Patent Description:
Fine Timing Measurement (FTM) techniques can allow an initiating wireless station (STA) to perform ranging against a responding STA, and compute the initiating STA's position. The initiating STA can be any suitable wireless device, including a laptop computer, a smartphone, a tablet, another suitable user device, or a wireless network infrastructure device. The responding STA can also be any suitable wireless device, but in an embodiment the responding STA is a wireless access point (AP) which participates in the ranging process by time-stamping wireless messages as needed and negotiating range parameters, including burst size, burst frequency, and others. For example, the AP can time-stamp physical layer convergence protocol (PLCP) protocol data units (PPDUs).

The initiating STA, however, does not have access to the AP's knowledge of the wireless network structure and radio frequency (RF) conditions. This can require the initiating STA to seek an excessive number of ranging requests with the AP. For example, the number of ranging requests to be used for all initiating STAs, regardless of environment, can be determined during laboratory testing in order to ensure that ranging is sufficiently accurate in the vast majority (e.g., <NUM>%) of envisioned deployments (e.g., sufficient requests for accurate ranging in the most stringent environments). But this is likely to result in unnecessary messaging, because most initiating STAs are actually located in less stringent environments and will not actually need this many requests to determine the range with the AP. This excess ranging, well beyond the number of requests actually needed, in most deployments, to characterize the environment and determine the range from the initiating STA to the AP, is undesirable. It can waste scarce WiFi air-time, cause unplanned contention and reduce the quality-of-experience (QoE) for users. Further, the ranging can be inaccurate, especially in reflective environments.

In <CIT> an apparatus may include circuitry and logic configured to cause an initiating station (STA) to initiate a first ranging measurement with a responding STA, the first ranging measurement including transmission of a Null-Data-Packet (NDP) Announcement (NDPA) from the initiating STA to the responding STA, transmission of an Uplink (UL) NDP from the initiating STA to the responding STA, and reception of a Downlink (DL) NDP from the responding STA; and to initiate a second ranging measurement with the responding STA at least a delay period after the first ranging measurement, the second ranging measurement including a measurement report from the responding STA, the measurement report including one or more measurement values corresponding to the first ranging measurement.

In <CIT>a client station (STA) performs a ranging protocol with an access point (AP). The distance between the STA and the AP is determined based on signal propagation of a plurality of concurrent sounding messages communicated between the STA and the AP.

<CIT> provides systems, methods and apparatuses, including computer programs encoded on computer storage media, for performing a ranging operation with a responder device. In one example, an apparatus exchanges a number of measurement frames with the responder device. The apparatus captures a number of timestamps based on the exchanged measurement frames. The apparatus estimates a carrier frequency offset between the responder device and the apparatus, and reports information indicative of the captured timestamps to the responder device.

Embodiments described herein include a method. The method includes determining channel state information at a wireless AP corresponding to a STA. The method further includes determining, at the AP based on the channel state information, one or more FTM parameters. The method further includes transmitting, based on the one or more FTM parameters, a plurality of FTM messages between the AP and the STA, wherein the STA is configured to determine an estimated range to the AP based on the plurality of FTM messages.

Embodiments further include a wireless AP, including a processor and a memory storing a program, which, when executed on the processor, performs an operation. The operation includes determining channel state information corresponding to a wireless STA. The operation further includes determining, based on the channel state information, one or more FTM parameters. The operation further includes transmitting, based on the one or more FTM parameters, a plurality of FTM messages between the AP and the STA, wherein the STA is configured to determine an estimated range to the AP based on the plurality of FTM messages.

Embodiments further include a wireless STA, including a processor and a memory storing a program, which, when executed on the processor, performs an operation. The operation includes receiving one or more FTM parameters from a wireless AP, wherein the AP is configured to determine the one or more FTM parameters based on channel state information corresponding to the STA. The operation further includes transmitting, based on the one or more FTM parameters, a plurality of FTM messages between the STA and the AP. The operation further includes determining an estimated range to the AP based on the plurality of FTM messages.

