# US 12,181,564 B1 · Dual round trip time mitigation for wireless local area network devices

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- Number: US 12,181,564 B1
- Document ID: US12181564B1
- Status: Granted
- Kind: B1
- Application number: 18/753,241
- Filed: 2024-06-25
- Granted: 2024-12-31
- Earliest claimed: 2023-12-20
- Assignees: SR Technologies, Inc.
- Applicants: SR Technologies, Inc.
- Inventors: Mark Passler; Kyle Patrick Kelly
- Web page: https://patentgrep.com/patent/US12181564B1

## CPC

- G01S 13/76: wherein pulse-type signals are transmitted
- G01S 7/006: {using shared front-end circuitry, e.g. antennas (G01S13/765, G01S13/825 take precedence)}
- G01S 13/765: {with exchange of information between interrogator and responder}
- H04W 56/0055: {determining timing error of reception due to propagation delay}
- H04W 64/00: Locating users or terminals {or network equipment} for network management purposes, e.g. mobility management
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

A method and devices are disclosed for geo-location of wireless local area network (WLAN) devices. According to one aspect, a method for determining a corrected round trip times (RTT) resulting from communication with a WD is provided. The WD is configured with one or two short interframe spacings (SIFS). The method includes performing RTT measurements at successive times. The method includes determining a presence of one or two modes based at least in part on peaks of a kernel density estimation (KDE) surface. The KDE surface is determined from the RTT measurements. When there is only one mode, a corrected RTT is determined based on the RTT measurements and a first SIFS. When there are two modes, a corrected RTT is determined based on the RTT measurements and the first SIFS plus an SIFS offset (Δ), Δ being based at least in part on a difference between the two modes.

## Claims

### Claim 1

A method in a first wireless device (WD) for determining a corrected round trip times (RTT) resulting from communication with a second WD, the second WD being configured with one or two short interframe spacings (SIFS), the method comprising:
performing a plurality of RTT measurements (RTTi) at successive times during a time period, T; and
determining a presence of one or two modes based at least in part on peaks of a kernel density estimation (KDE) surface, the KDE surface being determined from the plurality of RTT measurements, and:
when there is only one mode, then determining a corrected RTT based at least in part on the plurality of RTT measurements and a first SIFS; and
when there are two modes, then determining a corrected RTT based at least in part on the plurality of RTT measurements and the first SIFS plus an SIFS offset (Δ), Δ being based at least in part on a difference between the two modes.

### Claim 2 (depends on 1)

The method of claim 1, wherein the SIFS offset Δ is based at least in part on an average of previously determined SIFS offsets when there are two modes.

### Claim 3 (depends on 1)

The method of claim 1, wherein, when there is only one mode and when |RTTpeak−Ts−TOF|<|RTTpeak−Ts−Δ−TOF|, then the corrected RTT is determined as RTTpeak−Ts, and otherwise, then the corrected RTT is determined as RTTpeak−Ts−Δ, where RTTpeak is a peak RTT of the one mode, Ts is an offset corresponding to the first SIFS, Δ is the SIFS offset, and TOF is a time of flight.

### Claim 4 (depends on 1)

The method of claim 1, wherein determining the corrected RTT includes minimizing a sum of squared residuals, each squared residual being based at least in part on a difference between an RTTi and a total travel time, the total travel time being based at least in part on a target location parameter, α, determined by setting a gradient of the sum of squared residuals to zero.

### Claim 5 (depends on 4)

The method of claim 4, wherein a residual R(rtt)i is based at least in part on calculating R(rtt)i=[(RTTi−αOFF)+TOFi], where the subscript i denotes an ith RTT measurement of the plurality of RTT measurements and an ith time of flight TOFi, and αOFF is determined as Ts when there is only one mode and αOFF is determined as Ts−Δ when there are two modes.

### Claim 6 (depends on 1)

The method of claim 1, wherein, when there are two modes, the corrected RTT is determined as RTTpeak−αOFF, where αOFF is equal to Ts for a first mode of the two modes and αOFF is equal to Ts−Δ for a second mode of the two modes.

### Claim 7 (depends on 6)

The method of claim 6, further comprising determining whether to use αOFF=Ts or αOFF=Ts−Δ for corrected RTT determination is based at least in part on a numerical fitting process.

### Claim 8 (depends on 1)

The method of claim 1, wherein the KDE surface is determined by a superposition of kernel functions weighting each of the plurality of RTT measurements.

### Claim 9 (depends on 8)

The method of claim 8, wherein the kernel functions are Gaussian.

### Claim 10 (depends on 1)

The method of claim 1, wherein the time period T is selected to be less than the SIFS offset Δ.

### Claim 11

A first wireless device (WD) configured to determine a corrected round trip time (RTT) resulting from communication with a second WD, the second WD being configured with one or two short interframe spacings (SIFS), the first WD being configured to:
perform a plurality of RTT measurements (RTTi) at successive times during a time period, T; and
determine a presence of one or two modes based at least in part on peaks of a kernel density estimation (KDE) surface, the KDE surface being determined from the plurality of RTT measurements, and:
when there is only one mode, then determine a corrected RTT based at least in part on the plurality of RTT measurements and a first SIFS;
when there are two modes, then determine a corrected RTT based at least in part on the plurality of RTT measurements and the first SIFS plus an SIFS offset (Δ), Δ being based at least in part on a difference between the two modes.

### Claim 12 (depends on 11)

The first WD of claim 11, wherein the SIFS offset Δ is based at least in part on an average of previously determined SIFS offsets when there are two modes.

### Claim 13 (depends on 11)

The first WD of claim 11, wherein, when there is only one mode and when |RTTpeak−Ts−TOF|<|RTTpeak−Ts−Δ−TOF|, then the corrected RTT is determined as RTTpeak−Ts, and otherwise, then the corrected RTT is determined as RTTpeak−Ts−Δ, where RTTpeak is a peak RTT of the one mode, Ts is an offset corresponding to the first SIFS, Δ is the SIFS offset, and TOF is a time of flight.

### Claim 14 (depends on 11)

The first WD of claim 11, wherein determining the corrected RTT includes minimizing a sum of squared residuals, each squared residual being based at least in part on a difference between an RTTi and a total travel time, the total travel time being based at least in part on a target location parameter, α, determined by setting a gradient of the sum of squared residuals to zero.

### Claim 15 (depends on 14)

The first WD of claim 14, wherein a residual R(rtt)i is based at least in part on calculating R(rtt)i=[(RTTi−αOFF)+TOFi], where the subscript i denotes an ith RTT measurement of the plurality of RTT measurements and an ith time of flight TOFi, and αOFF is determined as Ts when there is only one mode and αOFF is determined as Ts−Δ when there are two modes.

### Claim 16 (depends on 11)

The first WD of claim 11, wherein, when there are two modes, the corrected RTT is determined as RTTpeak−αOFF, where αOFF is equal to Ts for a first mode of the two modes and αOFF is equal to Ts−Δ for a second mode of the two modes.

### Claim 17 (depends on 16)

The first WD of claim 16, wherein the first WD is configured to determine whether to use αOFF=Ts or αOFF=Ts−Δ for corrected RTT determination is based at least in part on a numerical fitting process.

### Claim 18 (depends on 11)

The first WD of claim 11, wherein the KDE surface is determined by a superposition of kernel functions weighting each of the plurality of RTT measurements.

### Claim 19 (depends on 18)

The first WD of claim 18, wherein the kernel functions are Gaussian.

### Claim 20 (depends on 11)

The first WD of claim 11, wherein the time period T is selected to be less than the SIFS offset Δ.