25,993 research outputs found
Low Complexity Hybrid Precoding and Channel Estimation Based on Hierarchical Multi-Beam Search for Millimeter-Wave MIMO Systems
In millimeter-wave (mmWave) MIMO systems, while a hybrid digital/analog
precoding structure offers the potential to increase the achievable rate, it
also faces the challenge of the need of a low-complexity design. In specific,
the hybrid precoding may require matrix operations with a scale of antenna
size, which is generally large in mmWave communication. Moreover, the channel
estimation is also rather time consuming due to the large number of antennas at
both Tx/Rx sides. In this paper, a low-complexity hybrid precoding and channel
estimation approach is proposed. In the channel estimation phase, a
hierarchical multi-beam search scheme is proposed to fast acquire
(the number of streams) multipath components (MPCs)/clusters with the highest
powers. In the hybrid precoding phase, the analog and digital precodings are
decoupled. The analog precoding is designed to steer along the
acquired MPCs/clusters at both Tx/Rx sides, shaping an equivalent
baseband channel, while the digital precoding
performs operations in the baseband with the reduced-scale channel. Performance
evaluations show that, compared with a state-of-the-art scheme, while achieving
a close or even better performance when the number of radio-frequency (RF)
chains or streams is small, both the computational complexity of the hybrid
precoding and the time complexity of the channel estimation are greatly
reduced.Comment: 11 pages, 9 figures. This paper reports a Low Complexity Hybrid
Precoding and Channel Estimation method for mmWave communication
Full-Duplex Millimeter-Wave Communication
The potential of doubling the spectrum efficiency of full-duplex (FD)
transmission motivates us to investigate FD millimeter-wave (FD-mmWave)
communication. To realize FD transmission in the mmWave band, we first
introduce possible antenna configurations for FD-mmWave transmission. It is
shown that, different from the cases in micro-wave band FD communications, the
configuration with separate Tx/Rx antenna arrays appears more flexible in
self-interference (SI) suppression while it may increase some cost and area
versus that with the same array. We then model the mmWave SI channel with
separate Tx/Rx arrays, where a near-field propagation model is adopted for the
line-of-sight (LOS) path, and it is found that the established LOS-SI channel
with separate Tx/Rx arrays also shows spatial sparsity. Based on the SI
channel, we further explore approaches to mitigate SI by signal processing, and
we focus on a new cancellation approach in FD-mmWave communication, i.e.,
beamforming cancellation. Centered on the constant-amplitude (CA) constraint of
the beamforming vectors, we propose several candidate solutions. Lastly, we
consider an FD-mmWave multi-user scenario, and show that even if there are no
FD users in an FD-mmWave cellular system, the FD benefit can still be exploited
in the FD base station. Candidate solutions are also discussed to mitigate both
SI and multi-user interference (MUI) simultaneously.Comment: This paper explores the combination of full duplex communication and
millimeter wave communication. (To appear in IEEE Wireless Communications
Codebook Design for Millimeter-Wave Channel Estimation with Hybrid Precoding Structure
In this paper, we study hierarchical codebook design for channel estimation
in millimeter-wave (mmWave) communications with a hybrid precoding structure.
Due to the limited saturation power of mmWave power amplifier (PA), we take the
per-antenna power constraint (PAPC) into consideration. We first propose a
metric, i.e., generalized detection probability (GDP), to evaluate the quality
of \emph{an arbitrary codeword}. This metric not only enables an optimization
approach for mmWave codebook design, but also can be used to compare the
performance of two different codewords/codebooks. To the best of our knowledge,
GDP is the first metric particularly for mmWave codebook design for channel
estimation. We then propose an approach to design a hierarchical codebook
exploiting BeaM Widening with Multi-RF-chain Sub-array technique (BMW-MS). To
obtain crucial parameters of BMW-MS, we provide two solutions, namely a
low-complexity search (LCS) solution to optimize the GDP metric and a
closed-form (CF) solution to pursue a flat beam pattern. Performance
comparisons show that BMW-MS/LCS and BMW-MS/CF achieve very close performances,
and they outperform the existing alternatives under the PAPC.Comment: 14 pages, 10 figures. Hierarchical codebook design for mmWave channel
estimation with a hybrid precoding structure. Submitted to TW
Enabling UAV Cellular with Millimeter-Wave Communication: Potentials and Approaches
To support high data rate urgent or ad hoc communications, we consider mmWave
UAV cellular networks and the associated challenges and solutions. To enable
fast beamforming training and tracking, we first investigate a hierarchical
structure of beamforming codebooks and design of hierarchical codebooks with
different beam widths via the sub-array techniques. We next examine the Doppler
effect as a result of UAV movement and find that the Doppler effect may not be
catastrophic when high gain directional transmission is used. We further
explore the use of millimeter wave spatial division multiple access and
demonstrate its clear advantage in improving the cellular network capacity. We
also explore different ways of dealing with signal blockage and point out that
possible adaptive UAV cruising algorithms would be necessary to counteract
signal blockage. Finally, we identify a close relationship between UAV
positioning and directional millimeter wave user discovery, where update of the
former may directly impact the latter and vice versa.Comment: This paper explores the potentials and approaches to exploit mmWave
communication to establish a UAV cellular. It is to appear in IEEE
Communications Magazin
Hierarchical Codebook Design for Beamforming Training in Millimeter-Wave Communication
In millimeter-wave communication, large antenna arrays are required to
