阅读说明：本技术 用于检测无线装置之间的距离改变的方法、设备和装置可读介质 (Method, apparatus, and device-readable medium for detecting a change in distance between wireless devices ) 是由 D·桑德曼 S·德维迪 M·洛佩兹 于 2019-02-21 设计创作，主要内容包括：在一个方面,提供一种用于检测第一无线装置和第二无线装置之间的距离改变的方法。方法包括：基于对在第一无线装置和第二无线装置之间传送的第一定时信号的测量来确定参数随时间的变化。参数的变化取决于无线装置之间的距离,并且包括：由于无线装置之间的相对时钟漂移而引起的周期性阶跃转变。方法还包括：基于参数的变化来预测预期发生周期性阶跃转变的时间；以及基于对第二定时信号的测量来确定参数的值。响应于确定参数的确定的值不同于参数的预期值来确定无线装置之间的距离已经改变。(In one aspect, a method for detecting a change in distance between a first wireless device and a second wireless device is provided. The method comprises the following steps: a change in a parameter over time is determined based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device. The parameter varies depending on the distance between the wireless devices and includes: periodic step transitions due to relative clock drift between wireless devices. The method further comprises the following steps: predicting a time at which a periodic step transition is expected to occur based on the change in the parameter; and determining a value of the parameter based on the measurement of the second timing signal. Determining that the distance between the wireless devices has changed in response to determining that the determined value of the parameter is different than an expected value of the parameter.)

1. A method of detecting a change in distance between a first wireless device and a second wireless device, the method comprising:

determining (704) a change in a parameter over time based on a measurement of a first timing signal transmitted between the first wireless device and the second wireless device, wherein the change in the parameter depends on a distance between the first wireless device and the second wireless device, and comprises: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device;

predicting (706) a time at which a periodic step transition is expected to occur based on the determined change in the parameter;

determining (708) a value of the parameter based on a measurement of a second timing signal that is subsequently transmitted between the first wireless device and the second wireless device proximate to the predicted time; and

determining (712) that the distance between the first wireless device and the second wireless device has changed in response to determining (710) that the determined value of the parameter is different than an expected value of the parameter.

2. The method of claim 1, wherein the expected value of the parameter is determined based on the change in the parameter over time.

3. The method of claim 1 or 2, wherein determining the value of the parameter based on a measurement of a second timing signal comprises: determining a first value of the parameter based on measurements taken prior to the predicted time; and determining a second value of the parameter based on measurements taken after the predicted time.

4. The method of claim 3, wherein the determining that the determined value of the parameter is different than the expected value of the parameter comprises determining one or more of:

the first value of the parameter is different from a first expected value of the parameter; and

the second value of the parameter is different from a second expected value of the parameter.

5. The method of any of claims 1-4, further comprising:

determining (702) a first time-averaged distance between the first wireless device and the second wireless device prior to determining a change in the parameter over time.

6. The method of any one of claims 1-5, further comprising:

in response to the determining (712) that the distance between the first wireless device and the second wireless device has changed, determining (714) a second time-averaged distance between the first wireless device and the second wireless device based on a measurement of a third timing signal transmitted between the first wireless device and the second wireless device.

7. The method of any of claims 1-6, wherein the resolution of the parameter is limited by a sampling frequency of the timing signal measurements, and the periodic step transitions are also a result of a limited resolution of the parameter.

8. The method of any of claims 1-7, wherein the parameter is a measured distance between the first wireless device and the second wireless device.

9. The method of claim 8, wherein the variation of the measured distance is a square wave.

10. The method of claim 9, wherein the square wave varies between a first value and a second value, and wherein the expected value of the parameter at the predicted time comprises: one of the first value and the second value.

11. The method of any of claims 1-7, wherein the parameter is a measured clock difference value between the first wireless device and the second wireless device.

12. The method of claim 11, wherein the measured clock difference value varies according to a step function.

13. The method of any one of claims 1-12, wherein the first and second timing signals are Fine Time Measurement (FTM) signals.

14. The method of any of claims 1-13, wherein each of the first and second wireless devices is a wireless access point (102) or a mobile station (104).

15. A node (800) for detecting a change in distance between a first wireless device and a second wireless device, the node (800) comprising: a processing circuit (802) and a device-readable medium (804) storing instructions that, when executed by the processing circuit (802), cause the node (800) to:

determining a change in a parameter over time based on a measurement of a first timing signal transmitted between the first wireless device and the second wireless device, wherein the change in the parameter is dependent on a distance between the first wireless device and the second wireless device, and comprising: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device;

predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter;

determining a value of the parameter based on a measurement of a second timing signal that is subsequently transmitted between the first wireless device and the second wireless device proximate to the predicted time; and

determining that the distance between the first wireless device and the second wireless device has changed in response to determining that the determined value of the parameter is different than an expected value of the parameter.

16. The node (800) of claim 15, wherein the expected value of the parameter is determined based on the change in the parameter over time.

