An efficient bandwidth demand estimation for delay reduction in IEEE 802.16j MMR WiMAX network

IEEE 802.16j MMR WiMAX networks allow the number of hops between the user and the MMR-BS to be more than two hops. The standard bandwidth request procedure in WiMAX network introduces much delay to the user data and acknowledgement of the TCP packet that affects the performance and throughput of the network. In this paper, we propose a new scheduling scheme to reduce the bandwidth request delay in MMR networks. In this scheme, the MMR-BS allocates bandwidth to its direct subordinate RSs without bandwidth request using Grey prediction algorithm to estimate the required bandwidth of each of its subordinate RS. Using this architecture, the access RS can allocate its subordinate MSs the required bandwidth without notification to the MMR-BS. Our scheduling architecture with efficient bandwidth demand estimation able to reduce delay significantly

Degeneracy in the characterization of non-transiting planets from transit timing variations

The transit timing variation (TTV) method allows the detection of non-transiting planets through their gravitational perturbations. Since TTVs are strongly enhanced in systems close to mean-motion resonances (MMR), even a low mass planet can produce an observable signal. This technique has thus been proposed to detect terrestrial planets. In this letter, we analyse TTV signals for systems in or close to MMR in order to illustrate the difficulties arising in the determination of planetary parameters. TTVs are computed numerically with an n-body integrator for a variety of systems close to MMR. The main features of these TTVs are also derived analytically. Systems deeply inside MMR do not produce particularly strong TTVs, while those close to MMR generate quasiperiodic TTVs characterised by a dominant long period term and a low amplitude remainder. If the remainder is too weak to be detected, then the signal is strongly degenerate and this prevents the determination of the planetary parameters. Even though an Earth mass planet can be detected by the TTV method if it is close to a MMR, it may not be possible to assert that this planet is actually an Earth mass planet. On the other hand, if the system is right in the center of a MMR, the high amplitude oscillation of the TTV signal vanishes and the detection of the perturber becomes as difficult as it is far from MMR.Comment: 5 pages, 3 figures, submitted to MNRA

2D cross-hole MMR - survey design and sensitivity analysis for cross-hole applications of the magnetometric resistivity method

The magnetometric resistivity (MMR) method measures low-level (typically < 1nT) magnetic fields associated with a low-frequency (1 - 20 Hz) electric current impressed into the ground to determine the subsurface resistivity structure. As a step towards the implementation of MMR for cross-hole imaging, in this Ph.D. thesis several aspects of survey design for near-surface applications are discussed. In numerical, laboratory and field studies the potential of MMR for advanced structural characterization and process monitoring at the field scale is assessed. The 2D cross-hole setup considers borehole measurements of the magnetic field as response to borehole current injection; in this case the magnetic field has only one non-zero component (perpendicular to the imaging plane – B$_{y}$). Optimal survey parameters are inferred from numerical studies regarding signal strength, source-generated noise level and resolving power. Modeling of MMR responses over 2D conductivity structures was performed using a newly developed 2.5D FE program MMRMod. It could be proven that current injection via vertical dipoles provides superior signal-to-noise ratio compared to other transmitter configurations. Analyzing resolving power in terms of sensitivity distribution reveals that dipole configurations reflect confined subsurface volumes, advantageous for tomographic surveys and that transmitter-receiver combinations exceeding an offset equal to the borehole separation do not contribute significantly to the overall crosshole resolution. With the assistance of laboratory testing two concepts for solving two major difficulties inherent in cross-hole MMR field surveying are derived: the correction for the arbitrary borehole sensor orientation and the correction for parasitic correlated noise fields induced by the measurement system itself. The (latter) measurement method with phase switching is thereby first-time successfully applied to the processing of MMR data. In addition, the proposed data processing procedure includes modern lock-in-technique and has proven to be an appropriate tool for an effective information extraction from the measured magnetic fields. Finally, cross-hole MMR data were collected during a water infiltration experiment at the Gorgonzola test site. Acquisition and processing are accomplished according to the developed tomographic measurement approach involving multiple-offset transmitter-receiver arrangements and repeated measurements with time (time-lapse mode). Data, obtained during initially conducted background measurement, are qualitatively validated based on two different conductivity models, one of which is obtained from the inversion of independently collected ERT data. Importantly, the comparison of field data with predicted model curves suggests better resolvability of contrasts by MMR than by ERT. Moreover, the analysis of time-lapse measurements reveals a clear spatiotemporal dependence of the anomalous MMRresponse (MMR response with respect to background value) based upon the water saturation

AMD-stability in presence of first order Mean Motion Resonances

The AMD-stability criterion allows to discriminate between a-priori stable planetary systems and systems for which the stability is not granted and needs further investigations. AMD-stability is based on the conservation of the Angular Momentum Deficit (AMD) in the averaged system at all orders of averaging. While the AMD criterion is rigorous, the conservation of the AMD is only granted in absence of mean-motion resonances (MMR). Here we extend the AMD-stability criterion to take into account mean-motion resonances, and more specifically the overlap of first order MMR. If the MMR islands overlap, the system will experience generalized chaos leading to instability. The Hamiltonian of two massive planets on coplanar quasi-circular orbits can be reduced to an integrable one degree of freedom problem for period ratios close to a first order MMR. We use the reduced Hamiltonian to derive a new overlap criterion for first order MMR. This stability criterion unifies the previous criteria proposed in the literature and admits the criteria obtained for initially circular and eccentric orbits as limit cases. We then improve the definition of AMD-stability to take into account the short term chaos generated by MMR overlap. We analyze the outcome of this improved definition of AMD-stability on selected multi-planet systems from the Extrasolar Planets Encyclopeadia.Comment: Accepted by A and A 07/10/1

On multiplicity of mappings between surfaces

Let M and N be two closed (not necessarily orientable) surfaces, and f a continuous map from M to N. By definition, the minimal multiplicity MMR[f] of the map f denotes the minimal integer k having the following property: f can be deformed into a map g such that the number |g^{-1}(c)| of preimages of any point c in N under g is at most k. We calculate MMR[f] for any map $f$ of positive absolute degree A(f). The answer is formulated in terms of A(f), [pi_1(N):f_#(pi_1(M))], and the Euler characteristics of M and N. For a map f with A(f)=0, we prove the inequalities 2 <= MMR[f] <= 4.Comment: This is the version published by Geometry & Topology Monographs on 29 April 200