Sports tracking

Abstract

A method of identifying position of electronic devices on a sports field. The method comprises retrieving a position measurement of at least three first moving electronic devices and calculating a linear distance between a second electronic device and the at least three first moving electronic devices using a short-range radio signal. The method also comprises calculating a position of the second electronic device based on the position measurements of the at least three first moving electronic devices and the linear distances.

Description

[0001] SPORTS TRACKING

[0002] BACKGROUND

[0003] The tracking and monitoring of athletes in real-time is of great interest to players, coaches, broadcasters and fans. In the past, this has been achieved using a combination of a Global Navigation Satellite System (GNSS) to identify position of the players and a wireless protocol, such as Bluetooth (RTM) or Wi-Fi (RTM) to offload data to remote servers.

[0004] GNSS based solutions, which remain the industry standard, are able to determine position to only an accuracy on the order of one meter and are even more inaccurate in dense or built-up areas, such as stadia. More recently there has been a shift to ultra-wideband (UWB) systems, which can accurately locate players and equipment in real-time and in such a way that the data is not affected by the noisy radio frequency (RF) environment that is often present in crowded stadia.

[0005] A typical UWB system uses a combination of tags (electronic devices which are mobile and which are actively tracked) and anchors (electronic devices which are fixed in known positions and form a reference system, relative to which the tags are located). The tags are worn by athletes, or are embedded within sports equipment, and are thus representative of movement of the athlete or the equipment.

[0006] The use of a set of stationary anchors for UWB ranging works well in many scenarios. If the positions of the anchors are accurately known then the mobile tags worn by the players may be located to a similarly high accuracy. However, there are scenarios where using fixed anchors is inconvenient. Installation of these fixed anchors is time-consuming, expensive and a source of irritation for potential users, since the players or equipment can only be tracked at the location where the anchors are installed, for example stadia or defined training pitches. The anchors must be accurately installed using complicated survey equipment to be confident of relative location. Stationary anchors are typically placed at high elevations to improve signal accuracy and to mitigate the human body effect which causes interference in the signals between the tags and the anchors (interference caused by the human body). For example anchors may be affixed to lighting poles or to the roof of a venue. This brings with it significant additional challenges. Mounting the anchors high-up is dangerous for the installation technicians and so the installation takes longer and is more expensive. Certain venues do not have convenient infrastructure on which to mount the anchors, and at these venues large tripods must be used, or long poles installed into the ground. This additional infrastructure adds to the cost of the installation. Moreover anchors often need to be accurately located using survey equipment which inhibits usability.

[0007] Tracking systems have been described which combine GNSS and UWB technologies for accuracy reasons or to mitigate the above deficiencies of the use of UWB. In contemporary sports situations GNSS is used to determine position while UWB is used to offload data to a single anchor to minimise the amount of pitch-side infrastructure needed and reduce the effect of the noisy RF stadium environment. UWB has also been proposed as an augmentation or alternative to GNSS, making use of fixed anchors placed around the field of play but using GNSS as the primary tracking technology. For example, WO 2017 / 174956 proposes a system where position is calculated using both a GNSS technique and an UWB technique and the best candidate position is chosen. In other fields, for example in the tracking of drones, GNSS and UWB technologies are used in conjunction with one another to enable the drone to navigate both indoors within a UWB infrastructure and outdoors where GNSS takes over.

[0008] GNSS-led solutions are generally undesirable as performing regular position measurements requires significant battery power which makes electronic devices heavy and impractical for use in high-performance events. Moreover the power requirements, size and weight of devices incorporating GNSS technology is prohibitive when incorporating the devices into equipment which will be affected by size and weight, such as a ball. Any incorporated electronics must be so light as to not affect the flight or feel of the ball and GNSS cannot therefore be used.

[0009] Contemplated alternatives for tracking the ball include the incorporation of a short-range beacon into the ball. The short range beacon indicates possession of the ball by proximity to a single data logger worn by a player. The beacons utilise radio frequency signals at a frequency which is not attenuated by the body of the players.

[0010] The reliance on pitch-side infrastructure such as stationary, fixed anchors in realtime sports tracking significantly limits the usage and adoption of sports tracking systems. Moreover there remains no practical solution to enable lightweight tracking of sports equipment, such as the ball, where no pitch-side infrastructure is available.

[0011] SUMMARY OF THE INVENTION

[0012] The present invention provides a system and method for accurate, real-time object tracking without the need for fixed anchors. The invention is further able to determine the position of an element without that element having a GNSS module.

[0013] According to an aspect of the invention there may be provided a method of identifying position of electronic devices on a sports field, the method comprising: retrieving a position measurement of at least three first moving electronic devices; calculating a linear distance between a second electronic device and the at least three first moving electronic devices using a short-range radio signal; and calculating a position of the second electronic device based on the position measurements of the at least three first moving electronic devices and the linear distances. The second electronic device may preferably be a moving electronic device.

[0014] In this way, the position of the second electronic device can be accurately determined without the need for fixed anchors around the periphery of the field and without the associated problems of installation of those anchors. Moreover, the second electronic device can be accurately located using a lightweight mechanism, e.g.. ultra-wideband signals or other wireless technology. A GNSS module is not required in the second electronic device which means that the location of a ball can be accurately tracked using the second moving electronic device where GNSS is prohibitive. The position of the second electronic device can be more accurately determined than those used for similar devices in the art and can be determined and / or data offloaded in real-time.

