A Lightweight Enhanced Long Range Physical Layer Design Method for Internet of Things
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摘要: 为了提高LoRa在衰落信道下的误码率性能，该文设计了一种轻量级的增强型长距离(EnLoRa)物理层。首先，采用循环码移位键控(CCSK)作为纠错码，级联对角矩阵交织和啁啾扩频(CSS)调制技术，构造了一种新的比特交织编码调制(BICM)结构。然后，基于该结构，提出了一种基于比特对数似然比信息的软CSS解调和软译码算法，并将译码输出后的外信息作为先验信息反馈至解调模块，进行迭代译码。仿真结果表明，与相同码率的LoRa系统对比，EnLoRa系统在高斯信道下的编码增益提高了0.8 dB，在瑞利信道下的编码增益提高了7 dB。在此基础之上，通过多次迭代译码，还可以获得最大2.5 dB的额外收益。时间复杂度增加不到10%，空间复杂度增幅可忽略不计。该方法可望进一步降低物联网节点的功耗，在室内、市区和工业等复杂多径场景具有较大的应用价值。Abstract: To improve the bit error rate performance of LoRa (Long Range) in fading channels, a lightweight Enhanced Long Range (EnLoRa) physical layer is designed. First, Cyclic Code Shift Keying (CCSK) is chosen as the error correction code, and the diagonal matrix interleaving and Chirp Spread Spectrum (CSS) modulation techniques are concatenated to construct a new Bit Interleaved Coded Modulation (BICM) structure. Then, based on this structure, a soft CSS demodulation and soft decoding algorithm based on bit log-likelihood ratio information is proposed. Further, the decoded external information is fed back to the demodulation module as a priori information for iteration decoding. The simulation results show that, compared with the LoRa system of the same code rate, the coding gain of the EnLoRa system under the Gaussian channel is increased by 0.8 dB, and the coding gain under the Rayleigh channel is increased by 7 dB. On this basis, through multiple iterations, an additional gain of up to 2.5 dB can be obtained. The time complexity is only increased by 10%, and the increase in space complexity is negligible. This method is expected to reduce further the power consumption of LoRa nodes and has great application value to complex multipath scenarios such as indoors, urban areas and industries.
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