In an embodiment, ranging between an arbitrary wireless STA and an AP can be improved by using channel quality observations to determine FTM ranging parameters and improve FTM calculations for another arbitrary STA. For example, an AP can use Angle-of-Arrival (AoA) antennas to determine general channel quality characteristics of a set of arbitrary STA. This channel quality information can be used to negotiate FTM parameters, resulting in improved ranging from the STA to the AP while avoiding unnecessary messaging. FTM is merely one example of suitable range finding techniques, and other techniques can be used. Further, the channel quality information can be used to improve the FTM calculations.

In an embodiment, an AP can include AoA analysis features, which can be used to capture channel state information (CSI) across n antennas (e.g., <NUM> antennas). The AP can compare observed CSI for a given antenna communicating with an STA against a reference value, and estimate the relative position of the STA to the AP. This can allow the AP to estimate the location of a remote STA, but does not assist the STA in measuring its own relative position to the AP because the STA does not have access to the channel state information.

CSI, however, can provide information about the deployment environment of the AP. For example, CSI can be used to distinguish an AP in a high ceilinged open space with good line of sight (LOS) to STAs from an AP in a lower ceilinged cubicle-rich environment with limited or non LOS (NLOS). CSI can also be used to identify the stability of the wireless channel as experienced by the STA (e.g. stationary vs. volatile). In an embodiment, by comparing consecutively measured CSIs and measuring the temporal correlation of the CSI trace for a given client, an AP can identify that the location of a given STA either remains unchanged (stationary) or is in motion (volatile).

In an embodiment, this CSI information can be used to improve ranging using FTM or another suitable range finding technique. For example, where the STA is not moving a single, longer, burst of FTM messaging may be sufficient, without requiring multiple bursts. As another example, where the STA is moving, a series of shorter bursts of FTM messaging may be more effective to capture the peaks and valleys of the volatile mobile channel.

Further, in an embodiment, the CSI profile over subcarriers for a given STA can indicate whether the wireless propagation environment includes multiple paths (e.g., reflected in the multiple peaks and valleys of the CSI in the frequency domain) or is dominated by a direct LOS path (e.g., reflected in a relatively flat CSI profile in the frequency domain). This can be used to further improve ranging. For example, as discussed above, CSI can be used to distinguish an AP with direct LOS to an STA from an AP with NLOS to the STA. Where the AP estimates direct LOS to the STA, a small number of short FTM bursts can be used but where an AP estimates NLOS a larger number of short FTM bursts can be used.

Where an AP estimates multiple paths (e.g., reflection), the STA may, by using FTM, over-estimate the distance to the AP because signals will take longer to propagate between the STA and the AP due to the reflection. In this example, the stochasticity of the signal can be used to estimate the degree of multi-path delay spread and improve the range estimation from FTM (e.g., by revising the timestamp values included in the FTM messaging to reflect the multi-path delay spread). This provides for more accurate ranging by the STA.

<FIG> illustrates determining a range of an STA from an AP, according to one embodiment. An indoor environment <NUM> includes a number of APs 102A-H and a number of STAs 104A-C. Each STA 104A-C can determine its range from the APs using FTM techniques (e.g., by exchanging timestamped messages). Example FTM techniques are discussed in more detail with regard to <FIG>. For example, the STA 104A can use FTM techniques to estimate the length of the distance <NUM> between the STA 104A and the AP 102A.

The STA 104A can similarly use FTM techniques to estimate the distance <NUM> to the AP <NUM>. The STA 104B can use FTM techniques to estimate the distance <NUM> to the AP <NUM>. The STA 104C can use FTM techniques to estimate the distance <NUM> to the AP 102C. This positioning information can be used by the STAs for a number of management purposes, including selecting an AP for connection and configuring a variety of radio transmission and other parameter. The positioning information can also be used for numerous application purposes, including augmented reality, social networking, health care monitoring, inventory control, etc..

<FIG> is a messaging diagram illustrating FTM techniques, according to one embodiment. As noted above, FTM is merely one example of a suitable range finding technique and other techniques can be used in place of, or in addition to, FTM. In an embodiment, FTM is initiated by an STA <NUM> to determine a distance from an AP <NUM>. The clock of the STA <NUM> and the AP <NUM> are not synchronized, and so the STA and AP must exchange a series of timestamps to identify the time taken for a wireless signal (e.g., a WiFi signal) to travel between the STA <NUM> and the AP <NUM>. This time can be used to estimate the distance between the STA <NUM> and the AP <NUM> because the time taken for the signal to travel the distance is proportional to the distance (e.g., based on the speed of light).

