1,450 research outputs found
DOA and Polarization Estimation for Non-Circular Signals in 3-D Millimeter Wave Polarized Massive MIMO Systems
In this paper, an algorithm of multiple signal classification (MUSIC) is
proposed for two-dimensional (2-D) direction of- arrival (DOA) and polarization
estimation of non-circular signal in three-dimensional (3-D) millimeter wave
polarized largescale/ massive multiple-input-multiple-output (MIMO) systems.
The traditional MUSIC-based algorithms can estimate either the DOA and
polarization for circular signal or the DOA for non-circular signal by using
spectrum search. By contrast, in the proposed algorithm only the DOA estimation
needs spectrum search, and the polarization estimation has a closedform
expression. First, a novel dimension-reduced MUSIC (DRMUSIC) is proposed for
DOA and polarization estimation of circular signal with low computational
complexity. Next, based on the quaternion theory, a novel algorithm named
quaternion non-circular MUSIC (QNC-MUSIC) is proposed for parameter estimation
of non-circular signal with high estimation accuracy. Then based on the DOA
estimation result using QNC-MUSIC, the polarization estimation of non-circular
signal is acquired by using the closed-form expression of the polarization
estimation in DR-MUSIC. In addition, the computational complexity analysis
shows that compared with the conventional DOA and polarization estimation
algorithms, our proposed QNC-MUSIC and DRMUSIC have much lower computational
complexity, especially when the source number is large. The stochastic
Cramer-Rao Bound (CRB) for the estimation of the 2-D DOA and polarization
parameters of the non-circular signals is derived as well. Finally, numerical
examples are provided to demonstrate that the proposed algorithms can improve
the parameter estimation performance when the large-scale/massive MIMO systems
are employed
Algebraic Channel Estimation Algorithms for FDD Massive MIMO systems
We consider downlink (DL) channel estimation for frequency division duplex
based massive MIMO systems under the multipath model. Our goal is to provide
fast and accurate channel estimation from a small amount of DL training
overhead. Prior art tackles this problem using compressive sensing or classic
array processing techniques (e.g., ESPRIT and MUSIC). However, these methods
have challenges in some scenarios, e.g., when the number of paths is greater
than the number of receive antennas. Tensor factorization methods can also be
used to handle such challenging cases, but it is hard to solve the associated
optimization problems. In this work, we propose an efficient channel estimation
framework to circumvent such difficulties. Specifically, a structural training
sequence that imposes a tensor structure on the received signal is proposed. We
show that with such a training sequence, the parameters of DL MIMO channels can
be provably identified even when the number of paths largely exceeds the number
of receive antennas---under very small training overhead. Our approach is a
judicious combination of Vandermonde tensor algebra and a carefully designed
conjugate-invariant training sequence. Unlike existing tensor-based channel
estimation methods that involve hard optimization problems, the proposed
approach consists of very lightweight algebraic operations, and thus real-time
implementation is within reach. Simulation results are carried out to showcase
the effectiveness of the proposed methods
Joint User Scheduling and Beam Selection Optimization for Beam-Based Massive MIMO Downlinks
In beam-based massive multiple-input multiple-output systems, signals are
processed spatially in the radio-frequency (RF) front-end and thereby the
number of RF chains can be reduced to save hardware cost, power consumptions
and pilot overhead. Most existing work focuses on how to select, or design
analog beams to achieve performance close to full digital systems. However,
since beams are strongly correlated (directed) to certain users, the selection
of beams and scheduling of users should be jointly considered. In this paper,
we formulate the joint user scheduling and beam selection problem based on the
Lyapunov-drift optimization framework and obtain the optimal scheduling policy
in a closed-form. For reduced overhead and computational cost, the proposed
scheduling schemes are based only upon statistical channel state information.
