Digital Signal Processing Seminar

The Smart Wireless LAN System: Adapting Smart Antennas for Wireless LAN Systems

Mr. Garret Okamoto
Dept. of Electrical and Computer Engineering
The University of Texas at Austin
Austin, TX

okamoto@ece.utexas.edu

Wednesday, April 29, 1998, 9:00 AM, ENS 602

The use of wireless local-area-network (LAN) systems has been increasing rapidly as prices have come down and a common standard has emerged. This standard is the IEEE 802.11 wireless LAN standard, which has been adopted worldwide. However, the 802.11 protocol has many critical limitations that limits the flexibility and usefulness of the systems. Because the bandwidth allocated in the standard is limited and only one user is allowed to transmit at a time, the throughput for each user is limited and users can experience long delays. In addition, the protocol was designed to accommodate only a few users with conventional data traffic and no provisions were made for multimedia or real-time applications. Not only is the throughput too low for applications such as voice, but the protocol does not include the priority designations that are required for real-time applications.

To alleviate these limitations, this dissertation presents the Smart Wireless LAN (SWL) system, which achieves throughput multiplication over the 802.11 protocol by exploiting the rich spatial diversity existing among spatially separated terminals. Spatial diversity is demonstrated by the amplitude and phase pattern of the data vectors received by an antenna array. Each transmitter located at a certain place has its unique pattern, also called a spatial signature. Once the spatial signatures are acquired, different co-channel signals can be separated based on their unique spatial signatures through beamforming. Therefore, we can increase the number of virtual time slots by enabling different terminals to transmit in the same time slots without significantly interfering with each other. In addition to the increase in throughput, this new protocol has additional features such as simple implementation, adaptability to multimedia traffic with diverse bandwidth requests, network security, guaranteed fairness in bandwidth sharing, and ease of adaptation to the 802.11 wireless LAN standard. Also, this protocol adds priority level designations to the packets to allow for delay-sensitive communication links for multimedia applications such as voice or video. Dynamic slot assignment algorithms and chip timing synchronization algorithms were created to satisfy the special requirements of adapting SDMA for wireless LANs. This dissertation will present a combination of throughput performance evaluation, computer simulations, and RF experimental studies to demonstrate the feasibility and benefits of the SWL protocol.

A list of digital signal processing seminars is available at from the ECE department Web pages under "Seminars". The Web address for the digital signal processing seminars is http://anchovy.ece.utexas.edu/seminars