Improve Spectrum Utilization Research Articles

Channel Assembling Strategy in Cognitive Radio Networks: a Queuing Based Approach

With channel assembling strategies (CAS), more capacity and spectrum utilization can be achieved. However, blocking and forced termination occurs whenever the primary user (PU) arrives individually, or in batch. Motivated by a realistic scenario in cognitive radio networks, we proposed a joint CAS with queue (CAS+Q) which take into account the dynamics of a wireless link and other factors that affect the quality and capacity of the accessible channel. For CAS+Q to be practical, it must consider the time varying wireless link, a finite buffer regime, the traffic classes and adaptive modulation and coding (AMC) scheme. The introduction of a queuing regime for secondary users (SUs) is to ensure that traffic that would have been blocked or forcibly terminated would otherwise be queued in a buffer and possibly served later. This is to improve spectrum utilization and more especially, minimize blocking and forced termination of the SUs services. An investigation of the proposed strategy (CAS+Q) featuring AMC showed improved system performance when compared to our previous study without a queuing regime. It also showed the impact of delays on the proposed strategy depending on the system parameters selected. Extensive system simulations validate the analytical investigation.

Power Control for D2D Underlay Cellular Networks With Channel Uncertainty

Device-to-device (D2D) communications underlying the cellular infrastructure are a technology that have been proposed recently as a promising solution to enhance cellular network capabilities. It improves spectrum utilization, overall throughput, and energy efficiency while enabling new peer-to-peer and location-based applications and services. However, interference is the major challenge, since the same resources are shared by both systems. Therefore, interference management techniques are required to keep the interference under control. In this paper, in order to mitigate interference, we consider centralized and distributed power control algorithms in a one-cell random network model. Existing results on D2D underlay networks assume perfect channel state information (CSI). This assumption is usually unrealistic in practice due to the dynamic nature of wireless channels. Thus, it is of great interest to study and evaluate achievable performances under channel uncertainty. Differently from previous works, we are assuming that the CSI may be imperfect and include estimation errors. In the centralized approach, we derive the optimal powers that maximize the coverage probability and the rate of the cellular user while scheduling as many D2D links as possible. These powers are computed at the base station (BS) and then delivered to the users, and hence the name “centralized”. For the distributed method, the ON–OFF power control and the truncated channel inversion are proposed. Expressions of coverage probabilities are established in the function of D2D links intensity, pathloss exponent, and estimation error variance. Results show the important influence of CSI error on achievable performances and thus how crucial it is to consider it while designing networks and evaluating performances.

Performance Comparison of Paraunitary Analysis Filter Bank Based Spectrum Sensing Technique over Multipath Channels

Background/Objectives: In earlier days of wireless communications, the demand for the spectrum is limited, because the wireless services may not require higher bandwidths. But as time passes radio spectrum has become one of the important and regulated resources for all the wireless services. From the past 10 to 15 years the spectrum needs were increased and it becomes a scarce resource. Methods/Statistical analysis: The information and communication technology industry in today’s scenario faces several global challenges like: Higher data services with improved Quality Of Service (QOS), scarcity of spectrum, and increased expenses of the services. Thus both the energy domains as well as spectral domain efficiencies were degraded, which made the researches to think in different ways, The other ways to improve spectrum utilization is the use of unlicensed spectrum or secondary access. In order to solve this spectrum utilization efficiency problem, Cognitive Radio (CR) concept was introduced. CR technology is an secondary access method in which an unlicensed Secondary Users (SUs) senses the whole radio spectrum and uses the licensed spectrum holes such that it does not cause any interference to the Primary Users (PUs). This way of spectrum access improves the efficiency of spectrum utilization. Findings: For sensing the spectrum of the primary user, several methods are proposed in literature. A method called Paraunitary Analysis Filter Bank based sensing method is analysed in this paper and its performance was compared with Filter bank based spectrum sensing and Energy Detection (ED) based spectrum sensing techniques. Application/Improvements: It can be used to reduce the interference in Femtocell networks by considering the macro user as a primary user and femto user as a secondary user to use the spectrum effectively and to increase the capacity of the cellular networks.

