Primary User

A resource allocation framework is presented for spectrum underlay in cognitive radio networks. We consider both interference constraints for primary users and quality of service (QoS) constraints for secondary users. Specifically, interference from secondary users to primary users is constrained to be below a tolerable limit. Also, signal to interference plus noise ratio (SINR) of each secondary user is maintained higher than a desired level for QoS insurance. We propose admission control algorithms to be used during high network load conditions which are performed jointly with power control so that QoS requirements of all admitted secondary users are satisfied while keeping the interference to primary users below the tolerable limit. If all secondary users can be supported at minimum rates, we allow them to increase their transmission rates and share the spectrum in a fair manner. We formulate the joint power/rate allocation with proportional and max-min fairness criteria as optimization problems. We show how to transform these optimization problems into a convex form so that their globally optimal solutions can be obtained. Numerical results show that the proposed admission control algorithms achieve performance very close to that of the optimal solution. Also, impacts of different system and QoS parameters on the network performance are investigated for the admission control, and rate/power allocation algorithms under different fairness criteria.

Highlights of information theoretic limits, models, and design ] I n recent years, the development of intelligent, adaptive wireless devices called cognitive radios, together with the introduction of secondary spectrum licensing, has led to a new paradigm in communications: cognitive networks. Cognitive networks are wireless networks that consist of several types of users: often a primary user (the primary licenseholder of a spectrum band) and secondary users (cognitive radios). These cognitive users employ their cognitive abilities to communicate without harming the primary users. The study of cognitive networks is relatively new and many questions are yet to be answered. In this article we highlight some of the recent information theoretic limits, models, and design of these promising networks. COGNITIVE NETWORKS ARE IMMINENT MOTIVATION AND DEFINITION OF A COGNITIVE NETWORK Cognitive networks are initiated by the apparent lack of spectrum under the current spectrum management policies. The right to use the wireless spectrum in the United States is controlled by the Federal Communications Commission (FCC). Most of the frequency bands useful to wireless communication have already been licensed by the FCC. However, the FCC has designated a few unlicensed bands, most notably the industrial scientific and medical (ISM) bands, over which the immensely popular WiFi devices transmit. These bands are filling up fast, and, despite their popularity, the vast majority of the wireless spectrum is in fact licensed. Currently, the primary license Cognitive Radio Networks

Cognitive Radios have been advanced as a technology for the opportunistic use of under-utilized spectrum since they are able to sense the spectrum and use frequency bands if no Primary user is detected. However, the required sensitivity is very demanding since any individual radio might face a deep fade. We propose light-weight cooperation in sensing based on hard decisions to mitigate the sensitivity requirements on individual radios. We show that the "link budget" that system designers have to reserve for fading is a significant function of the required probability of detection. Even a few cooperating users (~10-20) facing independent fades are enough to achieve practical threshold levels by drastically reducing individual detection requirements. Hard decisions perform almost as well as soft decisions in achieving these gains. Cooperative gains in a environment where shadowing is correlated, is limited by the cooperation footprint (area in which users cooperate). In essence, a few independent users are more robust than many correlated users. Unfortunately, cooperative gain is very sensitive to adversarial/failing Cognitive Radios. Radios that fail in a known way (always report the presence/absence of a Primary user) can be compensated for by censoring them. On the other hand, radios that fail in unmodeled ways or may be malicious, introduce a bound on achievable sensitivity reductions. As a rule of thumb, if we believe that 1/N users can fail in an unknown way, then the cooperation gains are limited to what is possible with N trusted users.

