4 research outputs found
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Cognitive MAC protocols for mobile Ad-Hoc networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The term of Cognitive Radio (CR) used to indicate that spectrum radio could be accessed dynamically and opportunistically by unlicensed users. In CR Networks, Interference between nodes, hidden terminal problem, and spectrum sensing errors are big issues to be widely discussed in the research field nowadays. To improve the performance of such kind of networks, this thesis proposes Cognitive Medium Access Control (MAC) protocols for Mobile Ad-Hoc Networks (MANETs). From the concept of CR, this thesis has been able to develop a cognitive MAC framework in which a cognitive process consisting of cognitive elements is considered, which can make efficient decisions to optimise the CR network. In this context, three different scenarios to maximize the secondary user's throughput have been proposed. We found that the throughput improvement depends on the transition probabilities. However, considering the past information state of the spectrum can dramatically increases the secondary user's throughput by up to 40%. Moreover, by increasing the number of channels, the throughput of the network can be improved about 25%. Furthermore, to study the impact of Physical (PHY) Layer errors on cognitive MAC layer in MANETs, in this thesis, a Sensing Error-Aware MAC protocols for MANETs has been proposed. The developed model has been able to improve the MAC layer performance under the challenge of sensing errors. In this context, the proposed model examined two sensing error probabilities: the false alarm probability and the missed detection probability. The simulation results have shown that both probabilities could be adapted to maintain the false alarm probability at certain values to achieve good results. Finally, in this thesis, a cooperative sensing scheme with interference mitigation for Cognitive Wireless Mesh Networks (CogMesh) has been proposed. Moreover, a prioritybased traffic scenario to analyze the problem of packet delay and a novel technique for dynamic channel allocation in CogMesh is presented. Considering each channel in the system as a sub-server, the average delay of the users' packets is reduced and the cooperative sensing scenario dramatically increases the network throughput 50% more as the number of arrival rate is increased
Cognitive Radio Systems
Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems
Modeling and Analysis of Cognitive Radio Ad Hoc Networks
Eine Welt ohne drahtlose Ad-Hoc Netzwerke ist heute kaum noch
vorstellbar.Auf Grund der geringen Kosten und des minimalen
Installationsaufwands werden gegenwärtig immer mehr Geräte in immer mehr
Anwendungsfeldern eingesetzt. Da die meisten dieser Netzwerke im
lizenzfreien ISM-Band operieren, ist dieses heute stark ausgelastet und
weist kaum noch freie Kapazitäten auf. Aktuelle Studien der Federal
Communication Commission (FCC) belegen allerdings, dass groĂźe Teile (bis zu
70%) der lizenzbehafteten Frequenzen ungenutzt sind. Dieser Umstand zeigt,
dass das Problem weniger die generelle Knappheit an freien Frequenzen ist,
sondern vielmehr in der ineffizienten Verteilung bzw.Nutzung der
verfĂĽgbaren Resourcen zu suchen ist. Das Hauptaugenmerk der vorliegenden
Dissertation liegt in der Verbesserung der Spektrumsauslastung, um dadurch
die weitere Entwicklung von drahtlosen Ad-Hoc Netzwerken zu ermöglichen.In
dieser Arbeit wird ein neues Spektrum-Management-Konzept mit dem
Namen Opportunistic Spectrum Access with Backup channel (OSAB) entwickelt und
vorgestellt. Das hierbei zugrunde liegende Konzept gestattet Secondary
Users (SUs)dynamisch und flexibel auf Frequenzen unlizenzierter als auch
lizensierterFrequenzbänder zu zugreifen, wenn diese vom Primary User (PU)
gerade nicht genutzt werden - es also keine Interferenzen geben kann.Da der
Zugriff auf das Frequenzspektrum heute existierender Systeme noch sehr
unflexibel ist, soll dieser in Zukunft durch Cognitive Radios (CR)weit
flexibler und dynamischer gestaltet werden können. Bei der Entstehung von
OSAB wurden speziell die unterschiedlichen Eigenschaften verschiedener
Frequenzbänder berücksichtigt.Der Hauptvorteil von lizenzbehafteten Bändern
ist, dass diese in hoher Anzahl verfĂĽgbar sind. Der Hauptvorteil von
lizenzfreien Frequenzen ergibt sich hingegen aus der Gleichstellung aller
Nutzer. Sobald ein SU einmal einen Kanal belegt hat, kann er nicht mehr aus
selbigem verdrängt werden.Kommuniziert OSAB in lizenzierten Bändern, so
wird stets ein Backup Channel (BC)vorgehalten um auf das plötzliche
Auftreten des PUs reagieren zu können.Das vorgeschlagene Konzept wurde in
dieser Arbeit auĂźerdem einer intensiven Analyse mittel Markov-Ketten
unterzogen. Die dabei erzielten Ergebnisse zeigen,dass OSAB den
Paketverlust und die erwartete Anzahl an Spektrum-Hand-Offs um 60% bzw. 17%
reduzieren kann.Um den Nutzen und die Vorteile von OSAB praktisch unter
Beweis zu stellen, wurde in der vorliegenden Arbeit weiterhin das
MAC-Protokoll SWITCH (opportunisticSpectrum access WITh backup CHannel)
entwickelt.SWITCH ist ein dezentrales, asynchrones, verbindungsbasiertes
MAC-Protokoll, welchesdurch das Backup-Channel-Konzept in der Lage ist,
effektiv auf das plötzliche Eintreffen von PUs zu reagieren.Jeder SU ist
dabei mit zwei Transceivern ausgestattet, wobei einer davon stets fĂĽr
die Kommunikation auf dem gemeinsam genutzten Kontroll-Kanal (Common Control
Channel) verantwortlich ist. Der zweite Transceiver ist so ausgelegt, dass
dieser periodisch alle ungenutzten Kanäle absucht und dynamisch auf diese
zugreifen kann. Um den Zustand eines Kanals (belegt/nicht belegt) korrekt
erkennen zu können wird in dieser Arbeit eine einfache aber effektive Form
des kooperativen Sensings genutzt. Die Performanz des Protokolls wurde mit
Hilfe von Simulationen evaluiert. Die Ergebnisse zeigen, dass SWITCH im
Vergleich zu anderen CR-MAC-Protokollen eine Verbesserung des Durchsatzes
von bemerkenswerten 91,7% erzielen konnte. Zusammenfassend kann gesagt
werden, dass die vorgeschlagenen Beiträge einen Schritt hin zu einer
effektiveren Nutzung der verfügbaren Funkressourcen und zur Erhöhung der
Kapazität von drahtlosen Ad-Hoc Netzwerken darstellen.Wireless ad hoc networks are becoming more ubiquitous in terms of devices,
application areas, etc. due to their low cost and minimal deployment
effort. Since all these networks operate in the unlicensed band, the
problems of congestion and spectrum scarcity have arisen. On the other
hand, a recent study by Federal Communications Commission (FCC) has
revealed that swathes of licensed bands, measured by 70%, are unutilized.
