低功耗广域网技术是近年来新兴的无线网络连接技术，可以为低成本物联网设备提供功耗低、远距离的网络连接。低功耗广域网具有功耗低、覆盖范围广、抗噪性强的特点，适合部署在大规模的物联网应用中，受到了学术界和工业界的广泛关注。但是，现有的低功耗广域网技术尚存在诸多问题，亟待改进。第一，现有低功耗广域网技术并发性能差，在连接大量物联网设备的场景下会频繁发生信号冲突，导致数据丢失、传输时延增大、网络可靠性下降、节点能耗上升；第二，现有技术的传输参数配置策略差，导致节点能量大量浪费，降低节点的电池寿命；第三，现有的低功耗广域网技术传输速率慢，上层应用传输大文件时存在传输时延长的问题。 针对低功耗广域网并发性差、节点能量浪费、传输时延长的问题，本文在低功耗广域网物理层、链路层和应用层展开研究，协同解决现存问题。本文提出了物理层正交信号调制方法，实现了高并发的网络通信；研究了链路层能效最优动态参数设置算法，降低了节点的能耗；设计了应用层大文件差分算法，压缩了文件传输体积，降低了网络传输时延。 本研究的贡献主要包括三个部分：（1）在物理层，提出了一种新的支持高并发和低信噪比解码的数据调制方法——正交分段连续调频技术。正交分段连续调频技术可以在保证低信噪比解码的同时，实现正交的数据调制。基于该调制方法，本文设计了支持高并发的物理层协议，实现了高并发、低功耗、远距离的数据传输；（2）在链路层，将能量利用效率作为系统优化目标，建立了能量利用效率动态预测模型，并提出了能效最优的传输参数动态配置方法，大幅降低了节点的传输功耗；（3）在应用层，以物联网节点在线更新应用为例，研究了大文件差分压缩算法。通过文件拆分，算法增加了程序文件之间的相似度。差分算法减少更新文件的体积，显著降低大文件的传输时延。 本研究实现了系统原型，在测试床平台进行了实地部署并展开了充分的实验验证。实验结果表明：本文提出的高并发物理层协议将低功耗广域网的并发性和网络容量提升了60倍以上，提出的传输参数配置方法将节点的能量利用效率平均提高了41.2\%，提出的大文件差分压缩算法将文件传输时延平均降低至原来的50.8\%。
Low Power Wide Area Networks (LPWANs) are emerging wireless network techniques in recent years, which have been shown promising in connecting low-cost IoT devices with long-distance and low-power communication. The LPWANs have the advantages of low power consumption, long-distance communication, and strong noise immunity. They are suitable for deployment in large-scale IoT applications. Therefore, they have attracted widespread attention from both academia and industry. However, existing LPWAN technologies still have many problems, which need to be improved urgently. First, existing LPWAN techniques support very limited concurrent transmissions. If a gateway connects massive of IoT devices, it suffers from severe packet collisions, causing data loss, increased transmission delay, decreased network reliability, and increased energy consumption. Second, the adopted LPWAN adaptive data rate strategy cannot select the optimal transmission parameter and causes huge energy waste, and shorten the nodes' battery life. Last but not least, an LPWAN network usually provides a low data rate connection. When an application tries to send a large file over LPWAN, it suffers from long transmission latency. To solve the above problems of limited concurrency, energy waste, and transmission delay, in this thesis, we conduct researches on the physical layer, link layer, and application layer of LPWANs to solve existing problems together. In this thesis, we propose a physical-layer orthogonal modulation method to achieve high-concurrency network communication. We explore a link-layer dynamic parameter setting algorithm to achieve optimal energy efficiency and reduce the node's energy consumption. We design an application-layer large file differencing algorithm to compress the file size and reduce the network transmission delay. The contributions of this thesis are mainly three-fold: (1) At the physical layer, we propose a new modulation method, Orthogonal Scatter Chirp Spreading Spectrum (OSCSS), that supports high concurrent transmission as well as low signal-to-noise ratio decoding. The OSCSS modulation technique can achieve orthogonal data transmission while ensuring low signal-to-noise ratio decoding. Based on the modulation method, we design a physical layer protocol that supports high concurrency, low power, and long-distance data transmission. (2) At the link layer, we adopt energy efficiency as the system optimization goal. We establish a dynamic energy efficiency prediction model, and propose a dynamic configuration method of transmission parameters, which achieves the best energy efficiency and greatly reduces the power consumption of nodes. (3) At the application layer, we propose a large file differencing and compression algorithm. The algorithm increases the similarity between program files through file splitting. The differencing algorithm reduces the size of updated files and significantly shortens the transmission delay of updating large files. In this thesis, we have implemented the system prototype and deployed it on a testbed. We have launched an extensive experimental verification. The experimental results show that the high-concurrency physical layer protocol proposed in this thesis increases the concurrency and network capacity of the LPWANs by more than 60 times. The proposed transmission parameter configuration method increases the energy efficiency of the node by 41.2\%. The large file differencing and compression algorithm reduces the average transmission delay to 50.8\%.
