Research

Recent Projects

Concurrent Wi-Fi Connections for Highly Mobile Clients (Sep.2009 - Present)
Design, implementation, and evaluation of a system that provides for concurrent Wi-Fi connections in highly mobile scenarios where connections are both intermittent and fleeting.
Advisors:Mark Corner, Brian Levine, PRISMS Lab, UMass [+]
Abstract:
We present the first in-depth analysis of the performance of attempting concurrent AP connections from highly mobile clients. Previous solutions for concurrent Wi-Fi are limited to stationary wireless clients and do not take into account a myriad of mobile factors. Through an analytical model, optimization framework, and numerous outdoor experiments, we show that connection duration, AP response times, channel scheduling, available and offered bandwidth, node speed, and DHCP joins all affect performance. Building on these results, we design, implement, and evaluate a system, Spider, that establishes and maintains concurrent connections to 802.11 APs in a mobile environment. The system uses multi-AP selection, channel-based scheduling, and opportunistic scanning to maximize throughput while mitigating the overhead of association and DHCP. While Spider can manage multiple channels, we empirically demonstrate that it achieves maximum throughput when using multiple APs on a single channel. Our evaluation shows that Spider provides a 400% improvement in throughput and 54% improvement in connectivity over stock Wi-Fi implementations.

Related Documents:

Augmenting Mobile WiFi Networks (Sep.2008 - Present)
Design, implementation, and evaluation of methods to patch communication holes in mobile networks.
Advisors:Mark Corner, Brian Levine, PRISMS Lab, UMass [+]
Abstract:
Open Wi-Fi networks offer a chance to have ubiquitous, mobile connectivity by opportunistically leveraging previously deployed resources. Open Wi-Fi access points are densely deployed in many cities, offering high bandwidth at no cost to the mobile node. Unfortunately, Wi-Fi networks are riddled with coverage holes, resulting in poor network performance, even if planned for blanket coverage. To back this claim, we present the results of a measurement study of a small city's Wi-Fi network---both planned and unplanned ---using mobile nodes, verified with data collected from a second city. We find that holes can be broadly classified into two categories: (1) permanent holes due to a lack of Wi-Fi coverage; and (2) transient holes that are due to mobility and channel characteristics. We show that these holes have a severe, adverse effect on the performance of network transport protocols. In this work, we investigate efficient and inexpensive ways for fixing these holes.

Related Documents:
- Technical Report (UM-CS-2009-039)

Digital Image Enhancement Using a Vehicular Image Capturing Platform (Jun.2009 - Present)
Advisors:Rui Wang, Brian Levine, Mark Corner, Graphics Group and PRISMS Lab, UMass [+]
Abstract
In this work, we define the quality transfer problem and present an approach to tackle it: Given a low-quality image taken from a mobile phone, how could you enhance it in a visually plausible way to include additional details. Our approach is based on creating a temporal, gps-tagged high-quality image data-set by building a vehicular image capturing platform to autonomously capture high- quality images from dierent areas of the city. For a given low-quality input image, close images from the data-set are selected which would be used for enhancement in a combined process of salient feature extraction and patch matching. We present the results of applying this technique to samples of images taken in downtown Amherst.

Related Documents
- Preliminary Work: Technical Report (UM-CS-2011-02)

DOME: Large-scale & Diverse Mobie Wireless Testbed (Sep.2007 - Present)
Analysis and evaluation of real-world mobile networks through DOME, a large-scale mobile testbed with temporal, technological, and spatial diversity.
Advisors:Mark Corner, Brian Levine, PRISMS Lab, UMass [+]
Abstract:
Mobile systems and networking researchers confront a myriad of challenges, including power consumption, channel and radio characteristics, mobility, and node density. Alone, each of these factors is complex, and their combination can be unpredictable and hard to model. These challenges have led to a great deal of mobile research confined to the world of simulation, producing results with little-to-no real-world validation. Our Diverse Outdoor Mobile Environment (DOME) has been built in response to these challenges. DOME consists of 40 computer-equipped buses, numerous battery-powered nomadic nodes, hundreds of organic WiFi access points, and a 26-node municipal WiFi mesh network.

Related Documents
- Paper
- Technical Report (UM-CS-2009-023)

Past Projects

Securing Hierarchical Sensor Networks (M.Sc Thesis) (Jun.2006 - Jun.2007)
Design & implementation of a security scheme in a multi-level hierarchical wireless sensor network that allows secure & authenticated aggregation processing in all the levels & accounts for dynamic cluster re-organization.
Advisor:Tassos Dimitriou, Algorithm and Security Lab, AIT [+]
Motivation:
Hierarchical processing in sensor networks offers a number of operational advantages that cannot be met by flat networks of sensors with their inherent limitations on power and processing capabilities. Using hierarchical architectures and in-network processing of information the communication overhead is minimized by combining data coming from different sources - thus eliminating redundancy, minimizing the number of transmissions and eventually saving network energy. The focus of this research is on securing such processing hierarchies. In particular security mechanisms must be developed that need to be adaptive to changes in the roles taken by the sensors. Hence the whole process of receiving/aggregating data and disseminating commands must be secured and explain how the security protocol can support changes to the roles of sensors in the network. This is necessary since the cooperative and collaborative nature of sensor networks may necessitate the use of configuration actions that lead to energy savings. Hence the protocol must support admission of new sensors and reorganization of existing clusters.

