Research On Relay Selection Strategy Based On Dynamic Threshold

In this paper, we mainly study the relay node selection strategi es of the wireless relay communication. Wireless relay communication is one of the primary technologies of 4G. During the construction of the network, relays communicate with the base station through the wireless backhaul link, which makes the network facilities intensive, facilitates the cost of the network contribution more economical compared with the deployment of traditional base stations, and shortens the distance between the terminals and the communication infrastructure. It helps enlarge t he coverage area of the cell, increase the transmission rate of data, and improve the communication quality of the edge and blind an gle users by the application of relay. If several relay nodes are available, different relay node selection strategies make a difference.The main content of this paper includes: The principle of LTE-A relay system and several hotspot techniques of relay research, the comparison between the opportunistic relay(OR) and selection cooperation(SC), the comparison between the selections of the relay with the best channel of first hop(FHSC) and of the second hop(SHSC) within the selection cooperation, the introduction of the diamond relay channel, the relay selection strategy based on dynamic threshold. The fading in each channel in this paper is assumed to be independent, slow and Rayleigh distributed in this paper and no channel coding is taken into consider ation. The channels are constant for the duration of one packed and vary independently from one packed to the next. The destination nodes collect the channel state information of the two hop links and the direct links and make the decision of which relay is the selected one.The simulations in this paper demonstrate that, selection cooperation makes better use of the direct link to avoid the state of outage. However opportunistic relay have advantage in the bit error rate(BER) over selection cooperation. FHSC and SHSC have their own advantage under different conditions in the matter of the performance of BER.According to different channel state of Rayleigh fading of channel, we proposed the relay selection strategy based on the dynamic threshold. In the re lay selection strategy based on the dynamic threshold, the relay nodes are classified into four groups. The first kind have perfect channel conditions of both two hops, the second kind have available channel conditions of both two hops which are inferior to the first kind, the third kind has perfect channel conditions of the first hop, but the second hop not. The forth kind, the channel conditions of both the two hops are not available.According to the classification of relay nodes, the state s of relay communication are divided into five groups. The first state, one of the first kind relay is selected as the transmitting relay. The second state, two of the second kind relay are selected, and at the same time, the diamond relay channel will be used. The third state, one of the second kind relay and two of the third kind relay are selected and the diamond relay channel will be used as well. The forth state, two or three relay of the third kind are selected. The fifth state is the outage state. The data transmitted during the outage state need to be retransmitted. The simulation demonstrates that the relay selection strategy based on dynamic threshold acquires faire performance in the respect of outage probability and does not worsen the performance of bit error rate meanwhile.