[0015] Preferably the short-range radio signal is an ultra wideband radio signal. Alternatively, the short-range radio signal may be Bluetooth (RTM), Bluetooth Low Energy, NB IOT, Zigbee or Thread. The short-range radio signal may be configured to create a local positioning system with the first moving electronic devices.

[0016] Preferably, the method further comprises adjusting one or more of the position measurements based on the linear distances. The accuracy of the position measurements of the first moving electronic devices can be corrected, calibrated or adjusted based on the relative position of the second moving electronic device. For example, where the first moving electronic device is attached to a player and the second moving electronic device is embedded within a ball, the ball device can correct for errors in the player position caused by bias, drift or interference. The ball device can thus act as a central ‘hub’ to correct the player device positions. The ball device is able to lock the player devices or ‘spokes’ by acting as a central fixed hub about which the other devices can be located. The linear distances determined using the ultra-wideband signal may be assumed to be more accurate or at least more consistent than the position determination of the first moving electronic devices, that is because of the GNSS accuracy or the human body effect.

[0017] The step of adjusting may comprise applying a least squares regression model to the position measurements and the linear distances to adjust the one or more position measurements. Other suitable regression, maximum likelihood, entropy or best fit models may be used. In this way, the adjustments may improve the position determination of the first moving electronic devices by using a common parameter, that is, the more accurate distance to the second moving electronic device.

[0018] The step of retrieving a position measurement may comprise retrieving a GNSS position measurement of at least three of the at least three first moving electronic devices. The use of GNSS measurements facilitates position determination without the use of pitch-side installations or infrastructure and as such the system can be used on training pitches or on any non-permanent location. The use of short-range radio signals such as ultra wideband to locate the second electronic device relative to the GNSS located devices means the second electronic devices can be located without a GNSS module as well as without pitch-side infrastructure. Accuracy problems caused by line of sight challenges are obviated.

[0019] The step of retrieving a position measurement may comprise: calculating a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal, wherein the at least three stationary anchors have a known position in a coordinate system.

[0020] The step of retrieving a position measurement may further comprise calculating a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal in a local positioning system, preferably an ultra wideband positioning system.

[0021] When the second moving electronic device is incorporated into a ball, for example, the ball can be located without communicating with pitch-side infrastructure and can be located accurately and with minimal power requirements. In addition, when combined with the step of adjusting above, the second moving electronic device can be used to compensate for errors in the position determination of the first moving electronic devices. This may mitigate some of the installation requirements of the pitch-side infrastructure and reduce accuracy problems caused by line of sight challenges or the human body effect.

[0022] Both a local positioning system such as ultra wideband and a global positioning system such as GNSS may be used to provide the position measurement of the first moving electronic devices or the second electronic device or any combination, with the calculated linear distances used to supplement or correct the calculated position measurements.

[0023] In this context, each refers to every one of two or more people or things regarded and identified separately.

[0024] The stationary anchors may be transitory and configured to be positioned around the periphery of a sports field.

[0025] The step of calculating a position of the second moving electronic device may comprise identifying the position of each electronic device in a coordinate system.

[0026] The second electronic device may be inserted into a sports ball. Thus the ball may be located without a full pitch-side infrastructure installation and preferably without a GNSS module.

[0027] Preferably the at least three first moving electronic devices may each be attached to an article of clothing worn by a sports player.

[0028] Calculating a linear distance using a short-range radio signal may comprise determining the linear distance using two-way ranging. Two-way ranging provides accurate determination of the linear distance. The two-way ranging may be for example symmetric two-way ranging.

[0029] The second electronic device may act as a master clock and each of the at least three first moving electronic devices may synchronise in time from the master clock. Thus, the hub of the architecture, i.e. the second moving electronic device, may be used to improve the accuracy of the system and act as a consistent element to enable synchronisation and correct for drift and bias. The master clock may be used to synchronise all the devices to the same time using a timing network.

[0030] The at least three first moving electronic devices may synchronise in time using the two-way ranging message, that is using the communication used to identify the linear distance between the first and second devices.

[0031] The method may further comprise: calculating a linear distance between the second electronic device and a stationary anchor, wherein the step of identifying a position of the second electronic device is further based on the linear distance between the second electronic device and a stationary anchor. Thus a stationary anchor may be used to improve the accuracy of the position determination without a full pitch-side infrastructure installation. The stationary anchor may also be used for data offload such that data offload can be facilitated in real-time while also contributing to positional accuracy.

[0032] The method may further comprise: calculating a linear distance between each of the at least three first moving electronic devices and a stationary anchor; and, adjusting the position measurements of the at least three first moving electronic devices based on the linear distance between each of the at least three first moving electronic devices and the stationary anchor. As above, the stationary anchor may be used to calibrate, compensate or adjust the position measurements. For example, if the position measurements are determined by GNSS, a full pitch-side infrastructure may not be required to compensate or calibrate the measurements.

[0033] The method may further comprise synchronising a clock of one or more of the electronic devices with the stationary anchor. Thus the stationary anchor which may optionally be used for data offload may also be used to synchronise the devices so as to compensate for drift or bias. The method may comprise determining a rigid topology of the electronic devices from the linear distances. The rigid topology may be used to adjust a position of one or more of the electronic devices or identify a position of a further electronic device. The rigid topology may for example be a rigid polytope where an amount of linear measurements between nodes are identified in order to make the topology rigid. A topology is rigid if it cannot be continuously deformed into another configuration.

