A Survey on Spectral Handoff Mechanisms for the Cognitive Radio Network

In a cognitive radio network, the cognitive radio (CR) devices also called as secondary users (SU's) need to change their operating frequency due to the inclusion of primary user (PU) in that frequency band. Thus when a PU arrives in a frequency band and asks for a channel in that band, it gets that band and occupies the channel which may be occupied by a SU. In this situation, the SU needs to find another channel in a different frequency band which leads to the spectral handoff. Thus in addition to the location based handoffs for the SU, spectral handoff also occur. This spectral handoff may be done several times for the SU. Thus this situation leads to the study of handoff mechanism. This paper carries out a survey of the handoff types and their mechanisms which have been already conceptualized. DOI: 10.17762/ijritcc2321-8169.15012

A New Protocol for Cooperative Spectrum Sharing in Mobile Cognitive Radio Networks

To optimize the usage of limited spectrum resources, cognitive radio (CR) can be used as a viable solution. The main contribution of this article is to propose a new protocol to increase throughput of mobile cooperative CR networks (CRNs). The key challenge in a CRN is how the nodes cooperate to access the channel in order to maximize the CRN's throughput. To minimize unnecessary blocking of CR transmission, we propose a so-called new frequency-range MAC protocol (NFRMAC). The proposed method is in fact a novel channel assignment mechanism that exploits the dependence between signal's attenuation model, signal's frequency, communication range, and interference level. Compared .to the conventional methods, the proposed algorithm considers a more realistic model for the mobility pattern of CR nodes and also adaptively selects the maximal transmission range of each node over which reliable transmission is possible. Simulation results indicate that using NFRMAC leads to an increase of the total CRN's throughput by 6% and reduces the blocking rate by 10% compared to those of conventional methods

A Review of Cross-layer Design in Dynamic Spectrum Access for Cognitive Radio Networks

Cognitive Radio (CR) is an intelligent radio that can dynamically access the radio spectrum. Secondary users in Cognitive Radio Network (CRN) can access the licensed spectrum without causing harmful interference to primary users. The performance of cognitive radio networking functionalities depends on the properties of the spectrum band in use. This necessitates a crosslayer design in the entire CR networking protocol stack. Current researches are investigating different techniques of using cognitive radio to reuse more locally unused spectrums to increase the total system capacity. This paper provides a comprehensive survey of cross-layer design in cognitive radio network. The cross-layer design approach jointly considers the functions of the layers to maximize the performance of CR networks.</p

Performance Analysis of Secondary Users in Cognitive Radio Networks

Cognitive radio technology is to improve the inefficient usage of limited spectrum resources when wireless networks coexist. Using this technology, the unlicensed users (secondary users) can opportunistically access the frequency band of licensed users (primary users). There are different kinds of cognitive radio networks. This thesis focuses on the interweave cognitive radio network, where the secondary users are only allowed to access the spectrum holes, i.e., the idle parts of the licensed spectrum band. The main task is to analyze the opportunistic dynamic spectrum allocation method based on selecting the largest available spectrum hole, where the goal is to have the maximum possible transmission rate for secondary users. The objective of this work is to give the service provider an estimation about the load of secondary users in different numbers of channels and various kinds of traffics in primary networks. The work starts with the investigation on the spectrum allocation for secondary users in a network of single-channel primary users. In our analysis, we propose a theoretical model to calculate the probability distribution of the length of the largest available spectrum hole. The contribution of this part is the modeling and performance analysis of the existing conventional method, which selects the largest available spectrum hole. The main contribution is the calculation of the conditional probability of having maximum consecutive idle channels under the condition of a given number of total channels and various number of busy channels. For any given number of channels, this conditional probability gives us the number of consecutive idle channels the secondary user can have, if we know the probability distribution of busy channels taken by primary users. The theoretical model works for any given number of total channels in the licensed frequency band, with numerical and simulation results confirming the precision of the proposed model. Later, we continue our study on the spectrum allocation in a cognitive radio network of multichannel primary users, where the secondary user temporarily takes the largest available spectrum hole. For the performance analysis, we basically need to solve two problems. First, we need to find the probability distribution of busy channels taken by primary users. Second, we need to determine the length of the largest available spectrum hole under the condition of primary users taking different channels. In the case of primary users taking multiple channels, the calculation of the conditional probability of having maximum consecutive idle channels under the condition of a given number of total channels and various number of busy channels, is approximately valid, especially in low-traffic networks. As such, the main contribution in this part is finding the probability distribution of busy channels taken by primary users. The solution scenario is based on a multidimensional Markov chain, with numerical and simulation results verifying the accuracy of the proposed model. Finally, an approximate one-dimensional Markov chain is also proposed to simplify the complicated multidimensional solution. We provide an approximate estimation for the load of the secondary user to avoid the calculation of the complex multidimensional Markov chain. The procedure significantly decreases the complexity, although we lose some information. The main concern in the one-dimensional approximation is to find the departure rates from each state of busy channels. It is actually the main challenge of this part and by approximation we provide the solution. At the end, the performance of the proposed model was validated by numerical and simulation results

