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[show abstract]
[hide abstract]
ABSTRACT: Microgrid (MG) is a promising component for future smart grid (SG)
deployment. The balance of supply and demand of electric energy is one of the
most important requirements of MG management. In this paper, we present a novel
framework for smart energy management based on the concept of
quality-of-service in electricity (QoSE). Specifically, the resident
electricity demand is classified into basic usage and quality usage. The basic
usage is always guaranteed by the MG, while the quality usage is controlled
based on the MG state. The microgrid control center (MGCC) aims to minimize the
MG operation cost and maintain the outage probability of quality usage, i.e.,
QoSE, below a target value, by scheduling electricity among renewable energy
resources, energy storage systems, and macrogrid. The problem is formulated as
a constrained stochastic programming problem. The Lyapunov optimization
technique is then applied to derive an adaptive electricity scheduling
algorithm by introducing the QoSE virtual queues and energy storage virtual
queues. The proposed algorithm is an online algorithm since it does not require
any statistics and future knowledge of the electricity supply, demand and price
processes. We derive several "hard" performance bounds for the proposed
algorithm, and evaluate its performance with trace-driven simulations. The
simulation results demonstrate the efficacy of the proposed electricity
scheduling algorithm.
01/2013;
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[show abstract]
[hide abstract]
ABSTRACT: Compressed sensing (CS) refers to the process of reconstructing a signal that is supposed to be sparse or compressible. CS has wide applications, such as in cognitive radio networks. In this paper, we investigate effective CS schemes for the trade-off between energy efficiency and estimation error. We propose an enhancement to a Bayesian estimation approach and an enhancement to the isotonic regression approach that is based on nearly isotonic regression. We also show how to compute the routing matrix for selecting active sensor nodes. The proposed enhancements are evaluated with trace-driven simulations. Considerable gaps
are observed between the original approaches and the proposed enhancements in the simulation results. The near isotonic regression method achieves the best performance among all the CS schemes examined in this paper.
Ad Hoc Networks 01/2013; · 2.11 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Compressed sensing (CS) refers to the process of reconstructing a signal that is supposed to be sparse or com-pressible. CS has wide applications, such as in cognitive radio networks. In this paper, we investigate effective CS schemes for balancing energy efficiency and estimation error. We propose an enhancement to a Bayesian estimation approach and an enhancement to the isotonic regression approach that is based on nearly isotonic regression. We also show how to compute the routing matrix for selecting active sensor nodes. The proposed enhancements are evaluated with trace-driven simulations. Con-siderable gaps are observed between the original approaches and the proposed enhancements in the simulation results. The near isotonic regression method achieves the best performance among all the CS schemes examined in this paper.
Globecom 2012 - Wireless Communications Symposium; 12/2012
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[hide abstract]
ABSTRACT: Although the technology of femtocells is highly promising, many challenging
problems should be addressed before fully harvesting its potential. In this
paper, we investigate the problem of cell association and handover management
in femtocell networks. Two extreme cases for cell association are first
discussed and analyzed. Then we propose our algorithm to maximize network
capacity while achieving fairness among users. Based on this algorithm, we
further develop a handover algorithm to reduce the number of unnecessary
handovers using Bayesian estimation. The proposed handover algorithm is
demonstrated to outperform a heuristic scheme with considerable gains in our
simulation study.
10/2012;
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[show abstract]
[hide abstract]
ABSTRACT: In this paper, we investigate the problem of cooperative relay in CR networks
for further enhanced network performance. In particular, we focus on the two
representative cooperative relay strategies, and develop optimal spectrum
sensing and $p$-Persistent CSMA for spectrum access. Then, we study the problem
of cooperative relay in CR networks for video streaming. We incorporate
interference alignment to allow transmitters collaboratively send encoded
signals to all CR users. In the cases of a single licensed channel and multiple
licensed channels with channel bonding, we develop an optimal distributed
algorithm with proven convergence and convergence speed. In the case of
multiple channels without channel bonding, we develop a greedy algorithm with
bounded performance.
09/2012;
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[hide abstract]
ABSTRACT: Video content delivery over wireless networks is expected to grow drastically
in the coming years. In this paper, we investigate the challenging problem of
video over cognitive radio (CR) networks. Although having high potential, this
problem brings about a new level of technical challenges. After reviewing
related work, we first address the problem of video over infrastructure-based
CR networks, and then extend the problem to video over non-infrastructure-based
ad hoc CR networks. We present formulations of cross-layer optimization
problems as well as effective algorithms to solving the problems. The proposed
algorithms are analyzed with respect to their optimality and validate with
simulations.
09/2012;
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[hide abstract]
ABSTRACT: In this paper, we investigate the problem of multi-user spatial division multiple access (MU SDMA) operation in mmWave wireless networks, within which directional antennas are used to combat the high path loss incurred in the 60GHz band. We study the feasibility of MU SDMA in mmWave networks and propose two MAC protocols to support CSMA/CA based uplink and downlink MU SDMA transmissions. The proposed protocols adopt virtual carrier sensing and allows multiple users to communicate with an access point (AP) simultaneously. Performance analysis and simulation results both show that the proposed protocols can achieve considerable performance improvements over a system that supports only single user (SU) operation.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: In this paper, we study the problem of power allocation for streaming
multiple variable-bit-rate (VBR) videos in the downlink of a cellular network.
