About

Mostafa Ammar is a Regents' Professor with the School of Computer Science at the Georgia Institute of Technology. He served as Associate Chair of the School of Computer Science from 2006 to 2012. Dr. Ammar received the S.B. and S.M. degrees from the Massachusetts Institute of Technology and the Ph.D. degree from the University of Waterloo, Ontario, Canada. His research interests are in network architectures, protocols, and services, with contributions in multicast communication and services, multimedia streaming, content distribution networks, network simulation, disruption-tolerant networks, and more recently, mobile cloud computing and network virtualization. He has published extensively in these areas and has received research funding from federal and defense agencies as well as industry partners including NSF, DARPA, AFOSR, ARL, CISCO, IBM, Intel, BellSouth, and Sprint. Dr. Ammar has supervised 35 PhD students, many of whom have gone on to distinguished careers in academia and industry. He is the co-author of the textbook 'Fundamentals of Telecommunication Networks' published by Wiley-Interscience in 1994. He has served the networking research community in multiple roles, including as Editor-in-Chief of the IEEE/ACM Transactions on Networking from 1999 to 2003, and as co-TPC Chair for several major conferences. He currently serves on the steering committee of the IEEE Transactions on Mobile Computing. His awards include the IBM Faculty Partnership Award, Best Paper Award at the 7th WWW conference, the GT Outstanding Doctoral Thesis Advisor Award, the IEEE Technical Committee on Computer Communications Outstanding Service Award, the ACM Mobihoc Best Paper Award, and multiple College of Computing Faculty Mentor and Teaching Effectiveness Awards. Dr. Ammar was elected Fellow of the IEEE in 2002 and Fellow of the ACM in 2003.

Research topics

• Computer Science
• Telecommunications
• Real-time computing
• Computer network
• Computer Security
• Artificial Intelligence
• Embedded system
• Computer vision
• Engineering
• Electrical engineering
• Computer graphics (images)
• Operating system

Selected publications

• On Improving Interactivity in Video Conferencing Applications

  2025-10-21

  article

  Video conferencing applications (VCAs) are a vital tool for business, education, and other important purposes. However, VCAs are vulnerable to network latency, which can cause issues in client interactivity, such as increased overlaps, longer silence durations, and a degradation of the turn-taking structure. In this paper, we propose two systems for improving VCA interactivity in the presence of high network latency: one based on adjustment of the latency between pairs of clients, and the other based on notifying clients of their high latency. Both systems are suitable for deployment within the VCA selective forwarding unit, the central server for the conference. We evaluate the systems using a client behavioral model with accompanying interactivity metrics, and show, among other results, improvements of up to $50 \%$ in the overlap rate and $40 \%$ in useful conversation time, as well as restoration of the turn taking structure to the state with no network latency.

  PublisherDOI

• 5G MEC Computation Handoff for Mobile Augmented Reality

  2024-08-12 · 5 citations

  articleOpen access

  The combination of 5G and Multi-access Edge Computing (MEC) can significantly reduce application delay by lowering transmission delay and bringing computational capabilities closer to the end user. Therefore, 5G MEC could enable excellent user experience in applications like Mobile Augmented Reality (MAR), which are computation-intensive, and delay and jitter-sensitive. However, existing 5G handoff algorithms often do not consider the computational load of MEC servers, are too complex for real-time execution, or do not integrate easily with the standard protocol stack. Thus they can impair the performance of 5G MEC.To address this gap, we propose Comp-HO, a handoff algorithm that finds a local solution to the joint problem of optimizing signal strength and computational load. Additionally, Comp-HO can easily be integrated into current LTE and 5G base stations thanks to its simplicity and standard-friendly deployability. Specifically, we evaluate Comp-HO through a custom NS-3 simulator which we calibrate via MAR prototype measurements from a real-world 5G testbed. We simulate both Comp-HO and several classic handoff algorithms. The results show that, even without a global optimum, the proposed algorithm still significantly reduces the number of large delays, caused by congestion at MECs, at the expense of a small increase in transmission delay.

  PublisherOA PDFDOI

• SigningRing: Signature-based Authentication using Inertial Sensors on a Ring Form-factor

  2024-06-03 · 7 citations

  articleOpen accessSenior author

  Commercial smart rings have demonstrated their utility in health applications such as sleep monitoring and fitness tracking. However, given the small size of a ring form-factor, the applicable scenarios of smart rings are still under-explored. This paper presents SigningRing, which proposes a novel functionality for the smart ring: employing the inertial sensor embedded in the smart ring for secure and fast user authentication. To access an account, the user wearing the ring will move their finger in air, tracing a signature-like pattern, as if signing their name. In our evaluation with 18 volunteers, SigningRing achieves 97.4% in balanced accuracy, with 99.8% true negative rate and 95.1% true positive rate.