[0034] Power consuming GNSS measurements need not be obtained with the same regularity as the UWB measurements. Once the topology of the nodes is known, the accurate UWB measurements can be used to identify distances or locations and more particularly distances changes. Thus, the GNSS measurements may be made less frequently while maintaining accuracy of the system.

[0035] Preferably the method further comprises determining arrangement of the device topology using an estimation algorithm configured to estimate parameters which best fit the position measurements (e.g. GNSS). Parameters include for example rotation, translation and reflection. More preferably the estimation algorithm includes a least-squares model. The inaccuracy of the position measurements can be compensated for using the accurate UWB measurements and the UWB measurement topology of which the accuracy can be confidently assumed is made to best fit the position measurements by solving for the rotation, translation and reflection parameters to approximate the topology to the position measurements.

[0036] According to a further aspect of the invention there may be provided a computer readable medium comprising instructions which when executed by a processor cause the processor to carry out the method of any of the above aspects of the invention.

[0037] According to a further aspect of the invention there may be provided a system for identifying position of moving electronic devices on a sports field, the method comprising: at least three first moving electronic devices configured to be embedded within sports equipment on a sports field, each first moving electronic device comprising a device antenna connected to a respective device transceiver; a second electronic device configured to be embedded within sports equipment on a sports field, the second electronic device comprising a device antenna connected to a respective device transceiver; and, a metric server, wherein the metric server is configured to: identify a linear distance between the second electronic device and the at least three first moving electronic devices using a short-range radio signal; retrieve a position measurement of the at least three first moving electronic devices; calculate a position of the second moving electronic device based on the position measurements of the at least three first moving electronic devices and the linear distances. The short-range radio signals may be ultra wideband radio signals.

[0038] The functionality of the metric server may be performed by one or more of the electronic devices or alternatively any pitch-side infrastructure.

[0039] The metric server may be further configured to adjust one or more of the position measurements based on the linear distances. The metric server may be further configured to apply a least squares regression model to the position measurements and the linear distances to adjust the one or more position measurements. The metric server may be configured to retrieve a position measurement by retrieving a GNSS position measurement of at least three of the at least three first moving electronic devices.

[0040] The system may comprise at least three stationary anchors and wherein the metric server is configured to retrieve a position measurement by identifying a linear distance between each of at least three of the at least three first moving electronic devices and three stationary anchors calculated using an ultra- wideband radio signal, wherein the three stationary anchors have a known position in a coordinate system. The three stationary anchors may be transitory and configured to be positioned around the periphery of a sports field. The metric server may be configured to calculate a position of the second electronic device by identifying the position of each electronic device in a coordinate system.

[0041] The metric server may be configured to: calculate a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal in a local positioning system, preferably an ultra wideband positioning system.

[0042] The second electronic device may be configured to be inserted into a sports ball.

[0043] The at least three first moving electronic devices may each be configured to be attached to an article of clothing worn by a sports player.

[0044] The linear distances may be determined using two-way ranging. The second electronic device may be configured to act as a master clock and each of the at least three first moving electronic devices may be configured to synchronise in time from the master clock. The at least three first moving electronic devices may be configured to synchronise in time using the two-way ranging message.

[0045] The metric server may be configured to identify the position of the second electronic device based on a calculated linear distance between the second electronic device and a stationary anchor. The metric server may be configured to adjust the position measurements of the at least three first moving electronic devices based on a calculated linear distance between each of the at least three first moving electronic devices and the stationary anchor. The electronic devices may be configured to synchronise a clock with the stationary anchor.

[0046] The metric server may be configured to determine a rigid topology of the electronic devices from the linear distances.

[0047] According to a further aspect of the invention there may be provided a method of adjusting a determined position of moving electronic devices on a sports field, the method comprising: retrieving a position measurement of at least three first moving electronic devices; calculating a linear distance between a second electronic device and the at least three first moving electronic devices using a short-range radio signal; and adjusting one or more of the position measurements based on the linear distances. The step of adjusting may comprise applying a least squares regression model to the position measurements and the linear distances to adjust the one or more position measurements. Other suitable regression or best fit models may be used.

[0048] DETAILED DESCRIPTION

[0049] Examples of systems and methods in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

[0050] Figure 1 shows a high-level schematic diagram of a prior art system;

[0051] Figure 2 shows a high-level schematic diagram of an alternative prior art system; Figure 3 shows a schematic diagram of three player tags and one ball tag;

[0052] Figure 4 shows a schematic diagram of a system for tracking objects on a sports field;

[0053] Figure 5 shows adjustment of position measurement of three player tags using distances to a ball tag; and,

[0054] Figure 6 shows a schematic diagram of a system for tracking objects on a sports field;

[0055] Figure 7 shows a schematic diagram of four tags, three anchors and a possible configuration on the field;

[0056] Figure 8 shows a flow diagram of a process according to an example of the present invention.

[0057] The following are examples of systems and methods for tracking and monitoring of movable elements, such as players and balls, in complex sports such as Rugby Football. The principles are also applicable to American Football, Soccer and other sports. The principles described are usable for performance analysis and training purposes as well as officiating and broadcasting. More specifically the exemplary concepts relate to a set of wearable devices on the players and devices embedded into the ball, or other equipment, which enable real-time detections to be made with high accuracy and precision without the need for fixed infrastructure and without prohibitive GNSS technology.

