Design And Application Of QC-LDPC Codes For Low-Power-Comsumption Optical Communication Systems

With the advent of the cloud era,network traffic has increased dramatically and high-speed optical communication network has been an increasingly urgent demand.However,in the coherent optical communication system,high speed or long distance will cause a large number of errors due to the influence of optical amplifier noise and transmission impairments.In the short distance direct detection systems,especially intensity-modulation and direct-detection(IM/DD)optical orthogonal frequency division multiplexing(OFDM)systems,the limited bandwidth of devices induces performance degradation.Therefore,it is necessary to introduce channel coding into optical communication systems.Low-density parity-check(LDPC)codes,as a member of forward error correction(FEC)codes,has been proved to be close to the Shannon limit in the late 19 th century.Quasi-cyclic low-density parity-check(QC-LDPC)codes,as the structured LDPC codes,has lower complexity for encoding and decoding and its quasi cyclic characteristic makes it more suitable for hardware implementation.This dissertation investigates the design of low-powerconsumption and low-latency QC-LDPC codes,and the optimal mapping between the QCLDPC and OFDM subcarriers in bandwidth-limited optical systems.The main contributions are as follows:(1)A construction of QC-LDPC code based on the finite number of iterations is proposed for the low-power-consumption and low-lantency optical communication system.In the EXIT chart,the minimum SNR for successful decoding under a finite number of iterations is used as the measure of degree distribution,which effectively solves the problem that the traditional optimal degree distribution based on an infinite number of iterations is not suitable for lowpower communication system.Simulations verified that the proposed QC-LDPC code achieved better performance than the QC-LDPC code designed with the traditional optimal degree distribution regardless of the modulation formats,the code rates,the number of iterations and the system bandwidth.(2)We have proposed a novel symbols allocation algorithm based on the reliability of the subcarriers for QC-LDPC coded IM/DD-OFDM systems.Results of 116.4Gb/s,2-km and101.7-Gb/s,5-km transmisstion experiments shows the proposed mapping is superior to the conventional mapping regardless of the received optical power,the code rate,the length of the cyclic prefix,the system bandwidth,the transmission distance,the number of decoding iterations.Moreover,this method is more suitable for low-power and low delay optical OFDM systems encoded by QC-LDPC codes based on a small number of decoding iterations.