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LiFi, light-fidelity, is a wireless technology that uses visible light for data transmission. It has several advantages, such as using a different part of electromagnetic spectrum than radio communication and providing enhanced privacy because light transmission is blocked by walls. Internet of Things applications with low-tomoderate data rates represent a promising arena for LiFi adoption. However, it is difficult to bring LiFi to IoT devices for several reasons, including some of LiFi’s strengths. We present TunnelLiFi, a new receiver architecture that acts like a bridge between the light and radio spectrums. A key aspect of TunnelLiFi’s design is the use of the unique self-oscillating mixing property of the tunnel diode oscillator, which enables the mixing of a photodiode signal with a locally generated radio frequency carrier signal while drawing under 100 μW of power consumption. In our experiments, Tunnel- LiFi demonstrates the ability to replicate the information contained in light signals onto radio signals at tens of microwatts, even in low-light conditions (300 lux) and at low bitrates (2.93 Kbps). We also show the potential of TunnelLiFi to support high bitrates. TunnelLiFi opens up new possibilities for LiFi technology by enabling communication in areas where light propagation is challenging. It also allows commodity IoT devices to receive LiFi transmissions using their existing transceivers, thus expanding the reach of LiFi. TRUE inpress

The past decade has seen a great interest in developing radio frequency sensing technology and its applications. At a basic level, these systems operate by tracking changes in the wireless signal reflected from a physical object. These reflections contain a wealth of information about the object, such as its motion and material. However, existing radio frequency sensing solutions are constrained by the complexity of the deployment and their high power consumption. This is because these systems extract weak reflections in presence of a strong incident signal. This paper introduces a new radio frequency sensing modality that allows tracking of the incident signal and not reflections from the object. This allows us to simplify the receiver and algorithm design significantly. We design the system using tunnel diode oscillators to generate a high-frequency carrier signal at only tens of microwatts of power consumption. The critical contribution that we make is to show that the frequency of the tunnel diode oscillator is sensitive to the physical environment. As an example, we demonstrate that performing simple hand gestures near the tunnel diode oscillator causes notable changes to its frequency. Thus, the receiver tracks the frequency of the carrier signal generated by the tunnel diode oscillator, and not reflections from physical objects. It enables inferring of sensing information using a commodity receiver costing only a few USD. Our system enables radio frequency sensing at low cost, complexity and power.

Light bulbs have been recently explored to design Light Fidelity (LiFi) communication to battery-free tags, thus complementing Radiofrequency (RF) backscatter in the uplink. In this paper, we show that LiFi and RF backscatter are complementary and have unexplored interactions. We introduce PassiveLiFi, a battery-free system that uses LiFi to transmit RF backscatter at a meagre power budget. We address several challenges on the system design in the LiFi transmitter, the tag and the RF receiver. We design the first LiFi transmitter that implements a chirp spread spectrum (CSS) using the visible light spectrum. We use a small bank of solar cells for communication and harvesting and reconfigure them based on the amount of harvested energy and desired data rate. We further alleviate the low responsiveness of solar cells with a new low-power receiver design in the tag. Experimental results with an RF carrier of 17 dBm show that we can generate RF backscatter with a range of 80.3 meters/𝜇W consumed in the tag, which is almost double with respect to prior work. European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 814215 TRUE inpress

The growth rate of Internet-of-Things (IoT) devices sold globally is constantly lower than the forecast. This deceleration is caused in part by the need for batteries and the scalability cost for their replacement. Backscatter has attracted significant interest over the past couple of years to enable sustainable sensing devices by eliminating batteries. IoT devices have been designed for transmitting sensed data with backscatter, but the question of efficient reception of data with battery-free devices is still open. As shown in this paper, classical low-power Radio Frequency (RF) envelope detectors are affected by low sensitivity, false detection alarms, and low energy efficiency. We argue that Light Fidelity (LiFi) can provide downlink and harvesting medium as LED lights are becoming pervasively deployed for illumination. We show, for the first time, that the advantages of LiFi and RF backscatter can be combined for battery-free communication. We design a low-power platform that leverages the complementary nature of these two mediums. We demonstrate that our platform removes energy-inefficiency in the downlink reception typical of RF backscatter, and significantly expands the deployment scenarios for battery-free tags when compared to conventional single-technology designs. TRUE pub

We introduce BackVLC, a system to connect battery-free IoT tags using LED bulbs. We make use of bulbs beyond illumination. We send data to the tags with visible light communication (VLC), and retrofit the bulbs with simple circuitry to enable the uplink channel current VLC systems lack, using Radio Frequency (RF) backscatter communication from the tags. Tags process and send data, harvesting energy from light and radio. We present our system design and implementation, evaluate it in preliminary simulation studies and experiments, and discuss the research challenges to develop a complete network architecture. BackVLC is the first work that combines VLC with RF backscatter. TRUE pub

We present the design of the first Visible Light Sensing (VLS) system that consumes only tens of μWs of power to sense and communicate. Unlike most existing VLS systems, we require no modification to the existing light infrastructure since we use unmodulated light as a sensing medium. We achieve this by designing a novel mechanism that uses solar cells to achieve a sub-μW power consumption for sensing. Further, we devise an ultra-low power transmission mechanism that backscatters sensor readings and avoids the processing and computational overhead of existing sensor systems. Our initial results show the ability to detect and transmit hand gestures or presence of people up to distances of 330m at a peak power of μWs. Further, we demonstrate that our system can operate in diverse light conditions (100 lx to 80 klx) where existing VLS designs fail due to saturation of the transimpedance amplifier (TIA).