17. The node (800) of claim 15 or 16, wherein the node (800) is caused to determine the value of the parameter based on a measurement of a second timing signal by: determining a first value of the parameter based on measurements taken prior to the predicted time; and determining a second value of the parameter based on measurements taken after the predicted time.

18. The node (800) of claim 17, wherein the determining that the determined value of the parameter is different than the expected value of the parameter comprises determining one or more of:

the first value of the parameter is different from a first expected value of the parameter; and

the second value of the parameter is different from a second expected value of the parameter.

19. The node (800) according to any one of claims 15-18, wherein the node (800) is further caused to:

determining a first time-averaged distance between the first wireless device and the second wireless device prior to determining a change in the parameter over time.

20. The node (800) according to any one of claims 15-19, wherein the node (800) is further caused to:

determining a second time-averaged distance between the first wireless device and the second wireless device based on a measurement of a third timing signal transmitted between the first wireless device and the second wireless device in response to the determination that the distance between the first wireless device and the second wireless device has changed.

21. The node (800) of any of claims 15-20, wherein a resolution of the parameter is limited by a sampling frequency of the timing signal measurements, and the periodic step transitions are also a result of a limited resolution of the parameter.

22. The node (800) of any of claims 15-21, wherein the parameter is a measured distance between the first wireless device and the second wireless device.

23. The node (800) of claim 22, wherein the change in the measured distance is a square wave.

24. The node (800) of claim 23, wherein the square wave varies between a first value and a second value, and wherein the expected value of the parameter at the predicted time comprises: one of the first value and the second value.

25. The node (800) of any of claims 15-21, wherein the parameter is a measured clock difference value between the first wireless device and the second wireless device.

26. The node (800) of claim 25, wherein the measured clock difference value varies according to a step function.

27. The node (800) of any of claims 15-26, wherein the first and second timing signals are Fine Time Measurement (FTM) signals.

28. The node (800) of any of claims 15-27, wherein each of the first and second wireless devices is a wireless access point (102) or a mobile station (104).

29. A device-readable medium (804) for detecting a change in distance between a first wireless device and a second wireless device, the device-readable medium storing instructions that, when executed by processing circuitry (802) of a node (800), cause the node (800) to:

determining a change in a parameter over time based on a measurement of a first timing signal transmitted between the first wireless device and the second wireless device, wherein the change in the parameter is dependent on a distance between the first wireless device and the second wireless device, and comprising: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device;

predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter;

determining a value of the parameter based on a measurement of a second timing signal that is subsequently transmitted between the first wireless device and the second wireless device proximate to the predicted time; and

determining that the distance between the first wireless device and the second wireless device has changed in response to determining that the determined value of the parameter is different than an expected value of the parameter.

Technical Field

Embodiments of the present disclosure relate to wireless devices, and in particular, to methods, apparatuses, and device-readable media for detecting a change in distance between wireless devices.

Background

In IEEE 802.11, time-of-flight measurements are used to determine the distance between wireless devices as part of the Fine Timing Measurement (FTM) protocol introduced in IEEE 802.11 mc. According to the FTM protocol, time-of-flight measurements of signals transmitted between a plurality of wireless devices and a target device may be used to estimate a location of the target device using triangulation.

The FTM procedure can be initiated by any wireless device supporting FTM protocol as the initiator. To initiate the FTM procedure, a first wireless device (referred to as an initiating device) transmits an initial FTM request frame. The frame is received at a second wireless device supporting FTM protocol as a responder, referred to as a responding device. The responding device responds to the initial FTM request frame with an acknowledgement. Upon receiving the acknowledgement, the initiating device initiates one or more FTM bursts with the responding device.

The FTM protocol introduces additional frames, namely FTM frames. The FTM burst begins with the responding device transmitting a FTM frame to the initiating device. The responding device then waits for an acknowledgement from the initiating device before transmitting a subsequent FTM frame. This process may be repeated one or more times as part of an FTM burst. The responding device records the transmit timestamp of the FTM frame and the receive timestamp of the corresponding acknowledgment. Similarly, the initiating device records a receive timestamp of the FTM message and a transmit timestamp of the corresponding acknowledgement. The FTM message and the transmission and reception timestamps of the corresponding acknowledgements are then used to determine the round trip time of the message from which the distance between the devices can be determined. If the initiating device is to calculate the distance between it and the responding device, the FTM frame transmitted by the responding device may comprise: an indication of a transmit timestamp of the FTM frame and a receive timestamp of a corresponding acknowledgement.

Thus, an estimate of the distance between two wireless devices can be obtained by using a single FTM burst comprising four messages. However, the accuracy of the range measurements obtained via the FTM protocol is limited by the sampling interval of the wireless device. For example, in a 20MHz channel sampled at a nominal rate, the distance between two wireless devices can only be determined to within ± 7.5 m.

Thus, the FTM protocol may be insensitive to small changes in the distance between two wireless devices. To more accurately measure distance, multiple FTM exchanges may be used and the average of the results may be calculated. However, this takes time and consumes energy in the wireless device.

