The Research And Realization Of Adaptive Modulation Algorithm For OFDM-PONs

With the development of modern network communication technology, differentbusiness especially high-definition TV, video conference, mobile multimedia andIPTV has proposed a dramatic increase demand of bandwidth, thus leading to afurther study about how to enhance the transmission rate for the next access network.Orthogonal frequency division multiplexing(OFDM) technique has a lot of notableadvantages like high spectrum efficiency, strong anti-interference ability and beingable to against single-mode optical fiber polarization mode dispersion effectively.Furthermore, OFDM technology can be implemented with digital signalprocessing(DSP) device, good capacity expansion capability through adoptingdifferent modulation format based on channel characteristic of different subcarriers.Optical OFDM technique is considered to be a very promising technology for thefuture access network, OFDM-PON technique has also become an optimizationscheme of the next generation optical access network(NG-PON2) internationalstandards.In this paper, we devoted ourselves to study the adaptive bit-loading andpower-loading algorithm and FPGA(Field-Programmable Gate Array)implementation in the uplink OFDM-PON system. Firstly, we analyze some basicproperties of fiber channel and put forward the optical communication system modelaccording to the optical fiber channel characteristic. With a combination of thetraditional wireless OFDM adaptive modulation algorithm, we analyze theperformance and complexity of different algorithm based on the optical fiber channeltransmission characteristic. Then, by taking account of the actual optical fiberchannel characteristic and system implementation, we proposed a simple andeffective adaptive algorithm based on channel characteristic and an improvedadaptive bit-loading and power-loading algorithm based on classical Levin Campelloalgorithm, demonstrated the feasibility of this algorithm through a large number ofexperiments. At last, we implemented the validity and reliability of the simplepower-loading algorithm by utilizing FPGA and verified them, laid the foundationfor further improving the performance of OFDM-PONs.