The STA <NUM> transmits an FTM request <NUM> to the AP <NUM>. The AP <NUM> responds with an Ack <NUM> (e.g., an acknowledgment). In an embodiment, the Ack <NUM> includes FTM parameters determined by the AP <NUM>. These parameters are discussed further below. Further, in an embodiment, the STA <NUM> and AP <NUM> can undertake a negotiation for the FTM parameters, exchanging messages identifying parameters to use.

At time T1, the AP <NUM> transmits an FTM ping <NUM> to the STA <NUM>. The STA <NUM> receives the FTM ping <NUM> at time T2. At time T3, the STA <NUM> transmits an Ack <NUM>. The AP <NUM> then, at time T5, transmits an FTM ping <NUM> to the STA <NUM>. This FTM ping <NUM> includes the timestamps T1 and T4 identifying the times at which the AP <NUM> transmitted the FTM ping <NUM> and received the Ack <NUM>.

The STA <NUM> receives the FTM ping <NUM> at time T6. The STA <NUM> can then use the timestamps T1, T2, T3, and T4 (T1 and T4 received from the AP <NUM>, T2 and T3 recorded locally by the STA) to compute the round trip time for message transmission between the STA <NUM> and the AP <NUM>. In an embodiment, this can be used to estimate the distance between the STA <NUM> and the AP <NUM> using the equation: <NUM> * distance = ((T<NUM> - T1) - (T3 - T2)) * c. In this equation, c is the speed of light, (T<NUM> - T<NUM>) computes the total round trip time, and (T<NUM> - T<NUM>) removes the turnaround time at the STA between receiving the FTM ping <NUM> and transmitting the Ack <NUM>.

In an embodiment, however, the round trip time measurements may not be sufficiently accurate, because of potential interference, motion of the STA, measurement error, etc. Therefore repeated measurements can be used to improve the accuracy of the distance estimation.

As illustrated in <FIG>, two more round-trips can be used to improve accuracy: FTM Ping <NUM> and Ack <NUM>, and FTM Ping <NUM> and Ack <NUM>. In an embodiment, the final FTM Ping <NUM> provides the timestamps T9 and T12 to the STA <NUM> to allow calculation of the round trip time between the FTM Ping <NUM> and the Ack <NUM>, but the travel time of the FTM Ping <NUM> itself is not used for distance estimation. The two additional round trips illustrated in <FIG> are merely for illustration. More, or fewer, round trips can be used. Further, many different parameters can be configured, including the time between round trips, the number of round trips in a burst, etc..

<FIG> is a block diagram illustrating a wireless STA <NUM> and an AP <NUM>, according to one embodiment. The STA <NUM> includes a processor <NUM>, a memory <NUM>, and network components <NUM>. The processor <NUM> generally retrieves and executes programming instructions stored in the memory <NUM>. The processor <NUM> is included to be representative of a single central processing unit (CPU), multiple CPUs, a single CPU having multiple processing cores, graphics processing units (GPUs) having multiple execution paths, and the like.

The network components <NUM> include the components necessary for the STA <NUM> to interface with a wireless communication network, as discussed above in relation to <FIG>. For example, the network components <NUM> can include WiFi or cellular network interface components and associated software.

Although the memory <NUM> is shown as a single entity, the memory <NUM> may include one or more memory devices having blocks of memory associated with physical addresses, such as random access memory (RAM), read only memory (ROM), flash memory, or other types of volatile and/or non-volatile memory. The memory <NUM> generally includes program code for performing various functions related to use of the STA <NUM>. The program code is generally described as various functional "applications" or "modules" within the memory <NUM>, although alternate implementations may have different functions and/or combinations of functions.

Within the memory <NUM>, a locator module <NUM> includes an FTM module <NUM>. In an embodiment, the FTM module <NUM> facilitates FTM range finding, as discussed above in relation to <FIG>. FTM is merely one example of a suitable range finding technique, and other techniques can be used. The locator module <NUM> facilitates identifying the range of the STA <NUM> from an AP (e.g., the AP <NUM>) and facilitates identifying the location of the STA <NUM> using the range information (e.g., in an indoor environment). This is discussed further with regard to <FIG> and after.