A proactive spectrum handoff scheme with efficient spectrum utilisation for cognitive radio ad hoc networks

This paper proposes a proactive spectrum handoff scheme for cognitive radio (CR) ad hoc networks by exploiting the efficient utilisation of the available wireless spectrum by CR. The novelty of this spectrum handoff scheme is that it is able to use the available free channels which are idle for one complete CR packet transmission as well as idle for less than one packet transmission. This has been done by channel scheduling and packet fragmentation to reduce unusable channels. In this scheme, spectrum sensing is done during packet transmission. The main contribution of the proposed spectrum handoff scheme is that it outperforms the existing proactive and reactive spectrum handoff schemes in terms of reduced CR average service time, improved throughput, and improved spectrum utilisation under the different primary user (PU) arrival rates. It is also analysed that the proposed spectrum handoff scheme is best suited scheme in heavy PU traffic arrival rates.

A proactive spectrum handoff scheme with efficient spectrum utilisation for cognitive radio ad hoc networks

This paper proposes a proactive spectrum handoff scheme for cognitive radio (CR) ad hoc networks by exploiting the efficient utilisation of the available wireless spectrum by CR. The novelty of this spectrum handoff scheme is that it is able to use the available free channels which are idle for one complete CR packet transmission as well as idle for less than one packet transmission. This has been done by channel scheduling and packet fragmentation to reduce unusable channels. In this scheme, spectrum sensing is done during packet transmission. The main contribution of the proposed spectrum handoff scheme is that it outperforms the existing proactive and reactive spectrum handoff schemes in terms of reduced CR average service time, improved throughput, and improved spectrum utilisation under the different primary user (PU) arrival rates. It is also analysed that the proposed spectrum handoff scheme is best suited scheme in heavy PU traffic arrival rates.

Efficient Use of Paired Spectrum Bands through TDD Small Cell Deployments

Traditionally, wireless cellular systems have been designed to operate in FDD paired bands that allocate the same amount of spectrum for both DL and UL communications. Such design is very convenient under symmetric DL/UL traffic conditions, as used to be the case when voice transmission was predominant. However, due to the overwhelming advent of data services, which involves large asymmetries between DL and UL, the conventional FDD solution becomes inefficient. In this regard, flexible duplexing concepts aim to derive procedures to improve spectrum utilization by adjusting resources to actual traffic demand. In this work, we review these concepts and propose the introduction of TDD SeNB to operate in the unused resources of an FDD-based system. This proposal alleviates the saturated DL/ UL transmission commonly found in FDD-based systems through user offloading toward a TDD system based on SeNBs. In this context, the flexible duplexing concept is analyzed from three points of view: regulation, LTE standardization, and technical solutions.

Multipath Activity Based Routing Protocol for Mobile ‎Cognitive Radio Ad Hoc Networks

Cognitive radio networks improve spectrum utilization by ‎sharing licensed spectrum with cognitive radio devices. In ‎cognitive radio ad hoc networks the routing protocol is one ‎of the most challenging tasks due to the changes in ‎frequency spectrum and the interrupted connectivity ‎caused by the primary user activity. In this paper, a multi‎path activity based routing protocol for cognitive radio ‎network (MACNRP) is proposed. The protocol utilizes ‎channel availability and creates multiple node-disjoint ‎routes between the source and destination nodes. The ‎proposed protocol is compared with D2CARP and FTCRP ‎protocols. The performance evaluation is conducted ‎through mathematical analysis and using OPNET ‎simulation. The performance of the proposed protocol ‎achieves an increase in network throughput; besides it ‎decreases the probability of route failure due to node ‎mobility and primary user activity. We have found that the ‎MACNRP scheme results in 50% to 75% reduction in ‎blocking probability and 33% to 78% improvement in ‎network throughput, with a reasonable additional routing ‎overhead and average packet delay. Due to the successful ‎reduction of collision between primary users and ‎cognitive users, the MACNRP scheme results in decreasing ‎the path failure rate by 50% to 87%.‎

