Conventional performance evaluation of IoT device lifetime typically considers only the battery state-of-charge and does not take into account the complex dynamics of the battery itself. Here, we present a IoT device lifetime model that more accurately reflects how batteries respond to IoT-typical loads.Our key insight is that an IoT device's power-saving sleep/wake cycle imposes intermittent pulse loads on the battery; the load duration and current depend on the operations(s) performed by the device during each awake interval. Our model therefore predicts the minimum output voltage that will be observed at the battery in response to a given pulse load. This value determines whether the battery is able to meet the input voltage requirements of the IoT device.We have developed an support vector regression (SVR)-based battery model using a dataset consisting of measurements of the voltage response of small lithium titanate (LTO) batteries to over 90K pulse loads. The model predicts the battery's minimum output voltage in response to a given pulse load with an RMAE (Root Mean Absolute Error) of less than 3% over the full operational range of the battery. The accuracy decreases at the more critical lower end of the voltage range, however, falling to ~ 8-10%RMAE.This pulse-response model allows us to create a "synthetic battery" and track its voltage response to a sequence of pulse loads, supporting a more realistic lifetime model where the IoT device fails as soon as the battery's predicted output voltage fails to meet its input voltage requirements.

Due to their popularity, large coverage areas, and diversity of radio technologies, Low Power Wide Area Networks (LPWAN) will experience high levels of cross-technology interference. In this work, we investigate the impact of LoRa interference on IEEE 802.15.4 (Wi-SUN) networks. Using hardware experiments, we characterize the interaction between these two very different radio technologies. In particular, we observe that the IEEE 802.15.4 Clear Channel Assessment (CCA) mechanism does not reliably detect interfering LoRa transmissions. We therefore propose an enhanced CCA mechanism based on a Multi-Layer Perceptron classifier and show that it significantly reduces the number of unsuccessful transmissions, while remaining compatible with the IEEE 802.15.4 standard.

The large number and wide diversity of IoT networks operating in unlicensed spectrum will create a complex and challenging interference environment. To avoid a 'tragedy of the commons', networks may need to more explicitly coordinate their use of the shared channel.

We present some preliminary results on LoRaWAN and IEEE 802.15.4-SUN interference in urban environments. The results are based on a simple simulation that is parameterized using PHY layer measurements of controlled interference scenarios.

We describe a testbed for studying battery discharge behavior and the lifetime of wireless devices under controlled temperature conditions and present preliminary measurement results.

The rapid growth of new radio technologies for Smart City/Building/Home applications means that models of cross-technology interference are needed to inform the development of higher layer protocols and applications. We systematically investigate interference interactions between LoRa and IEEE 802.15.4g networks. Our results show that LoRa can obtain high packet reception rates, even in presence of strong IEEE 802.15.4g interference. IEEE 802.15.4g is also shown to have some resilience to LoRa interference. Both effects are highly dependent on the LoRa radio's spreading factor and bandwidth configuration, as well as on the channelization. The results are shown to arise from the interaction between the two radios' modulation schemes. The data have implications for the design and analysis of protocols for both radio technologies.

No abstract available.

Simulation is an essential tool for evaluating the performance of wireless protocols and applications because of its cost effectiveness and its high level of control over the simulated system. As the research community envisions increasingly complex applications in areas like mobile social networks and wireless sensor networks, the need for trustworthy simulation of core communication protocols increases.

We describe early results from a program of experiments to characterize battery operation in the WSN regime.

We present a preliminary study of self-organizing TDMA for battery-constrained multihop wireless networks, such as sensor networks. Compared with existing TDMA approaches, this work emphasizes operation in the context of battery saving techniques that allow the radio to spend most of its time powered down, relying on some rendezvous mechanism to ensure that sender and receiver are simultaneously powered on and able to communicate. While such techniques reduce battery consumption, they also significantly limit the amount of information even local information that nodes can obtain from channel sensing or packet exchange. We therefore focus on self-organizing TDMA in the case of very limited state information. This work is also relevant to the practical case of independent, co-located sensor networks, which need to adapt to each other's presence without explicit coordination.

By definition, the operation of an asynchronous power save protocol permits an arbitrary distribution of nodes' wakeup schedules. This wakeup schedule distribution creates an uncoordinated pattern of times at which nodes attempt to transmit. Intuitively, we would expect that some patterns are more (or less) favorable than others for a given traffic pattern. We investigate the impact of this wakeup pattern on network capacity and present simulation data showing that the capacity associated with the best wakeup patterns is significantly larger than that of the worst. This result not only gives insight to the behavior of such protocols, but also acts as a feasibility study showing the potential benefit of mechanisms by which nodes adapt their wakeup schedules to obtain improved performance.

Energy-aware design and evaluation of network protocols requires knowledge of the energy consumption behavior of actual wireless interfaces. But little practical information is available about the energy consumption behavior of well-known wireless network interfaces and device specifications do not provide information in a form that is helpful to protocol developers. This paper describes a series of experiments which obtained detailed measurements of the energy consumption of an IEEE 802.11 wireless network interface operating in an ad hoc networking environment. The data is presented as a collection of linear equations for calculating the energy consumed in sending, receiving and discarding broadcast and point-to-point data packets of various sizes. Some implications for protocol design and evaluation in ad hoc networks are discussed.

We consider a real-time, distributed service to be dependable if it continues to have timely, predictable behavior even in the presence of partial failures. Services with this property are desirable in a host of real-time scenarios, including factory floor automation, medical monitoring equipment, and combat systems. Most distributed services built with contemporary fault-tolerance toolkits are not dependable; they exhibit unpredictable, albeit logically correct, behavioral patterns under failure conditions. We have designed and implemented middleware explicitly for real-time dependable services. We aimed at maintaining sub-second worst-case guarantees for failure detection and recovery, even when failures conspire with network load and CPU load to undermine determinism. The paper reports our experience in marrying software fault tolerance and real-time disciplines, from the definition of the requirements to the characterization of the resulting system.