Computer Science and Engineering

WiFi mesh networks with outdoor links have become an attractive
option to provide cost-effective broadband connectivity
to rural areas, especially in developing regions. It is
well understood that a TDMA-based approach is necessary
to provide good performance over such networks. While preliminary
prototypes of TDMA-based MAC protocols have
been developed, there is no implementation-based validation/
evaluation in multi-hop settings. In this work, we describe
the elements of a multi-hop MAC implementation
based on the open-source MADWIFI driver. We also present
an evaluation, with a detailed accounting of the various overheads,
on a 4-hop (5-node) path. We show that our implementation
has no system overheads, achieves good throughput,
and low delay/jitter.

The FRACTEL project makes use of long distance wireless links to connect rural and inaccessible areas to a nearby city providing internet, voice and video connectivity. We shall use high gain directional antennas and sectorized antennas for long distance communication over off-the-shelf WiFi hardware. Shorter distance links extend this connectivity to nearby locations. To support long distance links and quality of service requirements, we shall run a TDMA schedule over the FRAC-TEL infrastructure. In this project, we look at the issues of node synchronization which is critical for correct working of the TDMA schedule. Since FRACTEL has a tree topology, we can perform synchronization between two levels at a time and finally get the entire network to know the global clock time. Another aspect of this project is to optimize the power utilization of the nodes. We shall use a proxy based wakeup mechanism to let the main devices sleep while another low power device stays awake and listens for any wakeup calls. When it receives such a signal, it wakes up the main board. In this report, we discuss the steps taken so far in these aspects and the path ahead.

The retail business in India is expanding in leaps and bounds. With increasing competition, each retailer needs to correctly cope up with the impending demand. The retail firms need to take into account various factors including the lead time and the seasonality of goods. In this report, we study the various techniques used by retailers in India to perform demand forecasting and analysis. We present a case study done at Lakewood Malls Pvt. Ltd. where we understand that historical data and judgemental techniques are primarily used for forecasting of demand.

Inertial sensors continuously track the 3D orientation of a flying drone, serving as the bedrock for maneuvers and stabilization. However, even the best inertial measurement units (IMU) are prone to various types of correlated failures. We consider using multiple GPS receivers on the drone as a failsafe mechanism for IMU failures. The core challenge is in accurately computing the relative locations between each receiver pair, and translating these measurements into the drone's 3D orientation. Achieving IMU-like orientation requires the relative GPS distances to be accurate to a few centimeters-a difficult task given that GPS today is only accurate to around 1-4 meters. Moreover, GPS-based orientation needs to be precise even under sharp drone maneuvers, GPS signal blockage, and sudden bouts of missing data. This paper designs SafetyNet, an off-the-shelf GPS-only system that addresses these challenges through a series of techniques, culminating in a novel particle filter framework running over multi-GNSS systems (GPS, GLONASS, and SBAS). Results from 11 sessions of 5-7 minute flights report median orientation accuracies of 2 • even under overcast weather conditions. Of course, these improvements arise from an increase in cost due to the multiple GPS receivers, however, when safety is of interest, we believe that tradeoff is worthwhile. CCS Concepts •Computer systems organization → Embedded and cyberphysical systems;

This paper explores the possibility of injecting mobility into wireless network infrastructure. We envision WiFi access points on wheels that move to optimize user performance. Movements need not be all around the floor, neither do they have to operate on batteries. As a first step, WiFi APs at home could remain tethered to power and Ethernet outlets while moving in small areas (perhaps under the couch). If such systems prove successful, perhaps future buildings and cities could offer explicit support for network infrastructure mobility. This paper begins with a higher level discussion of robotic wireless networks-the opportunities and the hurdles-and then pivots by developing a smaller slice of the vision through a system called iMob. With iMob, a WiFi AP is mounted on a Roomba robot and made to periodically move within a 2x2 sqft region. The core research questions pertain to finding the best location to move to, such that the SNRs from its clients are strong, and the interferences from other APs are weak. Our measurements show that the richness of wireless multipath offers significant opportunitieseven within a 2x2 sqft region, locations exist that are 1.7x better than the average location in terms of throughput. When multiple APs in a neighborhood coordinate, the gains can be even higher. In sum, although infrastructure mobility has been discussed in the context of Google Balloons, ad hoc networks, and delay tolerant networks, we believe that the possibility of moving our personal devices in homes and offices is relatively unexplored, and could open doors to new kinds of innovation.

