Overview
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I am a Ph.D. candidate in WiNG (Wireless Networking
Group), UCLA Computer Science Department. My advisor is Prof. Songwu Lu. The following is the
list of ten research projects that I have been working on during my
Ph.D. years. In specific, I am the primary contributor for both design and
implementation of SCOPE, TTDD, URSA and UCAN, covering wireless and
mobile networking, sensor networking, wireless
network security, and hybrid wireless network architecture.
1. Wireless Mobile Networking
I worked as a summer intern at Mobile Networking Research Department, Bell-Labs in 2002: 5. Hybrid 3G/IEEE 802.11 Network Architecture |
Projects
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SCOPE: Self-coordinating Localized Packet Scheduling in Wireless Ad-hoc
Networks |
Overview: Distributed packet scheduling in a multihop, wireless
ad-hoc network is challenging since there is no centralized management or
infrastructure support:
EMLM-FQ achieves statistical short-term throughput and delay bounds over the shared wireless channel. We evaluate the effectiveness and efficiency of our design through analytical analysis, extensive simulations in ns-2, and our implementation in Mica2 Mote with CC1000 radio. For the simulator and TinyOS codes please email me. Design Goals: The solution for fair queueing in ad hoc wireless networks must:
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TRACK: TCP PeRformance in Ad-hoC networKs |
Overview: Our study of TCP over ad-hoc multihop wireless
networks reveals the following interesting results:
People:
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DIRAC: Distributed Software Router Architecture for Mobile Computing
Environment |
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Routers are expected to play an important role in the IP-based wireless
data network. Although a substantial number of techniques have been
proposed to improve wireless network performance under dynamic wireless
channel conditions and host mobility, a system support framework is still
missing. DIRAC is a flexible software-based router system that is designed for wireless networks to facilitate the implementation and evaluation of various channel-adaptive and mobility-aware protocols. DIRAC adopts a distributed architecture that is composed of two parts: a Router Core (RC) shared by the wireless subnets, and a Router Agent (RA) at each access point/base station. RAs expose wireless link-layer information to the RC and enforce the control commands issued by the RC. This approach allows the router to make adaptive decisions based on link-layer information feedback. It also permits the router to enforce its policies (e.g., policing) more effectively through underlying link-layer mechanisms. DIRAC is implemented as Click software modules, using off-the-shelf wireless hardware and commodity PC. We implement under DIRAC the prototypes of three wireless network services: link-layer assisted fast handover, channel-adaptive scheduling, and link-layer enforced policing. Our implementation and experiments show that our distributed wireless router provides a flexible framework, which enables advanced network-layer wireless services that are adaptive to channel conditions and host mobility. People:
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TTDD: Two-tier Data Dissemination in Large-scale Sensor
Networks |
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Sink mobility brings new challenges to large scale sensor networking. It
suggests that information about mobile sinks locations be continuously
propagated through the sensor field to keep all sensor nodes updated with
the direction of forwarding future data reports. Unfortunately frequent
location updates from multiple sinks can lead to both frequent collisions
in sensor transmissions as well excessive drain of sensors' limited battery
power supply.
We propose TTDD: a Two-Tier Data Dissemination approach that provides scalable and efficient data delivery to multiple mobile sinks. Each data source in TTDD proactively builds a grid structure which enables mobile sinks to continuously receive data on the move by flooding queries within a local cell only. TTDD's design exploits the fact that sensor nodes are both stationary and location-aware, to construct and maintain the grid structures with low overhead. We evaluate TTDD performance through ns-2 simulations and compare with existing data dissemination protocols for sensor networks such as Directed Diffusion, Declarative Routing Protocol and GRAB. Our results show that TTDD handles mobile sinks efficiently with comparable performance for stationary sinks. Please email for the ns-2 simulation codes. People:
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SEF: Statistical En-route Filtering in Large Sensor
Networks |
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Detection and early dropping of false data reports injected by attackers
are important to avoid false alarms, and conserve the en-route sensors'
limited battery energy and wireless channel bandwidth. This problem,
however, is challenging since sensors are usually un-attended: an attacker
can physically capture and obtain the security information stored in
them. Recent work that provides message authentication is insufficient
since false data reports can still be injected through compromised nodes.
