The Application Of Frequency Domain Partial Response Coding Technology In The NC-OFDM System

The appearance of cognitive radio technology has brought the huge revolutionary changes tothe wireless communication. According to the characteristics of the cognitive radio, OFDMtechnology is considered to be an effective way to be combined with it. The OFDM-based spectrumpool can be able to open or close the sub-carrier and better control the spectrum resources flexibly,but when the cognitive users access system, the radiation of OFDM will interfere the nearby bandsthat primary users have, so that the primary users’ transmission quality will deteriorate. This papermainly discusses about transmission process which is based on OFDM cognitive radio, how tosuppress the interference of cognitive users to the primary users which are nearby and how theproposed methods to improve the cognitive users’ frequency offset and PAPR.Firstly, this paper studies the system based on OFDM cognitive radio and the problem that theinterference between primary users and cognitive users, Then the out-of-band interferenceprinciple of NC-OFDM based cognitive radio is derived. This paper analyzes the common bandinterference suppression technology: windowing and deactivating the sub carriers lying adjacentlyto the allocated primary sub-bands then compare the simulation suppression result of these twomethods. Secondly, the improvement of the frequency domain partial response coding techniquesin cognitive system is studied, which can reduce the interference that cognitive users bring to theprimary users. Then we derivative the difference in the power spectral density and the interferencewith or without the partial response coding and simulate its performance. After that, combine thefrequency domain partial response coding with windowing or deactivating the sub carriers lyingadjacently to the allocated primary sub-bands. The simulation suggests that the combinations cansuppress the interference significantly and don’t waste too much output.Finally, with the increasing of the frequency domain partial response coding taps, the optimaltap coefficients which can reduce the sensitivity of NC-OFDM to frequency offset are derivative inorder to enhance the resistance capability. Followed by a discussion with the increasing of the taps,the ability of anti-frequency offset of the cognitive user as well as the improvement on PAPR. Thesimulation results show that the frequency domain partial response coding can be enough toimprove these two shortcomings.