GB2440189A

GB2440189A - Location tracking system

Info

Publication number: GB2440189A
Application number: GB0614074A
Authority: GB
Inventors: Robert Robertson; Andrew Lewis
Original assignee: Multitone Electronics PLC
Current assignee: Multitone Electronics PLC
Priority date: 2006-07-14
Filing date: 2006-07-14
Publication date: 2008-01-23
Anticipated expiration: 2026-07-14
Also published as: GB0614074D0; GB2440189B

Abstract

A location tracking system is disclosed operating on at least one radio channel. The system comprises a number of fixed base stations which provide full radio coverage over an area with defined boundaries by means of main beacon signals from individual base stations. The main beacon signals are synchronised and time spaced with respect to each other. The fixed base stations also provide limited range coverage by means of simultaneously transmitted location beacon signals using the same radio hardware as the main beacon signals, both under the control of a network co-ordinator unit. One or more mobile location devices operate within the coverage area, and are capable of receiving main and location beacon signals from one or more of the fixed base stations, in order to gain synchronism and determine location. In turn, each mobile location device transmits a location signal to identify its position within the coverage area.

Description

LOCATION TRACKING SYSTEMS

This invention relates to a location tracking system which may operate in conjunction with mobile products such as personal security alarms, pagers, equipment tracking devices and personnel location devices.

Systems are known to exist in which mobile personal security alarm devices utilize radio technology to allow the device wearer to raise an alann by transmitting a radio signal to summon assistance. In environments where the wearer is mobile e.g. within a building and its immediate surroundings, the physical location of the wearer is included in the alarm signal, allowing assistance to be rendered more quickly. Prior methods for determining the location of the alarm wearer have included the use of fixed beacons that emit or receive local signals allowing the location of the alarm to be determined. Where radio technologies were used for the beacon in these prior methods, radio equipment for position location was required in addition to the radio equipment used for reporting of the alarm message, with a consequent increase in cost and complexity of the overall system and need for additional radio spectrum.

According to the present invention there is provided a location tracking system operating on at least one radio communication channel and comprising a number of fixed base station transmitter/receivers giving full radio coverage over a site with defined boundaries by means of individual base station synchronised time spaced main beacon signals and limited coverage by means of simultaneously transmitted location beacon signals and operable to transmit both main and location beacon signals under the control of a network co-ordinator unit, and also comprising one or more mobile location devices operating within the coverage area and capable of receiving main and location beacon signals from one or more of the fixed base station transmitters in order to gain synchronism and determine location and in turn transmitting a location signal to identify the position of the respective mobile location device within the coverage area.

In a preferred embodiment of the invention, the radio location determining function in a mobile product does not need additional radio equipment to provide this function beyond that required to receive normal message transmissions such as text messages to a pager.

In the preferred embodiment, a common radio channel is used for both location and normal message communication purposes.

Preferably, batteries are used to avoid the additional cost and difficulty of running power cables around the site and therefore the location determining function shall require very little battery power such that the battery in the mobile location device will typically last in excess of! year before needing replacement and the battery in the radio device receiving the location signal will typically last in excess of 2 years. This is accomplished by using low power radio devices based on utilisation of the IEEE 802.15.4 standard (to which reference is directed) in both the mobile location device and the base station.

A specific embodiment of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a location tracking system; Figure 2 is a signal diagram of the main beacon timing in the system of Figure 1; Figure 3 is a signal diagram similar to that of Figure 1, but also including a location device transmission; Figure 4 is a schematic diagram of a location tracking system according to an embodiment of the invention; Figure 5 is a signal diagram of the beacon timing in the system of Figure 4; * Figure 6 is a block diagram of a base station in the system of Figure 4; and Figure 7 is a schematic circuit diagram of a base station in the system of Figure 4.

Figure 1 shows a location tracking system, including a mobile Location Device in an area that is within the range of three Base stations (Base Stations 1-3) capable of receiving signals from that device. The Base stations are under the control of a network Co-ordinatOr.

Figure 2 shows an example of the Main Beacon timing for Base stations using IEEE 802.15.4 transmissionS with beacons. In order to minimise battery consumption, Base stations regularly enable their transmitters/receivers during a small time window which is indicated by the transmission of a beacon from each unit at a different point in time. The frequency of the window is determined by the Beacon Interval and is typically 1 second. The network Co-ordiflatOr provides the source of system timing by transmitting a Co-ordinator Beacon from which all other devices take their timing either directly or via other Base stations.

When a Location Device wishes to transmit a Location signal, it selects a Base station from the Base station Beacons received with a good quality signal and synchronises the Location Device's transmission to the beacon of the selected Base station, transmitting the message at a time when the Base station is in receive mode, i.e. in the short period immediately following the transmission of its Beacon.

Figure 3 shows the time pattern when the Location Device is transmitting to Base station 2.

