EP3090419A1

EP3090419A1 - Low power position detecting system

Info

Publication number: EP3090419A1
Application number: EP14833589.6A
Authority: EP
Inventors: Stephen Braithwaite; Andrew Ackland
Original assignee: CYCLE ALERT HOLDINGS Ltd
Current assignee: CYCLE ALERT HOLDINGS Ltd
Priority date: 2014-01-03
Filing date: 2014-12-19
Publication date: 2016-11-09
Also published as: WO2015101780A1; GB201400055D0

Abstract

A position detection system having outstation readers (mounted for example on the side of a lorry) for detecting a signal from a transmitter tag (mounted for example on a bicycle) wherein the outstation readers can power down to reduce power consumption if there are no transmitter tags in the vicinity. A coordinator reader is preferably employed as an initial 'coarse' detector of transmitter tags (in that it detects that they are in the general vicinity without needing to detect precise location by means of e.g. signal strength) and can then be used to activate the outstation readers when needed which are used as 'fine- grained' detectors to detect transmitter location. The system can cope with changing numbers of transmitter tags with independent asynchronous transmission cycles and will minimise the power consumption of the outstation readers in real time.

Description

LOW POWER POSITION DETECTING SYSTEM

The present invention relates to a position detecting system, and in particular but not exclusively to a system for the avoidance of collisions between large vehicles and bicycles. The system enables the use of RFID (Radio Frequency ID) readers using substantially less power than a conventional, always-on RFID reader.

BACKGROUND TO THE INVENTION Systems which detect the presence of bicycles in the vicinity of a large vehicle (for example a lorry) are known. Such systems typically comprise a series of cameras mounted on the lorry and a video display system inside the lorry cab for displaying the view from each camera. The cameras are arranged to cover the areas around the lorry which are not visible to the driver in the lorry mirrors (the 'blindspots').

The disadvantage of this system however is that it relies on the driver processing a great deal of visual data (both from the cameras and the lorry mirrors), and thus is not very effective at giving the driver a simple and quick warning when a vulnerable vehicle is near. In addition, the system is not able to distinguish between vulnerable vehicles (such as bicycles) and non-vulnerable vehicles which happen to pass through the blindspots (such as motorcycles passing the lorry).

An alternative system includes means for detecting the presence of an object in the lorry's blindspot and then alerting the driver to the presence of the object by sounding an alarm or activating a warning light. The means for detecting can comprise a radar system or proximity sensor. The disadvantage of this system however is that it can be activated by the presence of objects which are not in the class of 'vulnerable vehicles', such as motorcycles, cars or lorries or even street furniture such as bollards or streetlights. WO 2013/144638 (Le Masurier), the contents of which are incorporated herein by reference, discloses a position detecting system for installation on a large vehicle (such as a lorry) comprising a detector for detecting a transmitter on a vulnerable vehicle such as a bicycle, a processor for calculating the position of the bicycle relative to the large vehicle, and a user interface for providing a visual indication of said position. The transmitter may be provided in the form of a battery-powered RFID tag carried by the bicycle and the lorry ideally has a plurality of detectors to enable accurate detection of the bicycle location (e.g. 8 detectors in total, 4 on each side of the lorry).

The advantage of this system is it is activated only by an object which is carrying or on which is mounted a transmitter. Thus the system avoids the false alerts which are a feature of many proximity sensors.

Ideally, the plurality of detectors located on (for example) the sides of the lorry are battery powered so that they can be mounted in any convenient position without the need for a wired power supply. There is thus a need for a system in which the plurality of detectors consume as little power as possible, in order to preserve battery life. Preferably, the detectors should draw substantially zero power when in a sleep state, and should draw current to receive the transmission of an active RFID tag for as short a time as possible.

SUMMARY OF THE INVENTION In a first aspect of the present invention, there is provided a position detecting system comprising

(a) a transmitter for association with a first object (such as a bicycle),

(b) at least one location detector for association with a second object (such as a lorry), which detector has an awake state and a sleep state in which it consumes less power than in the awake state,

(c) a transceiver for association with the second object, and

(d) a processor for calculating the position of the transmitter relative to the detector, wherein the transceiver is configured to receive a transmission from the transmitter which transmission includes (i) information identifying the transmitter and (ii) information concerning the time of a future transmission of the transmitter and wherein the transceiver is configured to transmit said information to the detector, wherein said detector is configured to transmit to the transceiver (this transmission being an optional rather than essential step), to listen for its response, and to enter its sleep state after it has received said information from the transceiver and is configured to enter its awake state in time to receive directly from the transmitter said future transmission including (i) information identifying the transmitter and (ii) information regarding the signal strength of said transmission,

and wherein the processor is configured to use said information from the detector to calculate the position of the transmitter relative to the detector. The technical advantage of the present invention is that the location detectors can power down to reduce power consumption and there is no need for them to be activated if there are no transmitter tags in the vicinity. The transceiver is preferably employed as an initial 'coarse' detector of transmitter tags (in that it detects that they are in the general vicinity without needing to detect precise location by means of e.g. signal strength) and can then be used to activate the detectors when needed which are used as 'fine-grained' detectors to detect transmitter location. The system can cope with changing numbers of transmitter tags with independent asynchronous transmission cycles and will minimise the power consumption of the detectors in real time. A suitable arrangement for a position detecting system in accordance with the invention is to provide an active RFID transmitter tag for each bicycle (or pedestrian as the case may be), a coordinator reader (located for example in the cab of the lorry) for reading the radio frequency signal from the tag, and at least one and preferably several so-called "outstation" readers disposed down either side of the lorry for calculating the location of the RFID tag.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example only to the accompanying drawings, in which: Figure 1 shows a perspective view of a large vehicle fitted with an embodiment of a position detecting system; and

