving equipment, a system as claimed in any one of claims 1 to 18, or for causing a programmable computer and associated radio transmitting and receiving equipment to perform a method as claimed in claim 19.