Type
Text
Type
Dissertation
Date
2009-05-01
Keywords
mobile broadband wireless connectivity | wireless network access | MAC protocol | MobiSteer
Language
en_US
Source
This work is sponsored by the Stony Brook University Graduate School in compliance with the requirements for completion of degree.
Identifier
http://hdl.handle.net/11401/70785
Publisher
The Graduate School, Stony Brook University: Stony Brook, NY.
Format
application/pdf
Abstract
There is an increasing demand for high quality ubiquitous mobile broadband wireless access in recent times. More and more computing devices are becoming mobile and are equipped with high processing power, memory capability, optimized user interfaces, and a variety of communication interfaces. So people using these devices expect good connectivity and high quality usage experience. In addition to hand held mobile devices, vehicles are also equipped with devices that need wireless access. Applications that are used by mobile users also demand high bandwidth and very good link quality. IEEE 802.11 based wireless network access is very attractive due to high data rate connectivity, low deployment cost, and free or low-cost network access to users. 802.11 based wireless networks, however, suffer from serious interference problems limiting their capacity due to the broadcast nature of the wireless medium and their use of the unlicensed spectrum band. They also suffer from poor connectivity due to shorter coverage area and highly varying wireless channel. To achieve good performance, two important issues need to be addressed – capacity improvement in dense deployments such as wireless infrastructures as well as efficient connectivity of mobile clients to the infrastructures. iii In this dissertation, we address both these challenges by proposing efficient MAC and network layer solutions that exploit physical layer diversities such as multi-channel support and directional communication. First, we address the capacity issue in broadband wireless mesh infrastructures where each wireless node is equipped with multiple radio interfaces. We develop practical centralized and distributed channel assignment techniques that minimize overall network interference and perform very close to lower bounds on the optimal. Experimental study on a multi-radio mesh testbed revealed interesting practical challenges such as interface and channel heterogeneity. We propose mechanisms to incorporate heterogeneous channel information to improve capacity further. To combat interference further, we study the benefits of using directional communication at each radio in the mesh nodes and propose a directional MAC protocol that reduces wireless interference through higher spatial reuse. We study various scenarios in which deafness and directional hidden terminal problems could occur and solve them efficiently. Next, we investigate mechanisms to improve connectivity in wireless networks in highly mobile scenarios. We study the use of steerable beam directional antennas to improve the duration and quality of connectivity between moving vehicles and fixed infrastructures (V2I scenarios), and between multiple vehicles (V2V scenarios) when they move at high speed. The main challenge here is that the directional antenna should be steered appropriately on a continuous basis when the vehicles are moving in order to maintain good link quality throughout the entire drive. To address this challenge, we develop a framework called MobiSteer that provides practical approaches to perform beam steering and access point selection in a vehicle-to-infrastructure (V2I) setting. The goal is to improve the signal-to-noise ratio (SNR) and reduce handoff overheads. MobiSteer is then extended to vehicle-to-vehicle (V2V) scenarios. On experimental testbeds, both these techniques are demonstrated to provide tremendous improvement in average SNR with resultant improvement in physical layer data rates and/or communication ranges. Finally, as a by-product of our MobiSteer framework, we develop a triangulation based technique to localize roadside 802.11 APs. Such localizations will be useful iv in obtaining realistic data sets about large-scale chaotic WiFi deployments in urban areas for use in modeling and analysis
Recommended Citation
Subramanian, Anand Prabhu, "Improving Capacity and Connectivity in Wireless Access Networks" (2009). Stony Brook Theses and Dissertations Collection, 2006-2020 (closed to submissions). 5.
https://commons.library.stonybrook.edu/stony-brook-theses-and-dissertations-collection/5