One of the major challenges faced by Augmented Reality (AR) systems is linking virtual content accurately on physical objects and locations. This problem is amplified for applications like mobile payment, device control or secure pairing that requires authentication. In this paper, we present an active LED tag system called GLITTER that uses a combination of Bluetooth Low-Energy (BLE) and modulated LEDs to anchor AR content with no a priori training or labeling of an environment. Unlike traditional optical markers that encode data spatially, each active optical marker encodes a tag’s identifier by blinking over time, improving both the tag density and range compared to AR tags and QR codes.We show that with a low-power BLE-enabled micro-controller and a single 5 mm LED, we are able to accurately link AR content from potentially hundreds of tags simultaneously on a standard mobile phone from as far as 30 meters. Expanding upon this, using active optical markers as a primitive, we show how a constellation of active optical markers can be used for full 3D pose estimation, which is required for many AR applications, using either a single LED on a planar surface or two or more arbitrarily positioned LEDs. Our design supports 108 unique codes in a single field of view with a detection latency of less than 400 ms even when held by hand.

In this demonstration, we present OpenChirp, an open-source Low-Power Wide-Area Networking (LPWAN) infrastructure. OpenChirp is a management framework that provides data context, storage, visualization, and access control over the web. At the physical layer of the system, we present LPRAN, a low-cost high-performance software-defined radio hardware platform that can receive signals up to -30 dB below the noise floor. Using our LPRAN hardware, it is possible to operate on raw I/Q streams in the cloud to perform collaborative tasks across multiple gateways such as jointly decoding weak signals and localization.

Low-Power Wide-Area Networks (LPWANs) are an emerging wireless platform which can support battery-powered devices lasting 10-years while communicating at low data-rates to gateways several kilometers away. Not all such devices will experience the promised 10 year battery life despite the high density of LPWAN gateways expected in cities. Transmission from devices located deep within buildings or in remote neighborhoods will suffer severe attenuation forcing the use of slow data-rates to reach even the closest gateway, thus resulting in battery drain. This paper presents Charm, a system that enhances both the battery life of client devices and the coverage of LPWANs in large urban deployments. Charm allows multiple LoRaWAN gateways to pool their received signals in the cloud, coherently combining them to detect weak signals that are not decodable at any individual gateway. Through a novel hardware and software design at the gateway, Charm carefully detects which chunks of the received signal need to be sent to the cloud, thereby saving uplink bandwidth. We present a scalable solution to decoding weak transmissions at city-scale by identifying the set of gateways whose signals need to be coherently combined over time. In evaluations over a test network and from simulations using traces from a large LoRaWAN deployment in Pittsburgh, Pennsylvania, Charm demonstrates a gain of up to 3x in range and 4x in client battery-life.

In this paper, we introduce Pulsar, a wireless time transfer platform that can achieve clock synchronization to better than five nanosecond between indoor or GPS-denied devices. Nanosecond-level clock synchronization is a missing capability for many real-time applications like next-generation wireless systems that leverage spatial multiplexing to improve channel capacity and provide services like time-of-flight localization. With fine-grained synchronization, both clock stability and propagation delays introduce significant sources of error. Pulsar leverages a stable clock source derived from a Chip-Scale Atomic Clock (CSAC) along with an Ultra-WideBand (UWB) radio able to perform sub-nanosecond packet timestamping to estimate and correct for clock offsets. We design and evaluate a proof-of-concept network-wide synchronization protocol for Pulsar that selects low-jitter links to both estimate the location of nodes and reduce cumulative synchronization error across multiple hops. The Pulsar platform and protocol together provide a phase synchronized one pulse per second (1PPS) signal and 10 MHz reference clock that can be easily integrated with typical enduser applications like software-defined radios and communication systems. We experimentally evaluate the Pulsar platform in terms of clock synchronization accuracy, Allan deviation between pairwise clocks and ranging accuracy to show a clock synchronization of better than five nanoseconds per hop with an average of 2.12 ns and a standard deviation of 0.84 ns. The platform is able to identify and avoid clock error in cases where there is heavy multi-path or non-Line-of-Sight signals.

Having a shared and accurate sense of time is critical to distributed Cyber-Physical Systems (CPS) and the Internet of Things (IoT). Thanks to decades of research in clock technologies and synchronization protocols, it is now possible to measure and synchronize time across distributed systems with unprecedented accuracy. However, applications have not benefited to the same extent due to limitations of the system services that help manage time, and hardware-OS and OS-application interfaces through which timing information flows to the application. Due to the importance of time awareness in a broad range of emerging applications, running on commodity platforms and operating systems, it is imperative to rethink how time is handled across the system stack. We advocate the adoption of a holistic notion of Quality of Time (QoT) that captures metrics such as resolution, accuracy, and stability. Building on this notion we propose an architecture in which the local perception of time is a controllable operating system primitive with observable uncertainty, and where time synchronization balances applications' timing demands with system resources such as energy and bandwidth. Our architecture features an expressive application programming interface that is centered around the abstraction of a timeline - a virtual temporal coordinate frame that is defined by an application to provide its components with a shared sense of time, with a desired accuracy and resolution. The timeline abstraction enables developers to easily write applications whose activities are choreographed across time and space. Leveraging open source hardware and software components, we have implemented an initial Linux realization of the proposed timeline-driven QoT stack on a standard embedded computing platform. Results from its evaluation are also presented.

In this demonstration we present Pulsar, a speed-of-light propagation-aware time synchronization platform. Pulsar uses ultra-wideband (UWB) radios for time transfer with each node backed by a chip scale atomic clock (CSAC) that in combination are able to provide accuracy on the order of 10's of nanoseconds for indoor applications. The demonstration will show two Pulsar boards generating a tightly synchronized PPS output that is able to adjust for the distance between the nodes. Even without communication, the devices maintain synchronization over multiple seconds due to a stable CSAC clocking the system.