We propose Statistical En-route Filtering (SEF) that filters injected false reports en-route as they are forwarded toward the data collection unit. SEF leverages the scale of the sensor network and the redundancy in sensor node deployment. In order to differentiate false data reports injected from compromised nodes, SEF relies on the collective efforts from both the sensors that generate data reports, and the sensors along data dissemination paths. SEF uses computationally efficient one-way hash functions for cryptographic computation to conserve the computation resources of small sensor nodes. In order to minimize the communication overhead and the corresponding energy consumption, we uses Bloom filter to compress the MACs while enabling en-route verification of the compressed MACs. Through analysis and extensive simulations, we show that with an overhead of 14 bytes per report, SEF is able to drop 80~90% false reports injected through a compromised node within 10 hops. People:
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LDK: Location-dependent Key Management for Sensor Networks
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Existing sensor security mechanisms provide little protection when some
nodes are compromised and their secret keys breached. Compromised nodes can
authenticate false data reports about non-existent events to the user. The
fidelity of sensing reports can be destroyed by a few compromised
nodes. Besides, attackers can simply blast the sensor network with false
data reports through compromised nodes, therefore effectively break down
the whole system. To secure sensing report generation against these attacks, we explore the "location-awareness" of sensors to develop a new security mechanism called Location Dependent Keys (LDK). In LDK, keys are not bound with the identities, but with the locations of nodes. LDK confines the impact of compromised nodes to their geographical locality, since an attacker can only launch attacks, e.g., injecting false data reports, from the location where victim sensor nodes are compromised. LDK further constrains the possibility of false positives by leveraging the sensing redundancy. At the same time, it eliminates false negatives and ensures that data reports for real events are generated and delivered to the user in spite of the disruption from compromised nodes. We implement the design in Mica2 motes, and evaluate its performance through both experiments and simulations. Our preliminary results show that LDK generates reports securely and efficiently. People:
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URSA: Ubiquitous and Robust Access Control for Mobile Ad-Hoc
Networks |
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Restricting network access of routing and packet forwarding to
well-behaving nodes, and denying access from misbehaving nodes are critical
for the proper functioning of a mobile ad-hoc network where cooperation
among all networking nodes is usually assumed. However, the lack of
a network infrastructure, the dynamics of the network topology and node
membership, and the potential attacks from inside the network by malicious
and/or non-cooperative selfish nodes make the conventional network access
control mechanisms not applicable. We propose URSA, a ubiquitous and robust access control solution for mobile ad-hoc networks. URSA implements ticket certification services through multiple-node consensus and fully localized instantiation, and uses tickets to identify and grant network access to well-behaving nodes. In URSA, no single node monopolizes the access decision or is completely trusted, and multiple nodes jointly monitor a local node and certify/revoke its ticket. Furthermore, URSA ticket certification services are fully localized into each node's neighborhood to ensure service ubiquity and resilience. We propose a fully distributed version of the polynomial secret sharing algorithm as the cryptographic foundation for URSA. We implement URSA using the GNU-PG package and demonstrate its feasibility in low-end portable devices such as PDA. We evaluate the scalability through ns-2 simulations show that our design effectively enforces access control in the highly dynamic, mobile ad-hoc network. People:
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Adaptive Security for Multi-layer Ad-hoc Networks |
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Secure communication is critical in military environments where the network
infrastructure is vulnerable to various attacks and compromises. A
conventional centralized solution breaks down when the security servers are
destroyed by the enemies. In this project we design and evaluate a security
framework for multi-layer ad-hoc wireless networks with unmanned aerial
vehicles (UAV). In battlefields, the framework adapts to the contingent
damages on network infrastructure. Depending on the availability of network infrastructure, our design is composed of two modes. In infrastructure mode, security services, specifically the authentication services, are implemented on UAVs that feature low overhead and flexible managements. When the UAVs fail or are destroyed, our system seamlessly switches to infrastructureless mode, a backup mechanism that maintains comparable security services among the surviving units. In the infrastructureless mode, the security services are localized to each node's vicinity to comply with the ad-hoc communication mechanism in the scenario. People:
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HOURS: Hierarchical Overlays Using Randomized
Structure |
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Hierarchical systems have been widely used to provide scalable distributed
services in the Internet. However, its service accessibility is vulnerable
to DoS attacks in an open service hierarchy due to its low
connectivity. During DoS attacks, ensuring high degree of service
accessibility for each surviving node, regardless of the failures of other
nodes that are directly under DoS attacks, is challenging due to two
reasons. First, the attackers can exploit the hierarchy topology
information to launch topology-aware large-scale DoS attacks. Second,
because the service is open, it is hard to adopt solutions that are based
on user authentication.
Our solution is to establish rich yet unpredictable connectivity in the hierarchy using HOURS (Hierarchical Overlays Using Randomized Structure). The base design of HOURS explores two ideas: hierarchical overlays and randomized overlays. In this design, each node guides its children to form an overlay network. Within an overlay, each node keeps a few random pointers to other sibling nodes as well as their children. This way, HOURS augments the service hierarchy with hierarchical overlays and enriches the connectivity. When certain nodes are under DoS attacks, the queries are forwarded cross the overlays to bypass these attacked nodes. People:
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UCAN: A Unified Cellular Ad-hoc Network |
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In third-generation (3G) wireless data networks, mobile users experiencing
poor channel quality usually have low data-rate connections with the
base-station. Providing service to low data-rate users is required for
maintaining fairness, but at the cost of reducing the cell's aggregate
throughput.
We propose the Unified Cellular and Ad-Hoc Network (UCAN) architecture for enhancing cell throughput, while maintaining fairness. In UCAN, a mobile client has both 3G cellular link and IEEE 802.11-based peer-to-peer links. The 3G base station forwards packets for destination clients with poor channel quality to proxy clients with better channel quality. The proxy clients then use an ad-hoc network composed of other mobile clients and IEEE 802.11 wireless links to forward the packets to the appropriate destinations, thereby improving cell throughput. We refine the 3G base station scheduling algorithm so that the throughput gains of active clients are distributed proportional to their average channel rate, thereby maintaining fairness. With the UCAN architecture in place, we propose novel greedy and on-demand protocols for proxy discovery and ad-hoc routing that explicitly leverage the existence of the 3G infrastructure to reduce complexity and improve reliability. We further propose a secure crediting mechanism to motivate users to participate in relaying packets for others. Through extensive simulations with HDR and IEEE 802.11b, we show that the UCAN architecture can improve individual user's throughput by up to 310% and the aggregate throughput of the HDR downlink by up to 60%. For the ns-2 simulation codes of the UCAN architecture please email me. People:
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