Estimation and reduction of CFO in OFDM system

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme. OFDM is sensitive to the carrier frequency offset (CFO) which may be caused due to difference in the carrier frequencies of transmitter and receiver. A well-known problem of OFDM is its sensitivity to frequency offset which occur due to the mismatch between transmitter and receiver local oscillator. Doppler shift and frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. Inter-carrier interference (ICI) is still a major concern OFDM system. It degrades the system performance significantly in multipath fading channels. Estimation of CFO are performed by using various methods, i.e. training sequence based and using pilot symbol. In this project work, we have done the estimation of CFO using pilot based. At the receiver, after serial to parallel conversion of the received signal, the cyclic prefix is removed first and then fed to an FFT block for de-multiplexing the multi-carrier signals. Following the FFT block, the pilot signals are extracted from the demultiplexed samples. The CFO estimation at pilot subcarriers is performed by MMSE. We send a pilot signal to the receiver, the pilot transmitted to receiver is separately and it compares the phases of all subcarriers at each OFDM symbol. When pilot is send only one input is known and others are zero then CFO is estimated by using set of equations After signal demodulation at the signal demapper, the information binary data is reconstructed at the receiver output. In this project, we focused on the estimation and reduction of CFO using MMSE and ZF techniques. The result shows the implementing equalization techniques like Zero-forcing (ZF) and Minimum mean square error (MMSE) for AWGN and Rayleigh fading channels. It improves the BER performance of the AWGN and Rayleigh channel.