Evaluation of block turbo codes for long-haul optical networks

Optical network traffic has been increasing significantly over the last decade, and strong forward error correction (FEC) is essential to deal with the traffic. While hard-decision codes have been used for the first and the second generation FECs, soft-decision codes are being actively studied as candidates for the third generation codes. The requirements for the third generation codes are over 10 dB net coding gain (NCG) with about 20 % overhead. According to Tzimpragos et al. [1], block turbo codes (BTCs) with 15 % and 20 % overhead obtained the NCGs of over 11 dB. In this paper, we study the BTC pool that targets the long-haul optical networks and evaluate the BTC candidates. In order to achieve the target bit error rate (BER) of 10-15, a large minimum distance is essential for the BTCs. Thus, we estimate the BER performances of the BTCs with the minimum distances of 24 and 36. Since the target BER requires extensive simulations, we estimate the NCGs by observing the BER down to 10-9 and conjecturing about the rest of the BER. We also compare the candidate BTCs in terms of the decoding-complexity.