Yevgeny Krivolapov

On Power and Throughput Tradeoffs of WiFi and Bluetooth in Smartphones

This paper describes a combined power and throughput performance study of WiFi and Bluetooth usage in smartphones. The work measures the obtained throughput in various settings while employing each of these technologies, and the power consumption level associated with them. In addition, the power requirements of Bluetooth and WiFi in their respective noncommunicating modes are also compared. The study reveals several interesting phenomena and tradeoffs. In particular, the paper identifies many situations in which WiFi is superior to Bluetooth, countering previous reports. The study also identifies a couple of scenarios that are better handled by Bluetooth. The conclusions from this study suggest preferred usage patterns, as well as operative suggestions for researchers and smartphone developers. This includes a cross-layer optimization for TCP/IP that could greatly improve the throughput to power ratio whenever the transmitter is more capable than the receiver.

On power and throughput tradeoffs of WiFi and Bluetooth in smartphones

This paper describes a combined power and throughput performance study of WiFi and Bluetooth usage in smartphones. The work measures the obtained throughput in various settings while employing each of these technologies, and the power consumption level associated with them. In addition, the power requirements of Bluetooth and WiFi in their respective noncommunicating modes are also compared. The study reveals several interesting phenomena and tradeoffs. In particular, the paper identifies many situations in which WiFi is superior to Bluetooth, countering previous reports. The study also identifies a couple of scenarios that are better handled by Bluetooth. The conclusions from this study suggest preferred usage patterns, as well as operative suggestions for researchers and smartphone developers. This includes a cross-layer optimization for TCP/IP that could greatly improve the throughput to power ratio whenever the transmitter is more capable than the receiver.

The nonlinear Schrödinger equation with a random potential: results and puzzles

The nonlinear Schrodinger equation (NLSE) with a random potential is motivated by experiments in optics and in atom optics and is a paradigm for the competition between the randomness and nonlinearity. The analysis of the NLSE with a random (Anderson like) potential has been done at various levels of control: numerical, analytical and rigorous. Yet this model equation presents us with a highly inconclusive and often contradictory picture. We will describe the main recent results obtained in this field and propose a list of specific problems to focus on, which we hope will enable to resolve these outstanding questions.

Spreading for the generalized nonlinear Schrödinger equation with disorder

The dynamics of an initially localized wave packet is studied for the generalized nonlinear Schrödinger equation with a random potential, where the nonlinear term is beta|psi|ppsi and p is arbitrary. Mainly short times for which the numerical calculations can be performed accurately are considered. Long time calculations are presented as well. In particular, the subdiffusive behavior where the average second moment of the wave packet is of the form m2 approximately t(alpha) is computed. Contrary to former heuristic arguments, no evidence for any critical behavior as function of p is found. The properties of alpha(p) for relatively short times are explored, a scaling property and a maximal value for p approximately 1/2 are found.

Double-humped states in the nonlinear Schrödinger equation with a random potential.

The role of double-humped states in spreading of wave packets for the nonlinear Schrödinger equation (NLSE) with a random potential is explored and the spreading mechanism is unraveled. Comparison to an NLSE with a double-well potential is made. There are two independent effects of the nonlinearity on the double-humped states for the NLSE: coupling to other states and destruction. The interplay between these effects is discussed.

Perturbation theory for the nonlinear Schrödinger equation with a random potential

A perturbation theory for the nonlinear Schrodinger equation in 1D on a lattice was developed. The small parameter is the strength of the nonlinearity. For this purpose secular terms were removed and a probabilistic bound on small denominators was developed. It was shown that the number of terms grows exponentially with the order. The results of the perturbation theory are compared with numerical calculations. An estimate on the remainder is obtained and it is demonstrated that the series is asymptotic.

Super-diffusion in optical realizations of Anderson localization

We discuss the dynamics of particles in one dimension in potentials that are random in both space and time. The results are applied to recent optics experiments on Anderson localization, in which the transverse spreading of a beam is suppressed by random fluctuations in the refractive index. If the refractive index fluctuates along the direction of the paraxial propagation of the beam, the localization is destroyed. We analyze this broken localization in terms of the spectral decomposition of the potential. When the potential has a discrete spectrum, the spread is controlled by the overlap of Chirikov resonances in phase space. As the number of Fourier components is increased, the resonances merge into a continuum, which is described by a Fokker–Planck equation. We express the diffusion coefficient in terms of the spectral intensity of the potential. For a general class of potentials that are commonly used in optics, the solutions to the Fokker–Planck equation exhibit anomalous diffusion in phase space, implying that when Anderson localization is broken by temporal fluctuations of the potential, the result is transport at a rate similar to a ballistic one or even faster. For a class of potentials which arise in some existing realizations of Anderson localization, atypical behavior is found.

A numerical and symbolical approximation of the nonlinear Anderson model

A modified perturbation theory in the strength of the nonlinear term is used to solve the Nonlinear Schroedinger Equation with a random potential. It is demonstrated that in some cases it is more efficient than other methods. Moreover we obtain error estimates. This approach can be useful for the solution of other nonlinear differential equations of physical relevance.

Quantum chaos of a mixed open system of kicked cold atoms.

The quantum and classical dynamics of particles kicked by a Gaussian attractive potential are studied. Classically, it is an open mixed system (the motion in some parts of the phase space is chaotic, and in some parts it is regular). The fidelity (Loschmidt echo) is found to exhibit oscillations that can be determined from classical considerations but are sensitive to phase space structures that are smaller than Plancks constant. Families of quasienergies are determined from classical phase space structures. Substantial differences between the classical and quantum dynamics are found for time-dependent scattering. It is argued that the system can be experimentally realized by cold atoms kicked by a Gaussian light beam.

Transport in time-dependent random potentials.

The classical dynamics in potentials that are random both in space and time is studied. The potentials are generated by a stationary process. This can be intuitively understood with the help of Chirikov resonances that are central in the theory of chaos, and explored quantitatively in the framework of the Fokker-Planck equation. In particular, a simple expression for the diffusion coefficient was obtained in terms of the average power density of the potential. The resulting anomalous diffusion in velocity is classified into universality classes. The general theory was applied and numerically tested for specific examples relevant for optics and atom optics.