general information
research groups
radioscience seminars
stanford courses
oral defense abstract
industrial affiliates
Oral Defense Abstracts

Date: Tuesday, April 29th, 2003
Time: 4:15 pm (refreshments 4:00)
Location: Packard #101

Special University Ph.D. Oral Examination
Capacity of Wireless Networks and Design Principles
Stavros Toumpis
Department of Electrical Engineering, Stanford University

We define and study capacity regions for wireless ad hoc networks with an arbitrary number of nodes and topology. These regions describe the set of achievable rate combinations between all source-destination pairs in the network under various transmission strategies, such as variable-rate transmission, single hop or multihop routing, power control and successive interference cancellation. Multihop cellular networks and networks with energy constraints are studied as special cases. With slight modifications, the developed formulation can handle node mobility and time-varying flat fading channels.

Using this framework, we then concentrate on the joint-layer design of wireless ad hoc networks. We show that using single routes for each data stream might significantly reduce the capacity of the network. We then study CSMA/CA, and find that its performance strongly depends on the choice of the accompanying routing protocol. We introduce two protocols that outperform CSMA/CA, both in terms of energy efficiency and achievable throughput. The *Progressive Back Off Algorithm (PBOA)* performs medium access jointly with power control. The *Progressive Ramp Up Algorithm* sacrifices energy efficiency in favor of higher throughput. Both protocols slot time, and are integrated with queuing disciplines that are more relaxed than the First In First Out (FIFO) rule. They are totally distributed and the overhead they require does not increase with the size and node density of the network.

We conclude with a brief discussion on the capacity of ad hoc networks with an asymptotically large number of nodes. We establish a lower bound on the aggregate throughput as a function of the number of nodes, under a general model for fading, and assuming the nodes to be immobile. We then assume node mobility, showing a fundamental trade-off between the packet delay and the aggregate throughput.

< back to top