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Improved Approximation of Storage-Rate Tradeoff for Caching with Multiple Demands

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Improved Approximation of Storage-Rate Tradeoff for Caching ...

作者： Sengupta, Avik Tandon, Ravi Next Generation and Standards Group Intel Corp. Santa ClaraCA95054 United States Department of Electrical and Computer Engineering University of Arizona TucsonAZ85721 United States

Caching at the network edge has emerged as a viable solution for alleviating the severe capacity crunch in modern content centric wireless networks by leveraging network load-balancing in the form of localized content storage and delivery. In this paper, we consider a cache-aided network, where the cache storage phase is assisted by a central server and users can demand multiple files at each transmission interval. To service these demands, we consider two delivery models: 1) centralized content delivery, where user demands at each transmission interval are serviced by the central server via multicast transmissions;and 2) device-to-device assisted distributed delivery, where users multicast to each other in order to service file demands. For such cache-aided networks, we present new results on the fundamental cache storage versus transmission rate tradeoff. Specifically, we develop a new technique for characterizing information theoretic lower bounds on the storage-rate tradeoff and show that the new lower bounds are strictly tighter than cut-set bounds from literature. Furthermore, using the new lower bounds, we improve the constant factor approximation of the optimal storage-rate tradeoff for cache-aided systems under both delivery models. © 1972-2012 IEEE.

关键词： Multicasting

Maximum production point tracking of a high-temperature power-to-gas system: A dynamic-model-based study

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arXiv 2018年

作者： Xing, Xuetao Lin, Jin Song, Yonghua Hu, Qiang State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing100084 China Department of Electrical and Computer Engineering University of Macau China Department of Electrical Engineering Tsinghua University Beijing100084 China Tsinghua-Sichuan Energy Internet Research Institute Chengdu610213 China

Power-to-gas (P2G) can be employed to balance renewable generation because of its feasibility to operate at fluctuating loading power. The fluctuating operation of low-temperature P2G loads can be achieved by controlling the electrolysis current alone. However, this method does not apply to high-temperature P2G (HT-P2G) technology with auxiliary parameters such as temperature and feed rates: Such parameters need simultaneous coordination with current due to their great impact on conversion efficiency. To improve the system performance of HT-P2G while tracking the dynamic power input, this paper proposes a maximum production point tracking (MPPT) strategy and coordinates the current, temperature and feed rates together. In addition, a comprehensive dynamic model of an HTP2G plant is established to test the performance of the proposed MPPT strategy, which is absent in previous studies that focused on steady states. The case study suggests that the MPPT operation responds to the external load command rapidly even though the internal transition and stabilization cost a few minutes. Moreover, the conversion efficiency and available loading capacity are both improved, which is definitely beneficial in the long run. Copyright © 2018, The Authors. All rights reserved.

关键词： Dynamic models

A New Topology of Multilevel VSC Converter for a Hybrid HVDC Transmission System

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A New Topology of Multilevel VSC Converter for a Hybrid HVDC...

作者： Jung, Jae-Jung Cui, Shenghui Lee, Joon-Hee Sul, Seung-Ki Department of Electrical and Computer Engineering Seoul National University Seoul08826 Korea Republic of Institute for Power Generation and Storage Systems RWTH Aachen University Aachen52062 Germany

This paper introduces a new multilevel converter topology for a hybrid HVDC system comprising line-commutated converter (LCC) and voltage source converter (VSC). Among the existing modular multilevel converter (MMC) topologies for the hybrid HVDC, a mixed MMC structure with half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) has characteristics of reduced system cost, low operation loss, but still keeping capability to cope with dc short-circuit fault. However, it is very difficult for the conventional hybrid MMC structure to balance the submodule capacitor voltages under dc-bus voltage sliding since each MMC arm is a mixture of HBSMs and FBSMs. To solve the defect of the conventional hybrid MMC structure, an asymmetric mixed MMC, in which one arm is made of series-connected HBSMs and other arm is made of FBSMs, is devised. The proposed asymmetric MMC can regulate the dc-bus voltage freely without uncontrollable submodule capacitor voltages. The problems of the conventional MMC structure and the validity of asymmetric MMC are verified by both computer simulation and experimental results. © 2016 IEEE.

关键词： Topology

MAC Rate Region of Low Resolution ADC Digital and Hybrid Beamforming Massive MIMO UL

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MAC Rate Region of Low Resolution ADC Digital and Hybrid Bea...

