Forming Technology Beam Two-hop Cooperative Communication Systems

Cooperative communication systems share their antennas or the relay nodes within the service area to form a virtual MIMO (Multiple input Multiple output) system,through mutual cooperation with each other, in this way, not only the advantages of MIMO technology can be obtained, but also provides new ideas for the further extension of MIMO technology. In addition, with the development of MIMO technology, research of cooperative communication got further in-depth development. Especially with the effectively combining of cooperative communication and beamforming technology, it provides possibility for rapid development of wireless communication in the future. However, the beamforming in the cooperative system is more complex:not only related with the cooperation method, but also be different with the beamforming in the traditional MIMO system.In this paper, we focus on the two hop cooperative communication systems, studied the beamforming problems under AF(Amplify and Forward)protocol. The main contents of this paper are as follows:1. Studying the channel capacity of cooperative system with Beamforming technique. From the traditional MIMO systems, this paper analyzed the channel capacity of cooperative system under different cooperation ways, studied the channel capacity of two jump cooperative system when the transmitting terminal using a beamforming scheme, then the expression of this channel capacity is given. Finally the simulation results show that the channel capacity of coordination system under this scheme have proportional relations with transmitting antenna numbers and their arrays numbers.2. Then this paper studied the beamforming problem of two hop cooperative system on the single user. When the channel state information of cooperative system is known, this paper divided the beamforming scheme into three situations:1) On a certain quality of service (Quality of Service, QoS) in order to minimize of the total relay transmit power, the beamforming vector is obtained by the method of Lagrange multipliers, then by the Matlab simulation, established a minimum total transmit power of relay terminal based on the given QoS under the optimal beamforming, as well as the BER performance of cooperative system under different channel conditions. The simulation results show that, the forward and backward link channel state of relay nodes will influence the minimum total transmit power of relay terminal, and when QoS is greater than a certain value, the minimum total transmit power of relay terminal will not exist.2) Maximizing the transmission rate between the source node and the destination node under a constraint of relay total power, the beamforming vector is obtained by matrix analysis method, relationship between the total power of the relay and transmission rate under the optimal beamforming are obtained through the Matlab simulation. The simulation results show that, in the same transmit power, the backward link channel state of relay node impacting on the transmission rate is more close, and when the transmit power exceeds a certain value, the maximum transmission rate of the system will no longer increase.3) In a individual relay power constraint, get the rate under the optimal beamforming with the help of Matlab toolbox to solve the Optimization problem which maximizing the transmission rate between the source node and the destination node, as well as get the BER performance of cooperative system under different channel conditions through the Matlab simulation,At last, we compare the difference between the latter two schemes through simulation. The results show that the performance of the latter two schemes is very close and significantly improve the system performance compared to a fixed allocation scheme...