223 research outputs found
Exploring the Physical Layer Frontiers of Cellular Uplink - The Vienna LTE-A Simulator
Communication systems in practice are subject to many technical/technological
constraints and restrictions. MIMO processing in current wireless
communications, as an example, mostly employs codebook based pre-coding to save
computational complexity at the transmitters and receivers. In such cases,
closed form expressions for capacity or bit-error probability are often
unattainable; effects of realistic signal processing algorithms on the
performance of practical communication systems rather have to be studied in
simulation environments. The Vienna {LTE-A} Uplink Simulator is a 3GPP {LTE-A}
standard compliant link level simulator that is publicly available under an
academic use license, facilitating reproducible evaluations of signal
processing algorithms and transceiver designs in wireless communications. This
paper reviews research results that have been obtained by means of the Vienna
LTE-A Uplink Simulator, highlights the effects of Single Carrier Frequency
Division Multiplexing (as the distinguishing feature to LTE-A downlink),
extends known link adaptation concepts to uplink transmission, shows the
implications of the uplink pilot pattern for gathering Channel State
Information at the receiver and completes with possible future research
directions.Comment: submitted to Eurasip Journal on Wireless Communications and
Networking on 07-Sep-2015, Manuscript ID: JWCN-D-15-0036
Statistical Precoder Design for Space-Time-Frequency Block Codes in Multiuser MISO-MC-CDMA Systems
In this paper, we present a space-time-frequency joint block coding (STFBC)
scheme to exploit the essential space-time-frequency degrees of freedom of
multiuser MISO-MC-CDMA systems. Specifically, we use a series of orthogonal
random codes to spread the space time code over several sub-carriers to obtain
multi-diversity gains, while multiuser parallel transmission is applied over
the same sub-carriers by making use of multiple orthogonal code channels.
Furthermore, to improve the system performance, we put forward to linear
precoding to the predetermined orthogonal STFBC, including transmitting
directions selection and power allocation over these directions. We propose a
precoder design method by making use of channel statistical information in time
domain based on the Kronecker correlation model for the channels, so feedback
amount can be decreased largely in multi-carrier systems. In addition, we give
the performance analysis from the perspectives of diversity order and coding
gain, respectively. Moreover, through asymptotic analysis, we derive some
simple precoder design methods, while guaranteeing a good performance. Finally,
numerical results validate our theoretical claims.Comment: 10 pages, 4 figures, 1 tabl
Principal Component Analysis (PCA)-based Massive-MIMO Channel Feedback
Channel-state-information (CSI) feedback methods are considered, especially
for massive or very large-scale multiple-input multiple-output (MIMO) systems.
To extract essential information from the CSI without redundancy that arises
from the highly correlated antennas, a receiver transforms (sparsifies) a
correlated CSI vector to an uncorrelated sparse CSI vector by using a
Karhunen-Loeve transform (KLT) matrix that consists of the eigen vectors of
covariance matrix of CSI vector and feeds back the essential components of the
sparse CSI, i.e., a principal component analysis method. A transmitter then
recovers the original CSI through the inverse transformation of the feedback
vector. Herein, to obtain the covariance matrix at transceiver, we derive
analytically the covariance matrix of spatially correlated Rayleigh fading
channels based on its statistics including transmit antennas' and receive
antennas' correlation matrices, channel variance, and channel delay profile.
With the knowledge of the channel statistics, the transceiver can readily
obtain the covariance matrix and KLT matrix. Compression feedback error and
bit-error-rate performance of the proposed method are analyzed. Numerical
results verify that the proposed method is promising, which reduces
significantly the feedback overhead of the massive-MIMO systems with marginal
performance degradation from full-CSI feedback (e.g., feedback amount reduction
by 80%, i.e., 1/5 of original CSI, with spectral efficiency reduction by only
2%). Furthermore, we show numerically that, for a given limited feedback
amount, we can find the optimal number of transmit antennas to achieve the
largest spectral efficiency, which is a new design framework.Comment: 10 pages, 5 figure
Efficient Downlink Channel Probing and Uplink Feedback in FDD Massive MIMO Systems
Massive Multiple-Input Multiple-Output (massive MIMO) is a variant of
multi-user MIMO in which the number of antennas at each Base Station (BS) is
very large and typically much larger than the number of users simultaneously
served. Massive MIMO can be implemented with Time Division Duplexing (TDD) or
Frequency Division Duplexing (FDD) operation. FDD massive MIMO systems are
particularly desirable due to their implementation in current wireless networks
and their efficiency in situations with symmetric traffic and delay-sensitive
applications. However, implementing FDD massive MIMO systems is known to be
challenging since it imposes a large feedback overhead in the Uplink (UL) to
obtain channel state information for the Downlink (DL). In recent years, a
considerable amount of research is dedicated to developing methods to reduce
the feedback overhead in such systems. In this paper, we use the sparse spatial
scattering properties of the environment to achieve this goal. The idea is to
estimate the support of the continuous, frequency-invariant scattering function
from UL channel observations and use this estimate to obtain the support of the
DL channel vector via appropriate interpolation. We use the resulting support
estimate to design an efficient DL probing and UL feedback scheme in which the
feedback dimension scales proportionally with the sparsity order of DL channel
vectors. Since the sparsity order is much less than the number of BS antennas
in almost all practically relevant scenarios, our method incurs much less
feedback overhead compared with the currently proposed methods in the
literature, such as those based on compressed-sensing. We use numerical
simulations to assess the performance of our probing-feedback algorithm and
compare it with these methods.Comment: 24 pages, 10 figure
Grassmannian Predictive Frequency Domain Compression for Limited Feedback Beamforming
