第五世代移動通信システム向けＭ２Ｍ通信方式に関する研究

在这项工作中，我们努力构建一个基于sub-GHz低功率广域（LPWA）技术的高效多跳网络。具体来说，我们研究了LoRa（一种可以提供数公里户外覆盖的物理层标准）和并发传输（CT）（一种最近提出的可以显著提高网络效率的多跳协议）的组合。这项工作的主要贡献有三个方面。1)由于CT通过允许同步的数据包冲突来提高网络效率，因此需要仔细检查物理层接收端在这种数据包冲突下的性能，以确保网络的可靠性。我们首先广泛评估了CT下LoRa接收器的性能，以验证LoRa与CT兼容。具体来说，我们发现，由于时域和频域的能量扩散效应，LoRa对CT引起的数据包碰撞具有鲁棒性。2)通过在中继分组之间引入时序偏移，进一步提高了CT下的接收性能。鉴于此，我们提出了一种定时延迟插入方法，即offset- ct方法，该方法在数据包之前添加随机定时延迟，同时防止定时偏移在多跳网络中发散。3)我们进行了概念验证实验，验证了基于ct的LoRa多跳网络（CT-LoRa）的可行性以及所提出的偏移ct方法带来的性能改进。

In this work, we strive to construct an efficient multi-hop network based on the sub-GHz low-power wide-area (LPWA) technology. Specifically, we investigate the combination of LoRa, a physical-layer standard that can provide severalkilometer outdoor coverage, and concurrent transmission (CT), a recently proposed multi-hop protocol that can significantly improve the network efficiency. The main contributions of this work are threefold. 1) Since the CT enhances the network efficiency by allowing synchronized packet collisions, the performance of the physical-layer receiver under such packet collisions needs to be carefully examined to ensure the network reliability. We first extensively evaluate the LoRa receiver performance under CT to verify that LoRa is compatible to CT. Specifically, we find that, due to the time-domain and frequency-domain energy spreading effect, LoRa is robust to the packet collisions resulting from CT. 2) We further find the receiver performance under CT can be further improved by introducing timing offsets between the relaying packets. In view of this, we propose a timing delay insertion method, the offset-CT method, that adds random timing delay before the packets while preventing the timing offset from diverging over the multi-hop network. 3) We conduct proof of- concept experiments to demonstrate the feasibility of CT-based LoRa multi-hop network (CT-LoRa) and the performance improvement brought by the proposed offset-CT method.