We consider a deterministic model for VBR video traffic and finite playout
buffer at the mobile users. The objective is to derive the optimal downlink
power allocation for the VBR video sessions, such that the video data can be
delivered in a timely fashion without causing playout buffer overflow and
underflow. The formulated problem is a nonlinear nonconvex optimization
problem. We analyze the convexity conditions for the formulated problem and
propose a two-step greedy approach to solve the problem. We also develop a
distributed algorithm based on the dual decomposition technique. The
performance of the proposed algorithms are validated with simulations using VBR
video traces under realistic scenarios.
05/2011;
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INFOCOM 2011. 30th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 10-15 April 2011, Shanghai, China; 01/2011
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Proceedings of the Global Communications Conference, GLOBECOM 2011, 5-9 December 2011, Houston, Texas, USA; 01/2011
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ABSTRACT: Free space optical (FSO) technology has been considered as a viable solution for broadband wireless networks. It has high potential for military communications for the next decade. In this paper, we investigate the problem of building robust spanning trees for FSO networks. We adopt algebraic connectivity as robustness measure, and formulate a 0-1 integer linear programming (ILP) problem. We present a fragment selection and merging (FSM) algorithm, which is executed in a distributed and asynchronous fashion to iteratively merge fragments until a spanning tree is formed. Our simulation study shows that FSM can achieve significantly improved connectivity at the cost of slightly degraded average link weight performance, compared to prior approaches. FSM can be used not only for FSO network bootstrapping, but also for auto-reconfiguration in response to network dynamics during operation.
MILITARY COMMUNICATIONS CONFERENCE, 2010 - MILCOM 2010; 12/2010
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ABSTRACT: We investigate the problem of streaming multiple videos over multi-hop cognitive radio (CR) networks. Fine-Granularity-Scalability (FGS) and Medium-Grain-Scalable (MGS) videos are adopted to accommodate the heterogeneity among channel availabilities and dynamic network conditions. We obtain a mixed integer nonlinear programming (MINLP) problem formulation, with objectives to maximize the overall received video quality and to achieve fairness among the video sessions, while bounding the collision rate with primary users under the presence of spectrum sensing errors. We first solve the MINLP problem using a centralized sequential fixing algorithm, and derive upper and lower bounds for the objective value. We then apply dual decomposition to develop a distributed algorithm and prove its optimality and convergence conditions. The proposed algorithms are evaluated with simulations and are shown to be effective in supporting concurrent scalable video sessions in multi-hop CR networks.
IEEE Transactions on Wireless Communications 12/2010; · 2.59 Impact Factor
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ABSTRACT: In this paper, we investigate the training problem of wireless local area networks (WLANs) with downlink multi-user multiple input multiple output (DL MU MIMO) capability. We extend the 802.11 MAC protocol and propose a few training protocols at the MAC layer to support DL MU MIMO. We provide a capacity analysis based on measurement results from an 802.11n systems, evaluate the overhead of these training protocols, and compare the performance of DL MU MIMO with that of a beam-forming (BF) based approach. Through simulation studies, we find that at high SNR and with implicit training, the DL MU MIMO mechanism provides significant performance gain over the BF based approach. Furthermore, our capacity analysis and simulation study also show that it is critical to define appropriate training intervals based on antenna configuration, channel mobility, and CSI feedback overhead.
Personal Indoor and Mobile Radio Communications (PIMRC), 2010 IEEE 21st International Symposium on; 10/2010
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ABSTRACT: In this paper, we investigate the problem of medium access control in mmWave wireless personal area networks (WPAN), within which directional antennas are used to combat the high path loss incurred in the 60GHz frequency band. The conventional CSMA/CA protocol does not work well with directional antennas due to impaired carrier sensing at the transmitters. We explain why existing directional MAC protocols do not work well at 60GHz and propose a novel directional CSMA/CA protocol designed specifically for 60GHz WPANs. Instead of relying on physical carrier sensing, the proposed protocol adopts virtual carrier sensing and relies on a central coordinator to distribute network allocation vector (NAV) information. Both performance analysis and simulation study show that the proposed mechanism incurs low overhead and has robust performance even when the network is heavily congested.
Wireless Communications and Networking Conference (WCNC), 2010 IEEE; 05/2010
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ABSTRACT: We investigate the problem of scalable video multicast in emerging cognitive radio (CR) networks. Although considerable advances have been made in CR research, such important problems have not been well studied. Naturally, 'bandwidth hungry' multimedia applications are excellent candidates for fully capitalizing the potential of CRs. We propose a crosslayer optimization approach to multicast video in CR networks. Specifically, we consider an infrastructure-based CR network collocated with N primary networks and model CR video multicast over the N channels as a mixed integer nonlinear programming (MINLP) problem. The objective is three-fold: to optimize the overall received video quality; to achieve proportional fairness among multicast users; and to keep the interference to primary users below a prescribed threshold. We propose a sequential fixing algorithm and a greedy algorithm to solve the MINLP, while the latter has low complexity and proven optimality gap. Our simulations with MPEG-4 fine grained scalability (FGS) video demonstrate the efficacy and superior performance of the proposed algorithms.