  PublisherOA PDFDOI

• QoE Metrics for Interactivity in Video Conferencing Applications

  2024-04-15 · 11 citations

  articleOpen access

  Video conferencing applications (VCAs) have become an indispensable tool for business, educational, and personal communications. There is, therefore, considerable interest in understanding and measuring the Quality of Experience (QoE) delivered by VCAs to their users. Video quality, one QoE measure, has received considerable attention in the literature. In this paper, we are concerned with another important aspect of VCA QoE, namely interactivity. We define this informally as the ability of a VCA to facilitate satisfying interaction among its users. Interactivity is primarily impacted by the media transmission latency among users which is, in turn, a function of network and application processing delays. Our goal in this work is to address two challenges in investigating interactivity-related QoE in VCAs. First, we propose a suite of meaningful quantifiable interactivity metrics, such as the proportion of silence time and rate of overlapping speech, that correlate well with conversational impairments and, hence, QoE perceptions. Second, we investigate scalable approaches for measuring these metrics. We develop a validated model for user behavior that enables realistic simulation of interactivity in VCA sessions. We also briefly consider an approach to measure interactivity metrics from packet traces. Through a set of experimental results, we demonstrate how our evaluation methodology provides a way for researchers, VCA service providers and network operators to perform large-scale investigations of how latency can interfere with user interactivity and impact VCA QoE.

  PublisherOA PDFDOI

• UWB-Auth: A UWB-based Two Factor Authentication Platform

  2024-05-20 · 4 citations

  articleOpen accessSenior author

  This paper presents an ultra-wideband (UWB) based two-factor authentication (2FA) platform, called UWB-Auth, designed as carriable or wearable devices. UWB-Auth eliminates various social engineering attacks, including phishing attack, 2FA-fatigue attack, co-located attack etc., on existing 2FA solutions like Duo and reveals simple and fast user interaction. The key innovation of UWB-Auth is a novel combination of location authentication via UWB, checking whether a legitimate token is in the vicinity of the login device with centimeter-level accuracy, followed by an abstraction layer allowing different knowledge-based or biometric-based authentication, ensuring the user's identity and intent to login. Moreover, UWB-Auth reverses the sequence in which the two factors are verified, providing robust defences against data breach. We develop 3 UWB-Auth prototypes: a key-chain token, a smartwatch with commercial knowledge/biometric factor, and a smartring with customized knowledge/biometric authentication algorithm to demonstrate the effectiveness of UWB-Auth. Overall, UWB-Auth completes the whole authentication process in 4 seconds, and completely rejects malicious requests when the token is 20cm or 10^\circ outside a small valid physical area near the login device. Even when a malicious entity gains physical access to the token, UWB-Auth stops attack attempts via knowledge and biometric authentication.

  PublisherDOI

• Safeguarding Smart Vehicles: GNN-Powered Real- Time IDS for CAN Networks

  2024-05-12

  article

  With the increasing integration of Controller Area Network (CAN) in modern vehicles, securing the communication network from malicious attacks is imperative. A novel Graph Neural Network (GNN)-based Intrusion Detection System (IDS) is proposed for real-time detection of several attacks, such as Denial of Service (DOS), fuzzy, and spoofing attacks. Our proposed model represents the CAN network as a graph, where nodes correspond to message arbitration ID and edges denote the communication sequence. Using Graph Attention Networks (GAT), our model captures the intricate relationships and dependencies between Electronic Circuit Units (ECUs), in real-time, enhancing its ability to discern normal behavior from malicious activity. The key to our system's success is its emphasis on achieving real-time capabilities. The GAT architecture optimizes computational efficiency for swift analysis of CAN traffic without compromising detection accuracy. Our system minimizes model complexity for enhanced deployability in resource-constrained vehicular environments. Comprehensive experiments on a diverse dataset showcase its ability to swiftly and accurately detect a range of attacks in real-time, with an overall accuracy of 99.75% for DOS attacks, 99.50% for fuzzy attacks, and 100% for spoofing attacks. Moreover, attack detection time is calculated to be 6.76 ms for DOS, 6.79 ms for fuzzy, and 6.69 ms for spoofing. These results made the model meet real-time detection constraints.