In this paper we consider a single cognitive radio seeking a transmission opportunity by sequentially sensing a number of statistically independent primary channels. We study the joint optimization of the time spent to sense a channel, the decision threshold to determine whether the channel is free or busy, together with the order with which the channels are sensed. The sensing time and decision threshold are assumed to be the same for all channels. The design objective is to maximize the expected secondary throughput taking sensing errors into account and penalizing for collisions that may disrupt the primary transmission. Motivated by the computational complexity of the problem, we propose suboptimal solutions that significantly reduce the complexity without sacrificing accuracy. Our results reveal a fundamental trade-off between minimizing the probability of collision with the primary user via reducing the sensing errors, which favors a longer sensing time, and increasing the secondary user's throughput, which favors shorter sensing time. The suboptimal approach, for plausible simulation scenarios, is found to reduce the computational complexity by more than 89%, while maintaining a nearoptimal throughput within 0.28% of the optimal performance. 1

In this paper we consider the problem of signal-tointerference-plus-noise ratio (SINR) balancing in the downlink of cognitive radio (CR) networks while simultaneously keeping interference levels at primary user (PU) receivers (RXs) below an acceptable threshold with uncertain channel state information available at the CR base-station (BS). We optimize the beamforming vectors at the CR BS so that the worst user SINR is maximized and transmit power constraints at the CR BS and interference constraints at the PU RXs are satisfied. With uncertainties in the channel bounded by a Euclidean ball, the semidefinite program (SDP) modeling the balancing problem is solved using the recently developed convex iteration technique without relaxing the rank constraints. Numerical simulations are conducted to show the effectiveness of the proposed technique in comparison to known approximations.

The decision to adopt International Accounting Standards (IAS) in Jamaica with effect from 1 July 2002, makes this paper particularly apposite. 1 This brief analysis aims to provide a concise, yet rigorous, account of the principles underlying the standards, as well as the most significant changes to result in financial reporting and their implications for policy making and financial stability. This predominantly non-mathematical discourse relies on recent publications on the related issues and integrates the theoretical contributions from accounting practitioners. The findings support expectations that the implementation of IAS would result in major changes in the content of financial statements and therefore significantly impact users of financial statement data.

Cognitive radio wireless networks are an emerging communication paradigm to effectively address spectrum scarcity challenge. Spectrum sensing plays a paramount role in cognitive radio, which is widely agreed to be the most promising method for alleviating the symptom of RF spectral scarcity. Dynamic access of unused spectrum via a cognitive radio asks for flexible radio circuits that can work at an arbitrary radio frequency. In this paper, we analyze the performance of spectrum sensing on GNU Radio system with USRP. We investigating spectrum scarcity and proposed the algorithm that performed and measuring the energy of Rx signal in a fixed bandwidth, W, over an observation time window, T. The results presented that it can detected of primary user signal over the fixed bandwidth which occupied the spectrum.

In today’s healthcare environment, communication and information technologies have made the delivery of nursing care more challenging, diverse, and complex. Due to the economy, policies to protect consumers and users, emerging diseases, workforce shortage, care delivery models, and globalization, there are many considerable changes in the practice of nursing informatics. As forecast by Hannah and Ball in the 3rd Edition of Where Caring and Technology Meet, nurses have become primary users in information technology, and nurses have also taken a leading role in the development, implementation, and evaluation of healthcare systems.

Cognitive radio technologies have emerged as a platform to solve the problem of spectrum scarcity for wireless applications since cognitive radios have the potential to utilize the idle licensed spectrum bands in an intelligent way without interfering with other licensed devices. However, most of the proposed protocols for opportunistic usage of the licensed spectrum bands assume that the participants involved in the protocols are honest and that there are no malicious adversaries that will attack the network. Using two examples, we demonstrate that in the presence of a malicious adversary the systems designed making these assumptions will fail to fulfill their goals of minimal disruption of the primary users and efficient utilization of the unused spectrum. We also briefly discuss some security design goals of the future cognitive DSA networks.