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

Cooperative Spectrum Sharing in Cognitive Radio Networking

Driven by the massive growth in communications data traffic as well as flourishing users' demands, we need to fully utilize the existing scarce spectrum resource. However, there have been several studies and reports over the years showing that a large portion of licensed spectrum is actually underutilized in both temporal and spatial domains. Moreover, aiming at facing the dilemma among the fixed spectrum allocation, the ever enormous increasing traffic demand and the limited spectrum resource, cognitive radio (CR) was proposed by Mitola to alleviate the under usage of spectrum. Thus, cognitive radio networking (CRN) has emerged as a promising paradigm to improve the spectrum efficiency and utilization by allowing secondary users (SUs) to utilize the spectrum hole of primary users (PUs). By using spectrum sensing, SUs can opportunistically access spectrum holes for secondary transmission without interfering the transmissions of the PUs and efficient spectrum utilization by multiple PUs and SUs requires reliable detection of PUs. Nevertheless, sensing errors such as false alarm and misdetection are inevitable in practical networks. Hence, the assumption that SUs always obtain the exact channel availability information is unreasonable. In addition, spectrum sensing must be carried out continuously and the SU must terminate its transmission as soon as it senses the re-occupancy by a PU. As a better alternative of spectrum sensing, cooperation has been leveraged in CRN, which is referred as cooperative cognitive radio networking (CCRN). In CCRN, in order to obtain the transmission opportunities, SUs negotiate with the PUs for accessing the spectrum by providing tangible service for PUs. In this thesis, we study cluster based spectrum sharing mechanism for CCRN and investigate on exploiting the cooperative technique in heterogeneous network. First, we develop cooperation protocols for CRN. Simultaneous transmission can be realized through quadrature signalling method in our proposed cooperation protocol. The optimal power allocation has been analyzed and closed-form solution has been derived for amplify and forward mode. Second, we study a cluster based spectrum sharing mechanism. The spectrum sharing is formulated as a combinatorial non-linear optimization problem which is NP-hard. Afterwards, we solve this problem by decomposing it into cluster allocation and time assignment, and we show that the result is close to the optimal solution. Third, we propose a macrocell-femtocell network cooperation scheme for heterogeneous networks under closed access mode. The cooperation between the femtocell network and macrocell network is investigated. By implementing the cooperation, not only the macrocell users' (MUEs') and femtocell users' (FUEs') utility can be improved compared with the non-cooperation case, but also the energy consumption as well as the interference from the femtocell network to the macrocell network can be reduced

