149 research outputs found
Low-complexity Location-aware Multi-user Massive MIMO Beamforming for High Speed Train Communications
Massive Multiple-input Multiple-output (MIMO) adaption is one of the primary
evolving objectives for the next generation high speed train (HST)
communication system. In this paper, we consider how to design an efficient
low-complexity location-aware beamforming for the multi-user (MU) massive MIMO
system in HST scenario. We first put forward a low-complexity beamforming based
on location information, where multiple users are considered. Then, without
considering inter-beam interference, a closed-form solution to maximize the
total service competence of base station (BS) is proposed in this MU HST
scenario. Finally, we present a location-aid searching-based suboptimal
solution to eliminate the inter-beam interference and maximize the BS service
competence. Various simulations are given to exhibit the advantages of our
proposed massive MIMO beamforming method.Comment: This paper has been accepted for future publication by VTC2017-Sprin
An Extended Fano's Inequality for the Finite Blocklength Coding
Fano's inequality reveals the relation between the conditional entropy and
the probability of error . It has been the key tool in proving the converse of
coding theorems in the past sixty years. In this paper, an extended Fano's
inequality is proposed, which is tighter and more applicable for codings in the
finite blocklength regime. Lower bounds on the mutual information and an upper
bound on the codebook size are also given, which are shown to be tighter than
the original Fano's inequality. Especially, the extended Fano's inequality is
tight for some symmetric channels such as the -ary symmetric channels (QSC).Comment: 5 pages, 4 figures, submitted to IEEE ISIT 201
A Queueing Characterization of Information Transmission over Block Fading Rayleigh Channels in the Low SNR
Unlike the AWGN (additive white gaussian noise) channel, fading channels
suffer from random channel gains besides the additive Gaussian noise. As a
result, the instantaneous channel capacity varies randomly along time, which
makes it insufficient to characterize the transmission capability of a fading
channel using data rate only. In this paper, the transmission capability of a
buffer-aided block Rayleigh fading channel is examined by a constant rate input
data stream, and reflected by several parameters such as the average queue
length, stationary queue length distribution, packet delay and overflow
probability. Both infinite-buffer model and finite-buffer model are considered.
Taking advantage of the memoryless property of the service provided by the
channel in each block in the the low SNR (signal-to-noise ratio) regime, the
information transmission over the channel is formulated as a \textit{discrete
time discrete state} queueing problem. The obtained results show that
block fading channels are unable to support a data rate close to their ergodic
capacity, no matter how long the buffer is, even seen from the application
layer. For the finite-buffer model, the overflow probability is derived with
explicit expression, and is shown to decrease exponentially when buffer size is
increased, even when the buffer size is very small.Comment: 29 pages, 11 figures. More details on the proof of Theorem 1 and
proposition 1 can be found in "Queueing analysis for block fading Rayleigh
channels in the low SNR regime ", IEEE WCSP 2013.It has been published by
IEEE Trans. on Veh. Technol. in Feb. 201
New-Type Hoeffding's Inequalities and Application in Tail Bounds
It is well known that Hoeffding's inequality has a lot of applications in the
signal and information processing fields. How to improve Hoeffding's inequality
and find the refinements of its applications have always attracted much
attentions. An improvement of Hoeffding inequality was recently given by Hertz
\cite{r1}. Eventhough such an improvement is not so big, it still can be used
to update many known results with original Hoeffding's inequality, especially
for Hoeffding-Azuma inequality for martingales. However, the results in
original Hoeffding's inequality and its refinement one by Hertz only considered
the first order moment of random variables. In this paper, we present a new
type of Hoeffding's inequalities, where the high order moments of random
variables are taken into account. It can get some considerable improvements in
the tail bounds evaluation compared with the known results. It is expected that
the developed new type Hoeffding's inequalities could get more interesting
applications in some related fields that use Hoeffding's results.Comment: 8 pages, 1 figur
Tracking Angles of Departure and Arrival in a Mobile Millimeter Wave Channel
Millimeter wave provides a very promising approach for meeting the
ever-growing traffic demand in next generation wireless networks. To utilize
this band, it is crucial to obtain the channel state information in order to
perform beamforming and combining to compensate for severe path loss. In
contrast to lower frequencies, a typical millimeter wave channel consists of a
few dominant paths. Thus it is generally sufficient to estimate the path gains,
angles of departure (AoDs), and angles of arrival (AoAs) of those paths.
Proposed in this paper is a dual timescale model to characterize abrupt channel
changes (e.g., blockage) and slow variations of AoDs and AoAs. This work
focuses on tracking the slow variations and detecting abrupt changes. A Kalman
filter based tracking algorithm and an abrupt change detection method are
proposed. The tracking algorithm is compared with the adaptive algorithm due to
Alkhateeb, Ayach, Leus and Heath (2014) in the case with single radio frequency
chain. Simulation results show that to achieve the same tracking performance,
the proposed algorithm requires much lower signal-to-noise-ratio (SNR) and much
fewer pilots than the other algorithm. Moreover, the change detection method
can always detect abrupt changes with moderate number of pilots and SNR.Comment: 6 pages, 7 figures, submitted to ICC 201
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