Disclosure of Invention

Embodiments of the present disclosure seek to address these and other problems.

In one aspect, the present disclosure provides a method of detecting a change in distance between a first wireless device and a second wireless device. The method comprises the following steps: a change in a parameter over time is determined based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device. The parameter varies depending on a distance between the first wireless device and the second wireless device, and includes: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device. The method further comprises the following steps: predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter; and determining a value of the parameter based on the measurement of the second timing signal. The second timing signal is then transmitted between the first wireless device and the second wireless device proximate to the predicted time. In response to determining that the determined value of the parameter is different from the expected value of the parameter, the method further comprises: it is determined that a distance between the first wireless device and the second wireless device has changed.

Apparatus and device readable media for performing the methods set forth above are also provided. For example, in one aspect, a node for detecting a change in distance between a first wireless device and a second wireless device is provided. The node comprises: a processing circuit and a device-readable medium storing instructions that, when executed by the processing circuit, cause a node to: determining a change in a parameter over time based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device, wherein the change in the parameter is dependent on a distance between the first wireless device and the second wireless device, and comprising: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device. The node is further caused to: predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter; and determining a value of the parameter based on the measurement of the second timing signal. The second timing signal is then transmitted between the first wireless device and the second wireless device proximate to the predicted time. In response to determining that the determined value of the parameter is different than the expected value of the parameter, further cause the node to: it is determined that a distance between the first wireless device and the second wireless device has changed.

In another aspect, an apparatus-readable medium for detecting a change in distance between a first wireless apparatus and a second wireless apparatus is provided. The apparatus-readable medium stores instructions that, when executed by the processing circuitry of the node, cause the node to: determining a change in a parameter over time based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device, wherein the change in the parameter is dependent on a distance between the first wireless device and the second wireless device, and comprising: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device. The node is further caused to: predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter; and determining a value of the parameter based on the measurement of the second timing signal. The second timing signal is then transmitted between the first wireless device and the second wireless device proximate to the predicted time. In response to determining that the determined value of the parameter is different than the expected value of the parameter, further cause the node to: it is determined that a distance between the first wireless device and the second wireless device has changed.

Drawings

For a better understanding of examples of the present disclosure, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

fig. 1 illustrates a wireless communication network in accordance with an embodiment of the present disclosure;

FIG. 2 is a signaling diagram of a fine timing measurement procedure;

FIG. 3 shows a signaling diagram of a simplified fine timing measurement exchange;

FIG. 4 is a graph showing the variation of measured distance between a first wireless device and a second wireless device over time;

FIG. 5 is a further diagram showing the variation of the measured distance between the first wireless device and the second wireless device over time;

FIG. 6 is a graph showing the variation over time of the clock difference value of a signal transmitted between a first wireless device and a second wireless device;

FIG. 7 is a flow chart of a method according to an embodiment of the present disclosure; and

fig. 8 and 9 are schematic diagrams of a node according to an embodiment of the present disclosure.

Detailed Description

Fig. 1 illustrates a wireless communication network 100 according to an embodiment of the present disclosure. Network 100 includes a wireless access point 102 that communicates with a mobile station 104. In one embodiment, network 100 implements the IEEE 802.11 standard (referred to as "Wi-Fi") and may implement one or more of its amendments, and includes a Wireless Local Area Network (WLAN). For convenience, the terms used herein may correspond to the terms used in the 802.11 standard (e.g., "access point," "station"). However, the concepts described herein may also be applied to other radio access technologies. For example, the network 100 may implement cellular radio access technologies such as those developed by the third generation partnership project (3 GPP), e.g., Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE), new air interfaces (NR), and so on. In such a case, the wireless access point 102 may be referred to as a base station, NodeB, eNodeB, gbnodeb, transmit-receive point (TRP), etc. Mobile station 104 may be referred to as User Equipment (UE), a wireless device, a wireless terminal device, etc. The term "node" is used herein to refer to any wireless device and any suitable network node.

Although fig. 1 shows a single wireless access point 102 and mobile station 104, those skilled in the art will appreciate that network 100 may include any number of wireless access points and mobile stations. In particular, as described above, multiple wireless access points 102 may be used to perform multiple FTM procedures with a mobile station 104 to triangulate its position.

Fig. 2 shows a signaling diagram of messages exchanged between a first wireless device 202 and a second wireless device 204 according to a Fine Timing Measurement (FTM) protocol. The first wireless device may be, for example, one of the wireless access point 102 and the mobile station 104 described with respect to fig. 1. The second wireless device may be, for example, the other of the wireless access point 102 and the mobile station 104 described with respect to fig. 1.

The process begins with the second wireless device 204 transmitting an FTM request frame 206 to the first wireless device 202. The FTM request frame may comprise: an indication of one or more parameters related to the FTM procedure. The one or more parameters may include, for example, one or more of the following parameters: a burst timeout parameter indicating a duration of each FTM burst, a burst period indicating a time interval from a start of one FTM burst to a start of a subsequent FTM burst, a number of FTM messages to be exchanged as part of each FTM burst, and a number of FTM bursts to be executed.

