Tradeoff between Quality-of-Service and resiliency: A mathematical framework applied to LTE networks

Adaptability in the presence of disruptive events is key to improve the resilience of the smart grid. As such, this paper presents a mathematical framework that quantifies the tradeoff between resilience and the Quality-of-Service (QoS) delivered by loads when they are information and communication technology (ICT) systems. The framework is based on the introduction of a quantity, named the over-demand factor, that measures the ratio between the resources required by the load under normal operating conditions and those available when in a degraded state. As a case study, the mathematical framework was applied to the study of the resilience-QoS tradeoff in an LTE base station. Moreover, the results from the study are applied to realistic power outage scenarios to obtain numerical results that provide insights into the resilience performance and operation of the LTE eNB. These results reveal that by trading off during disruptive events tolerable reductions in the QoS, it is possible to noticeably reduce the required size for a backup battery bank or to extend the operation from the backup batteries for the same planned autonomy. The results also show how trading off tolerable reductions in the QoS addresses the main issue with deployment of photovoltaic arrays as supplemental backup power source by noticeably reducing the solar panels size requirements to achieve a target availability level. Conversely, the framework allows to quantify the improvement in resilience from trading off QoS for a given PV array area.