Research On Cooperative Diversity Technology In Wireless Communications

Due to the limitations in size, power and cost, it's hard to equip multiple antennas at the one mobile terminal. Thus, cooperative diversity has been proposed. It means that mobile terminals share antennas of each other to generate a virtual MIMO that could achieve transmit diversity gain to combat the multipath fading in wireless channels, and improve the uplink channel performance efficiently.Firstly, various diversity technologies and the principle of cooperative diversity are outlined. Next, on the basis of two users'Classical Decode-and-Forward scheme and Coded Cooperation scheme, a cooperative diversity scheme combining adaptive modulation is proposed. The transmitters adaptively vary the modulation schemes by comparing the threshold with the returned near-instantaneous channel-quality information. Without sacrificing BER, this adaptive modulation scheme provides a higher average spectral efficiency by taking advantage of channel state information. Then, two users'Decode-and-Forward scheme and Coded Cooperation scheme based on network coding are investigated. Numerical results show that these two schemes based on network coding can achieve about 1.8dB gain over the classical schemes when bit error rate is 10-4.Finally, an improved Decode-and-Forward scheme based on orthogonal signaling is proposed, which introduces convolutional encoding to enhance the system performance. On the basis of two users'cooperative model, an improved relay scheme based on network coding and orthogonal modulation is proposed, which increases the diversity gain further, with no need for additional resources.