1. Forward Error Correcting Codes for Forward Error Correcting Codes for Optical Communication Systems University of Technology Dept. of computer Engineering and Information Technology BY Dr. Hussam Abd Ali Abdulridha

2. 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 to.

3. Optical Error Correcting Codes Block codes Block codes Convolutional Codes Convolutional Codes -Binary Block Code (BCH) -Non-Binary Block Code (RS) (G1) Concatenated Codes (G2) Concatenated Codes (G2) LDPC Codes (G3) LDPC Codes (G3) FEC FEC Turbo Codes Turbo Codes

4. 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 Coding Gain (dB)= (S/N) coding - (S/N) uncoding At the same BER

5. 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

6. Second Generation Outband FEC (Concatenated) - FEC-concatenation schemes made -recommendation ITU-T G.975.1 -Serial-concatenation of FEC codes - super-FEC is a conc. scheme with BCH(3860,3824) as the outer and BCH(2040,1930) as the inner code

7. 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 Check of the check Check of column Check of row Information Symbol n1n1 n2n2 k2k2 k1k1 Construction of a product code Input Row-Row code by C 2 Coding column- column using C 1 This bits check of the check

8. 3rd Generation Outband FEC (Super-FEC) - Low-Density Parity-Check (LDPC) coding - Low-Density Parity-Check (LDPC) coding - leverage iterative decoding - leverage iterative decoding - very high coding-gains - very high coding-gains

9. 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

10. Effect of Coding on QPSK receiver with coherent demodulation Sensitivity BER versus received power for coherent QPSK receiver operating at 1Gb/s rate and = 3.78*10 -4 incorporating coherent demodulation. Received power (dBm) BER LDPC code gives small increase in CG than concat. Of RS codes at the same code rate 0.81 1 dB RS gives higher CG than BCH at Same code rate 4.8 dB

11. Effect of Coding on QPSK receiver with differential demodulation Sensitivity BER versus for heterodyne QPSK receiver operating at 1Gb/s rate and P R = -46.93 dBm incorporating differential demodulation. BER versus for heterodyne QPSK receiver operating at 1Gb/s rate and P R = -46.93 dBm incorporating differential demodulation. Received power (dBm) BER RS gives higher than BCH at Same code rate 4.3dB LDPC code gives high CG than concat. Of RS at the same code rate 0.81 Decrease code rate in LDPC code gives small increase in CG 3.6 dB 2 dB

12. DESIGN CONSIDERATIONS - Processing delays: Optical communications are particu­larly sensitive to delays, - 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) - 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 - Rich statistics FEC: is not a panacea; it is rather introduced to obtain the necessary system margin to guarantee QoS