Bandwidth Efficient Cooperative Diversity Scheme Based on Constellation Rotation

A bandwidth efficient three-user cooperative diversity scheme is proposed. Each user has two partners who receive its symbols and rotate the phases of these symbols. Then, two partners retransmit the real parts and imaginary parts of these rotated symbols, respectively. This scheme can offer diversity order of three, and the bandwidth efficiency is only decreased by 1/2 compared to a noncooperative diversity scheme. The optimal rotation angles are derived when QPSK and 8PSK modulations are employed, respectively. Then, a new symbol mapping for 8PSK modulation is proposed, and it is a simple way to improve the system performance.