| The use of wireless local-area-network (LAN) systems has been increasing rapidly as prices have come down and a common standard has emerged, the IEEE 802.11 wireless LAN standard. However, the 802.11 protocol has many critical limitations that limit its flexibility and usefulness. 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 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 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 location has a unique pattern, also called a spatial signature. Once the spatial signatures are acquired, different co-channel signals can be separated through beamforming based on their unique spatial signatures. Therefore, we can increase the number of "virtual" time slots by enabling multiple terminals to transmit in the same time slots without significantly interfering with each other. In addition to the throughput increase, 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 standard. Also, this protocol adds priority level designations to follow for delay-sensitive communication links for multimedia applications such as voice. Dynamic slot assignment algorithms and chip timing synchronization algorithms were created to satisfy the special requirements of adapting the space-division-multiple-access (SDMA) technique 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 system. |
