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Vardakas J.S.,Iquadrat | Zorba N.,Qatar University | Verikoukis C.V.,Catalonia Technology Center of Telecomunications
IEEE Communications Surveys and Tutorials | Year: 2015

The smart grid concept continues to evolve and various methods have been developed to enhance the energy efficiency of the electricity infrastructure. Demand Response (DR) is considered as the most cost-effective and reliable solution for the smoothing of the demand curve, when the system is under stress. DR refers to a procedure that is applied to motivate changes in the customers' power consumption habits, in response to incentives regarding the electricity prices. In this paper, we provide a comprehensive review of various DR schemes and programs, based on the motivations offered to the consumers to participate in the program. We classify the proposed DR schemes according to their control mechanism, to the motivations offered to reduce the power consumption and to the DR decision variable. We also present various optimization models for the optimal control of the DR strategies that have been proposed so far. These models are also categorized, based on the target of the optimization procedure. The key aspects that should be considered in the optimization problem are the system's constraints and the computational complexity of the applied optimization algorithm. © 1998-2012 IEEE. Source

Vardakas J.S.,Iquadrat | Zorba N.,Qatar University | Verikoukis C.V.,Catalonia Technology Center of Telecomunications
Energy | Year: 2014

In this paper we present and analyze online and offline scheduling models for the determination of the maximum power consumption in a smart grid environment. The proposed load models consider that each consumer's residence is equipped with a certain number of appliances of different power demands and different operational times, while the appliances' feature of alternating between ON and OFF states is also incorporated. Each load model is correlated with a scheduling policy that aims to the reduction of the power consumption through the compression of power demands or the postponement of power requests. Furthermore, we associate each load model with a proper dynamic pricing process in order to provide consumers with incentives to contribute to the overall power consumption reduction. The evaluation of the load models through simulation reveals the consistency and the accuracy of the proposed analysis. © 2014 Elsevier Ltd. Source

Vardakas J.S.,Iquadrat | Zorba N.,Qatar University | Verikoukis C.V.,Catalonia Technology Center of Telecomunications
Applied Energy | Year: 2016

In this paper we propose novel and more realistic analytical models for the determination of the peak demand under four power demand control scenarios. Each scenario considers a finite number of appliances installed in a residential area, with diverse power demands and different arrival rates of power requests. We develop recursive formulas for the efficient calculation of the peak demand under each scenario, which take into account the finite population of the appliances. Moreover, we associate each scenario with a proper real-time pricing process in order to derive the social welfare. The proposed analysis is validated through simulations. Moreover, the performance evaluation of the proposed formulas reveals that the absence of the assumption of finite number of appliances could lead to serious peak-demand over-estimations. © 2015 Elsevier Ltd. Source

Niotaki K.,Catalonia Technology Center of Telecomunications | Georgiadis A.,Catalonia Technology Center of Telecomunications | Collado A.,Catalonia Technology Center of Telecomunications | Vardakas J.S.,Iquadrat
IEEE Transactions on Microwave Theory and Techniques | Year: 2014

In this work, the concept of dual-band resistance compression networks is introduced and applied to the design of rectifier circuits with improved performance. The use of resistance compression networks (RCNs) minimizes the sensitivity of rectifier circuits to variations in the surrounding environment, such as input power level and changes in the rectifier load. The proposed dual-band RCN can be used as the matching network located between the antenna and the rectifying element of a dual-band rectifier for energy harvesting applications. A dual-band ( 915 MHz /2.45 GHz) rectifier based on RCN is designed and characterized showing improved performance in comparison with a conventional dual-band envelope detector by exhibiting improved RF-dc conversion efficiency and reduced sensitivity versus output load and input power variations. © 1963-2012 IEEE. Source

Vardakas J.S.,Iquadrat | Moscholios I.D.,University of Peloponnese | Logothetis M.D.,University of Patras | Stylianakis V.G.,University of Patras
Optical Switching and Networking | Year: 2014

An Optical Code Division Multiple Access (OCDMA) Passive Optical Network (PON) is a highly promising PON configuration, thanks to the potential of OCDMA technology in eliminating channel contention and efficiently supporting multi-rate traffic with different QoS requirements. In this paper, we provide a mathematical framework for a call-level performance analysis of an OCDMA PON that accommodates multiple service-classes of bursty traffic with retries. Blocked calls of random arrivals may immediately retry several times, by requesting less resources (number of codewords) each time, in order to be admitted for service. The bursty nature of traffic is denoted by the fact that in-service calls may alternate between transmission and no-transmission periods. Our analysis takes into account user activity and the various components of additive noise. An approximate recursive formula is derived for the efficient calculation of call-level performance measures. The proposed analytical model is further extended to assess the performance of an OCDMA PON that provides QoS differentiation, through the utilization of multiple-weight optical codes. Both proposed models are verified through simulation and found to be absolutely satisfactory. Moreover, comparison of the new models with a model without retries shows the necessity and effectiveness of the new models. © 2014 Elsevier B.V. Source

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