| With the increasing demand of network bandwidth, the optical access network enters a stage of rapidly development. The new types of access network technology have attracted more attention. It should be achieved with high-speed, long-distance, flexible and efficient resource allocation. Because of the features of high bandwidth, high frequency spectrum efficiency, flexible bandwidth allocation, compatibility, and so on, orthogonal frequency division multiplexing passive optical network (OFDM-PON) possesses significant reaserch value. Currently, there are still key problems to be resolved in OFDM-PON. For example:the cost caused by complicated transmitting and receiving technology of optical OFDM signal is higher; the energy consumption to maintain a proper peak to average power ratio (PAPR) is higher; Due to sample rate of digital-to-analog converter/analog-to-digital converter (DAC/ADC), the access bandwidth of OFDM-PON is limited seriously; The dynamic bandwidth allocation (DBA) in time-and-frequency-combined domain is left to be designed, and et al.This dissertation focuses on the key technologies of uplink modulation, polarization division multiplexing (PDM) based on direct detection (DD), DBA based on time and frequency domain, and so on. The main research work and achievements are summarized as follows:Firstly, an uplink scheme of colorless optical network unit (ONU) based on reflective semiconductor optical amplifier (RSOA) and OFDM modulation was proposed. Simulation results show that the scheme is feasible. In the simulation, the transmmition distance is40km. With an upper limited of bit error rate (BER) as10-6, the modulation bandwidth of RSOA is increased from2.5Gbit/s to10Gbit/s level.Secondly, in order to solve the problems of needing wide linear range of laser caused by high PAPR and power consumption of ONU, an uplink scheme based on asymmetric clipping optical (ACO)-OFDM was proposed. The scheme has the following two characteristics:1). With the help of direct modulation laser biased at threshold point, the ACO-OFDM signal can be produced in optical domain which can reduce the complexity and cost of the system;2). Since the laser is as there is no data to be sent, to a certain extent, the scheme plays a role of power saving. Simulation results show that:compared with the traditional OFDM signal, the ACO-OFDM modulation efficiency is higher. When the bit error rate (BER) equals to3.8×10-3(Forward Error Correction FEC threshold) and tranmission is20km, about4.3dB emitting power can be saved in the same receiving sensitivity.Thirdly, for increasing the access bandwidth of the OFDM-PON, to overcome the limitation of DAC/ADC sample rate, a no guard band downlink modulation scheme of double side band (DSB)-PDM-direct detcction (DD)-OFDM-PON was proposed. It is no need to add guard band between carrier and signal, which is needed in typical intensity modulation. Simulation results show that:to achieving40Gbit/s level access bandwidth, the downlink scheme takes only10GSa/s DAC/ADC. Because of using DD-OFDM, the cost of scheme is lower. Supplemented by digital channel equalization, when the tranmmission distance is20km, the BER is less than3.8×10-3(FEC threshold).Fourthly, to improve the bandwidth ultilization, a novel dynamic bandwidth assignment algorithm based time and frequency domain is proposed, namely service based polling in pipeline (SPP) dynamic bandwidth algorithm which is based time and frequency domain. Compared with sequencial dynamic sub-carrier allocation (SDSCA) and interleaved polling with adaptive cycle time (IPACT) DBA, the algorithm can solve the problems of large granularity and idle time, etc. Simulation results show that:the algorithm can reduce the bandwidth fragment and package delay. When there is no package loss, the algorithme increased5and7percent of the bandwidth utilization ratio. |
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