Private Computation of Systematically Encoded Data with Colluding Servers

Private Computation (PC), recently introduced by Sun and Jafar, is a generalization of Private Information Retrieval (PIR) in which a user wishes to privately compute an arbitrary function of data stored across several servers. We construct a PC scheme which accounts for server collusion, coded data, and non-linear functions. For data replicated over several possibly colluding servers, our scheme computes arbitrary functions of the data with rate equal to the asymptotic capacity of PIR for this setup. For systematically encoded data stored over colluding servers, we privately compute arbitrary functions of the columns of the data matrix and calculate the rate explicitly for polynomial functions. The scheme is a generalization of previously studied star-product PIR schemes.Comment: Submitted to IEEE International Symposium on Information Theory 2018. Version 2 fixes some typos and adds some clarifying remark

Hybrid Channel Pre-Inversion and Interference Alignment Strategies

In this paper we consider strategies for MIMO interference channels which combine the notions of interference alignment and channel pre-inversion. Users collaborate to form data-sharing groups, enabling them to clear interference within a group, while interference alignment is employed to clear interference between groups. To improve the capacity of our schemes at finite SNR, we propose that the groups of users invert their subchannel using a regularized Tikhonov inverse. We provide a new sleeker derivation of the optimal Tikhonov parameter, and use random matrix theory to provide an explicit formula for the SINR as the size of the system increases, which we believe is a new result. For every possible grouping of K = 4 users each with N = 5 antennas, we completely classify the degrees of freedom available to each user when using such hybrid schemes, and construct explicit interference alignment strategies which maximize the sum DoF. Lastly, we provide simulation results which compute the ergodic capacity of such schemes.Comment: Submitted to ICC 201

Node Repair for Distributed Storage Systems over Fading Channels

Distributed storage systems and associated storage codes can efficiently store a large amount of data while ensuring that data is retrievable in case of node failure. The study of such systems, particularly the design of storage codes over finite fields, assumes that the physical channel through which the nodes communicate is error-free. This is not always the case, for example, in a wireless storage system. We study the probability that a subpacket is repaired incorrectly during node repair in a distributed storage system, in which the nodes communicate over an AWGN or Rayleigh fading channels. The asymptotic probability (as SNR increases) that a node is repaired incorrectly is shown to be completely determined by the repair locality of the DSS and the symbol error rate of the wireless channel. Lastly, we propose some design criteria for physical layer coding in this scenario, and use it to compute optimally rotated QAM constellations for use in wireless distributed storage systems.Comment: To appear in ISITA 201

Feasibility Study of a Multi-Purpose Aircraft Concept with a Leading-Edge Cross-Flow Fan

A wing-embedded Cross-Flow Fan (CFF) was first proposed as an active flow control (AFC) device nearly 40 years ago. The CFF can be employed as a propulsion device as well as a high-lift system. This thesis research focuses on investigating the use of CFF as a high-lift device for an Extremely Short Take-off and Landing (ESTOL) aircraft. The wing-embedded CFF performance analysis is mostly addressed from an aerodynamic perspective and focuses on using such AFC technology in the conceptual aircraft design process. In particular, the design trade study of an aircraft featuring CFF as a high-lift device applied to a conceptual design of a medium-range multi-purpose aircraft is performed. A sensitivity analysis is employed to investigate the impact of the CFF on the aircraft weight, aerodynamics, stability and control, and fight performance. The aircraft design modifications are introduced to maximize the aircraft mission performance given the fan specifications and constraints. Results indicate a reduction of the take-of field length by 18% and 22% depending on the CFF system integration with the payload penalty of 14% and 17%, respectively. The aircraft ferry range is also decreased compared to the baseline aircraft design. The scaling analysis of the aircraft concept is performed to determine the potential market for such AFC technology. The results show that a light GA airplane or a small-to-medium size UAV could benefit more from the wing-embedded CFF compared to more heavy airplanes

Analysis of Tourism Service Quality in Kołobrzeg Region by Means of Time Series Models

The undertaken study shows that methods that take into account time series can be successfully used in analysis of parameters of tourist comfort and in evaluation of hotel services.Przeprowadzone badania wskazują, że metody szeregów czasowych mogą być skutecznie zastosowane w badaniu wskaźników turystycznych i ocenie jakości usług hotelarskich