Research On Power Allocation Problem For The Cooperative Wireless Communication

In the past few years, the mobile communications have developed rapidly in the world, and 3G systems also have been put into commercial applications. In the future, in addition to good communication quality, B3G communication system should also provide satisfying data rate among multi-users simultaneously. Cooperation communication technology means that single antenna mobile users can share the virtual MIMO system composed by their antennas with each other through a certain way in multi-user communication environment. In this way, wireless link transmission reliability can be enhanced and channel capacity can be improved without any increasement in hardware complexity, which can also effectively expand the coverage of the wireless transmission,thus improve the transmission system's performance.In the cooperative communication system, information transmission is completed by signal source and relay nodes, thus resources allocation is an important issue in wireless cooperative diversity network research. Information transmission among signal sources and relay nodes consumes power。Diversity gain is obtained at the cost of the sum of the power consumption produced by signal sources and relay nodes. Therefore the research of power allocation between signal sources and relay nodes is meaningful.In the paper, based on the cooperative communications research, deep research on power allocation scheme is done and an allocation scheme with minimized BER average power based on the relay choice is established. The main work is as follows:(1)Based on the Alamouti-type of cooperative diversity, BER performance is analyzed in BPSK mode scheme. The results show that transmission with diversity technique has a lower error rate than transmission without diversity technique.(2)Some research on the AF and DF cooperative diversity is done. It shows that cooperative diversity link has a better performance when all the link channels are in the same state. And system does not need relay for transmission when the forward pass path channel is in the best state. (3) In order to reduce the system BER, an allocation scheme with minimized BER average power based on the relay choice is established. The scheme first choose relay nodes for sending information according to the channel gain coefficient between source node to relay node and relay node to destination node. On the condition that the total power is constant, theoretical derivation of the minimized BER average power optimization allocation method is given. The result of the simulation shows that, compared with the power distribution method, the power optimize allocation scheme can get a better error performance. Poor channel state between the nodes can lead to the failure of cooperation which will affect the performance of the system. In order to avoid this, a threshold a is brought into the procedure of relay choice. Only when the minimum value of channel gain coefficient between the source node to the likely relay nodes and likely relay node to destination node is greater than a, the node can be taken into consideration as a relay node. Taking DF cooperation mode as an example, the selection of the value of a should at least ensure that the information between source and relay nodes can be decoded correctly to avoid the decreasement of the system's performance caused by decoding errors. In general, relay selection method can further improve the performance of the system.