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    Phase transition to spatial Bloch-like oscillation in squeezed photonic lattices

    , Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 88, Issue 2 , 2013 ; 10502947 (ISSN) Nezhad, M. K ; Bahrampour, A. R ; Golshani, M ; Mahdavi, S. M ; Langari, A ; Sharif University of Technology
    2013
    Abstract
    We propose an exactly solvable waveguide lattice incorporating an inhomogeneous coupling coefficient. This structure provides classical analogs to the squeezed number and squeezed coherent intensity distribution in quantum optics where the propagation length plays the role of a squeezed amplitude. The intensity pattern is obtained in a closed form for an arbitrary distribution of the initial beam profile. We have also investigated the phase transition to the spatial Bloch-like oscillations by adding a linear gradient to the propagation constant of each waveguide (α). Our analytical results show that the Bloch-like oscillations appear above a critical value for the linear gradient of the... 

    Connectivity analysis of one-dimensional ad hoc networks with arbitrary spatial distribution for variable and fixed number of nodes

    , Article IEEE Transactions on Mobile Computing ; Volume 11, Issue 10 , 2012 , Pages 1425-1435 ; 15361233 (ISSN) Sharif Nassab, A ; Ashtiani, F ; Sharif University of Technology
    Abstract
    In this paper, we propose an analytical approach to compute the probability of connectivity for one-dimensional ad hoc networks. The proposed analysis gives the exact probability of connectivity for an arbitrary distribution of nodes, provided that nodes are independently and identically distributed. We conduct separate analyses for two cases; in the first case, the number of nodes varies by time under a stationary distribution and in the second case, there is a fixed (known) number of nodes in the network. Using the approaches presented in this work, we are able to derive closed-form formulas for the probability of connectivity for some spatial distributions, while for more complicated... 

    Design of signature sequences for overloaded CDMA and bounds on the sum capacity with arbitrary symbol alphabets

    , Article IEEE Transactions on Information Theory ; Volume 58, Issue 3 , 2012 , Pages 1441-1469 ; 00189448 (ISSN) Alishahi, K ; Dashmiz, S ; Pad, P ; Marvasti, F ; Sharif University of Technology
    2012
    Abstract
    In this paper, we explore some of the fundamentals of synchronous Code Division Multiple Access (CDMA) as applied to wireless and optical communication systems under very general settings (of any size) for the user symbols and the signature matrix entries. The channel is modeled by real/complex additive noise of arbitrary distribution. Two problems are addressed. The first problem concerns whether uniquely detectable overloaded matrices exist in the absence of additive noise under these general settings, and if so, whether there are any practical optimum detection algorithms. The second one is about the bounds for the sum channel capacity when user data and signature matrices employ any real...