13,600 research outputs found
Harmonic space and quaternionic manifolds
We find a principle of harmonic analyticity underlying the quaternionic
(quaternion-K\"ahler) geometry and solve the differential constraints which
define this geometry. To this end the original -dimensional quaternionic
manifold is extended to a bi-harmonic space. The latter includes additional
harmonic coordinates associated with both the tangent local group and
an extra rigid group rotating the complex structures. Then the
constraints can be rewritten as integrability conditions for the existence of
an analytic subspace in the bi-harmonic space and solved in terms of two
unconstrained potentials on the analytic subspace. Geometrically, the
potentials have the meaning of vielbeins associated with the harmonic
coordinates. We also establish a one-to-one correspondence between the
quaternionic spaces and off-shell supersymmetric sigma-models coupled to
supergravity. The general sigma-model Lagrangian when written in
the harmonic superspace is composed of the quaternionic potentials. Coordinates
of the analytic subspace are identified with superfields describing
matter hypermultiplets and a compensating hypermultiplet of supergravity.
As an illustration we present the potentials for the symmetric quaternionic
spaces.Comment: 44 pages, LATEX, JHU-TIPAC-920023, ENSLAPP-L-405-92, MPI-Ph/92-8
Modeling, Simulation and Analysis of Video Streaming Errors in Wireless Wideband Access Networks
Analysis of simulated models has become a veritable tool for
investigating network behavioral patterns vis-à-vis transmitted content. The
streaming video research domain employs modeling extensively due to availability
of relevant tools. A vast majority of which are presented on the FOSS platform.
The transmission of audio and video streaming services over different media is
becoming ever more popular. This widespread increase is accompanied by the
difficult task of maintaining the QoS of streaming video. The use of very accurate
coding techniques for transmissions over wireless networks alone cannot guarantee
a complete eradication of distortions characteristic of the video signal. A software-
hardware composite system has been developed for investigating the effect of
single bit error and bit packet errors in wideband wireless access systems on the
quality of H.264/AVC standard video streams. Numerical results of the modeling
and analysis of the effect of interference robustness on quality of video streaming
are presented and discussed. Analytic results also suggest that the Markov model
of packetization of error obtained from a real network for streaming video can be
used in the simulations of transmission of video across networks in the hardware-
software complex developed by the authors in a previous work
Effect of Video Streaming Space–Time Characteristics on Quality of Transmission over Wireless Telecommunication Networks
The spate in popularity of multimedia applications
has led to the need for optimization of bandwidth allocation
and usage in telecommunication networks. Modern
telecommunication networks should by their definition be able to maintain the quality of different applications with different Quality of Service (QoS) levels. QoS requirements are generally dependent on the parameters of network and
application layers of the OSI model. At the application layer QoS depends on factors such as resolution, bit rate, frame rate, video type, audio codecs, etc. At the network layer, distortions such as delay, jitter, packet loss, etc. are introduced. This paper presents simulation results of modeling video streaming over wireless communications networks. The differences in spatial and time characteristics of the different subject groups
were taken into account. Analysis of the influence of bit error rate (BER) and bit rate for video quality is also presented.
Simulation showed that different video subject groups affect
the perceived quality differently when transmitted over
networks. We show conclusively that in a transmission network
with a small error probabilities (BER = 10-6, BER = 10-5), the
minimum bit rate (128 kbps) guarantees an acceptable video
quality, corresponding to MOS > 3 for all types of frames
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