Licensed Spectrum Bands Research Articles

Worst-Case Cooperative Jamming for Secure Communications in CIoT Networks.

The Internet of Things (IoT) is a significant branch of the ongoing advances in the Internet and mobile communications. Yet, the use of a large number of IoT devices can severely worsen the spectrum scarcity problem. The usable spectrum resources are almost entirely occupied, and thus, the increasing demands of radio access from IoT devices cannot be met. To tackle this problem, the Cognitive Internet of Things (CIoT) has been proposed. In a CIoT network, secondary users, i.e., sensors and actuators, can access the licensed spectrum bands provided by licensed primary users (such as cellular telephones). Security is a major concern in CIoT networks. However, the traditional encryption method at upper layers (such as symmetric and asymmetric ciphers) may not be suitable for CIoT networks since these networks are composed of low-profile devices. In this paper, we address the security issues in spectrum-leasing-based CIoT networks using physical layer methods. Considering that the CIoT networks are cooperative in nature, we propose to employ cooperative jamming to achieve secure transmission. In our proposed cooperative jamming scheme, a certain secondary user is employed as the helper to harvest energy transmitted by the source and then uses the harvested energy to generate an artificial noise that jams the eavesdropper without interfering with the legitimate receivers. The goal is to minimize the Signal to Interference plus Noise Ratio (SINR) at the eavesdropper subject to the Quality of Service (QoS) constraints of the primary traffic and the secondary traffic. We formulate the minimization problem into a two-stage robust optimization problem based on the worst-case Channel State Information of the Eavesdropper (ECSI). By using Semi-Definite Programming (SDP), the optimal solutions of the transmit covariance matrices can be obtained. Moreover, in order to build an incentive mechanism for the secondary users, we propose an auction framework based on the cooperative jamming scheme. The proposed auction framework jointly formulates the helper selection and the corresponding energy allocation problems under the constraint of the eavesdropper's SINR. By adopting the Vickrey auction, truthfulness and individual rationality can be achieved. Simulation results demonstrate the effective performance of the cooperative jamming scheme and the auction framework.

Cognitive Radio, the Future of Wireless Communication: An Overview

Cognitive Radio (CR)has been drawing huge attention due to its capability to achieve spectrum optimisation. Limited availability of spectrum and inefficiency in spectrum usage are guiding the wireless technology towards a new communication paradigm to exploit the existing wireless spectrum opportunistically. It enables sharing ofspectrum amongst a Primary User (PU) which is licensed user and a Secondary User (SU) which is not licensed user. Later is normally gypsy user. The Dynamic Spectrum Access (DSA) used by CR is a new technique which allows sharing of spectrum in such a manner that SUs can access the spectrum holes (voids or temporarily unused part of spectrum) in the licensed spectrum bands of PUs. This work is aimed at generatingtheinterest withinstudent community to undertake research in field of CR which is both challenging and extremely useful.

Adaptive Two-stage Spectrum Sensing under Noise Uncertainty in Cognitive Radio Networks

To utilize licensed spectrum bands efficiently, spectrum sensing needs to be accurate and fast. The occurrence of noise uncertainty and the lower in received PU signal power due to the distance between the transmitter and the receiver, path loss, are the main challenges that has a great impact on the accuracy of spectrum sensing.
 In this paper, we propose a new scheme of two-stage spectrum sensing, “Adaptive Two-stage Spectrum Sensing (ATSS)”, under noise uncertainty environment. ATSS is a modified of a conventional two-stage spectrum sensing where the decision threshold of both stages are adapted on the distance, estimated noise variance and calculated noise uncertainty interval. Therefore, ATSS improves the detection performance of the existing spectrum sensing and is robust to noise uncertainty.
 The contribution of this paper is three-fold. First, an unreliable detection and wasted stage activation of a conventional two-stage spectrum sensing are reduced. Second, noise uncertainty is addressed. Third, a new parameter, critical distance ( ), is proposed in order to reduce computational burden and sensing time of the first stage.

