90,111 research outputs found
An intelligent genetic algorithm for PAPR reduction in a multi-carrier CDMA wireless system
Abstractâ A novel intelligent genetic algorithm (GA), called Minimum Distance guided GA (MDGA) is proposed for peak-average-power ratio (PAPR) reduction based on partial transmit sequence (PTS) scheme in a synchronous Multi-Carrier Code Division Multiple Access (MC-CDMA) system. In contrast to traditional GA, our MDGA starts with a balanced ratio of exploration and exploitation which is maintained throughout the process. It introduces a novel replacement strategy which increases significantly the convergence rate and reduce dramatically computational complexity as compared to the conventional GA. The simulation results demonstrate that, if compared to the PAPR reduction schemes using exhaustive search and traditional GA, our scheme achieves 99.52% and 50+% reduction in computational complexity respectively
Off-Shell NN Potential and Triton Binding Energy
The NONLOCAL Bonn-B potential predicts 8.0 MeV binding energy for the triton
(in a charge-dependent 34-channel Faddeev calculation) which is about 0.4 MeV
more than the predictions by LOCAL NN potentials. We pin down origin and size
of the nonlocality in the Bonn potential, in analytic and numeric form. The
nonlocality is due to the use of the correct off-shell Feynman amplitude of
one-boson-exchange avoiding the commonly used on-shell approximations which
yield the local potentials. We also illustrate how this off-shell behavior
leads to more binding energy. We emphasize that the increased binding energy is
not due to on-shell differences (differences in the fit of the NN data or phase
shifts). In particular, the Bonn-B potential reproduces accurately the
mixing parameter up to 350 MeV as determined in the recent
Nijmegen multi-energy NN phase-shift analysis. Adding the relativistic effect
from the relativistic nucleon propagators in the Faddeev equations, brings the
Bonn-B result up to 8.2 MeV triton binding. This leaves a difference of only
0.3 MeV to experiment, which may possibly be explained by refinements in the
treatment of relativity and the inclusion of other nonlocalities (e.~g.,
quark-gluon exchange at short range). Thus, it is conceivable that a realistic
NN potential which describes the NN data up to 300 MeV correctly may explain
the triton binding energy without recourse to 3-N forces; relativity would play
a major role for this result.Comment: 5 pages LaTeX and 2 figures (hardcopies, available upon reqest),
UI-NTH-940
Diversity gain for DVB-H by using transmitter/receiver cyclic delay diversity
The objective of this paper is to investigate different diversity techniques for broadcast networks that will minimize the complexity and improve received SNR of broadcast systems.
Resultant digital broadcast networks would require fewer transmitter sites and thus be more cost-effective and have less environmental impact. The techniques can be applied to DVB-T,
DVB-H and DAB systems that use Orthogonal Frequency Division Multplexing (OFDM). These are key radio broadcast network technologies, which are expected to complement emerging technologies
such as WiMAX and future 4G networks for delivery
of broadband content. Transmitter and receiver diversity technologies can increase the frequency and time selectivity of the resulting channel transfer function at the receiver. Diversity exploits the statistical nature of fading due to multipath and reduces the likelihood of deep fading by providing a diversity of transmission signals. Multiple signals are transmitted in such
a way as to ensure that several signals reach the receiver each with uncorrelated fading. Transmit diversity is more practical than receive diversity due to the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here comply with existing DVB standards and can be incorporated into existing systems without change. The diversity techniques introduced in this paper are applied to the DVB-H system. Bit error performance investigations were conducted by
simulation for different DVB-H and diversity parameters
Characterisation of real GPRS traffic with analytical tools
With GPRS and UMTS networks lunched, wireless multimedia services are commercially becoming the most attractive applications next to voice. Because of the nature of bursty, packet-switched schemes and multiple data rates, the traditional Erlang approach and Poisson models for characterising voice-centric services traffic are not suitable for studying wireless multimedia services traffic. Therefore, research on the characterisation of wireless multimedia services traffic is very challenging. The typical reference for the study of wireless multimedia services traffic is wired Internet services traffic. However, because of the differences in network protocol, bandwidth, and QoS requirements between wired and wireless services, their traffic characterisations may not be similar. Wired network Internet traffic shows self-similarity, long-range dependence and its file sizes exhibit heavy-tailedness. This paper reports the use of existing tools to analyse real GPRS traffic data to establish whether wireless multimedia services traffic have similar properties as wired Internet services traffic
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Future transmitter/receiver diversity schemes in broadcast wireless networks
An open diversity architecture for a cooperating broadcast wireless network is presented that exploits the strengths of the existing digital broadcast standards. Different diversity techniques for broadcast networks that will minimize the complexity of broadcast systems and improve received SNR of broadcast signals are described. Resulting digital broadcast networks could require fewer transmitter sites and thus be more cost-effective with less environmental impact. Transmit diversity is particularly investigated since it obviates the major disadvantage of receive diversity being the difficulty of locating two receive antennas far enough apart in a small mobile device. The schemes examined here are compatible with existing broadcast and cellular telecom standards and can be incorporated into existing systems without change
Inconsistences in Interacting Agegraphic Dark Energy Models
It is found that the origin agegraphic dark energy tracks the matter in the
matter-dominated epoch and then the subsequent dark-energy-dominated epoch
becomes impossible. It is argued that the difficulty can be removed when the
interaction between the agegraphic dark energy and dark matter is considered.
In the note, by discussing three different interacting models, we find that the
difficulty still stands even in the interacting models. Furthermore, we find
that in the interacting models, there exists the other serious inconsistence
that the existence of the radiation/matter-dominated epoch contradicts the
ability of agegraphic dark energy in driving the accelerated expansion. The
contradiction can be avoided in one of the three models if some constraints on
the parameters hold.Comment: 12 pages, no figure; analysis is added; conclusion is unchange
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