Maximum Likelihood CFO Estimation in OFDM Based Communication Systems

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for the next generation (3G/4G and beyond) wireless communication systems. These systems are very sensitive to the carrier frequency offset (CFO) that destroys the orthogonality property of the OFDM sub-carriers and introduces inter-carrier interference (ICI) which degrades the bit error rate (BER) performance. However, Inter Symbol Interference (ISI) that occurs during transmission can be totally averted by adding cyclic prefix (CP) to the OFDM symbol. Also adding CP reduces the level of CFO introduced during transmission. Nonetheless adding CP cannot protect ICI from occurring and distorting the transmitted symbol data at the receiver side. In this paper, we set the CP to vary in length depending on the channel conditions and obtained a better performance. We have also proposed a novel bandwidth efficient ML estimation technique that has a better bit error rate compared to that of conjugate cancellation method. We have also simulated and discussed bit-error-rate (BER) of the system against SNR under different channel conditions and compared it with other existing ICI mitigation techniques and found it better.