Research On Beamforming And Related Technologies For Cognitive Radio Networks

With the rapid development of wireless communications industry,various new intelligent devices and wireless services have emerged,which introduce the growth of wireless data traffic,thus the demand of spectrum resources has increased.However,due to the current fixed spectrum allocation policy,most of the allocated spectrum resources have not been utilized effectively.The contradiction between the increasing demand for spectrum and its low utilization is becoming more and more obvious,which seriously restricts the development of wireless communication.Then the cognitive radio has been considered to be an effective technology to enhance the spectrum utilization,which has attracted considerable attention.In addition,the combination of beamforming and cognitive radio is crucial to the development of future communications technologies,since it can be used to improve the spectrum utilization,overcome the channel fading effects,reduce the interference and improve the system capacity simultaneously.This paper mainly focuses on the beamforming design in cognitive radio networks(CRNs),in which the technologies of cooperative relaying,radio frequency energy harvesting and physical layer security have also been considered.In this paper,we have considered three scenarios,such as the distributed cognitive two-way relay networks,cognitive multiple input single output(MISO)simultaneous wireless information and power transmission networks(SWIPT)and primary-secondary cooperative cognitive radio networks(CCRNs)with energy harvesting(EH).The main works and innovative contributions of this paper are summarized as follows:1.The robust beamforming design in distributed cognitive two-way relay networks is studied.Firstly,with the assumption that the channel state information(CSI)errors are deterministic and bounded in a region,we design a worst-case distributed robust beamforming scheme.The scheme aims to maximize the minimum signal to interference plus noise ratio(SINR)of the secondary user(SU),while satisfy the constraints of the total power transmitted at the relay and the interference power at the primary user(PU).We propose an algorithm based on S-procedure and semidefinite relaxation(SDR)to transform the original non-convex problem into a convex optimization problem,then use the bisection method to solve it.The simulation results indicate that our proposed robust scheme can satisfy the communication requirements of PUs and SUs.Secondly,assuming the CSI errors follow a complex Gaussian distribution,we design the robust beamformer with the probabilistic constraints.We aim to design the robust beamformer which can minimize the total transmit power of the collaborative relays,while guarantee the outage probability of SINR beyond a target level at each SU,the outage probability of interference generated on the PU above the predetermined maximum tolerable interference power.Specifically,we propose a probabilistic approach based on two sorts of Bernstein-type inequalities and a worst-case approach based on S-Procedure.Both of the approaches are robust to the CSI errors,and moreover,the probabilistic method can provide higher feasibility rate and consumes less power.2.The beamforming design in the cognitive MISO SWIPT networks is studied.Firstly,assuming the CSI errors are deterministic and bounded in a region,we propose a scheme which jointly designs the robust beamforming vector and power splitting ratio(BFPS).The scheme aims to minimize the transmit power at the cognitive base station(CBS),while satisfies the probabilistic constraints of the SU SINR,the SU harvested energy and the interference power at the PU.In this paper,the robust BFPS algorithm based on Bernstein-type inequality and the robust BFPS algorithm based on S-Procedure are proposed,respectively,to solve the problem.The simulation results indicate that the two robust BFPS algorithms can satisfy the probabilistic constraints.Secondly,we propose a full-duplex energy harvesting cooperative jammer(EH-CJ)aided scheme to enhance the security for the network in the presence of multiple eavesdroppers.With the perfect CSI,we jointly design the transmit beamforming vector at the CBS and the noise covariance matrix at the EH-CJ,in order to maximize the secrecy rate of the SU,while subject to the transmit power constraints at the secondary transmitter(ST)and EH-CJ,and the interference constraint at the PU.We propose a two-stage optimization algorithm to solve the non-convex problem.In addition,we investigate the robust secrecy rate maximization design under the imperfect CSI scenario.Simulation results have validated that our proposed schemes can achieve better secrecy rate performance.3.The beamforming design in the CCRNs with EH is studied.We propose a novel wireless EH-CJ-aided transmission scheme,which can enhance the security for CCRNs in the presence of multiple multi-antenna eavesdroppers.Firstly,we maximize the achievable secrecy rate by jointly designing the retransmit beamforming matrix and transmit beamforming vector at the ST and the covariance matrix at the EH-CJ,while subject to the power constraints at the ST and information rate constraint at the PR.To solve this non-convex problem,we propose a two-stage optimization algorithm using the Charnes-Cooper transformation and SDR techniques.Secondly,for comparison purposes,and in order to show the superiority of our novel scheme,we also propose the isotropic JN scheme.Simulation results have demonstrated that the performance of our proposed EH-CJ-aided jointly design scheme outperforms the isotropic JN scheme and the scheme without the aid of EH-CJ.