[0058] Known state of the art systems for location detection in sports include those disclosed in GB 2,541 ,265, which is hereby incorporated by reference. In this example system, wearable devices use ultra-wideband transceivers to communicate with devices at the side of the field which calculate the position and orientation of the devices from the signals received. More widely used systems include data loggers which utilise the Global Navigation Satellite System (GNSS) as well as accelerometers and gyro sensors to track position and record the speed and position of a player as they move around a pitch. The position of the player and their wearable device is calculated using a series of satellites or nodes positioned around the playing area which communicate with the device using 2.4GHz wireless communication, such as Wi-Fi (RTM) or Bluetooth (RTM).

[0059] Figure 1 illustrates a system of the former example of the state of the art. In this example system, wearable devices use a combination of an ultra-wide band (UWB) transceiver and an Inertial Measurement Unit (IMU) to determine of the location, velocity, acceleration and angular orientation of the player. These devices may broadcast their data in real-time to apparatus at the side of the field or offload the data after the recording activity.

[0060] Known figure 1 illustrates a rugby pitch 10 on which is positioned an article of body armour 11 to be worn by a player, as is typical in Rugby Football. Positioned around the pitch 10 are a series of anchors 13. A central server (not shown) is used to process the data channelled from the players and equipment.

[0061] As will be understood, the terms beacons, radio-beacons, anchors and antennas signify the apparatus installed around the periphery of the field and are used interchangeably. The anchors may comprise an UWB receiver, a processor and one or more antennas. Embedded within the body armour 11 in this example is an electronic device 12 which includes an antenna and one or more ultra-wide band (UWB) transceivers. The UWB transceivers in the electronics device transmit a narrow pulse in the time domain, or ‘chirp’, which is detected by the anchors at different times. The anchors perform Angle of Arrival (AoA), Time Difference of Arrival (TDoA) or Time of Arrival (ToA) calculations to determine the player’s position. The principles behind AoA, TDoA and ToA are well known and will not be described in detail here. Similarly, the principles behind two-way ranging, symmetric two- way ranging and asymmetric two-way ranging which may be used are well known and well documented.

[0062] In the example of the art illustrated, to determine position, multiple signals can be compared to trilaterate and / or multilaterate the position once the relative positions of the fixed anchors are known. Each anchor may be connected to the others wirelessly or through fixed or wired communications. Each anchor may also be connected solely to a master anchor which gathers together data from each anchor and instructs each anchor to act. The master anchor may be connected to a server or the server may act as the master and coordinate the anchors.

[0063] The master anchor may also function to set the reference coordinates to (x,y,z) (0,0,0). Thus the reference frame against which the orientation of the device is determined is set by the master anchor. The coordinates of the reference frame are then based on the position of other anchors. In order to determine the reference frame for position and orientation, more than one point is needed. Each anchor position is determined relative to each other and then positioned on the frame, all relative to the master. The position and orientation of the device can therefore be considered to be relative to the frame set by the anchors. The origin may be placed anywhere on or around the pitch, but preferably the y-axis is placed at the halfway line. The other side of the halfway line would therefore be, for example, (0, 70, 0). The terms tag, electronic device, Sports Monitoring Device (SMD), wearable, and embedded device are used interchangeably throughout the present application.

[0064] Player tracking has been predominantly accomplished through the use of GNSS (for example GPS or Glonass) as an alternative to UWB as shown in figure 2. A GNSS receiver 22 is embedded within the body armour 11. GNSS receiver 22 measures the transmitting time of GNSS signals emitted from four or more GNSS satellites 24 and these measurements are used to obtain its position (i.e. , spatial coordinates) and reception time. Data from the GNSS receiver 22 can be offloaded using a wireless protocol, such as Bluetooth (RTM) or Wi-Fi (RTM), or using an UWB radio signal to a remote server (not shown). The coordinate system for the position is typically set using the GNSS technology.

[0065] As described above, the systems of figures 1 and 2 introduce inherent compromises. UWB systems require expensive and complicated infrastructure and cannot be easily translated to other arenas while GNSS systems are inaccurate and require heavy and power-consuming receivers.

[0066] In the present description a system is proposed for tracking tags accurately without the need for anchors. That is, without the need for fixed infrastructure of which the position is known to a high degree of accuracy. Moreover the systems propose a lightweight approach to tracking certain movable equipment without fixed anchors and without the installation of GNSS electronics within the device which is heavy and highly power consuming (thus requiring impractical charging and power infrastructure). In an example, it is not possible to install GNSS technology in a sports ball as to do so would affect gameplay.

[0067] The following provides examples according to aspects of the present invention. In the described detailed examples below, there are two types of tag. A first type of tag is configured to be embedded or attached to clothing worn by a player on the field. A second type of tag is configured to be inserted into a ball. Throughout the present description we will refer to the terms player tag and ball tag. By these terms it will be understood that either the player tag or ball tag could be incorporated into any equipment on the field and could incorporate functionality from the other type of tag. We use the terms player tag and ball tag merely for ease of understanding to refer to a first moving electronic device and second electronic device, which may also be moving. Conceptually, the ball tag is a lightweight tag and is thus suitable for being embedded in any equipment where weight is important.

[0068] It is emphasised that the second device may be any object of interest in the region of interest, for example a goal post or any other fixed or moving device to be positionally located relative to the moving players.

[0069] Each of the tags includes an UWB transceiver to determine relative distance to one or more of the other tags. UWB signals are used to determine a relative distance between the ball tag and at least three of the player tags. The system determines position of the player tags in a coordinate system and using the position of the player tags and the distance of the ball tag to the player tags, the system trilaterates and / or multilaterates the position of the player tag.

