Study In Some Robust Beamforming Problems In Wireless Communications

With the rapid development of 5G communication technology,communication spreads over every aspect of people's life.The development speed of communication becomes faster and faster,and the communication requirements become higher and higher.In the face of multi-user communication system,the communication quality must be guaranteed.In the face of eavesdropping communication system,communication security must be guaranteed.Facing the shortage of wireless spectrum resources,it is necessary to improve the utilization of spectrum resources.This paper focuses on two beamforming problems.Robust MISO downlink beamforming in the cognitive radio network.In order to improve the utilization of spectrum resources and realize spectrum sharing,the same channel can be used by both secondary users and primary users,while avoiding too much interference to primary users.Faced with this problem,we propose robust optimal beamforming technique to resolve the caused inference to the primary users under the assumption of uncertainty of channel state information(CSI).By establishing a communication network model,a robust multi input single output(MISO)downlink beamforming problem is proposed,which needs to minimize the transmitting power and satisfy the constraints of QoS and interference.This problem is a non-convex QCQP problem.In this paper,an algorithm is proposed by using convex optimization tools,and the extended form of S-Lemma can be used to transform this problem into a convex problem.Through matlab simulation,it can be found that its performance is better than the existing robust design,and the calculation cost is close to the traditional design.At the same time,the simulation verifies the correctness of the mathematical derivation and the validity of the robust beamforming scheme,and compares the system performance when different parameters are set.Beamforming design of simultaneous wireless information and power transfer(SWIPT)security communication system.Simultaneous wireless information and power transfertechnology may be attacked by malicious eavesdropper,because energy receiver not only obtains energy,but also receives and sends valid information of other legitimate users.Physical layer security technology is particularly important in simultaneous wireless information and power transfer communication system.The signal source sends a signal to the self-sustainable relay,in which it obtains energy from the received signal,and then uses the obtained energy to broadcast most of the signal to the target user.Eavesdroppers can steal signals from sources and relays and decode them.We have to solve two problems of information security and energy transmission.By establishing communication system model,the optimization problem is put forward.This problem needs to minimize transmission power,subject to meet the signal to noise ratio(SNR)requirements of relay and user,and satisfy the maximum SNR threshold and energy constraint of eavesdropper.Under the CSI imperfect constraint,the problem is non-convex.By means of the strong duality theorem of linear cone programming and a series of mathematical transformations such as s-lemma,this non-convex problem is transformed and relaxed into a convex problem.Then use Matlab CVX tool to solve this problem.The optimized beamforming vector can meet the communication requirement.