IEEE International Conference on Communications Workshops

作者： Kilian Roth Josef A. Nossek Next Generation and Standards Intel Deutschland GmbH Neubiberg Germany Department of Electrical and Computer Engineering Technical University Munich Germany

ISBN: (纸本)9781509015269

For 5G it will be important to leverage the available millimeter wave spectrum. To achieve an approximately omnidi-rectional coverage with a similar effective antenna aperture, an antenna array is required at both the mobile and basestation. Due to the large bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog front-end of the transceiver with a large number of antennas is especially power hungry. Two main solutions exist to reduce the power consumption: Hybrid BeamForming (HBF) and Digital BeamForming (DBF) with low resolution ADC. This work compares the uplink rate region for both systems assuming a basestation with a large number of antennas. We show, that in the low SNR regime, the performance of DBF even with about 1-2 bits of resolution outperforms the one of HBF in terms of the achievable sum rate. The higher the SNR, the higher also the required resolution of the ADC to achieve a similar performance compared to HBF. If there is a large spread in receive power of the signal from different users, systems with very low resolution (1-3 bit) suffer from a performance loss.

关键词： Array signal processing Quantization (signal) Antenna arrays Covariance matrices Power demand Aperture antennas

Modeling and analysis of secondary controlled virtual synchronous generator with dynamic droop for microgrid

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Modeling and analysis of secondary controlled virtual synchr...

2017 IEEE Conference on Energy Internet and Energy System Integration, EI2 2017

作者： Yan, Weihang Gao, David Wenzhong Zhang, Fang Cheng, Lin Yan, Shijie Department of Electrical and Computer Engineering University of Denver Denver United States State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Tsinghua University Beijing China College of Information Science and Technology Northeastern University Shenyang China

ISBN: (纸本)9781538614273

In this paper, a dynamic droop mechanism is proposed to damp the synchronizing oscillation that exists in a virtual synchronous generator based distributed generator system without varying the steady-state active-power-loop droop coefficient. In order to eliminate the steady-state error introduced due to load changes or generator trips, a distributed secondary controller based on extremum seeking is employed so that microgrid frequency can be restored to nominal value. Besides, the small-signal model of virtual synchronous generator system is presented under d-q reference frame where virtual synchronous generator is deployed as a PV node. Moreover, the linearized system model of virtual synchronous generator with dynamic droop mechanism is derived and its advantage is discussed. Finally, a modified IEEE 14 bus microgrid system is established in Matlab/Simulink platform. Simulation results demonstrate the validity and feasibility of the proposed method. © 2017 IEEE.

关键词： Dynamics

A Centralized Algorithm for Assigning MDC Video Application in Virtual Network

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China Communications 2016年第S1期13卷 158-166页

作者： ZHU Kai WU Chunming ZHOU Boyang CHEN Fei WANG Haoxue Next Generation Network Laboratory College of Computer Science and Technology Zhejiang University Henan Electrical Power Research Institute State Grid Corporation of China Information Engineering University

Providing services on demand is a major contributing factor to drive the increasingly development of the software defined network. However, it should supply all the current popular applications before it really attains widespread development. Multiple Description Coding(MDC) video applications, as a popular application in the current network, should be reasonably supported in this novel network virtualization environment. In this paper, we address this issue to assign MDC video application into virtual networks with an efficient centralized algorithm(CAMDV). Since this problem is an NP-hard problem, we design an algorithm that can effectively balance the user satisfaction and network resource cost. Previous work just builds a global multicast tree for each description to connect all the destination nodes by breadth-first search strategy or shortest path tree algorithm. But those methods could not achieve an optimal balance or a high-level user satisfaction. By introducing the hierarchical clustering scheme, our algorithm decomposes the whole mapping procedure into multicast tree construction and multipath description distribution. A serial of simulation experiments show that our centralized algorithm could achieve a better performance in balancing the user satisfaction and average mapping cost in comparison with its rivals.

