WO2019078779A1

WO2019078779A1 - Ftm procedures in wireless networks

Info

Publication number: WO2019078779A1
Application number: PCT/SE2018/051065
Authority: WO
Inventors: Hjalmar WENNERSTRÖM
Original assignee: TerraNet AB
Current assignee: TerraNet AB
Priority date: 2017-10-20
Filing date: 2018-10-18
Publication date: 2019-04-25
Anticipated expiration: 2020-04-20

Abstract

A wireless communication device performs an FTM session as an initiator or responder based on a current setting ([P_A]) of control parameters for the FTM session, so that the FTM session results in distance values indicative of a distance between the communication device and another communication device. Before the FTM session is performed, the device obtains an output signal (MS) of a motion sensor (15) in the device, determines an observed speed (OS_A) based at least on the output signal (MS), and determines the current setting ([P_A]) of the control parameters as a function of the observed speed (OS_A). For example, burst duration and burst period may be set based on predefined constraints (UD, ∆D). The device is thereby operable to dynamically adjust the current setting ([P_A]) to save energy and/or bandwidth, and to resolve or reduce contention issues in the wireless network, while providing for the FTM session to fulfill the predefined constraints.

Description

FTM PROCEDURES IN WIRELESS NETWORKS

Technical Field

The present invention relates generally to the field of wireless communication and, more particularly, to Fine Timing Measurement (FTM) procedures for determination of distance between two communication devices. Background Art

Various positioning techniques may be employed for determining the position of a wireless communication device, also denoted station herein, in relation to another station or in absolute coordinates. For example, positioning techniques may utilize the so-called Fine Timing Measurement (FTM) protocol for determining a value correspon- ding to the distance between the stations, and calculate the position of one of the stations based on the distance value by use of any well-known positioning technique, e.g. based on trilateration, multilateration, etc. The FTM protocol is well-known and standardized in accordance with the IEEE 802.11mc specification which is part of the IEEE 802.11-2016 standard. The FTM protocol provides a procedure for measuring and exchanging timestamps by wireless communication between two stations (nodes).

Generally, one of the stations (initiator or requester) transmits a setting of control parameters to the other station (responder) and thereby causes the responder to generate one or more bursts of FTM signals (frames) in accordance with this setting. The initiator, in turn, generates response signals (frames) to the FTM signals, and records timestamps for arrival of FTM signals and transmission of response signals. The responder records timestamps for transmission of FTM signals and arrival of response signals and includes corresponding timestamps in the FTM signals. By this FTM procedure, timestamps are exchanged between the stations, from the responder to the initiator, so as to allow the initiator to compute the above-mentioned distance value for each burst of FTM signals. Such a distance value may e.g. be a Round Trip Time (RTT), a Time of Flight (ToF), a distance, etc.

In a station that operates under the FTM protocol, it is vital to ensure that the resulting distance values are sufficiently accurate and represent relevant changes in distance between the stations.

In wireless communication systems, it is a general desire to reduce the required processing power, and thus power consumption, of the included stations. It is also desirable to ensure that the available communication channels in the wireless communication system are used as efficiently as possible. In this context, US2017/0156031 discloses FTM signal exchange between two wireless devices. One of the wireless devices determines its latest time of movement by use of a built-in movement sensor and includes the time of movement in a discovery frame for receipt by the other wireless device, which then may compare the received time of movement with a time of movement stored in memory and decide not to initiate an FTM session if the comparison indicates no movement or slight movement.

US2016/0366606 proposes to modify the FTM request frame, which starts an FTM session, to include a suspend FTM request field and a motion threshold field, and to modify an FTM response frame to include a motion detection field. Thereby, an initiator is allowed to indicate, by the FTM request frame, to a responder that the upcoming FTM session will be suspended if the motion threshold has not been crossed since a last FTM session. Upon receipt of the FTM request frame, the responder determines its movement by use of a built-in movement sensor, compares the movement to the motion threshold, and sets a bit in the motion detection field of the FTM response frame to indicate "movement" or "no movement". If "no movement" is indicated, the initiator may suspend the FTM session and no FTM measurements are performed.

While these techniques of disabling the FTM procedure by postponing the FTM session might save processing power, they do not ensure that the FTM session, when eventually performed, results in distance values that are sufficiently relevant and/or accurate and/or precise.

Brief Summary

It is an objective of the invention to at least partly overcome one or more limitations of the prior art.

Another objective is to enable reduced power consumption in stations that communicate in accordance with the FTM protocol, preferably without compromising the relevance and/or accuracy of the resulting distance values.

A further objective is to enable efficient of use of available communication channels in a wireless communication system with such stations.

One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by a communication device, a method of operating a communication device, and a computer-readable medium according to the independent claims, embodiments thereof being defined by the dependent claims.

In a first aspect, there is provided a communication device, comprising: a transceiver for wireless communication; logic and circuitry configured to perform an FTM (Fine Timing Measurement) session as an initiator or a responder, in relation to another communication device, based on a current setting of control parameters for the FTM session, so that the FTM session results in one or more distance values that are indicative of a distance between the communication device and the another

communication device; and a motion sensor configured to generate an output signal indicative of movement of the communication device. The logic and circuitry is further configured to determine, before performing the FTM session, an observed speed based at least on the output signal, and to determine the current setting of the control parameters as a function of the observed speed.

In a second aspect, there is provided a method of operating a communication device with a transceiver for wireless communication. The method comprises performing an FTM (Fine Timing Measurement) session as an initiator or a responder, in relation to another communication device, based on a current setting of control parameters for the FTM session, so that the FTM session results in one or more distance values that are indicative of a distance between the communication device and the another communication device. The method further comprises, before performing the FTM session: obtaining a output signal of a motion sensor in the communication device; determining an observed speed based at least on the output signal; and determining the current setting of the control parameters as a function of the observed speed.