[0070] Figure 3 schematically illustrates the principles described herein. In this example, the player tags 32 include a GNSS receiver and an UWB transceiver. The player tags each obtain their position using signals received from GNSS satellites 24. The ball tag 35 does not include a GNSS receiver, instead including only an UWB transceiver. The ball tag 35 and player tags 32 communicate with each other using UWB radio signals to determine a relative linear distance.

[0071] The relative linear distances and player tag 32 position measurements may be transmitted to a remote server (not shown), preferably using UWB as the data offload method. At the remote server, the relative linear distances and positions may be used to calculate the position of the ball tag. Similarly, the position measurements of the player tags 35 may be sent to the ball tag 35 which may calculate its position using the relative linear distances and the position measurements. Multilateration, trilateration or true range multilateration are examples of techniques which may be used to identify the position of the player tag using the relative linear distances.

[0072] It should be noted that at least three relative linear distances are preferred to accurately identify the position of the ball tag 35. Thus, further player tags 32 may only optionally communicate with the ball tag 35 but may determine position using GNSS.

[0073] The position of the ball tag 35 may be calculated according to the GNSS coordinate system. The GNSS measurements may alternatively be translated into a local coordinate system, for example, relative to the sports field and the ball tag 35 position may be calculated according to the local coordinate system. The coordinate system may be set by the sports field either through predetermined calculations, through an additional tag or anchor placed on or around the pitch (see below) or by mapping the GNSS data to known data for the sports field.

[0074] The anchors described herein may be stationery and transitory but not necessarily permanent.

[0075] The process by which tags may identify a relative linear distance to another tag is well known in the art. A preferred technique is ultra-wideband two-way ranging or, optionally, symmetric two-way ranging. Since there are no anchors (in this example) the tags identify their position relative to one another rather than relative to anchors. Accordingly each tag may be thought of to function as an anchor as well as a tag in standard two-way ranging parlance. Alternatively, the system may be thought of as having no anchors at all and only tags.

[0076] Throughout the present disclosure, reference will be made to ultra wideband as an example of a short-range radio signal suitable for calculating a distance. Any suitable wireless technology may be used such as ultra wideband, BlueTooth (RTM), Bluetooth Low Energy, NBIoT, Zigbee or Thread. In all instances, the wireless technology is used to determine a relative location of the tag while the other tags use a different locating technique. In one descriptive example, at any instant in time, the player tags form a local positioning system network where other objects of interest can be located with respect to them using any relevant technology. The player tags form a local positioning system network at any instant in time because at that instant they are stationary and are effectively anchors.

[0077] Since ranging techniques are well known and well documented, we do not describe them in detail here but for context we provide a high level summary. A first device A may send a poll message to a second device B. An acknowledgement of that poll is returned by the second device B. A final message is sent from the first device A in reply to the acknowledgement. From these three messages the second device B can identify its distance to the first device A. Each of the three messages may contain the time at which it was sent. By identifying the time at which the poll message received, the second device B can calculate the signal propagation delay of the poll message. The second device also knows the processing delay representative of the time it takes the second device to process the poll, generate the acknowledgement and transmit it. A further propagation delay is identified which is the time it takes for the acknowledgement message to return to the first device A. This time (or delay) is included in the final message from the first device A to the second device B. Using these three pieces of information, the second device B can accurately identify its linear distance from the first device A. Optionally, a verify message may be sent from the second device B to the first device A after the reply message so that the first device A can check the measurements and accurately determine its distance taking into account clock or other errors.

[0078] In certain embodiments the ball tag 35 may act as a master clock. The remaining tags 32 may synchronise in time with this master clock. Techniques for compensating for clock drift are well known in the art. For example, if a message is sent from the master tag at regular intervals, the other tags can time these messages relative to their own clocks. If these messages are identified at unexpected times then the clock may be inaccurate relative to the master. Not all tags need to communicate with the master to synchronise clocks, as the compensation can be propagated from tag to tag.

[0079] Optionally, a different device from the tags may act as the master to synchronise clocks and / or organise the timing network, for example, a pitch-side device or master anchor, as illustrated in examples below.

[0080] The techniques for compensating for clock drift may be part of a timing network. Such timing networks are well known. The timing network is used to arrange the communication of tags. Each tag may be assigned a seat or timeslot within which they may communicate to reduce interference. Accordingly the timing network may be used to assign each of the tags a time period within a wider time period during which distance measurements may be made to the other tags. The master may optionally arrange this orderly signalling.

[0081] In a preferred implementation, each tag may be assigned a predetermined seat prior to the process beginning and this may be given to the master tag to coordinate the position measurements. Alternatively a master tag may wake up and broadcast a message asking for replies from tags in communication range and the master may generate the list of tags and seats using a discovery process, that is, the master may optionally assign to the available tags a timeslot within which to send and receive its distance measurement messages.

[0082] The tags may each store the distance and / or GNSS position data associated with a timestamp of the time that measurement was made in a datalogger internal to the device.

[0083] These timestamped distance measurements may be offloaded to a remote server in real-time or offloaded in a batch. The specific method of data offloading to a server is not important to the innovation. The algorithms described may be performed at a remote server on saved measurements however it is equally contemplated that the location determined may be performed on one or more of the tags themselves and the accurately determined positions stored or sent to a remote location. Similarly the algorithms may be distributed across the devices, each performing certain steps at different locations.

[0084] Figure 4 illustrates schematically the system of figure 3 however in this example there is a static anchor 33. The static anchor 33 may comprise at least one antenna and an UWB transceiver. In this example the ball tag 35 may communicate using UWB with the static anchor 33 and using these signals the system can identify the relative linear distance of the ball tag 35 and the static anchor 33. This latter relative linear distance can be used in the position calculation of the ball tag 35. Since the static anchor 33 does not move, the position determination of the ball tag 35 can be improved.

