Reduced ML-decoding complexity, full-rate STBCs for 2a transmit antenna systems

Abstract

For an n_t transmit, n_r receive antenna system (n_t × n_r system), a {\it{full-rate}} space time block code (STBC) transmits n_min = min(n_t,n_r) complex symbols per channel use and in general, has an ML-decoding complexity of the order of M^n_tn_min (considering square designs), where M is the constellation size. In this paper, a scheme to obtain a full-rate STBC for 2^a transmit antennas and any n_r, with reduced ML-decoding complexity of the order of M^{n_t(n_min−3/4)−0.5}, is presented. The well known Silver code for 2 transmit antennas is a special case of the proposed scheme. Further, it is shown that the codes constructed using the scheme have higher ergodic capacity than the well known punctured Perfect codes for n_r < n_t. Simulation results of the symbol error rates are shown for 8×2 systems, where the comparison of the proposed code is with the punctured Perfect code for 8 transmit antennas. The proposed code matches the punctured Perfect code in error performance, while having reduced ML-decoding complexity and higher ergodic capacity.