The Research On The Optimal Power Allocation In The Ooperative Communication Systems

The multi-input multi-output (using multiple transmission and receiver antennas MIMO) technique has been proved to be able to greatly enhance the channel capacity of the wireless transmission systems under the same frequency spectrum. For this reason, it has been selected as the key technique in the4G wireless systems. However, this technique requires the end users to install many antennas and thus increases the size of the end user equipment, the complexity of the hardware, and the energy consumption. A. Sendonaris etc. has proposed a new spatial diversity technique, which is the cooperative communications. In this technique, the end users can share their antennas and other resources to form a virtual MIIMO system to resist the multi-path fading environment and enhance the system performance. This technique can also increase the cover area of the base station without increasing its transmission power. This technique has already been selected in the WiMax standard to use the MESH method to implement the cooperative communications. For these reasons, this technique has been a research focus in recent years. The optimal power allocation, the relay selectipn, and the outage probability are the main problems in this technique and are unsolved. This thesis carries out the research of the optimal power allocation under different cooperative modes and the number of cooperative nodes.The main content of this thesis are listed in the following.1First, the transmission features of wireless channels are described, including the transmission power loss, multi-path fading effects, and the statistical model of the wireless channels. Then, it introduces the principles of the cooperative communications and the classification of the cooperative networks, and analyzes the cooperative diversity and combination method. Through computer simulations, the comparison of several combination methods are given.2It reviews and describes an intelligent differential evolution algorithm.3It describes a communication system with multiple relay nodes and each node has a single antenna. It derives the symbol error rate of this system. Under the total power restriction, the symbol error rate is set as an objective function to use the differential evolve algorithm to decide the power allocation between the source node and the relay nodes. From the computer simulations, the comparison of the proposed algorithm is compared with the equal power allocation algorithm and the results show that there is3to5dB of the gain of the transmission power using4relays or6relays in the proposed algorithm.4An new communication protocol is proposed. The transmission processes have three stages. In the second stage, a best relay node and a relay node that is closest to it are selected and each relay node transmits its received information. The symbol error rate under this system is derived and the differential evolve algorithm is used to decide the power allocation between the source node and these two relay nodes. Computer simulation results show that this algorithm has better performance than the existing algorithms.Overall, the research of power allocation algorithms in cooperative communications has been carried out in this thesis, the proposed power allocation algorithm has better performance than the equal power allocation method and can reduce the symbol error rate to improve the system performance.