[0085] The static anchor 33 may also be used as the master clock (or master anchor) in a timing network in a similar manner to that described above. Additionally, the static anchor 33 may function to define the local coordinate system within which the tags 32, 35 are located. In this way, the static anchor can be located relative to the sports field and the tags 32, 35 accurately located on that field.

[0086] As illustrated in figure 4, data offload to a remote server 46 may be performed via the static anchor 33. Data from the player tags 32 may be sent via the ball tag 35 (or directly to the static anchor) and stored in a database 47 in communication with the server. The use of UWB for data offload allows the player’s biometric data and location to be transmitted in real-time, even in a crowded stadium environment. The terms remote server and metric server will be used interchangeably herein.

[0087] It is further proposed that the relative linear distances may be used to adjust, correct or otherwise calibrate the GNSS measurements. For example, since the UWB measurements are assumed to be of high accuracy, the relative distance measurements between the ball tag 35 and the player tag 32 can be used to correct the GNSS position measurements without the introduction of multiple pitch-side anchors and without accurately locating that infrastructure using survey equipment. It is contemplated that the adjustment, correction or calibration of the position measurements of the player tags may be performed using the relative linear distance measurements independently of calculating the position of the ball tag. That is, there may be no need to calculate a position of the ball tag but the ball tag may still be used to improve the position measurements of the player tags (calculated using GNSS here or UWB as described below).

[0088] Use of the ball as the adjustment ‘hub’ (see below) is beneficial as the ball is close to the players and moves with play in congested environments so may substantially improve accuracy of adjustment.

[0089] Preferably the implementation of the process applies an estimation algorithm to the data stored and the GNSS measurements. For example, the estimation algorithm may be a least squares or least square error algorithm to fit the data. Many different estimation, adaption or approximation algorithms are contemplated as would be understood by the skilled person. The preferred approach is a least-squares regression model, which solves for the most approximate adjusted parameters. Any suitable method for estimating the most likely combination of parameters to fit the GNSS measurements is contemplated here. Recall that the UWB measurements are considered more accurate in most circumstances and subsequently fit to inaccurate GNSS measurements in the best or most likely way.

[0090] In an example, a topology may be created from the relative linear distances. The topology may form a rigid polytope such that the algorithm may solve for a possible translation, rotation and flip of the topology that most likely fits the GNSS measurements. The algorithm can be considered to apply a sequence of linear transformations and minimise the variables by minimising an error function. The algorithm solves the linear transformation and does not need to actually calculate the translation, rotation and reflection parameters. In this example, sufficient relative linear distances between the player tags 32 and the ball tag 35 (or static anchor as explained elsewhere) will be required to form a rigid polytope. In other words the process finds a transformation that minimises the distance between the GNSS position information and the node while keeping the UWB topology intact. The linear transformations are solvable using any known technique.

[0091] Alternatively, the method may fix one node using its GNSS measurement and then match the remaining nodes to the most likely position by finding the best fit to the remaining measurements.

[0092] Conceptually, the adjustments are illustrated in figure 5. The tags are shown as whole circles and the GNSS measurements of the tags are shown as clear circles. The estimation algorithm solves for the best fit of possible parameters that fits the UWB measurements to the GNSS measurements. Since the UWB are considered to be more accurate than the GNSS measurements, preferably the UWB measurements do not change but the estimation algorithm determines the most likely approximation of that arrangement to the GNSS measurements.

[0093] In this way the process has used UWB measurements to compensate for inaccurate GNSS measurements. Alternatively it can be considered that the GNSS measurements are used to fix the UWB based measurements to a fixed configuration.

[0094] From figure 5 it can be seen that conceptually the system may be thought of as a ‘hub and spoke’ where the ball tag 35 is the ‘hub’ and the relative linear distances to the player tags 32 are the ‘spokes’.

[0095] Figure 6 illustrates an addition or alternative to the example of figures 3 and 4 in which the player tags 32 additionally communicate using UWB signals to the static anchor 33. The UWB signals can be used to offload data but additionally, can be used to provide a further relative linear distance measurement. The relative distance measurement between the player tag 32 and the static anchor 33 may be used to adjust the GNSS measurement of each player tag 32 either in isolation, in an additional calibration step performed in advance or as an addition to the estimation algorithm, e.g. the least-squares regression model. In this latter example, the relative linear distance to the static anchor is given the highest priority as it is considered the most reliable. That is, the relative distance measurements between the player tags 32, the ball tag 35 and the static anchor 33 can be used with a best-fit model to adjust position measurements of the GNSS measurements.

[0096] Similarly, compensation techniques known in the art may be used. For example, the relative linear distance measurement to the static anchor may be used as a candidate position with the best candidate chosen from the series of possible positions (GNSS, UWB, etc.).

[0097] In an alternative example to the GNSS example described above, the position measurements of the player tags may be identified using UWB signal measurements. This alternative example is illustrated in figure 7. Each of the tags 72, 35 includes an UWB transceiver. Positioned around the field are at least three static anchors 73. Using UWB signals transmitted between the player tags 72 and the static anchors 73, the system can identify the position of the player tags 72 in a local coordinate system set by the anchors 73. The determination of relative linear distance and subsequent calculation of position in a coordinate system has been described above and may be performed in any known manner.

