| Summary: | 博士 === 國立交通大學 === 光電系統博士學位學程 === 106 === 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.
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