In a third aspect, there is provided a computer-readable medium comprising program instructions which, when executed by a processor, cause the processor to perform the method of the second aspect. The computer-readable medium may be a tangible (non-transitory) product (e.g. magnetic medium, optical disk, read-only memory, flash memory, etc) or a propagating signal.

Any embodiment of the first aspect may be adapted and implemented as an embodiment of the second and third aspects.

Other objectives, as well as features, aspects and advantages of embodiments of the present invention will appear from the following detailed description, from the attached claims as well as from the drawings.

Brief Description of Drawings

The accompanying schematic drawings illustrate example embodiments of the invention.

FIG. 1A is a network diagram illustrating an exemplary network environment with two stations, and FIG. IB is an example of relative position and movement of the stations.

FIG. 2 is a timing diagram for timestamp measurement and signal exchange between the stations in FIGS 1A-1B during an FTM session.

FIG. 3 is a timing diagram for measurements made during a burst of FTM frames. FIG. 4 is a diagram to exemplify bursts of signals transmitted during an FTM session and associated control parameters and measurement values.

FIG. 5 is a functional block diagram of an initiator station in accordance with an embodiment.

FIG. 6 is a flow chart of an embodiment for defining one or more control parameters in an initiator or responder station.

FIG. 7 is a timing diagram of data items that may be generated and used in various embodiments of the invention.

FIG. 8A is a flow chart of an embodiment for determining an observed speed in an initiator or responder station, and FIGS 8B-8C are flow charts of alternative embodiments for determining an observed speed in an initiator station.

FIG. 9 is a flow chart of an embodiment for defining a control parameter in an initiator or responder station.

FIG. 10 is a flow chart of an embodiment of a measurement procedure in an initiator station.

FIGS 1 lA-1 IB are flow charts of embodiments for defining control parameters in a responder station.

FIG. 12 is a block diagram for a wireless station. Detailed Description of Example Embodiments

Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Like reference signs refer to like elements throughout.

Also, it will be understood that, where possible, any of the advantages, features, functions, devices or operational aspects of any of the embodiments of the present invention described or contemplated herein may be included in any of the other embodiments of the present invention described or contemplated herein. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form, and vice versa, unless explicitly stated otherwise. As used herein, "at least one" shall mean "one or more" and these phrases are intended to be interchangeable. Accordingly, the terms "a" and "an" shall mean "at least one" or "one or more," even though the phrase "one or more" or "at least one" is also used herein. As used herein, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. It will furthermore be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Well-known functions or constructions may not be described in detail for brevity and/or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

In the following description, embodiments of the invention will be exemplified with reference to the Fine Timing Measurement (FTM) protocol in accordance with the IEEE 802.11 standard for wireless local area network (WLAN) communication. The term "FTM protocol" is intended to include the current protocol also referred to as IEEE 802.11mc, as well as future IEEE 802.11 protocols that are based on the same principle of timestamp exchange. The embodiments described herein may utilize the FTM protocol for any type of wireless communication in accordance with IEEE802. i l, including but not limited to 802.11a, 802.1 lac, 802.11b, 802. l ip and 802.11s.

FIG. 1A is a network diagram illustrating an exemplary network environment suitable for FTM exchanges. The wireless network 10 in FIG. 1 includes two communication devices 10A, 10B, denoted nodes or stations in the following, which communicate in accordance with the IEEE 802.11 standard. The respective station 10A, 10B may be a stationary or non-stationary device of any structure. Examples of such devices include mobile phones, tablets, computers, access points, wearables, headsets, vehicles, IoT devices, etc.

FIG. IB illustrates a situation in which the stations 10A, 10B are moving during the FTM exchanges, as indicated by a respective velocity vector v_A, v_B. The distance between the stations 10A, 10B is determined based on the FTM exchanges and is indicated by a double-ended arrow.

In the following examples, station 10A operates as initiator station ("initiator") during the FTM exchange, and station 10B operates as responder station ("responder"). The initiator 10A thus initiates an FTM session with the responder 10B. As will be described below, an FTM session involves an exchange of timestamps between the stations 10A, 10B to allow the initiator 10A to determine at least one distance value. The distance value is indicative of the distance between the stations 10A, 10B and may be given in either time units or length units. For example, the distance value may be a distance (range), a time-of-flight (ToF), or a round-trip time (RTT). The distance value may be used for any conceivable purpose by the initiator 10A. In one example, the initiator 10A may determine, based on one or more distance values, a position in relative coordinates or geo-coordinates. To this end, the initiator 10A may, but need not, perform FTM exchanges with more than one responder 10B, and process the resulting distance values, e.g. by trilateration and/or by time-difference-of-arrival (TDOA) techniques, to determine the position of the initiator 10A or the position of the respective responder 10B, as is well-known in the art.

Reference is now made to FIG. 2, which is a timing diagram that exemplifies operations and signal exchanges between the initiator 10A and the responder 10B during an FTM session in accordance with the FTM protocol. As shown, the initiator 10A may transmit an initial FTM request (iFTMR) frame to request an FTM session with the responder 10B. The iFTMR frame may include parameters such as category, public action, trigger, LCI measurement request, location civic measurement request and one or more FTM parameters. The FTM parameters, denoted "control parameters" in the following, define the desired number and timing of the measurements to be performed during the FTM session, as will be further exemplified below. The responder 10B may acknowledge receipt of the iFTMR frame with an acknowledgement (ACK) frame. Alternatively, the responder 10B may refuse the request or return a message indicating a modification of one or more control parameters ("negotiation phase"). In one example, such a modification may be included in the first FTM frame (below).

