Research On Precoding In Cognitive Radio Networks Based On Relays

Wireless communications are changing our life in many aspects,including economy,health,education,and so on.There are more than 3 billion wireless equipment now,and the number is expected to exceed 100 billion in 2025.From the communications of voice to the applications of multimedia,demand for high data rates has grown rapidly.The resources of wireless spectrum are in short supply,and it cannot meet the rapid growth of devices.So it is very meaningful to research robust communications based on the efficiency.In this thesis,we proposed a novel robust precoder with imperfect channel state information(ICSI)for multi-input multi-output(MIMO)cognitive multiuser networks which are equipped with relays.In this model,the secondary users(SUs)are allowed to share the spectrum with the primary users(PUs)when the interference temperature(IT)is below a specific threshold.The transmitting strategy of relays is amplify-and-forward(AF),and the CSI error is characterized in terms of the spherical uncertainty region.We consider a minmax problem for the transmit power of the relays when mean square error(MSE)of the SUs and IT of the PU meet their corresponding thresholds.For solving the problem,we can use convex optimization and matrix theory so that it can be transformed into a semi-definite programming(SDP)problem.This thesis simulates four scenarios,one relay and one pair of SUs,one relay and two pairs of SUs,two relays and one pair of SUs,two relays and two pairs of SUs.Simulation results show three conclusions.Firstly,the proposed precoder can be used in these four scenarios,and it can serve a robust quality for SUs so that it improves the reliability of the system.Secondly,the proposed method increases the reliability at the cost of much power.Finally,in the same scenario,the power of two antennas is much bigger than its of three antennas;however,it is opposite with IT and MSE.