Since wireless network virtualization enables abstraction and sharing of infrastructure and radio spectrum resources, the overall expenses of wireless network deployment and operation can be reduced significantly. Moreover, wireless network virtualization can provide easier migration to newer products or technologies by isolating part of the network. Despite the potential vision of wireless network virtualization, several significant research challenges remain to be addressed before widespread deployment of wireless network virtualization, including isolation, control signaling, resource discovery and allocation, mobility management, network management and operation, and security as well as non-technical issues such as governance regulations, etc. In this paper, we provide a brief survey on some of the works that have already been done to achieve wireless network virtualization, and discuss some research issues and challenges. We identify several important aspects of wireless network virtualization: overview, motivations, framework, performance metrics, enabling technologies, and challenges. Finally, we explore some broader perspectives in realizing wireless network virtualization.

Wireless Network Virtualization: A Survey, Some Research Issues and Challenges

Traditional power grids are currently being transformed into smart grids (SGs). SGs feature multi-way communication among energy generation, transmission, distribution, and usage facilities. The reliable, efficient, and intelligent management of complex power systems requires integration of high-speed, reliable, and secure data information and communication technology into the SGs to monitor and regulate power generation and usage. Despite several challenges, such as trade-offs between wireless coverage and capacity as well as limited spectral resources in SGs, wireless communication is a promising SG communications technology. Cognitive radio networks (CRNs) in particular are highly promising for providing timely SG wireless communications by utilizing all available spectrum resources. We provide in this paper a comprehensive survey on the CRN communication paradigm in SGs, including the system architecture, communication network compositions, applications, and CR-based communication technologies. We highlight potential applications of CR-based SG systems. We survey CR-based spectrum sensing approaches with their major classifications. We also provide a survey on CR-based routing and MAC protocols, and describe interference mitigation schemes. We furthermore present open issues and research challenges faced by CR-based SG networks along with future directions.

Cognitive Radio for Smart Grids: Survey of Architectures, Spectrum Sensing Mechanisms, and Networking Protocols

Time-critical and delay-sensitive multimedia applications require more spectrum and transmission resources. With the provision of cognitive radios (CRs), the underutilized spectrum resources can be exploited to gain more bandwidth for the bandwidth hungry applications (multimedia applications). Cognitive radio networks (CRNs) also have the flexibility to adjust their transmission parameters according to the needs of multimedia services or applications. For this reason, wireless multimedia cognitive radio networks (WMCRNs) have gained much attentions in today’s research domain. In this paper, we present a comprehensive survey of WMCRNs. Various multimedia applications supported by CRNs, and various CR-based wireless networks are surveyed. We highlight the routing and link layer protocols used for WMCRNs. We cover the quality-of-experience design and security requirements for transmitting multimedia content over CRNs. We provide an in-depth study of white space, television white space, and cross-layer designs that have been used for WMCRNs. We also survey the major spectrum sensing approaches used for the communications of bandwidth hungry and time-critical data over CRNs.

Wireless Multimedia Cognitive Radio Networks: A Comprehensive Survey

Driven by the advent of sophisticated and ubiquitous applications, and the ever-growing need for information, wireless networks are without a doubt steadily evolving into profoundly more complex and dynamic systems. The user demands are progressively rampant, while application requirements continue to expand in both range and diversity. Future wireless networks, therefore, must be equipped with the ability to handle numerous, albeit challenging, requirements. Network reconfiguration, considered as a prominent network paradigm, is envisioned to play a key role in leveraging future network performance and considerably advancing current user experiences. This paper presents a comprehensive overview of reconfigurable wireless networks and an in-depth analysis of reconfiguration at all layers of the protocol stack. Such networks characteristically possess the ability to reconfigure and adapt their hardware and software components and architectures, thus enabling flexible delivery of broad services, as well as sustaining robust operation under highly dynamic conditions. The paper offers a unifying framework for research in reconfigurable wireless networks. This should provide the reader with a holistic view of concepts, methods, and strategies in reconfigurable wireless networks. Focus is given to reconfigurable systems in relatively new and emerging research areas such as cognitive radio networks, cross-layer reconfiguration, and software-defined networks. In addition, modern networks have to be intelligent and capable of self-organization. Thus, this paper discusses the concept of network intelligence as a means to enable reconfiguration in highly complex and dynamic networks. Key processes in network intelligence, such as reasoning, learning, and context awareness, are presented to illustrate how these methods can take reconfiguration to a new level. Finally, the paper is supported with several examples and case studies showing the tremendous impact of reconfiguration on wireless networks.

