An Elaborate Frequency Offset Estimation And Approximation of BER for OFDM Systems

This paper mainly analyzes the effect of frequency offset on the performance of OFDM communications systems. The most important requirement in an OFDM is frequency and time synchronization as this form the reason for orthogonality between the subcarriers. However a major problem in OFDM is its vulnerability to frequency offset errors between the transmitted and received signals, which may be caused by Doppler shift in the channel or by the difference between the transmitter and receiver local oscillator frequencies. In such situations, the orthogonality of the carriers is no longer maintained, which results in Intercarrier Interference (ICI). In this paper we study the effects that ICI can cause to the SNR in an OFDM system, and estimate the amount of frequency offset. In the first part of paper we give an algorithm for study the effect of frequency offset with SNR, then in second part of paper a mathematical model of OFDM systems with a cyclic prefix (CP) and with virtual subcarriers is derived and we propose a shift-invariance CFO estimation algorithm which is based upon DOA-MATRIX method. In the third part we discusses another method for estimating of frequency offset i.e. Conjugate ICI Cancellation scheme. [3] then Simulation results illustrate comparison of performance of these two methods for different values of frequency offset. Keywords— OFDM, SNR, ICI,IBI,BER, CFO,CP