Research Structure:
- Implement primitives that allow for cluster organization of the sensor nodes into multi-level hierarchies.
- Key establishment protocols between sensors and aggregators that allow for secure and authenticated aggregation processing for all levels of the network hierarchy.
- Extend the basic primitives to allow, for cluster reorganization and adaptive formation of new clusters taking security into mind.
- Study the efficiency and scalability properties of the protocol using a demonstrator to get experimental data.
Development Specific Details

The coding, testing and measurements is performed under TinyOS and on MICA2 and TMote platforms.
Real World Sensor Network Application for Protection of Caretta-Caretta Turtles (Jun.2006 - Jun.2007)
Design, implementation and deployment of a sensor network in order to protect endangered Caretta-Caretta turtles in Greek island of Zakynthos with support of WWF Hellas Organization.
Advisor:Tassos Dimitriou, Algorithm and Security Lab, AIT [+]
Motivation:
The loggerhead sea turtle known as the Caretta-Caretta has become an endangered specie that can only be found in the Mediterranean Sea. The turtles where leading a peaceful existence in the waters and beaches of Zakynthos but the extension and growth of touristy industry has interrupted their natural rhythms: many of them disappeared and the specie is now under direct threat. Our research group at AIT with the support of WWF Hellas Organization deploys a sensor network to monitor and protect an area close to the beach in Zakynthos from fire.

WWF claims that the ashes from a possible fire will be transferred to the beach in case of a rain, and that will damage the sand quality, affecting future nesting attempts.

Research Structure
- Design and implementation of the required distributed architecuter and related softwares
- Design, study, use and optimize power management techniques (especially in MAC Layer and Application Layer) in TinyOS suitable for the requirements of this application.
- Resolving real-world deployment challenges
Development Specific Details
- The coding, testing and measurements were performed under TinyOS and TMote platform.
Multiple and/or Directional Antennas for Sensor Network Nodes (Aug.2006 - Mar.2007)
Study the effects of using multiple and/or directional antennas on energy efficiency of transmission and reception as well as to find out new techniques for packet scheduling in MAC layer.
Advisor:Antonis Kalis, Wireless and Sensor Networks Lab, AIT [+]
Motivation:

One of the major causes of fast power drain in sensor networks is message overhearing. In order to resolve this problem several schemes have been proposed; try to eliminate message overhearing by associating schedules of periodic listen and sleep intervals. Most of these approaches are designed for sensor nodes with omni-directional antennas. However, in this research we are moving towards a new design of a MAC layer scheme that employs directional antennas for lifetime improvement of sensor nodes.

Research Structure:
- Design and implementation of several experiments dealing with different polarizations, different transmission powers, different distances and different angles in a network of multiple nodes with directional and omni-directional antennas.
- Optimal coloring is well studied.
Development Specific Details

The coding, testing and measurements are performed under TinyOS and CMU-Max (and RTLink) software environments and on MICAZ and CMU FireFly platforms respectively. A type of directional antenna created at AIT is also used in the experiments.
LEE: Lightweight Energy Efficient Encryption Algorithm (Sep.2006 - Mar.2007)
Design, analysis and implementation of an efficient block cipher suitable to be used in low-power tiny devices such as the sensor network nodes.
Advisor:Nikos Komninos, Algorithm and Security Lab, AIT [+]

Abstract:

Data confidentiality in wireless sensor networks is mainly achieved by RC5 and Skipjack encryption algorithms. However, both algorithms have their weaknesses, for example RC5 supports variable-bit rotations, which are computationally expensive operations and Skipjack uses a key length of 80-bits, which is subject to brute force attack. In this paper we introduce a light-weight energy-efficient encryption-algorithm (LEE) for tiny embedded devices, such as sensor network nodes. We present experimental results of LEE under real sensor nodes operating in TinyOS. We also discuss the secrecy of our algorithm by presenting a security analysis of various tests and cryptanalytic attacks.
Transparent Security Platform for Wireless Sensor Networks (Jan.2006 - Sep.2006)
Analysis, design & implementation of an energy-efficient, easy-to-use, scalable and flexible security platform under TinyOS that protects the WSN against replay and node capture attacks along with providing basic security services.
Advisor:Tassos Dimitriou, Algorithm and Security Lab, AIT [+]
Abstract:

We introduce a link layer security platform for wireless sensor networks. At the heart of this platform, lies our key management module facilitating an efficient scalable post-distribution key establishment that allows the platform to provide different security services. We have developed this framework under TinyOs and have tested it with MICA2 motes. To the best of our knowledge this is the first implemented security platform for sensor networks that provides acceptable resistance against node capture attacks and replay attacks. The provision of security services is completely transparent to the user of the framework. Furthermore, being highly scalable and lightweight, this platform is appropriate to be used in a wireless sensor network of hundreds of nodes.