Figure 2 shows a plan view from above of the large vehicle of Figure 1 fitted with an embodiment of a position detecting system.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring firstly to Figures 1 and 2, an embodiment of a position detecting system is shown generally at 10. The position detecting system 10 comprises eight outstation readers 14, 16, 18, 20, 22, 24, 26, 28 four of which are fitted spaced out at regular intervals along each side of a large vehicle 12.

A transmitting tag 32 is attached to a bicycle 34.

A coordinator reader 36 is mounted in the cab of vehicle 12 and is combined with an LED display for displaying information to the driver concerning the proximity of vulnerable vehicles such as bicycle 34. Coordinator reader 32 communicates wirelessly with outstation readers 14, 16, 18, 20, 22, 24, 26, 28 as will be described below.

Optionally, cameras 38 and 39 may be fitted in the cab of vehicle 12 to provide additional information to the driver concerning vehicles in his 'blind spot' .

Optionally, four outstation readers 14, 16, 18, 20 communicate wirelessly with a first transceiver 30 which is mounted to the left-hand side of the large vehicle 12. A further four outstation readers 22, 24, 26, 28 communicate wirelessly with a second transceiver 31 which is mounted to the right-hand side of the large vehicle 12. First and second transceivers then communicate wirelessly with coordinator reader 36 on behalf of outstation readers 14, 16, 18, 20, 22, 24, 26, 28.

Consider an RFID tag 32 mounted on a bicycle 34 with a regular transmission of data every T seconds on average. The tag 32 transmits a unique identifier and possibly other data (but unimportant to the invention). The tag may also transmit a code word that indicates the position in a pattern of time offsets that are added or subtracted to the mean transmission point to induce time hopping around the mean transmission point. This technique is used to mitigate against repeated collisions with other like tags transmitting at the same time and with the same transmission rate.

The RFID reader arrangement is formed of two types of component - a coordinator reader 36 and one or more outstation readers 14, 16, 18, 20, 22, 24, 26, 28. As in a conventional active RFID system, many tags may be in the vicinity of all readers, and information is to be obtained from them, usually the transmitted data and also its received signal strength which can then be used as a form of localisation.

When an active RFID tag 32 is presented to the system of readers, the coordinator reader 36 can receive from the tag 32. The receiver of the coordinator reader 36 is always powered on and can receive the transmission from a tag without notice, unlike an outstation reader 14, 16, 18, 20, 22, 24, 26, 28. When the coordinator reader 36 receives a new tag transmission, it receives its unique identifier and (if present) its time hop sequence phase identifier. Each outstation reader 14, 16, 18, 20, 22, 24, 26, 28 sends an occasional poll transmission (wirelessly if desired) to the coordinator reader 36 and listens for a short while afterward for any return transmission. This transmission may be on a separate radio channel (to a second receiver at the coordinator reader 36 if necessary) to mitigate against channel congestion if necessary.

When the coordinator reader 36 receives a new tag transmission, it sends a message to each outstation reader 14, 16, 18, 20, 22, 24, 26, 28 in a reply to its poll. The message contains the new tag ID, its optional time hop phase, and the expected time of the next tag transmission. The outstation reader 36 then sets its receiver frequency to listen for the expected new tag transmission and records such necessary data such as the tag

transmission data, and its signal strength. In the case of synchronous tag transmission, the outstation reader 36 then stores the time of receipt of the transmission and predicts when the next transmission from the tag 32 will take place, so tracking its transmissions without further help from the co-ordinating receiver, and switching to a low power state when not receiving. An outstation receiver 14, 16, 18, 20, 22, 24, 26, 28 may perform this operation for many tags, limited only by memory of its computing processor.

If however the transmissions are asynchronous (for example, on a randomised time cycle), it may not be possible for the outstation reader 14, 16, 18, 20, 22, 24, 26, 28 to be able to predict when the next transmission from the tag will take place. In that case, the coordinator reader 36 is employed again to receive the next tag transmission and to alert the outstation reader 14, 16, 18, 20, 22, 24, 26, 28 as before.