Dynamic Resource Allocation for Cooperative Spectrum Sharing in LTE Networks

Conventional spectrum sharing approaches assume that an unlicensed user accessing a licensed spectrum band autonomously operates by sensing (or detecting) the presence of the primary user, which is licensed to use the given band, with minimal coordination from the primary user. However, in this case, incorrect sensing decisions and resource allocation on the unlicensed secondary users' (SU) part can lead to undesired degradation of the primary users' performance. Therefore, there has been a recent paradigm shift to enable cooperative spectrum sharing, in which interaction is allowed between the primary and the secondary network for efficient spectrum utilization while limiting the interference experienced by a primary user. In this paper, we consider a cooperative spectrum sharing architecture in which the SU is assumed to be a cellular network. We then propose a novel fractional-frequency-reuse-based dynamic resource allocation (DRA) algorithm at the secondary (cellular) network. The joint DRA optimization involves simultaneous spectrum allocation across different base stations and then across users within a base station. It is an NP-hard problem and is prohibitively complex to solve for a large cellular network. Therefore, to reduce the complexity of the joint problem and offer a tractable solution, we formulate layered scheduling algorithms for cross-layer resource allocation. Furthermore, the feedback overhead between the layers is kept minimal. Finally, using simulations, we compare our proposed DRA scheme with other resource allocation schemes for sum system throughput, as well as for fairness in allocation. We also present the result for the case when the available primary spectrum varies over time and locations of SUs.

Ameliorated Resource Allocation in Two-Tier Femtocell–Macrocell Networks with Six Directional Antennas for Macrocells

Femtocells are deployed in the coverage area of traditional macrocell networks and can provide high data rates and good quality of service with low transmission power. In order to achieve the high spectral efficiency, allocated resources to the femtocells should be from the same licensed spectrum band of the macrocell network. Therefore, interference management is an important challenge in two-tier femtocell---macrocell networks. Previously, it was shown that cross-tier interference from macrocell to femtocell can be reduced by using directional antennas in macrocell tier. In this paper, we propose a new spectrum partitioning approach by dividing the spectrum to four sub-bands and then allocating them to different sectors of the macrocell with six directional antennas in a proper manner to reduce interferences. Therefore, first, we calculate the interference from the adjacent macrocells in different sectors. Then, based on the results of interference analysis, we propose a sub-band exchanging allocation strategy for improving the macrocells' and femtocells' performance. Moreover, we analyze the downlink outage probability of the two-tier femtocell---macrocell network based on the orthogonal-frequency-division-multiple-access. Finally, simulation and theoretical results demonstrate that the proposed cellular network achieves lower downlink outage probability of femtocell and macrocell in comparison with the previous cellular model and consequently, system throughput increases substantially.

A novel utility function for energy-efficient power control game in cognitive radio networks.

Spectrum scarcity is a major challenge in wireless communications systems requiring efficient usage and utilization. Cognitive radio network (CRN) is found as a promising technique to solve this problem of spectrum scarcity. It allows licensed and unlicensed users to share the same licensed spectrum band. Interference resulting from cognitive radios (CRs) has undesirable effects on quality of service (QoS) of both licensed and unlicensed systems where it causes degradation in received signal-to-noise ratio (SIR) of users. Power control is one of the most important techniques that can be used to mitigate interference and guarantee QoS in both systems. In this paper, we develop a new approach of a distributed power control for CRN based on utility and pricing. QoS of CR user is presented as a utility function via pricing and a distributed power control as a non-cooperative game in which users maximize their net utility (utility-price). We define the price as a real function of transmit power to increase pricing charge of the farthest CR users. We prove that the power control game proposed in this study has Nash Equilibrium as well as it is unique. The obtained results show that the proposed power control algorithm based on a new utility function has a significant reduction in transmit power consumption and high improvement in speed of convergence.

A Survey on Spectrum Occupancy Measurement for Cognitive Radio

In order to support the ever growing demand of wireless communication systems and wireless local area network based 802.11 devices, the regulators are developing techniques to overcome the permanent scarcity of radio resources. Spectrum sensing in cognitive radio (CR) is considered as a key technology which estimates the availability of the licensed spectrum band for additional usages. The underutilized licensed band can be exploited among the secondary users provided that they would not cause any interference to the primary user. So, evaluation of spectrum occupancy is the main approach towards the successful deployment of CR. This paper studies the various spectrum occupancy models used in diverse locations by research campaigns worldwide. The detail analyses of the empirical results in different scenarios of measurement have been compared. The purpose of this survey is to evaluate up to what percentage the whole spectrum band is occupied by different services.

Graph-Based Robust Resource Allocation for Cognitive Radio Networks

Cognitive radio (CR) technology is promising for next generation wireless networks. It allows unlicensed secondary users to use the licensed spectrum bands as long as they do not cause unacceptable interference to the primary users who own those bands. To efficiently allocate resources in CR networks, stable resource allocation based on graph theory is investigated, which takes all users' preferences into account. In this paper, we focus on improving robustness of the stable matching based resource allocation. A truncated scheme generating almost stable matchings is first investigated. Based on the properties of the truncated scheme, two types of edge-cutting algorithms, called direct edge-cutting (DEC) and Gale-Shapley based edge-cutting (GSEC), are developed to improve resource allocation robustness to the channel state information variation. To mitigate the problem that certain secondary users may not be able to find suitable resources after edge-cutting, multi-stage (MS) algorithms are then proposed. Numerical results show that the proposed algorithms are robust to the channel state information variation.

Performance Evaluation of Joint Path and Spectrum Diversity Based Routing Protocol in Cognitive Radio Ad Hoc Networks under Critical Conditions

Cognitive Radio (CR) technology has been introduced to solve the problems of spectrum underutilization and spectrum scarcity caused by improper spectrum management policies. The main concept of Cognitive Radio Ad Hoc Network (CRAHN) is that, in a wireless ad hoc network, the unlicensed users (or Secondary Users (SUs)) are allowed to access the temporally unused licensed spectrum bands for data communications without harmful interference to the licensed users (or Primary Users (PUs)). In CRAHNs, the mobile SUs communicate with each other without the use of any centralized network infrastructure. Routing in CRAHNs is an important task and faces various challenges including PU interference, frequent network topology changes, energy constraint, volatile bandwidth and fragile connectivity. In this study, an attempt is made to evaluate the performance of the Dual Diversity Cognitive Ad-hoc Routing Protocol (D2CARP) in CRAHNs under critical conditions, i.e., high node mobility rate and number of PUs. The D2CARP protocol is a joint path and spectrum diversity based routing protocol for CRAHNs. The performance evaluation is conducted through simulation using NS-2 simulator. The performance metrics to be considered include average throughput, percentage of packet loss, average end-to-end delay and average jitter. The simulation results prove that the protocol performance is significantly affected in the networks with high number of PUs and mobility rate, leading to high path failure rate and severe service outages.

Signal Detection for QPSK Based Cognitive Radio Systems using Support Vector Machines

Cognitive radio based network enables oppor- tunistic dynamic spectrum access by sensing, adopting and utilizing the unused portion of licensed spectrum bands. Cognitive radio is intelligent enough to adapt the commu- nication parameters of the unused licensed spectrum. Spec- trum sensing is one of the most important tasks of the cogni- tive radio cycle. In this paper, the auto-correlation function kernel based Support Vector Machine (SVM) classifier along with Welch's Periodogram detector is successfully imple- mented for the detection of four QPSK (Quadrature Phase Shift Keying) based signals propagating through an AWGN (Additive White Gaussian Noise) channel. It is shown that the combination of statistical signal processing and machine learning concepts improve the spectrum sensing process and spectrum sensing is possible even at low Signal to Noise Ra- tio (SNR) values up to 50 dB.

Comparative Study of Single-user Spectrum Sensing Techniques in Cognitive Radio Networks

Abstract Cognitive Radio is an emerging and fascinating technology, which promises solution to the spectrum scarcity problem. This influential technology has the power to change the future technological trends forever if employed properly. In Cognitive Radio Networks, an unlicensed (secondary) user utilizes the licensed spectrum band opportunistically without causing any interference to the primary transmission or licensed (primary) users. Spectrum Sensing is the foremost task for successful Opportunistic Spectrum Access. It is a cardinal function of cognitive radio to avert the harmful interference with licensed users and recognize the available spectrum for ameliorating spectrum utilization. Over the past decade, legions of spectrum sensing techniques have been proposed in the literature. In this paper, a brief survey of all the major contributions in the field of single user or non-cooperative spectrum sensing for cognitive radio networks have been discussed. A comparative study has been carried out based on various important parameters, which needs to be considered for real-time implementation of Cognitive Radio Networks.