关键词： multiple description coding video multipath programming hierarchical clustering scheme multicast tree construction network virtualization

Competitive resource allocation in HetNets: The impact of small-cell spectrum constraints and investment costs

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arXiv 2017年

作者： Chen, Cheng Berry, Randall A. Honig, Michael L. Subramanian, Vijay G. Department of Electrical Engineering and Computer Science Northwestern University EvanstonIL United States Next Generation and Standards Group Intel Corporation HillsboroOR Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI United States

Heterogeneous wireless networks with small-cell deployments in licensed and unlicensed spectrum bands are a promising approach for expanding wireless connectivity and service. As a result, wireless service providers (SPs) are adding small-cells to augment their existing macro-cell deployments. This added flexibility complicates network management, in particular, service pricing and spectrum allocations across macro- A nd smallcells. Further, these decisions depend on the degree of competition among SPs. Restrictions on shared spectrum access imposed by regulators, such as low power constraints that lead to small-cell deployments, along with the investment cost needed to add small cells to an existing network, also impact strategic decisions and market efficiency. If the revenue generated by small-cells does not cover the investment cost, then there will be no deployment even if it increases social welfare. We study the implications of such spectrum constraints and investment costs on resource allocation and pricing decisions by competitive SPs, along with the associated social welfare. Our results show that while the optimal resource allocation taking constraints and investment into account can be uniquely determined, adding those features with strategic SPs can have a substantial effect on the equilibrium market structure. Copyright © 2017, The Authors. All rights reserved.

关键词： Investments

Optimization of hydrogen yield of a high-temperature electrolysis system with coordinated temperature and feed factors at various loading conditions: a model-based study☆

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arXiv 2018年

作者： Xing, Xuetao Lin, Jin Song, Yonghua Hu, Qiang Zhou, You Mu, Shujun State Key Laboratory of Control and Simulation of Power Systems and Generation Equipment Department of Electrical Engineering Tsinghua University Beijing100084 China Department of Electrical and Computer Engineering University of Macau Macau China Tsinghua-Sichuan Energy Internet Research Institute Chengdu610213 China National Institute of Clean and Low Carbon Energy Beijing102211 China Zhejiang Zhentai Energy Tech. Co. Ltd. Lishui Zhejiang Province321400 China

High-temperature electrolysis (HTE) is a promising technology for achieving high-efficiency power-to-gas, which mitigates the renewable curtailment while promoting decarbonization by transforming wind or solar energy into fuels. Different from low-temperature electrolysis, a considerable amount of the input energy is consumed by auxiliary equipment in an HTE system for maintaining the temperature, so the studies on systematic energy description and parameter optimization of HTE are essentially required. A few published studies investigated HTE’s systematic optimization based on simulation, yet there is not a commonly used analytical optimization model which is more suitable for integration with power grid. To fill in this blank, a concise analytical operation model is proposed in this paper to coordinate the necessary power consumptions of auxiliaries under various loading conditions of an HTE system. First, this paper develops a comprehensive energy flow model for an HTE system based on the fundamentals extracted from the existing work, providing a quantitative description of the impacts of condition parameters, including the temperature and the feedstock flow rates. A concise operation model is then analytically proposed to search for the optimal operating states that maximize the hydrogen yield while meeting the desired system loading power by coordinating the temperature, the feedstock flows and the electrolysis current. The evaluation of system performance and the consideration of constraints caused by energy balances and necessary stack requirements are both included. In addition, analytical optimality conditions are obtained to locate the optimal operating states without performing nonlinear programming by further investigating the optimization method. In the case study, a numerical case of an HTE system is employed to validate the proposed operation model and optimization method, which proves that the proposed operation strategies not only improve the overal

关键词： Hydrogen production

Robust massive MIMO Equilization for mmWave systems with low resolution ADCs

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arXiv 2017年

作者： Roth, Kilian Nossek, Josef A. Next Generation and Standards Intel Deutschland GmbH Neubiberg Germany Department of Electrical and Computer Engineering Technical University Munich Munich Germany Department of Teleinformatics Engineering Federal University of Ceara Fortaleza Brazil

Leveraging the available millimeter wave spectrum will be important for 5G. In this work, we investigate the performance of digital beamforming with low resolution ADCs based on link level simulations including channel estimation, MIMO equalization and channel decoding. We consider the recently agreed 3GPP NR type 1 OFDM reference signals. The comparison shows sequential DCD outperforms MMSE-based MIMO equalization both in terms of detection performance and complexity. We also show that the DCD based algorithm is more robust to channel estimation errors. In contrast to the common believe we also show that the complexity of MMSE equalization for a massive MIMO system is not dominated by the matrix inversion but by the computation of the Gram matrix. Copyright © 2017, The Authors. All rights reserved.

关键词： Channel estimation