[0098] Note that not all tags need to be ranged to the static anchors 73. The three anchors 73 have been placed at known locations on the field corresponding to intersections of field lines demarking the area of play. These locations may be (- 50,35), (-50,70) and (0,70). For example, if the anchors are on tripods at a known height of, say, 1.6m then one can include their heights as (-50,35,1.6), (- 50,70,1.6) and (0,70,1.6). These anchors determine their range to certain ones of the tags and from those range measurements, using a known technique, determine the location of at least three of the player tags with respect to the coordinate system (which in this example is centred at the intersection of the halfway line and the touch line).

[0099] The ball tag 72 may communicate with the player tags 35 using UWB to identify the relative linear distances between the ball tag 35 and the player tags 72 in the manner described above. From the relative linear distances, the system determines the position of the ball tag 35 in the manner described above. Thus, the difference is in the manner of the determination of the position of the player tags 72 using UWB rather than GNSS, such that a GNSS receiver is not included in the player tag 72.

[0100] Moreover, any of the tags may utilise one or both of a global and local positioning system, with the distances between the ball tag and the player tag used to calibrate or compensate for positional measurements determined using the global or local positioning system

[0101] Figure 8 illustrates the above described process in the form of a flow diagram. First, at step 81 , the process retrieves a position measurement of the player devices. The position measurement may be determined using GNSS or UWB measurements made to static anchors positioned around the periphery of the sports field, as discussed above. At step 82, the process calculates a distance from the ball device to at least three player devices. Using the distance between the ball device and the at least three player devices and the position measurements of the player devices, the position of the ball device is calculated, at step 83. In a further optional step 84, the position measurement of the payer devices can be adjusted based on the distance measurements between the ball device and the at least three player devices.

[0102] Again, it is to be recalled that the player device may be a first moving electronic device configured to be attached to sports equipment and the ball device may be a second moving electronic device configured to be incorporated within a sports ball.

[0103] Exemplary tags or devices will now be described. The tag has a transceiver, antenna and a microcontroller.

[0104] The devices may have at least one 9-axis IMU for collecting linear acceleration, angular acceleration and orientation data. The IMU component optionally embedded in the devices includes a combination of accelerometers, gyroscopes and magnetometers to report characteristics over time. Data from the IMU can be combined with the position data, which constitutes a form of sensor fusion, to increase system robustness. The I MU may also be used to calculate the angular velocity components, and therefore the revolutions per minute, of the ball or player device.

[0105] The tag preferably comprises a control unit, for example comprising a microcontroller. The tag preferably includes a power supply to supply electrical power, for example to those sensors which require power to operate as well as to the components of the control unit. A lithium ion or lithium polymer battery may be used. The power supply may be provided on the same part of the sports equipment as the sensors but this is not essential.

[0106] The control unit and power supply may be provided in an electronics unit or device. Where the sports equipment is a rugby ball, the electronics unit could be located inside the ball. Where the sports equipment is body armour, the electronics unit may be located in a position corresponding to a point between the player’s shoulder blades, which is already common practice for devices which use GNSS enabled chipsets for location.

[0107] The tag will further include a GNSS enabled chipset and / or a UWB transceiver and one or antennas.

[0108] As described above, the exemplary system comprises a device to be located on the field on either the player or in some other equipment. The intelligence to perform this analysis may be spread across each node or may be performed centrally at a central server. The data may be logged in a database for subsequent retrieval and analysis.

[0109] Throughout the present description the terms analytic controller, server and microcontroller are used to describe processing units which perform certain functions. It will be understood that the terms used are not essential. What may be essential is the functionality described. However, the functionality may often be performed by processing and control units located remotely, within the described entities or elsewhere in the system as appropriate. Methods and processes described herein can be embodied as code (e.g., software code) and / or data. Such code and data can be stored on one or more computer-readable media, which may include any device or medium that can store code and / or data for use by a computer system. When a computer system reads and executes the code and / or data stored on a computer-readable medium, the computer system performs the methods and processes embodied as data structures and code stored within the computer-readable storage medium. In certain embodiments, one or more of the steps of the methods and processes described herein can be performed by a processor (e.g., a processor of a computer system or data storage system). It should be appreciated by those skilled in the art that computer-readable media include removable and non-removable structures / devices that can be used for storage of information, such as computer-readable instructions, data structures, program modules, and other data used by a computing system / environment. A computer-readable medium includes, but is not limited to, volatile memory such as random access memories (RAM, DRAM, SRAM); and non-volatile memory such as flash memory, various read-only-memories (ROM, PROM, EPROM, EEPROM), magnetic and ferromagnetic / ferroelectric memories (MRAM, FeRAM), and magnetic and optical storage devices (hard drives, magnetic tape, CDs, DVDs); network devices; or other media now known or later developed that is capable of storing computer-readable information / data. Computer-readable media should not be construed or interpreted to include any propagating signals.

Claims

26CLAIMS1. A method of identifying position of electronic devices on a sports field, the method comprising: retrieving a position measurement of at least three first moving electronic devices; calculating a linear distance between a second electronic device and the at least three first moving electronic devices using a short-range radio signal; and calculating a position of the second electronic device based on the position measurements of the at least three first moving electronic devices and the linear distances.

2. A method according to claim 1 , wherein the method further comprises adjusting one or more of the position measurements based on the linear distances.

3. A method according to claim 2, wherein the step of adjusting comprises applying a least squares regression model to the position measurements and the linear distances to adjust the one or more position measurements.

