Algorithms and Applications of Channel Impulse Response Length Estimation for MIMO-OFDM

Abstract — The performance of the widely applied timedomain 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 which is an upper bound for most of the actual instantaneous CIR length. In this article 1, we introduce an appropriate channel length estimation method- named as FCLI (Frequency Domain Channel Length Indicator) which estimates the CIR length minimizing the estimated mean square error of an instantaneous channel estimate. The simulation results present that the FCLI outperforms the approximation of cyclic prefix length. In addition, we investigate two applications of FCLI on 1) cyclic prefix adaptation OFDM systems in which we minimize the overhead of the cyclic prefix by the estimated CIR length and 2) cyclic prefix 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 cyclic prefix length, the overall system throughput of either cyclic prefix adaptation or cyclic prefix free OFDM transmission scheme is significantly enhanced regardless of perfect synchronization or practical distribution of time offsets. I