Under the current FTM standard, further messages (frames) may be exchanged between the initiator 10A and the responder 10B before the FTM session is started. During the FTM session, the responder 10B transmits a sequence of FTM frames in accordance with the control parameters, and the initiator 10A responds with an acknowledgement (ACK) frame to the respective FTM frame, where at least a subset of the FTM frames contains timestamps that are recorded by the responder 10B. Specifically, in the illustrated example, the responder 10B sends a first FTM frame, FTMl, and records the time of departure (ToD) for FTMl by timestamp tl(l). The initiator 10A records the time of arrival (To A) for FTMl by timestamp t2(l), and sends ACK in response to FTMl. The initiator 10A records ToD for ACK by timestamp t3(l). The responder 10B records ToA for ACK by timestamp t4(l), and includes the timestamps tl(l) and t4(l) in a second FTM frame, FTM2, which is received by the initiator 10A. Thereby, the initiator 10A is able to calculate a sample value for the first measurement. The sample value is indicative of the distance between the stations 10A, 10B and may be given in length units or time units. Examples of sample values include RTT, ToF and range. For example, RTT may be calculated as t4(l)-t3(l)+t2(l)-tl(l), ToF may be calculated as RTT/2, and the range may be calculated as ToF*c, where c is the propagation speed of the wireless signals (e.g. the speed of light). The FTM session is defined in terms of bursts of FTM frames. This is schematically illustrated in the timing diagram of FIG. 3, which shows a burst B comprising N measurements, designated by FTM_1, FTM_2, FTM_N. The respective measurement comprises an exchange of an FTM frame and an ACK frame as shown in FIG. 2. During each measurement, the timestamps presented in FIG. 2 are measured by the stations 10A, 10B, whereupon ToD of the FTM frame and ToA of the ACK frame are sent with the next FTM frame (of the next measurement). The time delay between FTM frames, designated by AFTM in FIG. 3, may be directly or indirectly defined by the above-mentioned control parameters. The FTM standard also sets a minimum value for the time delay AFTM.

According to the FTM standard, each of the stations 10A, 10B may terminate an ongoing FTM session at any time, by transmitting a frame with a dedicated parameter value.

FIG. 4 is a timing diagram to schematically illustrate an FTM session S between the stations 10A, 10B. The FTM session S comprises a number of consecutive bursts B, where each burst comprises a number of consecutive measurements FTM_1, FTM_2, FTM_N. In the illustrated example, the responder 10B sends N FTM frames during each burst B. Each burst has a burst duration BD. The bursts B are transmitted with a burst period BP, which is the time difference between initiations of consecutive bursts B. The above-mentioned control parameters for the FTM session may comprise the number of bursts (designated by #B in the following), the burst period BP, the burst duration BD, and the number of FTM frames for each burst.

According to the current FTM standard, the control parameter #B may be given by an exponent of an exponential function with base 2, with the exponent being set in the range of 0-14. The burst period BP may be set to multiples of 100 ms, given by a multiplicative factor in the range of 1-65535. Thus, BP may be as small as 100 ms and as large as approx. 1.8 hours. The burst duration BD may be set to certain discrete values in the range of 250 μ8 - 128 ms, given by a control value in the range of 0-15. In the current FTM standard, BD may be set to one of the following: 250 μ8, 500 μ8, 1 ms, 2 ms, 4 ms, 8 ms, 16 ms, 32 ms, 64 ms and 128 ms. It may also be possible to set an infinite BD. The number of FTM frames per burst, #FTM, may be set to an integer in the range of 1-31.

When the FTM session S is completed, the initiator 10A may request a new FTM session with the responder 10B by sending an iFTMR frame in accordance with FIG. 2.

As noted above, the initiator 10A may compute a sample value for each measurement, FTM_1, FTM2, FTM_N. These sample values are denoted "frame distances" in the following, since they are computed from timestamps that are measured based on a respective FTM frame. In FIG. 4, frame distances are designated by D. Typically, the initiator 10A computes an aggregated measurement value for each burst B, designated by D in FIG. 4 and denoted "burst distance" in the following. The burst distance D may be computed by an aggregation of the frame distances D measured for the burst B, e.g. by averaging. Alternatively, as well known in the art, the computation of frame distan- ces D may be omitted and the burst distance D may be computed as a function of the timestamps that are measured during the burst B.

Embodiments of the invention are based on the insight that it may be undesirable to use a nominal setting of the control parameters, since the nominal setting must be defined to ensure that proper distance values are generated by the FTM procedure in a worst-case scenario. For example, consider a use case in which the initiator 10A is a handheld tool which determines its distance to a responder 10B, e.g. a fixed access point. Here, the nominal setting may be defined to fulfill a requirement specification while the handheld tool is in use, typically while the handheld tool is moved around a maximum speed. Such a requirement specification may, e.g., define a required sampling rate of burst distances and a required accuracy of the burst distances. The initiator 10A will then operate with the nominal settings irrespective of the actual movement of the handheld tool, leading to a waste of energy and bandwidth, and possibly congestion in a wireless network that includes several handheld tools.

Embodiments of the invention provide an dynamic and automatic mechanism for adjusting an FTM procedure between two wireless stations so as to free up the resources of the involved stations as much as possible, e.g. to save energy and/or bandwidth, and to resolve or reduce contention issues in the wireless network, while ensuring that the resulting burst distances fulfill the requirement specification. Specifically, embodiments of the invention provide a technique of dynamically adjusting the setting of the control parameters for the FTM sessions that are performed so as to achieve the foregoing effect.

