To remotely monitor the physiological status of the human body, long range (LoRa) communication has been considered as an eminently suitable candidate for wireless body area networks (WBANs). Typically, a Rayleigh-lognormal fading channel is encountered by the LoRa links of the WBAN. In this context, we characterize the performance of the LoRa system in WBAN scenarios with an emphasis on the physical (PHY) layer and medium access control (MAC) layer in the face of Rayleigh-lognormal fading channels and the same spreading factor interference. Specifically, closed-form approximate bit error probability (BEP) expressions are derived for the LoRa system. The results show that increasing the SF and reducing the interference efficiently mitigate the shadowing effects. Moreover, in the quest for the most suitable MAC protocol for LoRa based WBANs, three MAC protocols are critically appraised, namely the pure ALOHA, slotted ALOHA, and carrier-sense multiple access. The coverage probability, energy efficiency, throughput, and system delay of the three MAC protocols are analyzed in Rayleigh-lognormal fading channel. Furthermore, the performance of the equal-interval-based and equal-area-based schemes is analyzed to guide the choice of the SF. Our simulation results confirm the accuracy of the mathematical analysis and provide some useful insights for the future design of LoRa based WBANs.

翻译：为远程监测人体生理状态，远程（Long Range，LoRa）通信技术已成为无线体域网（Wireless Body Area Networks，WBANs）的理想候选方案。一般而言，WBAN的LoRa链路会经历瑞利-对数正态衰落信道。在此背景下，本文重点针对物理层（PHY）和介质访问控制层（MAC），在瑞利-对数正态衰落信道及相同扩频因子干扰条件下，对LoRa系统在WBAN场景中的性能进行表征。具体而言，推导了LoRa系统的闭式近似误比特率（BEP）表达式。结果表明：增大扩频因子（SF）并降低干扰可有效抑制阴影效应。此外，为寻求最适合LoRa型WBAN的MAC协议，本文对纯ALOHA、时隙ALOHA及载波侦听多路访问三种MAC协议进行了批判性评估。在瑞利-对数正态衰落信道下分析了三种MAC协议的覆盖概率、能量效率、吞吐量及系统时延。同时，通过分析等间隔与等面积两种扩频因子分配方案的性能，为SF选择提供指导。仿真结果验证了数学分析的准确性，并为未来基于LoRa的WBAN设计提供了有益启示。