A low complexity semi-blind channel identification and source recovery method for transmission systems with guard intervals

A semi-blind channel identification method is proposed for block transmission systems with guard intervals. Usually, block transmission systems append a sequence of L-1 zeros (where L is an upper bound on the channel length), called a guard interval, to each block before transmitting the blocks so as to prevent interblock interference. The paper shows that by replacing the L-1 zeros between each block with specially chosen sequences of L known symbols, a penalty of just one extra symbol per block, it is possible to determine directly the channel coefficients from L consecutively received blocks. For non-time-varying channels, the scheme is equivalent to transmitting a training sequence every L blocks, and hence it can be considered as a way of distributing a training sequence over L blocks. The benefit of the proposed method is twofold. Firstly, due to its distributed nature, it outperforms the training sequence method when the channel varies with time. Secondly, it has a lower latency delay than the traditional training sequence based method, yet achieves the same or better performance. Also, the proposed method retains all the advantages of guard intervals.