GB2565388A - A presence warning device, app, a method and a system - Google Patents

Abstract

A presence warning device comprises detecting receiver 4 for use by the driver of a vehicle 6. The receiver is arranged and configured to receive a signal from beacon transmitter 10 associated with a road user 81,2,3. In use, the receiver is arranged based on a received signal to determine the presence of the beacon transmitter, but not its location relative to the vehicle, and to track the relative proximity of the beacon by processing the received signal therefrom. A presence model may be maintained to retain, update, and process information on the beacon transmitter. The detector may calculate proximity estimates within predetermined distance spans forming concentric rings around the detector. The device may determine acceleration of the transmitter in dependence on a received signal. In a second aspect a beacon transmitter is arranged to transmit a signal to inform a detector of its proximity to the vehicle.

Description

A Presence Warning Device, App, A Method and A System

The present invention relates to a presence warning device, a method, a system and an App.

In embodiments, the present invention relates to a presence warning system to improve road safety. Its purpose is to warn drivers of vehicles whenever possible of the presence of vulnerable road users (VRU). A VRU is designated to be principally, but not limited to, cyclists and also potentially motorcyclists, who are in the immediate vicinity of a driver’s vehicle and therefore potentially at risk of inadvertent collision. Other applications of the invention may include protection of VRU’s including electric bikes, mobility scooters, horse riders, children or other pedestrians not always alert to road dangers, roadside mechanics, couriers and other workers whose responsibilities require guiding vehicle movements in public or confined spaces or frequent entering and exiting of a vehicle.

Drivers always have primary responsibility to be aware of and alert to all other road users, particularly vulnerable ones, and to ensure their knowledge and visibility of them is not compromised. However, any driver’s general awareness can be less than ideal on occasion, particularly in situations where they may have been distracted; are tired or have lower than required levels of concentration; where they may look but do not actually see because their visual focus or attention is on other matters; or occasionally cannot see at all due to blind spots or obstacles beyond their control. Unfortunately, these issues give rise to the likelihood of accidents occurring, most often at road junctions at slow rather than high speed, through driver error or more generally when their behaviour cannot be anticipated by VRUs, such as sudden changes of direction when a driver may overcompensate once reverting to full concentration.

The present invention aims to overcome these issues and increase road safety for VRUs as well as other users, by providing continuous automatic presence and proximity detection between a driver and one or a plurality of vulnerable road users. Appropriate notification of presence and proximity detection ensures driver awareness remains fully effective, both by supplementing the normal cues from the road environment and by reducing the possibility of incidental distraction. A number of prior art solutions have been proposed to automate detection of the proximity of drivers to other vulnerable road users, including pedestrians, and vice versa. In general though the prior art suffers one or more barriers to adoption, whether voluntarily, or compulsorily by law or statute. Among these barriers are: high-cost of implementation; a plurality of systems or methods or means which are mutually incompatible; systems or methods with limited range or of limited reliability and therefore of questionable efficacy. The cost of implementation is not just devices and systems: any solution requiring skilled installation will also mean taking a vehicle off the road for a period of time and potential loss of income, a period that may lengthen according to the complexity of the system being fitted, the number of sensors, and any need for integration with the vehicle’s systems. Such costs and the other barriers have limited adoption of these systems to fleet and commercial operators, rather than the private vehicle owner. Maximising adoption will help to achieve a widespread increase in safety.

CATEGORISATION OF THE PRIOR ART

Among the prior art there are many methods that have been proposed to try to address issues similar to those addressed by the present application. Main principles of operation that have been suggested include: • Radio Frequency ID (RFID) “tags” (e.g. Cycle Alert) based systems, which rely on equipping vulnerable road users with these tags, and installing sensors on vehicles, usually at multiple points even on small ones. RFID detection has very limited proximity range, typically up to 2.5m. As such the ability for a driver to react in the time available is possibly too demanding, in very many situations above anything more than crawling speeds. The need for professional installation on vehicles also limits application to fleet and commercial operators. Furthermore, there are more than a few different RFID standards, which in turn means that there is more than one proprietary solution on the market, and any given tag is unlikely to be detected universally, compromising widespread adoption by vulnerable road users who would have to carry in principle all tag types to ensure the highest safety coverage; • Vision systems based on cameras and CCTV that may provide a direct visual feed to the driver, or may (also) use pattern recognition and motion detection on the video stream to provide supplemental automatic notifications. A vision system in essence does not need vulnerable road users to actively take part or adopt the use of any device, and hence such systems may detect as many of these road users as its ingenuity will allow. Cameras and CCTV are limited by field of view though, and for adequate visual coverage and analysis of a vehicle’s immediate vicinity, typically multiple sensors are required. Range may be adjusted by appropriate optical and or digital magnification, but not without affecting field of view and creating blind spots, or potentially increasing the number of sensors yet further. The main disadvantage of direct vision systems is that they are very distracting for the driver to use, more so than mirrors, because of the number of independent sensors to watch and interpret, and therefore often they are only enabled at very slow speeds, possibly even by law. Even where visual signals are processed automatically for higher level notifications, their reliability may only be usable at short distances to eliminate background clutter, limiting the ability for a driver to react in time. The cost of such systems is high, such that penetration into the market has been slow and limited in use primarily to professional drivers; • Ultrasound (e.g. Mobileye) based systems, similar in operation to sonic parking proximity sensors, rely on multiple beacons and sensors for adequate coverage around the vehicle periphery. In operation, an ultrasonic signal is reflected off vulnerable road users, and their proximity in the main is determined from the propagation delay or “echo”. The requirement for multiple sensors demands a professional or ideally factory installation in the vehicle. Ultrasound’s main advantage over RFID is that vulnerable road users do not need to invest in the system, and as per vision based systems, each installation may be proprietary. However, range is limited in the region of 3m, to avoid background clutter and false alarms. Once again the short range means there is very little time for a driver to react unless relative speeds are especially low; • Infrared based systems perform proximity detection using the body heat of vulnerable road users. Many of the limitations of ultrasound based systems apply here too: range; number of sensors; and professional or factory installation. A further disadvantage though is that infrared may be blinded by sunlight, reflections, and even movement of passive objects which do not themselves emit a heat signature; • Road infrastructure installed systems are usually based on road-buried vehicle- and VRU-presence detection loops or some of the methods above. Such systems avoid the need for vulnerable road users and vehicles to be equipped. However, since detection is localised, these installations are only really practical to use at junctions, and installation is costly for each individual instance, limiting their use to blackspots. The buried loops work best with stationary or very slowly moving road users. They may be used to notify presence of vulnerable road users to drivers through lit signs for example, but since these must be in front of the driver in the direction of travel, they are unlikely to reinforce awareness of things to the side or behind that could be detected only when it’s too late. Potentially they may be more effective at “being able to see around corners”, where the detection is relayed to other approaches to a junction. However, the more typical accidents caused by side-swipes and reversing are not readily ameliorated; • Radar based systems using radio frequencies are more sophisticated and capable than ultrasound, but rely on a similar principle of signal echo detection to determine proximity. However, being radio based these can cover much greater distances than sound based ones. Without requiring any investment by vulnerable road users, the systems may be proprietary. Radar though is possibly the highest cost of all systems, and installation is only really practically undertaken by motor manufacturers, requiring at least one radar device per vehicle quadrant to be covered. Because of its greater range, radar information must be processed to remove clutter and chaff, and much more signal processing is required if a driver is not to have to stare and interpret a visual display. Consequently the most appropriate application for these systems has been for informing the varied autonomous intelligence that is termed colloquially “driverless car”, rather than improving VRU safety through the widespread deployment by drivers of millions of existing vehicles, which will remain in the majority for a long time to come; • The most notable category for the present safety application, and into which category the present invention falls, is wireless based systems which rely on radio transmitters or beacons - one per vulnerable road user - and radio receivers or detectors - one per driver. Wireless signal communication between transmitter and receiver is indeed the most proven and promising technology for communicating proximity and presence. Among its advantages is the ability to design a preferred detection range quite freely by appropriate use of transmit power and receiver design. Wireless systems are reliable in multitudes of safety applications. Furthermore, radio devices may be sufficiently low-powered to be used continuously for very long periods, and even longer with greater degrees of power management sophistication according to utility. In particular, Bluetooth is a wireless technology that has already been used in very many devices, and is widespread on mobile handsets and many cheaper devices. That level of market penetration and its formal standardisation, means the costs of Bluetooth based systems is nominal, and these aspects make it advantageous to the wide adoption necessary for effective increases in road safety as demanded of the present application.

