低密度校验码LDPC

2.6 复杂度、吞吐量和解码时延

| 2.8　LDPC 码在 3GPP 中的应用 |

目前，LDPC 码已广泛应用到诸多通信系统中，例如，全球微波互联接入 （WiMAX）（IEEE 802.16e）、Wi-F（i IEEE 802.11n）[10]、DVB-S2[12] 等。
在 3GPP 讨论 LTE 方案的早期，LDPC 码也是 4G 信道编码的候选方案 [49]。 但考虑到实现复杂度，3GPP 最终选择 Turbo 码作为 3G 和 4G 信道编码的方 案而没有选择 LDPC 码。经过学术界和工业界的努力研究，LDPC 码最终进入 要求严格的 3GPP 5G-NR 标准 [13]。见表 2-17，LDPC 码在 3GPP 中是如何应用的 [14]。

| 2.9　未来发展 |

将来，LDPC 码将进一步发展。作者认为，其可能的方向如下。
（1）对短码更好的支持（优化出新的 BG3、BG4）。在物联网（IoT）和机 器类通信（MTC）中，常常需要发送小的数据块，而 IoT 和 MTC 又需要十分 节能，不能消耗过多的电量，这就需要性能好的基础矩阵。
（2）多边 LDPC 码 [23] 具有更低的误码平台，这有利于对误码严格要求的业 务（URLLC）。
（3）类似于 Turbo 码的并行级联 Gallager 码（PCGC，Turbo 码的内部 编码器是 LDPC 码）[50]。目前，PCGC 在码率 R = 0.3367 时，离香农限约 0.4 dB[50]。
（4）使用阶梯码（Staircase Code）[51] 形式的LDPC码 [52]。阶梯码的好处是， 可以做到很低的误码平台。

| 2.10　小结 |

这一章主要描述了 LDPC 码的产生和发展、基本原理、准循环 LDPC 码、 QC-LDPC 译码结构、LDPC 码在 5G-NR 标准中的进展、复杂度、吞吐量、 链路性能以及 LDPC 码在 3GPP 中的应用、未来发展等。总的来说，LDPC 码 的性能非常优越、复杂度较低、吞吐量高，可以进行并行解码，解码时延小。当然，LDPC 码也具有构造复杂、不适合短码等缺点。相信随着编码研究人员 的深入研究，LDPC 将有更为广泛的应用。

| 参考文献 |

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