Cognitive Radio Networks

Learning and Reasoning in Cognitive Radio Networks Liljana Gavrilovska, Vladimir Atanasovski, Irene Macaluso, and Luiz DaSilva Abstract—Cognitive radio networks challenge the traditional wireless networking paradigm by introducing concepts firmly stemmed into the Artificial Intelligence (AI) field, i.e., learning and reasoning. This fosters optimal resource usage and manage- ment allowing a plethora of potential applications such as sec- ondary spectrum access, cognitive wireless backbones, cognitive machine-to-machine etc. The majority of overview works in the field of cognitive radio networks deal with the notions of obser- vation and adaptations, which are not a distinguished cognitive radio networking aspect. Therefore, this paper provides insight into the mechanisms for obtaining and inferring knowledge that clearly set apart the cognitive radio networks from other wireless solutions.

1.1 Introduction One of the most prominent features of cognitive radio networks will be the ability to switch between radio access technologies, transmitting in different portions of the radio spectrum as unused frequency band slots arise [2, 3, 4]. This dynamic spectrum access is one of the fundamental requirements for transmitters to adapt to varying channel quality, network congestion, interference and service requirements. Cognitive radio networks (from now on called secondary networks) will also need to coexist with legacy ones (hereafter called primary networks), which have the right to their spectrum slice and thus can not accept interference. Based on these facts, under-utilization of the current spectrum and the need to increase the network capacity is pushing research towards new means of exploiting the wireless medium. In this direction, the Federal Communications Commission (FCC) Spectrum Pol- icy Task Force has published a report [5] in 2002, in which it thoroughly investigates the under utilization of the radio spectrum. While the FCC is in charge of determining the spectrum usage and its policies, the Whitespace Coalition, formed by companies such as Microsoft, Google, Dell, HP and Intel is studying ways to exploit the spectrum vacancies in the television band. Cognitive radio networks are envisioned to be able to opportunistically exploit those spectrum “left-overs”, by means of knowledge of the environment and cogni- tion capability, in order to adapt their radio parameters accordingly. Spectrum sensing is the technique that will enable cognitive radio networks to achieve this goal.

Cognitive Radio Networks (CRN) provide a platform for addressing the under utilization of the licensed spectra through a variety of Dynamic Spectrum Access (DSA) techniques[9][10]. In such environments, Secondary Users (SUs) are allowed to access licensed Primary Users (PU) spectra provided that they do not interfere with PU network operations. Since the SUs access to the licensed spectra is opportunistic, obtaining a shared communication channel between SUs must occur before any data transmissions can be undertaken. Therefore channel rendezvous plays a crucial role in network connectivity[5].

Cognitive radio is a promising technology aiming to improve the utilization of the radio electromagnetic spectrum. A cognitive radio is a smart device which runs radio applications software to perform signal processing. The use of this software enables the device to sense and understand its environment and actively change its mode of operation based on its observations. Unfortunately, this solution entails new security challenges. In this paper, we present a cross-layer attack to TCP connections in cognitive radio networks, analyze its impact on TCP throughput via analytical model and simulation, and propose potential countermeasures to mitigate it.

Palakkd, Kerala, India ABSTRACT The available radio spectrum is not used efficiently, therefore a new technology called Cognitive Radio (CR) is used to increase the spectrum utilization. The objective of CR is to use the available spectrum efficiently without any interference to the Primary Users (PUs). Spectrum sensing plays an essential part in cognitive radio networks inorder to obtain spectrum awareness. Energy detection, matched filter detection, cyclostationary detection etc are the most commonly used techniques for spectrum sensing.This paper proposes an Adaptive spectrum sensing technique in which a particular sensing method from matched filter detection, Energy detection or Wavelet based detection is chosen according to the information available and SNR of the received signal. This paper also investigates the performance of both Eigen value and Wavelet based sensing in low SNR regions.

The scarcity of bandwidth in the radio spectrum has become more vital since the demand for wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum bands and the inefficiency in their utilization have been smartly addressed by the cognitive radio (CR) technology which is an opportunistic network that senses the environment, observes the network changes, and then uses knowledge gained from the prior interaction with the network to make intelligent decisions by dynamically adapting transmission characteristics. In this thesis, recent research and survey about the advances in theory and applications of cognitive radio technology has been reviewed. The thesis starts with the essential background on cognitive radio techniques and systems and discusses those characteristics of CR technology, such as standards, applications and challenges that all can help make software radio more personal. It then presents advanced level material by extensively reviewing the work done so far in the area of cognitive radio networks and more specifically in medium access control (MAC) protocol of CR. The list of references will be useful to both researchers and practitioners in this area. Also, it can be adopted as a graduate-level textbook for an advanced course on wireless communication networks.

With the rapid increase in wireless devices, an effective improvement in the demand of efficient spectrum utilisation for gaining better connectivity is needed. Cognitive Radio (CR) is an emerging technology that exploits the inefficient utilisation of the unused spectrum dynamically. Since spectrum sharing is responsible for coordinating channels’ access for Cognitive Users (CUs), the Common Control Channel (CCC) is one of the existing methods used to exchange the control information between CUs. However, the unique characteristics and parameters of Cognitive Radio Networks (CRNs) present several possible threats targeting spectrum sensing, spectrum management, spectrum sharing, and spectrum mobility leading to the deterioration of the network performance. Thus, protection and detection security mechanisms are essential to maintaining the CRNs. This thesis presents a novel decentralised CR MAC protocol that successfully utilises the unused portion of the licensed band. The protocol achieves improved performance; communication time and throughput when compared to two benchmark protocols. Less communication time and higher throughput are accomplished by the protocol due to performing fast switching to the selected available data channel for initiating data transmission. The proposed protocol is then extended to two different versions based on two authentication approaches applied to it; one using Digital Signature and another is based on

ABSTRACT: With the increasing of communication applications in recent years, the demand for radio spectral resources has in- creased significantly. Cognitive radio scenario was proposed to improve spectrum efficiency in wireless communication systems. Sensing/monitoring of spectrum-availability has been identified as a key requirement for spectrum allocation in cognitive radio networks (CRNs). In this paper a framework model is designed to detect Primary and Secondary users and each spectrum is characterized by jointly considering primary user activity and spectrum sensing operations. In the final step the decision model is proposed to allocation the spectrum to the cognitive users without affecting the Primary Users. Spectrum decision is the ability of a cognitive radio (CR) to select the best available spectrum band to satisfy secondary users’ (SUs’) quality of service (QoS) requirements, without causing harmful interference to licensed or primary users (PUs).

“ SPECTRUM SENSING SCHEMES FOR COGNITIVE RADIO NETWORKS ” . Primarily, we submit our gratitude & sincere thanks to our supervisor Prof. Poonam Singh, Department of Electronics and Communication Engineering, for her constant motivation and Support during the course of our work in the last one year. We truly appreciate and value her esteemed guidance and encouragement from the beginning to the end of this thesis. We are indebted to her for having helped us shape the problem and providing insights towards the Solution.

In cognitive radio networks Dynamic Spectrum Allocation (DSA) policy is adopted instead of the Fixed Spectrum Allocation (FSA) policy, where unlicensed users known as seco[r]

2. Related Work There have been many research activities on proposing optimal spectrum-sensing strategies. In [7], authors introduced an energy-efficient cooperative spectrum-sensing scheme in sensor-aided cognitive radio networks. Authors addressed the energy minimization problem under accuracy constraint of the detection and false alarm probabilities. The bounds for the number of sensors to simultaneously guarantee the thresholds for high detection probability and low false alarm probability are derived. With these bounds, the optimization problem is formulated to find the optimal sensing interval and the optimal number of sensor that minimize the energy consumption. In [8] an optimal scheduling of each sensor active time is presented to extend the network lifetime. Authors divide the sensors into a number of feasible subsets, such that only one subset of sensors is turned on at a period of time under the necessary detection and false alarm thresholds constraints. Each subset is activated successively and non- activated sensors are put in a low-energy sleep mode, so as to extend the network lifetime.

causes collision amongst licensed and unlicensed users. Primary user emulation (PUE) attack is considered as a source of interference in CRN and causes signal detection errors. Malicious users are capable to harm spectrum sensing process. As an attacker, they may transmit fake signal as primary signal in licensed band. Detection of fake signal causes SUs preventing from spectrum access [6]. In [7], Chen et al., studied the use of PU location to identify primary user emulation attack (PUEA). They used directional antennas to determine the angle of primary signal, the time arrival, and signal strength of received signal for location of primary transmitter detection. The first analytical model to achieve a lower bound on the probability of successful PUEA was discussed in [8]. The authors considered fading into analysis and derived expressions for the probability of successful PUEA and provide a lower bound on the probability of successful PUEA using Fenton’s and Markov approximation, respectively. Moreover, authors in [9] applied Wald’s sequential probability ratio test to detect the attack by malicious users. Authors in [10] investigated strategies to combat primary user attack caused by selfish and malicious user attacks. They used game theory-based to counter primary user attack in cognitive radio networks. Authors in [11] studied primary user emulation attack in dynamic spectrum access without location information of users. They presented miss detection as a function of network radius with different number of SU for both theoretical and experimental studies. However, they did not present false detection probability and how the performance of received power by SU with a certain number of transmitted power from PU was not studied.

With the development of CR, extending to the level of network, cognitive radio networks (CRNs) emerge as the times require. Nowadays the operational aspects of CRN are being explored vigorously, and several potential security challenges for cognitive radio have gained lots of attention. In this paper, we explore the security issues on physical layer for cognitive radio networks. First, we give a brief overview of the CRNs, then we review several existing secure threats to the physical layer in CRNs and we propose a new kind of security problem. Next, we discuss the related countermeasures on how to defend against these attacks. Subsequently, we conduct an evaluation of these countermeasures, and make some future works for secure CRNs.

Economics of Spectrum Allocation in Cognitive Radio Networks Abstract Cognitive radio networks (CRNs) are emerging as a promising technology for the efficient use of radio spectrum. In these networks, there are two levels of networks on each channel, primary and secondary, and secondary users can use the channel whenever the primary is not using it. Spectrum allocation in CRNs poses several challenges not present in traditional wireless networks; the goal of this dissertation is to address some of the economic aspects thereof. Broadly, spectrum allocation in CRNs can be done in two ways- (i) one-step allocation in which the spectrum regulator simultaneously allocates spectrum to primary and secondary users in a single allocation and (ii) two-step allocation in which the spectrum regulator first allocates spectrum to primary users, who in turn, allocate unused portions on their channels to secondary users. For the two-step allocation scheme, we consider a spectrum market in which trading of bandwidth among primaries and secondaries is done. When the number of primaries and secondaries is small, we analyze price competition among the primaries using the framework of game theory and seek to find Nash equilibria. We analyze the cases both when all the players are located in a single small location and when they are spread over a large region and spatial reuse of spectrum is done. When the number of primaries and secondaries is large, we consider different types of spectrum contracts derived from raw spectrum and analyze the problem of optimal dynamic selection of a portfolio of long-term and short-term contracts to sell or buy from the points of view of primary and secondary users. For the one-step allocation scheme, we design an auction framework using which the spectrum regulator can simultaneously allocate spectrum to primary and secondary users with the objective of either maximizing its own revenue or maximizing the social welfare. We design different bidding languages, which the users can use to compactly express their bids in the auction, and polynomial-time algorithms for choosing the allocation of channels to the bidders.

◦ Determine which portions of the spectrum is available and detect the presence of licensed users when a user operates in a licensed band.  Spectrum decision[r]

Conservatoire National des Arts et Métiers (CNAM), Paris, France Correspondence: bellang@cnam.fr Manuscript communication: received 21 October 2010, accepted 12 January 2011 Abstract– The challenge of opportunistic networks is to maximize the usage of the spectrum by offering quick and easy access to independent systems and their users. A physical layer able to operate efficiently in an unsynchronized environment is needed and it is shown that the filter bank multicarrier (FBMC) technique can meet the objectives in terms of performance and flexibility. Then, a protocol must be developed to ensure global convergence and an overall transmission capacity close to the optimal possible value at a given place and a given time. An approach called “good neighbour” is presented, which consists of building the capacity requested by the users through a threshold regulated local search and with minimum changes in frequency band allocation to reduce interference non-stationarity to other systems. Finally, potential applications of opportunistic networks are reviewed and the conditions for proliferation of this kind of network are discussed.