Towards this end, asymptotic expressions of the downlink broadcast channel
capacity are derived. To address the weighted sum rate maximization problem in
the Lyapunov optimization, an algorithm based on block coordinated update is
proposed and proved to converge to the optimum of the relaxed problem. To
further reduce the complexity, an incremental greedy scheduling algorithm is
also proposed, whose performance is proved to be bounded within a constant
multiplicative factor. Simulation results based on widely-used spatial channel
models are given. It is shown that the proposed schemes are close to optimal,
and outperform several state-of-the-art schemes.Comment: Submitted to Trans. Wireless Commu
Joint Doppler and Channel Estimation with Nested Arrays for Millimeter Wave Communications
Channel estimation is essential for precoding/combining in millimeter wave
(mmWave) communications. However, accurate estimation is usually difficult
because the receiver can only observe the low-dimensional projection of the
received signals due to the hybrid architecture. We take the high speed
scenario into consideration where the Doppler effect caused by fast-moving
users can seriously deteriorate the channel estimation accuracy. In this paper,
we propose to incorporate the nested array into analog array architecture by
using RF switch networks with an objective of reducing the complexity and power
consumption of the system. Based on the covariance fitting criterion, a joint
Doppler and channel estimation method is proposed without need of discretizing
the angle space, and thus the model mismatch effect can be totally eliminated.
We also present an algorithmic implementation by solving the dual problem of
the original one in order to reduce the computational complexity. Numerical
simulations are provided to demonstrate the effectiveness and superiority of
our proposed method
Multi-Cell Multi-User Massive FD-MIMO: Downlink Precoding and Throughput Analysis
In this paper, downlink (DL) precoding and power allocation strategies are
identified for a time-division-duplex (TDD) multi-cell multi-user massive
Full-Dimension MIMO (FD-MIMO) network. Utilizing channel reciprocity, DL
channel state information (CSI) feedback is eliminated and the DL multi-user
MIMO precoding is linked to the uplink (UL) direction of arrival (DoA)
estimation through estimation of signal parameters via rotational invariance
technique (ESPRIT). Assuming non-orthogonal/non-ideal spreading sequences of
the UL pilots, the performance of the UL DoA estimation is analytically
characterized and the characterized DoA estimation error is incorporated into
the corresponding DL precoding and power allocation strategy. Simulation
results verify the accuracy of our analytical characterization of the DoA
estimation and demonstrate that the introduced multi-user MIMO precoding and
power allocation strategy outperforms existing zero-forcing based massive MIMO
strategies.Comment: 32 pages, 8 figures, submitted to IEEE Transactions on Wireless
Communication
Millimeter-Wave Beamformed Full-dimensional MIMO Channel Estimation Based on Atomic Norm Minimization
The millimeter-wave (mmWave) full-dimensional (FD) MIMO system employs planar
arrays at both the base station and user equipment and can simultaneously
support both azimuth and elevation beamforming. In this paper, we propose
atomic-norm-based methods for mmWave FD-MIMO channel estimation under both
uniform planar arrays (UPA) and non-uniform planar arrays (NUPA). Unlike
existing algorithms such as compressive sensing (CS) or subspace methods, the
atomic-norm-based algorithms do not require to discretize the angle spaces of
the angle of arrival (AoA) and angle of departure (AoD) into grids, thus
provide much better accuracy in estimation. In the UPA case, to reduce the
computational complexity, the original large-scale 4D atomic norm minimization
problem is approximately reformulated as a semi-definite program (SDP)
containing two decoupled two-level Toeplitz matrices. The SDP is then solved
via the alternating direction method of multipliers (ADMM) where each iteration
involves only closed-form computations. In the NUPA case, the atomic-norm-based
formulation for channel estimation becomes nonconvex and a
gradient-decent-based algorithm is proposed to solve the problem. Simulation
results show that the proposed algorithms achieve better performance than the
CS-based and subspace-based algorithms
Near-Optimal Hybrid Processing for Massive MIMO Systems via Matrix Decomposition
For the practical implementation of massive multiple-input multiple-output
(MIMO) systems, the hybrid processing (precoding/combining) structure is
promising to reduce the high cost rendered by large number of RF chains of the
traditional processing structure. The hybrid processing is performed through
low-dimensional digital baseband processing combined with analog RF processing
enabled by phase shifters. We propose to design hybrid RF and baseband
precoders/combiners for multi-stream transmission in point-to-point massive
MIMO systems, by directly decomposing the pre-designed unconstrained digital
precoder/combiner of a large dimension. The constant amplitude constraint of
analog RF processing results in the matrix decomposition problem non-convex.