Embodiments of the inventions are also based on an insight that the control parameters may be separated by their effect on the resulting burst distances. For example, #B may be seen to determine for how long the burst distances should be measured, BP may be seen to determine the sampling rate of the burst distances D, and BD may be seen to determine the accuracy of the burst distances. The term accuracy is used in its ordinary meaning and refers to systematic errors of data samples. A lack of accuracy may be caused by large changes in distance between stations during a burst B.

According to this insight, BD may be reduced with increasing movement of one or both stations 10A, 10B to ensure a required accuracy, and vice versa. Likewise, BP may be reduced with increasing movement of one or both stations 10A, 10B, and vice versa, to ensure that the burst distances D are generated at a sufficient rate to represent relevant changes in distance between the stations 10A, 10B. Embodiments of the invention are also based on the insight that it would be beneficial to gain information about the current movement of the respective station 10A, 10B, since this would make it possible to infer a current setting of the control parameters that may improve the use of resources while fulfilling the requirement specification.

Thus, in accordance with embodiments of the invention, a station that operates as either initiator 10A or responder 10B may determine the current setting of the control parameters for an FTM session based on an output signal of a motion sensor located in the station.

Reverting to the use case of a handheld tool as described above, it is realized that an initiator 10A (i.e. the tool) configured in accordance with embodiments of the invention may e.g. reduce the number of measurements per unit time with decreasing movement, as indicated by the motion sensor. For example, when the handheld tool is placed to rest, the number of measurements per unit time may be significantly reduced, thereby saving both energy and bandwidth.

Embodiments of the invention involve functions and structures that may be implemented in a station that operates as either an initiator 10A or a responder 10B. For reasons of simplicity, the following description will start by describing the functions and structures of an initiator 10A.

FIG. 5 is a functional block diagram of a station according to an embodiment of the present invention. The station is configured to operate as an initiator 10A and comprises an FTM module 11, which is configured to initiate and perform an FTM session as exemplified above with reference to FIGS 2-4. Based on the timestamps generated during the FTM session, the FTM module 11 computes and outputs one or more burst distances D (FIG. 4). The station further comprises a parameter estimator module 12, which is configured to determine a current setting of the control parameters for an upcoming FTM session. Thus, module 12 provides the current setting (designated [PA] in FIG. 5) to module 11, which then initiates the FTM session by including [PA], or part thereof, in an iFTMR frame (FIG. 2). The module 12 determines [PA] based on a set of predefined constraints 13, indicated by UD and AD in FIG. 5, and an observed speed OSA, which provided by a motion estimator module 14. The module 14 is configured to compute the observed speed OSA based on the output signal MS of a motion sensor 15 in the station. In some embodiments, as indicated in FIG. 5, the module 14 may also be configured to compute a motion variability VAR based on the output signal MS, for use by module 12 when determining the current setting [PA]. In some embodiments, as indicated by a dashed arrow in FIG. 5, module 14 may operate on the burst distances D generated by module 11 when computing the observed speed OSA- The motion sensor 15 is distinct from the FTM module 11 and may be any type of device that is configured to quantify movement of the station, preferably in relation a fixed reference point. In a non-limiting example, the motion sensor 15 may include one or more of a gyroscope, a magnetometer, an acceleration sensor, an inertial sensor, a speedometer, a GPS detector, an ultrasonic motion detector, a camera-based motion detector, and a radar detector. In certain installations, e.g. a vehicle, the motion sensor 15 may be configured to measure a rotation of a driven component, e.g. a wheel, by use of a suitable sensor, e.g. an optical or magnetic sensor. With reference to FIG. IB, the burst distances D generated by the FTM module 11 represents the distance between the stations 10A, 10B, and the motion signal MS generated by the motion sensor 15 represents the length of the speed vector v_A, designated by v_A in the following.

FIG. 6 illustrates an embodiment of a procedure 100A performed by an initiator 10A to determine the current setting [PA]. The procedure 100A may be implemented by modules 12 and 14 in FIG. 5. A specific purpose of the procedure 100A is to determine a value for the burst duration BD and/or the burst period BP. In step 101, a predefined update distance UD is input, e.g. retrieved from a memory in the station. The update distance UD is a constraint that defines a maximum change in distance between consecutive bursts B in the upcoming FTM session. In step 102, a predefined accuracy AD is input, e.g. from memory. The predefined accuracy AD is a constraint that defines a maximum measurement error for the burst distances D that will be generated during the upcoming FTM session. Step 103 computes the observed speed OSA based on the output signal MS. Embodiments of step 103 are described further below with reference to FIGS 8A-8C. Step 104 computes the burst duration BD as a function of the accuracy AD and the observed speed OSA (indicated by function fl in FIG. 6). In one example, fl is a function of AD/OS _A, e.g. BD < AD /OS_A. Preferably, BD is set to the largest possible value, recalling that BD can only be set to certain distinct values. Step 105 computes the burst period BP as a function of the burst distance BD, the update distance UD and the observed speed OSA (indicated by function f2 in FIG. 6). In one example, f2 is a function of UD/OS_A, e.g. BP ≤ BD + UD /OS_A. Preferably, BP is set to the largest possible value, recalling that BP can only be set to multiples of 100 ms. In step 106, at least one of BD and BP is included in the current setting [PA], which is then output, e.g. for use by the FTM module 11. Other control parameters, if present, may be set to predefined values in [PA] .

It should be understood that the constraints UD, AD may differ depending on the use case for the station.

A first example use case has AD = 0.1 m and UD = 2.0 m, which may be suitable for a wearable device. Assume that step 103 computes OSA = 1.4 m/s, which is typical walking speed of a human. Step 104 may then compute BD = AD/OS_A = 71.45 ms and set BD = 64 ms, and step 105 may compute BP = BD + UD /OS_A = 64 ms + 1428.5 ms = 1492.5 ms and set BP = 1400 ms.

