Research On Sidelobe Suppression Of OFDM Signals In Cognitive Radio

As the demand for sophisticated wireless mobile applications,including efficient modulation techniques,is constantly increasing,large bandwidths are required to support these applications.However,bandwidth is a limited resource.The current FCC spectrum allocation policy only allows licensed users access to the spectrum,but it has been proven that the current use of the licensed spectrum in time and frequency is inefficient.Therefore,the proposed concept of unlicensed,secondary users who temporarily borrow the spectrum from existing primary licensees to improve spectrum utilization,called the “spectrum pool”,which is based on dynamic spectrum access(DSA),this technology is called cognitive radio.Orthogonal Frequency Division Multiplexing(OFDM)is a promising candidate for cognitive radio transmission.OFDM supports high data rates that are resistant to channel degradation.In addition,some subcarriers can be deactivated,thereby creating an empty region in the signal spectrum.However,one of the biggest problems for OFDM transmission is high out-of-band emission(OOB),which is caused by a sinc function that represents characters for one time constant.Thus,due to the high level of sidelobes,interference may occur to an adjacent station.This thesis presents promising techniques for suppressing the interference of the sidelobes of the OFDM signal in cognitive radio systems.In the course of this work,a literary review of the existing methods of OFDM sidelobe suppression was carried out;it included articles and scientific works of many researchers both abroad and domestic.Studies have been conducted on the formation of OFDM in cognitive radio systems,and also on the formation of the OFDM signal and its main characteristics and distinctive features relative to other signal-code constructions.The simulation was done in GNU Radio software,this is free software,where using blocks you can create various telecommunication schemes.Since the goal of this work is to attenuate the sidelobes of the OFDM signal,the problem of high out-of-band emissions and traditional methods to reduce these problems,such as windowing and guard bands,were considered in detail.The last chapter described in detail two methods,the Advanced Subcarrier Weighting method and the Advanced Cancellation Carriers method.A simulation was conducted,during which the effect of these methods on reducing out-of-band emissions of an OFDM signal was studied.Simulations were conducted that examined the effectiveness of using these techniques with OFDM signals and the effectiveness of using these techniques in cognitive radio systems.