Related Documents
- Paper [PDF]
.Sense: A Secure Framework for WSN Data Acquisition, Monitoring & Command (Jan. 2006 - Aug. 2006)
Design, implementation & deployment of a distributed system acting as a tool to be used by non-advanced end-users for sensor network data acquisition & command providing a transparent end-to-end security service & end-user real-time interaction with the sensor network.
Advisors:
- Tassos Dimitriou, Algorithm and Security Lab, AIT
- Tina Wong, CyLab, CMU
[+]
Abstract:

".Sense" is an end-to-end security framework for sensor network data acquisition, monitoring and command. In order to provide security service inside the sensor network two security protocols are implemented. The first is a key establishment algorithm in which sensor nodes agree on common keys to use for securing communications among them. The second is a scheme in which the base station can issue commands in authenticated manner to the network. We are also using typical security schemes such as SSL to connect the end-users to the system.

Related Documents
- ".Sense" Online!
- ".Sense" Poster [PPT]
- ".Sense" Poster Proposal [PDF]
- How ".Sense" started and developed: find more information (documents, resources, etc.) here
- ".Sense" Initial Development Blog
Defining Novel Fuzzy Logic Operators (B.Sc Thesis)(Jan. 2004 - Jan. 2005)
Surveying flaws of classical reasoning systems and Defining T-Norm & S-Norm fuzzy operators based on diffusion phenomenon in nature.
Advisor:Saeed Bagheri Shouraki, Computer Eng. Dept., Sharif University of Technology [+]

Abstract:

This research project aims to investigate classical logic and the contemporary technology, detect the existing drawbacks and provide some directions to resolve them. Fuzzy logic is emphasized as a method that is able to solve the mentioned deficiencies in classical reasoning systems, at least at the implementation level. Furthermore, we will introduce and elaborate certain characteristics of a fuzzy operator called IDS (Ink Drop Spread) and we will try to introduce novel fuzzy T-Norms and S-Norms based on this operator and the physical equation of dissolving ink in water. On the other hand, by noticing at the importance of the concept of language in modelling different phenomena, as well as being aware of the fact that fuzzy logic itself tries to adjust the modelling process to the natural language and the usual reasoning of the human brain, we provide certain explications on the very concept of language and its related theories as well as its relation with human mind. We also emphesize why "language" has to be seriously taken into account in the process of modelling different phenomena in the world.
Design and Implementation of Small-Sized Soccer Player Robots (Sep. 2003 - Feb. 2004)
Responsible for primary studies in image processing and system planning as well as conducted feasibility studies of practical playing algorithms that accounted for mechanical limits.
Advisor:Mohammad Taghi Manzoori, Computer Eng. Dept., Sharif University of Technology
Design and Implementation of Simulated Soccer Player Robots (Sep. 2001 - Feb. 2003)
Responsible for analysis, design and implementation of a multi-agent system of virtual soccer players in preparation for competition against virtual opponents without human interference during the game.
Advisor:Jafar Habibi, Computer Eng. Dept., Sharif University of Technology [+]

More Information:

This is the vision of the RoboCup community:

By the year 2050, develop a team of fully autonomous humanoid robots that can win against the human world soccer champion team.

The interesting vision of this community provides an opportunity for extensive research in multi-agent systems and artificial intelligence. There several leagues (humanoid robots, middle-sized robots, small-sized robots and simulated robots)in which different teams from different educational institutes participate in a yearly event. Check out more information about Robocup here.

Sharif University has been an active participant in RoboCup leagues for quite a number of years. I was a member of Sharif Aras and Sharif Arvand simulated soccer player robots teams during my undergraduate studies. Together with other members of Sharif Aras, we got the fifth rank in German Open 2001. Check out the detailed results of the matches here.

Work Experience

Developer (Sep.2006 - Present)
Development of a security system for distributed mobile phone games
AIT/Intralot Co., Athens, Greece
Analyst, Software Designer & Implementer (Jun.2003 - Jun.2005)
Analysis, design, and implementation of PCP (Phone Call Pager), a distributed CORBA application under Microsoft Windows.
Nebras Informatics Co., Tehran, Iran
Systems Analyst (Jun.2002 - Sep.2002)
Responsible for analysis phase of a system utility software to be used by computer engineering students as an aid to their course studies.
Danesh Pajouhan Firm, Tehran, Iran
Developer (Sep.2001 - Jun.2002)
Web designer and developer in Sharif Virtual University project.
Responsible for analysis & design of a secure system for Hadi Systems Co. in order to protect its audio/visual products from being captured or cracked.
Sharif Computing Center, Tehran, Iran