The coronavirus pandemic is altering our way of life. As more establishments open, there is an expectation that people will follow physical distancing guidelines. The implementation, however, is poor; just putting up warning signs appealing the general public to keep a distance of 6 feet from others is hardly enough. In this paper we consider the design of a wearable device that raises an alarm if another similar device is detected within a set distance. It uses off-the-shelf ultra-wideband radio technology for real-time, accurate distance estimation from others in the vicinity. We design an one-to-all ranging protocol that is able to accurately estimate distance to neighboring devices and warn the user if the distance falls below a certain established threshold within a short time. The device must compensate for human occlusions and avoid unnecessary warnings when physical barriers exist between devices. We implement and evaluate our protocol in a small testbed with custom prototype hardware as well as in simulation. Our ranging protocol is capable of performing up to 10 distance measurements per second, while avoiding packet collisions. The overall percentage of rangings completed is around 65% in a 10-node network, and the distance accuracy is around 20cm even with frequent human occlusions. We believe this prototype will provide the first steps to ensure physical distancing in various real-world settings.

This paper shows the feasibility of identifying liquids by shining ultra-wideband (UWB) wireless signals through them. The core opportunity arises from the fact that wireless signals experience distinct slowdown and attenuation when passing through a liquid, manifesting in the phase, strength, and propagation delay of the outgoing signal. While this intuition is simple, building a robust system entails numerous challenges, including (1) pico-second scale time of flight estimation, (2) coping with integer ambiguity due to phase wraps, (3) pollution from hardware noise and multipath, and (4) compensating for the liquid-container's impact on the measurements. We address these challenges through multiple stages of signal processing without relying on any feature extraction or machine learning. Instead, we model the behavior of radio signals inside liquids (using principles of physics), and estimate the liquid's permittivity, which in turn identifies the liquid. Experiments across 33 different liquids (spread over the whole permittivity spectrum) show median permittivity error of 9%. This implies that coke can be discriminated from diet coke or pepsi, whole milk from 2% milk, and distilled water from saline water. Our end system, LiquID, is cheap, non-invasive, and amenable to real-world applications.

In this poster, we present the potential of extending 6Fit-a-Part, our recently proposed physical distancing platform, to enable interactive physical games in school campuses despite COVID-19 restrictions. To minimize the risk of infection, traditional physical games must be modified such that the inter-player distance remains beyond 6 feet at all times. Our wearable electronic gadget that beeps when it approaches another similar device can facilitate such games, however, it must first solve 3 fundamental challenges: high accuracy, low delay, and high robustness. We highlight that 6Fit-a-Part adopts an improved two way ranging protocol using ultra-wideband radio (UWB) which can provide accurate inter-player distance measurements in real-time. Furthermore, 6Fit-a-Part leverages wireless channel features to perform occlusion detection continuously so that erroneous measurements caused by human occlusions can be corrected. 6Fit-a-Part is designed to be a lightweight wearable device mak...

WiFi mesh networks with outdoor links have become an attractive option to provide cost-effective broadband connectivity to rural areas, especially in developing regions. It is well understood that a TDMA-based approach is necessary to provide good performance over such networks. While preliminary prototypes of TDMA-based MAC protocols have been developed, there is no implementation-based validation/evaluation in multi-hop settings. In this work, we describe the elements of a multi-hop MAC implementation based on the open-source MADWIFI driver. We also present an evaluation, with a detailed accounting of the various overheads, on a 4-hop (5-node) path. We show that our implementation has no system overheads, achieves good throughput, and low delay/jitter.

First responders, a critical lifeline of any society, often find themselves in precarious situations. The ability to track them real-time in unknown indoor environments, would significantly contributes to the success of their mission as well as their safety. In this work, we present the design, implementation and evaluation of TrackIO—a system capable of accurately localizing and tracking mobile responders realtime in large indoor environments. TrackIO leverages the mobile virtual infrastructure offered by unmanned aerial vehicles (UAVs), coupled with the balanced penetration-accuracy tradeoff offered by ultra-wideband (UWB), to accomplish this objective directly from outside, without relying on access to any indoor infrastructure. Towards a practical system, TrackIO incorporates four novel mechanisms in its design that address key challenges to enable tracking responders (i) who are mobile with potentially non-uniform velocities (e.g. during turns), (ii) deep indoors with challenge...

