13 research outputs found
A Kronecker-Based Sparse Compressive Sensing Matrix for Millimeter Wave Beam Alignment
Millimeter wave beam alignment (BA) is a challenging problem especially for
large number of antennas. Compressed sensing (CS) tools have been exploited due
to the sparse nature of such channels. This paper presents a novel
deterministic CS approach for BA. Our proposed sensing matrix which has a
Kronecker-based structure is sparse, which means it is computationally
efficient. We show that our proposed sensing matrix satisfies the restricted
isometry property (RIP) condition, which guarantees the reconstruction of the
sparse vector. Our approach outperforms existing random beamforming techniques
in practical low signal to noise ratio (SNR) scenarios.Comment: Accepted to 13th International Conference on Signal Processing and
Communication Systems (ICSPCS'2019
A Random Matrix Model for mmWave MIMO Systems
Random matrices are nowadays classical tools for modeling multiantenna wireless channels. Scattering phenomena typical of cellular frequencies and channel reciprocity features led to the adoption of matrices sampled either from the Gaussian Unitary Ensemble (GUE) or from more general Polynomial Ensembles (PE). Such matrices can be used to model the random impairments of the radio channel on the transmitted signal over a wireless link whose transmitter and receiver are both equipped with antenna arrays. The exploitation of the millimeter-wave (mmWave) frequency band, planned for 5G and beyond mobile networks, prevents the use of GUE and PE elements as candidate models for channel matrices. This is mainly due to the lack of scattering richness compared to microwave-based transmissions. In this work, we propose to model mmWave Multi-Input–MultiOutput (MIMO) systems via products of random Vandermonde matrices. We illustrate the physical motivation of our model selection, discuss the meaning of the parameters and their impact on the spectral properties of the random matrix at hand, and provide both a list of results of immediate use for performance analysis of mmWave MIMO systems, as well as a list of open problems in the field
Joint Radar Target Detection and Parameter Estimation with MIMO OTFS
Motivated by future automotive applications, we study the joint target
detection and parameter estimation problem using orthogonal time frequency
space (OTFS), a digital modulation format robust to time-frequency selective
channels. Assuming the transmitter is equipped with a mono-static MIMO radar,
we propose an efficient maximum likelihood based approach to detect targets and
estimate the corresponding delay, Doppler, and angle-of-arrival parameters. In
order to reduce the computational complexity associated to the high-dimensional
search, our scheme proceeds in two steps, i.e., target detection and coarse
parameter estimation followed by refined parameter estimation. Interestingly,
our numerical results demonstrate that the proposed scheme is able to identify
multiple targets if they are separated in at least one domain out of three
(delay, Doppler, and angle), while achieving the Cram\'er-Rao lower bound for
the parameter estimation
Beam Alignment in mmWave User-Centric Cell-Free Massive MIMO Systems
The problem of beam alignment (BA) in a cell-free massive multiple-input
multiple-output (CF-mMIMO) system operating at millimeter wave (mmWaves)
carrier frequencies is considered in this paper. Two estimation algorithms are
proposed, in association with a protocol that permits simultaneous estimation,
on a shared set of frequencies, for each user equipment (UE), of the direction
of arrival and departure of the radio waves associated to the strongest
propagation paths from each of the surrounding access points (APs), so that
UE-AP association can take place. The proposed procedure relies on the
existence of a reliable control channel at sub-6 GHz frequency, so as to enable
exchange of estimated values between the UEs and the network, and assumes that
APs can be identifies based on the prior knowledge of the orthogonal channels
and transmit beamforming codebook. A strategy for assigning codebook entries to
the several APs is also proposed, with the aim of minimizing the mutual
interference between APs that are assigned the same entry. Numerical results
show the effectiveness of the proposed detection strategy, thus enabling one
shot fast BA for CF-mMIMO systems.Comment: 6 pages, 3 figures, submitted to the 2021 IEEE Global Communications
Conference (GLOBECOM
Subspace Tracking and Least Squares Approaches to Channel Estimation in Millimeter Wave Multiuser MIMO
The problem of MIMO channel estimation at millimeter wave frequencies, both
in a single-user and in a multi-user setting, is tackled in this paper. Using a
subspace approach, we develop a protocol enabling the estimation of the right
(resp. left) singular vectors at the transmitter (resp. receiver) side; then,
we adapt the projection approximation subspace tracking with deflation and the
orthogonal Oja algorithms to our framework and obtain two channel estimation
algorithms. We also present an alternative algorithm based on the least squares
approach. The hybrid analog/digital nature of the beamformer is also explicitly
taken into account at the algorithm design stage. In order to limit the system
complexity, a fixed analog beamformer is used at both sides of the
communication links. The obtained numerical results, showing the accuracy in
the estimation of the channel matrix dominant singular vectors, the system
achievable spectral efficiency, and the system bit-error-rate, prove that the
proposed algorithms are effective, and that they compare favorably, in terms of
the performance-complexity trade-off, with respect to several competing
alternatives.Comment: To appear on the IEEE Transactions on Communication
Joint Analog Beam Selection and Digital Beamforming in Millimeter Wave Cell-Free Massive MIMO Systems
Cell-free massive MIMO systems consist of many distributed access points with
simple components that jointly serve the users. In millimeter wave bands, only
a limited set of predetermined beams can be supported. In a network that
consolidates these technologies, downlink analog beam selection stands as a
challenging task for the network sum-rate maximization. Low-cost digital
filters can improve the network sum-rate further. In this work, we propose
low-cost joint designs of analog beam selection and digital filters. The
proposed joint designs achieve significantly higher sum-rates than the disjoint
design benchmark. Supervised machine learning (ML) algorithms can efficiently
approximate the input-output mapping functions of the beam selection decisions
of the joint designs with low computational complexities. Since the training of
ML algorithms is performed off-line, we propose a well-constructed joint design
that combines multiple initializations, iterations, and selection features, as
well as beam conflict control, i.e., the same beam cannot be used for multiple
users. The numerical results indicate that ML algorithms can retain 99-100% of
the original sum-rate results achieved by the proposed well-constructed
designs.Comment: 14 pages, 11 figures. First submission date: August 19th, 2020. To be
published at IEEE Open Journal of the Communications Societ