Because the Location Device shown in Figure 1 is at a location where it is within * range of three Base station Beacons it could therefore report a location based on any or all Base station Beacons being received. Prior methods have been developed where signal strength is used from multiple beacons to determine location; this has not been successful due to variation in radio propagation and signal strength in actual operating environments. Consequently prior systems have often employed additional, low power, radio beacons for location determination that operate independently from the alarm radio channel.

Typically, an alarm unit would receive a location beacon from one location beacon at any one time, providing an accurate location determination; this additional radio equipment for location determination adds cost to the overall system.

Figure 4 shows a preferred embodiment of the invention which makes use of the same radio Base stations (as in Figures 1 to 3) that generate Main Beacons for receiving location signals from the Location Device to also provide a low power Location Beacon. The inner circle around each Base station represents the range of the low power Location Beacon. As shown in Figure 4, for example, the Location Device is within the range of Base station 3 only and can accurately report the location as close to Base station 3 if required. If the Location Device moves out of range of any Location Beacon, the last Beacon can be reported with the time since the Location Beacon was last received.

Figure 5 shows the beacon time frame with the low power Location Beacon.

The Location Beacon is transmitted simultaneously by all Base stations, with the Beacon contents showing the location information for each individual Base station.

As the beacon framing is synchronised and regularly repeated, a Location Device need only receive any beacon once to synchronise to the beacon frame and know when to enable its receiver for a brief period in order to receive a Location Beacon from any Base station within range. Transmission of simultaneous Location Beacons from all Base stations therefore miniinises the load on the battery of the Location Device. Similarly, as the Location Beacon is only transmitted for a brief period and at low radio power level, it makes minimal loading demands on the Base station battery.

Figure 6 shows a block diagram of a Base station. Main Beacons are received either directly from the Co-ordinator or via other Base stations. The local Base station uses the received Beacon to synchronise the generation of its own Main and Location Beacons.

Messages sent from the Co-ordinator may be included within a Main Beacon.

An implementation for the Base station and Location Device could use a low power radio transceiver with inbuilt microcontroller such as the Chipcon CC2430 IEEE 802.15.4. With this device supporting an implementation with a Beacon Interval of 1 second and up to 100 Base stations per I second interval, a Base station would consume approximately 0.5mA and the Location device approximately 0.2mA. If the Base station operated from 2 alkaline D cells, having a capacity of I 8Ah, it would run for 3 years. If the Location Device operated from 2 alkaline AA cells, having a capacity of 2Ah, it would run for I year.

Figure 7 shows a possible schematic diagram for a Base station using the Chipcon CC2430. The design uses a matching network to convert the balanced antenna interface of the CC2430 to an unbalanced 50 ohm co-axial connector.

The CC2430 contains all of the circuitry for running the Base station software and radio, with both Main Beacons and Location Beacons being generated by the same CC2430 hardware.

As described above, the Base stations are battery powered. However, as an alternative, the Base stations could be powered from the local AC mains power supply via a power adaptor so as to avoid the need to replace batteries periodically.

A number of implementations and applications are possible with the above-described system. For example, each Mobile Location Device may also be a personal alarm and/or a pager. Also, the Mobile Location Device may provide alarms on movement and/or location based theft detection of equipment.

Claims

CLAIMS

S 1. A location tracking system operating on at least one radio communication channel and comprising a number of fixed base station transmitterf receivers giving full radio coverage over a site with defined boundaries by means of individual base station synchronised time spaced main beacon signals and limited coverage by means of simultaneously transmitted location beacon signals and operable to transmit both main and location beacon signals under the control of a network co-ordinator unit, and also comprising one or more mobile location devices operating within the coverage area and capable of receiving main and location beacon signals from one or more of the fixed base station transmitters in order to gain synchronism and determine location and in turn transmitting a location signal to identify the position of the respective mobile location device within the coverage area.

2. A system according to claim 1, wherein each mobile location device is operable, upon receipt of a main beacon signal, to synchronise to the transmitted beacon signal frame, thereby to enable a receiver of the device for a period sufficient to receive a location beacon signal from a fixed base station within the limited coverage range.

3. A system according to claim 1 or claim 2, wherein the main beacon signals and the location beacon signals are transmitted over a common radio channel.

4. A system according to claim 1, claim 2 or claim 3, wherein the main beacon signals and the location beacon signals are transmitted using the same radio hardware.

5. A system according to any one of claims I to 4, wherein the base stations are battery powered.

6. A system according to any one of claims I to 4, wherein the base stations are powered from a mains power supply via a power adaptor.

7. A system according to any one of claims I to 6, wherein the or each mobile location device is also a personal alarm.

8. A system according to any one of claims I to 7, wherein the or each mobile location device is also a pager.

9. A system according to any one of claims I to 8, wherein the mobile location device is operable to provide alarms on movement/location based theft detection of equipment.

10. A location tracking system substantially as herein described with reference to and as illustrated in Figures 4 to 7 of the accompanying drawings.