Upon receiving the FTM request frame 206, the first wireless device 202 transmits an acknowledgement 208 to the second wireless device 204. Thus, the first wireless device 202 acts as a responding device and the second wireless device 204 acts as an initiating device.

At time t₁(1) The first wireless device 202 transmits a first FTM message 210 as part of a FTM burst. At time t₂(1) A first FTM message 210 is received at the second wireless device 204. In response to receiving the first FTM message 210, the second wireless device 204 at time t₃(1) An acknowledgement is transmitted to the first wireless device 202. At time t₄(1) An acknowledgement is received at the first wireless device 202. Thus, the first FTM message 210 and acknowledgement 212 form a first FTM exchange that is part of a FTM burst.

At time t₁(2) The first wireless device 202 transmits a second FTM message 214 to the second wireless device 204 as part of a second FTM exchange. The second FTM message 214 may comprise: the time at which the first FTM message 210 is transmitted by the first wireless device 202 and the time at which the corresponding acknowledgement 212 is received at the first wireless device 202 (i.e., time t)₁(1) And t₄(1) Measurement of). In response to a signal at time t₂(2) Upon receiving the second FTM message 214, the second wireless device 204 at time t₃(2) An acknowledgement 216 is transmitted to the first wireless device 202. The first wireless device 202 is at time t₄(2) An acknowledgement is received.

As described above, the time at which a particular message is received and transmitted is recorded at each wireless device 202, 204. However, the clocks at the first wireless device 202 and the second wireless device may be offset from each other such that the time recorded at the first wireless device 202From the corresponding time at the second wireless device 204Offset by a certain factor (factor) delta. Therefore, the temperature of the molten metal is controlled,

the time of flight of each signal transmitted between the first wireless device 202 and the second wireless device 204 is determined via the following equationIn relation to the time stamp of the respective signal:

wherein the relative clock skew can be expressed as:

assuming that the relative clock offset remains constant, the distance between the first wireless device and the second wireless device can be estimated according to the following equation:

wherein the content of the first and second substances,cis the speed of light.

Those skilled in the art will understand thatt ₄、t ₃、t ₂Andt ₁any means of calculating the distance between the first wireless device 202 and the second wireless device 204. In the illustrated embodiment, the distance may be calculated by the second wireless device 204 (the originating device) because it receives the pairt ₄Andt ₁is detected (e.g., in the second FTM frame 214). However, in an alternative embodiment, if transmission is to the first wireless device 202t ₃Andt ₂may be calculated by the first wireless device 202, or if transmitted by the first wireless device 202 and the second wireless device 204 to a third device (e.g., a network node)t ₄、t ₃、t ₂Andt ₁even the distance can be calculated by the third means.

As described above, the timing measurement is not accurate due to the sampling frequency of each clock, and thus the range estimate can be obtained by averaging over a large number of FTM exchanges. In the signaling diagram shown in fig. 2, only a single FTM burst is shown, but those skilled in the art will appreciate that more FTM bursts may be used to determine the range measurements. Further, the FTM burst shown in fig. 2 comprises two FTM switches, but it will be understood that each FTM burst may contain more FTM switches than shown. To includenFTM procedures for each FTM exchange may obtain a distance between two wireless devices according to the following equation:

this averaging process assumes that the clocks at the first and second wireless devices are running at the same rate so that the relative clock offset Δ does not change over time. In practice, however, the clocks may drift relative to each other, which means that the relative clock offset Δ changes over time.

The effect of clock drift on FTM range measurements can be demonstrated with reference to fig. 3. In (a), fig. 3 illustrates a first simplified FTM exchange between a first wireless device 302 and a second wireless device 304. The vertical axis shows time according to a local clock within each wireless device. It will be noted that in this example, the local clocks are not synchronized to the same value (i.e., there is an offset, as described above).

The exchange comprises the following steps: a first message (e.g., an FTM message) transmitted by the first wireless device 302 at time 1. The first message is received at the second wireless device 304 at a time between time 6 and time 7. However, due to the limited sampling rate of the second wireless device 304, the second wireless device 304 records the time of receiving the first message as time 7. The second wireless device 304 then transmits an acknowledgement to the first wireless device at time 7. The acknowledgement is received at the first wireless device 302 shortly before time 3, but is recorded as being received at time 3. Thus, this first FTM exchange gives the following time-of-flight estimates:

in (b), fig. 3 shows a second simplified FTM exchange between a first wireless device 302 and a second wireless device 304 where a clock at the second wireless device 304 has drifted relative to a clock at the first wireless device 302. In the second exchange, the first wireless device 302 transmits a second message to the second wireless device 304 at time 1, the second message being received at the second wireless device 304 shortly after time 6. Due to the limited sampling rate of the second wireless device 304, the time at which the message was received at the second wireless device 304 is recorded as 7. The second wireless device 304 responds with an acknowledgement message at time 7, which is received at the first wireless device 302 shortly after time 3 and recorded as received at the first wireless device 302 at time 4. Thus, this second FTM exchange gives the following time-of-flight estimates:

it will be noted that the actual time of flight in examples (a) and (b) is about 0.75. Thus, both measurements are greater than the actual time of flight. This is due to the fact that timing measurements are performed consistently at clock transitions after a relevant event (e.g., transmission or reception of a signal). Therefore, the measurements will consistently introduce some additional time. If averaged over multiple measurements, this extra time will equal half a clock cycle.