NOVELTY OVER THE PRIOR ART

The present invention overcomes one or more shortcomings of the prior art.

Definitions: by “explicit” is meant values that may have been derived from sensors or calculated by the transmitting device and which are sent as explicit direct information fields in data packets. By “implicit”, is meant values which may be derived or inferred by the receiving device from the characteristics or contents of received packets and are therefore indirect and potentially approximate values.

According to a first aspect of the present invention, there is provided a presence warning device comprising a detecting receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged to determine the presence of the beacon transmitter but not its location relative to the vehicle, and to track the relative proximity of the beacon by processing a received signal therefrom.

The invention provides a presence warning device that enables the driver of a vehicle or indeed anyone else in a vehicle who has an interest in it, to be aware of the presence of a road user such as a vulnerable road user which would include categories such as cyclists, riders of e-bikes, motor-bikes, horse riders and mobility scooters. By providing an app/ device that enables a driver to be aware of the presence but not the location it will ensure that the driver has information to make them extra cautious whilst not giving any degree of false security by appearing to tell the driver everything needed to know about the location of the vulnerable road user.

In an embodiment, the detector maintains a presence model to retain, update and process information on each detector connected to it.

In an embodiment, the detector calculates proximity estimates within predetermined distance spans forming concentric circles around the detector. The radius of the circles can be varied and set based on parameters such as the communication technology being used and the type of VRU, e.g. bicycle or motorbike, in mind.

In an embodiment, the receiver is arranged to receive and process data according to the BLE protocol. Use of such a protocol is particularly advantageous since it means that “data” in the sense of GPS, 3G, 4G or other such mobile internet data is not used to operate the system.

In an embodiment, the detector comprises an alarm to provide an indication to a user when a road user is detected to be within a defined proximity to the device.

In an embodiment, the device comprises a processor arranged to determine acceleration of the transmitter in dependence on a received signal.

In an embodiment, the processor is arranged to apply a filtering algorithm to apply a filter to a received signal from a transmitter to determine data relating to parameters of the transmitter.

In an embodiment, the filter is an infinite impulse response (HR) filter arranged to produce a moving average of all received signal strengths from a plurality of transmitters.

In an embodiment, the filter is arranged to optimise the HR using second order factors to thereby filter out variations in received signal strength due to atmospheric effects and/or reflections from a moving target.

In an embodiment, the device is arranged to update presence events to assess motion.

In an embodiment, the device is arranged to decay slowly the value stored as the last peak filtered signal strength thereby dealing with a situation in which a transmitter maintains a relatively constant distance from a detector.

In an embodiment, the receiver is arranged to measure the rate of change of a moving average of the proximity and/or second derivative of the proximity for the purpose of distinguishing distance of a transmitter from the receiver.

In an embodiment, the receiver is arranged to provide a notification in the form of one or more of a visual notification or an audible notification to a user.

In an embodiment, the device is embodied as a mobile telephone or computing device, such as a tablet device or a satellite navigation device, running thereon an App to provide the specified functionality.

In an embodiment, the device is embodied as a dedicated item of hardware, to provide the specified functionality.

In an embodiment, the detecting receiver is arranged to avoid repetition of alerts within a period of less than a predetermined time period.

In an embodiment, the predetermined period within which repetition of alerts is avoided is one of 5 seconds, 10 seconds and 30 seconds.

In an embodiment, the length of time within which repetition is avoided is determined based on parameters associated with the transmitter. The avoidance of repetition of alerts may be achieved by methods of filtering signals by a receiver from transmitters as described in greater detail below. It is an important embodiment since the avoidance of repetition ensures that the driver is not irritated or annoyed by the alerts whilst at the same time safely ensuring that alerts are issued when they are needed. Examples of parameters associated with the transmitter include such things as the speed the vehicle is moving.

According to a second aspect of the present invention, there is provided a presence warning system, comprising a detector according to the first aspect of the present invention and a plurality of beacon transmitters, each beacon transmitter being associated with a road user and arranged to communicate with the detector.

According to a third aspect of the present invention, there is provided a method of warning a driver of a vehicle of the presence of a road user, comprising providing a receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged to determine based on the received signal the presence of the beacon transmitter, but not its location relative to the vehicle and to track the relative proximity of the beacon by processing the received signal therefrom..

In an embodiment, the method comprises, at the receiver, measuring the rate of change of a moving average of the proximity and/or second derivative of the proximity for the purpose; and based thereon, distinguishing distance of a transmitter from the receiver.

According to a fourth aspect of the present invention, there is provided an App comprising program code, which when run on a computing device such as a mobile telephone causes the mobile telephone to function as a detecting receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged based on a received signal to determine the presence of the beacon transmitter but not its location relative to the vehicle, and to track the relative proximity of the beacon by processing the received signal therefrom.

Providing the invention in the form of an App has particular advantages in that user uptake can be achieved quickly since most people in most countries already have mobile telephones or the like which can run Apps and can therefore function either as a beacon/transmitter or receiver as described herein.

