Fountain Codes Applications In Wireless Cooperative Transmission

The fading of wireless channel is a huge factor which affects network performance in wireless relay networks. To against wireless fading effectively, diversity is employed. A common and effective technique of diversity is the space diversity, which employs multiple antennas. However, It's difficult to employ multiple antennas on wireless network terminal units. So, the scheme achieves fictitious multi-antenna diversity by introducing relay nodes in wireless network between receiver and transmitter.By using cooperative relay technology, we can improve the transmission rate, the reliability of wireless link, and the coverage of network. The coding scheme of Constant Bit Rate (CBR) which is used in most of cooperative transmission project misfits wireless systems, because of the statistics of wireless channel has its temporal spatial variability. The coding scheme with CBR can have good performances usually if we know Channel State Information (CSI) before. But it is hard to get CSI using feedback which source nodes send, and also it will waste a lot of resources.The fountain codes is a rateless coding which is appropriate in varying channel and BCMCS. In this paper, fountain codes based cooperative communication was prepared. It can be effective in reducing feedback information and coping with a rapidly changing wireless channel by using digital fountain codes.(1) First of all, two methods of selecting cooperative relay nodes are analyzed in multiple relay cooperative system, i.e., instant signal to noise ratio based fixed relay and threshold based self-adapting relay. The former method forwards information with fixed numbers of relay node which have the biggest signal noise ratio at the destination; and the latter selects cooperative nodes based on threshold in order to reduce interrupt possibility and have fewer numbers of relay node.(2) Applying fountain codes in multiple relay cooperative system, In view of the shortcoming of broadcast, multicast is adopted in sending out information of the source node. We analyze two transmission ways: synchronous & asynchronous transmission, the experiments show that relay nodes with multiple fountain codes can reduce energy consumption and transmission time effectively in multiple relay communication system. And asynchronous transmission has further reductions of transmission delay and energy.