Reconfigurable Wireless Networks

In this paper, we present a precise comprehensive analysis of the aggregate interference $I$ generated from an underlay network of cognitive radio (CR) nodes employing several transmit power control and receiver association schemes. Importantly, we consider spatial randomness by modeling CR transmitter nodes and receiver nodes as two independent Poisson point processes (PPPs). For the cognitive nodes, we investigate receiver association based on the distance or the instantaneous received power and power control based on the maximum possible transmitter–receiver distance, fixed or location-dependent cutoff power levels, feedback from the primary system, or the maximum number of available receivers. For each of these schemes, the exact moment generating function (mgf) and mean of aggregate $I$ power are derived for links with Rayleigh fading and exponential path loss. The resulting primary outage and the probability of secondary transmitter cutoff are also derived. Numerical results show that the secondary power thresholds and node densities significantly affect the aggregate $I$ , the primary receiver (PR) outage, and the secondary transmitter cutoff arising from the different schemes.

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Underlay Interference Analysis of Power Control and Receiver Association Schemes

Cognitive radio technology is a key enabler to reuse a finite, scarce, and expensive resource: the radio spectrum. Guaranteeing required levels of QoS to cognitive users and ensuring necessary protection to incumbent users are the two main challenges in opportunistic spectrum access. This article identifies the main requirements and challenges for QoS support in cognitive radio networks. A framework for a twofold cognitive manager is presented; one part managing spectrum availability on longer timescales and the other handling resource management on shorter timescales. This article gives particular focus to the functionalities of the latter cognitive manager related to resource management. Finally, we present a few key scenarios and describe how QoS can be managed with the proposed approach without disturbing the communications of incumbent users.

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Resource management for QoS support in cognitive radio networks

Optimizing the Quality of Service (QoS) support, providing seamless mobility and ensuring the protection of incumbent users are some of the challenges that arise when the radio spectrum is accessed in an opportunistic way. The functional concept of Cognitive Resource Manager (CRM) is presented providing cognition of the environment to optimize the allocation and exploitation of radio resources, to improve the access to these resources and to ensure mobility control in the opportunistic system. Requirements for the functional architecture of the CRM are identified and addressed by defining building blocks to manage cognitive access and mobility control as well as resource allocation and usage. These functional entities are described together with their interfaces inside the CRM and with other opportunistic system entities like the Spectrum Manager. Particular decision-making cases for resource control and usage are presented by means of message sequence flows taking the overall cognitive and opportunistic context into account. Finally selected algorithms for distributed power control that implement parts of the functionalities of the CRM while considering specific QoS constraints and protection of incumbent users are discussed. Results of simulations conducted for these algorithms in a dedicated scenario illustrate the performance achieved by this concept.

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Cognitive resource management for QoS support in mobile opportunistic communications

Spectrum resources unused in the spatio-temporal domain, so-called whitespace, can be utilised by opportunistic devices during the absence of their incumbent users. The possibility to opportunistically use whitespace implies the knowledge of diverse constraints: knowledge about whitespace utilisation, which can be obtained by spectrum sensing or from a data repository and constraints internal to the opportunistic system, such as quality of service (QoS) levels and mobility targets. The use of whitespace requires therefore a multi-faced management of the above constraints. In this paper, an architecture for use of whitespaces under QoS and mobility constraints is proposed. The proposed architecture flexibly adapts to different operating scenarios also described in this paper. Examples show how different realisations of the same architecture are derived. The interactions of constituent blocks are illustrated also with the help of charts, showing the management of context information and its use.

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Christophe Rosik

Papers

Resource management for QoS support in cognitive radio networks

Cognitive resource management for QoS support in mobile opportunistic communications

Flexible architecture for spectrum and resource management in the whitespace