The Research Of Weighted Coding Method In OFDM Cognitive Radio And Application

As increasingly high demand of people for wireless access, the demand for spectrum is increasing fast. But the limited spectrum resources will restrict the development of future wireless communications. So much attention has been paid to cognitive radio recently, which is considered to be the most effective method of solving the problem of spectrum management.Cognitive radio can sense the spectrum environment around and find the idle spectrum, then it adjust the communication parameters dynamically. So the spectrum utilization efficiency will be improved.OFDM technology has been a popular candidate technique for signal transmission of cognitive radio. it can flexibly configure the spectrum resources of the system and utilize it effectively. However, interference between sub-carriers will limit the depth of spectrum notch at the closed sub-carrier, which make it difficult to avoid the interference with the authorized users. The topic of this paper derives from the project of National Natural Science Foundation of China (60972079,60902046). New technique was proposed to enhance spectrum notch at the frequency of closed sub-carriers through the research. It can reduce or avoid the interference between different systems.Based on the research of cognitive radio and OFDM technology, a new coding technique was proposed to enhance the spectrum notch in this paper. For this method, the same dates are transmitted on the two adjacent subcarriers, and then weight the dates on the two adjacent subcarriers to make their sidelobes cancel each other out at special frequency, so as to enhance the depth of the spectrum notch. Theoretic analysis and simulation results show that, compared with other method, not only the method can enhance the spectrum notch but also has a good performance of anti-noise.The PAPR of OFDM signal is an important issue in engineering practice. For this, the PAPR of weighted coding OFDM was analyzed and studied in the paper. And PAPR reduction techniques for weighted coding OFDM signals were proposed.The paper is organized as follows. The related technique of cognitive and OFDM are introduced in the first two chapters. And in chapter three, the weighted coding method is proposed, analysis and emulation are also done. The PAPR and application of the signal with weighted coding method are researched in the four chapter.