A New STC Structure to Achieve Generalized Optimal Diversity with a Reduced Design Complexity

We propose a new space-time code (STC) structure that can achieve generalized optimal diversity (GOD) with a reduced design complexity, and also provide an increased coding gain. As a class of GOD STC structure, the new structure achieves the full diversity and an optimized coding gain with minimum delay irrespective of the number of transmit antennas (N_t) and the rate (R ), if the rate is less than or equal to the rank of the channel matrix. In the new structure, only R transmit antennas at a time slot are engaged in signal transmission, and a different set of R transmit antennas at a different time slot is used. N_t data symbols are combined together using complex weights for each antenna at a time slot. The same set of data symbols is repeated at all the remaining time slots in a code block, but is transmitted through different transmit antennas using different sets of combining weights at different time slots. In particular, the above structure eliminates cross-code product terms in the determinant of codeword difference matrices when R < N_t, thus increasing the coding gain. In addition, we propose a simplified code structure to facilitate the code design, in which a higher-rate GOD STC can be obtained by coupling R rate-one codes using different rotations. We apply two design constraints such as the power and orthogonality constraints, and provide some guidelines to reduce further the design complexity. In conclusion, the proposed structure provides a higher coding gain as compared with the original GOD structure [ 1 ] and the existing linear dispersion STCs (LD-STCs), when R < N_t and can reduce significantly the design complexity when the rate becomes higher and/or the number of transmit antennas gets larger.