In this paper, we consider the problem of spectrum sensing in cognitive radio, where unlicensed (secondary) users are allowed to share the vacant frequency bands from the licensed (primary) users. We propose two cooperation protocols to improve the detection probability compared to an existing protocol. In the first protocol, secondary users with higher detection probability constantly act as relays to help those with lower detection probability, while in the second protocol, the help-oriented users choose to relay signals according to the decision made during the first time slot. Analytical studies are provided to demonstrate the enhanced performance of our proposed protocols. Finally, simulation examples are presented to corroborate our analytical results.

This study examines the accounting practices and the degree of adoption of international accounting standards (IASs) by small and closely held companies in Bahrain. It finds that 86% (31) of the 36 companies responding to the questionnaire applied IASs and they considered IASs to be very relevant for them. All firms prepare balance sheets, and the majority prepares income statements

    In this paper, signal detection methods for spectrum sensing in IEEE 802.22 wireless RAN systems are discussed. As most of the manmade signals can be treated as cyclostationary random process, the spectral correlation function is effective for detecting of these signals. In WRAN systems, due to the specific detection environment, the computational complexity of the spectral correlation based method is significantly reduced. Peak detection in the high SNR environment together with contour figure based unique patterns search method in the low SNR environment are proposed for the primary user signal detection.

Despite its practical performance limitations, energy detection has gained popularity during the last years as a spectrum sensing technique for dynamic spectrum access in cognitive radio networks. The main advantages of energy detectionbased spectrum sensing are its simplicity, low computational and implementation costs as well as its ability to work irrespective of the actual signal to be detected. Since no prior knowledge is required, energy detection can be employed when the secondary receiver cannot gather sufficient information about the primary user signal. Due to the generality of its operating principle, the energy detector performance would not be expected to depend on the type of primary signal being detected. In this context, this paper evaluates the performance of energy detectionbased spectrum sensing for several real-world primary signals of various radio technologies. The obtained results indicate that the detection performances may vary notably with the considered primary signal but converge under certain conditions. The practical consequences of the different observed performances for several primary radio technologies are illustrated and discussed.

Wireless technology is expanding its domain and with it is growing the need for more frequencies for communication. Cognitive radio offers a solution to this problem by using the concept of Dynamic spectrum access instead of fixed spectrum allocation. Such radios are capable of sensing the RF spectrum for identifying idle frequency bands. It then transmits opportunistically so as to avoid interference with primary user over same band. In cognitive radio, intelligent spectrum sensing forms the major and most important part. Out of the various sensing techniques, we will give an overview of some of the prominent non-cooperative techniques. The paper deals with comparative study of these methods.

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

Trust is an important concept in human interactions which facilitates the formation and continued existence of functional human societies. The radio frequency spectrum is a limited natural resource and hence its efficient use is of the greatest importance. Cognitive radio is a smart wireless communication system that is conscious of its surrounding environment, learns from the environment and adapts its internal states by making corresponding changes in certain operating parameters in real time. In this paper, we search the adaptive characteristics of cognitive radio in secure and reliable communication. But how a communication system can be made reliable such that there occur no eavesdropping and information leakage. The possible solutions include integrating the merits of spread spectrum modulation, using encryption algorithms and it's potential to switch over various frequency bands. In the development of future wireless communication systems, the spectrum utilization will play an important key role due to the shortage of unallocated spectrum. The main tasks of the cognitive radio are to provide highly reliable communications whenever and wherever needed and how to utilize the radio spectrum efficiently. Cognitive radio can be the best communication system in an emergency condition as Earthquake, flood and Tsunami etc when all communication systems are failed to provide information and to communicate each other.

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

This paper is a theoretical analysis of formal annotation and ontology for the expression of the semantics of document. They are found wanting in this respect, not only for technical reasons, but because they embody a fundamentally misunderstood model of the process of signification. We propose an alternative model in which the interpretation context plays a fundamental role in the definition of an activity game that includes all actions performed on a document, including accessing external data. We briefly discuss it and its current technical embodiment.

