Energy- and Delay-Aware Two-Hop NOMA-Enabled Massive Cellular IoT Communications

Providing energy-efficient and delay-aware channel access in cellular networks is essential to many anticipated massive Internet of Things (IoT) applications. However, as the number of devices increases, the contention over the limited network radio resources increases, leading to network congestion. The congestion increases the channel access delay and energy consumption of IoT devices, and reduces the number of supported devices. Node clustering and data aggregation are potential approaches to support the massive number of devices while meeting the various service quality requirements of diverse applications. As the number of devices increases, optimizing the node clustering and data aggregation process becomes critical as many tradeoffs arise among different network performance metrics. In this article, we present a novel nonorthogonal multiple access-enabled two-stage transmission architecture to enable massive cellular IoT communications. Concepts from queuing theory and stochastic geometry are jointly exploited to derive tractable models for different network performance parameters, such as coverage probability, two-hop access delay, and the number of served devices per transmission frame. The established models characterize relations among various network parameters, and hence facilitate the design of two-stage transmission architecture. The numerical results demonstrate that the proposed solution improves the overall access delay and energy efficiency as compared to traditional-orthogonal-multiple-access-based clustered networks. They also highlight that, for the scenario considered, there is an optimal number of aggregators at which the tradeoffs among the different network performance measures are optimized.