The AP <NUM> includes a processor <NUM>, a memory <NUM>, and network components <NUM>. The processor <NUM> generally retrieves and executes programming instructions stored in the memory <NUM>. The processor <NUM> is included to be representative of a single central processing unit (CPU), multiple CPUs, a single CPU having multiple processing cores, graphics processing units (GPUs) having multiple execution paths, and the like.

The network components <NUM> include the components necessary for the AP <NUM> to interface with a wireless communication network, as discussed above in relation to <FIG>. For example, the network components <NUM> can include WiFi or cellular network interface components and associated software.

Although the memory <NUM> is shown as a single entity, the memory <NUM> may include one or more memory devices having blocks of memory associated with physical addresses, such as random access memory (RAM), read only memory (ROM), flash memory, or other types of volatile and/or non-volatile memory. The memory <NUM> generally includes program code for performing various functions related to use of the AP <NUM>. The program code is generally described as various functional "applications" or "modules" within the memory <NUM>, although alternate implementations may have different functions and/or combinations of functions.

Within the memory <NUM>, the channel quality module <NUM> uses an angle of arrival module <NUM> (e.g., using a number of angle of arrival antennas) to identify channel quality information. The FTM module <NUM> facilitates use of FTM techniques to allow an STA (e.g., the STA <NUM>) to identify its range from the AP <NUM>. This is discussed further in relation to <FIG> and after.

<FIG> is a flowchart <NUM> illustrating ranging between an STA and an AP using FTM and channel quality, according to an embodiment. At block <NUM> an AP (e.g., the AP <NUM> illustrated in <FIG>) receives an FTM request (e.g., the FTM request <NUM> illustrated in <FIG>) from an STA (e.g., the STA <NUM> illustrated in <FIG>). As discussed above, FTM is merely one suitable technique for ranging between an STA and an AP, and other suitable techniques can be used. As discussed above, FTM generally works well in a laboratory environment but, in some circumstances, may have flaws in practice. For example, FTM may be inaccurate or may waste bandwidth in reflective or obstacle filled environments. As another example, non-optimal access points may respond to FTM messages from an STA, causing further problems. In an embodiment, channel quality information and other techniques can be used to improve FTM.

At block <NUM>, a channel quality module (e.g., the channel quality module <NUM> illustrated in <FIG>) determines channel quality for the channel with the STA. In the invention, two parameters are used to characterize the channel quality: stability (i.e., coherence) and delay spread (i.e., power-delay-profile). In an embodiment, stability measures the coherence of the channel and can be used to determine a variety of FTM parameters, including how frequently FTM bursts should be transmitted for accurate ranging from the STA to the AP. In an embodiment, delay spread can be used to determine additional FTM parameters, including how many FTM samples to include in an FTM burst, for accurate ranging from the STA to the AP. This is discussed further with regard to <FIG>, below.

At block <NUM>, an FTM module (e.g., the FTM module <NUM> in the AP <NUM> illustrated in <FIG>) determines FTM parameters based on the channel quality information. In an embodiment, the FTM module can determine FTM channel sounding parameters based on the channel quality information. For example, the FTM module can determine the number of FTM bursts, the duration, FTM frames per burst, and other suitable parameters based on the channel quality information.

For example, a channel with a relatively high delay spread (e.g. 100ns) could require a larger number of bursts to achieve high location accuracy (e.g., the STA may be NLOS to the AP). By contrast, a channel with a relatively low delay spread (e.g., 5ns) could require fewer bursts (e.g., the STA may be in LOS to the AP). Similarly, a channel that is stationary with a relatively high <NUM> coherence time (Tc) can be characterized by a longer burst period (e.g. <NUM>/<NUM>) whereas a more volatile channel could use a shorter burst period (e.g. <NUM>) to force characterization while the channel is likely to stable. In an embodiment, determining the FTM parameters can be a negotiation between an AP and an STA. For example, an AP can propose initial parameters, and an STA can either agree to the parameters or proposed modified parameters.

At block <NUM>, the FTM module uses the FTM parameters to find the range of the STA to the AP. For example, the FTM module can use the number of bursts, duration, FTM frames per burst, and other parameters to transmit FTM messages in a suitable fashion (e.g., as illustrated in <FIG>) to determine the range of the STA to the AP. In an embodiment, this greatly improves the bandwidth usage and the number of message transmissions, while also improving the accuracy of the ranging.

