386 research outputs found
Hybrid Transceiver Optimization for Multi-Hop Communications
Multi-hop communication with the aid of large-scale antenna arrays will play
a vital role in future emergence communication systems. In this paper, we
investigate amplify-and-forward based and multiple-input multiple-output
assisted multi-hop communication, in which all nodes employ hybrid
transceivers. Moreover, channel errors are taken into account in our hybrid
transceiver design. Based on the matrix-monotonic optimization framework, the
optimal structures of the robust hybrid transceivers are derived. By utilizing
these optimal structures, the optimizations of analog transceivers and digital
transceivers can be separated without loss of optimality. This fact greatly
simplifies the joint optimization of analog and digital transceivers. Since the
optimization of analog transceivers under unit-modulus constraints is
non-convex, a projection type algorithm is proposed for analog transceiver
optimization to overcome this difficulty. Based on the derived analog
transceivers, the optimal digital transceivers can then be derived using
matrix-monotonic optimization. Numeral results obtained demonstrate the
performance advantages of the proposed hybrid transceiver designs over other
existing solutions.Comment: 32 pages, 6 figures. This manuscript has been submitted to IEEE
Journal on Selected Areas in Communications (special issue on Multiple
Antenna Technologies for Beyond 5G
Spectral and Energy Efficiency of Multi-pair Massive MIMO Relay Network with Hybrid Processing
We consider a multi-pair massive multiple-input multiple-output (MIMO) relay
network, where the relay is equipped with a large number, N, of antennas, but
driven by a far smaller number, L, of radio frequency (RF) chains. We assume
that K pairs of users are scheduled for simultaneous transmission, where K
satisfies 2K = L. A hybrid signal processing scheme is presented for both
uplink and downlink transmissions of the network. Analytical expressions of
both spectral and energy efficiency are derived with respect to the RF chain
number under imperfect channel estimation. It is revealed that, under the
condition N > 4L^2/pi, the transmit power of each user and the relay can be
respectively scaled down by 1=sqrt(N) and 2K=sqrt(N) if pilot power scales with
signal power, or they can be respectively scaled down by 1=N and 2K=N if the
pilot power is kept fixed, while maintaining an asymptotically unchanged
spectral efficiency (SE). While regarding energy efficiency (EE) of the
network, the optimal EE is shown to be achieved when Pr = 2KPs, where Pr and Ps
respectively refer to the transmit power of the relay and each source terminal.
We show that the network EE is a quasi-concave function with respect to the
number of RF-chains which, therefore, admits a unique globally optimal choice
of the RF-chain number. Numerical simulations are conducted to verify our
observations.Comment: 32 pages, to appear in IEEE Transactions on Communications, early
access availabl
Symbol-level and Multicast Precoding for Multiuser Multiantenna Downlink: A Survey, Classification and Challenges
Precoding has been conventionally considered as an effective means of
mitigating the interference and efficiently exploiting the available in the
multiantenna downlink channel, where multiple users are simultaneously served
with independent information over the same channel resources. The early works
in this area were focused on transmitting an individual information stream to
each user by constructing weighted linear combinations of symbol blocks
(codewords). However, more recent works have moved beyond this traditional view
by: i) transmitting distinct data streams to groups of users and ii) applying
precoding on a symbol-per-symbol basis. In this context, the current survey
presents a unified view and classification of precoding techniques with respect
to two main axes: i) the switching rate of the precoding weights, leading to
the classes of block- and symbol-level precoding, ii) the number of users that
each stream is addressed to, hence unicast-/multicast-/broadcast- precoding.