A second example use case has AD = 0.1 m and UD = 3.0 m, which may be suitable if the station is a car. Assume that step 103 computes OSA = 30 m/s, which is typical driving speed of a car. Step 104 may then compute BD = AD /OS_A = 3.33 ms and set BD = 2 ms, and step 105 may compute BP = BD + UD /OS_A = 2 ms + 100 ms = 102 ms and set BP = 100 ms.

A third example use case has AD = 0.01 m and UD = 10 m, which may be suitable if the station is an industrial robot. Assume that step 103 computes OSA = 0.1 m/s. Step 104 may compute BD = AD /OS_A = 100 ms and set BD = 100 ms, and step 105 may compute BP = BD + UD/OS_A = 100 ms + 100000 ms = 100100 ms and set

BP = 100100 ms.

There are many alternatives to the functions fl and f2. In one alternative, the function f2 also includes an observed acceleration OAA, which is determined based on the output signal MS of the motion sensor 15, e.g. BP < BD + At, wherein BD is the burst duration, and At is given by the equation UD = OS_A ^■ At + 1/2^■ OA_A ^■ (At)².

Such an alternative may improve the ability of the procedure 100A to define [PA] such that the FTM session meets its constraints.

The procedure 100A in FIG. 5 may involve a further step (not shown) that switches to the use of predefined values for BD and BP when the observed speed OSA falls below a predefined threshold value, to avoid division by values close to zero in fl and/or f2.

In the following, different embodiments for computing the observed speed OSA (step 103) will be described with reference to FIGS 8A-8C. To facilitate understanding, reference is first made to FIG. 7 which graphically illustrates, along a time line, data items that may be generated by an initiator station 10A, where each dot corresponds to such a data item. The initiator 10A (e.g. by module 11) initiates and performs a sequence of FTM sessions S, each involving a sequence of bursts B and resulting in a corresponding sequence of burst distances D . The onset of each FTM session S is indicated by a dash-dotted line. The respective FTM session is performed in accordance a current setting [PA] determined by the initiator 10A (e.g. by module 12) before the respective FTM session. As indicated by a solid arrow, the current setting [PA] is determined based on a "station speed" v_A which thus, in this example, is the observed speed OSA- The station speed v_A is generated based on one or more momen- tary speed values v_MS that are derived from the output signal MS of the motion sensor 15 (e.g. by module 14). The respective speed value v_MS may be a data sample in the output signal MS or may be calculated based on the output signal MS. The momentary speed values v_MS may be generated continuously, as shown, or on demand. As indicated by arrows in FIG. 7, it is also possible to compute (e.g. by module 14) a relative speed v_AB between the stations 10A, 10B based on at least two previously generated burst distances D. The relative speed v_AB may thus represent the change in distance between the stations 10A, 10B per unit time. In some embodiments, the relative speed v_AB may be used when computing the observed speed OSA (e.g. by module 14).

FIG. 8A illustrates a procedure 103A for computing the observed speed OSA according to a first embodiment of step 103 in FIG. 6. In step 110, one or more speed values v_MS are obtained from the output signal MS, and the station speed v_A is computed by operating a function f3 on the speed value(s) v_MS. The function f3 may set the station speed v_A equal to one speed value, e.g. the most recent v_MS as indicated by a solid arrow in FIG. 7. Alternatively, as indicated by additional dashed arrows in FIG. 7, f3 may compute the station speed v_A based on two or more speed values v_MS, e.g. as an average, optionally weighted, or as an extrapolated (projected) value. In step 111, the observed speed OSA is set to the station speed v_A. Generally, step 111 may set OSA as a function of v_A, e.g. by applying a weight factor. The procedure 103A is simple and robust and may be particularly useful in use cases when the responder 10B is known to be fixed or move at much lower speeds than the initiator 10A.

FIGS 8B-8C illustrate embodiments that also factor in the relative speed v_AB when computing the observed speed OSA- Such embodiments thus also take into account the movement of the responder 10B in relation to the initiator 10A and may thereby, at least for some use cases, result in an improved current setting [PA]. For example, if the initiator 10A is a first car, which is parked next to a road, and the responder 10B is a second car moving at high speed on the road towards the first car, v_A will be zero and v_AB will be large. In this situation, it may be undesirable to define [PA] solely based on v_A, since this may lead to burst distances D that are both inaccurate (by large BD) and too sparse (by large BP). On the other hand, when the first and second cars move at high speed in the same direction on the road, v_A will be large and v_AB will be close to zero. In such a situation, it may be desirable to define [PA] based on v_A, to ensure that the burst distances D are generated with adequate accuracy and at a sufficient rate even if the second car should suddenly break during the forthcoming FTM session.

The procedure 103B in FIG. 8B includes step 112, which may be identical to step 110 (procedure 103A) and computes the station speed v_A. In step 113, the relative speed v_AB is computed by operating a function f4 on previously generated burst distances D. For example, f4 may compute the rate of change between the most recent samples, an average rate of change for three or more samples, or a maximum rate of change between consecutive data samples over time period, e.g. the most recent FTM session. In step 114, the relative speed v_AB is compared to the station speed v_A. If v_AB exceeds v_A, OSA is set to v_AB in step 115. Otherwise, OSA is set to v_A in step 116. Generally, steps 115, 116 may set OSA as a function of v_A and v_AB, respectively, e.g. by applying a weight factor. The procedure 103B thus computes the observed speed OSA as a function of the largest of the station speed v_A and the relative speed v_AB .

