# US 7,609,615 B2 · Method and apparatus for performing channel compensation and symbol demodulation for coherent demodulation in an OFDM system

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- Number: US 7,609,615 B2
- Document ID: US7609615B2
- Status: Granted
- Kind: B2
- Application number: 11/455,784
- Filed: 2006-06-20
- Published: 2006-12-21
- Granted: 2009-10-27
- Earliest claimed: 2005-06-20
- Assignees: Samsung Electronics Co., Ltd.
- Inventors: Eun-Jeong Yim; Ji-Won Ha; Hee-Jin Roh; Sung-Jin Park
- Web page: https://patentgrep.com/patent/US7609615B2

## CPC

- H04L 25/0212: {of impulse response}
- H04L 25/03292: {with channel estimation circuitry}
- H04L 25/03318: {Provision of soft decisions}
- H04L 27/265: {Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators (H04L27/26524 takes precedence)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A method and apparatus for performing channel compensation and symbol demodulation using an estimated channel impulse response during coherent demodulation of a received Orthogonal Frequency Division Multiplexing (OFDM) signal are provided. In the apparatus, an FFT processor IFFT-processes a received signal. A channel compensator generates a channel-compensated signal by multiplying the FFT received signal by an estimated channel impulse response and calculates the power of the estimated channel impulse response. A symbol demodulator sets the power of the estimated channel impulse response as a reference point defining a minimum distance between signal points in a signal constellation, and decides soft metric values for channel decoding using the reference point and I-channel and Q-channel signal components of the channel-compensated signal. A decoder recovers information bits by decoding the soft metric values.

## Claims

### Claim 1

A method of performing channel compensation and symbol demodulation on a received signal in an Orthogonal Frequency Division Multiplexing (OFDM) system, the method comprising:
generating a channel-compensated signal by multiplying a fast Fourier transform (FFT) received signal by an estimated channel impulse response;
calculating the power of the estimated channel impulse response; and
setting the power of the estimated channel impulse response as a reference point value defining a minimum distance between signal points in a signal constellation used for modulation of the FFT received signal, and deciding soft metric values for channel decoding of the channel-compensated signal using the reference point value, I-channel and Q-channel signal components of the channel-compensated signal, and a multiple of the reference point value corresponding to the distance of a signal point closest to the origin to each axis in the signal constellation,
wherein 16-ary Quadrature Amplitude Modulation (16QAM) is used and the channel-compensated signal modulates the deciding of soft metric values which comprises deciding soft metric values for the channel-compensated signal by
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### Claim 2 (depends on 1)

The method of claim 1, wherein the generating of the channel-compensated signal comprises:
multiplying an I-channel signal component and a Q-channel signal component of the received signal respectively by an I-channel signal component and a Q-channel signal component of the estimated channel impulse response, summing the products from the multiplications, and outputting the sum as the I-channel signal component of the channel-compensated signal; and
multiplying the I-channel signal component and the Q-channel signal component of the received signal respectively by the Q-channel signal component and the I-channel signal component of the estimated channel impulse response, summing the products from the multiplications, and outputting the sum as the Q-channel signal component of the channel-compensated signal.

### Claim 3

A receiving apparatus in an Orthogonal Frequency Division Multiplexing (OFDM) system, comprising:
a Fast Fourier Transform (FFT) processor for Inverse Fast Fourier transform (IFFT)-processing a received signal;
a channel compensator for generating a channel-compensated signal by multiplying the FFT received signal by an estimated channel impulse response and calculating the power of the estimated channel impulse response;
a symbol demodulator for setting the power of the estimated channel impulse response as a reference point value defining a minimum distance between signal points in a signal constellation used for modulation of the FFT received signal, and deciding soft metric values for channel decoding of the channel-compensated signal using the reference point value, I-channel and Q-channel signal components of the channel-compensated signal, and a multiple of the reference point value corresponding to the distance of a signal point closest to the origin to each axis in the signal constellation; and
a decoder for recovering information bits by decoding the soft metric values,
wherein the symbol demodulator uses 16-ary Quadrature Amplitude Modulation (16QAM) and decides soft metric values which comprises the deciding of soft metric values for the channel-compensated signal by
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where Yk and Xk denote the Q-channel signal component and the I-channel signal component of the channel-compensated signal, respectively, (Sk,3), (Sk,2), (Sk,1) and (Sk,0) denote the soft metric values, a comprises the reference point value, S denotes the multiple of the reference point value corresponding to the distance of a signal point closest to the origin to each axis in the signal constellation, equal to the minimum distance between signal points, and k denotes a symbol index.

### Claim 4 (depends on 3)

The receiving apparatus of claim 3, wherein the channel compensator comprises:
a first complex multiplier for multiplying an I-channel signal component and a Q-channel signal component of the received signal respectively by an I-channel signal component and a Q-channel signal component of the estimated channel impulse response, summing the products from the multiplications, and outputting the sum as the I-channel signal component of the channel-compensated signal to the symbol demodulator;
a second complex multiplier for multiplying the I-channel signal component and the Q-channel signal component of the received signal respectively by the Q-channel signal component and the I-channel signal component of the estimated channel impulse response, summing the products from the multiplications, and outputting the sum as the Q-channel signal component of the channel-compensated signal to the symbol demodulator; and
a power calculator for calculating the power of the channel impulse response as the reference point value.