Cognitive Radio Used In Power Line Communications Based On OFDM

With the increasing need of Broad-band Service, such as high-speed data, video and internet, the power line has attracted people's attention due to its characteristics as a communication media—no more investment in laying line, convenience in building communication web, simple access to ports, being able to be built with first power grid, rapid speed of constructing and less investment in building. But power line communication (PLC) has been in a mal-condition. To realize fast, reliable data transmission, appropriate modulation technology must be adopted, however, the modulation technology nowadays has its limit, and a lot of communication service such as remote reading system and connecting the internet with power line is affected. Thus the development of PLC is limited to some degree.The rapid development of cognitive radio provides us a great inspiration. By analyzing channel condition of PLC, associating with the technology of CR, this paper suggests a Power Line Communications system based on OFDM and CR, and presents the cognitive process and a detection method in this system. Also, based on OFDM and CR, this system remedies the defects of modulation technology in PLC in the past, and inherits the superiority of OFDM technology. Furthermore, in this system, the PLC signal spectrum and the channel are intelligently managed by utilizing spectrum allocation technology. This system also improves the anti-interference ability in complex channel and greatly enhances the reliability, validity and the spectrum utilization in communications.Moreover, this paper consults spectrum distribution model based on interference temperature, and then, with associating the PLC channel condition, the former OFDM adaptive algorithm of spectrum distribution is improved. The experiment has proved that the realization of this algorithm solves the problem of insensitivity of the channel estimate error which is caused by the situation that the adaptive technology acquired the channel information feedback by the channel estimate from receiving end. The algorithm also changes the estimate into the detection and prediction of channel condition, and solve the problem that channel condition cannot be estimated if the sending end does not send information. Therefore, the performance of OFDM adaptive system is further improved, which provides a new method for the development of PLC in the future.