13,468 research outputs found
Aspects of Warped AdS/CFT Correspondence
In this paper we apply the thermodynamics method to investigate the
holographic pictures for the BTZ black hole, the spacelike and the null warped
black holes in three-dimensional topologically massive gravity (TMG) and new
massive gravity (NMG). Even though there are higher derivative terms in these
theories, the thermodynamics method is still effective. It gives consistent
results with the ones obtained by using asymptotical symmetry group (ASG)
analysis. In doing the ASG analysis we develop a brute-force realization of the
Barnich-Brandt-Compere formalism with Mathematica code, which also allows us to
calculate the masses and the angular momenta of the black holes. In particular,
we propose the warped AdS/CFT correspondence in the new massive
gravity, which states that quantum gravity in the warped spacetime could
holographically dual to a two-dimensional CFT with
c_R=c_L=\f{24}{Gm\b^2\sr{2(21-4\b^2)}}.Comment: 22 pages, references added, published version, link of Mathematica
code changed to https://s.yunio.com/Mtus0z or http://pan.baidu.com/s/1mToF
A Split-Reduced Successive Cancellation List Decoder for Polar Codes
This paper focuses on low complexity successive cancellation list (SCL)
decoding of polar codes. In particular, using the fact that splitting may be
unnecessary when the reliability of decoding the unfrozen bit is sufficiently
high, a novel splitting rule is proposed. Based on this rule, it is conjectured
that, if the correct path survives at some stage, it tends to survive till
termination without splitting with high probability. On the other hand, the
incorrect paths are more likely to split at the following stages. Motivated by
these observations, a simple counter that counts the successive number of
stages without splitting is introduced for each decoding path to facilitate the
identification of correct and incorrect path. Specifically, any path with
counter value larger than a predefined threshold \omega is deemed to be the
correct path, which will survive at the decoding stage, while other paths with
counter value smaller than the threshold will be pruned, thereby reducing the
decoding complexity. Furthermore, it is proved that there exists a unique
unfrozen bit u_{N-K_1+1}, after which the successive cancellation decoder
achieves the same error performance as the maximum likelihood decoder if all
the prior unfrozen bits are correctly decoded, which enables further complexity
reduction. Simulation results demonstrate that the proposed low complexity SCL
decoder attains performance similar to that of the conventional SCL decoder,
while achieving substantial complexity reduction.Comment: Accepted for publication in IEEE Journal on Selected Areas in
Communications - Special Issue on Recent Advances In Capacity Approaching
Code
Equivalent topological invariants of topological insulators
A time-reversal invariant topological insulator can be generally defined by
the effective topological field theory with a quantized \theta coefficient,
which can only take values of 0 or \pi. This theory is generally valid for an
arbitrarily interacting system and the quantization of the \theta invariant can
be directly measured experimentally. Reduced to the case of a non-interacting
system, the \theta invariant can be expressed as an integral over the entire
three dimensional Brillouin zone. Alternatively, non-interacting insulators can
be classified by topological invariants defined over discrete time-reversal
invariant momenta. In this paper, we show the complete equivalence between the
integral and the discrete invariants of the topological insulator.Comment: Published version. Typos correcte
Optimization and Analysis of Wireless Powered Multi-antenna Cooperative Systems
In this paper, we consider a three-node cooperative wireless powered
communication system consisting of a multi-antenna hybrid access point (H-AP)
and a single-antenna relay and a single-antenna user. The energy constrained
relay and user first harvest energy in the downlink and then the relay assists
the user using the harvested power for information transmission in the uplink.
The optimal energy beamforming vector and the time split between harvest and
cooperation are investigated. To reduce the computational complexity,
suboptimal designs are also studied, where closed-form expressions are derived
for the energy beamforming vector and the time split. For comparison purposes,
we also present a detailed performance analysis in terms of the achievable
outage probability and the average throughput of an intuitive energy
beamforming scheme, where the H-AP directs all the energy towards the user. The
findings of the paper suggest that implementing multiple antennas at the H-AP
can significantly improve the system performance, and the closed-form
suboptimal energy beamforming vector and time split yields near optimal
performance. Also, for the intuitive beamforming scheme, a diversity order of
(N+1)/2 can be achieved, where N is the number of antennas at the H-AP
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