Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios

We present the \epsilon-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the \epsilon-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the \epsilon-outage capacity of the cut-set bound and demonstrate that the ratio between the \epsilon-outage capacity of incremental relaying and the cut-set bound lies within 1/\sqrt{2} and 1. Furthermore, we derive lower bounds on the \epsilon-outage capacity for the case of K relays.Comment: 5 pages, 4 figures, to be presented at VTC Fall 2009 in Anchorage, Alask

Motion Induced Radiation from a Vibrating Cavity

We study the radiation emitted by a cavity moving in vacuum. We give a quantitative estimate of the photon production inside the cavity as well as of the photon flux radiated from the cavity. A resonance enhancement occurs not only when the cavity length is modulated but also for a global oscillation of the cavity. For a high finesse cavity the emitted radiation surpasses radiation from a single mirror by orders of magnitude.Comment: 4 pages, to appear in Physical Review Letter

Dynamical Casimir Effect in a Leaky Cavity at Finite Temperature

The phenomenon of particle creation within an almost resonantly vibrating cavity with losses is investigated for the example of a massless scalar field at finite temperature. A leaky cavity is designed via the insertion of a dispersive mirror into a larger ideal cavity (the reservoir). In the case of parametric resonance the rotating wave approximation allows for the construction of an effective Hamiltonian. The number of produced particles is then calculated using response theory as well as a non-perturbative approach. In addition we study the associated master equation and briefly discuss the effects of detuning. The exponential growth of the particle numbers and the strong enhancement at finite temperatures found earlier for ideal cavities turn out to be essentially preserved. The relevance of the results for experimental tests of quantum radiation via the dynamical Casimir effect is addressed. Furthermore the generalization to the electromagnetic field is outlined.Comment: 48 pages, 8 figures typos corrected & references added and update

Interference Mitigation for Energy Detection in a Multiband Impulse Radio UWB System

On-Off-Keying with energy detection is a promising candidate when aiming at simple receiver concepts, due to the fact that simple energy detection reduces receiver complexity. On the other hand, data rates are low and interference mitigation by correlation is no longer possible. This paper proposes and analyzes a method for mitigating asynchronous interferers in energy detection receivers by adapting the maximum likelihood decision rule. It is shown that detection in the presence of interferers is improved and detection in absence of interferers is not declined

The role of Surface Plasmon modes in the Casimir Effect

In this paper we study the role of surface plasmon modes in the Casimir effect. First we write the Casimir energy as a sum over the modes of a real cavity. We may identify two sorts of modes, two evanescent surface plasmon modes and propagative modes. As one of the surface plasmon modes becomes propagative for some choice of parameters we adopt an adiabatic mode definition where we follow this mode into the propagative sector and count it together with the surface plasmon contribution, calling this contribution "plasmonic". The remaining modes are propagative cavity modes, which we call "photonic". The Casimir energy contains two main contributions, one coming from the plasmonic, the other from the photonic modes. Surprisingly we find that the plasmonic contribution to the Casimir energy becomes repulsive for intermediate and large mirror separations. Alternatively, we discuss the common surface plasmon defintion, which includes only evanescent waves, where this effect is not found. We show that, in contrast to an intuitive expectation, for both definitions the Casimir energy is the sum of two very large contributions which nearly cancel each other. The contribution of surface plasmons to the Casimir energy plays a fundamental role not only at short but also at large distances.Comment: 10 pages, 3 figures. TQMFA200

Interference phenomena in the photon production between two oscillating walls

We study the photon production in a 1D cavity whose left and right walls oscillate with the frequency $\Omega_{L}$ and $\Omega_{R}$, respectively. For $\Omega_{L} \neq \Omega_{R},$ the number of generated photons by the parametric resonance is the sum of the photon numbers produced when the left and the right wall oscillates separately. But for $\Omega_{L} = \Omega_{R}$, the interference term proportional to $\cos \phi$ is found additionally, where $\phi$ is the phase difference between two oscillations of the walls.Comment: 7 pages, RevTeX, no figures, a sign error correcte

Radioscience simulations in General Relativity and in alternative theories of gravity

In this communication, we focus on the possibility to test GR with radioscience experiments. We present a new software that in a first step simulates the Range/Doppler signals directly from the space time metric (thus in GR and in alternative theories of gravity). In a second step, a least-squares fit of the involved parameters is performed in GR. This software allows one to get the order of magnitude and the signature of the modifications induced by an alternative theory of gravity on radioscience signals. As examples, we present some simulations for the Cassini mission in Post-Einsteinian gravity and with the MOND External Field Effect.Comment: 4 pages; Proceedings of "Les Rencontres de Moriond 2011 - Gravitation session

Post-Einsteinian tests of linearized gravitation

The general relativistic treatment of gravitation can be extended by preserving the geometrical nature of the theory but modifying the form of the coupling between curvature and stress tensors. The gravitation constant is thus replaced by two running coupling constants which depend on scale and differ in the sectors of traceless and traced tensors. When calculated in the solar system in a linearized approximation, the metric is described by two gravitation potentials. This extends the parametrized post-Newtonian (PPN) phenomenological framework while allowing one to preserve compatibility with gravity tests performed in the solar system. Consequences of this extension are drawn here for phenomena correctly treated in the linear approximation. We obtain a Pioneer-like anomaly for probes with an eccentric motion as well as a range dependence of Eddington parameter $\gamma$ to be seen in light deflection experiments.Comment: 15 pages. Accepted version, to appear in Classical and Quantum Gravit

Speed Meter As a Quantum Nondemolition Measuring Device for Force

Quantum noise is an important issue for advanced LIGO. Although it is in principle possible to beat the Standard Quantum Limit (SQL), no practical recipe has been found yet. This paper dicusses quantum noise in the context of speedmeter-a devise monitoring the speed of the testmass. The scheme proposed to overcome SQL in this case might be more practical than the methods based on monitoring position of the testmass.Comment: 7 pages of RevTex, 1 postscript figur

The Schrodinger particle in an oscillating spherical cavity

We study a Schrodinger particle in an infinite spherical well with an oscillating wall. Parametric resonances emerge when the oscillation frequency is equal to the energy difference between two eigenstates of the static cavity. Whereas an analytic calculation based on a two-level system approximation reproduces the numerical results at low driving amplitudes, epsilon, we observe a drastic change of behaviour when epsilon > 0.1, when new resonance states appear bearing no apparent relation to the eigenstates of the static system.Comment: 9 pages, 6 figures, corrected typo