Investigation On Cooperative Relay Transmission Technology In Cognitive Radio Networks

The higher spectrum availability and transmission rate are required to satisfy the rapid de-velopment of wireless communications service.Spectrum resource sharing and cooperative transmission based on multiple nodes are becoming the core technology of the new genera-tion wireless communications.Cognitive radio technology allows the secondary user access and utilize the licensed spectrum owned by the primary user so that the limited radio spec-trum resource can be fully made use of to achieve the spectrum sharing for the primary user and the secondary use,which provides an efficient way to solve the dilemma between the spectrum underutilization and the crowded wireless applications.Cooperative relay trans-mission technology can improve the system transmission rate and enhance the communica-tions coverage by multiple nodes forming the virtual multiple-input multiple-output array.Recently,cooperative relay transmission technology is integrated into cognitive radio net-works to improve the spectrum sensing and transmission performance of the secondary user.For the cognitive cooperative relay transmission under spectrum sharing constraint,the co-operative communications between the source node of the secondary networks and the relay node efficiently relief the system performance loss caused by the primary interference lim-its.Cognitive cooperative relay transmission technology fully utilizes the space cooperative diversity and spectrum sharing to improve the end-to-end performance of the cognitive ra-dio networks.However,to avoid affecting the communication quality of the primary user,the transmission powers of the transmission nodes in the secondary networks are required to meet the extra constraints.Therefore,the theory and analysis in cognitive cooperative relay transmission are different from the conventional cooperative relay transmission.With this regard,in this paper,we focus on the investigation and performance analysis of un-derlay spectrum sharing cognitive cooperative relay transmission.The main contents and contributions are as follows:Firstly,the underlay cognitive cooperative relay transmission is respectively investigated for the scenario with single primary user's interference and for the scenario with multiple primary users' interference.For the further performance improvement of the secondary user,the relay selection scheme based on the signal-to-noise ratio is designed under the condition that the reliable communications of the primary user are guaranteed.To reveal additional insights into the performance of selective cooperation and incremental decode-and-forward relaying,the outage gap between the two schemes is theoretically evaluated o'ver Rayleigh fading channels.It is shown that the cognitive cooperative relay networks cannot obtain the diversity gain in the presence of multiple primary transmitters.Secondly,for the case of single primary receiver and the case of multiple primary transmit-ters and multiple receivers,an optimal and a sub-optimal "source-relay" selection schemes are respectively proposed in underlay cognitive multiple sources multiple relays cooperative transmission.The outage performance for the proposed schemes are analyzed over Rayleigh fading environment.Under joint constraints of the secondary maximum transmission pow-er and single primary interference power,exact and asymptotic expressions for the outage probability of the proposed "source-relay" selection schemes are derived.The theoretical results indicate that the cognitive networks can simultaneously obtain the multiple user di-versity gain and the cooperative diversity gain when the secondary direct link is available.To further evaluate the effect of multiple primary transmitters and multiple primary receivers on the cognitive multiple sources multiple relays cooperative transmission,we propose an adaptive power control scheme based on multiple primary outage limits and discuss the out-age performance of the secondary user for different scenario and scheme.Thirdly,considering the instantaneous channel state information of the interference links and the relay selection links being imperfect,the outage probability and the interference prob-ability for the underlay cognitive cooperative relay transmission are investigated to achieve the perfornance exchange and trade-off between the primary user and the secondary user.When the instantaneous channel state information of the interference links between the sec-ondary transmission nodes and the multiple primary receivers are imperfect,it is proved that the transmission of the secondary user always interfere with the primary communications.In order to decrease interference caused by the secondary user on primary user,a power con-trol scheme is proposed based on the statistical channel state information of the interference links.In this case,the performance of the secondary user and the interference probability of the primary user are analyzed,respectively.Our results show that the proposed power control scheme greatly decreases the interference caused by the secondary user on primary user while the performance of the secondary network is not degraded.Finally,we investigate the cognitive cooperative relay transmission in the presence of the hardware impairment of the transmission nodes and reception nodes.The performance anal-ysis is formulated to lay a theoretical foundation for the practical design of the cognitive relay networks.Considering the joint constraints of the secondary maximum transmission power and the single primary interference power and undertaking the effect of the hardware impairment on the transmission signals and reception signals,exact outage probability and diversity order for the cognitive cooperative relay transmission are respectively derived for the case that the direct secondary link is unavailable and the case that the selective combin-ing is utilized to combine the signals received in the secondary destination.The theoretical results show that the diversity gain for the cognitive cooperative relay transmission is not affected by the hardware impairment of the system nodes.