This highlights that the actual problem is not the scarcity of spectrum but
inefficient allocation policies and usage. Therefore, this dissertation is
focused on improving spectrum utilization and efficiency to tackle the
spectrum scarcity problem and support further wireless ad hoc networks.This
thesis proposes a new spectrum management concept called opportunistic
spectrum access with backup channel (OSAB). The proposed concept provides
secondary users (SUs) (e.g. ad hoc users) with the ability to adaptively
and dynamically exploit channels from both licensed and unlicensed bands
without interfering the legacy users of licensed bands, i.e. the so called
primary users (PUs). Since existing radio systems offer very limited
flexibility, cognitive radios (CR), which can sense and adapt to radio
environments, are exploited to support such a dynamic concept. For the
development of OSAB, the channels' characteristics from each band are taken
into consideration. The main advantage of licensed channels is their
availability in significant numbers, whereas, the main advantage of
unlicensed channels is that all users have the same rights to channel
access and thus no preemption occurs once a user obtains a channel. In
addition, OSAB uses a backup channel (BC) to handle the appearance of PUs
and thus facilitates SU communication. The proposed concept is extensively
evaluated using a Markov chain model and compared to existing spectrum
management approaches such as opportunistic spectrum access (OSA). The
results indicate that OSAB decreases the dropping probability and the
expected number of spectrum handoffs for SUs compared to OSA by 60% and 17%
respectively.In order to apply OSAB practically, we develop a MAC protocol
that reacts efficiently to sudden appearance of PUs. The new protocol is
named opportunistic Spectrum access WITh backup CHannel (SWITCH) protocol.
SWITCH is a decentralized, asynchronous, and contention-based MAC protocol.
The BC's concept makes SWITCH extremely robust to the appearance of PUs.
Each SU is equipped with two transceivers, one is tuned to a common control
channel for the negotiation purpose with other SUs while the other is
designed specifically to periodically sense and dynamically use the
identified unused channels. To obtain the channel state accurately, we
propose an efficient spectrum sensing strategy. This strategy is based on
cooperative spectrum sensing among SUs. The performance of proposed
protocol is evaluated through simulations. The results show that SWITCH
accomplishes a remarkable 91.7% throughput gain over other CR-MAC
protocolsTo conclude, the proposed contributions are a step forward towards
efficient use of available radio resources and improve the spectrum
capacity for wireless ad hoc networks
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Spectrum utilization using game theory
This thesis was submitted for the degree of Master of Philosophy and awarded by Brunel University.Spectrum utilization is the most recent communications issue which takes great deal of attention from communication researchers where most of the efforts have been dedicated for spectral efficient utilization. Spectrum sharing is one of the solutions considered in the problem of lack of available frequency for new communication services which are unlicensed. In this work we propose an optimal method for spectrum utilization to increase spectral efficiency. It considers the problem of spectrum holes found in Primary User's (PU) band and detected using one of the spectral sensing methods. The solution is formulated with the help of Game theory approach in such a way that the primary user who has unoccupied frequency can share it with a group of secondary users (SU) in a competitive way. One of the SUs will be a secondary primary user (SPU), share available frequency from PU then offer his sharing to serve other SUs in different rate of sharing. Each user in the group of secondary users has a chance to be secondary primary user depending on reputation of each SU. Enhancing reputation is the only way for any SU to assure a share in the spectrum where it considered the factor of increasing or decreasing rate of sharing as well as factor of being SPU or an ordinary SU. A theoretical non-cooperative game model is introduced in a comparison with a proposed non-dynamic technique which depends on number of subscribers who occupy frequency in each time period. Multi-users compete on sharing the frequency from one of the users who offers sharing at a time when he has low number of subscribers that occupy his band. It is found that non-dynamic sharing results in inefficient spectrum utilization which is one of the reasons of spectrum scarcity where this resource is allocated in fixed way. Spectrum sharing using game theory solves this problem by its ability to make users compete to gain highest rate of spectrum allocation according to the real requirement of each user at each time interval. The problem of urgent case is also discussed when the primary user comes back to using his band which is the specific band of sharing with the secondary users group. SPU makes it easy to unload the required band from multi-users because PU does not need to request his band from each SU in the group