KRATOS: An Open Source Hardware-Software Platform for Rapid Research in LPWANs

Long-range (LoRa) radio technologies have recently gained momentum in the IoT landscape, allowing low-power communications over distances up to several kilometers. As a result, more and more LoRa networks are being deployed. However, commercially available LoRa devices are expensive and propriety, creating a barrier to entry and possibly slowing down developments and deployments of novel applications. Using open-source hardware and software platforms would allow more developers to test and build intelligent devices resulting in a better overall development ecosystem, lower barriers to entry, and rapid growth in the number of IoT applications. Toward this goal, this paper presents the design, implementation, and evaluation of KRATOS, a low-cost LoRa platform running ContikiOS. Both, our hardware and software designs are released as an open- source to the research community.Comment: Accepted at WiMob 201

Wake-up Radio based Approach to Low-Power and Low-Latency Communication in the Internet of Things

For the Internet of Things to flourish a long lasting energy supply for remotely deployed large- scale sensor networks is of paramount importance. An uninterrupted power supply is required by these nodes to carry out tasks such as sensing, data processing, and data communication. Of these, radio communication remains the primary battery consuming activity in wireless systems. Advances in MAC protocols have enabled significant lifetime improvements by putting the main transceiver in sleep mode for extended periods. However, the sensor nodes still waste energy due to two main issues. First, the nodes periodically wake-up to sample the channel even when there is no data for it to receive, leading to idle listening cost. On the other side, the sending node must repeatedly transmit packets until the receiver wakes up and acknowledges receipt, leading to energy wastage due to over-transmission. In systems with the low data rate, idle listening and over-transmission can begin to dominate energy costs. In this thesis, we take a novel hardware approach to eliminate energy overhead in WSNs by addition of a second, extremely low-power wake-up radio component. This approach leverages an always-on wake-up receiver to delegate the task of listening to the channel for a trigger and then waking up a higher power transceiver when required. With this on-demand approach, energy constrained devices are able to drastically reduce power consumption without sacrificing the application requirements in terms of reliability and network latency. As a first major contribution, we survey a large body of work to identify the benefits and limitations of the current wake-up radio hardware technology. We also present a new taxonomy for categorizing the wake-up radios and the respective protocols, further highlighting the main issues and challenges that must be addressed while designing systems based on wake-up radios. Our survey forms a guideline for assisting application and system designers to make appropriate choices while utilizing this new technology. Secondly, this thesis proposes a first-ever benchmarking framework to enable accurate and repeatable profiling of wake-up radios. Specifically, we outline a set of specifications to follow when benchmarking wake-up radio-based systems, leading to more consistent and therefore comparable evaluations whether in simulation or testbed for current and future systems. To quantitatively assess whether wake-up technology can provide energy savings superior to duty cycled MACs, reliable tools are required to accurately model the wake-up radio hardware and its performance in combination with the upper layers of the stack. As our third contribution, we provide an open-source simulator, WaCo for development and evaluation of wake-up radio protocols across all layers of the software stack. Using our tool together with a newly proposed wake-up radio MAC layer, we provide an exhaustive evaluation of the wake-up radio system for periodic data collection applications. Our evaluations highlight that wake-up technology is indeed effective in extending the network lifetime by shrinking the overall energy consumption. To close the gap between the simulation and the real world experiments, we adopt a cutting edge wake-up radio hardware and build a Wake-up Lab, a modular dual-radio prototype. Using our Wake-up Lab, we thoroughly evaluate the performance of the wake-up radio solution in a realistic office environment. Our in-depth system-wide evaluation reveals that wake-up radio-based systems can achieve significant improvements over traditional duty cycling MACs by eliminating periodic receive checks and reducing unnecessary main radio transmissions while maintaining end-to-end latency on the order of tens of milliseconds in a multi-hop network. As a step toward sustainable wireless sensing, this thesis presents a proof of concept system where an extremely low-power switch coupled with a wake-up receiver is continuously powered by a plant microbial fuel cell (PMFC) and a new receiver-initiated MAC-level communication protocol for on-demand data collection. MFC converts the chemical energy into electricity by exploiting the metabolism of bacteria found in the sediment, thus offering a promising power source for autonomous sensing system. However, sources such as PMFCs are severely limited in the quantity of energy they can generate, unable to directly power the sensor nodes. Therefore, we consider radical hardware solutions in combination with the communication stacks to reduce this power gap. Thanks, to the hardware-software co-design proposed above, we were able to reduce the overall power consumption to a point where an extremely low-power PMFC source can sustain the sensor node’s operation with a data sampling rate of over 30 seconds. Finally, we propose to enhance the LoRa based low-power wide area networks by fusing wake-up receivers and long-range wireless technologies. The current LoRaWAN architecture is mainly designed and optimized for up-links where the remote end devices disseminate data to the gateway using pure ALOHA techniques. As such, this limits the ability of the gateway to control, reconfigure, or query the specific end devices, crucial for many Internet of Things applications. To shift the communication modality from push to pull based, we propose a new network architecture that leverages wake-up receiver and a receiver-initiated On-demand TDMA MAC. The former allows the gateway to trigger the remote device when there is data to be collected else keep the device in sleep mode, while the latter allows retrieving data efficiently from the nodes without congesting the network. Our testbed experiments reveal that the proposed system significantly improves energy efficiency by offering network reliability of 100% with end devices dissipating only a few microwatts of power during periods of inactivity. By moving away from the realm of pure ALOHA communication to wake-up receivers, we were able to exploit the low power modes of the sensor node more effectively. Through these contributions, this thesis pushes forward the applicability of ultra-low power wake-up radios, by quantitatively measuring the trade-offs, energy efficiency, reliability, and latency. Further, by demonstrating superior performance via proof of concepts, this thesis provides a stepping stone towards the goal of achieving energy-neutral, yet responsive communication systems using wake-up radio technology

