MIMO communications using offset modulations

This paper explores the use of offset QPSK in a space-time coded multi-input multi-output channel by demonstrating its use with the 2 × 1 Alamouti space-time code. It is shown that the desirable orthogonalization produced by the Alamouti space-time code when used with non-offset QPSK does not carrier over to the case of offset QPSK. A least-squares detector is formulated whose performance is shown to be very close to optimal for slowly varying channel gains in an AWGN environment. The basic trellis structure of the detector is presented and applied to unshaped offset QPSK and shaped offset QPSK.