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Tesi etd-04182011-182709


Thesis type
Tesi di dottorato di ricerca
Author
GARDELLIN, VANESSA
URN
etd-04182011-182709
Title
The Spectrum Shortage Problem: Channel Assignment and Cognitive Networks
Settore scientifico disciplinare
ING-INF/05
Corso di studi
INGEGNERIA DELL'INFORMAZIONE
Commissione
tutor Prof. Lenzini, Luciano
tutor Prof. Anastasi, Giuseppe
tutor Prof. Das, Sajal K.
Parole chiave
  • Multi-Radio Multi-Channel Wireless Mesh Networks
  • Self-Coexistence
  • Cognitive Networks
  • Channel Assignment
Data inizio appello
11/05/2011;
Consultabilità
completa
Riassunto analitico
Recent studies have shown that the proliferation of wireless applications and services, experienced in the last decade, is leading to the challenging spectrum shortage problem.<br>We provide a general overview regarding the spectrum shortage problem from the point of view of different technologies.<br>First, we propose solutions based on multi-radio multi-channel wireless mesh networks in order to improve the usage of unlicensed wireless resources.<br>Then, we move our focus on cognitive networks in order to analyze issues and solutions to opportunistically use licensed wireless resources.<br><br>In wireless mesh networks, the spectrum shortage problem is addressed equipping each device with multiple radios which are turned on different orthogonal channels.<br>We propose G-PaMeLA, which splits in local sub-problems the joint channel assignment and routing problem in multi-radio multi-channel wireless mesh networks.<br>Results demonstrate that G-PaMeLA significantly improves network performance, in terms of packet loss and throughput fairness compared to algorithms in the literature.<br>Unfortunately, even if orthogonal channels are used, wireless mesh networks result in what is called spectrum overcrowding.<br><br>In order to address the spectrum overcrowding problem, careful analysis on spectrum frequencies has been conducted.<br>These studies identified the possibility of transmitting on licensed channels, which are surprisingly underutilized.<br>With the aim of addressing the resources problem using licensed channels, cognitive access and mesh networks have been developed.<br><br>In cognitive access networks, we identify as the major problem the self-coexistence, which is the ability to access channels on a non-interfering basis with respect to licensed and unlicensed wireless devices.<br>We propose two game theoretic frameworks which differentiate in having non-cooperative (NoRa) and cooperative (HeCtor) cognitive devices, respectively.<br>Results show that HeCtor achieves higher throughput than NoRa but at the cost of higher computational complexity, which leads to a smaller throughput in cases where rapid changes occur in channels&#39; occupancy.<br>In contrast, NoRa attains the same throughput independent of the variability in channels&#39; occupancy, hence cognitive devices adapt faster to such changes.<br><br>In cognitive mesh networks, we analyze the coordination problem among cognitive devices because it is the major concern in implementing mesh networks in environments which change in time and space.<br>We propose Connor, a clustering algorithm to address the coordination problem, which establishes common local control channels.<br>Connor, in contrast with existing algorithms in the literature, does not require synchronization among cognitive mesh devices and allows a fast re-clustering when changes occur in channel&#39;s occupancy by licensed users.<br>Results show that Connor performs better than existing algorithms in term of number of channels used for control purposes and time to reach and stay on stable configurations.
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