# US 10,313,175 B2 · Method for estimating CFO in wireless LAN system that uses 16 QAM

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- Number: US 10,313,175 B2
- Document ID: US10313175B2
- Status: Granted
- Kind: B2
- Application number: 15/580,262
- Filed: 2016-01-20
- Published: 2018-06-21
- Granted: 2019-06-04
- Earliest claimed: 2015-06-08
- Assignees: LG Electronics Inc.
- Applicants: LG Electronics Inc.
- Inventors: Kilbom Lee; Jiwon Kang; Kitae Kim; Kungmin Park; Heejin Kim
- Web page: https://patentgrep.com/patent/US10313175B2

## CPC

- H04L 27/38: Demodulator circuits; Receiver circuits
- H04L 27/2655: {Synchronisation arrangements}
- H04L 27/2657: {Carrier synchronisation}
- H04L 27/2672: {Frequency domain}
- H04L 27/2676: {Blind, i.e. without using known symbols}
- H04L 27/34: Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04W 84/12: WLAN [Wireless Local Area Networks]
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)

## Abstract

Disclosed is a method for estimating a CFO, the method comprising: measuring a size ratio of a signal pair received in two consecutive OFDM symbols of a predetermined subcarrier; determining the received signal pair as a signal pair to be used for estimating a residual CFO when the size ratio is within a first threshold range; and estimating the residual CFO, using only the received signal pair which has been determined to be used for estimating the residual CFO.

## Claims

### Claim 1

A method of estimating a carrier frequency offset (CFO) by a reception module in a wireless communication system using 16-quadrature amplitude modulation (QAM), the method comprising:
measuring a size ratio between a pair of signals received on two consecutive orthogonal frequency division multiplexing (OFDM) symbols for a specific subcarrier;
based on determination that the size ratio belongs to a first threshold range, determining the pair of received signals as a pair to be used for estimating a residual CFO; and
estimating the residual CFO using only the pair of received signals that are determined to be used for estimating the residual CFO.

### Claim 2 (depends on 1)

The method of claim 1, further
comprising measuring a phase difference between the pair of received signals,
wherein when the size ratio belongs to the first threshold range and the phase difference belongs to a second threshold range, the pair of received signals is determined as a pair to be used for estimating the residual CFO.

### Claim 3 (depends on 2)

The method of claim 2, further
comprising when the phase difference does not belong to the second threshold range and belongs to a third threshold range, changing a phase of multiplication of the pair of received signals as much as a predetermined value.

### Claim 4 (depends on 3)

The method of claim 3, further
comprising when the phase difference does not belong to the second threshold range and does not belong to the third threshold range, determining not to use the pair of received signals for estimating the residual CFO.

### Claim 5 (depends on 3)

The method of claim 3, wherein the second threshold range indicates a range within a predetermined value from one value among 0°, 90°, 180°, and 270°.

### Claim 6 (depends on 3)

The method of claim 3, wherein the third threshold range indicates a range within a predetermined value from one value among 46°, 136°, 226°, and 316°.

### Claim 7 (depends on 1)

The method of claim 1, wherein the first threshold range indicates a range within a predetermined value from one value among 1, ⅓, and 3.

### Claim 8 (depends on 1)

The method of claim 1, wherein the step of estimating the residual CFO estimates the residual CFO according to a blind scheme which is applied when quadrature phase shift keying (QPSK) is used.

### Claim 9

A communication device for estimating a carrier frequency offset (CFO) in a wireless communication system using 16-quadrature amplitude modulation (QAM), the communication device comprising:
a memory;
and
a processor operably coupled with the memory and configured to:
measure a size ratio between a pair of signals received on two consecutive orthogonal frequency division multiplexing (OFDM) symbols for a specific subcarrier;
based on determination that the size ratio belongs to a first threshold range, determines the pair of received signals as a pair to be used for estimating a residual CFO; and
estimate the residual CFO using only the pair of received signals that are determined to be used for estimating the residual CFO.

### Claim 10 (depends on 9)

The communication device of claim 9, wherein the processor is further configured to:
measure a phase difference between the pair of received signals; and
when the size ratio belongs to the first threshold range and the phase difference belongs to a second threshold range, determine the pair of received signals as a pair to be used for estimating the residual CFO.

### Claim 11 (depends on 10)

The communication device of claim 10, wherein the processor is further configured to, when the phase difference does not belong to the second threshold range and belongs to a third threshold range, change a phase of multiplication of the pair of received signals as much as a predetermined value.

### Claim 12 (depends on 11)

The communication device of claim 11, wherein the processor is further configured to, when the phase difference does not belong to the second threshold range and does not belong to the third threshold range, determine not to use the pair of received signals for estimating the residual CFO.

### Claim 13 (depends on 11)

The communication device of claim 11, wherein the second threshold range indicates a range within a predetermined value from one value among 0°, 90°, 180°, and 270°.

### Claim 14 (depends on 11)

The communication device of claim 11, wherein the third threshold range indicates a range within a predetermined value from one value among 46°, 136°, 226°, and 316°.

### Claim 15 (depends on 9)

The communication device of claim 9, wherein the first threshold range indicates a range within a predetermined value from one value among 1, ⅓, and 3.

### Claim 16 (depends on 9)

The communication device of claim 9, wherein the processor is further configured to estimate the residual CFO according to a blind scheme which is applied when quadrature phase shift keying (QPSK) is used.