The procedure 103C in FIG. 8C includes step 117 which may be identical to step

110 (procedure 103A) and computes the station speed v_A, and step 118 which may be identical to step 113 (procedure 103B) and computes the relative speed v_AB . In step 119, the observed speed OSA is computed by operating a function f5 on the station speed v_A and the relative speed v_AB . The function may involve a linear or non-linear combination of v_A and v_AB, e.g. according to OS_A = k_A ^■ v_A + k_AB · v_AB, where k_A, k_AB are weight factors. The weight factors may be predefined and fixed. Alternatively, the weight factors may be intermittently updated based on historic speed values v_MS and/or burst distances D, or equivalently, historic values of the station speed v_A and/or the relative speed v_AB . In one example, the weight factors are given by k_A = v_A/(v_A + v_AB) and

^AB — ^VAB / .^VA + ^VAB ) - I¹¹ another example, the weight factors are given by k_A— VAR(¾)/(VAR(¾) + VAR(^s)) and k_AB = VAR(v_AB)/(VAR(v_A) + VAR(v_AB)), where VAR is a variability function that represents the variation among the data samples. Thus,

represent the variation among preceding values of station speed and relative speed, respectively (cf. FIG. 7). For example, the variability function VAR may generate a variance, a standard deviation, a (normalized) sum of differences between consecutive data samples ("total variation"), a (normalized) sum of differences between the data samples and their mean ("mean deviation"), an interquartile range, etc.

FIG. 9 illustrates an embodiment of a procedure 100B performed by an initiator 10A to determine the current setting [PA]. The procedure 100B may be implemented by modules 12 and 14 in FIG. 5 and may be performed in combination with the procedure 100A. A specific purpose of procedure 100B is to determine the number of bursts (#B) based on the motion stability of the initiator 10A. The underlying rationale is that if there is little variability among the speed values v_MS before the upcoming FTM session, it is likely that the observed speed OSA will relevant for a longer time period, and the number of bursts may therefore be increased. In step 120, a first variability VARl is computed by operating a function f6 on a recent set of speed values v_MS, which may include any combination of speed values generated in advance of an upcoming FTM session (cf. FIG. 7), e.g. within a given time period, during a given number of bursts, a given number of FTM sessions, etc. VARl represents the variation among the speed values v_MS, and f6 may be any suitable function, including the above-mentioned examples of the variability function VAR. Reverting to FIG. 5, it may be noted that VAR, which is obtained by module 12 from module 14, may correspond to VARl. Step 122 compares VAR1 to a first variability threshold TH1, which sets an upper limit for the variability. If VAR1 exceeds TH1, step 121 proceeds to step 122 which retrieves a predefined value of #B and outputs a corresponding [PA]. The control parameters BD and/or BP may be set by procedure 100A or be predefined. If VAR1 does not exceed TH1, step 121 proceeds to step 123 which compares VAR1 to a second variability threshold TH2 (<TH1). If VAR1 exceeds TH2, step 123 proceeds to step 124 which decreases #B compared to the most recent [PA], and outputs a thus updated [PA]. If VAR1 exceeds TH2, step 123 proceeds to step 124 which instead increases #B and outputs a thus updated [PA] .

FIG. 10 illustrates an embodiment of a measurement procedure 200, during which the motion stability is continuously evaluated with respect to an abort condition. The motion stability may be evaluated based on the speed values v_MS and/or the burst distances D . The underlying rationale is that if sudden large changes in motion occur, it may be advantageous to prematurely stop an ongoing FTM session, update [PA] and initiate a new FTM session with the updated [PA]. This is likely to improve both quality and relevance of the resulting burst distances D when motion suddenly increases, and save energy and bandwidth when motion suddenly decreases. For example, a handheld tool that has been placed to rest and operates an FTM session with large BD, BP and #B, may quickly abort the FTM session and start a new FTM session with reduced BD, BP and #B whenever the motion sensor indicates that someone has lifted the tool.

The measurement procedure 200 involves two parallel and independent processes, represented by steps 201-202 and steps 204-208, respectively. Steps 201-202 implement a measurement function. In step 201, a current setting [PA] is input, e.g. given by procedure 100A and/or procedure 100B. In step 202, an FTM session is initiated with the current setting [PA] and resulting burst distances D are computed. Steps 204-208 implement a monitoring function. Step 204 computes a second variability VAR2 by operating a function f7 on a recent set of speed values v_MS. Step 205 compares VAR2 to a third variability threshold TH3. If VAR2 exceeds TH3, step 205 proceeds to step 206 which aborts the ongoing FTM session and initiates an update of [PA], e.g. by procedure 100A and/or procedure 100B, and then proceeds to step 201. Alternatively, a predefined [PA] may be used in step 201. If VAR2 does not exceed TH3, step 205 proceeds to step 207 which computes a third variability VAR3 by operating a function f8 on a recent set of burst distances D. Step 208 compares VAR3 to a fourth variability threshold TH4. If VAR3 exceeds TH4, step 208 proceeds to step 206. If VAR3 does not exceed TH3, step 205 proceeds to step 204. It should be understood that f7 and f8 may be any suitable function, including the above-mentioned examples of the variability function VAR. Further, VAR in FIG. 5 may correspond to VAR2 and/or VAR3. As noted above, at least a subset of the functions and structures which have been described in relation to an initiator 10A may also, or alternatively, be implemented in a responder 10B. Such a responder 10B may be configured in accordance with FIG. 5, although with an FTM module 11 that is configured to perform an FTM session without generating burst distances. In one embodiment, the responder 10B implements procedure 100A (FIG. 6) to determine a current setting for a forthcoming FTM session which is initiated by an initiator 10A. The current setting for the responder 10B is designated by [PBL The responder 10B may e.g. apply [P_B] when executing the FTM session, instead of the current setting [PA] received with the iFTMR frame (FIG. 2). In one embodiment, the responder 10B implements the procedure 103A (FIG. 8A) to compute the observed speed for use in procedure 100A. The observed speed of the responder 10B is designated by OSB- In one embodiment, the responder 10B implements procedure 100B (FIG. 9) to determine the current setting [P_B] .

