Research On Cooperative Communication With Opportunistic Relay Selection Strategy

The cooperative communication technology developed in recent years enables users to transmit information to the destination in a cooperative manner,and abandons the way in which each user preempts the channel resources with other users in order to transmit messages independently.This has effectively broken through the performance bottleneck of traditional wireless communication technology and become one of the key technologies to promote the development of wireless communication.As one of the multi-relay cooperative communication strategies,the opportunistic relay selection(ORS)not only has excellent cooperative diversity gain,but also has the advantages of low cooperative overhead,easy physical implementation and being free from the limitation of network size.In this paper,the cooperative communication strategy,technology and scheme of ORS,as well as the communication performance under various adverse factors and different constraints are studied.The main contributions and innovative achievements in the paper include:(1)A new incremental opportunistic relay selection cooperative communication strategy(IORS)under the condition of total power constraint is proposed.Aiming at the target of low spectrum efficiency of ORS with two-stage relay forwarding,the three-node incremental relay cooperative strategy is extended to multi-relay cooperative communication,and a under the total power constraint condition IORS cooperative communication strategy is proposed.The essential idea is to choose the source node to the destination node to communicate directly or to cooperate with ORS when the capacity of the wireless link of the source node to the destination node can’t meet the quality requirements of communication.Theoretical and simulation results show that the proposed strategy has higher spectral efficiency and lower outage probability than the ORS with two-stage relay forwarding under the total power constraint.(2)Based on decode-and-forward(DF)IORS/ORS under the total power constraint condition cooperative communication strategy and combined with antenna diversity technique to resist cascading(shadow)fading and asymmetrical channel fading,new schemes are proposed.Because of the simple form and a few adjustable parameters,the traditional distribution functions such as Rayleigh,Nakagami,Rician and Lognormal are difficult to accurately describe the wireless channel characteristics in practice.In this paper,proceeding from the latest research results of Shankar P M and others on the characteristics of wireless channel fading,cooperative communication models founded on cascaded(shadow)fading and asymmetric channel fading and antenna diversity technology are established.The theoretical and simulation results show that under the total power constraint condition,DF-IOR/ORS can achieve cooperative diversity gain,effectively reduce the influence of channel cascade(shadow)fading and asymmetric channel fading and the conclusion has more general applicability.In comparison with under the total power constraint condition DF-ORS,the proposed DF-IORS has better cooperative communication performance.The performance of under the total power constraint condition DF-IORS/ORS cooperative communication is further improved by using antenna diversity technology.(3)The schemes based on under the total power constraint condition DF-IORS/ORS cooperative communication strategy and combined with diversity technique to resist random common channel interference(CCI)are proposed.Because frequency multiplexing technology is used in modern wireless communication to improve frequency utilization and communication capacity,the CCI produced has no less influence on wireless communication than noise,and channel(shadow)fading.The performances of DF-IORS/ORS under the total power constraint condition and combined with antenna diversity technique to resist CCI such as interference limited,interference and noise coexistence are studied.The theoretical and simulation results show that under the total power constraint condition DF-IOR/ORS can resist CCI effectively.Compared with DF-ORS,the proposed DF-IORS has higher spectral efficiency and lower outage probability.Combined with antenna diversity technology,the performance of cooperative communication can be further improved.(4)Based on DF-IORS/ORS and AF-IORS/ORS cooperative communication strategy,new schemes of constructing cooperative communication network with random nodes under the total power constraint condition are proposed.According to the randomness of the number or location of the relay nodes within a geographic area,many existing cooperative communication strategies are difficult to implement or implement with huge overhead while IORS/ORS have great advantages resulting in network size and topology changing at any time.In this paper,DF-IORS/ORS and AF-IORS/ORS cooperative communication models under the total power constraint condition based on random and random geometry theory are proposed.The constraints such as path loss,co-channel interference,channel cascade(shadow)fading and antenna radiation range and gain are discussed.The theoretical and simulation results show that when the number of relay nodes involved in cooperation satisfies the Poisson distribution or satisfies a two-dimensional homogeneous Poisson point process in a geographical region,the signal experiences path loss,co-channel interference,fading and shadow,the proposed schemes not only achieve cooperative diversity gain but also reduce the randomness of nodes by equalizing antenna gain and network size.It is advantageous to extend the network coverage and prolong the network life,improve mobility and layout of temporary cooperative networks.