Cognitive Radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum aware communication paradigm in wireless communications. Such networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse Quality-of-Service (QoS) requirements. Specifically, in Cognitive Radio Ad Hoc Networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, current research challenges of the CRAHNs are presented. First, spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. Moreover, the influence of these functions on the performance of the upper layer protocols are investigated and open research issues in these areas are also outlined. Finally, the proposed tools, and best simulator to solve research challenges in spectrum management are explained. This gives an insight in choosing the suitable tool, and the suitable simulator that fit for solving different challenges.

Scientists at the International Rice Research Institute (IRRI), based in the Philippines, generate a huge volume of research results emanating from multi-donor-funded projects on rice and ricerelated subject matter. In rice research, as in other fields, there is a strong push to provide free open access to these vital information resources in a variety of modes that are convenient to researchers located in both the developing and developed world. The main objective is to disseminate, as widely possible, the results of IRRI's research on rice, a crop, which feeds nearly half of the world's 6.6 billion inhabitants. Currently, some instruments for open access are already in place at IRRI, such as links to full-text publications posted on the institute's Web site (www.irri.org), especially via the Library branch site (http://ricelib.irri.cgiar.org), the Rice Knowledge Bank (www.knowledgebank.irri.org), and publications catalog (www.irri.org/publications/catalog). The joint initiatives of the Library and the Institute's main science publishing units, particularly the Communication and Publications Services and the Training Center, typify a convergence of practices in information and publishing management to overcome hurdles that both activities face. This paper demonstrates how the links between these two fields in the middle of the scholarly publishing chain can bridge the gap between public goods (knowledge about rice in this case) and the intended primary users, namely researchers and extensionists in the national agricultural research and extension systems (NARES) in the developing countries that IRRI serves. This paper also discusses the publishing processes and models in a donor-driven international research organization that delivers public goods. To meet their missions, organizations such as IRRI must seek a range of demand and supply models for the scholarly publications in their supply chain. Open access publishing is one model-among others-to adopt. But first, the onus is to overcome obstacles such as intellectual property rights, dwindling funds, and connectivity to name just three major ones. Donors, IRRI's NARES partners, governments, and finally rice farmers and consumers expect public institutions such as IRRI to create and share information for the common good. Public institutions are currently caught up in an information delivery transition from traditional paper to electronic files over the Internet. Even though we are in the digital age, not everyone is connected. Information that will provide impact to IRRI's constituent clients must be delivered to them through whatever open access form that is appropriate and useful, being it "cutting edge" digital versions or traditional "books-on-the-shelf" hard copies. This paper addresses this dilemma and will hopefully encourage thinking to optimize the enabling power that can be provided by open access publishing.

Authorization, authentication, and accounting schemes for WiMAX (Worldwide Interoperability for Microwave Access) are the focus of this paper. WiMAX works as a wireless metropolitan area network (MAN) technology, based on IEEE 802.16 specifications, which was designed to provide high-throughput wireless broadband connections (up to 70 Mbps for fixed scheme and up to 15 Mbps for mobile scheme) over long distances (up to 30 miles) , which is described as a "framework for the evolution of wireless broadband". The main focus of the authentication and authorization is based on the privacy key management $extensible authentication protocol for pairwise key manegement "EAP-PKM" and the accounting issue

In this paper, we present an analytical model as well as a practical mechanism to detect denial of service (DoS) attacks on secondary users in dynamic spectrum access (DSA) networks. In particular, we analyze primary user emulation attacks (PUEA) in cognitive radio networks without using any location information and therefore can do away with dedicated sensor networks. We present an analysis using Fenton's approximation and Wald's sequential probability ratio test (WSPRT) to detect PUEA. Simulation results demonstrate that it is possible to keep the probability of success of PUEA low, while still keeping the probability of missing the return of the primary low as well.