Rameez Khan 1 , Prof. Vijay Prakash 2 Department of Electronics and Communication Engineering, RKDF College of Engineering, Bhopal Abstract — Cognitive radio (CR) is an engineering that addresses the issue of shortage of range and prepares for efficient utilization of the same. Cognitive Radio Sensor Networks (CRSN) requests vitality effective and a practical co-agent range sensing procedures which performs well in blurring and shadowing environment with ideal qualities of sensing parameters at low computational complexities. In cognitive radio (CR) systems, multi-CR participation regularly happens throughout range sensing, to adapt to remote blurring impacts and the concealed terminal issue. In this paper we considered, client collaboration pick up offers channel differences against blurring, as well as takes into consideration lessened testing expenses for every CR, which is especially pertinent when the screened range has wide data transfer capacity. Without channel information, Crs separately gather advanced estimations from an area of the wide range through specific filtering, with discretionary compressive examining to further lessen testing rates. The results speaking to all the estimations are displayed to have a low rank property, with the rank request being the same as the measure of the non zero backing of the screened wide range. Likewise, an atomic standard minimization issue is defined to together distinguish the nonzero help and henceforth the general range inhabitation.

LEACH is one of the first topological hierarchal techniques to be implemented in wireless sensor networks [20], [21]. Energy consumption in wireless systems is directly proportional to the distance, single hop communication is expensive in terms of energy consumption. However, provided that transmission distance is short and/or the radio electronics is high, direct transmission energy is more energy-efficient on a global scale than minimum transmission energy (MTE) routing protocol. LEACH protocol uses only two layers for communication. One is for communication within the clusters and the other is between the cluster heads and sink. Given the duties, a cluster head consumes significantly more energy than a normal node. In order to spread this energy usage over multiple nodes, the role of being a cluster head is rotated periodically among the nodes of the cluster in order to balance the load. LEACH forms clusters by using a distributed algorithm, where nodes make autonomous decisions without any centralised control. Initially a node decides to be a cluster head with a probability p and broadcasts its decision via an advertisement message. Clusters are formed depending upon the signal strength of the advertisement message each node receives. Nodes will go for the one which has the strongest signal. The role of the cluster head is then rotated periodically by getting each node to choose a random number ‘‘T’’ between 0 and 1. A node that has not become a cluster head for the previous round can become a cluster head for the current round if the number is less than the following threshold:

In this paper, we investigate the problem of cooperative relay in CR networks. We assume a primary network with multiple licensed bands and a CR network consisting of multiple cooperative relay links. Each cooperative relay link consists of a CR transmitter, a CR relay, and a CR receiver. The objective is to develop effective mechanisms to integrate these two wireless communication technologies, and to provide an analysis for the comparison of two representative cooperative relay strategies, i.e., decode-and-forward (DF) and amplify-and-forward (AF), in the context of CR networks. We first consider cooperative spectrum sensing by the CR nodes. We model both types of sensing errors, i.e., miss detection and false alarm, and derive the optimal value for the sensing threshold. Next, we incorporate DF and AF into the p-Persistent Carrier Sense Multiple Access (CSMA) protocol for channel access for the CR nodes. We develop closed-form expressions for the network-wide capacities achieved by DF and AF, respectively, as well as that for the case of direct link transmission for comparison purpose.

Conclusion and Further Research In this thesis, we focused on two spectrum sharing techniques for cognitive radio net- works; namely interweave access and underlay access. In the interweave approach, the widely acknowledged spectrum pooling model was adopted and the secondary user QoS parameters were derived. These parameters included, forced termina- tion probability, blocking probability and throughput. In the underlay approach, a sensing and access architecture was proposed. The scheme is suitable for femto- cell deployment in the downlink spectrum of cellular networks. The femto - macro coexistence was analyzed using SINR as a performance metric. The mathematical intractability of deriving the victim receiver’s SINR probability distribution in a fad- ing channel environment was addressed using Gaussian quadratures and Steffensen’s inequality.