Ambient Internet of Things (A-IoT) devices, as a critical enabler of future green IoT networks, have attracted broad interest from both industry and academia due to their ability to operate without batteries and with low maintenance costs. To accommodate their dynamic and constrained energy budget, an ultra-low-power connectivity protocol is required. Due to the severely limited transmit power of A-IoT devices, multi-hop connectivity is an interesting paradigm to extend their range. However, commonly used protocols for multi-hop communication may not be suitable for A-IoT due to excessive overhead related to channel access procedures, coordinated routing, and tight time synchronization requirements. This paper presents a novel network connectivity protocol based on symbol-synchronous transmissions, which allows battery-less relay nodes to participate in the forwarding process in an ad-hoc manner, without the need for synchronization or coordination. This allows them to adapt their duty cycle to the available harvested energy. Simulation results show that the proposed protocol can ensure high reliability in data packet delivery while significantly reducing the energy consumption of each relay node. We also investigate the relationship between wake-up probability and network density. For example, a 400-node network in a 625 m2 area can achieve a packet error rate below 1 % with an average awake time of 6 % per node, achieving an energy consumption reduction of 88 % compared to the baseline approach.

翻译：环境物联网（A-IoT）设备作为未来绿色物联网网络的关键使能技术，因其无需电池且维护成本低的特点，引起了工业界和学术界的广泛关注。为适应其动态且受限的能量预算，需采用超低功耗连接协议。由于A-IoT设备的发射功率严重受限，多跳连接成为扩展其覆盖范围的有效范式。然而，由于信道接入流程、协调路由及严格时间同步需求带来的过高开销，传统多跳通信协议可能不适用于A-IoT。本文提出一种基于符号同步传输的新型网络连接协议，使无电池中继节点无需同步或协调即可以自组织方式参与转发过程，从而根据可用能量自适应调整占空比。仿真结果表明，所提协议能确保数据包传输的高可靠性，同时显著降低各中继节点的能耗。我们还研究了唤醒概率与网络密度之间的关系。例如，在625 m²区域内的400节点网络中，当每个节点平均唤醒时间占比为6%时，可达到低于1%的误包率，较基线方法实现88%的能耗降低。