In an embodiment, the channel quality determination (e.g., as discussed above with regard to block <NUM> and below with regard to <FIG>) occurs in real-time along with the FTM techniques. Further, the FTM module can monitor channel quality over time and modify FTM parameters throughout the FTM process. In an embodiment, the AP can identify changes in channel quality over time and can modify FTM parameters based on the changes. For example, the AP can determine that an obstacle (e.g., a person) has come between the STA and the AP. The AP can therefore modify the FTM parameters to improve the FTM process (e.g., providing for shorter bursts with longer wait times between bursts).

In an embodiment, the FTM module can further track FTM measurements over time, and discard FTM messages that appear to be inaccurate or outliers. This can be done by an FTM module in the AP (e.g., the FTM module <NUM> illustrated in <FIG>) or in an STA (e.g., the FTM module <NUM> illustrated in <FIG>). In an embodiment, this can be done without using channel quality information. Alternatively, inaccurate or outlier messages can be identified using channel quality information. For example, a longer than expected travel time for an FTM message may be accurate if the channel quality reflects an obstacle appearing between the STA and the AP. But a longer than expected travel time for an FTM message may be inaccurate if the channel quality reflects a high quality channel (e.g., clear LOS) between the STA and the AP.

<FIG> is a flowchart for determining channel quality, according to one embodiment. In an embodiment, <FIG> corresponds with block <NUM> illustrated in <FIG>. At block <NUM>, a channel quality module (e.g., the channel quality module <NUM> in the AP <NUM> illustrated in <FIG>) receives channel state information.

In an embodiment, existing channel quality solutions can be used. For example, many APs uses an antenna array on the AP (e.g., <NUM> antennas) to determine AoA information and estimate channel quality. FTM (and similar techniques) uses time of arrival (TOA) information (e.g., the rising edge of a PPDU preamble) for ranging. This means that channel quality information (e.g., channel-state-information (CSI)) from any Orthogonal Frequency Division Muliplexing (OFDM) PPDU preamble received by the antenna array can be used, for a given <NUM> channel. In an embodiment, channel quality information determined by the AoA antenna is used, but AoA information itself is not used. Use of AoA antenna is merely one example of a technique to determine channel quality, and other techniques can be used. Further, AoA antenna techniques can be used to further refine the channel estimate since this allows for many distinct, time-separated, but spatially related, channel samples. For example, <NUM> samples (e.g., <NUM> samples of <NUM> elements each <NUM>) can be used.

At block <NUM>, the channel quality module determines channel stability. As discussed above, channel stability is one parameter of channel quality that can be used to determine FTM parameters. In an embodiment, channel stability (i.e., coherence) can be determined based on measuring phase and/or amplitude of a signal over time. A channel in which phase and/or amplitude varies significantly is less coherent than a channel in which phase and/or amplitude remain stable.

For example, assume an AP includes <NUM> antennas for determining AoA information. Each set of <NUM> coincident samples can be treated as a channel sample by, for example, averaging the samples. This can be repeated (i.e. sampling different sets of <NUM> antennas until all <NUM> are sampled) until an evolution of the channel coherence (Tc) can be formed. In an embodiment, this requires a sufficient number of repetitions to cover suitable coherence times. The channel quality module can estimate the time over which the Tc is relatively stable. This can distinguish STAs that are mobile from STAs that are stationary, but include non-motion related distortions. Further, FTM transmissions with relatively long intervals can be discarded as unlikely to be accurate, and only data burst sequences selected. This can improve accuracy.

At block <NUM>, the channel quality module determines delay spread. Delay spread is another parameter of channel quality that can be used to determine FTM parameters. In an embodiment, this can be determined by estimating individual path delays for the channel. For example, long training field (LTF) samples (e.g., <NUM> LTF samples) can be used with AoA antennas to identify shifted peaks in sub-carriers. This can be used to estimate individual path delays for the sub-carriers and determine delay spread for the channel.