Location Privacy in Cognitive Radio Networks: A Survey

Cognitive radio networks (CRNs) have emerged as an essential technology to enable dynamic and opportunistic spectrum access which aims to exploit underutilized licensed channels to solve the spectrum scarcity problem. Despite the great benefits that CRNs offer in terms of their ability to improve spectrum utilization efficiency, they suffer from user location privacy issues. Knowing that their whereabouts may be exposed can discourage users from joining and participating in the CRNs, thereby potentially hindering the adoption and deployment of this technology in future generation networks. The location information leakage issue in the CRN context has recently started to gain attention from the research community due to its importance, and several research efforts have been made to tackle it. However, to the best of our knowledge, none of these works have tried to identify the vulnerabilities that are behind this issue or discuss the approaches that could be deployed to prevent it. In this paper, we try to fill this gap by providing a comprehensive survey that investigates the various location privacy risks and threats that may arise from the different components of this CRN technology, and explores the different privacy attacks and countermeasure solutions that have been proposed in the literature to cope with this location privacy issue. We also discuss some open research problems, related to this issue, that need to be overcome by the research community to take advantage of the benefits of this key CRN technology without having to sacrifice the users' privacy.

RF-CoHetNet: An Architecture for Cognitive Heterogeneous Networks Powered by RF-Energy

Energy efficiency is an important focus area of 5G mobile technology. Due to global warming, it is important to lower the global CO2 footprint, even with the expectation of massively increasing cellular data traffic. The ability of HetNets to support high capacity makes it a significant driver for the success of 4G and indispensable in 5G. Small cells equipped with cognitive radio (CR) techniques could improve spectrum utilization by opportunistic spectrum access and intelligent interference mitigation. In this article, we propose an RF-CoHetNet, a novel heterogeneous cellular network system where small cells possess CR capabilities and are wirelessly powered by electromagnetic RF-energy. Under this system architecture, both energy efficiency and spectral efficiency can be achieved by properly switching small cells to harvesting mode or allocating channels/power to serve their users. We show that RF-energy harvesting can provide a promising solution to further improve the energy efficiency of the whole system. Through RF-energy harvesting, the unavoidable interference turns out to be a useful energy resource to support partial power consumption in the small cell. We further propose a heuristic algorithm to minimize the total system energy consumption under the system capacity constraint. From the numerical results, we give some insights into the possibility of RF-CoHetNet deployment.

Guest Editorial: LTE in Unlicensed Spectrum

The articles in this special section focus on the deployment of Long Term Evolution in unlicensed spectrum. These articles cover various design issues such as network architecture, protocol development, network coexistence, unlicensed spectrum access, and practical implementation. Fifth generation (5G) cellular networks will face a rigorous challenge in the ever increasing data rate requirement. To meet such anticipated data growth demand, the industry and academia have developed many cutting edge techniques to improve spectrum utilization. However, the scarcity of spectral resources is still a fundamental bottleneck for network capacity enhancement. Recently, the rich available bandwidth on the 5.8 GHz unlicensed national information infrastructure (U-NII) spectrum has stimulated substantial interest from cellular operators to use the unlicensed spectrum for LTE. In 2015, the LTE-Unlicensed (LTE-U) Forum formally launched the LTE-U specification, and the Third Generation Partnership Project (3GPP) has pushed the standardization of licensed assisted access (LAA)into its Releases 13 and 14. However, the LTE-U technology is still in its infancy, and there are lots of challenges that need to be solved, such as network coexistence among different radio access technologies, unlicensed spectrum sharing and access, and quality of service (QoS) provision on unlicensed spectrum. This Feature Topic aims to provide a comprehensive overview of this appealing technology, harmonizing recent results and key challenges, as well as highlighting future important directions.

