Improved quasi-orthogonal codes through constellation rotation

Orthogonal codes are a class of space-time block codes that achieve full diversity gain, though typically at a loss of code rate. Such codes have simple single-symbol decoders. The code rate can be made higher by constructing quasi-orthogonal codes (such as those proposed last year in [1], [2]) which trade a small loss of performance for full rate coding. In this paper, which builds on previous work in [1], we propose a novel rotation technique for improving the performance of quasi-orthogonal codes in terms of bit-error rate (BER). Numerical simulations show that significant improvements to previously reported results without rotation can be attained.