IEEE Journal on Selected Areas in Communications 05/2010; · 3.41 Impact Factor
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ABSTRACT: Several geographic (or position-based) routing protocols have been proposed for data dissemination in wireless sensor networks. In these protocols, routing is based on the positions of neighboring nodes. In particular, the next-hop node is selected according to either a distance-based strategy, which favors a neighbor with the largest distance progress toward the sink, or a direction-based strategy, which favors a neighbor with the lowest angle deviation toward the sink. In this paper, we propose a novel hybrid geographic routing (HGR) scheme that combines both distance- and direction-based strategies in a flexible manner. To further facilitate a tradeoff between energy consumption and end-to-end delay, we propose two dynamic HGR (DHGR) mechanisms based on the basic HGR scheme, which are designed to satisfy constraints on the average end-to-end delay of specific applications while minimizing energy consumption. Packet-delivery decisions are locally made, and the state at a node is independent of the number of nodes in the network; thus, DHGR has the inherent scaling property of geographic routing. The effectiveness of the proposed schemes is evaluated by analysis and extensive simulations.
IEEE Transactions on Vehicular Technology 12/2009; · 1.92 Impact Factor
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ABSTRACT: As streaming videos are becoming increasingly popular, it is important to understand the end-to-end streaming system and to develop effective algorithms for quality control. In this paper, we address the problem of rate control for streaming videos with a control-theoretic approach. Among the various control knobs, video bit rate is one of the most effective in the sense that it has a direct impact on the interaction between the video coder and network system. While increasing rate reduces the coder-induced distortion, it may also cause congestion at a bottleneck link. The packet loss due to congestion will, then, increase the distortion of the decoded video. We model end-to-end video steaming as a feedback control system, taking into account video codec and sequence characteristics, rate control, active queue management, and receiver feedback. We then develop effective proportional (P) controllers to stabilize the received video quality as well as the bottleneck link queue, for both homogeneous and heterogeneous video systems. Simulation results are presented to demonstrate the efficacy of the P controllers and the viability of the proposed control-theoretic approach.
IEEE Transactions on Multimedia 11/2009; · 1.93 Impact Factor
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ABSTRACT: Cognitive Radio (CR) is a new wireless communications and networking paradigm that is enabled by the Software Defined Radio (SDR) technology and a recent change in spectrum regulation policy. As the first commercial application of CR technology, IEEE 802.22 wireless regional area networks (WRAN) aim to offer broadband wireless access by efficiently utilizing ldquowhite spacesrdquo in the broadcast TV bands. In this paper, we evaluate the performance of an IEEE 802.22 WRAN base station (BS) cognitive engine (CE) testbed developed at Wireless@Virginia Tech on supporting video applications. We investigate the important problem of utility function selection and its impact on the received video quality. Through testbed experiments, we find that a video-specific utility function achieves significant improvements on received video quality over a general purpose utility function, indicating the efficacy of cross-layer design and more importantly, the need for adopting dynamic situation- and application-aware utility functions at the CE, rather than a predefined static one.
Testbeds and Research Infrastructures for the Development of Networks & Communities and Workshops, 2009. TridentCom 2009. 5th International Conference on; 05/2009
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ABSTRACT: Performance evaluation of cognitive radio (CR) networks is an important problem but has received relatively limited attention from the CR community. Unlike traditional radios, a cognitive radio may change its objectives as radio scenarios vary. Because of the dynamic pairing of objectives and contexts, it is imperative for cognitive radio network designers to have a firm understanding of the interrelationships among goals, performance metrics, utility functions, link/network performance, and operating environments. In this paper, we first overview various performance metrics at the node, network, and application levels. From a game-theoretic viewpoint, we then show that the performance evaluation of cognitive radio networks exhibits the interdependent nature of actions, goals, decisions, observations, and context. We discuss the interrelationships among metrics, utility functions, cognitive engine algorithms, and achieved performance, as well as various testing scenarios. We propose the radio environment map-based scenario-driven testing (REM-SDT) for thorough performance evaluation of cognitive radios. An IEEE 802.22 WRAN cognitive engine testbed is presented to provide further insights into this important problem area.
Proceedings of the IEEE 05/2009; · 6.81 Impact Factor
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ABSTRACT: In a multihop wireless network environment, it has been shown that IEEE 802.11 media access control (MAC) suffers from a low-throughput problem, which is largely due to the inefficiency in carrier sensing and spatial reuse. In this paper, we present a location-assisted MAC protocol that schedules ldquofeasiblerdquo concurrent transmissions in a multihop wireless network. A simple procedure based on location information is adopted in the proposed MAC to validate the feasibility of a concurrent transmission. Our simulation results show that the proposed scheme can effectively increase the throughput and reduce the average end-to-end delay of multihop wireless networks.
IEEE Transactions on Vehicular Technology 02/2009; · 1.92 Impact Factor