It will be apparent to those skilled in the art that the measured distance between the first wireless device 302 and the second wireless device 304 varies periodically in a square wave when there is relative clock drift between the wireless devices 302, 304. The skilled person will understand that the term "square wave" may be seen as comprising, for example, a rectangular wave.

This is illustrated in fig. 4, where fig. 4 shows the variation of the measured distance between the first wireless device and the second wireless device as a function of time. The distance is measured based on a timing signal transmitted between the first wireless device and the second wireless device. In this particular example, the signal is transmitted on a 20MHz channel sampled at a nominal rate. The clocks at the wireless devices each have a 4 parts per million (4 ppm) accuracy, resulting in a relative clock drift of 8ppm between the two wireless devices. As shown, the actual distance between the two wireless devices is constant at 17.5 m. However, the measured distance varies according to a square wave varying between a first value (22.5 m) and a second value (30 m), wherein a periodic step change occurs when the wave transitions from the first value to the second value. Periodic step changes due to relative timing between wireless devicesClock drift occurs. Period of square wave versus sampling timeT _S And relative clock driftAre all sensitive and are composed ofIt is given.

As described above, existing methods for detecting a change in range between two wireless devices determine an average from a large number of FTM exchanges to obtain a single range measurement. To detect a change in distance between two wireless devices, the process must be repeated at least twice to determine an initial distance estimate (before the distance has changed) and a second distance estimate (after the distance has changed). Thus, existing methods for detecting distance changes using time-of-flight measurements require a large number of FTM exchanges. Furthermore, due to the limited accuracy of the distance estimation (which is due to the limited sampling rate), existing methods may not be sensitive to small changes in distance.

Embodiments of the present disclosure address these matters, and others. One aspect provides a method comprising: a change in the parameter over time is determined, wherein the change in the parameter is dependent on a distance between the first wireless device and the second wireless device. The change in the parameter comprises a periodic step transition. By determining whether a measured value of a parameter at a time proximate to a predicted periodic step transition is different from an expected value of the parameter at the time, it may be determined whether a distance between the first wireless device and the second wireless device has changed. Accordingly, embodiments of the present disclosure enable detection of a change in distance between wireless devices while reducing overhead signaling. Furthermore, embodiments of the present disclosure allow for detecting: small changes in the distance between wireless devices that may otherwise be difficult or impossible to detect using existing FTM procedures.

As described above, the measured distance between two wireless devices, measured using the FTM, varies as a square wave when there is relative clock drift between the two wireless devices. Embodiments of the present disclosure utilize the property of measured distance over time to detect a change in distance between two wireless devices. This is described in more detail with reference to fig. 5.

Fig. 5 shows how the temporal variation of the measured distance between two wireless devices changes when the actual distance between the two wireless devices changes. The dotted line shows the change in the measured distance between the two wireless devices when the distance between the two wireless devices is 17.5m (as in fig. 4). When the distance between the wireless devices increases to 20.5m (shown by the dotted line), the peaks in the square wave widen, causing the time at which the transition occurs to changeWhereinDIs a change in the distance of the object,is the period of the square wave and,is the sampling time, andcis the speed of light. Thus, the duration of the minimum and maximum values of the square wave function is sensitive to changes in the distance between wireless devices.

Embodiments of the present disclosure use this attribute to detect a change in distance between the first wireless device and the second wireless device. In one aspect, a change in a measured distance between a first wireless device and a second wireless device over time is determined. Thus, in the embodiment shown in fig. 5, multiple measurements are performed on the distance between the first wireless device and the second wireless device in order to determine the change in the measured distance over time (shown by the dotted line). Based on the determined measured distance versus time, a time at which a periodic step transition is expected to occur is predicted. For example, in the embodiment shown in fig. 5, the periodic step transition at 7.292 μ s may be predicted based on the periodic step transition occurring at 1.042 μ s and the period of the square wave (6.250 μ s).

Then, the measured distance between the first wireless device and the second wireless device is determined at a time close to the predicted transition (e.g., at a time close to 7.292 μ s) and compared to an expected value of the measured distance to determine whether the distance between the wireless devices has changed.