4. A method according to any preceding claim, wherein the step of retrieving a position measurement comprises retrieving a GNSS position measurement of at least three of the at least three first moving electronic devices.

5. A method according to any preceding claim, wherein the step of retrieving a position measurement comprises: calculating a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal, wherein the at least three stationary anchors have a known position in a coordinate system.

6. A method according to claim 5, wherein the step of retrieving a position measurement comprises:calculating a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal in a local positioning system, preferably an ultra wideband positioning system.

7. A method according to claim 5 or 6, wherein the three stationary anchors are transitory and configured to be positioned around the periphery of a sports field.

8. A method according to any preceding claim, wherein the step of calculating a position of the second electronic device comprises identifying the position of each electronic device in a coordinate system.

9. A method according to any preceding claim, wherein the second electronic device is inserted into a sports ball.

10. A method according to any preceding claim, wherein the at least three first moving electronic devices are each attached to an article of clothing worn by a sports player.

11. A method according to any preceding claim, wherein calculating a linear distance using a short-range radio signal comprises determining the linear distance using two-way ranging.

12. A method according to any preceding claim, wherein the second electronic device acts as a master clock and each of the at least three first moving electronic devices synchronise in time from the master clock.

13. A method according to any of claims 11 or 12, wherein the at least three first moving electronic devices synchronise in time using the two-way ranging message.

14. A method according to any preceding claim, wherein the method further comprises:calculating a linear distance between the second electronic device and a stationary anchor; wherein the step of identifying a position of the second moving electronic device is further based on the linear distance between the second electronic device and a stationary anchor.

15. A method according to claim 14, wherein the method further comprises: calculating a linear distance between each of the at least three first moving electronic devices and a stationary anchor; and, adjusting the position measurements of the at least three first moving electronic devices based on the linear distance between each of the at least three first moving electronic devices and the stationary anchor.

16. A method according to claim 14 or 15, wherein the method further comprises: synchronising a clock of one or more of the electronic devices with the stationary anchor.

17. A method according to any preceding claim, wherein the method comprises determining a rigid topology of the electronic devices from the linear distances.

18. A method according to any preceding claim, wherein the short-range radio signals are ultra wideband radio signals.

19. A computer readable medium comprising instructions which when executed by a processor cause the processor to carry out the method of any of claims 1 to 18.

20. A system for identifying position of electronic devices on a sports field, the method comprising: at least three first moving electronic devices configured to be embedded within sports equipment on a sports field, each first moving electronic device comprising a device antenna connected to a respective device transceiver;29 a second electronic device configured to be embedded within sports equipment on a sports field, the second electronic device comprising a device antenna connected to a respective device transceiver; and, a metric server, wherein the metric server is configured to: identify a linear distance between the second moving electronic device and the at least three first moving electronic devices using a short- range radio signal; retrieve a position measurement of the at least three first moving electronic devices; calculate a position of the second electronic device based on the position measurements of the at least three first moving electronic devices and the linear distances.

21. A system according to claim 20, wherein the metric server is further configured to adjust one or more of the position measurements based on the linear distances.

22. A system according to claim 21 , wherein the metric server is further configured to apply a least squares regression model to the position measurements and the linear distances to adjust the one or more position measurements.

23. A system according to any of claims 20 to 22, wherein the metric server is configured to retrieve a position measurement by retrieving a GNSS position measurement of at least three of the at least three first moving electronic devices.

24. A system according to any of claims 20 to 23, wherein the system comprises at least three stationary anchors and wherein the metric server is configured to retrieve a position measurement by identifying a linear distance between each of at least three of the at least three first moving electronic devices and three stationary anchors calculated using a short-range radio signal,30 wherein the three stationary anchors have a known position in a coordinate system.

25. A system according to claim 24, wherein the metric server is configured to: calculate a linear distance between each of at least three of the at least three first moving electronic devices and at least three stationary anchors using a short-range radio signal in a local positioning system, preferably an ultra wideband positioning system.

26. A system according to claim 24 or 25, wherein the three stationary anchors are transitory and configured to be positioned around the periphery of a sports field.

27. A system according to any of claims 20 to 26, wherein the metric server is configured to calculate a position of the second electronic device by identifying the position of each electronic device in a coordinate system.

28. A system according to any of claims 20 to 27, wherein the second electronic device is configured to be inserted into a sports ball.

29. A system according to any of claims 20 to 28, wherein the at least three first moving electronic devices are each configured to be attached to an article of clothing worn by a sports player.

30. A system according to any of claims 20 to 29, wherein the linear distances are determined using two-way ranging.

31. A system according to any of claims 20 to 30, wherein the second electronic device is configured to act as a master clock and each of the at least three first moving electronic devices are configured to synchronise in time from the master clock.3132. A system according to any of claims 30 or 31 , wherein the at least three first moving electronic devices are configured to synchronise in time using the two-way ranging message.

33. A system according to any of claims 20 to 32, wherein the metric server is configured to identify the position of the second moving electronic device based on a calculated linear distance between the second electronic device and a stationary anchor.

34. A system according to claim 33, wherein the metric server is configured to adjust the position measurements of the at least three first moving electronic devices based on a calculated linear distance between each of the at least three first moving electronic devices and the stationary anchor.

35. A system according to claim 33 or 34, wherein the electronic devices are configured to synchronise a clock with the stationary anchor.

36. A system according to any of claims 20 to 35, wherein the metric server is configured to determine a rigid topology of the electronic devices from the linear distances.

37. A system according to any of claims 20 to 26, wherein the short-range radio signals are ultra wideband radio signals.

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