The integration of device-to-device communication in future cellular systems

The usage of mobile data services over cellular spectrum has been dramatically increased in the last decade. The increment led to an explosive growth in user’s booming data demands over the cellular spectrum band. However, the current technologies have a limitation in the allocated spectrum resources, compared to the data demands. This leads to insufficient throughput using the current technologies in the next few years. Improving the throughput with user’s data demands necessitates finding an efficient approach to offload data booming. Device-to-Device (D2D) communication has been proposed as an unconventional mobile paradigm with a scalable manner to offload the mobile data traffic of the local peer-to-peer mobile users by sharing the resources the cellular networks without traversing the base stations. Applying such paradigm increases the spectrum utilization which improves the total throughput in a given cell. However, many issues negatively influence the performance of D2D communication over the cellular spectrum band such as interference from the cellular users, the low activity of the cellular users over the allocated resources in time which reduces spectrum utilization and the dynamic cellular environment which impacts the link performance of D2D communication and may leads to not meet the desired quality of service requirements of the data services. Solving the aforementioned issues requires: i) developing the appropriate access paradigms of the D2D communication to meet the desired quality of service requirements of mobile data services; ii) increasing the spectrum utilization of licensed band by enabling unlicensed users to invest the spectrum holes; and iii) developing the link adaptation processes to overcome the dynamic behavior of the cellular system and improve the throughput in D2D communication links. This dissertation presents the aforementioned solutions for the D2D communication which improve the total throughput in the cell. The dissertation has three main contributions: i) position-based hybrid access paradigm for D2D communication; ii) hybrid access paradigm for unlicensed peer-to-peer users (unlicensed D2D communication); and iii) an algorithm for link adaptation of unlicensed D2D communication. First, the thesis develops a position-based model for maximizing the throughput of D2D communication using different access paradigms. This model defines the regions in the cell in which the D2D communication can be performed with the desired QoS. Then, a position-based hybrid access paradigm is presented which selects a given access paradigm used by D2D pairs in order to improve the total throughput in the cell. The proposed access paradigms are evaluated using numerical simulations and the results show improvements in the total throughput and the number of satisfied D2D communications in the cell, compared to recent access paradigms. Second, an integration of cognitive radio technology with the unlicensed D2D pairs to apply dynamic spectrum access is presented. The recent access paradigms of cognitive radio and their achievable throughput are studied. Then, a position-based hybrid access paradigm is introduced to increase the regions of unlicensed D2D communication. The evaluation of the proposed access paradigm is performed using numerical simulations. The results show improvement in the throughput over the cell and the area used by unlicensed D2D communications, compared to recent access paradigms. Third, the dynamic behavior of the cellular environment and its interaction with the unlicensed D2D communication is studied. One possible solution presented applying artificial intelligence technique as a cognitive engine to perform link adaptation efficiently. Based on this study, a Self-Organized Link Adaptation (SOLinA) algorithm is presented to adapt the link of unlicensed D2D communication autonomously and determine the link configuration which improves the throughput of the system. The evaluation of the proposed algorithm is performed using simulations of unlicensed D2D communication within dynamic cellular environment. The results of the simulations show that SOLinA outperforms the previous work in the throughput under different separations between the unlicensed D2D communication, different cellular system requirements and at different user’s positions in the cell.In der letzten Dekade nahm der Einsatz mobile Datendienste in zellularen Netzen stark zu und führte zu einem exponentiellen Anstieg der Nutzerdaten. Die aktuellen Technologien weisen jedoch, bezogen auf das