Siddhartha Mallik

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We consider the problem of code design for a set of parallel correlated Rayleigh fading channels. This design problem arises whenever a channel can be decomposed into parallel channels, for example in OFDM schemes using Weyl-Heisenberg bases over underspread fading channels [1]. Schemes involving rotations of integer lattices have been proposed in [2] as a(More)
The simplest purely imaginary and piecewise constant PT -symmetric potential located inside a larger box is studied. Unless its strength exceeds a certain critical value, all the spectrum of its bound states remains real and discrete. We interpret such a model as an initial element of the generalized non-Hermitian Witten’s hierarchy of solvable Hamiltonians(More)
In the framework of SUSYQM extended to deal with non-Hermitian Hamiltonians, we analyze three sets of complex potentials with real spectra, recently derived by a potential algebraic approach based upon the complex Lie algebra sl(2,C). This extends to the complex domain the well-known relationship between SUSYQM and potential algebras for Hermitian(More)
We study the problem of modulation and coding for doubly dispersive, i.e., time and frequency selective fading channels. Using the recent result that under-spread linear systems are approximately diagonalized by biorthogonal Weyl-Heisenberg bases, we arrive at a canonical formulation of modulation and code design. For coherent reception with maximum(More)
We extend an earlier, configuration space method to find the Wilson coefficients of operators appearing in the short distance expansion of thermal correlation functions of different quark bilinears. Considering all the different correlation functions, there arise, up to dimension four, two new operators, in addition to the two appearing already in the(More)
This is a short review on the thermal, spectral representation in the real-time version of the finite temperature quantum field theory. After presenting a clear derivation of the spectral representation, we discuss the properties of its spectral function. Two applications of this representation are then considered. One is the solution of the Dyson equation(More)