On-Demand TDMA for Energy Efficient Data Collection with LoRa and Wake-up Receiver

Low-power and long-range communication tech- nologies such as LoRa are becoming popular in IoT applications due to their ability to cover kilometers range with milliwatt of power consumption. One of the major drawbacks of LoRa is the data latency and the traffic congestion when the number of devices in the network increases. Especially, the latency arises due to the extreme duty cycling of LoRa end-nodes for reducing the overall energy consumption. To overcome this drawback, we propose a heterogeneous network architecture and an energy-efficient On-demand TDMA communication scheme improving both the device lifetime and the data latency of standard LoRa networks. We combine the capabilities of micro- watt wake-up receivers to achieve ultra-low power states and pure asynchronous communication together with the long-range connectivity of LoRa. Experimental results show a data reliability of 100% and a round-trip latency on the order of milliseconds with end devices dissipating less than 46 mJ when active and 1.83 {\\mu}W during periods of inactivity, lasting up to 3 years on a 1200 mAh Lithium battery. Comment: Accepted at WiMob 201

On-Demand LoRa: Asynchronous TDMA for Energy Efficient and Low Latency Communication in IoT

Energy efficiency is crucial in the design of battery-powered end devices, such as smart sensors for the Internet of Things applications. Wireless communication between these distributed smart devices consumes significant energy, and even more when data need to reach several kilometers in distance. Low-power and long-range communication technologies such as LoRaWAN are becoming popular in IoT applications. However, LoRaWAN has drawbacks in terms of (i) data latency; (ii) limited control over the end devices by the gateway; and (iii) high rate of packet collisions in a dense network. To overcome these drawbacks, we present an energy-efficient network architecture and a high-efficiency on-demand time-division multiple access (TDMA) communication protocol for IoT improving both the energy efficiency and the latency of standard LoRa networks. We combine the capabilities of short-range wake-up radios to achieve ultra-low power states and asynchronous communication together with the long-range connectivity of LoRa. The proposed approach still works with the standard LoRa protocol, but improves performance with an on-demand TDMA. Thanks to the proposed network and protocol, we achieve a packet delivery ratio of 100% by eliminating the possibility of packet collisions. The network also achieves a round-trip latency on the order of milliseconds with sensing devices dissipating less than 46 mJ when active and 1.83 μ W during periods of inactivity and can last up to three years on a 1200-mAh lithium polymer battery

WaCo: A Wake-Up Radio COOJA Extension for Simulating Ultra Low Power Radios

Radio communication remains the primary battery consuming activity in wireless systems. Advances in MAC protocols have enabled significant lifetime improvements, but in systems with low data rate, idle listening, and other communication artifacts can begin to dominate costs. One proposal to combat this is the addition of a second, extremely low power radio component that is always-on. As a consequence of the extremely low power, such radios are incapable of decoding general data, and thus are often delegated the task of listening for a trigger, leading to the terminology wake-up radio, as this extremely low power radio is used to wake up a higher power radio, which is then used for data communication. While wake-up technology has been steadily evolving over the last decade in the hardware arena, few protocols have been developed to exploit it. In this work, we present WaCo, our wake-up radio COOJA extension that allows exploration of the capabilities of the wake-up radio from the desktop environment. We also use our extended simulator to concretely show the potential benefits of the wake-up radio hardware with two, standard data collection protocols. Our results simultaneously confirm that wake-up technology has tremendous potential and that our simulator extension provides an effective mechanism for such exploration