John S. Baras


Medium Access Control and Quality-of-Service Routing for Mobile Ad Hoc Networks

Chenxi Zhu

Doctoral Dissertation, Number: CSHCN PhD 2001-3, Year: 2001, Advisor: John S. Baras

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A mobile ad hoc network is an autonomous system consisting solely of mobile terminals connected with wireless links. This type of network has received considerable interest in recent years due to its capability to be deployed quickly without any fixed infrastructure. Nodes self-organize and re-configure as they join, move, or leave the network. How to design distributed protocols capable of handling the dynamic nature of these networks is an interesting but difficult topic.

When TDMA is used, distributed protocols are needed to generate transmission schedules. An important issue is how to produce a schedule quickly. This is critical when the network is large or the network changes frequently. Here we develop two fully distributed protocols for generating or updating TDMA schedules. Contention is incorporated into the scheduling protocols for them to work independently of the network size. The schedule can be generated at multiple parts of the network simultaneously. In the Five-Phase Reservation Protocol (FPRP), a broadcast schedule is produced when nodes contend among themselves using a new five-phase message exchange mechanism. In the Evolutionary-TDMA scheduling protocol (E-TDMA), schedules are updated when nodes contend to reserve transmission slots of different types (unicast, multicast, broadcast). Both are scalable protocols suitable for large or dynamic networks.

Another issue related to medium access control is transmission power control. Our contribution to power control is to develop a channel probing scheme for networks applying power control, which allows a node to probe a channel and estimate the channel condition. It can be used for dynamic channel allocation in a TDMA or FDMA system, or admission control in a DS/CDMA system. It is a fully distributed scheme which requires little communication overhead. Multiple links can probe a channel simultaneously and each makes individual yet correct decisions.

The last topic is Quality-of-Service routing. An efficient distributed scheme is developed to calculate the end-to-end bandwidth of a route. By incorporating this scheme with the AODV protocol, we developed an on-demand QoS routing protocol which can support CBR sessions by establishing QoS routes with reserved bandwidth. It repairs a route when it breaks.Load balancing and route redundancy are also achieved. It is applicable for small networks or short routes under relatively low mobility.

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