Novel Migitation Techniques for OFDM in a Doppler Spread Channel – Part II

P. Chayratsami (Thailand) and M.A. Wickert (USA)


OFDM, COFDM, ICI, sequential detection,estimation


The performance of an Orthogonal Frequency Division Multiplexing (OFDM) system degrades in the Doppler spread channel due to intercarrier interference (ICI) resulting from loss of orthogonality. In [1], it is shown that the ICI is reduced by upsampling followed by an LN-point FFT at an OFDM receiver. Also, the sequential interference cancellation (SIC) detection has been proposed under the assumption of perfect channel estimation and results in lower error floor. This paper presents the extension of the results of [1] under imperfect channel estimation. The timedomain estimation based on pilot signals is proposed for use in SIC detection. The channel estimation uses a comb-type pilot arrangement and least-square (LS) estimation. Also, the proposed estimation is compared with the existing frequencydomain estimation in terms of the error probability performance. In addition, a coded OFDM (COFDM) system with punctured convolutional codes and SIC detection scheme is investigated by computer simulation under both perfect and imperfect channel estimations. The bit error rate (BER) of a COFDM-SIC system for BPSK modulation scheme leads to better performance than that of an uncoded system, and significant gain when the interleaver size is sufficiently large.

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