1,124 research outputs found
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
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
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
Iterative Eigenvalue Decomposition and Multipath-Grouping Tx/Rx Joint Beamforming for Millimeter-Wave Communication
We investigate Tx/Rx joint beamforming in millimeter-wave communications
(MMWC). As the multipath components (MPCs) have different steering angles and
independent fadings, beamforming aims at achieving array gain as well as
diversity gain in this scenario. A sub-optimal beamforming scheme is proposed
to find the antenna weight vectors (AWVs) at Tx/Rx via iterative eigenvalue
decomposition (EVD), provided that full channel state information (CSI) is
available at both the transmitter and receiver. To make this scheme practically
feasible in MMWC, a corresponding training approach is suggested to avoid the
channel estimation and iterative EVD computation. As in fast fading scenario
the training approach may be time-consuming due to frequent training, another
beamforming scheme, which exploits the quasi-static steering angles in MMWC, is
proposed to reduce the overhead and increase the system reliability by
multipath grouping (MPG). The scheme first groups the MPCs and then
concurrently beamforms towards multiple steering angles of the grouped MPCs, so
that both array gain and diversity gain are achieved. Performance comparisons
show that, compared with the corresponding state-of-the-art schemes, the
iterative EVD scheme with the training approach achieves the same performance
with a reduced overhead and complexity, while the MPG scheme achieves better
performance with an approximately equivalent complexity.Comment: 13 pages, 12 figure
Persistent spectral based machine learning (PerSpect ML) for drug design
In this paper, we propose persistent spectral based machine learning
(PerSpect ML) models for drug design. Persistent spectral models, including
persistent spectral graph, persistent spectral simplicial complex and
persistent spectral hypergraph, are proposed based on spectral graph theory,
spectral simplicial complex theory and spectral hypergraph theory,
respectively. Different from all previous spectral models, a filtration
process, as proposed in persistent homology, is introduced to generate
multiscale spectral models. More specifically, from the filtration process, a
series of nested topological representations, i,e., graphs, simplicial
complexes, and hypergraphs, can be systematically generated and their spectral
information can be obtained. Persistent spectral variables are defined as the
function of spectral variables over the filtration value. Mathematically,
persistent multiplicity (of zero eigenvalues) is exactly the persistent Betti
number (or Betti curve). We consider 11 persistent spectral variables and use
them as the feature for machine learning models in protein-ligand binding
affinity prediction. We systematically test our models on three most
commonly-used databases, including PDBbind-2007, PDBbind-2013 and PDBbind-2016.
Our results, for all these databases, are better than all existing models, as
far as we know. This demonstrates the great power of our PerSpect ML in
molecular data analysis and drug design.Comment: 17 pages; 8 Figures; 3 table
Millimeter-Wave Communication with Non-Orthogonal Multiple Access for 5G
To further improve the system capacity for 5G, we explore the integration of
non-orthogonal multiple access (NOMA) in mmWave communications (mmWave-NOMA)
for future 5G systems. Compared with the conventional NOMA, the distinguishing
feature of mmWave-NOMA is that, it is usually characterized by transmit/receive
beamforming with large antenna arrays. In this paper, we focus on the design
challenges of mmWave-NOMA due to beamforming. Firstly, we study how beamforming
affects the sum-rate performance of mmWave-NOMA, and find that with
conventional single-beam forming, the performance may be offset by the relative
angle between NOMA users. Then, we consider multi-beam forming for mmWave-NOMA,
which is shown to be able to achieve promising performance enhancement as well
as robustness. We further investigate the challenging joint design of the
intertwined power allocation and user pairing for mmWave-NOMA. We also discuss
the challenges and propose some potential solutions in detail. Finally, we
consider hybrid spatial division multiple access (SDMA) and NOMA in mmWave
communications, where some possible system configurations and the corresponding
solutions are discussed to address the multi-user issues including multi-user
precoding and multi-user interference (MUI) mitigation.Comment: This paper explores mmWave communications with NOMA for 5G, and
focuses on the beamforming issues with phased array
Persistent spin currents in electron systems with spin-orbit interaction
We investigate the persistent spin currents in one- and two-dimensional
electron systems with spin-orbit interaction in thermodynamics equilibrium at
absolute zero temperature. The persistent spin current is the intrinsic one
which is connected with the Berry phases in the configuration spaces of an
electron system and winding numbers in the field configurations of electrons.
When the topological space of the configuration of a system has the nontrivial
first homotopy groups, the persistent spin currents in the system could be
nonzero and not easily destroyed by impurity scattering in ballistic limit. The
non-vanishing background spin currents in infinite two-dimensional electron
system found by Rashba could be realized by the transport persistent spin
currents in a finite torus electron system with spin-orbit interaction. In this
sense, we meet the challenge proposed by Rashba
Joint Tx-Rx Beamforming and Power Allocation for 5G Millimeter-Wave Non-Orthogonal Multiple Access (MmWave-NOMA) Networks
In this paper, we investigate the combination of non-orthogonal multiple
access and millimeter-Wave communications (mmWave-NOMA). A downlink cellular
system is considered, where an analog phased array is equipped at both the base
station and users. A joint Tx-Rx beamforming and power allocation problem is
formulated to maximize the achievable sum rate (ASR) subject to a minimum rate
constraint for each user. As the problem is non-convex, we propose a
sub-optimal solution with three stages. In the first stage, the optimal power
allocation with a closed form is obtained for an arbitrary fixed Tx-Rx
beamforming. In the second stage, the optimal Rx beamforming with a closed form
is designed for an arbitrary fixed Tx beamforming. In the third stage, the
original problem is reduced to a Tx beamforming problem by using the previous
results, and a boundary-compressed particle swarm optimization (BC-PSO)
algorithm is proposed to obtain a sub-optimal solution. Extensive performance
evaluations are conducted to verify the rational of the proposed solution, and
the results show that the proposed sub-optimal solution can achieve a
near-upper-bound performance in terms of ASR, which is significantly improved
compared with those of the state-of-the-art schemes and the conventional mmWave
orthogonal multiple access (mmWave-OMA) system.Comment: 11Pages, 10 figure
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