Design and analysis of channel reservation scheme in Cognitive Radio Networks

The primary aim of a Cognitive Radio Network (CRN) is to provide higher spectrum utilization through an opportunistic usage of the licensed spectrum bands by the unlicensed Secondary Users (SUs). However, these SUs face unpredictable interruptions in their transmissions due to sudden arrival of the licensed Primary Users (PUs), resulting in either handoff or dropping instances. The channel reservation policy for the PUs is one such solution that reduces the probability of their interference, though at the cost of lower system throughput. This paper provides a complete study of the channel reservation scheme in a CRN. Initially, the system model is defined along with an architectural framework to address the practical constraints involved in implementing the channel reservation strategy. A novel design approach is then adopted to develop the mathematical models, followed by an evaluation of the network parameters to obtain a tradeoff between the decrease in interference and low spectrum utilization when some channels are reserved in the CRN. The optimal number of channels to be reserved is also determined. In addition, as a potential application of the channel reservation policy, an analytical framework is designed for the VoIP applications in the CRN, that highlights significant improvement in the VoIP call quality. Finally, an extensive analysis in the real-life like simulation models validates the inferences drawn from the mathematical models, recording over 50% improvement in the interference-free transmission of the SUs with the channel reservation scheme in the CRN.

Multi-Agent Reinforcement Learning Based Opportunistic Routing and Channel Assignment for Mobile Cognitive Radio Ad Hoc Network

Opportunistic spectrum access using cognitive radio technology enables exploring vacant licensed spectrum bands and thereby improving the spectrum utilization. However, it will have a significant i...

Zero-Determinant Strategies: A Game-Theoretic Approach for Sharing Licensed Spectrum Bands

We consider private commons for secondary sharing of licensed spectrum bands with no access coordination provided by the primary license holder. In such environments, heterogeneity in demand patterns of the secondary users can lead to constant changes in the interference levels, and thus can be a source of volatility to the utilities of the users. In this paper, we consider secondary users to be service providers that provide downlink services. We formulate the spectrum sharing problem as a non-cooperative iterated game of power control where service providers change their power levels to fix their long-term average rates at utility-maximizing values. First, we show that in any iterated 2x 2 game, the structure of the single-stage game dictates the degree of control that a service provider can exert on the long-term outcome of the game. Then we show that if service providers use binary actions either to access or not to access the channel at any round of the game, then the long-term rate can be fixed regardless of the strategy of the opponent. We identify these rates and show that they can be achieved using mixed Markovian strategies which will be also identified.

A Cooperative Transmission Scheme for Improving the Secondary Access in Cognitive Radio Networks

In this paper, we examine the problem of secondary access blocking in cognitive radio networks when secondary trans- missions cause unacceptably high interference to primary trans- missions. In general, the access of secondary users (SUs) to a licensed spectrum band is only allowed when this access does not alter the performance of primary users that can be defined by the primary QoS requirement. In this paper, we propose a cooperative scheme that allows SUs to increase their access to the spectrum band and access the spectrum even when the primary QoS is not satisfied. Using relay selection and a proper power allocation method, we show that the secondary outage performance can be significantly improved, whereas the primary outage performance is either not altered or slightly improved. Moreover, closed-form expressions of the primary and secondary outage probabilities are derived, and the achieved diversity order is calculated. Finally, analytical and simulation results illustrate the primary outage performance and secondary outage performance of the proposed scheme and show its advantages compared with conventional schemes.

A Joint Routing and Time-Slot Assignment Algorithm for Multi-Hop Cognitive Radio Networks with Primary-User Protection

Cognitive radio has recently emerged as a promising technology to improve the utilization efficiency of the radio spectrum. In cognitive radio networks, secondary users (SUs) must avoid causing any harmful interference to primary users (PUs) and transparently utilize the licensed spectrum bands. In this paper, we study the PUprotection issue in multi-hop cognitive radio networks. In such networks, secondary users carefully select paths and time slots to reduce the interference to PUs. We formulate the routing and time-slot assignment problem into a mixed integer linear programming (MILP). To solve the MILP which is NP-Hard in general, we propose an algorithm named RSAA (Routing and Slot Assignment Algorithm). By relaxing the integral constraints of the MILP, RSAA first solves the max flow from the source to the destination. Based on the max flow, RSAA constructs a new network topology. On the new topology, RSAA uses branch and bound method to get the near optimal assignment of time slots and paths. The theoretical analyses show that the complexity of our proposed algorithm is O(N^4). Also, simulation results demonstrate that our proposed algorithm can obtain near-optimal throughputs for SUs.

