Research On Channel Estimation And Coding In OFDM-pon

With the development and innovation of network, IPTV, cloud storage,HD video and other high bandwidth services are constantly growing. Theaccess network also face higher challenge. The passive optical network(PON), with the great features of high bandwidth, low cost and goodreliability, is considered as one of the most promising wired accesssolution to satisfy the last mile broadband access. In the past few years,PON has being the main technology for the Fiber to the x (FFTx).Orthogonal frequency division multiplexing (OFDM) is mainly usedin the wireless and wired broadband system in the beginning, and has beenadopted by a variety of important criteria, such as the European DigitalVideo Broadcasting (DVB), IEEE Wi-Fi, the Long Term Evolution (LTE),etc. While it can effectively repress the dispersion, OFDM is applied tooptical communications and can be used to realize large-capacity andlong-distance transmission. In2007, NEC Labs proposed the concept ofOFDM-PON system for the first time. Taking the advantage of high speeddigital signal processing, OFDM-PON can achieve ultra-high speed opticalaccess flexibly.To reduce the deployment cost of PON, OFDM-PON should supportlonger transmission distance and greater splitting ratio, which also meansto have sufficient optical power budget. The traditional way to enlarge thepower budget is to increase the optical power into the fiber, but it will alsointensify the nonlinear effects in the system. Therefore, how to improve thereceiver sensitivity at certain transmit power so as to increase theallowance of power budget is the key and difficult issue in OFDM-PON.As the premise of correct demodulation, channel estimation has great effect on the system sensitivity. And, Forward error correction (FEC)coding can compensate the dispersion and improve the bit error rate (BER)performance of the system. So, it’s also an effective method to improve theequivalent receiver sensitivity.In the thesis, experimental studies are carried on the channelestimation and coding in OFDM-PON as follows:Firstly, we proposed the grouped pilot based channel estimation andexperimental study its performance on the intensity modulation and directdetection OFDM-PON. Experimental results show that the proposedchannel estimation algorithm can effectively improve the receiversensitivity of the system, and its performance is superior to the existingchannel estimation algorithm. Meanwhile, we also proposed a transformdomain processing channel estimation. It is shown that by undertakingtransform domain processing this algorithm can get greater error rateperformance improvement than other channel estimation algorithms underthe same pilot overhead.Secondly, based on channel estimation, we studied the impact oflow-density parity check code (LDPC) on the performance of theOFDM-PON system. Experimental results show that the LDPC canimprove the bit error rate significantly and release the requirement ofreceived optical power.