A Low-Complexity Solution to Decode Diversity-Oriented Block Codes in MIMO Systems with Inter-Symbol Interference

In this paper we first propose a block-code based general model to combat the Inter-Symbol Interference (ISI) caused by frequency selective channels in a Multi-Input Multi-Output (MIMO) system and/or by asynchronous cooperative transmissions. The general model is not only exemplified by the Time-Reversed Space-Time Block Code (TR-STBC) scheme, but also by the Asynchronous Cooperative Liner Dispersion Codes (ACLDC) scheme. In these schemes a guard interval has to be inserted between adjacent transmission blocks to mitigate the effect of ISI. Consequently, this could degrade the effective symbol rate for a small block size. A larger block size would enhance the effective symbol rate and also substantially increase the decoding complexity. In the general model proposed in this paper, we further present a novel low-complexity breadth-adjustable tree-search algorithm and compare it with Sphere-Decoding (SD) based algorithms. With simulation results we will illustrate that our algorithm is able to achieve the optimal performance in terms of Bit Error Rate (BER) with a complexity much lower than the SD-based algorithms, whether the ACLDC or TR-STBC scheme is employed. Through simulations we further demonstrate that when the block size of the ACLDC is equivalent to 20, the complexity of the proposed algorithm is only a fraction of 10^-8 that of the Maximum Likelihood (ML) algorithm. This would allow us to practically enhance the effective symbol rate without any performance degradation.