FIGS 11A-11B are flow charts of procedures 300A, 300B for operating a responder station 10B in accordance with further embodiments. In both procedures 300A, 300B, the responder 10B determines a current setting [P_B] based on the output signal of a motion sensor, e.g. as described hereinabove, while also taking into account a proposed setting [PA] received from an initiator 10A. To the extent that [PA] reflects the movement of the initiator 10A, the procedures 300A, 300B provide an alternative or supplementary way of taking the movement of both the initiator 10A and the responder 10B into account when determining the current setting [P_B] for an upcoming FTM session.

The procedure 300A in FIG. 11A involves a step 130 of receiving a proposed setting [PA] from the initiator 10A. The proposed setting [PA] may or may not have been set in by the initiator 10A as a function of an observed speed OSA- In step 131, the responder 10B determines a current setting [P_B] by performing procedure 100A (FIG. 6), based on an observed speed OS_B obtained by procedure 103A (FIG. 8A), and optionally by performing procedure 100B (FIG. 9). For example, step 131 may determine at least part of the current setting [P_B] based on one or more speed values v_B that are derived from the output signal MS of a motion sensor 15 in the responder 10B. In step 132, the responder 10B selectively updates [P_B] based on [PA]. In one example, [P_B] is replaced in its entirety by [PA] if a specific condition is fulfilled, e.g. if at least one of BP, BD and #B is smaller in [PA] than in [P_B] . In another example, [P_B] is updated to contain the smallest value in [PA] and [P_B] of at least one of BD, BP and #B. Thus, if BD is smaller in [PA] than in [P_B] , then BD in [P_B] is replaced by BD in [PA]. In step 133, the responder 10B returns the updated [P_B] to the initiator 10A in accordance with the FTM procedure. In step 134, the responder 10B transmits FTM frames in accordance with the updated [P_B]. The skilled person understands that step 133 may be performed as part of step 134.

Procedure 300B in FIG. 1 IB presumes that the initiator 10A has derived the proposed setting [PA] as a function of an observed speed OSA, in accordance with proce- dure 100A (FIG. 6). In step 135, which may be identical to step 130, the responder 10B receives a proposed setting [PA] from the initiator 10A. In step 136, the responder 10B computes or estimates the observed speed OSA that was used by the initiator 10A when determining [PA], by operating a function f9 on [PA]. For example, the function f9 may be defined with knowledge of at least one of the functions Π, f2 and at least one of the constraints AD, UD, and may operate on at least one of BD and BP in [PA]. In step 137, the responder 10B computes the observed speed OS_B by performing procedure 103A (FIG. 8A). In step 138, the responder 10B defines the current setting [P_B] as a function of OSA and OS_B- For example, BD and/or BP may be determined in accordance with procedure 100A (FIG. 6), but where OSA is replaced by a combination of OSA and OS_B, e.g. a sum, optionally weighted, or the largest value of OSA and OS_B- In step 139, the responder 10B returns [P_B] to the initiator 10A in accordance with the FTM procedure. In step 140, the responder 10B transmits FTM frames in accordance with [P_B]. The skilled person understands that step 139 may be performed as part of step 140.

FIG. 12 is a block diagram of an exemplary communication station 20 according to some embodiments. The station 20 may e.g. be the same as the station 10A or station 10B in FIG. 1. The station 20 may also be switchable between a first mode, in which it operates as an initiator 10A, and a second mode, in which it operates as a responder 10B. The station 20 comprises a controller 22, a memory 23, a transceiver 24, an antenna 25 and the above-mentioned motion sensor 15. The controller or control unit 22 is responsible for the overall operation of the station 20 and may be implemented by any commercially available CPU ("Central Processing Unit"), DSP ("Digital Signal

Processor"), microprocessor or other electronic programmable logic device. The controller 22 may be implemented using instructions that enable hardware functionality, e.g. executable computer program instructions that may be stored on the memory 23. The controller 22 may be configured to read the instructions from the memory 23 and execute these instructions to control the operation of the station 20, e.g. to implement the modules 11, 12 and 14 in FIG. 5. The memory 23 may be implemented using any commonly known technology for computer-readable memories such as ROM, RAM, SRAM, DRAM, CMOS, FLASH, DDR, SDRAM or some other memory technology. The transceiver 24 is configured for communication in accordance with any relevant wireless communication standard. The antenna 25 may include any suitable configuration, structure and/or arrangement of one or more antenna elements, components, units, assemblies and/or arrays. The operation of the station 20 may be controlled by a combination of circuitry and logic, where the circuitry may comprise the processor 22 and the memory 23, as well as further hardware, and the logic may be at least partly provided as executable program instructions. The program instructions may be provided to the station on a computer-readable medium, which may be a tangible (non-transitory) product (e.g. magnetic medium, optical disk, read-only memory, flash memory, etc) or a transitory product, such as a propagating signal.

The description given above relates to various general and specific embodiments, but the scope of the invention is limited only by the appended claims.

Claims

1. A communication device, comprising:

a transceiver (24) for wireless communication,

logic and circuitry (22, 23) configured to perform an FTM (Fine Timing

Measurement) session as an initiator (10A) or a responder (10B), in relation to another communication device, based on a current setting ([PA] ; [PB]) of control parameters for the FTM session, so that the FTM session results in one or more distance values that are indicative of a distance between the communication device and the another

communication device, and

a motion sensor (15) configured to generate an output signal (MS) indicative of movement of the communication device,

wherein said logic and circuitry (22, 23) is further configured to determine, before performing the FTM session, an observed speed (OSA; OSB) based at least on the output signal (MS), and to determine the current setting ([PA] ; [PB]) of the control parameters as a function of the observed speed (OSA; OSB).