Cognitive radio (CR) technology is an innovative radio design philosophy in order to increase the spectrum utilization by exploiting the unused spectrum in dynamically changing environments. Specifically, the CR technology will allow a group of potential users (referred to as secondary users) to access available spectrum resources unused by primary users (PUs) for whom the band has been licensed. The spectrum available for secondary users (SUs) depends on PUs' activity in the licensed spectrum. In this paper, we develop a queuing analytic framework to study important performance measures experienced by SUs in a CR network. We study queuing delay and buffer statistics of SUs' packets by modeling PUs' activity as a two state Markov chain and SUs' channel quality variation as a finite state Markov chain (FSMC). In order to allocate available channels among the SUs, an opportunistic channel allocation scheme is considered. The proposed framework facilitates to design an admission controller for SUs' network in order to maintain a given quality service (QoS) requirement which is specified in the form of statistical delay guarantee.

This paper investigates the problem of interference minimization which restricts the secondary users (SUs) quality of service (QoS) while coexisting the primary users (PUs), using distributed beamforming for a bidirectional cognitive relay network. We consider a network which consists of two secondary transceivers and K cognitive relay nodes and a primary network with a transmitter and receiver, all equipped with single-antenna. For effective use of spectrum we propose a two-step two-way relaying for cognitive relay networks. Our aim is to design the beamforming coefficients for a bidirectional cognitive relay network through interference minimization approach subject to two constraints on each transceiver QoS which is solved using convex optimization. Our simulation results demonstrate that our distributed relay beamforming scheme improve network performance significantly so that the interference power is decreased by increasing the number of relay nodes while QoS of the secondary network is guaranteed.

In this paper, we propose a novel simple heuristic algorithm for scheduling the secondary link activation and provide a dynamic spectrum sharing in cognitive radio networks. This algorithm is presented for spectrum underlay where primary and secondary users transmit simultaneously on the same frequency bands in cognitive radio networks. The proposed algorithm is based on a graph-theoretical model. First, the

Dynamic spectrum access has proposed tiering radios into two groups: Primary Users (PUs) and Secondary Users (SUs). PUs are assumed to have reserved spectrum available to them, while SUs (operating in overlay mode) must share whatever spectrum is available. The threat of Emulation Attacks, in which users pretend to be of a type they are not (either PU or SU) in order to gain unauthorized access to spectrum, has the potential to severely degrade the expected performance of the system. We analyze this problem within a Bayesian game framework, in which users are unsure of the legitimacy of the claimed type of other users. We show that depending on radios' beliefs about the fraction of PUs in the system, a policy maker can control the occurrence of emulation attacks by adjusting the gains and costs associated with performing or checking for emulation attacks.

Spectrum sensing is an essential enabling functionality for cognitive radio networks to detect spectrum holes and opportunistically use the under-utilized frequency bands without causing harmful interference to legacy networks. This paper introduces a novel wideband spectrum sensing technique, called multiband joint detection, which jointly detects the signal energy levels over multiple frequency bands rather than consider one band at a time. The proposed strategy is efficient in improving the dynamic spectrum utilization and reducing interference to the primary users. The spectrum sensing problem is formulated as a class of optimization problems in interference limited cognitive radio networks. By exploiting the hidden convexity in the seemingly non-convex problem formulations, optimal solutions for multiband joint detection are obtained under practical conditions. Simulation results show that the proposed spectrum sensing schemes can considerably improve the system performance. This paper establishes important principles for the design of wideband spectrum sensing algorithms in cognitive radio networks.

Efficient design of cognitive radio networks calls for secondary users implementing adaptive resource allocation, which requires knowl edge of the channel state information in order to limit interference inflicted to primary users. In this context, the present paper develops stochastic resource allocation algorithms maximizing the sum-rate of secondary users while adhering to "average power" and "proba bility of interference" constraints. These constraints guarantee that the probability of the secondary network interfering with the primary one stays below a pre-specified level. The optimal schemes turn out to be a function of the quality of the secondary network links, the activity of the primary users, and the associated Lagrange multipli ers. The focus is on algorithms that: i) use stochastic approximation tools to estimate the multipliers; and ii) are able to cope with imper fections in the information of the primary network state.

