Comprehensive survey on quality of service provisioning approaches in cognitive radio networks : part one

Much interest in Cognitive Radio Networks (CRNs) has been raised recently by enabling unlicensed (secondary) users to utilize the unused portions of the licensed spectrum. CRN utilization of residual spectrum bands of Primary (licensed) Networks (PNs) must avoid harmful interference to the users of PNs and other overlapping CRNs. The coexisting of CRNs depends on four components: Spectrum Sensing, Spectrum Decision, Spectrum Sharing, and Spectrum Mobility. Various approaches have been proposed to improve Quality of Service (QoS) provisioning in CRNs within fluctuating spectrum availability. However, CRN implementation poses many technical challenges due to a sporadic usage of licensed spectrum bands, which will be increased after deploying CRNs. Unlike traditional surveys of CRNs, this paper addresses QoS provisioning approaches of CRN components and provides an up-to-date comprehensive survey of the recent improvement in these approaches. Major features of the open research challenges of each approach are investigated. Due to the extensive nature of the topic, this paper is the first part of the survey which investigates QoS approaches on spectrum sensing and decision components respectively. The remaining approaches of spectrum sharing and mobility components will be investigated in the next part

Spectrum Sharing in Dynamic Spectrum Access Networks: WPE-II Written Report

A study by Federal Communication Commission shows that most of the spectrum in current wireless networks is unused most of the time, while some spectrum is heavily used. Recently dynamic spectrum access (DSA) has been proposed to solve this spectrum inefficiency problem, by allowing users to opportunistically access to unused spectrum. One important question in DSA is how to efficiently share spectrum among users so that spectrum utilization can be increased and wireless interference can be reduced. Spectrum sharing can be formalized as a graph coloring problem. In this report we focus on surveying spectrum sharing techniques in DSA networks and present four representative techniques in different taxonomy domains, including centralized, distributed with/without common control channel, and a real case study of DSA networks --- DARPA neXt Gen- eration (XG) radios. Their strengths and limitations are evaluated and compared in detail. Finally, we discuss the challenges in current spectrum sharing research and possible future directions

Design and optimisation of a low cost Cognitive Mesh Network

Wireless Mesh Networks (WMNs) have been touted as the most promising wireless technology in providing high-bandwidth Internet access to rural, remote and under-served areas, with relatively lower investment cost as compared to traditional access networks. WMNs structurally comprise of mesh routers and mesh clients. Furthermore, WMNs have an envisaged ability to provide a heterogeneous network system that integrates wireless technologies such as IEEE 802.22 WRAN, IEEE 802.16 WiMAX, IEEE 802.11 Wi-Fi, Blue-tooth etc. The recent proliferation of new devices on the market such as smart phones and, tablets, and the growing number of resource hungry applications has placed a serious strain on spectrum availability which gives rise to the spectrum scarcity problem. The spectrum scarcity problem essentially results in increased spectrum prices that hamper the growth and efficient performance of WMNs as well as subsequent transformation of WMN into the envisaged next generation networks. Recent developments in TV white space communications technology and the emergence of Cognitive radio devices that facilitate Dynamic Spectrum Access (DSA) have provided an opportunity to mitigate the spectrum scarcity problem. To solve the scarcity problem, this thesis reconsiders the classical Network Engineering (NE) and Traffic Engineering (TE) problems to objectively design a low cost Cognitive Mesh network that promotes efficient resources utilization and thereby achieve better Quality of Service (QoS) levels

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

Spectrum measurement, sensing, analysis and simulation in the context of cognitive radio

The radio frequency (RF) spectrum is a scarce natural resource, currently regulated locally by national agencies. Spectrum has been assigned to different services and it is very difficult for emerging wireless technologies to gain access due to rigid spectmm policy and heavy opportunity cost. Current spectrum management by licensing causes artificial spectrum scarcity. Spectrum monitoring shows that many frequencies and times are unused. Dynamic spectrum access (DSA) is a potential solution to low spectrum efficiency. In DSA, an unlicensed user opportunistically uses vacant licensed spectrum with the help of cognitive radio. Cognitive radio is a key enabling technology for DSA. In a cognitive radio system, an unlicensed Secondary User (SU) identifies vacant licensed spectrum allocated to a Primary User (PU) and uses it without harmful interference to the PU. Cognitive radio increases spectrum usage efficiency while protecting legacy-licensed systems. The purpose of this thesis is to bring together a group of CR concepts and explore how we can make the transition from conventional radio to cognitive radio. Specific goals of the thesis are firstly the measurement of the radio spectrum to understand the current spectrum usage in the Humber region, UK in the context of cognitive radio. Secondly, to characterise the performance of cyclostationary feature detectors through theoretical analysis, hardware implementation, and real-time performance measurements. Thirdly, to mitigate the effect of degradation due to multipath fading and shadowing, the use of -wideband cooperative sensing techniques using adaptive sensing technique and multi-bit soft decision is proposed, which it is believed will introduce more spectral opportunities over wider frequency ranges and achieve higher opportunistic aggregate throughput.Understanding spectrum usage is the first step toward the future deployment of cognitive radio systems. Several spectrum usage measurement campaigns have been performed, mainly in the USA and Europe. These studies show locality and time dependence. In the first part of this thesis a spectrum usage measurement campaign in the Humber region, is reported. Spectrum usage patterns are identified and noise is characterised. A significant amount of spectrum was shown to be underutilized and available for the secondary use. The second part addresses the question: how can you tell if a spectrum channel is being used? Two spectrum sensing techniques are evaluated: Energy Detection and Cyclostationary Feature Detection. The performance of these techniques is compared using the measurements performed in the second part of the thesis. Cyclostationary feature detection is shown to be more robust to noise. The final part of the thesis considers the identification of vacant channels by combining spectrum measurements from multiple locations, known as cooperative sensing. Wideband cooperative sensing is proposed using multi resolution spectrum sensing (MRSS) with a multi-bit decision technique. Next, a two-stage adaptive system with cooperative wideband sensing is proposed based on the combination of energy detection and cyclostationary feature detection. Simulations using the system above indicate that the two-stage adaptive sensing cooperative wideband outperforms single site detection in terms of detection success and mean detection time in the context of wideband cooperative sensing

