Space-time block coding with hybrid transmit antenna/code selection

Assuming that a feedback channel is available and the fading coefficients are known at the transmitter, Gore and Paulraj have proposed a transmit antenna selection scheme that uses the Alamouti code with the best pair of antennas, selected from m greater than or equal to 3 transmit antennas available, where the selection criterion is to minimize the instantaneous probability of error. They have showed that a diversity order of m is achieved, as if all the m antennas were used. The advantage is that only two RF chains are required, reducing the transmitter cost. In this paper, full-rate, non-orthogonal space-time block codes are produced by repeating and permuting columns of the Alamouti code matrix. These codes need only two RF chains, have decoding delay equal to two, and their maximum likelihood decoders based on linear processing are essentially the same as that of the Alamouti code. Based on the instantaneous fading coefficients, the transmitter selects either one of the proposed codes with three antennas or the Alamouti code with two antennas. Simulations results for a simple case indicate that full diversity is achieved in spite of using non-orthogonal codes, and a coding gain of up to 1 dB over Gore and Paulraj's scheme is observed.