A New ICI Self-Cancellation Scheme Based on Repeated Symbol in OFDM Systems

Frequency offsets in OFDM communication systems distort the orthogonality between subcarriers, and then result in intercarrier interference (ICI). This paper studies a new ICI self-cancellation scheme for combating the impact of ICI on OFDM systems. Its basic idea is that ICI components are canceled by using repeated symbols on time domain. At first, the two repeated symbol blocks on time domain, in which the 1st block is formed by inserting zero in the symbol block of a conventional OFDM system, and the 2nd block is formed by inversing and shifting cyclic right from the 1st block, are respectively transmitted at the transmitter. At the receiver, the received data symbols are divided into two paths corresponding to the two symbol blocks transmitted, and then the two data symbol streams are combined. Finally, the resultant symbol sequence is detected to obtain the estimation of original data symbols as a conventional OFDM system. By theoretical analysis and calculation for the new scheme, it is obviously shown that the ICI components contained in received signals can be effectively reduced, and the carrier-to-interference power ratio (CIR) of this scheme is at least 10dB better than that of a conventional OFDM system. Meanwhile, comparing with other similar techniques, this new scheme is better than another similar scheme at normalized frequency offset ε > 0.2. Consequently, this scheme can remarkably improve the performance of OFDM communication systems due to frequency offsets.