A DIVERSE BAND-AWARE DYNAMIC SPECTRUM ACCESS ARCHITECTURE FOR CONNECTIVITY IN RURAL COMMUNITIES

Ubiquitous connectivity plays an important role in improving the quality of life in terms of economic development, health and well being, social justice and equity, as well as in providing new educational opportunities. However, rural communities which account for 46% of the world\u27s population lacks access to proper connectivity to avail such societal benefits, creating a huge digital divide between the urban and rural areas. A primary reason is that the Information and Communication Technologies (ICT) providers have less incentives to invest in rural areas due to lack of promising revenue returns. Existing research and industrial attempts in providing connectivity to rural communities suffer from severe drawbacks, such as expensive wireless spectrum licenses and infrastructures, under- and over-provisioning of spectrum resources while handling heterogeneous traffic, lack of novel wireless technologies tailored to the unique challenges and requirements of rural communities (e.g., agricultural fields). Leveraging the recent advances in Dynamic Spectrum Access (DSA) technologies like wide band spectrum analyzers and spectrum access systems, and multi-radio access technologies (multi-RAT), this dissertation proposes a novel Diverse Band-aware DSA (d-DSA) network architecture, that addresses the drawbacks of existing standard and DSA wireless solutions, and extends ubiquitous connectivity to rural communities; a step forward in the direction of the societal and economic improvements in rural communities, and hence, narrowing the digital divide between the rural and urban societies. According to this paradigm, a certain wireless device is equipped with software defined radios (SDRs) that are capable of accessing multiple (un)licensed spectrum bands, such as, TV, LTE, GSM, CBRS, ISM, and possibly futuristic mmWaves. In order to fully exploit the potential of the d-DSA paradigm, while meeting heterogeneous traffic demands that may be generated in rural communities, we design efficient routing strategies and optimization techniques, which are based on a variety of tools such as graph modeling, integer linear programming, dynamic programming, and heuristic design. Our results on realistic traces in a large variety of rural scenarios show that the proposed techniques are able to meet the heterogeneous traffic requirements of rural applications, while ensuring energy efficiency and robustness of the architecture for providing connectivity to rural communities

PARTE : automatic program partitioning for efficient computation over encrypted data

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 45-47).Many modern applications outsource their data storage and computation needs to third parties. Although this lifts many infrastructure burdens from the application developer, he must deal with an increased risk of data leakage (i.e. there are more distributed copies of the data, the third party may be insecure and/or untrustworthy). Oftentimes, the most practical option is to tolerate this risk. This is far from ideal and in case of highly sensitive data (e.g. medical records, location history) it is unacceptable. We present PARTE, a tool to aid application developers in lowering the risk of data leakage. PARTE statically analyzes a program's source, annotated to indicate types which will hold sensitive data (i.e. data that should not be leaked), and outputs a partitioned version of the source. One partition will operate only on encrypted copies of sensitive data to lower the risk of data leakage and can safely be run by a third party or otherwise untrusted environment. The second partition must have plaintext access to sensitive data and therefore should be run in a trusted environment. Program execution will flow between the partitions, levaraging third party resources when data leakage risk is low. Further, we identify operations which, if efficiently supported by some encryption scheme, would improve the performance of partitioned execution. To demonstrate the feasiblity of these ideas, we implement PARTE in Haskell and run it on a web application, hpaste, which allows users to upload and share text snippets. The partitioned hpaste services web request 1.2 - 2.5 x slower than the original hpaste. We find this overhead to be moderately high. Moreover, the partitioning does not allow much code to run on encrypted data. We discuss why we feel our techniques did not produce an attractive partitioning and offer insight on new research directions which could yield better results.by Meelap Shah.S.M

Interference Alignment in Regenerating Codes for Distributed Storage: Necessity and Code Constructions

Regenerating codes are a class of recently developed codes for distributed storage that, like Reed-Solomon codes, permit data recovery from any arbitrary k of n nodes. However regenerating codes possess in addition, the ability to repair a failed node by connecting to any arbitrary d nodes and downloading an amount of data that is typically far less than the size of the data file. This amount of download is termed the repair bandwidth. Minimum storage regenerating (MSR) codes are a subclass of regenerating codes that require the least amount of network storage; every such code is a maximum distance separable (MDS) code. Further, when a replacement node stores data identical to that in the failed node, the repair is termed as exact. The four principal results of the paper are (a) the explicit construction of a class of MDS codes for d = n-1 >= 2k-1 termed the MISER code, that achieves the cut-set bound on the repair bandwidth for the exact-repair of systematic nodes, (b) proof of the necessity of interference alignment in exact-repair MSR codes, (c) a proof showing the impossibility of constructing linear, exact-repair MSR codes for d < 2k-3 in the absence of symbol extension, and (d) the construction, also explicit, of MSR codes for d = k+1. Interference alignment (IA) is a theme that runs throughout the paper: the MISER code is built on the principles of IA and IA is also a crucial component to the non-existence proof for d < 2k-3. To the best of our knowledge, the constructions presented in this paper are the first, explicit constructions of regenerating codes that achieve the cut-set bound.Comment: 38 pages, 12 figures, submitted to the IEEE Transactions on Information Theory;v3 - The title has been modified to better reflect the contributions of the submission. The paper is extensively revised with several carefully constructed figures and example

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

Comparison study for internal and external modes of fixation for fractures of distal end radius

Background: Fractures of the distal radius continue to be one of the most common skeletal injuries. The methods which are commonly practiced are closed manipulation and plaster cast, pins and plaster, percutaneous pinning, external fixation and open reduction and internal fixation with or without bone graft. Surgeons are increasingly faced with the dilemma of when to consider operative management and when cast immobilization is the optimal treatment.Methods: 47 cases of distal end radius fractures were operated in the orthopedic department of a tertiary care centre. The purpose of the present study was to compare the results of external and internal fixation methods for the treatment of fractures of distal end of radius. Patients operated by external fixation were classified as Group A and those operated by internal fixation were classified as group B. Patients were classified according to AO Classification. Patients were followed at regular intervals depending on the case and time of operation and evaluated by Gartland and Werley score.Results: In our study, 29 patients were of extraarticular type, of which 86.20% had an excellent score and 18 patients were of intraarticular type, of which 83.33% had an excellent score. But when compared to groups A and B, the percentage of excellent score obtained in group B was more than that in group A in both extraarticular and intraarticular fractures. Yuan-kun et al did a study on intraarticular distal end radius fractures and evaluated the patients by Gartland and Werley point system, concluding that plating gives better results than external fixation supplemented by K wiring. Conclusions: We concluded that no method of fixation can be said superior to the other. Each method has fracture-specific indication. The results of open reduction and internal fixation can be better than external fixation in initial months, but in the long run, both the methods can have excellent score, provided the fixation is good and properly indicated