Analysis Of The Effects Of Modulator Nonlinearity On Multiplexing Access Signal In RoF System

In recent years, with the rapid development of the mobile network, varieties of applications have appeared in the network and the network traffic has largely increased at the same time. The current low frequency wireless access network cannot satisfy the current requirements any more. Thus, to find a higher frequency and larger bandwidth wireless communication technology is on the way. The Radio over Fiber (RoF)technology combine the flexibility of the radio communication with the low attenuation and large capacity of optical fiber communication. Using RoF technique, a wide coverage and high capacity wireless access network can be easily achieved. As a result, RoF technology has been studied and developed widely nowadays. In this thesis, the intermediate frequency RoF system based on intensity modulation-direct detection (IM-DD) has been studied. And the effects of the electro-optical modulator nonlinearity on the multiple user access network have been analyzed, too. The main work in the thesis are as follows:Firstly, the system model and key technologies of the RoF technology have been studied. Then, the characters of different kinds of RoF system have been compared. The math models of Mach-Zender Modulator (MZM) and Electro-absorption Modulator(EAM) have been studied, too. After comparison of different RoF schemes, IM-DD based RoF system is chosen as the key point in this research.In the downlink research, Orthognal Frequency Multiple Access (OFDMA) signal is chosen as the base band signal. Then the downlink system model has been described and the math model has also been discussed. Then, the performance curves of downlink using MZM and EAM are analyzed through simulation, respectively. For the effects of modulation format distribution and received optical power, their influences on the downlink are show through symbol error rate and the received optical power requirements have been obtained, too. Regarding to the MZM nonlinearity, the effects of the modulation index on the downlink have also been discussed and the modulation index requirements for different modulation format in each subcarrier have been studied, too.As the OFDMA signal has a high peak to average power ratio (PAPR), the amplitude can easily exceed the EAM linearity area and the system performance will decrease severely.So, in the EAM based downlink, the simulation has been conducted to prove the influence of clipping on the OFDMA signal.As to the uplink, low PAPR signal Single Carrier-Frequency Division Multiple Acess (SC-FDMA) signal is chosen as the modulation signal and the system model and the math model of the IM-DD RoF system uplink will be analyzed, too. The performance curves using MZM and EAM with two different SC-FDMA realization in the uplink have been analyzed. The influences of the modulation format and the received optical power on the uplink have also been discussed. The same as the downlink, the influence of modulation format distribution, received optical power and modulation index of MZM have been analyzed. In this process, the received optical power and modulation index requirements in the uplink have also been shown.