Research On Cooperative Communication

MIMO has obvious advantages in alleviating the effect of multipath fading, increasing channel capacity and signal quality. However, due to limitations in size, power and cost, antenna array is not exercisable to implement for mobile devices. Cooperative communication(or cooperative diversity) has been proposed to overcome this difficulty, by sharing each other’s single antenna, it constitutes virtual MIMO system to obtain transmitting space diversity.Typical wireless channels and diversity techniques are given first in this dissertation, and an introduction of available cooperation methods is made. According to the number of participating users, cooperative communication methods can be divided into: basic two-user cooperation and multi-user cooperation. Basic two-user cooperation and multi-user cooperation schemes are discussed on the whole, and the methods of relay’s signal processing and adaption to channel measurements are analyzed too.As low spectral efficiency in traditional and alamouti space-time cooperation methods, an improved method is proposed. It needs four time slots for one complete cooperative transmission for traditional and alamouti cooperation methods, while only three time slots are needed in the improved method, which result in higher spectral efficiency. In the situation of several users sharing one relay, traditional methods don’t consider the channel condition difference and provide same relay service to these users, which results in a high network outage probability. In order to overcome this problem, a new method is proposed, which provides channel suitable relay service by using unequal error protection block code modulation and multi-stage decoding. Not only the users’ performance is improved but also the network performance is equilibrated.