Research On Cooperative Diversity In Wireless Communication System

With the increase in the wireless communication demand, people are seeking better wireless transmission services. But transmission over wireless channels suffers from multi-path fading, which is the biggest problem that affects the data rate and quality of service. Diversity is a powerful technique to mitigate fading. The MIMO technology based on spatial diversity had obvious advantages in mitigating fading, and can greatly increase the channel capacity, so it received widespread attention. However, in practice, because of the size, weight, and energy, it is hard to equip multiple antennas at the mobile terminals. Thus a new diversity is proposed ,which is called cooperative divercity. It means that mobile terminals share antennas of each other, which can be form a vitual antenna array to get the same gain as conventional MIMO technique did.Firstly, based on the profoundly understanding of the character of wireless channels, this dissertation researches all kinds of diversity and combination, and cooperative diversity's working principle, system model, kinds of cooperative protocol and explain related problem that currently existed. Secondly, using the experimental method, and under the hardware condition of STC and nRF905, the three node experiment was finished following the decoded forword protocol. Thirdly, upper layer protocol was desighed based on the idea of cross-layer, which included the frame structure and algorithm implementation process in MAC and NWK layers. And the wireless network node program was finished.Finally, this dissertation researched the coded cooperative diversity, and proposed the scheme based on CDMA.And the experimental result showed that cooperative divercity can improved the reliability of information transmission and reduce the outage probability. The simulation results showed that it can significantly improve the system performance and obtain the diversity gain without increasing the system overhead.