Low-Complexity Estimation of CFO and Frequency Independent I/Q Mismatch for OFDM Systems

Ying Chen,A.D.S Jayalath,Jian(Andrew) Zhang

doi:10.1155/2009/542187

Ying Chen, A.D.S Jayalath + Show 1 more

Open Access

https://doi.org/10.1155/2009/542187

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Abstract

CFO and I/Q mismatch could cause significant performance degradation to OFDM systems. Their estimation and compensation are generally difficult as they are entangled in the received signal. In this paper, we propose some low-complexity estimation and compensation schemes in the receiver, which are robust to various CFO and I/Q mismatch values although the performance is slightly degraded for very small CFO. These schemes consist of three steps: forming a cosine estimator free of I/Q mismatch interference, estimating I/Q mismatch using the estimated cosine value, and forming a sine estimator using samples after I/Q mismatch compensation. These estimators are based on the perception that an estimate of cosine serves much better as the basis for I/Q mismatch estimation than the estimate of CFO derived from the cosine function. Simulation results show that the proposed schemes can improve system performance significantly, and they are robust to CFO and I/Q mismatch.

Highlights

Orthogonal Frequency Division Multiplexing (OFDM) becomes the foundation technique for broadband wireless communications because of its various advantages including high spectrum efficiency, low complexity equalization and great flexibility in resource optimization
We propose some carrier frequency offset (CFO) and I/Q mismatch joint estimators, which only require the periodicity of training sequences instead of the actual signal values
At least 3 periodical training sequence are required for the proposed estimator, we assume 7 short training symbols are available for CFO and I/Q mismatch estimation which is the minimum requirement of the methods in [10]

Summary

Introduction

Orthogonal Frequency Division Multiplexing (OFDM) becomes the foundation technique for broadband wireless communications because of its various advantages including high spectrum efficiency, low complexity equalization and great flexibility in resource optimization. In [9, 10], CFO estimators based on three identical training symbols are proposed. Different to [10], our scheme only requires one group of three identical training symbols by forming an approximated estimator for the CFO. We propose some novel estimation schemes which are robust to any values of both transmitter and receiver I/Q mismatch, and have better accuracy of the I/Q mismatch estimation for small CFO. The schemes use a group of at least three identical training symbols, which are generally present in the preamble of current systems, for example, WLAN and WiMAX systems They serially estimate I/Q mismatch and CFO with low complexity, without incurring iterative process.

Problem Formulation and System Structure

Simulation Results

Conclusions