Study On The Multiple Relay Selection Scheme In DF Cooperative Communication System Under The Coexistence Of Multiple Channel Types

Relay selection technology is the key technology of cooperation communication systems. Mu ltiple relay selection refers to select one or more than one relay nodes forwarding data from the s ource node to assist the source node in data transmission. Because it select more than one relay n odes to forward data, so it needs to merge the signals of different links at the destination node. M aximum ratio combining, selective combining and equal gain combining are the three major mer ging ways, of which maximum ratio combining has optimal performance and is most widely use d. This article also uses the maximum ratio combining technique. In this sense, the realization o f multiple relay selection should utilize maximum ratio combining. So far, the performance of m aximum ratio combining is based on the hypothesis of a single channel type only. However, in th e actual communication scenario, there exists different type of channel in accordance with the re al channel conditions. Therefore, it is necessary to study the performance of maximum ratio com bining under multiple types of channel environment.This paper uses the mixture Gamma distribution to characterize the distribution of the signal-to-noise ratio under various types of channel. Then, the performance of the maximum ratio comb ining is studied under a variety of channels. On this basis, a novel multiple relay selection suitabl e for multiple types of channel coexisting in the communication scenario is proposed. The main c ontributions are as follows:(1)By introducing a mixture Gamma distribution to describe various types of channel, we obt ained the expressions of the signal-to-noise ratio after the maximum ratio combining the channel capacity and the outage probability under various types of channel. Numerical results show that t he theoretical analysis matches the simulation well. At the same time, it can be seen that under th e same parameter settings, the values of the channel capacity and the outage probability are differ ent from one type of channel to another. This tells us that it is very necessary to analyze the perfo rmance of maximum ratio combining in the multiple channel coexistence scenario.(2)We proposed a novel multiple relay selection method in DF cooperative communication n etwork in the presence of multiple channel types. This method determine the channel types of the relay links and the candidate relay nodes, and select the candidate relay combination with the lar gest channel capacity or the minimum outage probability for data forwarding. The numerical res ults show that the proposed multiple relay selection method is superior to the best SNR relay sele ction in the literature and also less complex than the latter. In addition, The proposed method can be used in the scenario of multiple channel coexistence.