There is the long-standing assumption that radio communication in the range of hundreds of meters needs to consume mWs of power at the transmitting device. In this paper, we demonstrate that this is not necessarily the case for some devices equipped with backscatter radios. We present LoRea an architecture consisting of a tag, a reader and multiple carrier generators that overcomes the power, cost and range limitations of existing systems such as Computational Radio Frequency Identification~(CRFID). LoRea achieves this by: First, generating narrow-band backscatter transmissions that improve receiver sensitivity. Second, mitigating self-interference without the complex designs employed on RFID readers by keeping carrier signal and backscattered signal apart in frequency. Finally, decoupling carrier generation from the reader and using devices such as WiFi routers and sensor nodes as a source of the carrier signal. An off-the-shelf implementation of LoRea costs 70 USD, a drastic reduction in price considering commercial RFID readers cost 2000 USD. LoRea's range scales with the carrier strength, and proximity to the carrier source and achieves a maximum range of 3.4 kilometre when the tag is located at 1 meter distance from a 28 dBm carrier source while consuming 70 microwatts at the tag. When the tag is equidistant from the carrier source and the receiver, we can communicate upto 75 meter, a significant improvement over existing RFID readers., Accepted and presented at ACM SenSys 2017, Delft, Netherlands

The sensing modalities available in an Internet-of-Things (IoT) network are usually fixed before deployment, when the operator selects a suitable IoT platform. Retrofitting a deployment with additional sensors can be cumbersome, because it requires either modifying the deployed hardware or adding new devices that then have to be maintained. In this paper, we present our vision and work towards passive sensor tags: battery-free devices that allow to augment existing IoT deployments with additional sensing capabilities without the need to modify the existing deployment. Our passive sensor tags use backscatter transmissions to communicate with the deployed network. Crucially, they do this in a way that is compatible with the deployed network's radio protocol, and without the need for additional infrastructure. We present an FPGA-based prototype of a passive sensor tag that can communicate with unmodified 802.15.4 IoT devices. Our initial experiments with the prototype support the feasibility of our approach. We also lay out the next steps towards fully realizing the vision of passive sensor tags.

The sensing capabilities of an Internet-of-Things (IoT) network are usually fixed at deployment. Adding new sensing modalities is a cumbersome process because it requires altering the deployed hardware. We introduce passive sensor tags that allow to easily and seamlessly add new sensors to existing IoT deployments without requiring hardware modifications or additional energy sources. Passive sensor tags employ backscatter communication to generate transmissions that can be decoded by the radio transceivers present in today's IoT devices. Furthermore, unlike recent works, our approach does not require dedicated infrastructure to generate the unmodulated carrier used for backscatter communication. The demo showcases our prototype of a passive sensor tag collecting sensor data and delivering it to unmodified commodity IoT devices using passive 802.15.4 transmissions.

We present DPT: a wireless sensor network protocol for bulk traffic that uniquely leverages electronically switchable directional (ESD) antennas. Bulk traffic is found in several scenarios and supporting protocols based on standard antenna technology abound. ESD antennas may improve performance in these scenarios; for example, by reducing channel contention as the antenna can steer the radiated energy only towards the intended receivers, and by extending the communication range at no additional energy cost. The corresponding protocol support, however, is largely missing. DPT addresses precisely this issue. First, while the network is quiescent, we collect link metrics across all possible antenna configurations. We use this information to formulate a constraint satisfaction problem (CSP) that allows us to find two multi-hop disjoint paths connecting source and sink, along with the corresponding antenna configurations. Domain-specific heuristics we conceive ameliorate the processing demands in solving the CSP, improving scalability. Second, the routing configuration we obtain is injected back into the network. During the actual bulk transfer, the source funnels data through the two paths by quickly alternating between them. Packet forwarding occurs deterministically at every hop. This allows the source to implicitly "clock" the entire pipeline, sparing the need of proactively synchronizing the transmissions across the two paths. Our results, obtained in a real testbed using 802.15.4-compliant radios and custom ESD antennas we built, indicate that DPT approaches the maximum throughput supported by the link layer, peaking at 21 4 kbit/s in the settings we test. SecThings

Radio tomographic imaging (RTI) enables device free localisation of people and objects in many challenging environments and situations. Its basic principle is to detect the changes in the statistics of radio signals due to the radio link obstruction by people or objects. However, the localisation accuracy of RTI suffers from complicated multipath propagation behaviours in radio links. We propose to use inexpensive and energy efficient electronically switched directional (ESD) antennas to improve the quality of radio link behaviour observations, and therefore, the localisation accuracy of RTI. We implement a directional RTI (dRTI) system to understand how directional antennas can be used to improve RTI localisation accuracy. We also study the impact of the choice of antenna directions on the localisation accuracy of dRTI and propose methods to effectively choose informative antenna directions to improve localisation accuracy while reducing overhead. Furthermore, we analyse radio link obstruction performance in both theory and simulation, as well as false positives and false negatives of the obstruction measurements to show the superiority of the directional communication for RTI. We evaluate the performance of dRTI in diverse indoor environments and show that dRTI significantly outperforms the existing RTI localisation methods based on omni-directional antennas.