achieve high power gain by steering towards each other with narrow beams, which
poses the problem to efficiently search the best beam direction in the angle
domain at both Tx and Rx sides. As the exhaustive search is time consuming,
hierarchical search has been widely accepted to reduce the complexity, and its
performance is highly dependent on the codebook design. In this paper, we
propose two basic criteria for the hierarchical codebook design, and devise an
efficient hierarchical codebook by jointly exploiting sub-array and
deactivation (turning-off) antenna processing techniques, where closed-form
expressions are provided to generate the codebook. Performance evaluations are
conducted under different system and channel models. Results show superiority
of the proposed codebook over the existing alternatives.Comment: 13 pages, 11 figures. To appear in IEEE Trans. Wireless Commn. This
paper proposes the BMW-SS approach to design a fully-hierarchical codebook
for mmWave communication
Error Correction in Polynomial Remainder Codes with Non-Pairwise Coprime Moduli and Robust Chinese Remainder Theorem for Polynomials
This paper investigates polynomial remainder codes with non-pairwise coprime
moduli. We first consider a robust reconstruction problem for polynomials from
erroneous residues when the degrees of all residue errors are assumed small,
namely robust Chinese Remainder Theorem (CRT) for polynomials. It basically
says that a polynomial can be reconstructed from erroneous residues such that
the degree of the reconstruction error is upper bounded by whenever the
degrees of all residue errors are upper bounded by , where a sufficient
condition for and a reconstruction algorithm are obtained. By releasing
the constraint that all residue errors have small degrees, another robust
reconstruction is then presented when there are multiple unrestricted errors
and an arbitrary number of errors with small degrees in the residues. By making
full use of redundancy in moduli, we obtain a stronger residue error correction
capability in the sense that apart from the number of errors that can be
corrected in the previous existing result, some errors with small degrees can
be also corrected in the residues. With this newly obtained result,
improvements in uncorrected error probability and burst error correction
capability in a data transmission are illustrated.Comment: 12 pages, 2 figure
Minimum Degree-Weighted Distance Decoding for Polynomial Residue Codes with Non-Pairwise Coprime Moduli
This paper presents a new decoding for polynomial residue codes, called the
minimum degree-weighted distance decoding. The newly proposed decoding is based
on the degree-weighted distance and different from the traditional minimum
Hamming distance decoding. It is shown that for the two types of minimum
distance decoders, i.e., the minimum degree-weighted distance decoding and the
minimum Hamming distance decoding, one is not absolutely stronger than the
other, but they can complement each other from different points of view.Comment: 4 page
The Deconfinement Phase Transition in the Interior of Neutron Stars
The deconfinement phase transition which happens in the interior of neutron
stars are investigated. Coupled with the spin evolution of the stars, the
effect of entropy production and deconfinement heat generation during the
deconfinement phase transition in the mixed phase of the neutron stars are
discussed. The entropy production of deconfinement phase transition can be act
as a signature of phase transition, but less important and does not
significantly change the thermal evolution of neutron stars. The deconfinement
heat can change the thermal evolution of neutron star distinctly.Comment: 5 pages. To appear in Proceedings for "Compact stars in the QCD phase
diagram II (CSQCD II), May 20-24, 2009, KIAA at Peking University, Beijing -
P. R. China [http://vega.bac.pku.edu.cn/rxxu/csqcd.htm
Robust Polynomial Reconstruction via Chinese Remainder Theorem in the Presence of Small Degree Residue Errors
Based on unique decoding of the polynomial residue code with non-pairwise
coprime moduli, a polynomial with degree less than that of the least common
multiple (lcm) of all the moduli can be accurately reconstructed when the
number of residue errors is less than half the minimum distance of the code.
However, once the number of residue errors is beyond half the minimum distance
of the code, the unique decoding may fail and lead to a large reconstruction
error. In this paper, assuming that all the residues are allowed to have errors
with small degrees, we consider how to reconstruct the polynomial as accurately
as possible in the sense that a reconstructed polynomial is obtained with only
the last number of coefficients being possibly erroneous, when the
residues are affected by errors with degrees upper bounded by . In this
regard, we first propose a multi-level robust Chinese remainder theorem (CRT)
for polynomials, namely, a trade-off between the dynamic range of the degree of
the polynomial to be reconstructed and the residue error bound is
formulated. Furthermore, a simple closed-form reconstruction algorithm is also
proposed.Comment: 5 page
Mid-to-Far Infrared Spectral Energy Distribution of Galaxies in Spitzer First Look Survey Field
We made model fitting to the mid-to-far infrared spectral energy
distributions (SEDs) for different categories of galaxies in the main
extragalactic field of the {\it Spitzer} First Look Survey with the aid of
spectroscopic information from the Sloan Digital Sky Survey. We find that the
mid-to-far infrared SEDs of HII galaxies, mixture type galaxies and LINERs can
be well fitted by the one-parameter () dust model of Dale et al. plus
the 13 Gyr dust-free elliptical galaxy model. The statistics of values
indicates that all these galaxies tend to be quiescent, although the HII
galaxies are relatively more active than the LINERs. The mid-infrared SEDs of
absorption galaxies are well fitted simply by the 13 Gyr dust-free elliptical
galaxy template, and the near-to-mid infrared SEDs of QSOs can be represented
by AGN NGC 5506.Comment: 12 pages with 8 figures, will be appeared in ChJAA, Vol.7 (2007),
No.
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