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 große 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 verfügbaren 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 verfügbar 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 außerdem 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 für 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

Generalised Radio Resource Sharing Framework for Heterogeneous Radio Networks

Recent years have seen a significant interest in quantitative measurements of licensed and unlicensed spectrum use. Several research groups, companies and regulatory bodies have conducted studies of varying times and locations with the aim to capture the over- all utilisation rate of spectrum. The studies have shown that large amount of allocated spectrum are under-utilised, and create the so called \spectrum holes", resulting in a waste of valuable frequency resources. In order to satisfy the requirements of increased demands of spectrum resources and to improve spectrum utilisation, dynamic spectrum sharing (DSS) is proposed in the literature along with cognitive radio networks (CRNs). DSS and CRNs have been studied from many perspectives, for example spectrum sensing to identify the idle channels has been under the microscope to improve detection proba- bility. As well as spectrum sensing, the DSS performance analysis remains an important topic moving towards better spectrum utilisation to meet the exponential growth of traffi�c demand. In this dissertation we have studied both techniques to achieve different objectives such as enhancing the probability of detection and spectrum utilisation. In order to improve spectrum sensing decisions we have proposed a cooperative spec- trum sensing scheme which takes the propagation conditions into consideration. The proposed location aware scheme shows an improved performance over conventional hard combination scheme, highlighting the requirements of location awareness in cognitive radio networks (CRNs). Due to the exponentially growing wireless applications and services, traffi�c demand is increasing rapidly. To cope with such growth wireless network operators seek radio resource cooperation strategies for their users with the highest possible grade of service (GoS). However, it is diffi�cult to fathom the potential benefits of such cooperation, thus we propose a set of analytical models for DSS to analyse the blocking probability gain and degradation for operators. The thesis focuses on examining the performance gains that DSS can entail, in different scenarios. A number of dynamic spectrum sharing scenarios are proposed. The proposed models focus on measuring the blocking probability of secondary network operators as a trade-o� with a marginal increase of the blocking probability of a primary network in return of monetary rewards. We derived the global balance equation and an explicit expression of the blocking probability for each model. The robustness of the proposed analytical models is evaluated under different scenarios by considering varying tra�c intensities, different network sizes and adding reserved resources (or pooled capacity). The results show that the blocking probabilities can be reduced significantly with the proposed analytical DSS models in comparison to the existing local spectrum access schemes. In addition to the sharing models, we further assume that the secondary operator aims to borrow spectrum bandwidths from primary operators when more spectrum resources available for borrowing than the actual demand considering a merchant mode. Two optimisation models are proposed using stochastic optimisation models in which the secondary operator (i) spends the minimum amount of money to achieve the target GoS assuming an unrestricted budget or (ii) gains the maximum amount of pro�t to achieve the target GoS assuming restricted budget. Results obtained from each model are then compared with results derived from algorithms in which spectrum borrowings were random. Comparisons showed that the gain in the results obtained from our pro- posed stochastic optimisation model is significantly higher than heuristic counterparts. A post-optimisation performance analysis of the operators in the form of analysis of blocking probability in various scenarios is investigated to determine the probable per- formance gain and degradation of the secondary and primary operators respectively. We mathematically model the sharing agreement scenario and derive the closed form solution of blocking probabilities for each operator. Results show how the secondary and primary operators perform in terms of blocking probability under various offered loads and sharing capacity. The simulation results demonstrate that at most trading windows, the proposed opti- mal algorithms outperforms their heuristic counterparts. When we consider 80 cells, the proposed pro�t maximisation algorithm results in 33.3% gain in net pro�t to the secondary operators as well as facilitating 2.35% more resources than the heuristic ap- proach. In addition, the cost minimisation algorithm results in 46.34% gain over the heuristic algorithm when considering the same number of cells (80)