| At present, Forward Error Correction (FEC) technologies are widely applied in optical communication systems in order that the error can be found and corrected by adding a small quantity of the redundant information in the signal, as a result, the tolerance of the Optical Signal Noise Ratio (OSNR) for the receiving end is reduced to improve the Bit Error Rate (BER) performance of optical communication systems, enhance the reliability of optical communication systems, extend the transmission distance of optical signals, decrease the transmitting power of the optical transmitter and reduce the cost of optical communication systems.The ITU-T has developed the researches of the FEC codes for the rapid development of optical communication systems for recent years, and the relative recommendations such as ITU-T G.707, G.975, G.709, G.975.1 and so forth have been proposed one after the other. However, with the increasing development of optical communication systems toward longer distance, larger capacity and higher bit rate, the further improvements of the transmission rate and distance are heavily limited due to the accumulated optical effects such as the dispersion and Polarization-Mode Dispersion (PMD) and the accumulated nonlinear optical effect such as Four-Wave Mixing (FWM), Stimulated Raman Scattering (SRS), Stimulated Brillouin Scattering (SBS) in transmission optical fibers. As a result, it has been becoming necessary to develop the novel more powerful Super Forward Error Correction (SFEC) code type in order to gain the higher Net Coding Gain (NCG) and the better error-correction performance to meet the requirements of the rapid development for optical communication systems, compensate for serious transmission quality degradation and avoid using the dispersion-compensating technologies to need the expensive and complex devices and so forth. Seeing that this developing trend of optical communication systems, it is very necessary to deeply research the novel scheme of the SFEC code type, theoretically analyze and practically verify its application in optical communication systems so as to better and better apply it in optical communication systems to improve the communication quality of optical communication systems and decrease the cost of optical communication systems.The research of the SFEC coding technologies has been taken as one of the research subjects for the optical fiber communication innovation technologies of the National Key Science and Technology Development Program of China (863 Program). This subject is researched under the condition of taking the National"863"Key Item of China (Grant No. 2A001AA122012) of the Research and Implementation of the Ultra Long-Haul Wavelength-Division Multiplexing (WDM) Optical Communication Technologies as its application background,and the improvement of the optical communication quality for the SFEC coding technologies, based on the concatenated code, Block Turbo Code (BTC) and Low-Density Parity-Check (LDPC) code, has emphatically been researched, it ultimately embodies in the obtainment of the higher NCG and the improvement of the better BER in optical communication systems.The schemes of the SFEC code type for high-speed ultra long-haul optical communication systems have been researched in this dissertation, and the main achievements are as follows:①The channel model (namely, Additive White Guassian Noise (AWGN) channel model ) of optical communication systems is established by analyzing the noises in optical communication systems, and based on the channel model, the BER in optical communication systems has been analyzed. Based on above analyses as well as the performance analyses of the FEC code types, the main construction principles of the FEC code types for optical communication systems are proposed, this establishes a firm foundation in the construction and simulation research of the FEC code type for optical communication systems.②The classic FEC coding technologies in optical communication systems has been studied. It is also indicated that the classic FEC code types haven't been able to meet the requirements of the increasing development of optical communication systems toward longer distance, larger capacity and higher bit rate by the simulating and analyzing these classic FEC code types and analyzing the characteristics and development trend of optical communication systems, and so it is necessary that the SFEC coding technologies with more powerful error-correction performance should be studied. In addition, the design and application of the FEC coding technologies in the Optical Transponder Unit (OTU) of optical communication systems are analyzed.