Diversity analysis of orthogonal space-time modulation for distributed wireless relays

For ad hoc mobile networks, parallel wireless relays with space-time modulation have recently been discovered, and their potential to increase network capacity has been found to be significant. In this paper, we provide an analytical study of the diversity factor achievable by two relays with orthogonal space-time modulation. Unlike two transmitters or two receivers in the conventional MIMO setting for which the averaged bit error rate (BER) is proportional to 1/SNR², the averaged BER of two relays is shown to be proportional to ln(SNR)/SNR². This insight explains a difference between the diversity of multiple relays and the diversity of multiple receivers/transmitters. A switching scheme applied to two relays is also analyzed.