Design And Simulation Of Dynamic Spectrum Sharing Communication System Physical Layer Transmission Link

With the developing of wireless technology and the growing number of wireless users, the spectrum resource is becoming scarcer and scarcer, while some bands, such as TV band, have not been fully utilized, resulted in serious waste. In order to solve this problem effectively, the corresponding cognitive radio technology has been proposed. Supported by this technology, system is permited to communicate in free spectrum bands which are detected by sensing technology. This thesis focuses on designing and simulating the physical layer of dynamic spectrum sharing communication system which based on cognitive radio.Firstly, this paper has studied the transmitter and receiver's each module of the physical layer, including interleaving algorithm, pilot insertion, channel estimation algorithm, demodulation algorithm, SNR estimation algorithm and so on, compared different algorithms of each part of this communication system's link performance and analyzed those algorithms'complexity, selected the appropriate link of physical layer transmission scheme into practice. In the case of the system with a large number of virtual sub-carriers, an improved DFT-based channel estimation algorithm has been proposed. At the end, eight-link simulation results under different modulation and different turbo rate have been provided.Secondly, fixed-point simulation has been used for DSP implementation link, tested system performance loss from the floating link to the fixed-point implementation. Determined the DSP implementation link's scaling value by studied the dynamic range of data variables in the part of a series of processing.At the end, the efficient fixed-point system link has been obtained by fixed-point analysis and four-link simulation performance results have been provided for the DSP implementation.Finally, the problem of adjacent channel interference suppression which caused by cognitive users of this communication system has been studied. Adjacent channel interference suppression is constraint the spectrum of cognitive users to avoid interference of the fist users, optimize the system transmission performance. According to the mechanism of adjacent channel interference generated, this article bases on the system needs has studied three kinds of interference suppression algorithms including sub-carrier cancellation algorthm, the constellation expansion algorithm and time domain windowing algorithm, comparied the complexity and system performance of the three algorithms, a suitable adjacent channel interference suppression scheme of communication system--time domain windowing algorithm has been selected.