[论文解读] Low Complexity Belief Propagation Polar Code Decoders

Syed Mohsin Abbas, YouZhe Fan+2 more|arXiv (Cornell University)|May 19, 2015

Error Correcting Code Techniques参考文献 16被引用 8

一句话总结

该论文通过引入子因子图冻结（sub-factor-graph freezing），提出了一种低复杂度的极化码信念传播（BP）译码器，有效降低了平均迭代次数和计算量。通过将逐次消除译码（SCD）原理融入BP，该方法在保持与传统BP相当性能的同时，显著降低了延迟和能耗，仿真结果验证了其有效性。

ABSTRACT

Since its invention, polar code has received a lot of attention because of its capacity-achieving performance and low encoding and decoding complexity. Successive cancellation decoding (SCD) and belief propagation decoding (BPD) are two of the most popular approaches for decoding polar codes. SCD is able to achieve good error-correcting performance and is less computationally expensive as compared to BPD. However SCDs suffer from long latency and low throughput due to the serial nature of the successive cancellation algorithm. BPD is parallel in nature and hence is more attractive for high throughput applications. However since it is iterative in nature, the required latency and energy dissipation increases linearly with the number of iterations. In this work, we borrow the idea of SCD and propose a novel scheme based on sub-factor-graph freezing to reduce the average number of computations as well as the average number of iterations required by BPD, which directly translates into lower latency and energy dissipation. Simulation results show that the proposed scheme has no performance degradation and achieves significant reduction in computation complexity over the existing methods.

研究动机与目标

• 降低极化码信念传播（BP）译码的计算复杂度和延迟。
• 解决传统BP译码中能耗高和迭代性过强的问题。
• 利用逐次消除译码（SCD）的结构特性，提升BP译码效率。
• 在保持纠错性能的前提下，最小化BP译码的平均迭代次数和计算量。

提出的方法

• 所提方法引入子因子图冻结，即根据类似SCD的决策，对因子图中的部分因子节点进行冻结。
• 冻结可减少BP迭代过程中的活跃计算量，从而降低平均复杂度。
• 该方案采用混合方法，结合SCD的决策顺序与BP的并行译码结构。
• 冻结的子因子图被迭代更新，从而减少达到收敛所需的迭代次数。
• 算法动态识别并冻结冗余或影响较小的因子节点，以加速收敛。
• 该方法在保持BP并行性的同时，减少了消息传递操作的数量。

实验结果

研究问题

• RQ1 信念传播译码的迭代特性能否被缓解，以降低延迟和能耗？
• RQ2 如何将逐次消除译码原理融入信念传播，以降低复杂度？
• RQ3 子因子图冻结对BP译码平均迭代次数有何影响？
• RQ4 在降低计算负载的同时，能否避免性能下降？

主要发现

• 所提方案在纠错性能上与传统信念传播译码完全相当。
• 与标准BP译码相比，平均迭代次数显著减少。
• 由于因子图中活跃的消息传递操作减少，计算复杂度降低。
• 由于迭代和计算量减少，延迟和能量损耗均得以降低。