Based on an alternate optimization technique, the non-convex matrix
decomposition problem can be decoupled into a series of convex sub-problems and
effectively solved by restricting the phase increment of each entry in the RF
precoder/combiner within a small vicinity of its preceding iterate. A singular
value decomposition based technique is proposed to secure an initial point
sufficiently close to the global solution of the original non-convex problem.
Through simulation, the convergence of the alternate optimization for such a
matrix decomposition based hybrid processing (MD-HP) scheme is examined, and
the performance of the MD-HP scheme is demonstrated to be near-optimal
Beam Tracking for UAV Mounted SatCom on-the-Move with Massive Antenna Array
Unmanned aerial vehicle (UAV)-satellite communication has drawn dramatic
attention for its potential to build the integrated space-air-ground network
and the seamless wide-area coverage. The key challenge to UAV-satellite
communication is its unstable beam pointing due to the UAV navigation, which is
a typical SatCom on-the-move scenario. In this paper, we propose a blind beam
tracking approach for Ka-band UAVsatellite communication system, where UAV is
equipped with a large-scale antenna array. The effects of UAV navigation are
firstly released through the mechanical adjustment, which could approximately
point the beam towards the target satellite through beam stabilization and
dynamic isolation. Specially, the attitude information can be realtimely
derived from data fusion of lowcost sensors. Then, the precision of the beam
pointing is blindly refined through electrically adjusting the weight of the
massive antennas, where an array structure based simultaneous perturbation
algorithm is designed. Simulation results are provided to demonstrate the
superiority of the proposed method over the existing ones
Channel Reconstruction for SVD-ZF Precoding in Massive 3D-MIMO Systems Low-Complexity Algorithm
In this paper, we study the low-complexity channel reconstruction methods for
downlink precoding in massive MIMO systems. When the user is allocated less
streams than the number of its antennas, the BS or user usually utilizes the
singular value decomposition (SVD) factorizations to get the effective
channels, whose dimension is equal to the num of streams. This process is
called channel reconstruction in BS for TDD mode. However, with the increasing
of antennas in BS, the computation burden of SVD is becoming incredibly high.
As a countermeasure, we propose a series of novel low-complexity channel
reconstruction methods for downlink zero-forcing precoding (ZF). We adopt
randomized algorithms to construct an approximate SVD, which could reduce the
dimensions of the matrix, especially when approximating an input matrix with a
low-rank element. Besides, this method could automatically modify the
parameters to adapt arbitrary number demand of streams from users. The
simulation results show that the proposed methods only cost less than 30% float
computation than the traditional SVD-ZF method, while keeping nearly the same
performance of 1Gbps with 128 BS antennas.Comment: 7 pages, 6 figures, received by 2016 IEEE 83rd Vehicular Technology
Conference. arXiv admin note: substantial text overlap with arXiv:1510.0850
Overview of Full-Dimension MIMO in LTE-Advanced Pro
Multiple-input multiple-output (MIMO) systems with a large number of
basestation antennas, often called massive MIMO, have received much attention
in academia and industry as a means to improve the spectral efficiency, energy
efficiency, and processing complexity of next generation cellular system.
Mobile communication industry has initiated a feasibility study of massive MIMO
systems to meet the increasing demand of future wireless systems. Field trials
of the proof-of-concept systems have demonstrated the potential gain of the
Full-Dimension MIMO (FD-MIMO), an official name for the MIMO enhancement in 3rd
generation partnership project (3GPP). 3GPP initiated standardization activity
for the seamless integration of this technology into current 4G LTE systems. In
this article, we provide an overview of the FD-MIMO system, with emphasis on
the discussion and debate conducted on the standardization process of Release
13. We present key features for FD-MIMO systems, a summary of the major issues
for the standardization and practical system design, and performance
evaluations for typical FD-MIMO scenarios
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