TY - JOUR

T1 - A low-complexity zero-forcing CFO compensation scheme for OFDMA uplink systems

AU - Hsu, Chao Yuan

AU - Wu, Wen-Rong

PY - 2008/10/1

Y1 - 2008/10/1

N2 - Similar to the conventional orthogonal frequency-division multiplexing (OFDM) system, an OFDM multiple access (OFDMA) system will have a carrier frequency offset (CFO) problem. Since CFOs of all users are different, CFO compensation in the OFDMA uplink system is much more involved. A simple, yet efficient, method is the zero-forcing (ZF) compensation method. However, it involves an inverse of an N x N CFO-induced ICI matrix, where N is the number of subcarriers. Thus, the complexity can become very high when N is large, a case commonly seen in OFDMA systems. In this work, we propose a low-complexity ZF method to overcome the problem. The main idea is to use Newton's method to solve matrix inversion iteratively. We explore the structure of the CFO-induced ICI matrix and develop a method that can implement Newton's method with fast Fourier transforms (FFTs). As a result, the required computational complexity is significantly reduced from O(N3) to ο(2N log2 N). Simulations show that, with only three iterations, the proposed method can have similar performance to the direct ZF method.

AB - Similar to the conventional orthogonal frequency-division multiplexing (OFDM) system, an OFDM multiple access (OFDMA) system will have a carrier frequency offset (CFO) problem. Since CFOs of all users are different, CFO compensation in the OFDMA uplink system is much more involved. A simple, yet efficient, method is the zero-forcing (ZF) compensation method. However, it involves an inverse of an N x N CFO-induced ICI matrix, where N is the number of subcarriers. Thus, the complexity can become very high when N is large, a case commonly seen in OFDMA systems. In this work, we propose a low-complexity ZF method to overcome the problem. The main idea is to use Newton's method to solve matrix inversion iteratively. We explore the structure of the CFO-induced ICI matrix and develop a method that can implement Newton's method with fast Fourier transforms (FFTs). As a result, the required computational complexity is significantly reduced from O(N3) to ο(2N log2 N). Simulations show that, with only three iterations, the proposed method can have similar performance to the direct ZF method.

KW - Carrier frequency offset (CFO)

KW - Fast fourier transform (FFT)

KW - Intercarrier interference (ICI)

KW - Newton's method

KW - Orthogonal frequency-division multiple access (OFDMA)

UR - http://www.scopus.com/inward/record.url?scp=55149108517&partnerID=8YFLogxK

U2 - 10.1109/T-WC.2008.070177

DO - 10.1109/T-WC.2008.070177

M3 - Article

AN - SCOPUS:55149108517

SN - 1536-1276

VL - 7

SP - 3657

EP - 3661

JO - IEEE Transactions on Wireless Communications

JF - IEEE Transactions on Wireless Communications

IS - 10

M1 - 4657306

ER -