In this paper, we describe a new technique to restore the cyclicity of the received signal when the cyclic prefix (CP) is not sufficient for OFDM systems. The proposed technique efficiently restores the cyclicity of the ith received symbol by adding the weighted (i + 1)th received symbol to the ith received symbol. The iterative CP reconstruction (CPR) procedure is obtained using the proposed technique and the residual intersymbol interference cancellation (RISIC) algorithm. In addition, we apply the CPR method to the Alamouti space-time block coded (STBC) OFDM system. It is shown that in the STBC OFDM, tail cancellation as well as cyclic reconstruction of the CPR procedure should be repeated. Simulation results show that the proposed CPR algorithm outperforms the conventional RISIC in the symbol error rate even when the channel impulse response is longer than a half of the symbol duration, for multiple antenna applications.

This paper discusses a far-end crosstalk (FEXT) canceller for twisted-pair transmission. Many twisted-pair systems such as fiber-to-the-curb, very high-speed digital subscriber line, and high-speed LAN systems, use frequency-division duplexing (FDD) for duplex transmission. It is shown that the maximum reach of FDD twisted-pair system is limited by the performance of its upstream channel, which is assumed to be located at higher frequencies than the downstream channel. In order to improve the performance of such an FDD transceiver, FEXT cancellation is introduced for the channel at higher frequencies. A system arrangement and its blind startup procedure are studied when the FEXT canceller and equalizer are jointly adapted to combat channel intersymbol interference, FEXT, and other additive noise. We investigate the initial convergence and the steady-state behavior of the proposed twisted-pair system without requiring transmission of an ideal training sequence. Measured characteristics as well as analytical model of the FEXT channel are used to estimate the time span needed for the FEXT canceller. It is also shown that the memory span for the FEXT canceller is almost independent of the channel, thus making our results useful for the twisted-pair system over all different channels.