I-WLAN:
Intelligent Wireless Local Area Networking
December 2004
Abstract:
Future wireless networks require intelligent components that can automate,
scale and manage the network in order to handle the demand for ubiquitous
access. In this dissertation, we first
evaluate existing problems, and then we introduce components that improve the performance
of existing systems.
We introduce a new Markov model for Distributed Coordination of Function
of IEEE 802.11 with which we formulate the throughput and delay for saturated and
non-saturated traffic. We introduce a novel formulation for individual
throughput when stations operate with mixed data rates. We introduce an admission control mechanism
to maintain the highest achievable throughput by controlling the access. After that we use our throughput formulation
to obtain the performance of an indoor network. We introduce a packet size adjustment
scheme with respect to data rate so that a slow station sends small packets to
prevent throttling of the network.
We introduce a frame aggregation scheme for wireless voice over IP. We introduce
a fast and fair sub-optimal algorithm to allocate sub-carriers and bits adaptively
in an OFDMA system for point-to-multipoint communication, and investigate MAC
performance of the wireless LAN with adaptive antennas for point-to-point communication.
We find that ignoring the consecutive transmission probability in the
previous Markov models is incomplete.
Consequently, our model which takes this into account is closer to the
standard. We find that the individual
throughput of a station is the same for fast and slow stations, and slow stations throttle the performance, since the CSMA/CA
scheme gives equal access but not equal
time of channel usage. Our packet size optimization scheme increases the throughput
of the total network and the fast station but not that of the slow
station. The admission control mechanism
can tune the network from random access to controlled access. Network
management can monitor the whole network and do real-time adjustments for optimum
performance. Our frame aggregation
scheme for wireless voice over IP reduces the number of access by concatenating
the packets in the accesses point in order to be sent at one time. The results
of our resource allocation scheme for adaptive sub-carrier and bit allocation
is appealing and can be close to optimal.
We find that a directional antenna increases the performance
significantly and can provide enhancements
for wireless LANs.
Department of Electrical Engineering and Computer
Science
[pdf file] (5.2MB)