Feedback transmissions are used to acknowledge correct packet reception, trigger erroneous packet re-transmissions, and adapt transmission parameters (e.g., rate and power). Despite the paramount role of feedback in establishing reliable communication links, the majority of the literature overlooks its impact by assuming genie-aided systems relying on flawless and instantaneous feedback. An idealistic feedback assumption is no longer valid for large-scale Internet of Things (IoT), which has energy-constrained devices, susceptible to interference, and serves delay-sensitive applications. Furthermore, feedback-free operation is necessitated for IoT receivers with stringent energy constraints. In this context, this paper explicitly accounts for the impact of feedback in energy-constrained and delay-sensitive large-scale IoT networks. We consider a time-slotted system with closed-loop and open-loop rate adaptation schemes, where packets are fragmented to operate at a reliable transmission rate satisfying packet delivery deadlines. In the closed-loop scheme, the delivery of each fragment is acknowledged through an error-prone feedback channel. The open-loop scheme has no feedback mechanism, and hence, a predetermined fragment repetition strategy is employed to improve transmission reliability. Using tools from stochastic geometry and queueing theory, we develop a novel spatiotemporal framework to optimize the number of fragments for both schemes and repetitions for the open-loop scheme. To this end, we quantify the impact of feedback on the network performance in terms of transmission reliability, latency, and energy consumption.

翻译：反馈传输用于确认数据包的正确接收、触发错误数据包的重传以及自适应调整传输参数（如速率和功率）。尽管反馈在建立可靠通信链路中起着关键作用，但大多数文献通过假设依赖完美瞬时反馈的“神谕辅助”系统而忽略了其影响。这种理想化的反馈假设在大规模物联网中不再成立——该网络包含能量受限、易受干扰且服务于延迟敏感应用的设备。此外，对于能量严格受限的物联网接收器，无反馈操作成为必要需求。在此背景下，本文明确考虑了反馈对能量受限且延迟敏感的大规模物联网网络的影响。我们研究了一种时隙系统，其中采用闭环和开环速率自适应方案，数据包被分片传输以在满足交付截止时间的前提下实现可靠传输速率。在闭环方案中，每个分片的交付通过存在错误的反馈信道确认；开环方案则没有反馈机制，因此采用预定的分片重复策略以提高传输可靠性。利用随机几何和排队论工具，我们开发了一种新型时空框架，用于优化两种方案下的分片数量以及开环方案中的重复次数。最终，我们从传输可靠性、延迟和能耗角度量化了反馈对网络性能的影响。