Robust Spectrum Sensing With Crowd Sensors

This paper investigates the issue of cooperative spectrum sensing with a crowd of low-end personal spectrum sensors (such as smartphones, tablets, and in-vehicle sensors), where the sensing data from crowd sensors that may be unreliable, untrustworthy, or even malicious. Moreover, due to either unexpected equipment failures or malicious behaviors, every crowd sensor could sporadically and randomly contribute with abnormal data, which makes the existing cooperative sensing schemes ineffective. To tackle these challenges, we first propose a generalized modeling approach for sensing data with an arbitrary abnormal component. Under this model, we then analyze the impact of general abnormal data on the performance of the cooperative sensing, by deriving closed-form expressions of the probabilities of global false alarm and global detection. To improve sensing data quality and enhance cooperative sensing performance, we further formulate an optimization problem as stable principal component pursuit, and develop a data cleansing-based robust spectrum sensing algorithm to solve it, where the under-utilization of licensed spectrum bands and the sparsity of nonzero abnormal data are jointly exploited to robustly cleanse out the potential nonzero abnormal data component from the original corrupted sensing data. Extensive simulation results demonstrate that the proposed robust sensing scheme performs well under various abnormal data parameter configurations.

PERFORMANCE OPTIMIZATION OF COGNITIVE RADIO WITH WIDEBAND SPECTRUM SENSING

Cognitive radio (CR) technology allows the unlicensed user to access the licensed spectrum bands. Spectrum sensing is an essential function in cognitive radio to detect the spectrum holes and opportunistically use the underutilized frequency bands without causing interference to primary user (PU). In this paper we are maximizing the throughput capacity of cognitive radio user and hence the performance of spectrum sensing and protection to licensed user improves over a wideband spectrum sensing band. The simulation of cognitive radio is done by analyzing the performance of energy detector spectrum sensing technique to detect primary user and to formulate the optimization using multiband joint detection method to achieve suitable trade-off between secondary user access and primary user network. The main aim of this paper is to maximize the probability of detection and to decrease the probabilities of miss detection and false alarm. To maximize the throughput it requires minimizing the throughput loss caused by miss detection and the significant reduction in probability of false alarm helps in achieving the spectral efficiency from the secondary users perspective. The simulation results show that the performance increases with the multiband joint detection method.

Spectrum‐sharing broadcast channels using fountain codes: energy, delay and throughput

In this study, the authors develop a transmission protocol for cognitive radio networks, whereby fountain codes are exploited in the broadcast channels and secondary users help with the broadcast from the base station (BS) to primary users (PUs). With fountain codes, the BS broadcasts to the secondary transmitter (ST) as well as PUs simultaneously, and stops broadcasting once the ST has received sufficient codeword to decode the original information reliably. Then, the ST will resume the broadcasting to PUs until all of them can decode the original information successfully. While broadcasting, the ST transmits information over its own link, that is, to the secondary receiver, based on dirty paper coding technique. As such, the energy expenditure at the BS is reduced and, moreover, secondary links have more opportunities to access the licensed spectrum band. To evaluate the performance of the developed scheme, they analyse its energy expenditure, broadcast time as well as the throughput over secondary links, and achieve the corresponding closed-form expressions. Compared with the traditional broadcast protocol without the secondary's help, illustrative numerical results substantiate the validity of the author's derivations, which also demonstrate the efficiency of the developed scheme both on the energy savings and on the spectrum utilisation.

Routing and channel selection from cognitive radio network’s perspective: A survey

The fixed spectrum allocation causes inefficient utilization of licensed spectrum bands, due to which Cognitive Radio Networks (CRNs) emerged as a promising solution. Cognitive radio networks opportunistically utilize the spectrum holes, i.e., spectrum not in use by Primary Users (or PUs or licensed users) and allocate the spectrum dynamically. For every network including cognitive radio networks, routing is very important. Routing is the backbone of communication for transferring data from one machine to another in a multi-hop fashion. A good routing protocol is required for efficient communication and a good routing protocol is based on channel selection strategy. Therefore, a good channel selection strategy is required for efficient routing protocol so that routes should be stable and exist for longer time. In this paper, we focus on joint channel selection and routing from the perspective of cognitive radio networks. In this context, we provide a comprehensive survey on routing and channel selection in CRNs. More specifically, the importance of joint channel selection and routing for cognitive radio networks is first highlighted. Then classification and challenges of channel selection and routing are discussed in details. Routing with efficient channel selection in cognitive radio networks is then discussed by describing many routing strategies for cognitive radio networks, routing metrics, performance parameters, primary user activity modeling and spectrum aware strategies. Then guidelines for the development of efficient routing protocols are discussed. Subsequently, in last, a case study for channel selection strategy ‘Spectrum Aware Dynamic Channel Assignment’ (SA-DCA) is presented and illustrated that how routing can get benefit from it.