Simulation Research On Power Allocation Schemes In Cooperative Relaying Communication Systems

Currently,3G system has been put into commercial use. With the future B3G and 4G communication systems,3G faces the challenges of providing high data transfer rates and simultaneous communication of a large number of users in terms of good communication quality. Meanwhile, multipath fading seriously degrades the performance of wireless communication. Multiple-input and multiple-output (MIMO) technology achieves diversity gain through installing multiple antennas on the transmitter and receiver, thereby effectively confronting multipath fading effects. But in real communication systems, due to the restrictions such as size, power, cost, etc, the mobile terminals can not configure multiple antennas, which have limited the application of MIMO technology. In this case, cooperative communication technology came into being. It forms a virtual MIMO system by mutually sharing the antennas among numbers of adjacent single-antenna users. In cooperative communication, the information transmission is completed by source nodes and relay nodes which need power consumption to realize this procession. The diversity gain is based on the cost of total power consumption. Therefore, there is great practical significance on optimal power allocation between source and relay nodes.The main work in this thesis is listed as follows:Firstly, the Alamouti-type of cooperative diversity scheme is analyzed on its BER performance. The results show that comparing with no diversity transmission technique, diversity has a lower error rate.Secondly, the thesis conducts a detailed study on the two kind of cooperative diversity agreements:amplify-forward (AF) and decode-forward (DF), and compares their performance by simulation. It is shown through simulation results that, cooperative diversity link has better performance when all the link channels share the same state; System does not need relay for transmission when the forward pass path channel is in the best state.Next, the problem of power allocation in three-node cooperative communication system is analyzed. Under the conditon that the total power is constant, the performance of three power allcation schemes are simulated and compared. The comparison results certificate the advantages of the best power allocation scheme. Combined with optimal power allocation algorithm, the method on how to choose the best location of relay nodes is given and the conclusion is verified by the comparison between simulation results and theoretical value.Finally, the relay power allocation scheme of optimum spectrum efficiency is researched, and simulation analysis is conducted on the spectrum efficiency when the channel parameters change. Based on the relationship between system capacity and the maximum transmission rate, this method obtains the results that the quality of branch channels in cooperative link has a certain impact on the performance of cooperative communication system. The simulation results show that, when the first hop link channel is in a better state, AF and DF can obtain high spectrum efficiency using this power allocation method; when the first hop link channel is in a worse state, the direct transmission gains the highest spectrum efficiency.