$\text{M}^{3}$ -STEP: Matching-Based Multi-Radio Multi-Channel Spectrum Trading With Evolving Preferences

Spectrum trading not only improves spectrum utilization but also benefits both secondary users (SUs) with more accessing opportunities and primary users (PUs) with monetary gains. Although the existing centralized designs consider the special features of spectrum trading (e.g., frequency reuse, interference mitigation, multi-radio multi-channel transmissions, and so on), they still have to face many practical but challenging issues, such as the new infrastructure deployment, the extra control overhead, and the scalability issues. To address those issues, in this paper, we propose a novel matching-based multi-radio multi-channel spectrum trading ( $\text{M}^{3}$ -STEP) scheme in cognitive radio (CR) networks. We employ conflict graph to characterize the interference relationship among SUs with multiple CR radios, and formulate the centralized PUs’ revenue maximization problem under multiple constrains. In view of the NP-hardness of solving the problem and no existence of centralized entity, we develop the $\text{M}^{3}$ -STEP algorithms based on conflict graph observed by PUs, solve the problem via dynamic matching with evolving preferences, and prove its pairwise stability. Simulation results show that the proposed $\text{M}^{3}$ -STEP algorithm achieves close to optimal performance and outperforms other distributed algorithms without considering spectrum reuse.

Software-Defined Elastic Optical Network Node Supporting Spectrum Defragmentation

The elastic optical network (EON) benefits from improved spectrum utilization, but also faces new challenges in resource allocation. The spectrum continuity and contiguity constraints in routing and spectrum allocation can cause spectrum fragmentation, which would increase traffic blocking. In this paper, we present an EON node structure supporting spectrum defragmentation and a novel software-defined networking (SDN)-based control scheme to resolve the fragmentation problem. In the proposed node, bulk traffic can be spectrally separated and fit into multiple fragments. This way, fragmentation-induced traffic blocking can be mitigated intelligently. Moreover, the SDN control scheme features effective physical-layer abstraction, which is compatible with different defragmentation implementations. We experimentally demonstrate the software-defined EON node on a laboratorial test-bed. Four-wave-mixing-based spectrum multicasting is applied to implement defragmentation, and the corresponding operation procedure of the node Agent is presented. The captured controlling messages and measured signal performance confirm the effectiveness of the solution.

Energy efficiency-based joint spectrum handoff and resource allocation algorithm for heterogeneous CRNs

Cognitive radio networks (CRNs) are expected to improve spectrum utilization significantly by allowing secondary users (SUs) to opportunistically access the licensed spectrum of primary users (PUs). In an integrated network consisting of multiple heterogeneous CRNs, SUs with multiple interfaces may have to conduct inter-system or intra-system spectrum handoff due to the arrival of PUs or performance degradation on serving spectrum. In this case, designing an optimal spectrum handoff scheme which offers quality of service (QoS) guarantee and performance enhancement of the SUs is of particular importance. On the other hand, resource allocation strategy on target channel also plays an important role in affecting the transmission performance of handoff SUs. In this paper, we jointly design spectrum handoff and resource allocation strategy for handoff SUs in heterogeneously integrated CRNs. To achieve joint resource management among various CRNs, we propose a joint radio resource management architecture, based on which the proposed spectrum handoff and resource allocation scheme can be conducted. Jointly considering the transmission performance of the handoff SUs, we formulate the total energy efficiency of the SUs and design an optimization problem which maximizes the energy efficiency subject to spectrum handoff, QoS, and power constraints of the SUs. An iterative algorithm is proposed to solve the formulated nonlinear fractional optimization problem. Within each iteration, the optimization problem is transformed equivalently into two subproblems, i.e., power allocation subproblem of each SU-spectrum pair and spectrum handoff subproblem for all the SUs. The two subproblems are solved, respectively, through applying Lagrange dual method and the Kuhn-Munkres (K-M) algorithm. Numerical results demonstrate the efficiency of the proposed algorithm.

