Alexis Kwasinski

Increasing sustainability and resiliency of cellular network infrastructure by harvesting renewable energy

The carbon footprint of cellular base stations is a source of concern not only because of their power consumption, which accounts for more than half of all of the cellular infrastructure, but also because of the large rate of growth in their deployment. This article discusses how the use of harvested renewable energy can contribute to solving this problem. The article also addresses the challenges associated with harvesting wind and solar energy, namely the variability in available energy and the large physical footprint of energy harvesters. This article explains that these challenges can be better addressed by jointly considering the harvested energy availability and the dynamic characteristics of base station power consumption. A realization of this approach is the recently introduced idea of a sustainable wireless area that integrates energy harvesters and a group of base stations in a microgrid architecture. This architecture enables an integrated harvested energy-cellular traffic management technique that shapes the traffic serviced by a base station based on the predicted availability of renewable energy. As a result, longer periods of operation powered from renewable energy are achieved while degradation of the users qualityof- experience (QoE) is minimal and occasional. This article also explains how harvested renewable energy also increases the resiliency of cellular networks because they do not depend on lifelines for operation.

Japan's Pivot to Resilience: How Two Microgrids Fared After the 2011 Earthquake

Japan was an early leader in microgrid research, with the four demonstrations funded by the New Energy and Industrial Technology Development Organization (NEDO) between 2003 and 2008 being particularly influential. In addition, there have been several notable private sector projects, as well as some remote island, dc power, and sustainable community demonstrations. Objectives for the four NEDO projects were primarily to demonstrate the high penetration of local small-scale renewables,local control of diverse resources, islanding, reliability, and heterogeneous power quality (HeQ).

Decentralized Hierarchical Control of Active Power Distribution Nodes

This paper explores control strategies for active power distribution nodes (APDNs) using a hierarchical approach. The proposed APDN consists of multiple bidirectional interface modules and an embedded energy storage that is commonly connected to these modules. Such configuration properties make the APDN attractive as a major interface unit for active power flow control in microgrids and power distribution networks. A two-level hierarchy is considered so that the primary level performs load sharing using droop control, and the secondary level performs embedded energy storage management. The stability of the proposed control framework is studied and the proposed design is verified by an experimental setup.

Role of energy storage in a microgrid for increased use of photovoltaic systems in wireless communication networks

This paper explores the design and operation of a dc microgrid formed by a few base stations that is powered primarily from photovoltaic (PV) arrays coupled to batteries. First, the control architecture is described with a focus on the high-level controller. This controller optimizes operation so batteries are not subject to excessive cycling and deep discharges thanks to an integrated management of base station load through a strategy based on traffic shaping. The technique used to control traffic is extensively explained and verified with case studies that are based on systems using configurations expected to be observed in practical applications.

Traffic management for sustainable LTE networks

This paper presents a technique to reduce the carbon footprint of cellular network through the use of renewable energy as a power source. Novel to other approaches in the literature, the presented technique adapts the traffic conditions and Quality of Experience (QoE) goals. Through effectively integrating energy and traffic management, the presented technique shapes the traffic serviced by the base station based on the predicted renewable energy surplus or deficit, and by controllably reducing the real-time video quality and increasing the data traffic delay. Simulation results show an increase of fifty percent in the proportion of time that the base station is powered from renewable sources with a very small, controlled and bounded impact on real time traffic quality and data delay.

Integrating cross-layer LTE resources and energy management for increased powering of base stations from renewable energy

This paper studies a cross-layer technique to increase the powering of an LTE macro base station from renewable energy. The cross-layer technique integrates the management of the transmit antennas and LTE frames with, at the application layer, video compression factor and data traffic delay. Importantly, the management of these cellular network components is integrated with the base station energy system by adapting the transmission of the cellular network based on the projected renewable energy availability. The overall system presents a tradeoff between increased use of renewable energy and an increase in video distortion and data delay up to predefined limits. Simulation results show that the studied technique effectively increases the percentage of time that an LTE base station is able to operate powered only from renewable energy (up to 98.5%) while at the same time increasing within small, acceptable levels, video distortion and data delay a third of the time.

Empirically validated availability model of information and communication technologies facilities under hurricane conditions

This paper presents case studies of information and communications technology facilities performance under hurricane conditions supported by empirical data. The paper uses availability models along with outage data and field damage assessments to evaluate ICT site power supply availability. The study use hurricanes Katrina (2005), Ike (2008) and Sandy (2012) as case studies. The analysis focuses on first refueling cycle for the diesel genset for various impacted regions for various refueling time characteristics. Additionally, battery backup times are also considered. It is found that the expected availability of ICT sites standby supply systems during these hurricanes was below accepted standards in the telecom industry. The effects of cooling infrastructure and energy storage on ICT site availability are also discussed.

Decentralized control of a vehicular microgrid with constant power loads

Constant power loads may form a major proportion of the system loads in automotive power systems. Without proper control the presence of constant power loads in a multi-converter environment can cause system instability. In this paper, the concept of autonomous control of a dc microgrid is extended to automotive power systems. An autonomous control law is derived for an automotive power system which consists of system of parallel connected boost converters supplying a constant power load. The control law derived using the passivity based approach consists of two stages. The first, primary stage involves a non-linear droop of the microgrid voltage with respect to the current supplied by each of the converters thereby enabling current sharing. The primary controller also damps the oscillations in the dc microgrid caused by the presence of the constant power load. The secondary controller adjusts for the voltage deviations due to the primary controller without affecting the current sharing. The conditions to ensure the asymptotic stability of the equilibrium points are derived. Experimental results are presented to verify the proposed control law.

Field technical surveys: An essential tool for improving critical infrastructure and lifeline systems resiliency to disasters

This paper explores critical infrastructure resiliency. The discussion initially introduces concepts and notions that are important for the analysis. Disasters are not seen as a single event but rather as cycles with distinct phases. These concepts and notions support the conclusion that critical infrastructures are cyber-physical-social systems that have not only interconnected physical components but also include processes as an integral constituting part. The discussion also indicates that the reliability concept of availability can be used as a metric for resiliency and for characterizing degree of dependence among infrastructures. Such metric allows a quantifiable approach for critical infrastructures planning and operation. Field technical surveys are then seen as a key tool to be able to quantify availability and, thus, assess resiliency. Finally, this paper explains approaches to conduct field technical surveys and their steps.

Numerical evaluation of communication networks resilience with a focus on power supply performance during natural disasters

This paper presents a quantitative framework for measuring and characterizing resilience of information and communications technology facilities with a focus on their power supply. Although the focus of the presented framework is for communication networks power supply, it is also applicable to power grids in general. The proposed framework uses a measure analogous to availability in order to measure resilience of communication systems power supply. A dynamic notion of dependency is discussed and a mathematical quantifiable relationship showing how dependencies affect resilience is explained. The importance of energy storage as a regulator for dependencies is also explored and additional related definitions and metrics are provided. This discussion is presented in practical context by using actual data and photographic records from recent natural disasters.