新穎低取樣率接收端與數位訊號處理應用於第五代無線光纖網路

Abstract

目前，光載無線訊號網路之高傳輸速率與高適應性使其將被應用於第五代行動通訊系統，本論文將整合第五代行動通訊與光纖網路，討論系統層面臨的問題並提出數位訊號處理技術與新穎架構用以完善系統設計，其中包含簡化接收端複雜度、降低峰值對均值功率比、提升系統傳輸速率，實驗驗證將證明提出的數位訊號處理技術與架構於未來第五代行動通訊的潛力。 針對簡化多使者光纖網路的接收端複雜度與降低類比數位轉換器的設計難度，我們提出低取樣率接收端取代傳統高取樣率接收端，並提出演算法用以避免低取樣率接收產生的交疊效應，提出的演算法也同時降低接收端的數位訊號處理複雜度並提高系統安全性。為了降低峰值對均值功率比，我們採用單載波頻分多址調變技術取代傳統OFDM調變技術並與低取樣率接收技術整合，於光纖網路應用中，因接收端的數位訊號處理複雜度降低，單載波頻分多址調變訊號得以應用於下行系統，實驗驗證43.63Gbit/s光纖網路可同時服務32個500MSample/s接收取樣率的使用者，其比數位轉換器的取樣率可被降低至傳統接收端最低需求的3.125%，相較於OFDM調變系統，低非線性特性可提升12.5%資料傳輸速率。我們透過提出的直流歸零演算法更進一步降低低取樣率單載波頻分多址光纖網路的複雜度，使得接收端將不再需要傅立葉轉換與反傅立葉轉換，如此接收端不再需要任何解調器與數位訊號處理，因此27.15Gbit/s光纖網路系統可同時服務16個無解調器使用者，且每個使用者的接收端取樣率僅為1GSample/s。 60GHz頻段可以提供之大頻寬使得資料傳輸速率相較於第四代行動通訊系統大幅提升，整合無線系統與光纖網路並簡化系統架構，我們應用低取樣速率技術於多使用者60GHz OFDM光載微波無線訊號系統，相較於傳統架構，數位類比轉換器的取樣率需求可降低至原本的3.125%並維持資料傳輸速率。IQ不平衡效應已是各個無線系統存在的問題，為提升系統品質，我們提出新式預先IQ失衡補償演算法來搭配低取樣率接收系統，其可成功改善3dB訊雜比。多輸入多輸出天線技術透過提高頻譜使用效率來提升資料傳輸速率，我們提出一個二對二60GHz光載微波訊號系統來提供未來第五代行動通訊的需求，透過單個平行馬赫-曾德爾調變器完成二對二光纖網路，我們應用位元負載演算法來解決60GHz頻帶的不平整頻率響應並提升10%資料傳輸速率，實驗證明61.5Gbits二對二光載微波訊號系統可支持25公里光纖與3公尺無線傳輸。同時，我們提出新的低取樣率接收技術來與二對二天線技術整合，並透過實驗量測來優化射頻濾波器的參數，48.48Gbit/s二對二光載微波系統可同時服務32個156.25-MSample/s接收取樣率的使用者。最後，為解決單載波分頻多址調變於60GHz頻帶無法適應不平整頻率響應的問題，我們提出單載波分頻多址的位元負載演算法並於一對一60GHz光載微波訊號系統中完成實驗驗證，最終資料傳輸速率成功提升至45.5Gbit/s，改善量為8.3%。

Recently, high system capacity and high reliability makes the radio-over-fiber system plays an important role in 5th generation wireless system. This dissertation investigates 5th generation wireless system and radio-over-fiber. The main challenges of physical layer in future system are discussed, and then we propose novel system architecture and digital signal processing to modify the system design. The modifications include simplifying complexity of receiver, reducing peak-to-average power ratio (PAPR), and improving system capacity, which will be experimentally demonstrated the potential in future communication access. To simplify the multiple-user optical access network and relax the difficult of analog-to-digital convertor (ADC) design, we proposed a novel sub-Nyquist receiving scheme to replace the traditional receiver. Meanwhile, an algorithm is also proposed to guarantee the receivers can be aliasing-free and improve the system security. To reduce the PAPR, we investigate single-carrier frequency-division-multiplex-access (SC-FDMA) modulation with sub-Nyquist receiving technology. Because the receiver’s complexity is greatly reduced, SC-FDMA modulation will be suitable to apply in down-link stream. A 32-user 43.63-Gbit/s optical access network is experimentally demonstrated, wherein the ADC sampling rate of each user is 500 MSample/s. Meanwhile, due to the lower PAPR, system capacity can be improves 12.5% than that of orthogonality frequency division multiplexing (OFDM). We proposed a DC-zeroing algorithm to further reduce the receiver. With DC-zeroing algorithm, discrete Fourier transform (DFT), inverse DFT (IDFT), and any demodulator are no longer need. A 27.15-Gbit/s optical access network can support 16 users with 1Gsample/s DFT/IDFT-free receiver. 60-GHz frequency can offer larger available bandwidth than that of 4th generation wireless system. To investigate and simplify wireless-optical access system, we apply sub-Nyquist receiving scheme in multiple-user 60-GHz OFDM radio-over-fiber (RoF) system. Comparing to tradition RoF system, the ADC sampling rate can be reduced to 3.125% of the Nyquist sampling theorem without any capacity penalty. IQ-imbalance effect is a well-known issue in current wireless communication system. To improve signal performance, we propose novel pre-IQ compensation algorithm to meet sub-Nyquist receiving scheme and it can improve the signal-to-noise ratio (SNR) about 3 dB. Multi-input multi-output (MIMO) technology can improve system capacity through increasing the spectrum efficiency. We propose a 60-GHz 2×2 MIMO RoF system based on single dual-parallel Mach-Zhnder modulator (DP-MZM) to support the high-speed 5th wireless-over-fiber access network. With bit-loading algorithm to meet the uneven frequency response around 60 GHz, a 61.5-Gbit/s 2×2 RoF system with 25-km fiber transmission and 3-m wireless transmission can be achieved. Moreover, we propose a new algorithm to investigate the sub-Nyquist receiving scheme with MIMO RoF system, and then the important parameters of RF filter is optimized via experiment measurement. A 48.48-Gbit/s 2×2 OFDM RoF system can support 32 users at the same time, wherein the ADCs sampling rate of each user is 156.25 Msample/s. Lastly, to makes SC-FDMA modulation has the ability to meet the uneven frequency response of 60-GHz frequency band, we propose a bit-loading algorithm for SC-FDMA modulation then apply it in 60-GHz RoF system. The data rate of SC-FDMA system can be improved to 45.5 Gbit/s which has 8.3% improvement than that without proposed algorithm.