18,094 research outputs found
Finite temperature damping of collective modes of a BCS-BEC crossover superfluid
A new mechanism is proposed to explain the puzzling damping of collective
excitations, which was recently observed in the experiments of strongly
interacting Fermi gases below the superfluid critical temperature on the
fermionic (BCS) side of Feshbach resonance. Sound velocity, superfluid density
and damping rate are calculated with effective field theory. We find that a
dominant damping process is due to the interaction between superfluid phonons
and thermally excited fermionic quasiparticles, in contrast to the previously
proposed pair-breaking mechanism. Results from our effective model are compared
quantitatively with recent experimental findings, showing a good agreement.Comment: final version, 9 pages, 4 figure
Cooperative Transmission Protocols with High Spectral Efficiency and High Diversity Order Using Multiuser Detection and Network Coding
Cooperative transmission is an emerging communication technique that takes
advantages of the broadcast nature of wireless channels. However, due to low
spectral efficiency and the requirement of orthogonal channels, its potential
for use in future wireless networks is limited. In this paper, by making use of
multiuser detection (MUD) and network coding, cooperative transmission
protocols with high spectral efficiency, diversity order, and coding gain are
developed. Compared with the traditional cooperative transmission protocols
with single-user detection, in which the diversity gain is only for one source
user, the proposed MUD cooperative transmission protocols have the merits that
the improvement of one user's link can also benefit the other users. In
addition, using MUD at the relay provides an environment in which network
coding can be employed. The coding gain and high diversity order can be
obtained by fully utilizing the link between the relay and the destination.
From the analysis and simulation results, it is seen that the proposed
protocols achieve higher diversity gain, better asymptotic efficiency, and
lower bit error rate, compared to traditional MUD and to existing cooperative
transmission protocols.Comment: to appear, in the proceedings of IEEE International Conference on
Communications, Glasgow, Scotland, 24-28 June 200
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
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