Algorithms and applications of channel impulse response length estimation for MIMO-OFDM

The performance of the widely applied time-domain channel estimation for SISO- and MIMO-OFDM systems strongly depends on the preciseness of information regarding maximum channel impulse response (CIR) length. In practice the required CIR length is usually approximated by the length of the cyclic prefix (CP) which is an upper bound for most of the actual instantaneous CIR length. In this article, we introduce an appropriate channel length estimation method-named as Frequency Domain Channel Length Indicator (FCLI) which estimates the CIR length minimising the estimated mean square error (MSE) of an instantaneous channel estimate. The simulation results present that the FCLI outperforms the approximation of CP length. In addition, we investigate two applications of FCLI on (1) CP adaptation OFDM systems in which we minimise the overhead of the CP by the estimated CIR length and (2) CP-free OFDM systems in which we directly re-construct the structure of cyclic repetition with reduced error. Compared to the traditional channel estimation with the approximation of CP length, the overall system throughput of either CP adaptation or CP-free OFDM transmission scheme is significantly enhanced regardless of perfect synchronisation or practical distribution of time offsets. Copyright (c) 2007 John Wiley & Sons, Ltd.