Furthermore, the classified techniques are compared through representative
numerical results to demonstrate their relative performance and uncover
fundamental insights. Finally, a list of open theoretical problems and
practical challenges are presented to inspire further research in this area.Comment: Submitted to IEEE Communications Surveys & Tutorial
Performance Analysis of Multi-Cell Millimeter Wave Massive MIMO Networks with Low-Precision ADCs
In this paper, we investigate a multi-cell millimeter wave (mmWave) massive
multiple-input multiple-output (MIMO) network with low-precision
analog-to-digital converters (ADCs) at the base station (BS). Each cell serves
multiple users and each user is equipped with multiple antennas but driven by a
single RF chain. We first introduce a channel estimation strategy for the
mmWave massive MIMO network and analyze the achievable rate with imperfect
channel state information. Then, we derive an insightful lower bound for the
achievable rate, which becomes tight with a growing number of users. The bound
clearly demonstrates the impacts of the number of antennas and the ADC
precision, especially for a single-cell mmWave network at low signal-to-noise
ratio (SNR). It characterizes the tradeoff among various system parameters. Our
analytical results are finally confirmed by extensive computer simulations.Comment: 16 pages, 9 figure
Hybrid Precoding Based on Non-Uniform Quantization Codebook to Reduce Feedback Overhead in Millimeter Wave MIMO Systems
In this paper, we focus on the design of the hybrid analog/digital precoding
in millimeter wave multiple-input multiple-output (MIMO) systems. To reduce the
feedback overhead, we propose two non-uniform quantization (NUQ) codebook based
hybrid precoding schemes for two main hybrid precoding implementations, i.e.,
the full-connected structure and the sub-connected structure. Specifically, we
firstly group the angles of the arrive/departure (AOAs/AODs) of the scattering
paths into several spatial lobes by exploiting the sparseness property of the
millimeter wave in the angular domain, which divides the total angular domain
into effective spatial lobes' coverage angles and ineffective coverage angles.
Then, we map the quantization bits non-uniformly to different coverage angles
and construct NUQ codebooks, where high numbers of quantization bits are
employed for the effective coverage angles to quantize AoAs/AoDs and zero
quantization bit is employed for ineffective coverage angles. Finally, two
low-complexity hybrid analog/digital precoding schemes are proposed based on
NUQ codebooks. Simulation results demonstrate that, the proposed two NUQ
codebook based hybrid precoding schemes achieve near-optimal spectral
efficiencies and show the superiority in reducing the feedback overhead
compared with the uniform quantization (UQ) codebook based works, e.g., at
least 12.5% feedback overhead could be reduced for a system with 144/36
transmitting/receiving antennas.Comment: 29 pages, 12 figure
A Framework on Hybrid MIMO Transceiver Design based on Matrix-Monotonic Optimization
Hybrid transceiver can strike a balance between complexity and performance of
multiple-input multiple-output (MIMO) systems. In this paper, we develop a
unified framework on hybrid MIMO transceiver design using matrix-monotonic
optimization. The proposed framework addresses general hybrid transceiver
design, rather than just limiting to certain high frequency bands, such as
millimeter wave (mmWave) or terahertz bands or relying on the sparsity of some
specific wireless channels. In the proposed framework, analog and digital parts
of a transceiver, either linear or nonlinear, are jointly optimized. Based on
matrix-monotonic optimization, we demonstrate that the combination of the
optimal analog precoders and processors are equivalent to eigenchannel
selection for various optimal hybrid MIMO transceivers. From the optimal
structure, several effective algorithms are derived to compute the analog
transceivers under unit modulus constraints. Furthermore, in order to reduce
computation complexity, a simple random algorithm is introduced for analog
transceiver optimization. Once the analog part of a transceiver is determined,
the closed-form digital part can be obtained. Numerical results verify the
advantages of the proposed design.Comment: 13 pages,7 figures, IEEE Signal Processing 201
Millimeter Wave Cellular Networks: A MAC Layer Perspective
The millimeter wave (mmWave) frequency band is seen as a key enabler of
multi-gigabit wireless access in future cellular networks. In order to overcome
the propagation challenges, mmWave systems use a large number of antenna
elements both at the base station and at the user equipment, which lead to high
directivity gains, fully-directional communications, and possible noise-limited
operations. The fundamental differences between mmWave networks and traditional
ones challenge the classical design constraints, objectives, and available
degrees of freedom. This paper addresses the implications that highly
directional communication has on the design of an efficient medium access
control (MAC) layer. The paper discusses key MAC layer issues, such as
