969 research outputs found
Finite-Blocklength Bounds on the Maximum Coding Rate of Rician Fading Channels with Applications to Pilot-Assisted Transmission
We present nonasymptotic bounds on the maximum coding rate achievable over a
Rician block-fading channel for a fixed packet size and a fixed packet error
probability. Our bounds, which apply to the scenario where no a priori channel
state information is available at the receiver, allow one to quantify the
tradeoff between the rate gains resulting from the exploitation of
time-frequency diversity and the rate loss resulting from fast channel
variations and pilot-symbol overhead
On Channel Estimation for 802.11p in Highly Time-Varying Vehicular Channels
Vehicular wireless channels are highly time-varying and the pilot pattern in
the 802.11p orthogonal frequency-division multiplexing frame has been shown to
be ill suited for long data packets. The high frame error rate in off-the-shelf
chipsets with noniterative receiver configurations is mostly due to the use of
outdated channel estimates for equalization. This paper deals with improving
the channel estimation in 802.11p systems using a cross layered approach, where
known data bits are inserted in the higher layers and a modified receiver makes
use of these bits as training data for improved channel estimation. We also
describe a noniterative receiver configuration for utilizing the additional
training bits and show through simulations that frame error rates close to the
case with perfect channel knowledge can be achieved.Comment: 6 pages, 11 figures, conferenc
On Medium Access and Physical Layer Standards for Cooperative Intelligent Transport Systems in Europe
In this paper, we will outline the current European development of wireless communications to support cooperative Intelligent Transport Systems (ITS). The focus will be on spectrum allocation and the physical and medium access control layers of the ITS-G5 access technology, which is under specification by the European Telecommunications Standards Institute (ETSI). The European ITS architecture and European standardization will also be briefly discussed
Tunneling between edge states in a quantum spin Hall system
We analyze a quantum spin Hall (QSH) device with a point contact connecting
two of its edges. The contact supports a net spin tunneling current that can be
probed experimentally via a two-terminal resistance measurement. We find that
the low-bias tunneling current and the differential conductance exhibit scaling
with voltage and temperature that depend nonlinearly on the strength of the
electron-electron interaction.Comment: 4 pages, 3 figures; published versio
Short Packets over Block-Memoryless Fading Channels: Pilot-Assisted or Noncoherent Transmission?
We present nonasymptotic upper and lower bounds on the maximum coding rate
achievable when transmitting short packets over a Rician memoryless
block-fading channel for a given requirement on the packet error probability.
We focus on the practically relevant scenario in which there is no \emph{a
priori} channel state information available at the transmitter and at the
receiver. An upper bound built upon the min-max converse is compared to two
lower bounds: the first one relies on a noncoherent transmission strategy in
which the fading channel is not estimated explicitly at the receiver; the
second one employs pilot-assisted transmission (PAT) followed by
maximum-likelihood channel estimation and scaled mismatched nearest-neighbor
decoding at the receiver. Our bounds are tight enough to unveil the optimum
number of diversity branches that a packet should span so that the energy per
bit required to achieve a target packet error probability is minimized, for a
given constraint on the code rate and the packet size. Furthermore, the bounds
reveal that noncoherent transmission is more energy efficient than PAT, even
when the number of pilot symbols and their power is optimized. For example, for
the case when a coded packet of symbols is transmitted using a channel
code of rate bits/channel use, over a block-fading channel with block
size equal to symbols, PAT requires an additional dB of energy per
information bit to achieve a packet error probability of compared to
a suitably designed noncoherent transmission scheme. Finally, we devise a PAT
scheme based on punctured tail-biting quasi-cyclic codes and ordered statistics
decoding, whose performance are close ( dB gap at packet error
probability) to the ones predicted by our PAT lower bound. This shows that the
PAT lower bound provides useful guidelines on the design of actual PAT schemes.Comment: 30 pages, 5 figures, journa
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