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  • 1
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    Measurement Based Self-Optimization in Random Access Communications (2011)
    Details
    Publication Date: 2020-08-05
    Description: The current work considers random access communications within a single cell and provides an algorithmic suggestion for the almost optimal coordination of user actions. In the scenario considered, an access effort is successful if (a) the signal is detected at the receiver and (b) no collision occurs. The first event is controlled by the user transmission power and the second by the choice of access (back-off) probability. These constitute the user action pair. The algorithm aims at exploiting information from measurements and user reports, in order to estimate current values of the system situation. Based on these, two optimization problems can be formulated and solved for the so called contention level and transmission power level at the base station side. The methodology to find the optimal values is based on minimization of a drift function. The two values are broadcast in order to help the users update their actions ``almost optimally``. In this way the wireless cell can achieve self-optimization, without outside coordination, by relying on such intelligent information exchange and parameter estimation. Numerical results illustrate the great benefits of the suggested algorithm, compared to scenarios where the actions remain fixed, at a very low or even zero cost in power expenditure and delay.
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Formation of segmental clusters during relaxation of a fully extended polyethylene chain at 300 K: A molecular dynamics simulation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8835-8841 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations were performed on the relaxation of fully extended polyethylene chains, varying in length from 600 to 4000 CH2 units. When a chain has more than 1200 CH2 units, the relaxation proceeds in three stages, subglobule formation, subglobule growth, and subglobule coalescence into one globule. In the stage of subglobule growth, the number of subglobules is almost a constant because of kinetic barrier, which is different from the results based on Monte Carlo simulations of polymer collapse in dilute solution. The difference of lamella thickness between MD simulations and experiments is discussed. The degree of adjacent reentry is calculated, and amounts between 0.4 and 0.5 for the formed lamellae. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478789
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Interface roughness scattering in GaAs–AlGaAs modulation-doped heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3329-3331 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the influence of interface roughness scattering on the mobility of two-dimensional electron gas (2DEG) in GaAs–AlGaAs modulation-doped heterostructures (MDH) both experimentally and theoretically. When the background ionized impurity concentration in the GaAs layer is smaller than 2.5×1015 cm−3, our investigation shows that interface roughness scattering is the dominant scattering mechanism in the high 2DEG density (Ns≥5×1011 cm−2) GaAs–AlGaAs MDH. We also demonstrate that interface roughness scattering is about an order of magnitude stronger than alloy disorder scattering in GaAs–AlGaAs MDH if the AlGaAs/GaAs interface fluctuation is only one monolayer of GaAs. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112382
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    Paper (German National Licenses)
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