geforderte Datenvolumen, Einschränkungen auf, die auch in den kommenden Jahren zu einem unzureichenden Durchsatz führen werden. Die Erhöhung des Durchsatzes für Nutzerdaten erfordert die Suche nach einem effizienten Ansatz um das steigende Datenvolumen zu bewältigen. Ein möglicher Ansatz ist Device-to-Device (D2D) Kommunikation als ein unkonventionelles, mobiles Paradigma, das hohen Datenverkehr skalierbar auf lokale Peer-to -Peer- Anwender überträgt. Dabei werden die Ressourcen zwischen D2D- und zellularen Nutzern aufgeteilt, wobei der D2DDatenverkehr direkt zwischen Endgeräten, d.h. ohne Einsatz der Basis Station erfolgt. Dadurch kann das Frequenzspektrum effizienter genutzt, und somit der Gesamtdurchsatz der Zelle erhöht werden. Zugleich wirken sich mehrere Faktoren negativ auf den Durchsatz der D2D-Kommunikation im zellularen Spektralband aus, wie z. B. die Interferenz zellularer Endgeräte, die weiterhin direkt mit der Basisstation kommunizieren. Zusätzlich reduziert geringe Aktivität der zellularen Endgeräte über die zugewiesenen Ressourcen die Spektraleffizienz, mit negativer Auswirkung auf den Durchsatz der D2DVerbinding. Das kann dazu führen, dass die gewünschte Qualität des Datendiensts nicht erreicht wird. Die Lösung der oben genannten Probleme erfordert: i) die Entwicklung entsprechender Zugriffsmechanismen für die D2D-Kommunikation, um die gewünschte Qualität der Service-Anforderungen mobiler Datendienst zu erreichen; ii) die Auslastung des Funkspektrums des lizenzierten Bands zu erhöhen, indem nicht lizenzierten Nutzern temporär freie Bereiche des Spektrums verwenden; und iii) die Entwicklung eines Prozesses zur Link-Adaption unter Berücksichtigung des dynamischen Verhaltens des zellularen Systems, so dass sich der Durchsatz der D2D-Verbindung erhöht . Die vorliegende Arbeit stellt die oben genannten Lösungen für die D2D-Kommunikation, die den Gesamtdurchsatz in der Zelle erhöhen sollen, vor. Die Hauptbeiträge sind: i) ein positionsbasierter, hybrider Zugriffsmechanismus für die D2D-Kommunikation; ii) ein hybrider Zugriffsmechanismus für unlizenzierte Peer-to-Peer Nutzer (unlizenzierte D2D-Kommunikation); und iii) ein Algorithmus zur Link-Adaption der unlizenzierten D2D-Kommunikation. Zuerst wird in dieser Arbeit ein positions-basiertes Modell entwickelt, um den Durchsatz der D2D-Kommunikation zu maximieren, wobei unterschiedliche Zugriffsmechanismen eingesetzt werden. Im Modell werden die Regionen in der Zelle definiert, in der die D2D-Kommunikation mit der gewünschten Service-Qualität (QoS) durchgeführt werden kann. Anschließend wird ein positionsbasierter, hybrider Zugriffsmechanismus vorgestellt, der beim Einsatz für ein D2D-Paar zur Erhöhung des Gesamtumsatzes der Zelle führt. Die vorgeschlagenen Zugriffsmechanismen werden durch numerische Simulationen evaluiert. Die Ergebnisse zeigen Verbesserungen im Gesamtdurchsatz und der Anzahl der zufriedenen D2D-Kommunikationen in der Zelle. Als nächster Schritt wird kognitive Funktechnik (Cognitive Radio) in das unlizenzierte D2D-Paar integriert, wodurch ein dynamischer Zugriff auf das Funkspektrum erreicht wird. Die neu eingeführten Zugriffsmechanismen und der jeweilig erreichbare Durchsatz werden untersucht. Als Ergebnis wird ein positionsbasierter, hybrider Zugriffsmechanismus eingeführt, um die Regionen mit unlizenzierter D2D-Kommunikation zu vergrößern. Zur Evaluierung des vorgeschlagenen Zugriffsmechanismus werden numerische Simulationen eingesetzt. Die erzielten Ergebnisse weisen Verbesserungen im Durchsatz, sowohl innerhalb der Zelle, als auch in der unlizenzierten D2D-Kommunikation, nach. Als letzter Schritt wird das dynamische Verhalten der zellularen Umgebung, sowie ihrer Interaktion mit der unlizenzierten D2D-Kommunikation untersucht. Als eine mögliche Lösung wird der Einsatz künstlicher Intelligenz als eine kognitive Maschine vorgestellt, um die Funkverbindung effizient zu adaptieren. Auf Basis der Studie wird der Algorithmus „Self-Organized Link Adaptation” (SOLinA) vorgestellt, um die Funkverbindung der unlizenzierten D2D-Kommunikation autonom anzupassen und die Verbindungskonfiguration so anzupassen, dass der Systemdurchsatz erhöht wird. Evaluiert wird der vorgeschlagene Algorithmus durch Simulationen der unlizenzierten D2D-Kommumikation innerhalb einer dynamischen zellularen Umgebung. Die neuesten Simulationsergebnisse zeigen, dass SOLinA die zuvor erzielten Ergebnisse beim Durchsatz, sowohl für unterschiedliche Konstellationen der unlizenzierten D2D-Kommunikation, als auch für unterschiedliche Anforderungen an das zellulare System und für variierende Positionen der Nutzer in der Zelle übertrifft