High-precision tracking of a pen-like instrument's movements is desirable in a wide range of fields spanning education, robotics, and art, to name a few. The key challenge in doing so stems from the impracticality of embedding electronics in the tip of such instruments (a pen, marker, scalpel, etc.) as well as the difficulties in instrumenting the surface that it works on. In this paper, we present ITrackU, a movement digitization system that does not require modifications to the surface or the tracked instrument's tip. ITrackU fuses locations obtained using ultra-wideband radios (UWB), with an inertial and magnetic unit (IMU) and a pressure sensor, yielding multidimensional improvements in accuracy, range, cost, and robustness, over existing works. ITrackU embeds a micro-transmitter at the base of a pen which creates a trackable beacon, that is localized from the corners of a writing surface. Fused with inertial motion sensor and a pressure sensor, ITrackU enables accurate ...

This paper explores the possibility of bringing IoT to sports analytics, particularly to the game of Cricket. We develop solutions to track a ball’s 3D trajectory and spin with inexpensive sensors and radios embedded in the ball. Unique challenges arise rendering existing localization and motion tracking solutions inadequate. Our system, iBall, mitigates these problems by fusing disparate sources of partial information – wireless, inertial sensing, and motion models – into a non-linear error minimization framework. Measured against a mm-level ground truth, the median ball location error is at 8cm while rotational error remains below 12◦ even at the end of the flight. The results do not rely on any calibration or training, hence we expect the core techniques to extend to other sports like baseball, with some domain-specific modifications.

IoT-based analytics for sports has several applications. Patterns of balls, racquets, and players are being analyzed for coaching, strategic insights, and predictions. iBall provides a significantly cheaper alternative to million dollar camera-based solutions. Real-time analytics should be possible anytime, anywhere. Aspiring players in local clubs could read out their own performance from their smartphone screens; school coaches could offer quantifiable feedback to their students. In this paper, we elaborate on our experience in developing iBall’s IoT platform – particularly on details from early ball prototyping, ground truth extraction and the technical platform. This includes several challenges in system design and engineering to satisfy various requirements of sensor embedding, impact resistance, high sampling rate, sensor calibration, synchronization, etc. iBall considers a case study of cricket ball tracking. However, the platform is also applicable to tracking other sporting...

A wireless signal travels through various paths and reaches a receiver multiple times. These paths remain fairly stable in an undisturbed environment if nothing is moving in the space. However, if humans are present in such a space, reflections from their bodies will constantly alter the multi-path behavior of the wireless signals and cause disturbances in the received wireless power-delay profile. This work explores various ways in which such signal disturbances can be used to perform intrusion detection providing an enhanced physical security system. Since wireless signals can pass through walls, they can monitor a larger multi-room area without requiring additional hardware. We further explore if it is possible to allow a friendly entity, such as a pet or a guard, to freely move in the monitored space without triggering an alarm, and yet remain vigilant about intrusions into the home. This work explores using wireless disturbances in 4 modes: (1) line-of-sight obstruction, (2) detecting proximal movements, (3) separating friendly movements, (4) using minimal infrastructure. We demonstrate intrusion detection capabilities using ultra-wideband (UWB) wireless radios. Our preliminary results show promise, and we feel confident that this work will open up a new direction for physical security spanning use cases such as home security, security of high-value public spaces (such as museums), and industrial security. CCS CONCEPTS • Computer systems organization → Sensors and actuators; • Human-centered computing → Ubiquitous and mobile computing systems and tools.

In this work, we explore if informative art can represent a user's indoor trajectory and promote user's self-reflection, creating a new type of interactive space. Under the assumption that the simplicity of a digital picture frame can be an appealing way to represent indoor activities and further create a dyadic relationship between users and the space they occupy, we present Travelogue, a pictureframe like self-contained system which can sense human movement using wireless signal reflections in a device free manner. Breaking away from traditional dashboard-based visualization techniques, Travelogue only renders the high-level extent and location of users' activities in different informative arts. Our preliminary user study with 12 participants shows most users found Travelogue intuitive, unobtrusive, and aesthetically pleasing, as well as a desired tool for self-reflection on indoor activity. CCS CONCEPTS • Human-centered computing → Ubiquitous and mobile computing systems and tools.

Visual body signals are designated body poses that deliver an application-specific message. Such signals are widely used for fast message communication in sports (signaling by umpires and referees), transportation (naval officers and aircraft marshallers), and construction (signaling by riggers and crane operators), to list a few examples. Automatic interpretation of such signals can help maintaining safer operations in these industries, help in record-keeping for auditing or accident investigation purposes, and function as a score-keeper in sports. When automation of these signals is desired, it is traditionally performed from a viewer's perspective by running computer vision algorithms on camera feeds. However, computer vision based approaches suffer from performance deterioration in scenarios such as lighting variations, occlusions, etc., might face resolution limitations, and can be challenging to install. Our work, ViSig, breaks with tradition by instead deploying on-body s...