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Abstract

In wireless environments, transmission and 1 reception costs dominate system power consumption, motivating 2 research effort on new technologies capable of reducing the 3 footprint of the radio, paving the way for the Internet of 4 Things. The most important challenge is to reduce power 5 consumption when receivers are idle, the so called idle-listening 6 cost. One approach proposes switching off the main receiver, 7 then introduces new wake-up circuitry capable of detecting 8 an incoming transmission, optionally discriminating the packet 9 destination using addressing, then switching on the main radio 10 only when required. This wake-up receiver technology represents 11 the ultimate frontier in low power radio communication. In 12 this paper, we present a comprehensive literature review of 13 the research progress in wake-up radio (WuR) hardware and 14 relevant networking software. First, we present an overview of 15 the WuR system architecture, including challenges to hardware 16 design and a comparison of solutions presented throughout the 17 last decade. Next, we present various medium access control and 18 routing protocols as well as diverse ways to exploit WuRs, both 19 as an extension of pre-existing systems and as a new concept to 20 manage low-power networking.

Abstract-Data prediction is proposed in wireless sensor networks (WSNs) to extend the system lifetime by enabling the sink to determine the data sampled, within some accuracy bounds, with only minimal communication from source nodes. Several theoretical studies clearly demonstrate the tremendous potential of this approach, able to suppress the vast majority of data reports at the source nodes. Nevertheless, the techniques employed are relatively complex, and their feasibility on resource-scarce WSN devices is often not ascertained. More generally, the literature lacks reports from real-world deployments, quantifying the overall system-wide lifetime improvements determined by the interplay of data prediction with the underlying network. These two aspects, feasibility and system-wide gains, are key in determining the practical usefulness of data prediction in real-world WSN applications. In this paper, we describe Derivative-Based Prediction (DBP), a novel data prediction technique much simpler than those found in the literature. Evaluation with real data sets from diverse WSN deployments shows that DBP often performs better than the competition, with data suppression rates up to 99% and good prediction accuracy. However, experiments with a real WSN in a road tunnel show that, when the network stack is taken into consideration, DBP only triples lifetime-a remarkable result per se, but a far cry from the data suppression rates above. To fully achieve the energy savings enabled by data prediction, the data and network layers must be jointly optimized. In our testbed experiments, a simple tuning of the MAC and routing stack, taking into account the operation of DBP, yields a remarkable seven-fold lifetime improvement w.r.t. the mainstream periodic reporting.

Wireless sensor networks (WSNs) are envisioned for a number of application scenarios. Never- theless, the few in-the-field experiences typically focus on the features of a specific system, and rarely report about the characteristics of the target environment, especially with respect to the behavior and performance of low-power wireless communication. The TRITon project, funded by our local administration, aims to improve safety and reduce maintenance costs of road tunnels, using a WSN-based control infrastructure. The access to real tunnels within TRITon gives us the opportunity to experimentally assess the peculiarities of this environment, hitherto not in- vestigated in the WSN field. We report about three deployments: (i) an operational road tunnel, enabling us to assess the impact of vehicular traffic; (ii) a nonoperational tunnel, providing insights into analogous scenarios (e.g., underground mines) without vehicles; (iii) a vineyard, serving as a baseline representative of the existing literature. Our setup, replicated in each deployment, uses mainstream WSN hardware, and popular MAC and routing protocols. We analyze and compare the deployments with respect to reliability, stability, and asymmetry of links, the accuracy of link quality estimators, and the impact of these aspects on MAC and routing layers. Our analysis shows that a number of criteria commonly used in the design of WSN protocols do not hold in tunnels. Therefore, our results are useful for designing networking solutions operating efficiently in similar environments