In another aspect of the present invention there is provided a wireless beacon transmitter used by VRUs, and a wireless detecting receiver used by drivers of vehicles, whereby a signal and information is communicated from the former to the latter, such that any single receiver may determine both the presence of one or a plurality of beacons, and to track each beacon’s relative proximity implicitly, by processing the respective received signal strength. The processing of the received signal strength addresses the characteristics of wireless propagation in the preferred radio band, which may be impaired predominantly by indirect propagation of the signal which may follow multiple paths between a beacon and a detector, or by reflection, absorption, and attenuation. The processing referred to includes: • filtering algorithms designed and adjusted appropriately to the environment characteristics and the objective of the safety application; • algorithms to minimise “false negatives” of presence and proximity changes that may be caused by lost signals, corrupted information, or nulls - positions from which there is no viable path for transmission between beacon and detector.

In another aspect of the present invention a receiving detector maintains a “Presence Model” to retain, update and process information on each VRU, for which purpose each VRU is distinguished by a unique identifier that is protected from being inadvertently or maliciously imitated, so called “false positives”, the Presence Model providing the means among other purposes, to track the continued presence of each beacon, the duration of its presence in terms of a count of received packets of information; the filtered signal strength for the purposes of determining proximity; the calibrated signal strength of the transmitter by which signal strength to propagation distance may be initially determined prior to proximity processing; and also the processes of: • Flushing stale entries from Presence Model after a period of inactivity to simply retain a reliable view of still actively present VRUs; • Recording and updating a peak-signal strength metric appropriately, and automatically decaying that metric by which to derive a pragmatic relative motion assessment as well as an estimation of nearest proximity.

In another aspect of the present invention a receiving detector categorises proximity estimates within several distance bands forming concentric rings such as circles of certain radius, or “safety rings”, for the purposes of pragmatic resolution of proximity; relative motion studies; use by drivers of different sizes of vehicle and by which to decide when to trigger or vary warning notifications to the driver of said vehicles. Instead of circles, some other concentric shape could be used as the shape of the rings. For examples an ellipse could be used. The proximity bands provide the means for an adaptive model of presence and proximity that may include: • Adjusting behaviour according to time within any given proximity band; • Adjusting behaviour according to the rate of transition between proximity bands; • Adjusting behaviour according to VRUs considered as approaching, departing or relatively stationary/traversing proximity bands.

In another aspect of the present invention a receiving detector notifies the driver by several and varied means, and in an appropriate manner so as not to cause or exacerbate any distraction, but raise awareness of any relevant change of state in any of the underlying received signal processing algorithms, or within the notification state machine and process itself. The notifications may take the form of: • Differentiating just one or two or a plurality of states of VRU presence; • Varying visual indications such as lights or displays in a such a manner to make them highly noticeable, particularly to the human peripheral vision, such as: i. Stepped colour indications to represent changes of state, for example by proximity band; by number of VRUs; or any other context change; ii. Jittering the indicator position on similar change of state or timeouts; iii. Changing the indication shape on similar change of state or timeouts; • Varying audible notifications such as generating , modulating, or attenuating sounds to represent changes of state, in such a manner to make them highly noticeable, such as playing a familiar sound, with or without attenuating or muting music on the occasions of: i. Entry of one or a plurality of VRUs into inner proximity band only, or movement between proximity bands, or any entry into any proximity band; ii. Timeout reminder for one or a plurality of VRUs remaining in the inner proximity band, or any proximity band.

The aspects of present invention may be further enhanced by: • Determining acceleration or variation of speed by adapting the threshold for notification accordingly; • Varying the beacon wireless transmission power according to VRU travelling speed to save power or alternatively maximise range; • Associating a user with a particular device unique identifier by means of authentication, encryption and non-repudiation using public/private key exchanges with an Internet based cloud service;

The present invention may therefore provide one or more of the following advantages: • Sufficiently low-cost and widely available hardware so as not to be a barrier to the widest possible adoption. • The wireless technologies it is able to use are widely available, and may be used in their standardised form without modification. In one preferred embodiment the wireless standard used is Bluetooth Low Energy, a capability available on the majority of mobile devices already owned and in use in many countries. • In operation the present invention provides reassurance to drivers and reinforces their awareness, without engendering any false sense of security. It is focussed on an asymmetric role of protecting VRUs by notifying drivers of vehicles with information of VRUs in their immediate vicinity. • There is no action of collision prediction, autonomous override of any function of the vehicle, or notification to VRUs. VRUs contribute passively to safety by the only requirement of owning and carrying a device. Drivers have a (minimum) onus on them to adopt and use a device for the present safety application.

The present invention is simple to adopt and to use, in certain preferred implementations with no need for any installation, and typically with only one device, sensor or application to acquire, the latter for use on a smart phone or other mobile device. • The device or application is intrinsically automated and self-configuring, and simple to understand through highly intuitive interfaces. • Notifications to the driver are designed not to cause problematic distraction, and can be instinctively understood, will not annoy to the extent of creating a desire to tamper with or disable the device, and ensure untrammelled concentration on the road and control of the vehicle. • To notify a driver in a way that distinguishes the presence of precisely one VRU versus two or more. This feature is very beneficial in reducing a false sense of security which may occur when a driver sees a VRU, but may have the mistaken belief that they are the sole cause of a notification. If the notification signifies more than one VRU, whether or not a driver is inclined to count VRUs is moot, but without question they will be on the look-out for more than one VRU (without knowing the upper bound) which is an effective enhancement of awareness.

In practice not every vulnerable road user or driver may have a device, but if they do and it is operational when they are on the road, those armed with a device will be able to reliably detect the presence of other users in as many contexts as possible, and where there is no detection, will not be left with the impression that all is clear - i.e. there is still the possibility for an unequipped or undetected road user to be in the vicinity. However, as adoption increases, such occurrences will diminish, although can never be fully eliminated.

The prior art emphasises position or relative direction of a VRU to the driver. For the present invention it is unnecessary, first of all because there is no intention to predict collision vectors, and moreover the present inventors have recognised that direction is certainly not useful in situations of more than one or a few VRUs in the immediate vicinity. Such information is liable to distract and confuse, and thereby undermine the safety goal.

Accordingly, the present system is arranged to inform a vehicle driver of the presence of, but not the location of the other road user relative to the vehicle. Even where the argument could be made for distinguishing general direction for one or more VRUs in terms of “to the left” or “to the right” for turning vehicles (“behind” and especially “in-front” have less merit), the potential for creating a false sense of security, where for example an “all clear” of a given direction, is no different to an “all clear” generally which is deliberately avoided in the present invention. Misinterpretation, and the difficulty for a driver to distinguish direction notifications, or worse the potential for unwelcome annoyance caused by “I am turning right, why am I getting notifications about presence to my left” and vice versa, mean that direction information is avoided and general presence and proximity bands are deemed sufficient for the purpose at hand.

