Relaying in the Internet of Things (IoT): A Survey

Abstract

The deployment of relays between Internet of Things (IoT) end devices and gateways can improve link quality. In cellular-based IoT, relays have the potential to reduce base station overload. The energy expended in single-hop long-range communication can be reduced if relays listen to transmissions of end devices and forward these observations to gateways. However, incorporating relays into IoT networks faces some challenges. IoT end devices are designed primarily for uplink communication of small-sized observations toward the network; hence, opportunistically using end devices as relays needs a redesign of both the medium access control (MAC) layer protocol of such end devices and possible addition of new communication interfaces. Additionally, the wake-up time of IoT end devices needs to be synchronized with that of the relays. For cellular-based IoT, the possibility of using infrastructure relays exists, and noncellular IoT networks can leverage the presence of mobile devices for relaying, for example, in remote healthcare. However, the latter presents problems of incentivizing relay participation and managing the mobility of relays. Furthermore, although relays can increase the lifetime of IoT networks, deploying relays implies the need for additional batteries to power them. This can erode the energy efficiency gain that relays offer. Therefore, designing relay-assisted IoT networks that provide acceptable trade-offs is key, and this goes beyond adding an extra transmit RF chain to a relay-enabled IoT end device. There has been increasing research interest in IoT relaying, as demonstrated in the available literature. Works that consider these issues are surveyed in this paper to provide insight into the state of the art, provide design insights for network designers and motivate future research directions.

Buyers Collusion in Incentivized Forwarding Networks: A Multi-Agent Reinforcement Learning Study

“…Incentivized relaying in communication networks is a method proposed and studied in the literature to enable cooperative communication and forwarding in specific application networks [1]. It has potential applications in IoT networks, future cellular networks, smart cities, smart homes, wearable devices, and smart grids, where multi-hop mesh network architectures can enhance network spectral and energy efficiencies [2].…”

Joint Power Control and Resource Allocation with Rate Fairness Consideration for SWIPT-Based Cognitive Two-Way Relay Networks

“…The relay technique can expand the transmission distance and improve the transmission reliability of the system. Integrating relay and cognitive techniques can further improve the transmission performance of the system [10,11]. In [12], the closed-form expression of outage probability for a cognitive multi-hop relay network is derived over Rayleigh fading channels, and an optimization problem to minimize the outage probability of the cognitive relay network is formulated and solved.…”

Relay-assisted wireless energy harvesting for multihop clustered IoT network

“…Many researchers suggested that clustering is one of the prominent solutions to reduce the energy consumption of the network [6][7][8][9] . Clustering reduces the interchange of redundant messages among the SNs by conserving the communication bandwidth [6] .…”

“…In this strategy, the CH accumulates the data from SNs and sends them to the sink node. However, CHs near the sink node may experience considerable energy consumption and rapid energy depletion, which can lead to hotspots in the network [8,9] . One of the potential strategies to prevent the hot spot problem is uneven clustering, which results in varying cluster sizes with respect to the distance between the sink node and CHs; i.e., as distance increases, the cluster size also increases.…”