Differential space-time modulation based on quasi-orthogonal codes

This paper proposes a low complexity differential modulation scheme for multiple-antenna systems where neither the transmitter nor the receiver knows channel knowledge. Our scheme is based on quasi-orthogonal codes. We consider a wireless system with four transmit antennas. At the transmitter, symbol pairs are jointly mapped to construct quasi- orthogonal codes and the codes are used to perform differential encoding. At the receiver, a simple pair-wise decoder is derived to demodulate symbol pairs. We compare the bit error rate (BER) performance and computational complexity of our scheme with that of other differential detection schemes. Comparison results show that the proposed scheme has good performance and low decoding complexity.