Differential modulation based on quasi-orthogonal codes

In this paper, we propose a differential modulation scheme bused on quasi-orthogonal space-time block codes when neither the transmitter nor the receiver has the knowledge of the channel. We consider a system with four transmit antennas and divide it into two subsystems. Each subsystem contains two transmit antennas and uses a differential space-time block code modulation. Based on the encoding and decoding for the two subsystems, we derive the overall encoding and decoding algorithm for the original system. Compared with the existing differential modulation schemes for four transmit antennas, our scheme has lower bit error rate and provides pair-wise decoding complexity.