Research Areas of WAM Lab

Routing Protocols for Ad hoc Networks

We are developing efficient and adaptive routing protocols for wireless mobile networks to accommodate vulnerable wireless links of limited bandwidth. We are focusing on designing a routing protocol that scales well to large networks and provides QoS to multimedia traffic. Hierarchical routing and on-demand routing schemes are being implemented and evaluated.

Publications

Multicast in Wireless Networks

Tree based traditional multicast protocols for wired networks (e.g., CBT, PIM, DVMRP, etc.) have been modified and implemented under the mobile wireless enviroment. A new scalable multicast protocol, FGMP (Forwarding Group Multicast Protocol) is proposed and evaluated. FGMP is based on the notion of a forwarding group which forms the wireless multicast mesh. The FGMP takes advantage of the inherent wireless broadcast transmission property and is suitable for dynamic network topologies.

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QoS Adaptive Audio/Video Tool for Multihop Wireless Networks

On our multihop, wireless platform testbed, we are adaptively streaming real-time audio and video. In order to provide acceptable end-to-end communications in a highly unpredictable multihop wireless environment, our experiment incorporates encoding/decoding, adaptation and layering techniques, as well as captioning, speech recognition and synthesizer tools.

Publications

Medium Access Control Protocols for Ad hoc Networks

We are interested in providing QoS for multimedia traffic (such as audio and video) in wireless ad hoc networks. We have developed two MAC schemes which originate from the IEEE 802.11 standard to support these requirements.

MACA/PR uses the MACA RTS/CTS mechanism only for the first packet; subsequent packets are transmitted with a reservation scheme that is appropriate for the periodic and bursty nature of the multimedia traffic.
MACA-BI (Multiple Access with Collision Avoidance By Invitation) is based on an invitation mechanism consisting of two-way handshake. The RTS control packet is suppressed. The CTS control packet is replaced by the RTR (Ready To Receive) packet, which is used to "invite" neighbors. MACA-BI greatly improves efficiency when radio turn-around time is significant with respect to packet transmission time (high speed networks) while still preserving the collision free property of MACA schemes. More importantly, it reduces congestion in hot spots where many neighbors are trying to transmit to the same node.

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Clustering with Power Control in Wireless Networks

Power control is a necessity in multihop networks, both to save power and to optimize spatial reuse. In this context, we are looking for an optimal clustering scheme allowing all the participating nodes adjust their power to a power efficient and/or bandwidth efficient way. Power control is required for CDMA, but is applicable also to non-CDMA networks if each node can adjust its transmission power.

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TCP Performance over Wireless Networks

Reliability and congestion control networks are generally achieved using TCP. Because of this dual role of reliable delivery and congestion control, the interaction of TCP and lower protocol layers causes unexpected behaviours in wireless networks. In our research, we consider "multiple" TCP connections in a "multihop" wireless environment and expose the interference between different hops along the path (hidden terminal problem). We focus on two main issues: the impact of TCP window size on performance, and; the fair sharing among multiple connections. We also analyze TCP behavior for different MAC protocols.

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Wireless ATM Networks

We are studying issues such as bandwidth allocation and QoS support in Wireless ATM networks. Different bandwidth allocation strategies are evaluated and simulation results are compared.

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Mobility Modeling

We are investigating and modeling the mobility for different application scenario and studying the performance impact on wireless ad-hoc networks. Group mobility with reference points home agents is currently in the state of development.

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Simulation Development

Wireless networks feature very complex models with many variables and interacting components. Often, the relationships between underlying variables are nonlinear or even unpredictable. This makes a closed-form solution impossible. Furthermore, enormous computational resources are demanded for numerical solutions. These characterizations make wireless networks well suited for parallel/distributed simulation platforms, such as PARSEC. We use and develop the following parallel simulation tools:

GloMoSim is a collection of parallelized building blocks modeling mobility, radio propagation and wireless network protocols (from MAC to the TCP). It addresses scalability and speed issues providing simulation technology for thousands of mobile node networks.
MANETSIM is an attempt to deliver a high-level, object-oriented, platform independent wireless network simulator to comply with good software engineering requirements.

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Satellite Networks

We evaluate the performance of various mobile Internet applications in representative LEO and GEO scenarios. Our purpose is to understand the impact of these various features and options on different applications in different environments. We developed a channel propagation model that includes shadowing from surrounding building skylines and terminal mobility. The model parameters are based on actual data in a built-up area. The results are based on utilization of ns2 simulator opportunely upgraded.

Publications

Questions and Comments to: yenglee@cs.ucla.edu [ H ome Page ]