F. Richard Yu

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

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.

Software-Defined Networking (SDN) and Distributed Denial of Service (DDoS) Attacks in Cloud Computing Environments: A Survey, Some Research Issues, and Challenges

Distributed Denial of Service (DDoS) attacks in cloud computing environments are growing due to the essential characteristics of cloud computing. With recent advances in software-defined networking (SDN), SDN-based cloud brings us new chances to defeat DDoS attacks in cloud computing environments. Nevertheless, there is a contradictory relationship between SDN and DDoS attacks. On one hand, the capabilities of SDN, including software-based traffic analysis, centralized control, global view of the network, dynamic updating of forwarding rules, make it easier to detect and react to DDoS attacks. On the other hand, the security of SDN itself remains to be addressed, and potential DDoS vulnerabilities exist across SDN platforms. In this paper, we discuss the new trends and characteristics of DDoS attacks in cloud computing, and provide a comprehensive survey of defense mechanisms against DDoS attacks using SDN. In addition, we review the studies about launching DDoS attacks on SDN, as well as the methods against DDoS attacks in SDN. To the best of our knowledge, the contradictory relationship between SDN and DDoS attacks has not been well addressed in previous works. This work can help to understand how to make full use of SDNs advantages to defeat DDoS attacks in cloud computing environments and how to prevent SDN itself from becoming a victim of DDoS attacks, which are important for the smooth evolution of SDN-based cloud without the distraction of DDoS attacks.

In-Band Full-Duplex Relaying: A Survey, Research Issues and Challenges

Recent advances in self-interference cancellation techniques enable in-band full-duplex wireless systems, which transmit and receive simultaneously in the same frequency band with high spectrum efficiency. As a typical application of in-band full-duplex wireless, in-band full-duplex relaying (FDR) is a promising technology to integrate the merits of in-band full-duplex wireless and relaying technology. However, several significant research challenges remain to be addressed before its widespread deployment, including small-size full-duplex device design, channel modeling and estimation, cross-layer/joint resource management, interference management, security, etc. In this paper, we provide a brief survey on some of the works that have already been done for in-band FDR, and discuss the related research issues and challenges. We identify several important aspects of in-band FDR: basics, enabling technologies, information-theoretical performance analysis, key design issues and challenges. Finally, we also explore some broader perspectives for in-band FDR.

When the Smart Grid Meets Energy-Efficient Communications: Green Wireless Cellular Networks Powered by the Smart Grid

Recently, there is great interest in considering the energy efficiency aspect of cellular networks. On the other hand, the power grid infrastructure, which provides electricity to cellular networks, is experiencing a significant shift from the traditional electricity grid to the smart grid. When a cellular network is powered by the smart grid, only considering energy efficiency in the cellular network may not be enough. In this paper, we consider not only energy-efficient communications but also the dynamics of the smart grid in designing green wireless cellular networks. Specifically, the dynamic operation of cellular base stations depends on the traffic, real-time electricity price, and the pollutant level associated with electricity generation. Coordinated multipoint (CoMP) is used to ensure acceptable service quality in the cells whose base stations have been shut down. The active base stations decide on which retailers to procure electricity from and how much electricity to procure. We formulate the system as a Stackelberg game, which has two levels: a cellular network level and a smart grid level. Simulation results show that the smart grid has significant impacts on green wireless cellular networks, and our proposed scheme can significantly reduce operational expenditure and CO_2 emissions in green wireless cellular networks.

Distributed Optimal Relay Selection in Wireless Cooperative Networks With Finite-State Markov Channels

Relay selection is crucial in improving the performance of wireless cooperative networks. Most previous works for relay selection use the current observed channel conditions to make the relay-selection decision for the subsequent frame. However, this memoryless channel assumption is often not realistic given the time-varying nature of some mobile environments. In this paper, we consider finite-state Markov channels in the relay-selection problem. Moreover, we also incorporate adaptive modulation and coding, as well as residual relay energy in the relay-selection process. The objectives of the proposed scheme are to increase spectral efficiency, mitigate error propagation, and maximize the network lifetime. The formulation of the proposed relay-selection scheme is based on recent advances in stochastic control algorithms. The obtained relay-selection policy has an indexability property that dramatically reduces the computation and implementation complexity. In addition, there is no need for a centralized control point in the network, and relays can freely join and leave from the set of potential relays. Simulation results are presented to show the effectiveness of the proposed scheme.