  PublisherDOI

• UTrack3D: 3D Tracking Using Ultra-wideband (UWB) Radios

  2024-06-03 · 8 citations

  articleOpen accessSenior author

  Recording 3D movements of a user's hand, robotic arms, or an object, even in a small confined space, has several applications in AR/VR, robotics, movement science, and 3D modeling and rendering. Existing camera-based tracking systems, though extremely accurate, are quite expensive and suffer from issues of occlusion and face difficulties when operating in extremely dark or extremely bright environments. We contend that trading-off a bit of accuracy while reducing costs and enabling more flexible operating environment might be worth exploring. This paper presents UTrack3D, a table-top setup that tracks the movements of an object in 3D space using embedded low-cost ultra-wideband (UWB) radios. The core idea is to continuously track the changes in phase as captured from UWB signal's channel impulse response (CIR) derived from the UWB messages received at a set of dual-antenna UWB receivers. Each of our custom dual-antenna receivers captures the UWB signal from two corners of a cuboid allowing us to perform relative phase measurements. The main challenges in the solution are caused by a location-dependant large variation in the signal amplitudes and corruption of the CIR due to multipath. UTrack3D tackles these challenges via a signal processing pipeline fusing a forward localization process which tracks the object's location using UWB CIR phase, and a posterior location check process, which validates the estimated location. UTrack3D is implemented on commercial-off-the-shelf (COTS) UWB chips, and provides a 90th percentile accuracy of 9 mm in a table-top 3D region (1.5m × 0.8m × 0.8m). We evaluate the effects of additional UWB receivers, effect of different movement speeds, and effect of small-scale signal blocking using different materials. We expect UTrack3D to allow researchers a rich new environment for further advancing UWB-based 3D tracking.

  PublisherOA PDFDOI

• The Price is Right? The Economic Value of Sharing Sensors

  IEEE Transactions on Computational Social Systems · 2023-12-07 · 1 citations

  article

  We study user's valuations of smartphone sensing resources and the factors mediating them through a systematic auction study with 108 bids from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$N=18$</tex-math></inline-formula> participants, two resource use conditions [fixed battery (FB) and variable battery (VB)] and three sensors (camera, microphone, and GPS) with differing energy and privacy costs. We use a second-price sealed-bid reverse auction as this allows us to elicit the participants’ truthful perceived value for sharing resources. We show that most users would be willing to share even highly-privacy intrusive sensors if they are sufficiently compensated. At the FB level, participants placed much lower value for sharing GPS (€13) than camera (€30) or microphone (€32.5). The values people place on sharing access to resources generally reflect four considerations: 1) the perceived value of the sensor type; 2) the value of the data captured by the sensor; 3) the impact of sharing on the device; and 4) personal variations related to sharing motives, personal tendencies, and the broader sharing context. We address the practical impact of our results by presenting two case studies (collaborative sensing and collaborative AI). Finally, we derive design implications for sharing sensing resources on personal devices.

  PublisherDOI

• ViSig

  Proceedings of the ACM on Interactive Mobile Wearable and Ubiquitous Technologies · 2023-03-27 · 9 citations

  articleOpen accessSenior author

  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 sensors for signal interpretation. Our key innovation is the fusion of ultra-wideband (UWB) sensors for capturing on-body distance measurements, inertial sensors (IMU) for capturing orientation of a few body segments, and photodiodes for finger signal recognition, enabling a robust interpretation of signals. By deploying only a small number of sensors, we show that body signals can be interpreted unambiguously in many different settings, including in games of Cricket, Baseball, and Football, and in operational safety use-cases such as crane operations and flag semaphores for maritime navigation, with &gt; 90% accuracy. Overall, we have seen substantial promise in this approach and expect a large body of future follow-on work to start using UWB and IMU fused modalities for the more general human pose estimation problems.

  PublisherOA PDFDOI

• A Measurement-Derived Functional Model for the Interaction Between Congestion Control and QoE in Video Conferencing

  Lecture notes in computer science · 2023-01-01 · 10 citations

  book-chapter
  PublisherDOI

Recent grants

• NETS-NECO: The WAM Continuum: Unified Design and Operation for Wireless and Mobile Networks

  NSF · $450k · 2008–2012

• ITR: Message Ferrying: Mobility-Assisted Data Delivery in Highly Partitioned Networks

  NSF · $325k · 2003–2007

• CSR: Small: Collaborative Research: Towards Collaborative Overlay Problem Diagnosis Using Evidential Reasoning and Adaptive Monitoring

  NSF · $250k · 2010–2013

• Nets-NBD: Routing in Multi-Layered Networks

  NSF · $352k · 2007–2011

• NeTS: Medium: Collaborative Research: Tango: Performance and Fault Management in Cellular Networks through Device-Network Cooperation

  NSF · $375k · 2014–2018

Frequent coauthors

• Ellen Zegura

  Georgia Institute of Technology

  101 shared

• Qi He

  22 shared

• Mustaque Ahamad

  Georgia Institute of Technology

  21 shared

• George F. Riley

  Georgia Institute of Technology

  17 shared

• Constantinos Dovrolis

  Atlanta Technical College

  13 shared

• Pan Hui

  13 shared

• Kevin C. Almeroth

  Osaka University

  12 shared

• Wenrui Zhao

  State Key Laboratory of Remote Sensing Science

  12 shared

Education

• Ph.D., Computer Science

  University of California, Los Angeles

  1992

• M.S., Computer Science

  University of California, Los Angeles

  1987

• B.S., Computer Science

  University of California, Los Angeles

  1985

Awards & honors

• IBM Faculty Partnership Award (1996)
• Best Paper Award at the 7th WWW conference (1998)
• GT Outstanding Doctoral Thesis Advisor Award (2006)
• Outstanding Service Award from the IEEE Technical Committee…
• ACM Mobihoc Best Paper Award (2012)