We consider the overlay cognitive radio channel where the cognitive user is admitted to transmit simultaneously with the primary user provided that the instantaneous rate of primary link is not degraded. Assuming causal knowledge of the primary user's message at the cognitive transmitter (CT), we analyze the transmission rates of the cognitive user in the singleinput multiple-output (SIMO) and the multiple-input singleoutput (MISO) configurations. In particular, the CT uses a part of its transmit power to assist the primary user in delivering the primary user's message and the other part of its power is used to deliver its own message. The transmit power and the beamformers are designed to maximize the rate of the cognitive user while fixing the the rate of the primary user. Our simulation results show that the proposed scheme yields improved system performance compared to the interweave scheme where any interference to the primary user is prohibited.

| Cognitive radio is an exciting emerging technology that has the potential of dealing with the stringent requirement and scarcity of the radio spectrum. Such revolutionary and transforming technology represents a paradigm shift in the design of wireless systems, as it will allow the agile and efficient utilization of the radio spectrum by offering distributed terminals or radio cells the ability of radio sensing, self-adaptation, and dynamic spectrum sharing. Cooperative communications and networking is another new communication technology paradigm that allows distributed terminals in a wireless network to collaborate through some distributed transmission or signal processing so as to realize a new form of space diversity to combat the detrimental effects of fading channels. In this paper, we consider the application of these technologies to spectrum sensing and spectrum sharing. One of the most important challenges for cognitive radio systems is to identify the presence of primary (licensed) users over a wide range of spectrum at a particular time and specific geographic location. We consider the use of cooperative spectrum sensing in cognitive radio systems to enhance the reliability of detecting primary users. We shall describe spectrum sensing for cognitive radios and propose robust cooperative spectrum sensing techniques for a practical framework employing cognitive radios. We also investigate cooperative communications for spectrum sharing in a cognitive wireless relay network. To exploit the maximum spectrum opportunities, we present a cognitive space-time-frequency coding technique that can opportunistically adjust its coding structure by adapting itself to the dynamic spectrum environment.

Primary user emulation attacks are a potential security threat to cognitive radio networks. In this work, we attempt to characterize an advanced primary user emulation attack and an advanced countermeasure against such an attack. Specifically, we show that both the attacker and the defender can apply estimation techniques and learning methods to obtain the key information of the environment and thus design better strategies. We further demonstrate that the advanced attack strategy can defeat the naive defense technique that focuses only on the received signal power, whereas the advanced defense strategy that exploits the invariant of communication channels can counteract the advanced attack effectively. 208 978-1-4244-5736-6/09/$26.00 ©2009 IEEE

In this paper, we analyze the performance of a secondary link in a cognitive radio (CR) system operating under statistical quality of service (QoS) delay constraints. In particular, we quantify analytically the performance improvement for the secondary user (SU) when applying a feedback based sensing scheme under the "SINR Interference" model. We leverage the concept of effective capacity (EC) introduced earlier in the literature to quantify the wireless link performance under delay constraints, in an attempt to opportunistically support real-time applications. Towards this objective, we study a two-link network, a single secondary link and a primary network abstracted to a single primary link, with and without primary feedback exploitation. We analytically prove that exploiting primary feedback at the secondary transmitter improves the EC of the secondary user and decreases the secondary user average transmitted power. Finally, we present numerical results that support ou...

