3,790 research outputs found
An Energy Efficiency Perspective on Training for Fading Channels
In this paper, the bit energy requirements of training-based transmission
over block Rayleigh fading channels are studied. Pilot signals are employed to
obtain the minimum mean-square-error (MMSE) estimate of the channel fading
coefficients. Energy efficiency is analyzed in the worst case scenario where
the channel estimate is assumed to be perfect and the error in the estimate is
considered as another source of additive Gaussian noise. It is shown that bit
energy requirement grows without bound as the snr goes to zero, and the minimum
bit energy is achieved at a nonzero snr value below which one should not
operate. The effect of the block length on both the minimum bit energy and the
snr value at which the minimum is achieved is investigated. Flash training
schemes are analyzed and shown to improve the energy efficiency in the low-snr
regime. Energy efficiency analysis is also carried out when peak power
constraints are imposed on pilot signals.Comment: To appear in the Proc. of the 2007 IEEE International Symposium on
Information Theor
Throughput Analysis of Buffer-Constrained Wireless Systems in the Finite Blocklength Regime
In this paper, wireless systems operating under queueing constraints in the
form of limitations on the buffer violation probabilities are considered. The
throughput under such constraints is captured by the effective capacity
formulation. It is assumed that finite blocklength codes are employed for
transmission. Under this assumption, a recent result on the channel coding rate
in the finite blocklength regime is incorporated into the analysis and the
throughput achieved with such codes in the presence of queueing constraints and
decoding errors is identified. Performance of different transmission strategies
(e.g., variable-rate, variable-power, and fixed-rate transmissions) is studied.
Interactions between the throughput, queueing constraints, coding blocklength,
decoding error probabilities, and signal-to-noise ratio are investigated and
several conclusions with important practical implications are drawn
A strategic shift of automobile manufacturing firms in Turkey
This paper examines major business environmental changes influencing a strategic shift of automobile manufacturing firms in Turkey. Within a conceptual model consisting of environmental forces, strategic shift, and mediating variables, including firm size, ownership pattern, and market entry mode, it empirically investigates how such market changes influenced the business strategies of automotive firms in Turkey. The findings indicate that the multinational automotive firms in Turkey have shifted their strategic focus from relying solely on the domestic market to balancing domestic and export markets because of environmental forces. The paper concludes with discussions and suggestions for further research on the subject.market environment; strategic shift; FDI; foreign direct investment; export performance; multinational corporations.
Holographic equilibration in confining gauge theories under external magnetic fields
We investigate the effect of external magnetic fields on equilibration in the
improved holographic QCD theory in the deconfined phase using the AdS/CFT
correspondence. In particular we calculate the quasinormal mode spectra in the
corresponding black brane solutions and study their dependence on temperature,
momentum and magnetic field, both in the scalar and the shear channels. We find
complex patterns in the motion of quasinormal modes on the complex plane,
including certain cross overs between the lowest lying modes under varying
magnetic field, momentum and temperature. We also discover a critical value of
the magnetic field above which the hydrodynamic approximation breaks
down, as the imaginary part of the first excited quasi-normal mode in the shear
channel becomes smaller than that of the hydro mode.Comment: 20 pages, 13 figures. v2: discussion on the instability we reported
in the first version is corrected. v3: range of B in figures increased,
discussion on the breakdown of hydrodynamics added, abstract and references
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