Abstract — Frequency domain channel correlation can be exploited to reduce feedback in limited feedback beamforming multiple-input multiple-output orthogonal frequency division multiplexing wireless systems. Prior methods rely on downsampling, interpolation, or clustering the channel state information in the frequency domain. The resulting compressed samples are quantized using one-shot quantization on the Grassmann manifold. The resolution, unfortunately, is limited. We propose a new frequency domain compression technique to obtain high resolution channel state information. The key idea is to use predictive coding on the Grassmann manifold, exploiting the correlation between adjacent subcarriers. I
MIMO Broadcast Channels with Finite Rate Feedback
Multiple transmit antennas in a downlink channel can provide tremendous
capacity (i.e. multiplexing) gains, even when receivers have only single
antennas. However, receiver and transmitter channel state information is
generally required. In this paper, a system where each receiver has perfect
channel knowledge, but the transmitter only receives quantized information
regarding the channel instantiation is analyzed. The well known zero forcing
transmission technique is considered, and simple expressions for the throughput
degradation due to finite rate feedback are derived. A key finding is that the
feedback rate per mobile must be increased linearly with the SNR (in dB) in
order to achieve the full multiplexing gain, which is in sharp contrast to
point-to-point MIMO systems in which it is not necessary to increase the
feedback rate as a function of the SNR.Comment: Submitted to IEEE Trans. Information Theory, 34 page
Impact of Limited Feedback on MIMO-OFDM Systems using Joint Beamforming
In multi input multi output antenna systems, beamforming is a technique for
guarding against the negative effects of fading. However, this technique
requires the transmitter to have perfect knowledge of the channel which is
often not available a priori. A solution to overcome this problem is to design
the beamforming vector using a limited number of feedback bits sent from the
receiver to the transmitter. In the case of limited feedback, the beamforming
vector is limited to lie in a codebook that is known to both the transmitter
and receiver.When the feedback is strictly limited, important issues are how to
quantize the information needed at the transmitter and how much improvement in
associated performance can be obtained as a function of the amount of feedback
available.In this paper channel quantization schema using simple approach to
codebook design (random vector quantization)is illustrated. Performance results
show that even with a few bits of feedback, performance can be close to that
with perfect channel knowledge at the transmitter
Low-Complexity Robust Adaptive Beamforming Algorithms Based on Shrinkage for Mismatch Estimation
In this paper, we propose low-complexity robust adaptive beamforming (RAB)
techniques that based on shrinkage methods. The only prior knowledge required
by the proposed algorithms are the angular sector in which the actual steering
vector is located and the antenna array geometry. We firstly present a
Low-Complexity Shrinkage-Based Mismatch Estimation (LOCSME) algorithm to
estimate the desired signal steering vector mismatch, in which the
interference-plus-noise covariance (INC) matrix is estimated with Oracle
Approximating Shrinkage (OAS) method and the weights are computed with matrix
inversions. We then develop low-cost stochastic gradient (SG) recursions to
estimate the INC matrix and update the beamforming weights, resulting in the
proposed LOCSME-SG algorithm. Simulation results show that both LOCSME and
LOCSME-SG achieve very good output signal-to-interference-plus-noise ratio
(SINR) compared to previously reported adaptive RAB algorithms.Comment: 8 pages, 2 figures, WSA. arXiv admin note: text overlap with
arXiv:1311.233
Compensation of IQ-Imbalance and Phase Noise in MIMO-OFDM Systems
The degrading effect of RF impairments on the performance of wireless
communication systems is more pronounced in MIMO-OFDM transmission. Two of the
most common impairments that significantly limit the performance of MIMO-OFDM
transceivers are IQ-imbalance and phase noise. Low-complexity estimation and
compensation techniques that can jointly remove the effect of these impairments
are highly desirable. In this paper, we propose a simple joint estimation and
compensation technique to estimate channel, phase noise and IQ-imbalance
parameters in MIMO-OFDM systems under multipath slow fading channels. A
subcarrier multiplexed preamble structure to estimate the channel and
impairment parameters with minimum overhead is introduced and used in the
estimation of IQ-imbalance parameters as well as the initial estimation of
effective channel matrix including common phase error (CPE). We then use a
novel tracking method based on the second order statistics of the inter-carrier
interference (ICI) and noise to update the effective channel matrix throughout
an OFDM frame. Simulation results for a variety of scenarios show that the
proposed low-complexity estimation and compensation technique can efficiently
improve the performance of MIMO-OFDM systems in terms of bit-error-rate (BER)
Implementation of Deep-Learning-Based CSI Feedback Reporting on 5G NR-Compliant Link-Level Simulator
Advances in machine learning have widened the range of its applications in many fields. In particular, deep learning has attracted much interest for its ability to provide solutions where the derivation of a rigorous mathematical model of the problem is troublesome. Our interest was drawn to the application of deep learning for channel state information feedback reporting, a crucial problem in frequency division duplexing (FDD) 5G networks, where knowledge of the channel characteristics is fundamental to exploiting the full potential of multiple-input multiple-output (MIMO) systems. We designed a framework adopting a 5G New Radio convolutional neural network, called NR-CsiNet, with the aim of compressing the channel matrix experienced by the user at the receiver side and then reconstructing it at the transmitter side. In contrast to similar solutions, our framework is based on a 5G New Radio fully compliant simulator, thus implementing a channel generator based on the latest 3GPP 3-D channel model. Moreover, realistic 5G scenarios are considered by including multi-receiving antenna schemes and noisy downlink channel estimation. Simulations were carried out to analyze and compare the performance with current feedback reporting schemes, showing promising results for this approach from the point of view of the block error rate and throughput of the 5G data channel
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