Reduced ML-decoding complexity, full-rate STBCs for 4 transmit antenna systems

For an n_t transmit, n_r receive antenna system (n_t × n_r system), a full-rate space time block code (STBC) transmits min (n_t, n_r) complex symbols per channel use. In this paper, a scheme to obtain a full-rate STBC for 4 transmit antennas and any n_r, with reduced ML-decoding complexity is presented. The weight matrices of the proposed STBC are obtained from the unitary matrix representations of a Clifford Algebra. By puncturing the symbols of the STBC, full rate designs can be obtained for n_r <; 4. For any value of n_r, the proposed design offers the least ML-decoding complexity among known codes. The proposed design is comparable in error performance to the well known Perfect code for 4 transmit antennas while offering lower ML-decoding complexity. Further, when n_r <; 4, the proposed design has higher ergodic capacity than the punctured Perfect code. Simulation results which corroborate these claims are presented.