# US 7,609,772 B2 · Apparatus and method for optimally compensating for imbalance between in-phase and quadrature-phase in a zero-IF OFDM receiver

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 7,609,772 B2
- Document ID: US7609772B2
- Status: Granted
- Kind: B2
- Application number: 11/148,179
- Filed: 2005-06-09
- Published: 2006-08-17
- Granted: 2009-10-27
- Earliest claimed: 2005-02-17
- Assignees: Samsung Electronics Co., Ltd.
- Inventors: Hyun-Seok Yu; Hyun-Seok Oh; Ji-Won Ha; Min-Goo Kim
- Web page: https://patentgrep.com/patent/US7609772B2

## CPC

- H04L 25/061: {providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of DC offset (removal of DC offset in coupling arrangements H04L25/029, H04L25/0296)}
- H04L 27/265: {Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators (H04L27/26524 takes precedence)}
- H04L 2027/0016: {Stabilisation of local oscillators}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An optimum I/Q imbalance compensating apparatus and method in a zero-IF OFDM receiver. In the apparatus, a first compensator generates a first symbol by removing interference from a second distorted symbol on an (Ns−m+1)th subcarrier from a first distorted symbol on an mth subcarrier by a first compensation coefficient in an OFDM FFT signal of Ns subcarriers. A first hard decider generates a first compensated symbol by hard-decision on the first symbol, an error calculator generates an error symbol by subtracting the first received symbol from the first compensated symbol. A second compensator generates a second symbol by eliminating interference from the first distorted symbol from the second distorted symbol using a second compensation coefficient. A second hard decider generates a second compensated symbol by hard-decision on the second symbol, and an adaptive controller updates the first compensation coefficient using the error symbol and the second compensation symbol.

## Claims

### Claim 1

An apparatus for optimally compensating in-phase/quadrature-phase imbalance in a zero-intermediate frequency (IF) orthogonal frequency division multiplexing (OFDM) receiver, comprising:
a first compensator for generating a first received symbol by eliminating an interference component caused by a second distorted symbol on an (Ns−m+1)th subcarrier from a first distorted symbol on an mth subcarrier using a predetermined first compensation coefficient in a received OFDM signal including Ns subcarriers after a fast-Fourier-transform of the OFDM signal;
a first hard decider for generating a first compensated symbol by performing a hard decision on the first received symbol;
an error calculator for generating an error symbol by subtracting the first compensated symbol from the first received symbol;
a second compensator for generating a second received symbol by eliminating an interference component caused by the first distorted symbol from the second distorted symbol using a predetermined second compensation coefficient;
a second hard decider for generating a second compensated symbol by performing a hard decision on the second received symbol; and
an adaptive controller for updating the first compensation coefficient for the first compensator based on the error symbol and the second compensation symbol.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein the first compensation coefficient is updated by
w[n+1]=w[n]+μa*Ns−m+1[n]e*m[n]
where w[n+1] is an updated compensation coefficient, w[n] is the compensation coefficient before updating, μ is a step size, aNs−m+1 is the second compensated symbol, * is the conjugation operation and em is the error symbol.

### Claim 3 (depends on 1)

The apparatus of claim 1, wherein the first compensator comprises:
a conjugate calculator for calculating a conjugate symbol of the second distorted symbol;
an adaptive compensator for compensating for the conjugate symbol by the compensation coefficient; and
a subtractor for subtracting the output of the adaptive compensator from the first distorted symbol and outputting the result as the first received symbol.

### Claim 4

A method of optimally compensating in-phase/quadrature-phase imbalance in a zero-intermediate frequency (IF) orthogonal frequency division multiplexing (OFDM) receiver, comprising the steps of:
generating a first received symbol by eliminating an interference component caused by a second distorted symbol on an (Ns−m+1)th subcarrier from a first distorted symbol on an mth subcarrier using a predetermined first compensation coefficient in a received OFDM signal including Ns subcarriers after fast-Fourier-transform of the OFDM signal;
generating a first compensated symbol by performing a hard decision on the first received symbol;
generating an error symbol by subtracting the first compensated symbol from the first received symbol;
generating a second received symbol by eliminating an interference component caused by the first distorted symbol from the second distorted symbol using a predetermined second compensation coefficient;
generating a second compensated symbol by performing a hard decision on the second received symbol; and
updating the first compensation coefficient for the first compensator based on the error symbol and the second compensation symbol.

### Claim 5 (depends on 4)

The method of claim 4, wherein the first compensation coefficient is updated by
w[n+1]=w[n]+μa*Ns−m+1[n]e*m[n]
where w[n+1] is an updated compensation coefficient, w[n] is the compensation coefficient before updating, μ is a step size, aNs−m+1 is the second compensated symbol, * is the conjugation operation and em is the error symbol.

### Claim 6 (depends on 4)

The method of claim 4, wherein the first received symbol generating step comprises the steps of:
calculating a conjugate symbol of the second distorted symbol;
adaptively compensating for the conjugate symbol by the compensation coefficient; and
subtracting the output of the adaptive compensator from the adaptively compensated symbol and outputting the result as the first received symbol.