Prediction of collision is also not useful to drivers, as there may be more than one VRU in the vicinity, and a driver may very quickly be overloaded by too much information. No prediction can be 100% reliable or an accurate reflection of the environment, and false alarms may for example make a driver take evasive action - unexpected braking or turning -which in and of itself may cause an accident. Furthermore, it is a logical induction that there may be more than one collision predicted at a time, and the driver could be very confused by the prior art, rather than having their awareness enhanced. If collision prediction is useful at all, it would be more in the domain of autonomous functions of the vehicle, rather than being of value to a human driver that must interpret the situation without assistance. Furthermore, reliable predication of collision, if possible at all, would require far more sophisticated and expensive hardware than is envisioned for implementation of the present invention.

The road is a highly dynamic environment, where speeds and relative distances change continuously, both for expected and unexpected conditions. Some of the most risky situations that have high potential for collisions to occur are where a VRU catches up with vehicles that suddenly turn at junctions, or the classic instance of a vehicle door being opened suddenly in the path of a VRU travelling quickly. Detection systems of the prior art that are limited to a single threshold of distance are often inadequate in detecting the dynamic nature of the road environment and its rate of change. VRUs approaching a driver’s vehicle quickly but that are outside immediate detection range will not be notified until within the threshold, by which time it could easily be too late.

Unlike the prior art relative position, direction, speed and collision estimation processes, the aim of the present invention is simply to reinforce awareness, for which information of the precise position and direction or bearing or time to impact of a VRU is unimportant. It is of deliberate intent that the onus remains on the driver to be alert and look for a clear path in any direction of travel before starting a manoeuvre. Consequently it is sufficient to be informed of VRU presence, or a potential change of presence that may have been overlooked, which then should inspire the driver to look more carefully.

In addition to presence of a VRU, for the purposes of appropriate management of notifications to raise not lower awareness, the present invention takes into account distance much more fully, as well as speed or the rate of change of distance. This maximises its benefit to improving road safety, by implementing an adaptive combination of presence and proximity detection.

In particular presence and proximity are not confined to just one inner distance band, but several concentric or otherwise nested bands. For example in one preferred embodiment the radii of these bands might be >70m; 35m - 70m; 15m - 35m; and <15m (metres) from the driver’s device. (Refer to FIG. 2) The concentric bands are sized and selected to detect overall as many VRUs as possible, without placing too great a reliance on accurate measurement of distance. A VRU may be categorised by the band it occupies, its rate of change of traversing bands or the dwell time in a band, and these factors used to determine a status of “approaching”, “departing”, “traversing” or relatively stationary (close to the same speed of the vehicle). Furthermore, optionally, the vehicle’s own speed may be taken into account, either through integration with the vehicle systems of more preferably by use of tracking capabilities in the sensor itself, such as a GPS sensor typically already present in smart-phone based implementations. Such an implementation is used to provide additional options regarding the situational notifications, rather than perform any prediction of collision. Presence and proximity are therefore a more complex mix, and may be varied according to a VRU’s categorisation of those two metrics, and this provides the ability for more nuanced and refined notifications.

In one preferred embodiment, a VRU has a transmitting beacon that is configured to be unchanging in its operation. In this case, all of the intelligence is in the receiving device. In particular, the transmitting beacon uses constant transmit power that has been calibrated, i.e. measured by calibrated equipment at a fixed distance, and thereby determining its maximum detectable range. In an alternative embodiment, the VRU’s device is made more sophisticated and changes its transmitting power between stepped and equally calibrated levels. This may be performed particularly to increase or decrease the detection range, and also potentially to save power. One parameter that may drive this change would be the VRU’s speed of travel.

Some of these dynamic techniques enable the present application to be configurable for use in different types of vehicle: privately owned cars and vans; commercially owned cars, vans, HGVs, buses and coaches, offering suitable adaptation to size and blind spot distances with minimal involvement of the users themselves. This may be facilitated by programming by fleet and commercial operators, or by the vendor, or by manual selection of the vehicle type by a driver.

DETAILED DESCRIPTION OF INVENTION

The following is described with reference to the figures:

Figure 1a: An overview of the safety application, one or more VRUs and vehicles, both equipped and not;

Figure 1b: a schematic view of a receiver for use in a presence detection system; Figure 2: Proximity bands around a vehicle (of any type);

Figure 3: AdvA packet format and unique identifier construct with symmetric encryption;

Figure 4: Additional scan data packet format;

Figure 5: Cloud based registration and asymmetric encryption;

Figure 6: Presence Model table and data;

Figure 7A and 7B: A functional layering of the system main processes;

Figure 8: Presence Model update and pruning flowchart;

Figure 9: 3D diagram of signal propagation with reflection, absorption, attenuation, nulls, and simultaneous paths VRU to vehicle;

Figure 10: Step 1 HR moving average filtering graph;

Figure 11: Step 2 RSSI to proximity determination graph according to equation, and designated proximity band;

Figure 12: Steps 4/5 Peak signal strength detection graph with decay process, and dB step change detection;

Figure 13a and 13b: Exemplar device and app displays (shapes, jitter, blink);

Figure 14a and 14b: Visual and Audible notification flowchart.

The present invention is typically implemented as a system made up of two types of unit: a wireless transmitting beacon device carried by a VRU; and a receiving device carried by a driver or deployed in their vehicle. A device may be a hardware device, a combination of hardware and firmware, or a software application run on a more general computing device, which in one preferred embodiment may be a smart phone or other mobile device. A beacon or a detector may also perform the dual role of transmitter and receiver (transceiver), for example for the purposes of relaying information to other devices to overcome local “nulls” that may obscure VRU presence for a subset of devices but not others, or more generally for mesh networking between devices.

Figure 1a shows a schematic view of a presence warning system 2, including a receiver 4 associated with and in this case integrated into a car 6. A number of cyclists 8 are in general proximity to the car 6. Of the four cyclists 81 to 84 in proximity to the car 6, three 81 to 83 have with them a transmitter or beacon 10 arranged to transmit signals for reception by a receiver such as that 4 associated with the car 6. The receiver is arranged to determine the presence of the beacon transmitter(s) but not their locations relative to the vehicle 6, and to track the relative proximity of the beacon(s) by processing a received signal therefrom. The receiver is then able to communicate this information to a driver of the vehicle 6 such that the driver will be made aware that there are a number of cyclists (or other such vulnerable road users) in relatively close proximity to the car 6. The driver is not informed of the locations of the cyclists but simply that there are a number of VRUs close by such that extra caution might be needed. It is noted that the cyclist 84 which does not actually have a transmitter in use, could nonetheless benefit from the awareness that the driver has of the mere presence of one or more VRUs. The term vulnerable road user may include any user of the roads who has a higher risk of accident or who would be more seriously hurt in the event of an accident. The term includes categories such as cyclists, riders of e-bikes or motor-bikes, horse riders and mobility scooters.

