My research work spans multiple areas including computer networks, wireless communication, mobile computing, sensor networks and system building. Over the time I contributed to the following projects:

Long Range RF Energy Harvesting

Uninterrupted long range RF energy harvesting can revolutionize current battery-free sensing and networking market. Existing RF energy harvesting is either opportunistic through ambient signals or on demand through dedicated nearby transmitters (readers). This work envisions long range multiband RF energy harvesting using a few multitband readers that supplement ambient energy. We design and implement multiband readers for RF energy harvesting that politely co-exists with traditional communication radios through a combination of careful scheduling of transmissions, carrier sense and signal repeating. Moreover, we propose a frequency selection algorithm to efficiently transfer energy through the most rewarding frequencies.

Publications

    • Long Range Wireless Energy Harvesting using Multiband Non-Interfering Energy Source
      Mohamed Ibrahim, Atul Bansal, Kuang Yuan, and Swarun Kumar
      Under review 2022.
      [PDF] [BibTex]

WiFi Fine Time Measurements

Precise indoor positioning, to obtain room-level location or to support indoor navigation has remained stubbornly challenging due to the large effort required to create and maintain WiFi surveys. Similar challenges exist in urban canyons, where GPS accuracy is degraded due to multipath and WiFi positioning cannot entirely replace it. Recently, IEEE 802.11-2016 standardized a FTM protocol that supports such ideas. I introduced for the academic community an open platform for experimenting with FTM as well as a general, repeatable, and accurate measurement framework for evaluating time-based ranging systems. With this open FTM tool, various research applications can be prototyped and experimented for indoor and outdoor sensing. My research shows as well that vehicles can be tracked with meter-level accuracy using WiFi FTMs, an order of magnitude improvement over current mass market vehicle built-in navigation.

Publications

    • Vi-Fi: Associating Moving Subjects across Vision and Wireless Sensors
      Hansi Liu, Abrar Alali, Mohamed Ibrahim, Bryan Bo Cao, Nicholas Meegan, Hongyu Li, Marco Gruteser, Shubham Jain, Kristin Dana, Ashwin Ashok, Bin Cheng, Hongsheng Lu
      ACM/IEEE IPSN 2022.
      [PDF] [BibTex]
    • Wi-Go: Accurate and Scalable Vehicle Positioning using WiFi Fine Timing Measurement
      Mohamed Ibrahim, Ali Rostami, Bo Yu, Hansi Liu, Minitha Jawahar, Viet Nguyen, Marco Gruteser, Fan Bai, and Richard Howard
      ACM MobiSys 2020.
      [PDF] [BibTex]
    • Verification: Accuracy Evaluation of WiFi Fine TimeMeasurements on an Open Platform
      Mohamed Ibrahim, Hansi Liu, Minitha Jawahar, Viet Nguyen, Marco Gruteser, Richard Howard, Bo Yu, and Fan Bai
      ACM MobiCom 2018.
      [PDF] [BibTex]

Enforcing Radio Astronomy Quiet Zonen

A clear realization of how wireless networking can benefit from wireless sensing is shown in TranQuil. In which, we address the problem of detecting and localization WiFi AP interfering with Radio astronomy observatories from a kilometer away. However, the range of a WiFi AP is around 100 m, it can still interfere with extremely sensitive radio astronomy towers, which listen to cosmic radiations from space. While radio quiet zones are enforced by law to prohibit transmissions in nearby areas to such observatories, interference still happens due to lack of awareness or accidentally. In this project, we design a long range detection and localization system of WiFi transmitter using an enhanced WiFi beacon packet detection pipeline and time-difference-of-arrival techniques. We evaluate this system in Green Bank observatory, one of the largest radio astronomy observatory in the world, and our system can track WiFi interferer with median error of 13.2 m from about a kilometer away.

Publications

Body-guided Communication

This work studies how wireless signal propagates over human body for secure, low-energy and less interference communication. In this work, we propose on body guided communication using capacitive coupling to secure every touch when users interact with a variety of devices and objects. With this communication system, the transmitted signal only travels through a user’s body and limits the ability to decode the signal off the body. Moreover, this system can construct an energy efficient and secure network of on body devices and support various applications in smart homes and cities. For example, identifying each person in a household through screen touching can personalize the usage of their home amenities and provide convenient and energy efficient access control mechanism.

Publications

Activity Sensing using Ceiling Photosensors

This paper explores the feasibility of tracking motion and activities of humans using visible light. Shadows created by casting visible light on humans and objects are sensed using sensors that are embedded along with the light sources. Existing Visible Light Sensing (VLS) techniques require either light sensors deployed on the floor or a person carrying a device. Our approach seeks to measure light reflected off the floor to achieve an entirely device-free and light-source based system. We co-locate photosensors with LED light sources to observe the changes in light level occurring on the floor.

Publications

Over-the-air TV Detection using Mobile Phones

This work introduces a mobile sensing technique to detect a nearby active television, the channel it is tuned to, and whether it is receiving this channel over the air. This technique can find applications in tracking TV viewership, second screen services and advertising, as well as improving the efficiency of TV whitespace spectrum usage. The technique uses a three-stage detection process. It first uses a probabilistic model on audio recordings from mobile phones to detect likely TV sounds in the area. It then correlates the recording with known TV channel audio to identify the channel and improve detection robustness. Finally, it applies a latency analysis to determine whether programming is received over-the-air or through alternate means such as cable or satellite TV.

Publications

Large-Scale Framework for Cognitive Radio Routing Protocols Testing

Building testbeds for Cognitive Radio Networks (CRNs) is one of the main challenges that can affect the wide deployability of such networks. In this project we develop a framework that facilitates the development of cost-efficient large-scale CRNs routing protocols testbeds. The framework allows the designers to focus on the CRNs routing protocols by abstracting the PHY and MAC layers while providing the necessary cross layer functionalities. CogFrame, our developed framework, allows the development of testbeds that work with standard computers and WiFi cards to reduce the cost while allowing integrating with other special hardware for more flexibility. It also provides different modules for implementing and emulating complex scenarios such as regulatory authority policies, mobility management, topology management.

Publications

Project Websites

CellSense: An Accurate Energy-Efficient GSM Positioning System

Context-aware applications have been gaining huge interest in the last few years. With cell phones becoming ubiquitous computing devices, cell phone localization has become an important research problem. In this project, we present CellSense, a probabilistic RSSI-based fingerprinting location determination system for GSM phones. We discuss the challenges of implementing a probabilistic fingerprinting localization technique in GSM networks and present the details of the CellSense system and how it addresses these challenges. We then extend the proposed system using a hybrid technique that combines probabilistic and deterministic estimation to achieve both high accuracy and low computational overhead.

Publications