Combined-Weight Sphere Decoder in Bad Channel

For BLAST system, the optimal ML detection is infeasible when antenna number and modulation level is high, there have been some attempts to find more efficient algorithm to replace ML detection, such as sphere decoding (SD). Whereas the bad channel with large condition number still aggravates the computation complexity of SD. In this paper, we firstly explain the reason why the condition number influences the performance and the complexity of detection algorithm. Secondly, an algorithm of combining weight at high layer is proposed for SD, aiming to reduce the probability of accessing into the high layer of the tree in the searching process of SD so as to decrease the complexity. According to whether the magnitude of condition number is distinguished or not, there are two types, i.e. the partially combined-weight SD and the fully combined weight SD. The simulation results prove that the proposed algorithm can cut down the complexity distinctly, even to more than 20% at low SNR and high condition number.