Comparison Analysis of Various SLM Schemes for PAPR Reduction of OFDM Systems

[[abstract]]在近代的通訊技術發展中,正交分頻多工系統已經受到越來越多的歡迎,因為此系統透過多載波調變傳輸技術可以提供高資料傳輸速率。然而,正交多頻分工系統必須克服高峰均值的問題。過高的系統峰均值可能導致系統產生運作效率的降低與提高功率放大器的成本。而這次的研究將專注於單輸入單輸出的正交分頻多工系統中,並選擇使用選擇性映射系統來做為降低系統峰均值的方法。 在使用選擇性映射系統來降低峰均值的問題中,對於這個主題的研究與相關的文章的顯示,當選擇性映射系統中的相位旋轉序列增加時,將會提高正交分頻多工系統中反快速傅立葉運算的複雜度。因此,我們將要利用傅立葉運算中的線性組合特性以降低傅立葉運算的複雜度。這個方法將可以製造出更多的相位選轉序列而不會使傅立葉運算的複雜度過於提高。除此之外,我們還將利用兩種以選擇性映射理論為基礎的系統並且組合這兩種系統的性能以進一步提高降低正交分頻多工系統的峰均值。[[abstract]]In recent development of communication technology, orthogonal frequency division multiplexing (OFDM) systems have become much more popular, because they could provide high data rate transmission with multi-carrier modulation. However, OFDM systems have to overcome the high peak-to-average power ratio (PAPR) problems which would reduce the e_ciency of OFDM systems and increase the cost of the radio frequency power ampli_er. For single-input single-output OFDM systems, the PAPR reduction techniques with various selected mapping (SLM) schemes would be investigated and analyzed in this thesis. For the PAPR reduction with SLM methods, a survey of the related papers has shown that the number of the inverse fast Fourier transform (IFFT) would become large as the number of phase rotation sequences is increased. Therefore, the linear combination properties of Fourier transform is adopted to reduce the computational complexity with only minor degradation of performance. This algorithm can generate more alternative OFDM signal sequences without increasing the number of IFFTs. In addition, the hybrid SLM-based scheme consisting of a modi_ed SLM method and a widely-linear SLM technique is proposed to solve PAPR reduction problem. As a result, the advantages of both modi_ed SLM and widely-linear SLM strategies are obtained to further increase alternative OFDM symbol sequences with lower complexity for achieving the purpose of PAPR reduction.[[note]]碩