As will be explained below, the receiver 4 may be a dedicated piece of hardware that a driver has bought and set up or it may be the driver’s mobile telephone or computing device, such as a tablet device or a satellite navigation device running a particular App using the integrated connectivity of the mobile telephone itself to facilitate communication with the one or more transmitters/beacons. In one example the hardware is embodied as a keyring with a housing containing the required processing and notification functionality described in greater detail below. That way if the driver uses it to hold his vehicle keys, it means it will always be in the vehicle when the vehicle is being driven.

In the example shown, there is direct line of sight between the various transmitters and the receiver. The system can work irrespective of whether or not there is line of sight between a transmitter and a receiver.

The preferred wireless standard selected for these purposes is Bluetooth Low Energy (BLE), because of its wide availability, compatibility, range, low cost and low power demands.

Those skilled in the art will appreciate that any other wireless standards and protocols and versions of Bluetooth specification could be employed instead, with some or all of the advantages of Bluetooth LE. Advantageously the wireless standard is preferably not modified by the present invention.

Each beacon transmits an advertisement packet periodically, the interval between these being of a preferred order of 350ms, although it is possible to configure shorter or longer periods. This interval is selected as a balance between power conservation to reduce the number of transmissions, versus responsiveness and performance of the detector’s algorithms relative to the needs of the safety application. In a preferred embodiment the advertisement reuses the standard BLE advertisement, but it will be appreciated this may be any packet communicated for the purposes of the safety application. The packets used for the safety application are distinct and not the same as the standardised BLE capabilities of ‘Indoor Positioning’, ‘Find-Me’ and ‘Proximity’ profiles.

Figure 1b is a schematic view of a receiver 4 for use in a presence detection system. In the example shown the receiver 4 is provided with a housing 12 which may form part of a keyring with a connector 14 for connection to the ring itself. The housing 12 can be any desired shape and in the example shown is rectangular/cuboid. However a preferred shape might be a smooth surfaced housing in the form of, say, a pebble or a kidney. A receiving antenna 16, such as a BLE receiving antenna, is provided coupled to a signal filter 18 arranged to provide an output signal for further processing to the microprocessor 20. The filter 18 may be provided as an integrated part of the microprocessor 20. A memory 22 is arranged coupled to the microprocessor and in use can function to store data relating to detected beacons or transmitters. Described below are ways in which stored data can be used to generate such a thing as a presence map. The memory can be arranged in communication with the microprocessor to automatically remove data entries relating to a transmitter after some predetermined time period or if no refreshed transmission is received from the identified transmitter. Such processing is described in detail below.

The receiver 4 further includes a display 24 for providing or notifying a driver when a VRU is detected. This could be an electronic display such as an LCD display or one or more LEDs arranged to illuminate when a VRU or associated transmitter is detected. It is preferable that the display functions to alert a driver to the presence of a VRU and so some form of easily noticeable light or display is preferred. The receiver 4 also includes an audible alarm output 28 which may be an integrated speaker in communications directly with the microprocessor or with the display 24. A power source 26 is provided which may be a battery, e.g. such as a rechargeable and/or replaceable battery. A USB socket 30 may be provided to enable charging of the battery and/or to provide a means to download stored data from the memory 22. It will be appreciated that the hardware described with reference to Figure 1a may be provided as an appropriately configured chipset or semiconductor device.

In the example shown, the receiver is a dedicated piece of hardware. It will be appreciated that in some examples a mobile telephone or computing device, such as a tablet device or a satellite navigation device with an appropriate App downloaded can function as the receiver and/or one of the transmitters. The present invention therefore includes as one of its aspect an App, which when run on a mobile telephone or other computing device causes it to function like as receiver or transmitter as described herein.

Referring to FIG. 3, a receiver or detector monitors the BLE receive channel for all advertisements being transmitted, which may or may not be relevant to the present application, since Bluetooth is an open and widely used standard. Whenever an advertisement is received it is checked to see if it is a valid and relevant beacon, determined by the advertisement having the unique packet structure of the application and associated field properties.

It is important for a relevant beacon’s advertisements to be determined as valid, to prevent unwanted effects from occurring. The first is to prevent the inadvertent imitation of such a signal by a transmitter using the same channel and or wireless standard, but for another application. This would have the unwanted side-effect of false alarms or false positives, and thereby potentially undermine the credibility of the safety application, and run counter to the desired high-market penetration needed to maximise the overall safety benefit.

The second unwanted effect is any malicious attempt to either copy a valid beacon or mimic one in the vicinity, either identically to deliberately fool or undermine a detector, or fake (“spoof”) the genuine article. The latter is less of an issue, since if such a beacon is fully operational and carried by a VRU, it confers an equal safety benefit. However, in view of ensuring reliability of the safety application, it is preferred to thwart such an occurrence.

Bluetooth advertisements are employed by the present invention where each contains a unique identifier (ID) for the beacon and one or more fields to determine its validity for the safety application. In one preferred embodiment the unique ID may be the BLE ‘advertising address’ (AdvA), also known less formally as the BLE Media Access Control (MAC) address.

Advantageously, as part of the Bluetooth standard, that ID is generated randomly each time a beacon resets or reboots, which ensures low coincidence of the same ID being used. However, other portions of the packet payload may be used in addition for ID purposes, or in lieu of the AdvA. In the same or another preferred embodiment the 37 byte protocol data unit (PDU) of the BLE advertisement packet is used, of which for example 20 bytes may be dedicated to ensuring either the validity or the unique ID of the beacon, or both purposes simultaneously to be described shortly. In one preferred embodiment the standard altBeacon protocol is adopted only for validity checking purposes. For example the transmitted altBeacon payload data may contain a value common to all VRU beacons performing the safety application. Alternatively, the same payload data may contain a value that represents a unique mathematical relationship to the unique ID such as a hash value, which determines its validity to very high probability. In another preferred embodiment the altBeacon protocol data field is used to send a unique ID, effectively a serial number for each device, to be verified as being valid by a detector. In another preferred embodiment a proprietary version of the altBeacon protocol is employed similarly, but by which a greater portion may be dedicated to any of the previous purposes. Refer to Figure 3.

In a conventional beacon most of the information transmitted is unchanging, i.e. the advertisement structure, beacon identifier and validity fields are the same in every packet sent. This makes any naive attempt to authenticate, or likewise encrypt the packet somewhat pointless, since there is not enough variance (if any) in the information to prevent brute-force attacks.

