Forward Error Correcting Codes for Optical Communication Systems

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

2. 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 . Optical Error Correcting Codes FEC challenges in Optical Comm. systems

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

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

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 -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

7. Product Codes - Serially concatenated codes using two or more short block codesto form long block codes • IfC1 )n1, k1)of minimum distancedmin1andC2) n2, k2)of minimum distancedmin2are two systematic linear block codes Coding column-column using C1 n2 k2 Check of row This bits check of the check Information Symbol Input Row-Row code by C2 k1 n1 Check of column Check of the check Construction of a product code

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

9. Low-Density Parity Check Codes (LDPC) - LDPC codes havelarge minimum Hamming distance - Parity-check matrix of a simple linear block code (Local code) used to generate LDPC code matrix - LDPC codes matrix depend onLocal code, codeword length, andpermutation matrix

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

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

12. 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

13. Thank you