Chunlei Liu, "Wireless Network Enhancements Using Congestion Coherence, Faster Congestion Feedback, Media Access Control and AAL2 Voice Trunking," PhD Dissertation, The Ohio State University, 2001, xvi + 194.

Advisor: Professor Raj Jain.

Rapid development of wireless communications in recent years has imposed great challenges for network support. As most current networking protocols were designed mainly for wired networks, many assumptions that make these protocols efficient in wired networks are no longer true and cause severe performance degradation in wireless environment. An urgent task for today's networking research is to identify such deficiencies and to enhance these protocols.

This dissertation contains four major enhancement results. The first result is a wireless TCP enhancement scheme called Congestion Coherence. Through a statistical analysis, we find the leading contributor of wireless TCP performance degradation is the timeout resulting from frequent packet losses. This scheme uses ECN to reduce number of timeouts, and based on the observation that congestion neither happens nor disappears suddenly, uses the sequential coherence of packet marking to determine cause of packet losses. Simulations show this scheme works better than existing enhancements and produces good performance.

The second result is a Mark-Front Strategyto deliver faster congestion feedback in networks that use the newly standardized ECN protocol. By choosing to mark the packet in the front of the queue, Mark-Front Strategy delivers faster feedback than traditional congestion feedback mechanisms. Our analysis show Mark-Front Strategy requires smaller buffers, and yields higher throughput and better fairness.

A MAC protocol to supports real-time applications in an asymmetric and half-duplex environment is our third result. Several innovative features are used to ensure optimal utilization of the asymmetric bandwidth.

In the last result, we use a Markovian chain to model the AAL2 voice trunking process and analyze the tradeoff between delay and bandwidth efficiency. This analysis gives a guideline for setting the packing timer. The result is adopted by a 3GPP industrial standard.

This study provides insight into congestion control and quality of service in wireless networks. The proposed enhancements will help to bring high-performance and high-quality services to mobile subscribers.

Complete dissertation in Adobe Acrobat 3.0 Format (3,823,098 Bytes)

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