<FIG> is a flowchart <NUM> illustrating improved ranging between an STA and an AP in a reflective environment, according to one embodiment. At block <NUM>, a channel quality module (e.g., the channel quality module <NUM> in the AP <NUM> illustrated in <FIG>) determines whether the AP and STA are in a multiple path environment. As discussed above, the CSI profile over subcarriers for a given STA can indicate whether the wireless propagation environment includes multiple paths (e.g., reflected in the multiple peaks and valleys of the CSI in the frequency domain) or is dominated by a direct LOS path (e.g., reflected in a relatively flat CSI profile in the frequency domain). If the wireless propagation environment between the AP and the STA includes multiple paths, the flow proceeds to block <NUM>. If not, the flow ends.

At block <NUM>, the channel quality module estimates the reflection pattern. In an embodiment, the channel quality module can use the stochasticity of the signal to estimate the degree of multi-path delay spread between the AP and the STA and improve the range estimation from FTM (e.g., by revising the timestamp values included in the FTM messaging to reflect the multi-path delay spread). This can improve ranging using FTM because, where an AP estimates multiple paths the STA may, by using FTM, over-estimate the distance to the AP because signals will take longer to propagate between the STA and the AP due to the reflection.

At block <NUM>, an FTM module (e.g., the FTM module <NUM> in the AP <NUM> illustrated in <FIG>) determines the range between the STA and the AP, using the reflection pattern. For example, the FTM module <NUM> can instruct the STA (e.g., the locator module <NUM> in the STA <NUM> illustrated in <FIG>) to apply one or more coefficients to the timestamp values (e.g., the timestamps illustrated in <FIG>) to improve the accuracy of the distance estimation in the reflective environment. That is, the locator module can apply coefficients to modify the timestamp values so that the FTM calculations take into account the reflective paths and improve the accuracy of the range estimation.

<FIG> illustrates location estimation for a wireless STA <NUM> among multiple APs 702A-C in an environment <NUM>, according to one embodiment. In an embodiment, an STA <NUM> is determining its location relative to the APs 702A-C. Further, in an embodiment, the environment <NUM> is reflective, creating multiple transmission paths between the STA <NUM> and the APs 702A-C. Assuming the STA <NUM> and the APs 702A-C do not implement the improved FTM techniques illustrated in <FIG>, the location estimation can only determine that the STA <NUM> is within the region <NUM>. This is because the environment <NUM> is reflective, and so the FTM techniques between the STA <NUM> and the APs 702A-C are therefore less accurate.

<FIG> illustrates location estimation for a wireless STA <NUM> among multiple APs 712A-C in an environment <NUM>, according to one embodiment. In an embodiment, the STA <NUM> is determining its location relative to the APs 712A-C. Further, in an embodiment, the environment <NUM> is again reflective, creating multiple transmission paths between the STA <NUM> and the APs 712A-C. The STA <NUM> and the APs 712A-C, however, implement the improved FTM techniques for reflective environments illustrated in <FIG>. Therefore, the location of the STA <NUM> can be narrowed to the region <NUM> (smaller than the region <NUM> illustrated in <FIG>). This is because the improved FTM techniques illustrated in <FIG> make the FTM techniques between the STA <NUM> and the APs 712A-C more accurate in the reflective environment <NUM>.

In the current disclosure, reference is made to various embodiments. However, the scope of the present disclosure is not limited to specific described embodiments. Instead, any combination of the described features and elements, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Additionally, when elements of the embodiments are described in the form of "at least one of A and B," it will be understood that embodiments including element A exclusively, including element B exclusively, and including element A and B are each contemplated. Furthermore, although some embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages disclosed herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to "the invention" shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).

" Furthermore, embodiments may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied/carried thereon for causing one or more processors to carry out any of the methods described herein.

Claim 1:
A method, comprising:
determining channel state information at a wireless access point, AP,
corresponding to a wireless station, STA, comprising determining using a plurality of angle of arrival, AoA, antennas at the AP: i) a channel stability measurement corresponding to the AP and the STA and ii) a delay spread measurement corresponding to the AP and the STA;
determining, at the AP based on the channel state information comprising the channel stability measurement and the delay spread measurement, one or more fine timing measurement, FTM, parameters; and
transmitting, based on the one or more FTM parameters, a plurality of FTM messages between the AP and the STA, wherein the STA is configured to determine an estimated range to the AP based on the plurality of FTM messages.