Efficient Space-Time Codes Derived from Quasi-Orthogonal Structures

We propose a new class of block codes that outperforms known space-time block codes at low rates. The new codes are designed by starting with a quasiorthogonal structure, and then making certain modifications to increase the coding gain distance. By using appropriate rotations and set partitions for two quasi-orthogonal codes, and combining subsets of their codewords, we are able to obtain higher coding gain distance at a given rate, and thus improve performance. Simulations confirm the advantages of this code compared to other codes operating at the same rate and SNR. We also provide an efficient ML decoding algorithm for the new code.