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 -