This document includes definitions, calculations and measurements of building energy use for use in energy performance analyses and is provided by the National Renewable Energy Laboratory ("NREL"), which is operated by the Midwest Research Institute ("MRI") for the U.S. Department of Energy ("DOE"). Access to and use of the information contained in this document shall impose the following obligations on the user, as set forth in this Agreement. The user is granted the right, without any fee or cost, to use, copy, modify, alter, enhance and distribute the information in this document for any purpose whatsoever, except commercial sales or other commercial purposes, provided that this entire notice appears in all copies of this document. Further, the user agrees to credit DOE/NREL/MRI in any publication that results from or includes any of the information contained in this document. The names DOE/NREL/MRI, however, may not be used in any advertising or publicity to endorse or promote any product or commercial entity unless prior specific written permission is obtained from the DOE/NREL/MRI. The user also understands that DOE/NREL/MRI is not obligated to provide the user with any support or assistance of any kind whatsoever with regard to the use of the information contained in this document or to provide the user with any updates, revisions or new versions of the information contained in this document.

The spectrum sensing problem has gained new aspects with cognitive radio and opportunistic spectrum access concepts. It is one of the most challenging issues in cognitive radio systems. In this paper, a survey of spectrum sensing methodologies for cognitive radio is presented. Various aspects of spectrum sensing problem are studied from a cognitive radio perspective and multi-dimensional spectrum sensing concept is introduced. Challenges associated with spectrum sensing are given and enabling spectrum sensing methods are reviewed. The paper explains the cooperative sensing concept and its various forms. External sensing algorithms and other alternative sensing methods are discussed. Furthermore, statistical modeling of network traffic and utilization of these models for prediction of primary user behavior is studied. Finally, sensing features of some current wireless standards are given.

Cognitive radio (CR) technology allows a secondary or cognitive user (CU) to opportunistically access frequency band of a primary user (PU) when it is not in use. However, a CU needs to perform spectrum sensing periodically to avoid causing harmful interference and thereby protecting the quality of service of PUs. A conventional frame structure for CR operation consists of sensing time slot and data transmission time slot which run consecutively. Basically, a longer sensing time produces a higher probability of detection and therefore, better PU protection. However, longer sensing time will reduce the amount of time for data transmission and hence affects the achievable throughput of a CU. In this paper, we study the fundamental tradeoff between sensing time and achievable throughput of the CUs. Based on energy detection scheme, we propose and investigate the feasibility of using Particle Swarm Optimization (PSO) in the design of sensing slot duration to maximize the achievable throughput for CUs for a given frame duration. The results show an encouraging 8.89% increase in throughput with respect to the probability of false alarm, a reduced sensing time by 80% while achieving 97.8% of normalized throughput for CU system with PSO.

In this paper we propose a novel power allocation scheme for Hybrid Overlay-Underlay spectrum sharing technique in OFDM-Based Cognitive Radio (CR) Systems. In OFDM-Based Cognitive Radio systems, the interference power limits of the primary users (PUs) introduce subcarriers transmit power constraints for the secondary user (SU). The power allocation among the subcarriers of SU should be subjected to both the sum transmit power constraint ( � ) as well as the tolerable interference (Q) that is imposed to primary user (PU) due to transmit power and the leakage of sidelobes signal. Different from previous works, we deal with a more general case in where the subcarriers sidelobes signals are specially considered in both Idle and Busy bands. A general power allocation algorithm is proposed to obtain the optimal solution (by dual decomposition method) that maximizes the capacity while satisfying both these constraints. We have divided the assigned power into two kinds: (the allocated power to subcarriers which are active in the Idle band) and (the power allocated to subcarriers which are active in the Busy band). Numerical results revealed that the current Hybrid Overlay-Underlay approach is more efficient than both overlay and underlay schemes.

We consider the problem of Spectrum Sensing in Cognitive Radio Systems. We have developed a distributed algorithm that the Secondary users can run to sense the channel cooperatively. It is based on sequential detection algorithms which optimally use the past observations. We use the algorithm on secondary users with energy detectors although it can be used with matched filter and other spectrum sensing algorithms also. The algorithm provides very low detection delays and also consumes little energy. Furthermore it causes low interference to the primary users. We compare this algorithm to several recently proposed algorithms and show that it detects changes in spectrum faster than these algorithms and uses significantly less energy.