③The code types of the SFEC concatenated codes in optical communication systems have been analyzed and studied. After the current three concatenated codes of the inner-outer concatenated code, the parallel-concatenated code and the successive concatenated code with interleaving are theoretically analyzed and simulated, it is shown that the inner-outer concatenated code has greater redundancy and the decoding implementation of the parallel-concatenated code are too complex, however, the successive concatenated code with interleaving are a superior coding scheme with the advantages such as the better error-correction performance, moderate redundancy and easy implementation, so it can better be used in high-speed ultra long-haul optical communication systems. In the meantime, the two improved novel successive concatenated codes with interleaving that have excellent performances of the RS(255,239)+RS(255,239) code and the RS(255,239)+RS(255,223) code are proposed, in addition, based on the ITU-T G.709, the frame structure of the improved successive concatenated code with interleaving is proposed and designed to use it in optical communication systems, this lays a firm foundation and pioneers a direction in its practical applications and hardware design in optical communication systems.④A novel concatenated code type of RS(255,239)+BCH(1023,963) code with 13.34% redundancy, based on the concatenated code, is presented after the characteristics of the concatenated code for optical communication systems and the performance of the SFEC code types in ITU-T G.975.1 have deeply been analyzed and studied. The simulation results show that this novel code type, compared with the RS(255,239)+CSOC(k0/n0=6/7,J=8) code in ITU-T G.975.1, has a lower redundancy and the better error-correction performance, furthermore, its NCG is respectively 0.60dB, 0.57dB more than that of RS(255,239)+ CSOC(k0/n0=6/7,J=8) code and BCH(3860,3824)+BCH(2040,1930) code in ITU-T G.975.1 at the third iteration for the BER of 10-12, so its error-correction performance is better. Thus, the novel concatenated code type can better be used in ultra high-speed, ultra large-capacity and ultra long-haul optical communication systems, and it can be regarded as a candidate code type of the SFEC code. In addition, the design and implementation of the novel concatenated code type are also discussed.⑤A novel SFEC code type (namely, BCH(64,57)×BCH(64,57) code type) for optical communication systems, based on BTCs, was proposed. The simulation results show that the NCG of BCH(64,57)×BCH(64,57) code at the sixth iteration is 0.34dB more than that of RS (255,239)+CSOC(k0/n0 =6/7, J=8) code in ITU-T G.975.1 at the third iteration for the BER of 10-12. The analysis results show that the novel BTC has the advantageous characteristics such as the shorter component code and the rapid encoding/decoding speed, thus, it reduces not only the complexity for implementing the software/hardware but also the time delay for the encoding/decoding. Therefore, the novel BTC code type can be used in ultra high-speed, ultra large-capacity and ultra long-haul optical communication systems, and it can also be regarded as a candidate code type of the SFEC code. In the meanwhile, the design and implementation of the novel BTC are also probed.⑥Both the novel LDPC(3969,3720) code with 6.69% redundancy and the novel LDPC(8281,7920) code with 4.56% redundancy for optical communication systems, based on LDPC codes, are constructed. The simulation results show that the NCGs of the two novel LDPC codes at the eighteenth iteration for the BER of 10-12, compared with those of the BCH(3860,3824)+BCH(2040,1930) code with 6.69% redundancy and the RS(255,239)+ CSOC(k0/n0=6/7,J=8) code with 24.48% redundancy in ITU-T G.975.1, are slightly lower, but the decoding of the LDPC codes in the hardware can parallelly be implemented, so the decoding velocities of the two novel code types are very rapid, furthermore, compared with the concatenated codes in ITU-T G.975.1, the complexities of implementing the two novel LDPC codes are relatively lower. Therefore, in consideration of the above advantages, the two novel LDPC codes can also be regarded as the two candidate code types of the SFEC code. In addition, the design and implementation of the novel LDPC codes are also discussed.⑦In the course of studying the LDPC code, the construction principles of the LDPC code types for optical communication systems are proposed and a novel construction algorithm (namely, Recursive Search algorithm: RS algorithm) of the LDPC code for optical communication systems is presented, moreover, it is theoretically proved that the LDPC code whose bipartite graph has no four-cycle can be constructed by applying the RS algorithm. The two simpler and more practical methods which can construct the LDPC code whose bipartite graph has no four-cycle are proposed by further analyzing the RS algorithm, and the correctness of the two methods is theoretically proved. Compared with the previous construction algorithms of the LDPC codes, the bipartite graph of the LDPC code constructed by applying the RS algorithm has no four-cycle, and it has the excellent performance, furthermore, this RS algorithm can save the hardware overhead, so it can better suit for high-speed ultra long-haul optical communication systems.
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