Pico-satellite (picosat) constellations aim to become the de facto connectivity solution for Internet of Things (IoT) devices. These constellations rely on a large number of small picosats and offer global plug-and-play connectivity at low data rates, without the need for Earth-based gateways. As picosat constellations scale, they run into new bottlenecks due to their traditional medium access designs optimized for single (or few) satellite operations. We present CosMAC - a new constellation-scale medium access and scheduling system for picosat networks. CosMAC includes a new overlap-aware medium access approach for uplink from IoT to picosats and a new network layer that schedules downlink traffic from satellites. We empirically evaluate CosMAC using measurements from three picosats and large-scale trace-driven simulations for a 173 picosat network supporting 100k devices. Our results demonstrate that CosMAC can improve the overall network throughput by up to 6.5X over prior state-of-the-art satellite medium access schemes.

Implantable and edible medical devices promise to provide continuous, directed, and comfortable healthcare treatments. Communicating with such devices and localizing them is a fundamental, but challenging, mobile networking problem. Recent work has focused on leveraging near field magnetism-based systems to avoid the challenges of attenuation, refraction, and reflection experienced by radio waves. However, these systems suffer from limited range, and require fingerprinting-based localization techniques. We present InnerCompass, a magnetic backscatter system for in-body communication and localization. InnerCompass relies on new magnetism-native design insights that enhance the range of these devices. We design the first analytical model for magnetic-field-based localization, that generalizes across different scenarios. We've implemented InnerCompass and evaluated it in porcine tissue. Our results show that Inner-Compass can communicate at 5 Kbps at a distance of 25 cm, and localize with an accuracy of 5 mm.

The advent of radio sensing that works through walls & obstacles challenges the notion of indoor privacy. An eavesdropper can deploy such sensing to snoop on their neighbors and a smart sensor embedded with such sensing capabilities can perform large scale behavioral and health data mining. We present RF-Protect, a new framework that enables privacy by injecting fake humans in the sensed data. RF-Protect consists of a novel hardware reflector design that modifies radio waves to create reflections at arbitrary locations in the environment and a new generative mechanism to create realistic human trajectories. RF-Protect's design doesn't require any high bandwidth hardware or physical motion. We implement RF-Protect using commodity hardware and validate its ability to generate fake human trajectories.

Large constellations of Low Earth Orbit satellites promise to provide near real-time high-resolution Earth imagery. Yet, getting this large amount of data back to Earth is challenging because of their low orbits and fast motion through space. Centralized architectures with few multi-million dollar ground stations incur large hour-level data download latency and are hard to scale. We propose a geographically distributed ground station design, L2D2, that uses low-cost commodity hardware to offer low latency robust downlink. L2D2 is the first system to use a hybrid ground station model, where only a subset of ground stations are uplink-capable. We design new algorithms for scheduling and rate adaptation that enable low latency and high robustness despite the limitations of the receive-only ground stations. We evaluate L2D2 through a combination of trace-driven simulations and real-world satellite-ground station measurements. Our results demonstrate that L2D2's geographically distributed design can reduce data downlink latency from 90 minutes to 21 minutes.

We present a demonstration of Jive (Joint Integration of VLC and Encryption), a novel encryption key sharing framework utilizing the emerging wireless technology Visible Light Communication (VLC). Based on the idea of transmitting data by modulating light, we are able to (1) share a secret key within a constrained physical space and (2) leverage this shared key to communicate encrypted information among co-located mobile devices. In this demonstration, we showcase our complete implementation of Jive: a VLC transmitter and a VLC receiver. Both endpoints are built using off-the-shelf components. The VLC link is used to distribute a randomly generated secret key that can only be "observed" by VLC receivers that are physically in the same space as the transmitter. Each receiver is connected over a serial connection to an Android device; we developed applications for Android that take the key from the VLC receiver and subsequently use the key to encrypt or decrypt application data. Our demo invites participants to create their own encrypted messages in the Android application and interact with the VLC prototype as it transmits encryption keys, thus illustrating our system's ability to bootstrap security among physically co-located devices.

This paper investigates a novel encryption key sharing mechanism using the emerging wireless technology Visible Light Communication (VLC). Based on the idea of transmitting data by modulating light, we are able to (1) share a secret key within a constrained physical space and (2) communicate encrypted information among co-located mobile devices using the shared key. We present the demonstration Jive (Joint Integration of VLC and Encryption), a framework to support secret key sharing over Visible Light Communication. In defining Jive, we tackle challenges related to data encoding, message synchronization, and environmental noise to build a reliable, low complexity system using off-the shelf hardware. Our system is capable of sending encryption keys at speeds of more than 750bps using ultra short, high speed light pulses imperceptible to the human eye. Additionally, we have developed an application for Android that interfaces with the VLC device through serial communication so that applications running on mobile devices can subsequently use the keys to encrypt application data. Experimental results illustrate the high accuracy of our system across a variety of different variables. Finally, we position our system for use by a variety of applications that require a high-level of data security among physically co-located devices.