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CR-based NC-OFDM system PAPR reduction technology

Author: LiangZuo
Tutor: ShaoJianHua
School: Nanjing Normal University
Course: Circuits and Systems
Keywords: Non-contiguous OFDM PAPR PTS Adaptive Selection
CLC: TN919.3
Type: Master's thesis
Year: 2011
Downloads: 49
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Abstract


Cognitive radio (CR) is a wireless communication technology that the free spectrum in the spectrum pooling can be used intelligently and the utilization rate of spectrum can be improved by it, meanwhile the authorized users wouldn’t be harmfully affected by the cognitive users. Non-contiguous orthogonal frequency division multiplexing (NC-OFDM) technology which has been improved from the conventional OFDM technology is a new transmission technology, and it can be applied to cognitive radio (CR) in the physical layer. The communication interference from the cognitive users to the authorized users can be avoided because NC-OFDM system can collect spectral information from the spectrum pooling to allocating and shutting the sub carriers freely when the data is being transmitted quickly. However, its peak-to-average power ratio (PAPR) performance is more prominent than the conventional OFDM system because that its sub carriers are not contiguous, and the conventional PAPR reduction algorithm is not suitable for NC-OFDM system. Therefore, to improve the PAPR performance of NC-OFDM system by proposing a new improved partial transmit sequences (PTS) algorithm is the purpose of this study.There are several main tasks have been included in this paper at following aspects. First, the transceiver model of the conventional OFDM system has been improved because of the distribution feature of the spectrum which is in the spectrum pooling of CR, then the sub carries can be opened and closed freely by NC-OFDM system to achieve the purpose of transferring high-speed data. After that, a hardware implementation by the cooperation between FPGA and DSP has been proposed. Secondly, the distribution of PAPR in NC-OFDM system has been analyzed and its high PAPR causes and defects in the conventional PAPR reduction algorithms has been demonstrated. Thirdly, the improved methods and the implement programs of the adjacent partition (APTS) and the interweave partition (IPTS) algorithm have been proposed by the principle of the conventional PTS, besides, its feasibility, advantages and disadvantages have been compared by the simulation. Then, according to the advantages and disadvantages of the improved APTS algorithm and the improved IPTS algorithm, a new optimized adaptive selective PTS algorithm has been proposed to improve the PAPR performance of NC-OFDM system. Finally, the FPGA implementations of NC-OFDM system based on CR has been proposed by its transceiver model. The simulation result shows that the PAPR performance of NC-OFDM system can be improved effectively by the optimized adaptive selective PTS algorithm which has lower computational complexity and less auxiliary information. Besides, the transmission efficiency of NC-OFDM system has been enhanced at the same time when the communication capability has been improved. In a word, the feasibility and the practically of the new optimized adaptive selective PTS algorithm has been proved.

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