Rather than each beacon transmitting fixed identifiers and validity codes along with only a small amount of changing information between advertisements (sequence number and or timestamp for example), in one preferred embodiment the present invention reserves some altBeacon data space to transmit a random pattern along with the other information of interest to increase greatly the entropy of each advertisement. In addition, rather than sending the information in plaintext, a symmetric secret key, or one from a set of secret keys, is used to generate a non-forgeable Message Authentication Code (MAC) and hash or sign the unique ID and or validity codes, for example these are called hash digests by those skilled in the art, along with the random field components. The irreversibility of the MAC ensures that unique IDs and validity codes are unknowable just by listening to advertisements, and also very difficult to simulate or copy. However, the same mechanism allows a detector which symmetrically knows the secret key in common with beacons, to determine with very high probability that the packet was generated by a valid and non-copied beacon, and that the message itself is not tampered with or copied as only a beacon with the correct secret key could have signed it.

In a preferred embodiment, to safeguard generating and distributing the secret key or keys and maintaining confidentiality of the keys, a hardware authentication module is used for these purposes. The hardware solution is selected to ensure compatibility between physical devices and applications run on a computing device, such that all forms of beacon and detector may collaborate in this manner, since these capabilities are also generally available in standard mobile communications devices. The hardware authentication module is used in the beacon and detector so that they may sign the MAC, and validate MAC signing respectively. This method is effective and secure at preventing cloning, spoofing and faking of beacons, and also helps prevent cloning of detectors, since without the shared secret key any such detectors will be unable to validate beacons of the present invention. Ensuring rejection of spurious beacons may also assist in suppressing a malicious (distributed) denial of service (DDOS) attack at a road junction say, by simulating very many VRUs simultaneously to overwhelm detectors, if at all possible. In a preferred embodiment SHA-256 symmetric encryption is used for advertisement signing.

In another preferred embodiment, BLE protocols may be used to determine via the advertisement whether a beacon has further scan data, which may be sent in a scan response packet. By ensuring that the safety application advertisements do communicate this feature, a detector can request that extra scan data be sent in a packet following in sequence with an advertisement. These packets are identical in size and very similar in format to the BLE advertisements, and which may be used to effectively increase the available space for identifiers, randomised fields, or any other data communications purposes, and the role may be shared and or divided across both packet types. A scan response may be requested from a beacon just once in order to test validity or authenticity, or may be requested to follow each and every advertisement where the information is regularly spread across both packet types. In another preferred embodiment, the detector may open up a two way communication stream or connection with a beacon for the purposes of transferring once or more times fields which uniquely identify or validate or authenticate a beacon, although consideration must be given to this capability still allowing the beacon to be visible to more than one detector simultaneously.

In other applications in support of the safety application, it may be desirable to associate a particular beacon with a particular user, or equally a particular detector with a particular driver. This may serve to configure devices at manufacture, as well as add valuable services over and above the primary safety application such as: voluntary registration for value added services such as proximity profiling and suggesting practical proposals to improve safety; maintenance; updates; customer support; application and or device enablement. The hardware security module may also support asymmetric public/private key encryption when an application or a device communicates with an Internet cloud service directly using the mobile network or a computing and networking platform, for example as illustrated in FIG. 5. The communication between application and device and the user’s computing and networking platform may also be over BLE. Users may register a unique identifier for their device or application that is signed by their secret key, and or encrypted by the public key of the Internet cloud service. In a preferred embodiment the information would include the unique serial number of the device, which may also be included on the packaged documentation accompanying a device.

The receiver or detector, when operational, continually maintains a Presence Model, such as is illustrated in FIG. 6. The Presence Model is preferably maintained in memory storage which may be volatile or non-volatile. The state of this model and/or changes in this state are then used to generate notifications according to a separate set of rules which may be independent of the internal rules of the Presence Model itself.

The Presence Model is effectively a list of all valid VRU beacons currently being detected, and which is modified by the reception, or lack of, valid VRU beacons in the vicinity.

Each valid beacon advertisement packet received provides instantaneous information that may be fed into the Presence Model that typically comprises: • a unique identifier for the beacon; • the calibrated signal strength of the beacon i.e. the reference signal strength indication (RSSI) at 1m in free air, transmitted in the altBeacon payload; • and a measurement of the actual received signal strength.

Referring to FIGS. 7A, 7B and 8, for each valid beacon’s advertisement received, the detector accepts the packet and determines if there is already an entry in the Presence Model with that device ID, or makes a new one in a manner that is readily searchable. For each new entry in the list the detector records, some or all of: • the unique ID of the beacon; • the time of first receipt, in seconds or milliseconds, or at the resolution required for advertisement frequency and internal processes; • the latest time of receipt, which is the time of first receipt initially; • the RSSI calibrated value, typically at 1m; • the instantaneous received signal strength; • a filtered value of received signal strength, initially set to the instantaneous value; • an advertised presence received count, set to one. A new presence event is passed to higher layer processing.

If there is already an entry in the list with the unique ID, the detector will update only relevant information: • the latest time of receipt, in seconds or the resolution required for advertisement frequency; • the RSSI value calibrated, typically at 1m, which should not change but is checked for the sake of uniqueness of the beacon should the ID not be for whichever reason; • the instantaneous received signal strength; • the advertised presence received count is incremented by one.

An updated presence event is passed to higher layer processing.

Periodically (preferably once per 5 seconds but any shorter or longer interval is possible) the presence list is pruned, by removing entries of beacon IDs for which no advertisements have been received for more than a certain interval. The preferred interval is 15 seconds, but any value lower or greater than this is possible. This removes stale records from the model.

Thus, at any point in time, the detector has a list of valid beacons that are present within receive range, their time of first detection, along with their most recent values and the receive time of the latest values.

The Bluetooth carrier frequency of 2.4Ghz results in an extremely directional signal propagation, and it is prone to incidence factors of absorption, scattering as well as reflection by different mediums, as illustrated schematically in FIG. 9. A detector may receive signals from any one beacon that may have propagated by various paths: line-of-sight or the shortest path; or the much more likely longer indirect paths that may have been reflected from a road surface, other vehicles etc. and in all likelihood have done so more than once between VRU and vehicle.

Therefore, the received signal strength will vary greatly due to these incidental factors and myriad paths between beacon and detector, and in raw form, does not reveal much about range, especially as angle of arrival is not measurable without multiple and wide-spaced antennas. Furthermore, both beacon and detector will be changing relative position (not necessarily range), at times slowly and at others rapidly, adding to the degree of variability in signal strength from advertisement to advertisement as the relative positioning within their environment changes and consequently the possible paths.

