Mobile access network includes backhaul and fronthaul transmission system. To support the requirements of high capacity, low cost and low power consumption in fronthaul transmission systems, radio over fiber (RoF) technology has become the most popular solution for fronthaul transmission. Current fronthaul transmission technology is based on digitized CPRI RoF transmission (CPRI- common protocol radio interface). However, the conventional CPRI RoF leads to fronthaul systems with high complexity, and high-power consumption. To simplify, 1-bit delta-sigma modulation based digital RoF fronthaul system was proposed, in which the complexity and power consumption of the antenna tower units by moving complicated signal processing to central baseband units are reduced. When 1-bit delta-sigma modulation is used, an electrical bandpass filter is only required at the antenna tower to convert a digital signal to an analog RF signal for a downlink fronthaul. 
In this thesis, comprehensive studies and comparison of three 1-bit delta-sigma modulations (DSM) in fronthaul optical transmission are given, which are two bandpass and one envelope delta-sigma modulation. The first bandpass 1-bit DSM considered (type-I) is based on a mixed-signal and a bandpass ΔΣ modulator, and the second bandpass 1-bit DSM considered (type-II) is based on all-digital signal and two low-pass ΔΣ modulators. 
First, the ΔΣ modulator, i.e. the core unit of the DSM, is designed for a long-term evolution (LTE) signal of 200 MHz. In the ΔΣ modulator, the loop filter plays a significant role, and thus it is first optimized. Based on theoretical analysis, simulations and experiments, the Chebyshev-based loop filter is selected because it has a narrower transition band and wider stopband. Moreover, it is found that the order of the loop filter should be matched with input signal bandwidth. 
Among the three DSMs, it is found by simulations and experiments that bandpass DSM type Ⅰ is the simplest system, and it also leads to the best optical transmission. However, the bandpass DSM type Ⅰ is the highest in the design difficulty because it uses a bandpass ΔΣ modulator. The bandpass DSM type Ⅱ is the easiest system to be implemented by hardware for its all-digital structure. However, due to a wider signal spectrum, the type-II is more sensitive to fiber dispersion, and the wider signal spectrum is induced by digital carrier. 
It is found that harmonic noise can be added to the signal band in the envelope DSM when the signal is not narrow, such as 200 MHz in this thesis. Further, it is shown that this noise becomes the dominating factor in transmission performance. Therefore, the envelope DSM leads to the worst transmission performance among the three DSMs. 
DSM generated NRZ is also compared to conventional NRZ. It is found that the DSM generated NRZ leads to worse transmission performance than conventional NRZ, i.e., more sensitive to fiber dispersion, which is due to the fact that the DSM generated NRZ has a larger optical spectrum. To reduce the effect of fiber dispersion, it is demonstrated that the digital up-sampling after DSM can be used to reduce the optical bit rate, and thus transmission is much less sensitive to fiber dispersion.