| Currently, with the wave of acceleration in backbone network, access network which is located in the terminal of network system and regarded as the bottleneck of data rate, is now meeting a rapid development period. With the standardizing and applying of10G Passive Optical Network (10G-PON), the research and standardization of next generation PON version2(NG-PON2) technologies are extremely urgent. OFDMA-PON is proposed as one of the most expected technical candidate solution to be applied in NG-PON2.Optical OFDM technology has shown attractive prospect in PON due to its high spectral efficiency, longer reach and robust resistance to inter symbol interference (ISI) which is mainly caused by chromatic dispersion (CD). And its inherent structure of subcarriers has also provided another scheduling mechanism to allocate channel resources. Moreover there exist natural connections between WiMax, UWB, WiFi, etc., for sharing the same modulation method-OFDM, which induces excellent compatibility. The superiorities described above have made OFDMA-PON a promising candidate for future broadband access network.This thesis focuses on the existing problems and key technologies of OFDMA-PON systems, primarily includes two aspects:Modulation technologies and system implementation. The main contributions of this doctoral dissertation are summarized as follows.1. Modulation Technologies:(1) Energy-saving modulation technologies in OFDMA-PON system: Energy-saving modulation scheme based on Asymmetric Clipping Optical Orthogonal Frequency Division Multiplexing (ACO-OFDM) has been proposed here, and5Gb/s ACO-OFDM upstream transmission experiment has been implemented to evaluate performance, and a structure of2-ONUs (ONU:Optical Network Unit) scheme based on ACO-OFDMA has also been deeply studied in apect as power imbalance and phase mismatch.(2) Modulation scheme to mitigate PAPR of OFDM signal: CE-MSK-OFDM has been proposed, which has shown great superiority by mitigating inherent drawbacks of CE-QPSK-OFDM and MSK-OFDM.2.5Gb/s CE-MSK-OFDM signal are transmitted over a100km standard single mode fiber to confirm its advantage in mitigating intercarrier interference and show3.5dB improvements in received power at FEC limit compared with CE-QPSK-OFDM.2. System Implementation(1) Frequency offset estimation algorithm based on DD-OFDMA-PON: Wide range frequency offset estimation algorithm-digital spectrum frequency offset estimation, has been proposed:frequency offset is estimated according to spectrum of received DD-OFDM signal, and then is used for frequency down-conversion in digital domain to obtain baseband OFDM signal. The validity of the method is confirmed by an experiment of20Gb/s OFDM-PON downstream transmission, and the bit error rate has achieved7.7 X10-4after20-Km transmission.(2) I/Q imbalance compensation algorithm based on CO-OFDM-PON system:Pilot-aided&GSOP algorithm has been proposed and confirmed by36Gb/s CO-QPSK-OFDM experiment. Meanwhile a novel compensation algorithm based on the statistical properties of received signal has been proposed and simulated.(3) OFDMA-PON colorless technologies:The pricinpal idea is based on applying Centralized-Light-Source structure and directly reuses the downstream light as the upstream carrier. Meanwhile, we have chosen Inverse-Duobinary-RZ (IDRZ) for downstream pattern, which performs better than conventional Inverse-RZ (IRZ) in resistance to CD, and suppression for nonlinearity. The two proposed WDM-PON architectures listed as follow:1) IDRZ downstream and DPSK upstream;2) IDRZ downstream and OFDM upstream.In summary, OFDMA-PON is a promising candidate for next generation PON.The thesis investigates key technologies and existing problems in OFDMA-PON comprehensively. |
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