2. The communication device of claim 1, wherein said logic and circuitry (22, 23) is configured to obtain one or more speed values (v_MS) from the output signal (MS), and to determine the observed speed (OSA; OSB) as a function of the one or more speed values (v_MS).

3. The communication device of claim 1 or 2, wherein said logic and circuitry (22, 23) is further configured to determine the current setting ([PA] ; [PB]) based on at least one of a predefined update distance (UD), which represents a maximum change in distance between consecutive bursts (B) of FTM frames in the FTM session, and a predefined accuracy (AD), which represents a maximum measurement error for the one or more distance values that are generated during the FTM session.

4. The communication device of claim 3, wherein said control parameters comprise one or more of: a count (#B) of bursts (B) of FTM frames to be transmitted during the FTM session, a burst duration (BD) of the respective burst (B) of FTM frames, and a burst period (BP) representing a time difference between initiations of consecutive bursts (B) of FTM frames.

5. The communication device of claim 4, wherein said logic and circuitry (22, 23) is configured to determine the burst duration (BD) for the FTM session as a function of the predefined accuracy (AD) and the observed speed (OSA; OSB).

6. The communication device of claim 5, wherein said logic and circuitry (22, 23) is configured to determine the burst duration as: BD < AD /OS, wherein AD is the predefined accuracy, and OS is the observed speed.

7. The communication device of any one of claims 4-6, wherein said logic and circuitry (22, 23) is configured to determine the burst period (BP) for the FTM session as a function of the burst distance (BD), the update distance (UD) and the observed speed (OS_A; OS_B).

8. The communication device of claim 7, wherein said logic and circuitry (22, 23) is configured to determine the burst period as: BP < BD + UD /OS, wherein BD is the burst duration, UD is the update distance, and OS is the observed speed.

9. The communication device of claim 7, wherein said logic and circuitry (22, 23) is configured to determine the burst period as: BP < BD + At, wherein BD is the burst duration, and At is given by the equation UD = OS^■ At + -^■ OA^■ (At) , wherein UD is the update distance, OS is the observed speed and OA is an observed acceleration which is determined by said logic and circuitry (22, 23) based at least on the output signal (MS).

10. The communication device of any one of claims 4-9, wherein said logic and circuitry (22, 23) is configured to compute a variability (VAR) of speed values (v_MS) obtained from the output signal (MS) before performing the FTM session, and determine the count (#B) of bursts (B) for the FTM session as a function of the variability (VAR).

11. The communication device of any one of claims 4- 10, wherein said logic and circuitry (22, 23) is configured to, during the FTM session, obtain a time sequence of speed values (v_MS) from the output signal (MS), repeatedly compute a variability

(VARl) for a recent set of speed values (v_MS) in said time sequence, and abort the FTM session if the variability (VARl) exceeds a predefined variability threshold (TH3).

12. The communication device of any one of claims 2- 11, wherein said logic and circuitry (22, 23) is configured to perform the FTM session as an initiator (10A), and wherein said logic and circuitry (22, 23) is further configured to determine the observed speed (OSA) as a function of the one or more speed values (v_MS) obtained from the output signal (MS) and distance values (D) computed by said logic and circuitry (22, 23) for bursts of FTM frames transmitted during a preceding FTM session.

13. The communication device of claim 12, wherein said logic and circuitry (22, 23) is configured to determine the observed speed (OSA) as a weighted combination of a first speed (v_A) given by the one or more speed values (v_MS) and a second speed v_AB) given by the distance values (D).

14. The communication device of claim 13, wherein said logic and circuitry (22, 23) is configured to determine a weight for the weighted combination based on the one or more speed values (v_MS) obtained from the output signal (MS) and the distance values (D).

15. The communication device of claim 12, wherein said logic and circuitry (22, 23) is configured to determine the observed speed (OSA) as a function of the largest of a first speed (v_A) given by the one or more speed values (v_MS) and a second speed v_AB) given by the distance values (D).

16. The communication device of any preceding claim, wherein said logic and circuitry (22, 23) is configured to perform the FTM session as a responder ( 10B), and wherein said logic and circuitry (22, 23) is further configured to receive a proposed setting ([PA]) of the control parameters from an initiator ( 10A), and selectively update, before performing the FTM session, the current setting ([PB]) based on the proposed setting ([P_A]).

17. The communication device of any one of claims 1- 15, wherein said logic and circuitry (22, 23) is configured to perform the FTM session as a responder ( 10B), and wherein said logic and circuitry (22, 23) is further configured to receive a proposed setting ([PA]) of the control parameters from an initiator ( 10A), and estimate an initiator speed (OSA) of the initiator (10A) based on the proposed setting ([PA]), wherein said logic and circuitry (22, 23) is configured to determine the current setting ([PB]) as a function of the initiator speed (OSA) and the observed speed (OSB).

18. A method of operating a communication device with a transceiver (24) for wireless communication, said method comprising:

performing an FTM (Fine Timing Measurement) session as an initiator ( 10A) or a responder (10B), in relation to another communication device, based on a current setting ([PA] ; [PB]) of control parameters for the FTM session, so that the FTM session results in one or more distance values that are indicative of a distance between the communication device and the another communication device,

said method further comprising, before performing the FTM session:

obtaining an output signal (MS) of a motion sensor (25) in the communication device,

determining an observed speed (OSA; OS_B) based at least on the output signal (MS), and

determining the current setting ([PA] ; [P_B]) of the control parameters as a function of the observed speed (OSA; OS_B).

19. A computer-readable medium comprising program instructions which, when executed by a control unit (22), cause the control unit (22) to perform the method of claim 18.