Dynamic Resource Allocation for Heterogeneous Services in Cognitive Radio Networks With Imperfect Channel Sensing

Resources in cognitive radio networks (CRNs) should dynamically be allocated according to the sensed radio environment. Although some work has been done for dynamic resource allocation in CRNs, many works assume that the radio environment can perfectly be sensed. However, in practice, it is difficult for the secondary network to have the perfect knowledge of a dynamic radio environment in CRNs. In this paper, we study the dynamic resource allocation problem for heterogeneous services in CRNs with imperfect channel sensing. We formulate the power and channel allocation problem as a mixed-integer programming problem under constraints. The computational complexity is enormous to solve the problem. To reduce the computational complexity, we tackle this problem in two steps. First, we solve the optimal power allocation problem using the Lagrangian dual method under the assumption of known channel allocation. Next, we solve the joint power and channel allocation problem using the discrete stochastic optimization method, which has low computational complexity and fast convergence to approximate to the optimal solution. Another advantage of this method is that it can track the changing radio environment to dynamically allocate the resources. Simulation results are presented to demonstrate the effectiveness of the proposed scheme.

Opportunistic communications in interference alignment networks with wireless power transfer

IA is a promising technology for interference management in wireless networks. However, there are still some practical challenges. Signal to interference plus noise ratio (SINR) decrease is one of the key challenging issues due to the inherent property of IA and channel fading. Recent advances in OC, including multiuser diversity and antenna selection, can be applied in IA wireless networks to improve the SINR performance. In this article we review some existing research work on OC-based IA wireless networks. In addition, we propose a novel simultaneous wireless information and power transfer scheme based on OC in IA wireless networks. Simulation results are presented to show the performance comparison of these schemes. The methods to reduce the complexity of the OC-based IA algorithms are finally summarized.

Cross-Layer Design for TCP Performance Improvement in Cognitive Radio Networks

In cognitive radio (CR) networks, the end-to-end transmission-control protocol (TCP) performance experienced by secondary users is a very important factor that evaluates the secondary user perceived quality of service (QoS). Most previous works in CR networks ignore the TCP performance. In this paper, we take a cross-layer design approach to jointly consider the spectrum sensing, access decision, physical-layer modulation and coding scheme, and data-link layer frame size in CR networks to maximize the TCP throughput in CR networks. The wireless channel and the primary network usage are modeled as a finite-state Markov process. Due to the miss detection and the estimation error experienced by secondary users, the system state cannot be directly observed. Consequently, we formulate the cross-layer TCP throughput optimization problem as a partially observable Markov decision process (POMDP). Simulation results show that the design parameters in CR networks have a significant impact on the TCP throughput, and the TCP throughput can be substantially improved if the low-layer parameters in CR networks are optimized jointly.

Biologically inspired consensus-based spectrum sensing in mobile Ad Hoc networks with cognitive radios

Cognitive radios, which are capable of sensing their surrounding environment and adapting their internal parameters, have been considered in mobile ad hoc networks. Secondary users can cooperatively sense the spectrum to detect the presence of primary users. In this article we present a novel biologically inspired consensus-based cooperative spectrum sensing scheme in CR-MANETs. Our scheme is based on recent advances in consensus algorithms that have taken inspiration from self-organizing behavior of animal groups such as birds, fish, ants, honeybees, and others. Unlike the existing cooperative spectrum sensing schemes, such as the OR-rule or the 1-out-of-N rule, there is no need for a common receiver to do the data fusion for reaching the final decision. A secondary user needs only to set up local interactions without a centralized node in CR-MANETs. Simulation results are presented to show the effectiveness of the proposed scheme.

Prediction-Based Topology Control and Routing in Cognitive Radio Mobile Ad Hoc Networks

Cognitive radio (CR) technology will have significant impacts on upper layer performance in mobile ad hoc networks (MANETs). In this paper, we study topology control and routing in CR-MANETs. We propose a distributed Prediction-based Cognitive Topology Control (PCTC) scheme to provision cognition capability to routing in CR-MANETs. PCTC is a midware-like cross-layer module residing between CR module and routing. The proposed PCTC scheme uses cognitive link availability prediction, which is aware of the interference to primary users, to predict the available duration of links in CR-MANETs. Based on the link prediction, PCTC constructs an efficient and reliable topology, which is aimed at mitigating re-routing frequency and improving end-to-end network performance such as throughput and delay. Simulation results are presented to show the effectiveness of the proposed scheme.