# US 11,910,423 B2 · Systems and methods for reducing false radar detection

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- Number: US 11,910,423 B2
- Document ID: US11910423B2
- Status: Granted
- Kind: B2
- Application number: 17/512,098
- Filed: 2021-10-27
- Published: 2023-04-27
- Granted: 2024-02-20
- Earliest claimed: 2021-10-27
- Assignees: Cisco Technology, Inc.
- Applicants: Cisco Technology, Inc.
- Inventors: Fred J. Anderson; Paul Jeffrey Stager; Evgeny Yankevich; Matthew Aaron Silverman
- Web page: https://patentgrep.com/patent/US11910423B2

## CPC

- H04W 72/541: using the level of interference
- G01S 7/021: {Auxiliary means for detecting or identifying radar signals or the like, e.g. radar jamming signals}
- H04W 72/0453: Resources in frequency domain, e.g. a carrier in FDMA
- H04W 84/12: WLAN [Wireless Local Area Networks]
- H04W 88/08: Access point devices
- H04W 92/18: between terminal devices
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- 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

## Abstract

Methods and systems for distinguishing between radar signals and Wi-Fi signals are provided. When a set of electromagnetic signals are received, various tests are performed on the signals to determine if the signals are associated with radar pulses or if the signals are more likely to be associated with stray Wi-Fi signals or other non-radar interference. One such test relies on the relatively small variance of frequencies used by radar pulses when compared to the high variation of Wi-Fi signals. Another test relies on the relatively low peak to average power ratio of signals associated with radar pulses when compared to Wi-Fi signals. The tests described herein are an improvement on existing methods for distinguishing radar signals from Wi-Fi signals and result in less switching of Wi-Fi channels due to erroneously detected radar signals.

## Claims

### Claim 1

A method comprising:
while communicating on a first channel, receiving a set of electromagnetic signals by a computing device;
estimating frequencies for the set of electromagnetic signals by the computing device;
calculating a variance of the estimated frequencies by the computing device;
based on the calculated variance, determining whether the set of electromagnetic signals are radar signals by the computing device; and
if it is determined that the set of electromagnetic signals are not radar signals, continuing to communicate on the first channel by the computing device.

### Claim 2 (depends on 1)

The method of claim 1, further comprising if it is determined that the set of electromagnetic signals are radar signals:
stopping communication on the first channel;
selecting a second channel; and
communicating on the second channel.

### Claim 3 (depends on 1)

The method of claim 1, wherein the first communication channel is a DFS Wi-Fi channel.

### Claim 4 (depends on 1)

The method of claim 1, wherein the computing device is an access point.

### Claim 5 (depends on 1)

The method of claim 1, wherein determining whether the set of electromagnetic signals are radar signals comprises determining whether the calculated variance satisfies a variance threshold.

### Claim 6 (depends on 5)

The method of claim 5, wherein the calculated variance satisfies the variance threshold when the calculated variance is less than the variance threshold.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
calculating a power for each electromagnetic signal of the set of electromagnetic signals;
determining a peak power from the calculated powers;
determining an average power from the calculated powers;
based on the determined average power and the determined peak power, determining whether the set of electromagnetic signals are radar signals.

### Claim 8 (depends on 7)

The method of claim 7, wherein determining whether the set of electromagnetic signals are radar signals comprises:
calculating a ratio of the calculated peak power to the calculated average power; and
determining whether the calculated ratio satisfies a ratio threshold.

### Claim 9 (depends on 8)

The method of claim 8, wherein the calculated ratio satisfies the ratio threshold when the calculated ratio is less than the ratio threshold.

### Claim 10 (depends on 1)

The method of claim 1, wherein the set of electromagnetic signals comprises one or more of on-channel and off-channel corrupted Wi-Fi frames or off-channel power leaks.

### Claim 11

A method comprising:
while communicating on a first channel, receiving a set of electromagnetic signals by a computing device;
calculating a power for each electromagnetic signal of the set of electromagnetic signals by the computing device;
determining a peak power from the calculated powers by the computing device;
determining an average power from the calculated powers by the computing device;
based on the determined average power and the determined peak power, determining whether the set of electromagnetic signals are radar signals by the computing device; and
if it is determined that the set of electromagnetic signals are not radar signals, continuing to communicate on the first channel by the computing device.

### Claim 12 (depends on 11)

The method of claim 11, further comprising if it is determined that the set of electromagnetic signals are radar signals:
stopping communication on the first channel;
selecting a second channel; and
communicating on the second channel.

### Claim 13 (depends on 11)

The method of claim 11, wherein the first communication channel is a DFS Wi-Fi channel.

### Claim 14 (depends on 11)

The method of claim 11, wherein the computing device is an access point.

### Claim 15 (depends on 11)

The method of claim 11, wherein determining whether the set of electromagnetic signals are radar signals comprises:
calculating a ratio of the calculated peak power to the calculated average power; and
determining whether the calculated ratio satisfies a ratio threshold.

### Claim 16 (depends on 15)

The method of claim 15, wherein the calculated ratio satisfies the ratio threshold when the calculated ratio is less than the ratio threshold.

### Claim 17 (depends on 11)

The method of claim 11, further comprising:
estimating frequencies for the set of electromagnetic signals;
calculating a variance of the estimated frequencies; and
based on the calculated variance, determining whether the set of electromagnetic signals are radar signals.

### Claim 18 (depends on 17)

The method of claim 17, wherein determining whether the set of electromagnetic signals are radar signals comprises determining whether the calculated variance satisfies a variance threshold.

### Claim 19 (depends on 18)

The method of claim 18, wherein the calculated variance satisfies the variance threshold when the calculated variance is less than the variance threshold.

### Claim 20

A system comprising:
at least one computing device; and
a non-transitory computer-readable medium storing computer-executable instructions that when executed by the at least one computing device causes the at least one computing device to:
while communicating on a first channel, receive a set of electromagnetic signals;
estimate frequencies for the set of electromagnetic signals;
calculate a variance of the estimated frequencies;
based on the calculated variance, determine whether the set of electromagnetic signals are radar signals;
if it is determined that the set of electromagnetic signals are not radar signals, continue to communicate on the first channel; and
if it is determined that the set of electromagnetic signals are radar signals:
stop communication on the first channel;
select a second channel; and
communicate on the second channel.