在5G 無線通訊系統中，要求更高的頻譜效率、更高的能源效率、更低的延遲時間以
及更大量的連結數目。循環前綴正交分頻多工(CP-OFDM) 不適用於5G 無線通訊系統，
因為有高次頻帶外發射(out-of-subband emission) 與高峰均功率比(peak-to-average power ratio)，另外插入循環前綴（CP）以減輕多重路徑干擾效應會導致額外的浪費並降低頻譜效率。

為了提高頻譜效率，許多新的波形被提出。那些波形屬於無循環前綴的離散傅立葉轉
換擴展正交分頻多工系統(Cyclic Prefix Free DFT-s-OFDM Based System)。他們使用可調整的保護間隔來提高頻譜效率，但是其中許多不能有效緩解次頻帶外發射(out-of-subband emission)，有些其中甚至降低了傳輸可靠性。即使有人提出降低次頻帶外發射的方法，但此仍有許多改善空間。因此，本論文的目的是設計一個合適的頻譜預編碼器以降低次頻帶外發射在無循環前綴的離散傅立葉轉換擴展正交分頻多工系統中。

在本文中，我們提出了一種頻譜預編碼器以降低次頻帶外發射，並提出一種尾部預編
碼器以降低多重路徑干擾效應，提高傳輸可靠性。由於尾部預編碼器的設計與頻譜預編碼器，我們提出了聯合最佳化演算法(joint optimization algorithm) 去設計最佳的預編碼架構。

模擬結果顯示該方法與其他無循環前綴的離散傅立葉轉換擴展正交分頻多工系統想比
具有較低的次頻帶外發射和更低的錯誤率。因此，我們認為設計的頻譜預編碼器非常適用於無循環前綴的離散傅立葉轉換擴展正交分頻多工系統。

The fifth generation (5G) wireless communication system, also called New Radio (NR), is regarded as a promising and important technique. The properties of 5G wireless communication system includes higher spectral efficiency, higher energy efficiency, better link reliability and lower latency.

Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM)applied in LTE may not suitable for supporting 5G system. The disadvantages of CP-OFDM are known to be large out-of-subband emission (OSBE)and large peak-to-average power ratio (PAPR). In addition, insertion of a cyclic prefix (CP) to mitigate the multipath effect introduces additional overhead and lowers spectral efficiency which is one of the most important requirements in 5G wireless communication system.

To improve spectral efficiency, many new waveforms are proposed. Those methods belong to cyclic prefix free DFT-s-OFDM based systems. They use flexible guard interval to increase spectral efficiency, but many of them do not effectively mitigate OSBE and some of them even degenerate detection reliability. Even if some methods are proposed to lower the OSBE, but there are still a room for this method to mitigate OSBE more. Therefore, the purpose of this paper is to design a proper spectral precoder to lower the OSBE of cyclic prefix free DFT-s-OFDM based systems.

In this paper we propose a spectral precoder to lower OSBE and a tail precoder to mitigate ISI and improve detection reliability. The design of tail precoder is related to the spectral precoder, so an optimization algorithm considering the tail precoder and the spectral precoder is designed.

The simulation results also indicate that the proposed method has lower OSBE and better error performance than other cyclic prefix free DFT-s-OFDM based systems. Therefore, we believe that the proposed spectral precoder will be one of the best candidates to lower OSBE for cyclic prefix free DFT-s-OFDM based systems.

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