In the illustrated example, the predicted transition is offset from the predicted transition on both sides of the predicted transitionThe square wave is evaluated at points 502 and 504. By selecting in this exampleD=3, it is possible to detect a change in distance of at least 3 m. Thus, based on the change in the measured distance, it is determined: the measured distance will have an expected value of 30m at point 502 before the predicted step transition and 22.5m at point 504 after the predicted step transition. As shown in the figure, the measured distance is instead determined to have a value of 30m at point 504, which is different from the expected value of 22.5 m. Thus, it was determined that the distance had increased by at least 3 m. If the state has changed instead at point 502, it is determined that the distance between the first wireless device and the second wireless device has decreased by at least 3 m.

Although the above description has been in relation to the variation of the measured distance between the first wireless device and the second wireless device, it will be appreciated by those skilled in the art that the same method may be applied to other parameters whose variation over time depends on the distance between the first wireless device and the second wireless device.

Thus, further embodiments of the present disclosure relate to clock difference valuesChange over time. As shown in FIG. 6, the clock difference is the time at which the signal was recorded as being transmitted at the first wireless deviceAnd the time at which the signal was recorded as being received at the second wireless deviceThe difference between them. It will be noted that it is possible to note,the clock difference value will vary with time of flight variations (e.g., with a change in distance between the first wireless device and the second wireless device); however, the clock offset between the first wireless device and the second wireless device is unknown, and thus the time of flight itself cannot be resolved from a single measurement. The solid black line in fig. 6 shows the actual time of flight of the signal transmitted between the first wireless device and the second wireless device.

The dotted line shows the difference in clock for signals transmitted between the first wireless device and the second wireless device when there is relative clock drift between the clock at the first wireless device and the clock at the second wireless deviceA change in the measurement of (a). Clock difference value although the distance between the first wireless device and the second wireless device is not changedAccording to an increasing step function change in which a periodic step transition occurs due to relative clock drift between the first wireless device and the second wireless device. The time between step transitions in the step function also depends on the distance between the first wireless device and the second wireless device.

It will be apparent that the clock difference value may instead vary according to a decreasing step function, for example in the case where the relative clock drift between the wireless devices is negative.

To aid understanding, the dashed lines in fig. 6 illustrate the transmission of signals transmitted between a first wireless device and a second wireless deviceOf drift compensation, i.e. where a clock difference value has already been setIs adjusted to account for relative clock drift between the first wireless device and the second wireless device (andthus taking clock skew into account). It can be seen that the drift compensated clock difference varies as a square wave function in a similar manner to the measured distance described above. As with the square wave described above with respect to fig. 5, the time at which each periodic step transition occurs is sensitive to the distance between the first wireless device and the second wireless device. Thus, replacing the measured distances in fig. 5 with clock difference values, the same method outlined above with respect to fig. 5 can also be applied to fig. 6.

Fig. 7 is a flow chart of a method of detecting a change in distance between a first wireless device and a second wireless device according to an embodiment of the disclosure. For example, the method may be performed in the first wireless device or the second wireless device. In alternative examples, the first wireless device and the second wireless device may form part of a wireless communications network, and the method may be performed by a network node in the wireless communications network that is separate from the first wireless device and the second wireless device.

The method begins in step 702, and in step 702, an initial distance between a first wireless device and a second wireless device is determined. Those skilled in the art will appreciate that there are many suitable methods for determining the distance between wireless devices.

In one embodiment, the initial distance is a time-averaged distance measurement. A time-averaged distance measurement may be determined based on the plurality of timing signals. The timing signal may be an FTM signal and may comprise one or more FTM bursts. For example, the initial distance may be determined by averaging the measured distances over multiple FTM signals or FTM bursts using the FTM procedure described above with reference to fig. 2.

In an alternative embodiment, the initial distance between wireless devices may be determined based on the location data of the wireless devices. For example, the initial distance between wireless devices may be determined based on positioning data obtained from a satellite navigation system such as GPS, GLONASS, etc.

The method then proceeds to step 704 where a change in the parameter over time is determined based on a measurement of a first timing signal transmitted between the first wireless device and the second wireless device in step 704. The first timing signal may be, for example, an FTM signal. Accordingly, the first timing signal may be transmitted as part of an FTM procedure. For example, the first timing signal may consist of a single FTM burst.

The parameter may be a measured distance between the first wireless device and the second wireless device. In this regard, the measured distance is based on a single FTM swap (i.e., two FTM frames and corresponding acknowledgements), and/or the measured distance is not averaged over multiple measurements. Thus, as described above with respect to fig. 5, the change in the measured distance may be a square wave. As mentioned above, the term "square wave" can be considered to mean: a square wave or a rectangular wave (i.e. the duration of the minimum in the square wave may be equal to or different from the duration of the maximum in the square wave).

In an alternative example, the parameter may be a clock difference between the first wireless device and the second wireless device. Thus, in one example, the parameter is a time at which the signal was recorded as being transmitted from one of the wireless devicesAnd the time at which the signal was recorded as being received at another one of the wireless devicesThe difference between them.

The parameter varies depending on a distance between the first wireless device and the second wireless device, and includes: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device. The variation of the parameter may also depend on the sampling frequency of the timing signal measurement. Thus, the periodic step transition may also be the result of a limited resolution of the parameter (e.g. a quantization of the parameter due to a limited sampling frequency of the timing signal measurements).