There are also “nulls”, relative positions between beacon and detector, for which there is no possible path for the transmitted signal to reach the detector with sufficient received signal strength. For example the metal body of most vehicles is a Faraday cage with limited apertures. As a result a beacon may disappear for a short period, say one or more advertisement intervals, and then reappear, despite remaining transmitting continuously and within normal receive range.

To overcome these issues the detector applies filtering algorithms that have been tuned as well as specifically developed for the present application as shown in figures 10, 11, 12.

As a first step in one preferred embodiment the detector uses a first order Infinite Impulse Response (HR) filter to effectively produce a moving average of all the received signal strengths recorded in the advertisements from each beacon. For example the filter equation is: y(n) = ax(n) + (1-a)y(n-1) where x(n) is the nth input sample, y(n) is the nth output sample, and a is a coefficient to tune the filter response.

Usually a is a scalar value selected for good step and impulse response performance, and tuned to the working environment of the safety application. In another preferred embodiment this filter is further extended to account for potentially lost advertisement packets or irregular advertisement periodicity. For these purposes a is selected to be: a = exp( -T / tau ) where 7" is the time since the last advertisement, and tau is the time filter constant.

Although there may be multiple transmission paths between a beacon and a detector, the time intervals between arrivals of the same transmitted packet would be extremely short compared to the duration of a packet. Bluetooth receivers may see these packets as either increasing or decreasing the signal strength, but a single value for signal strength will be passed on to higher processing layers. The moving average will be biased by the greater occurrence of reflected signal paths than the line-of-sight paths that typically occur. The Iine-of-sight paths ought to provide a truer indication of range. However, it is not sufficient to determine simply a maximum receive signal strength. For example, a steadily approaching beacon’s signal strength may increase or decrease depending on the path of the signal, and furthermore, line-of-sight paths are not guaranteed to occur perhaps at all. A second step in the preferred embodiment is to compute the range or proximity from the moving average (filtered) signal strength by the relation: RSSI = -10nlog(d) + RSSavg

Where: • RSSI is the received signal strength indication (dBm) that is calibrated for the beacon at a distance of 1m, and transmitted with each and every advertisement; • n is the signal propagation constant. This is a factor of 2 in free space, but may be adjusted for the particular environment in which greater losses occur; • RSSavg is the moving average (filtered) signal strength determined by the detector • d is the distance or range that may derived at this first step.

The range calculated is not intended to be accurate, but to provide an estimate of which proximity band a beacon may fall into. The preferred proximity bands are: • < 15m a very useful range of close proximity to a small vehicle; • 15 - 35m a very useful range of close proximity to a large vehicle (bus, HGV), or a range of potential danger in the immediate vicinity of a small vehicle; • 35 - 70m a range of potential danger in the immediate environs of any vehicle; • > 70m a range of reinforced awareness, particularly useful a less busy junctions which may be poorly lit. A third step in the preferred embodiment is to optimise the HR further with second order factors to filter out variations in received signal strength due to atmospheric effects, changing reflections etc. off a moving target. This may be achieved by suitable adjustment of the signal propagation constant, for example n = 1.6 is more representative of such factors. It may also be achieved by second and higher order filter terms. Additional filter orders may also be used to give more weight to stronger signals that may come in succession, since they will more likely represent direct signal paths. A fourth step in the preferred embodiment is to use updated presence events to assess motion. It is desirable for the detector to be able to determine whether a beacon is approaching or not, in order to provide a degree of prediction of movement between proximity bands, and to further mitigate the noise of the incoming signals. One preferred embodiment of motion detection is a peak signal strength detection algorithm. The detector may keep a record of the largest filtered received signal strength value from all the filtering steps, or just some of them. If the current filtered signal strength is ever greater than the previously stored peak value, then a VRU is deemed to have got closer by a significant amount. In a preferred embodiment a doubling or more of filtered average signal strength for example by 3 - 6dB, is sufficiently discernable and may be used to signify the transition between distance bands. A motion event is passed to higher layer processing. A fifth step in the preferred embodiment is periodically, for example 5 seconds but which may be more or less, to decay slowly the value stored as last peak filtered signal strength. This value is decayed slowly to address a situation in which a VRU beacon may be maintaining a relatively constant distance from the detector, e.g. cycling alongside. By decaying the signal, there is the ability to cater to the likelihood that the VRU beacon may enter nulls or suffer false negatives due to other packet loss. When a VRU beacon signal is again received, a motion event can be issued to ensure the significance of close presence is reinforced and sufficiently spaced intervals not to be a nuisance. Decaying the moving average signal, and not just the peak signal also lends a smoothing effect to the filtering process. A sixth step in the preferred embodiment is to suppress “impossible”, improbable, or fleeting glimpses of beacons. For example a beacon passing some way off at speed normal or parallel to the direction of travel of a vehicle may appear and disappear quickly, and not have a sustained presence. In order to increase the specificity (reduce false positives or unsustained presence with no normal approach or departure) such fleeting glimpses of beacons are suppressed by requiring a certain number of advertisements to be received within a certain window of time. These two parameters are fully configurable according to the environment. If an insufficient count of advertisements occurs in the designated time period, then the beacon will be simply ignored. A seventh step in the preferred embodiment is to measure the rate of change of the moving average of the proximity (velocity) and/or the second derivative of the same (acceleration) for the purposes of distinguishing distance, but also fast moving beacons versus close and slow moving ones, or for example beacons which may be suddenly accelerating either uniformly or non-uniformly - the third derivative. This information may optionally be fed up to the notification system. For example, if a beacon approaches a vehicle relatively fast, then even though it might be at a distant proximity band, e.g. > 75m, as it is moving fast enough it might cause an audible alert that it could be very close to the vehicle before the next audible alert would normally have been generated simply by calmer entry into a close proximity band, e.g. < 15m, or before a timeout has occurred for a VRU already in such a band.

Notifications to a driver from their device comprise one or more of the following (see FIGS. 13 and 14): • Visual notifications, which are always on, in all situations. Visual notifications from the device may take the form of a light or lit icon on a device’s display. When displayed on a mobile handset for example, the icon may be chosen to be smaller than the whole display available but on top of other applications (for example satellite navigation applications), and freely positioned by the user or automatically as required in landscape and portrait orientations.

Notifications may be communicated to the driver through the use of colour, flashing or blinking, and variations in blinking cadence among others. In a preferred embodiment where proximity detection range is divided into concentric circular bands of different radii, a stepped colour change may be used to indicate the proximity band(s) which have detected VRU presence: for example >70m green; 35m - 70m blue; 15m - 35m amber; <15m red, and in a preferred embodiment Presence in a more proximate band may take priority over a band further away, or the colour may alternate at a low frequency between the colours of the band(s) that contain presence.