synchronization, random access, handover, channelization, interference
management, scheduling, and association. The paper provides an integrated view
on MAC layer issues for cellular networks, identifies new challenges and
tradeoffs, and provides novel insights and solution approaches.Comment: 21 pages, 9 figures, 2 tables, to appear in IEEE Transactions on
Communication
A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges
With the explosive growth of mobile data demand, the fifth generation (5G)
mobile network would exploit the enormous amount of spectrum in the millimeter
wave (mmWave) bands to greatly increase communication capacity. There are
fundamental differences between mmWave communications and existing other
communication systems, in terms of high propagation loss, directivity, and
sensitivity to blockage. These characteristics of mmWave communications pose
several challenges to fully exploit the potential of mmWave communications,
including integrated circuits and system design, interference management,
spatial reuse, anti-blockage, and dynamics control. To address these
challenges, we carry out a survey of existing solutions and standards, and
propose design guidelines in architectures and protocols for mmWave
communications. We also discuss the potential applications of mmWave
communications in the 5G network, including the small cell access, the cellular
access, and the wireless backhaul. Finally, we discuss relevant open research
issues including the new physical layer technology, software-defined network
architecture, measurements of network state information, efficient control
mechanisms, and heterogeneous networking, which should be further investigated
to facilitate the deployment of mmWave communication systems in the future 5G
networks.Comment: 17 pages, 8 figures, 7 tables, Journal pape
An alternating direction algorithm for hybrid precoding and combining in millimeter wave MIMO systems
Millimeter-wave (mmWave) technology is one of the most promising candidates for future wireless communication systems as it can offer large underutilized bandwidths and eases the implementation of large antenna arrays which are required to help overcome the severe signal attenuation that occurs at these frequencies. To reduce the high cost and power consumption of a fully digital mmWave precoder and combiner, hybrid analog/digital designs based on analog phase shifters are often adopted. In this work we derive an iterative algorithm for the hybrid precoding and combining design for spatial multiplexing in mmWave massive multiple-input multiple-output (MIMO) systems. To cope with the difficulty of handling the hardware constraint imposed by the analog phase shifters we use the alternating direction method of the multipliers (ADMM) to split the hybrid design problem into a sequence of smaller subproblems. This results in an iterative algorithm where the design of the analog precoder/combiner consists of a closed form solution followed by a simple projection over the set of matrices with equal magnitude elements. It is initially developed for the fully-connected structure and then extended to the partially-connected architecture which allows simpler hardware implementation. Furthermore, to cope with the more likely wideband scenarios where the channel is frequency selective, we also extend the algorithm to an orthogonal frequency division multiplexing (OFDM) based mmWave system. Simulation results in different scenarios show that the proposed design algorithms are capable of achieving performances close to the optimal fully digital solution and can work with a broad range of configuration of antennas, RF chains and data streams.info:eu-repo/semantics/acceptedVersio
MmWave Amplify-and-Forward MIMO Relay Networks with Hybrid Precoding/Combining Design
In this paper, we consider the amplify-and-forward relay networks in mmWave
systems and propose a hybrid precoder/combiner design approach. The phase-only
RF precoding/combining matrices are first designed to support multi-stream
transmission, where we compensate the phase for the eigenmodes of the channel.
Then, the baseband precoders/combiners are performed to achieve the maximum
mutual information. Based on the data processing inequality for the mutual
information, we first jointly design the baseband source and relay nodes to
maximize the mutual information before the destination baseband receiver. The
proposed low-complexity iterative algorithm for the source and relay nodes is
based on the equivalence between mutual information maximization and the
weighted MMSE. After we obtain the optimal precoder and combiner for the source
and relay nodes, we implement the MMSE-SIC filter at the baseband receiver to
keep the mutual information unchanged, thus obtaining the optimal mutual
information for the whole relay system. Simulation results show that our
algorithm achieves better performance with lower complexity compared with other
algorithms in the literature. In addition, we also propose a robust joint
transceiver design for imperfect channel state information
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