Detection of Alamouti Space-Time Encoded Offset QPSK

The Alamouti space-time code (STC) is attractive because of the low complexity of its associated detection algorithm. However, when this code is applied to offset modulations such as offset QPSK (OQPSK), the offset complicates the detection process. The Maximum Likelihood (ML) detector for Alamouti encoded OQPSK is much more complex than the ML detector for QPSK. We present two alternate detection algorithms: one which duplicates the simplicity of the non- offset QPSK Alamouti detector with a cost in bit error rate performance and one which matches the performance of the ML detector with less complexity than the ML detector.