CARRIER FREQUENCY OFFSET ESTIMATION TECHNIQUES IN OFDM SYSTEM

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is being used in both wireless and wireline communication. It is a multi-carrier modulation and as well as a multiplexing technique that is being used in third, fourth and fifth Generation mobile technology. OFDM can cater high data rate applications in a fading environment. OFDM suffers phase variations, timing offset, and high peak to average power ratio (PAPR), carrier frequency offset etc., in which Carrier Frequency Offset (CFO) is one of the major issues. This carrier frequency offset destroys the orthogonality among the sub-carriers and hence causes inter-carrier interference (ICI) in the OFDM symbols. In this thesis; we have studied and analyzed CFO on received signal phase and constellation, different techniques to estimate CFO in presence of multipath with AWGN channel for OFDM system. We may classify CFO estimation techniques as time domain (pre-FFT) and frequency domain (Post-FFT). Frequency domain based Moose method, depends on repetition of a data symbol and comparison of the phases of each of the carriers between the successive symbols is being done for CFO estimation. Using the repetitive pattern in the training symbol, CFO estimation range can be increased by decreasing the distance between two blocks of samples for correlation. In CFO estimation using cyclic prefix, CFO can be derived from the phase angle of the product of the cyclic prefix and corresponding rear portion of the OFDM symbol. All of the above methods does not take consideration of phase noise, so another MAP based CFO estimation method name “JCPCE” algorithm works when phase noise is also taken into consideration, it not only estimate CFO but also estimate phase noise and Channel response. Estimation range for “JCPCE” is <0.5, so when system has limited computational power and to improve estimation range, modified moose estimation using JCPCE method can be used for CFO estimation. Its CFO estimation range is <1.