5.1 Conclusion
To provide an area efficient and more powerful error correcting capability for optical com-munication systems, this thesis proposes a novel decision-confined decoding algorithm and its area-efficient architecture for soft RS codes. By confining the degree of error-locator polynomial, our approach determines the more likely candidate sequence which leads to only one candidate sequence being decoded. From our simulation, our method, for RS (255,239) codes, can achieve 0.4 dB coding gain at 104 CER over hard decoders.
Unlike Chase-type methods using several hard RS decoders and determining the most probable candidate, our proposal only demands one, leading to significant hardware complex-ity reduction. By using Gray code based bit-flipping method, which leads to only one bit of these LRPs flipped between each successive candidate, the syndrome for the next candidate can be updated with much more efficient method without recalculating it. In order to meet our timing schedule, we combine the advantage of half-iteration BM and RiBM algorithm and proposed a half-iteration RiBM algorithm and its homogeneous architecture. Moreover, by removing the calculation of error evaluator polynomial and applying BP-based method to compute the error values, the hardware cost can be further reduced. According to the
measurement results, the proposed soft RS decoder can achieve 2.56 Gb/s throughput with 45.3 K gate. As a result, our proposal can fully meet the criterion of optical communica-tions applicacommunica-tions and provide more powerful correcting ability with a high-speed and area efficient solution to support longer transmission distance.
5.2 Future Works
Although our proposal can provide an area-efficient RS decoder with better performance gain over traditional hard RS decoders, we still have some design challenge for improvement.
Compared with Chase-type methods, our design needs to flip more LRPs to achieve the competitive coding gain, leading to double operations of KES. Therefore the critical path will also be doubled over hard decoders. In the future, we will investigate new approaches to find more efficient methods for determining the characteristic of out of correction. If it can be done, the number of flipped bits, or the number of candidate sequence will be reduced while maintaining the error performance. Moreover, the throughput and the hardware cost can also be enhanced.
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