It will be appreciated that the system requires the coordinator reader 36 and the outstation readers 14, 16, 18, 20, 22, 24, 26, 28 to have a common understanding of time. This is achieved by having the coordinator reader 36 transfer time information to the outstation readers 14, 16, 18, 20, 22, 24, 26, 28 as a count of clock cycles (of a clock of nominal frequency known to the coordinator reader 36) until the next transmission from the RFID tag 32 is due (equally it could be clock cycles since the last transmission from the RFID tag 32 was, or was due to be, received). The coordinator reader 36 uses this count to determine when the next transmission from the RFID tag 32 is due relative to the time of receipt of the coordinator's message, allowing for message allowing for any pipeline delays in the transmission of the message from coordinator to outstation. Outstation readers 14, 16, 18, 20, 22, 24, 26, 28 may feedback their received data to the coordinating reader 36 by sending a transmission (wirelessly if desired) every time a tag transmission is received. This is desirable if the co-ordinating reader 36 needs to receive measurements from the outstation readers 14, 16, 18, 20, 22, 24, 26, 28 with minimum delay (latency). The transmission from each outstation reader may be offset by an agreed amount from the tag reception time to avoid collisions (wireless or other shared medium such as a multidrop wire) from other associated outstation readers. In addition, a further, random, offset may be applied to the outstation reader transmission to mitigate other nearby RFID reader systems responding to the same tag reception.

An example of an embodiment of the invention is with a traffic alert system for vehicles to alert drivers of the presence of pedestrians or cyclists, for instance. The pedestrian or cyclist carries an active RFID tag of the type described. The vehicle has a coordinating RFID reader at the driver's position, powered from the vehicle power supply. The outstation readers are battery powered and conveniently positioned (without wiring installation) around the vehicle, between two and six or more per side. When the tag and vehicle are in communication range, the co-coordinating reader informs the outstation reader of the presence of the tag immediately after their regular poll transmission. The outstation readers then transmit back the ID and signal strength measurement of the tag. The co-ordinating reader then can process the results of the measurements to determine the position and identity of the RFID tag. The system is robust to several vehicles receiving the same tag transmission. The outstation readers can operate with a power efficiency gain of between 100 and 1000, giving the possibility of fit-for-life batteries.

It will be appreciated that the present system has alternative uses to the transport safety sector. For example, it could be used to track the location of a person, for example to alert a relative if someone suffering from advanced dementia left the safety of their house.

An established method for synchronising a battery-operated receiver (outstation, in this description) to an asynchronous transmission from, for example, a tag, is to have the outstation receiver circuitry turn on for at least the transmission period of the tag to receive one tag transmission, and then for the outstation to go into its sleep state. Subsequent tag transmissions may then be received by the outstation waking up at the expected time of the next tag transmission. This method is commonly used in Wireless meshed networks, particularly Time Synchronised Mesh Network protocols such as Wireless HART, and is convenient when the need to synchronise to a tag (or other regular transmission such as a network beacon transmission or other wireless transmitter) is a rare occurrence such as on installation of the outstation device. It is not a convenient method when introduction of a new tag is a common occurrence or, particularly, when there is no tag in range to be received since the battery usage during the initial listening period may amount to a significant and unwanted consumption, considerably shortening the life of the battery.

All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.

The disclosures in UK patent application number 1400055.8, from which this application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims

1. A position detecting system including

(a) a transmitter for association with a first object (such as a bicycle),

(c) a transceiver for association with the second object, and

(d) a processor for calculating the position of the transmitter relative to the detector, wherein the transceiver is configured to receive a transmission from the transmitter which transmission includes (i) information identifying the transmitter and (ii) information concerning the time of a future transmission of the transmitter and wherein the transceiver is configured to transmit said information to the detector,

wherein said detector is configured to transmit to the transceiver, to listen for its response, and to enter its sleep state after it has received said information from the transceiver and is configured to enter its awake state in time to receive directly from the transmitter said future transmission including (i) information identifying the transmitter and (ii) information regarding the signal strength of said transmission,

and wherein the processor is configured to use said information from the detector to calculate the position of the transmitter relative to the detector.

2. A position detecting system as claimed in claim 1, wherein the transceiver is always powered on and can receive a transmission from the transmitter without notice.

3. A position detecting system as claimed in claim 1 or 2, additionally including a receiver associated with the transceiver, which receiver is configured to receive a signal from the detector which signal does not have the same wavelength as signals between the transmitter and transceiver and/or signals between the transceiver and detector, thereby reducing channel congestion.

4. A position detecting system as claimed in any preceding claim, wherein the information transmitted to the detector by the transceiver additionally includes a count of clock cycles for a clock of nominal frequency until the next transmission from the transmitter to the transceiver.

5. A position detecting system as claimed in any preceding claim, wherein the transmission from the detector to the transceiver is offset from the predicted reception time of the transmission from the transmitter to the transceiver.

6. A position detecting system as claimed in claim 5, wherein said offset is either fixed or randomised.

7. A position detecting system as claimed in any preceding claim, including a plurality of location detectors.

8. A position detecting system as claimed in claim 7, wherein the transceiver is configured to identify the detectors individually.

9. A position detecting system as claimed in claim 7 or 8, wherein the processor is configured to identify the detectors individually.

10. A vehicle having a position detector system as claimed in any preceding claim fitted thereto.

11. A bicycle having a transmitter fitted thereto, wherein the transmitter is configured to be suitable for use in a position detector system as claimed in any of claims 1 to 9.