Proof-of-Concept System for Opportunistic Spectrum Access in Multi-user Decentralized Networks

Poor utilization of an electromagnetic spectrum and ever increasing demand for spectrum to support dataintensive services envisioned in 5G have led to surge of interests in paradigms such as cognitive radio,device-to-device communications, unlicensed LTE etc. Such paradigms can improve spectrum utilization viaopportunistic spectrum access (OSA) in which secondary (i.e., unlicensed) users (SUs) are allowed to transmitin the vacant licensed bands given that they do not cause any interference to the active licensed users. Over thelast decade, various spectrum detectors to check the status (i.e. vacant or occupied) of the frequency band havebeen studied and demonstrated but little attention has been paid to the task of frequency band selection fromwideband input signal. This is a challenging task especially in the decentralized network where SUs do notshare any information with each other. In this paper, a new decision making policy (DMP) has been proposedfor frequency band characterization and orthogonalization of SUs into optimal set of frequency bands. Inthe proposed DMP, Bayesian UCB (Bayes-UCB) algorithm is used for accurate characterization of frequencybands. Furthermore, Bayes-UCB based orthogonization scheme is proposed replacing existing randomizationbased schemes. Then, a testbed using USRP has been developed as a proof-of-concept system for analyzingthe performance of DMPs using real radio signals. Based on experimental results, we show that the proposedDMP is superior in terms of improvement in spectrum utilization when compared to existing DMPs. Addedadvantages of fewer number of frequency band switching as well as collisions make the proposed DMP energyefficient and hence, suitable for resource-constrained battery-operated radio terminals.

Spectrum-Efficient Resource Allocation Framework for Cooperative Opportunistic Wireless Networks

Dynamic spectrum access (DSA) is a promising approach to alleviate spectrum scarcity and improve spectrum utilization. Recently, several cooperative communication schemes have been proposed to further enhance spectrum utilization in DSA networks. Existing cooperation designs are either tailored for primary-secondary user (PU-SU) cooperation and not applicable to SU cooperation, or focus on the potential benefits of SUs cooperation without investigating how SUs agree on cooperating and the conditions that lead to improve their performance. In this paper, we introduce a spectrum-efficient resource allocation framework based on SUs cooperation, where the resources include the free spectrum access time, available channels, and relays. First, we formulate the interactions between the cooperating SUs and a PU using a discrete-time Markov chain (DTMC). Using this DTMC and Nash bargaining, we determine the new spectrum access times for SUs based on every nodes utility. We also derive the conditions under which all SUs improve their performance by cooperation. Second, considering a multi-channel multi-SU infrastructure network, we formulate two optimization problems for jointly allocating channels to SUs and selecting the cooperating SU pairs. We corroborate our analytical findings with detailed simulations that evaluate SUs cooperation gains and the optimality of the proposed joint allocation schemes.

A General Privacy-Preserving Auction Mechanism for Secondary Spectrum Markets

Auctions are among the best-known market-based tools to solve the problem of dynamic spectrum redistribution. In recent years, a good number of strategy-proof auction mechanisms have been proposed to improve spectrum utilization and to prevent market manipulation. However, the issue of privacy preservation in spectrum auctions remains open. On the one hand, truthful bidding reveals bidders' private valuations of the spectrum. On the other hand, coverage/interference areas of the bidders may be revealed to determine conflicts. In this paper, we present PISA, which is a PrIvacy preserving and Strategy-proof Auction mechanism for spectrum allocation. PISA provides protection for both bid privacy and coverage/interference area privacy leveraging a privacy-preserving integer comparison protocol, which is well applicable in other contexts. We not only theoretically prove the privacy-preserving properties of PISA, but also extensively evaluate its performance. Evaluation results show that PISA achieves good spectrum allocation efficiency with light computation and communication overheads.

Hybrid Overlay/Underlay Cognitive Radio Network With MC-CDMA

Cognitive radio allows secondary users (SUs) to exploit the underutilized radio spectrum of the primary networks. To fully utilize the primary spectrum and maximize spectral efficiency, overlay and underlay transmissions, which exploit the white and gray spaces, respectively, should be used together. However, for underlay, the SUs need to transmit at low power to avoid causing harmful interference to the primary users (PUs), whereas the PUs will cause high interference to the SUs. Thus, interference mitigation is a major issue in underlay spectrum utilization. In this paper, a hybrid transmission system that exploits both overlay and underlay is proposed using multicarrier code-division multiple access due to its interference rejection and diversity exploitation capabilities. Unlike existing approaches, which separate the use of overlay and underlay spectrum, the proposed schemes utilize the entire spectrum for underlay transmission to minimize the PU interference while using the spectrum holes for overlay transmission to maximize the data rate. Two techniques that operate at full-load and overload scenarios are proposed. The overload system is then extended to the multiuser underlay case to further improve spectrum utilization.

