Explicit Construction of Optimal Exact Regenerating Codes for Distributed Storage

Erasure coding techniques are used to increase the reliability of distributed storage systems while minimizing storage overhead. Also of interest is minimization of the bandwidth required to repair the system following a node failure. In a recent paper, Wu et al. characterize the tradeoff between the repair bandwidth and the amount of data stored per node. They also prove the existence of regenerating codes that achieve this tradeoff. In this paper, we introduce Exact Regenerating Codes, which are regenerating codes possessing the additional property of being able to duplicate the data stored at a failed node. Such codes require low processing and communication overheads, making the system practical and easy to maintain. Explicit construction of exact regenerating codes is provided for the minimum bandwidth point on the storage-repair bandwidth tradeoff, relevant to distributed-mail-server applications. A subspace based approach is provided and shown to yield necessary and sufficient conditions on a linear code to possess the exact regeneration property as well as prove the uniqueness of our construction. Also included in the paper, is an explicit construction of regenerating codes for the minimum storage point for parameters relevant to storage in peer-to-peer systems. This construction supports a variable number of nodes and can handle multiple, simultaneous node failures. All constructions given in the paper are of low complexity, requiring low field size in particular.Comment: 7 pages, 2 figures, in the Proceedings of Allerton Conference on Communication, Control and Computing, September 200

Energy Management System Considering Battery Lifetime

The contribution of renewable energy resources in the global energy generation has been increasing at a fast pace. Variability and uncertainty are the two main issues related to renewable energy integration. Thus, energy storage systems (ESSs) are used in such systems to smooth the power generated by the renewable energy sources. In order to ensure reliable and economic operation of the system, energy management system (EMS) is implemented to control the dispatch of the available resources. ESS such as a battery requires significant capital investment and frequent replacement. A battery has a maximum lifetime called float life, regardless of energy throughput. Furthermore, the useful lifetime of these batteries varies considerably based on the operating conditions. Generally, the batteries are used excessively without considering the impact on the useful lifetime when used in systems that are isolated from the utility. On the contrary, the batteries are rarely used in the systems that are connected to the utility such that the available output is wasted at the end of the float life of the batteries. Thus, the consideration of the battery lifetime characteristics in EMS can maximize the battery utilization during its useful life. In this work, implementation of EMS including the battery lifetime for the operation of hybrid power systems– a remote microgrid, and a data center are investigated. Implementation of EMS for the annual operation of a remote microgrid considering the battery lifetime is performed. A heuristic search technique– genetic implementor (genitor) algorithm has been implemented as the inclusion of fuel consumption of diesel generator and battery degradation models in objective function yields in high nonlinearity. The fuel consumption and battery output minimization are achieved. Similar to a remote microgrid, EMS can also be implemented in large scale systems like data centers. Data centers consume a large amount of energy and have backup resources allocated for emergency conditions. These resources can be utilized to participate in demand response (DR) to reduce the peak load demand. Real-time dispatch module of a data center is developed to consume daily allocated budget for battery usage to ensure utilization of the battery. The real-time operational cost of a data center is reduced for participation in DR as compared to the operational cost without DR

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs