Transcript Slide 1
University of Technology Dept. of computer Engineering and Information Technology Forward Error Correcting Codes for Optical Communication Systems BY Dr. Hussam Abd Ali Abdulridha Optical Error Correcting Codes FEC challenges in Optical Comm. systems -Very high information rate between 1Gb/s to 40Gb/s. -High Coding Gain with low code rate greater than 0.7. - Low BER between 1012 to1015 . Optical Error Correcting Codes FEC Block codes Convolutional Codes -Binary Block Code (BCH) Turbo Codes -Non-Binary Block Code (RS) (G1) Concatenated Codes (G2) LDPC Codes (G3) Channel coding parameters code generation (N,K) Code rate = (n-k)/n Bit redundancy (r )= (n-k) N: codeword length K: information length Coding Gain (dB)= (S/N) coding (S/N) uncoding At the same BER First Generation Outband FEC (Single Code) - Reed-Solomon (RS) codes - code-symbol interleaving of a number of individual RS-codes - for instance 16-way interleaved RS(255,239) codes in the case of ITU-T G.709 Second Generation Outband FEC (Concatenated) - FEC-concatenation schemes made -Serial-concatenation of FEC codes -recommendation ITU-T G.975.1 - super-FEC is a conc. scheme with BCH(3860,3824) as the outer and BCH(2040,1930) as the inner code Product Codes - Serially concatenated codes using two or more short block codes to form long block codes -If C1) n1, k1) of minimum distance dmin1 and C2 )n2, k2) of minimum distance dmin2 are two systematic linear block codes n2 Coding columncolumn using C1 k2 Input Row-Row code by C2 k1 Information Symbol n1 Check of column Check of row Check of the check Construction of a product code This bits check of the check 3rd Generation Outband FEC (Super-FEC) - Low-Density Parity-Check (LDPC) coding - leverage iterative decoding - very high coding-gains Low-Density Parity Check Codes (LDPC) - LDPC codes have large minimum Hamming distance - Parity-check matrix of a simple linear block code (Local code) used to generate LDPC code matrix - LDPC codes matrix depend on Local code, codeword length, and permutation matrix Effect of Coding on QPSK receiver with coherent demodulation Sensitivity 0 10 UNCODED LDPC(3969,3591) LDPC(3969,3213) LDPC(3969,2835) -2 10 UNCODED BCH(255,239)+BCH(255,239) BCH(255,239)+BCH(255,223) BCH(255,223)+BCH(255,223) RS(255,239)+RS(255,239) RS(255,239)+RS(255,223) RS(255,223)+RS(255,223) -2 10 -4 10 -4 10 BER -6 10 -6 10 LDPC code gives small increase in CG than concat. Of RS codes at the same code rate 0.81 -8 10 -8 10 1 dB 4.8 dB -10 10 -10 10 -12 -12 10 -64 RS gives higher CG than BCH at Same code rate -62 -60 -58 -56 -54 -52 10 -62 -60 -50 -48 Received power (dBm) -58 -56 -54 -52 -50 -48 BER versus received power for coherent QPSK receiver operating at 1Gb/s rate and = 3.78*10-4 incorporating coherent demodulation. Effect of Coding on QPSK receiver with differential demodulation Sensitivity 0 10 UNCODED LDPC(3969,3591) LDPC(3969,3213) LDPC(3969,2835) -2 10 UNCODED BCH(255,239)+BCH(255,239) BCH(255,239)+BCH(255,223) BCH(255,223)+BCH(255,223) RS(255,239)+RS(255,239) RS(255,239)+RS(255,223) RS(255,223)+RS(255,223) -2 10 -4 10 -4 10 LDPC code gives high CG than concat. Of RS at the same code rate 0.81 BER -6 10 -8 10 -6 10 Decrease code rate in LDPC code gives small increase in CG -8 10 3.6 dB -10 2 dB -12 -12 -62 4.3dB -10 10 10 10 RS gives higher than BCH at Same code rate 10 -60 -58 -56 -54 -52 -50 -48 -46 -60 -58 -56 -54 -52 -50 -48 Received power (dBm) BER versus for heterodyne QPSK receiver operating at 1Gb/s rate and PR = -46.93 dBm incorporating differential demodulation. -46 DESIGN CONSIDERATIONS - Processing delays: Optical communications are particularly sensitive to delays, - Configurable redundancy: Optical networking applications of different range require different levels of protection, with respect to the Quality of Service (QoS) - Rich statistics FEC: is not a panacea; it is rather introduced to obtain the necessary system margin to guarantee QoS