Decoding of quasi-orthogonal space-time block code with noise whitening

Quasi-Orthogonal Space-Time Block Code (QO-STBC) can provide full-rate transmission and low decoding complexity. Full-level of transmit diversity can be achieved if constellation rotation technique has been used. In this paper, the design and application of noise whitening filter for the receiver of QO-STBC are discussed in detail. Such filter facilitates the use of standard equalizer or decoder that have been designed for white noise on the received QO-STBC signals, which tend to suffer from colored noise after matched filtering. This eliminates the need for dedicated decoding metric for signals with colored noise. It is found that only maximum likelihood decoding and sphere decoding can take advantage of the constellation rotation code design technique to achieve full diversity. Analytical results show that the SNR of the estimated symbol is independent to the angle of constellation rotation if symbol-by-symbol decoding schemes are used. This confirms with the simulation results where the performance of linear equalizers and decision feedback equalizers are the same for both constellation rotated and non-constellation rotated QO-STBC.