Visual notifications may be further enhanced for awareness without being distracting by: o Implementing a slight lateral movement/jitter on a change of colour or a flash, as this technique increases detection by the human eye in peripheral vision without any need to move eyes towards the device; o Implementing changes of shape to enhance the communication: a circular shape for the visual indicator by default may become a diamond/rhombus and a hazard triangle according to the distance band; o Implementing the change of shape or colour or jitter as representative of a count of VRU devices detected, or by the rate of approach of one of more VRU devices, or any other context change in a fully programmable manner. • Audible notifications, which may only apply to a subset of or all situations. Audible notifications from the device may take the form of one or more sounds, ideally of short duration, which are played directly by the device or through the vehicle audio system.

The sounds may be additional to other sounds, music or conversations already in progress, or may cause any other in-progress sounds to be muted or attenuated. In a preferred embodiment there may be an audible notification of a bike bell (tring) for a significant event such as a VRU newly entering a distance band. In a preferred embodiment this may be reserved only for new presence within the innermost distance band for which road user reaction times are significant determinants of safety. Another audible notification may not play again until either all VRU devices have left the band and a new VRU device is again first detected, or may play again following a time-out on a new VRU device being detected even when there are already other VRU devices still present in the band.

Audible notifications may be further enhanced for awareness without being distracting by: o Implementing notifications for more than one new VRU being detected; o Implementing notifications following a time-out regardless of a new VRU being detected but where there is continued presence in a (critical or innermost) distance band; o Implementing variations in pitch or cadence to signify other events such as VRU speed of approach, VRU presence density, VRU departure; o Implementing more than one sound for different events; o Implementing some user programmability in the choice of sound; • Haptic notifications, which may only apply to a subset of or all situations. Haptic notifications from the device may take the form of communication with additional wired or wireless devices or the vehicle systems in the form of a vibration or change of feel. In a preferred embodiment this may be a vibration of the steering wheel or the smoothness/roughness of a steering wheel cover for example.

In a preferred embodiment a VRU would have no notifications from their device. They would use the road normally and rely on their own awareness. A VRU device would normally have no detection capability, unless used automatically to relay information without the VRU being aware, and the VRU should simply assume all drivers may be unequipped and take normal precautions, and assume any driver is unaware of their presence.

In a preferred embodiment, a driver’s device provides no “clear of VRUs” signal. This encourages the driver to remain aware, and that awareness is simply reinforced by any (further) notification. Time-outs ensure that notifications are sufficiently spaced not to annoy, yet frequent enough for reinforcement, and remain credible and not haphazard, which may cause the device to cease to be used.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.

Claims (27)

CLAIMS:

1. A presence warning device comprising a detecting receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged based on a received signal to determine the presence of the beacon transmitter but not its location relative to the vehicle, and to track the relative proximity of the beacon by processing the received signal therefrom.

2. A presence warning device according to claim 1, wherein the detector maintains a presence model to retain, update and process information on each detector connected to it.

3. A device according to claims 1 or 2, wherein the detector calculates proximity estimates within predetermined distance spans forming concentric rings around the detector.

4. A device according to any claims 1 to 3, wherein the receiver is arranged to receive and process data according to the BLE protocol.

5. A device according to any of claims 1 to 4, wherein the detector comprises an alarm to provide an indication to a user when a road user is detected to be within a defined proximity to the device.

6. A device according to any of claims 1 to 5, comprising a processor arranged to determine acceleration of the transmitter in dependence on a received signal.

7. A device according to any of claims 1 to 6, wherein the processor is arranged to apply a filtering algorithm to apply a filter to a received signal from a transmitter to determine data relating to parameters of the transmitter.

8. A device according to any of claims 1 to 7, wherein the detecting receiver is arranged to avoid repetition of alerts within a period of less than a predetermined time period.

9. A device according to claim 8, in which the predetermined period within which repetition of alerts is avoided is one of 5 seconds, 10 seconds and 30 seconds.

10. A device according to claim 8 or 9 in which the length of time within which repetition is avoided is determined based on parameters associated with the transmitter.

11. A device according to claim 7, wherein the filter is an infinite impulse response (HR) filter arranged to produce a moving average of all received signal strengths for each transmitter.

12. A device according to claim 11, wherein the filter is arranged to optimise the HR using second order factors to thereby filter out variations in received signal strength due to atmospheric effects and/or reflections from a moving target.

13. A device according to claim 12, arranged to update presence events to assess motion.

14. A device according to claim 13, arranged to decay slowly the value stored as the last peak filtered signal strength thereby dealing with a situation in which a transmitter maintains a relatively constant distance from a detector.

15. A device according to any of claims 1 to 14, in which the receiver is arranged to measure the rate of change of a moving average of the proximity and/or second derivative of the proximity for the purpose of distinguishing distance of a transmitter from the receiver.

16. A device according to any of claims 1 to 15, wherein the receiver is arranged to provide a notification in the form of one or more of a visual notification or an audible notification to a user.

17. A device according to any of claims 1 to 16, embodied as a mobile telephone or computing device running thereon an App to provide the specified functionality.

18. A device according to any of claims 1 to 16, embodied as a dedicated item of hardware, to provide the specified functionality.

19. A presence warning system, comprising a detector according to any one or more of claims 1 to 18 and a plurality of beacon transmitters, each beacon transmitter being associated with a road user and arranged to communicate with the detector.

20. A method of warning a driver of a vehicle of the presence of a road user, comprising providing a receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged to determine based on the received signal the presence of the beacon transmitter, but not its location relative to the vehicle and to track the relative proximity of the beacon by processing the received signal therefrom.

21. A method according to claim 17, comprising, at the receiver, measuring the rate of change of a moving average of the proximity and/or second derivative of the proximity for the purpose; and based thereon, distinguishing distance of a transmitter from the receiver.

22. A method according to claim 20 or 21, comprising using a receiver according to any one or more of claims 1 to 19.

23. A beacon transmitter associated with a road user and arranged to communicate with a detector, the transmitter being arranged to transmit a signal to inform a detector of its proximity to a vehicle, but not its location relative to the vehicle.

24. A transmitter according to claim 19, in which the transmitter is arranged to communicate using BLE protocol.

25. A transmitter according to claim 23 or 24, arranged to communicate with a receiver according to any of claims 1 to 19.

26. An App comprising program code, which when run on a computing device such as a mobile telephone causes the mobile telephone to function as a detecting receiver for use by the driver of a vehicle, the receiver being arranged and configured to receive a signal from a beacon transmitter associated with a road user, whereby, in use, the receiver is arranged based on a received signal to determine the presence of the beacon transmitter but not its location relative to the vehicle, and to track the relative proximity of the beacon by processing the received signal therefrom.

27. An App according to claim 26, wherein the receiver that the mobile telephone is caused to function as, is a receiver according to any one or more of claims 1 to 19.