Low-complexity branch metric calculation for decoding of space-time trellis codes

Space-time trellis codes (STTC) have recently been proposed to use in the coded multiple-input multiple-output (Coded MIMO) communications. Viterbi algorithm is the basic decoder used to retrieve the transmitted information, by which the impaired information can be corrected by the path record determined by accumulating the branch metrics. However, the computational complexity of the branch metric in Viterbi decoding for STTC is extremely high in spite of its high reliability. Moreover, the computational complexity also increases significantly along with the number of antennas and the order of modulation. To reduce the computational burden, we propose a new method to compute the branch metrics in the geometric view. The degree of complexity reduction is very impressive at sacrifice of a little degradation of coding gain. The simulation results show that more complexity reduction can be achieved when more antennas and higher order of modulation are applied.