Cognitive Radio Adaptive Modulation Technology

With the increasing number of radio equipments,the spectrum resources are becoming more and more stringent.Cognitive radio is a kind of methods to solve the problem.Cognitive radio has changed the way of using the electromagnetic spectrum which is licensed by governments and it allows unlicensed users to opportunistically access spectrum hole of licensed users to improve actual spectrum utilization rate. Adaptive modulation technique that can dynamically adjust the mode of modulation based on channels conditions is very important in adaptive transmission technique.It aims for making full use of wireless channels to improve reliability of transmission, transmission rate and spectrum efficiency.Therefore combining cognitive radio with adaptive modulation technique is very useful and significative.This thesis investigates the adaptive M-QAM techniques in cognitive radio and mainly analyzes performance of throughput and symbol error rate(SER).There are altogether five chapters in the paper.Its main works are as follow:Spectrum sensing technique that is a key technique of cognitive radio is introduced and summarized,and matched filter detection and energy detection which are usual spectrum detection technology are simulated and analyzed in Chapter 2.Performances of system throughput with adaptive M-QAM for packet transmission in Rayleigh fading channel with ideal channel estimation and inaccurate channel estimation are presented in Chapter 3,and the results show packet size and channel estimation are quietly sensitive for the throughput.Chapter 4 analyzes two adaptive M-QAM schemes in cognitive radio.The first scheme without interference of primary users chooses the size of constellation M according to the result of channel estimation.In the scheme the performances of transmission rate and SER are studied,and comparing with that of ideal channel estimation the performances fall off.In the second scheme with interference of primary user,SER is qualitatively analyzed,and the result shows that the effect of interference of primary user on SER is quietly obvious and the reliability of transmission is very poor.In this case SER is evidently improved by diversity technique to achieve the practical requirement of transmission.In order to validate the correctness to achieve the practical requirement of transmission.In order to validate the correctness of the theoretical results,some related date and curves are acquired by designing the appropriate MATLAB programs in each part of the paper.