Once the change in the parameter has been determined, the method continues to step 706, where step 706 includes: predicting a time at which a periodic step transition in the change in the parameter is expected to occur based on the determined change in the parameter. The time of prediction may be determined based on a model or function fitted to the determined change of the parameter. The predicted time may be determined based on one or more characteristics of the determined change in the parameter. For example, the predicted time at which a periodic step transition is expected to occur may be determined based on the frequency of change of the parameter (or equivalently, based on the period of change of the parameter). In another example, the predicted time may be determined based on a duty cycle of the change in the parameter. Thus, in case the variation is a square wave, the predicted time may be determined based on the predicted duration spent at the upper value of the parameter and/or the predicted duration spent at the lower value of the parameter.

The method then continues to step 708, where in step 708, values for the parameters are determined at the following times: this time is close to the predicted time of the periodic step change. The value of the parameter is determined based on a measurement of a second timing signal transmitted between the first wireless device and the second wireless device at a time proximate to the predicted time (i.e., after the first timing signal). The second timing signal may be an FTM signal. For example, the second timing signal may consist of a single FTM burst or a single FTM switch.

The values of the parameters may be determined at predetermined intervals from the predicted time.

In particular embodiments, at a time that may be predicted from the distanceAt intervals of (2) determining the value of the parameter, whereinIs the period of the change of the parameter,is the time of the sampling, and,cis the speed of light, andDis the minimum detectable change in distance.

The value of the parameter may be determined at more than one time close to the predicted time of the periodic step change. In an embodiment, the first value of the parameter is determined based on a measurement taken before the predicted time of the periodic step change and the second value of the parameter is determined based on a measurement taken after the predicted time of the periodic step change. Thus, the parameters may be determined before and after the predicted time of the periodic step change.

The interval may be selected based on an expected noise level in the parameters. Noise in this context may be considered to comprise, for example, channel noise and/or clock noise. Those skilled in the art will appreciate that noise may affect the time at which the periodic step transitions of the parameters occur. Thus, the spacing may be selected to be large enough to reduce the risk of falsely detecting a change in distance between the first wireless device and the second wireless device based on noise. For example, the smallest detectable change in distance may be selectedDSuch that the measurement is performed sufficiently far away from the predicted step transition.

The method then proceeds to step 710 where the value of the parameter determined in step 708 is compared to an expected value of the parameter in step 710. The expected value of the parameter may be determined based on the change in the parameter over time in a manner similar to the predicted time of the step transition. The expected value of the parameter may be determined based on a model or function fitted to the determined change of the parameter. The expected value of the parameter may be determined based on one or more characteristics of the determined change in the parameter.

If the determined parameter values do not differ from the expected parameter values (i.e. they are the same, or they are the same within a certain confidence interval), it can be determined that: the distance between the first wireless device and the second wireless device has not changed, or has not changed by more than a detectable distanceD. In the illustrated embodiment, the method returns to step 706, where in step 706, the time of additional periodic step transitions is predicted. Thus, the method may continue with predicting the periodic step change and comparing a value of the parameter proximate to the predicted periodic step transition to an expected value to detect a change in distance between the first wireless device and the second wireless device.

Alternatively, if the determined value of the parameter is different from the expected value of the parameter, the method continues to step 712, where it is determined in step 712Determining: the distance between the first wireless device and the second wireless device has changed, or has changed by at least a detectable distanceD. Thus, in the embodiment described above with respect to fig. 5 where two wireless devices are initially separated by 17.5m, the expected values for the measured distance at points 502 and 504 would be 30m and 22.5m, respectively. By comparing these expected values of the measured distance with the determined values 30m and 30m respectively: the distance between the first wireless device and the second wireless device has changed. Further, it may be determined whether the distance between the wireless devices has increased or decreased by comparing an expected value of the measured distance to a determined value of the measured distance, which is based on measurements made before and after the predicted time.

The method may then optionally continue to step 714 where, in response to determining that the distance between the first wireless device and the second wireless device has changed, the distance between the first wireless device and the second wireless device is re-determined in step 714. This step may be substantially similar to step 702 described above. Thus, the distance may be a time-averaged distance. A time-averaged distance measurement may be determined based on the plurality of timing signals. The timing signal may be an FTM signal and may comprise one or more FTM bursts. For example, the distance may be determined by averaging the measured distances over multiple FTM signals or FTM bursts using the FTM procedure described above with reference to fig. 2. In an alternative embodiment, the initial distance between wireless devices may be determined based on the location data of the wireless devices. For example, the initial distance between wireless devices may be determined based on positioning data obtained from a satellite navigation system such as GPS, GLONASS, etc.

