Orthogonal Frequency Division Multiplexing In The Channel Estimation And Interference Cancellation

OFDM technique is widely used in wireless communication systems, improving the communication system capability.The channel estimation technique makes a key role in the OFDM techniques.The channel information is needed in signal processing procedures.Meanwhile,the interference cancellation algorithm is adapted to cancel the inter-carrier interference and inter-symbol interference.This thesis mainly proposes some combined algorithms of channel estimation and interference cancellation.In time invariant system,a combination of channel estimation and ISI cancellation method is proposed for OFDM systems without cyclic prefix(CP).Channel vector of temporal domain,which can be converted to the channel characteristic of frequency domain after FFT,is estimated with the least square(LS) algorithm. Combining detection with ISI cancellation,iterative interference cancellation can be implemented in this paper.Simulation results show that the performance of proposed channel estimation algorithm is more accurate and its BER is close to the OFDM system with CP.In OFDM systems,a time-varying multi-path fading channel leads to the loss of sub-carrier orthogonality which in turn causes the inter-carrier interference and increases inaccuracies in signal detection.In this paper, an iterative ICI cancellation and MMSE estimation algorithm is proposed. Avoiding the inaccurate assumption in conventional one-tap ICI cancellation that ICI is modeled as AWGN,MMSE principle is used to estimate the initial value of signal,followed by the iterative ICI cancellation and MMSE equalization.Extensive simulations show that a small number of iterations can cancel the ICI effectively,improving the system performance.