Survey on Spectrum monitoring for OFDM based Cognitive Radio Networks

Cognitive radio is a novel approach for improving the utilization of the radio electromagnetic spectrum.When a frequency band has primary and secondary users, the cognitive radios of the secondary users must monitor the band and be ready to cease their transmissions if a primary user's radio begins to transmit. Conventional spectrum sensing requires the secondary radios to refrain from communicating while they check for the emergence of primary signals. This paper gives an overview of different spectrum monitoring The radio spectrum is becoming increasingly congested everyday with the increasing number of wireless devices. Also wide ranges of spectrum is rarely used where as other bands are heavily used. The unoccupied portions of the licensed spectrum can only be used by licensed users. CR system uses its gained experience to plan future actions and adapt to improve the overall communication quality and meet user's needs. Thus a CR can be defined as an intelligent wireless system that is aware of its surrounding environment through sensing and measurements. CR autonomously exploit locally unused spectrum to improve spectrum utilization. CR's ability to sense and be aware of its operational environment, and dynamically adjust its radio operating parameters accordingly can be achieved by making the physical layer (PHY) highly flexible and adaptable. one of the most widely used technologies in current wireless communications systems is a multicarrier transmission known as orthogonal frequency division multiplexing (OFDM).OFDM can overcome many problems that arise with high bit rate communications, the biggest of which is time dispersion. The symbol stream that bears data is split into several lower rate streams and these streams are transmitted on different carriers. This splitting increases the symbol duration by the number of orthogonally overlapping carriers (subcarriers), multipath echoes affect only a small portion of the neighboring symbols.

A spectrum auction algorithm for cognitive distributed antenna systems

Distribute antenna system (DAS) can provide high date rate transmission to satisfy the service requirements for the rapid growing wireless applications. Besides, the increasing deployment of wireless applications make the demand for spectrum resource grow rapidly, thus cognitive radio (CR) has emerged as a promising technology to improve spectrum utilization, and spectrum auction is a promising approach to allocate spectrum bands in CR. A few existing works considered the combination of DAS and CR to get better system performance, but they have never studied the spectrum auction in these systems. In this paper, we will study the spectrum auction problem for cognitive DAS to improve spectrum utilization. Cognitive DAS with antennas deployed in a distributed manner in the secondary system can achieve higher spectrum utilization and reduce interference between primary users (PUs) and secondary users (SUs), and thus we can get a better system performance. According to the performance of SUs that can be obtained in cognitive DAS, the SUs compete for PU's licensed spectrum bands through auction. The objective of the spectrum auction is to maximize social welfare, which is formulated as aninteger programming problem to allocate spectrum bands to SUs who value them best. A Lagrangian relaxation algorithm is developed to obtain the optimal allocation. Finally, we demonstrate the performance of the cognitive DAS and the auction mechanism through simulations.

Spectrum Handoff Method Based on Extenics for Cognitive Radio Sensor Networks

A spectrum handoff model and optimal channel decision method based on Extenics have been proposed in order to resolve the optimal channel decision problem of spectrum handoff in Cognitive Radio Sensor Networks. The method of matter-element Extenics is used to analyses the spectrum handoff process. The channel state through the spectrum sensing and status information of the primary users is analyzed and transformed by matter-element Extenics. Then the parameters to determine the best channel are calculated on the basis of Extenics correlation function. Finally the optimal channel is selected. The simulation results show that the proposed method can improve spectrum utilization efficiency of Cognitive Radio Sensor Networks and can reduce the interrupt probability of second users.