The measurements performed in steps 702 and 714 may require a greater amount of signaling than the measurements performed in step 708. For example, the distance measured in steps 702 and 714 may be based on an average of multiple timing measurements (e.g., multiple FTM switches and/or multiple FTM bursts). In contrast, the measured range in step 708 may be based on a single FTM switch or a single FTM burst. Accordingly, embodiments of the present disclosure reduce overhead signaling by obtaining a more accurate measurement of the distance between wireless devices only when a change in distance between the wireless devices has been detected.

Thus, FIG. 7 sets forth a method that allows for detecting a change in distance between wireless devices.

Fig. 8 is a schematic diagram of a node or processing device 800 for detecting a change in distance between a first wireless device and a second wireless device, according to an embodiment of the disclosure. For example, the node or processing device 800 may be configured to perform the method described above with respect to fig. 7. The node or processing device 800 may be, for example, a first wireless device or a second wireless device. Alternatively, one or more of the first wireless device and the second wireless device may form part of a wireless communications network, and the node or processing device 800 may be a node in the wireless communications network.

The node or processing device 800 comprises: processing circuitry 802 and a device-readable medium (e.g., memory) 804. The device-readable medium 804 stores instructions that, when executed by the processing circuit 802, cause the node or processing device 800 to: a change in a parameter over time is determined based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device. The parameter varies depending on a distance between the first wireless device and the second wireless device, and includes: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device. The node or processing means 800 is further caused to: predicting a time at which a periodic step transition is expected to occur based on the determined change in the parameter; and determining a value of the parameter based on the measurement of the second timing signal. The second timing signal is then transmitted between the first wireless device and the second wireless device proximate to the predicted time. In response to determining that the determined value of the parameter is different from the expected value of the parameter, the node or processing device 800 is further caused to: it is determined that a distance between the first wireless device and the second wireless device has changed.

In the illustrated embodiment, node 800 further includes: one or more interfaces 806 for receiving signals from other nodes and/or transmitting signals to other nodes. The interface 806 may use any suitable communication technology, such as electronic signaling, optical signaling, or wireless (radio) signaling.

Although fig. 8 shows the processing circuit 802, the memory 804, and the interface(s) 806 coupled together in series, those skilled in the art will appreciate that the nodes or components of the processing device 800 may be coupled together in any suitable manner (e.g., via a bus or other internal connection).

Fig. 9 is a schematic illustration of a node or processing device 900 for detecting a change in distance between a first wireless device and a second wireless device according to further embodiments of the present disclosure. For example, node or processing device 900 may be configured to perform the method of fig. 7. The node or processing device 900 may be, for example, a first wireless device or a second wireless device. Alternatively, one or more of the first wireless device and the second wireless device may form part of a wireless communications network, and the node or processing device 900 may be a node in the wireless communications network.

The node or processing device 900 includes a parameter change determination module 902. The parameter change determination module 902 is configured to: a change in a parameter over time is determined based on a measurement of a first timing signal transmitted between a first wireless device and a second wireless device. The parameter varies depending on a distance between the first wireless device and the second wireless device, and includes: periodic step transitions due to relative clock drift between the first wireless device and the second wireless device.

As shown, the node or processing device 900 further includes a prediction module 904 configured to: predicting a time at which the periodic step transition is expected to occur based on the determined change in the parameter.

The node or processing device 900 further comprises a comparison module 906. The comparison module 906 is configured to: the value of the parameter is determined based on a measurement of a second timing signal, wherein the second timing signal is subsequently transmitted between the first wireless device and the second wireless device proximate to the predicted time. In response to determining that the determined value of the parameter is different than the expected value of the parameter, the comparison module 906 is further configured to: it is determined that a distance between the first wireless device and the second wireless device has changed.

Node or processing device 900 may also include: one or more interface modules (not shown) for receiving and/or transmitting signals from/to other nodes of the network. The interface may use any suitable communication technology, such as electronic signaling, optical signaling, or wireless (radio) signaling.

The modules described above with respect to fig. 9 may include any combination of hardware and/or software. For example, in an embodiment, a module is implemented entirely in hardware. As noted above, a hardware implementation may include or encompass, but is not limited to: digital Signal Processor (DSP) hardware, reduced instruction set processors, hardware (e.g., digital or analog) circuits including, but not limited to, application specific integrated circuit(s) (ASICs) and/or field programmable gate array(s) (FPGA (s)), and where appropriate, state machines capable of performing such functions. In another embodiment, the modules may be implemented entirely in software. In still other embodiments, modules may be implemented in a combination of hardware and software.

Accordingly, the present disclosure provides methods, apparatuses, and device-readable media for detecting a change in distance between wireless devices. In particular, the occurrence of periodic step transitions in the variation of the parameter with time is used to: the expected value of the parameter proximate to the predicted periodic step transition is compared to the determined value of the parameter to determine whether the distance between the first wireless device and the second wireless device has changed.

It should be noted that the above-mentioned embodiments illustrate rather than limit the concepts disclosed herein, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The word "comprising" does not exclude the presence of elements or steps other than those listed in a statement, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several of the units recited in the statement. Any reference signs in the claims should not be construed as limiting their scope.