934 research outputs found
An Overview of Signal Processing Techniques for Millimeter Wave MIMO Systems
Communication at millimeter wave (mmWave) frequencies is defining a new era
of wireless communication. The mmWave band offers higher bandwidth
communication channels versus those presently used in commercial wireless
systems. The applications of mmWave are immense: wireless local and personal
area networks in the unlicensed band, 5G cellular systems, not to mention
vehicular area networks, ad hoc networks, and wearables. Signal processing is
critical for enabling the next generation of mmWave communication. Due to the
use of large antenna arrays at the transmitter and receiver, combined with
radio frequency and mixed signal power constraints, new multiple-input
multiple-output (MIMO) communication signal processing techniques are needed.
Because of the wide bandwidths, low complexity transceiver algorithms become
important. There are opportunities to exploit techniques like compressed
sensing for channel estimation and beamforming. This article provides an
overview of signal processing challenges in mmWave wireless systems, with an
emphasis on those faced by using MIMO communication at higher carrier
frequencies.Comment: Submitted to IEEE Journal of Selected Topics in Signal Processin
Codeword Selection and Hybrid Precoding for Multiuser Millimeter Wave Massive MIMO Systems
Aiming at maximizing the achievable sum-rate of wideband multiuser mmWave
massive MIMO systems, the hybrid precoding is studied. Since each computation
of the achievable sum-rate can be performed only after the analog precoder and
digital precoder are both determined, the maximization of the achievable
sum-rate has intractable computational complexity. By introducing the
interference free (IF) achievable sum-rate, the design of the analog and
digital precoders can be decoupled. To avoid the beam conflict and maximize the
IF achievable sum-rate, a Hungarian-based codeword selection algorithm is
proposed for the analog precoding design. Simulation results verify the
effectiveness of the proposed scheme and show that better performance can be
achieved compared with existing schemes
A Hardware-Efficient Hybrid Beamforming Solution for mmWave MIMO Systems
In millimeter wave (mmWave) communication systems, existing hybrid
beamforming solutions generally require a large number of high-resolution phase
shifters (PSs) to realize analog beamformers, which still suffer from high
hardware complexity and power consumption. Targeting at this problem, this
article introduces a novel hardware-efficient hybrid precoding/combining
architecture, which only employs a limited number of simple phase over-samplers
(POSs) and a switch (SW) network to achieve maximum hardware efficiency while
maintaining satisfactory spectral efficiency performance. The POS can be
realized by a simple circuit and simultaneously outputs several parallel
signals with different phases. With the aid of a simple switch network, the
analog precoder/combiner is implemented by feeding the signals with appropriate
phases to antenna arrays or RF chains. We analyze the design challenges of this
POS-SW-based hybrid beamforming architecture and present potential solutions to
the fundamental issues, especially the precoder/combiner design and the channel
estimation strategy. Simulation results demonstrate that this
hardware-efficient structure can achieve comparable spectral efficiency but
much higher energy efficiency than that of the traditional structures
Dynamic Subarrays for Hybrid Precoding in Wideband mmWave MIMO Systems
Hybrid analog/digital precoding architectures can address the trade-off
between achievable spectral efficiency and power consumption in large-scale
MIMO systems. This makes it a promising candidate for millimeter wave systems,
which require deploying large antenna arrays at both the transmitter and
receiver to guarantee sufficient received signal power. Most prior work on
hybrid precoding focused on narrowband channels and assumed fully-connected
hybrid architectures. MmWave systems, though, are expected to be wideband with
frequency selectivity. In this paper, a closed-form solution for
fully-connected OFDM-based hybrid analog/digital precoding is developed for
frequency selective mmWave systems. This solution is then extended to
partially-connected but fixed architectures in which each RF chain is connected
to a specific subset of the antennas. The derived solutions give insights into
how the hybrid subarray structures should be designed. Based on them, a novel
technique that dynamically constructs the hybrid subarrays based on the
long-term channel characteristics is developed. Simulation results show that
the proposed hybrid precoding solutions achieve spectral efficiencies close to
that obtained with fully-digital architectures in wideband mmWave channels.
Further, the results indicate that the developed dynamic subarray solution
outperforms the fixed hybrid subarray structures in various system and channel
conditions.Comment: submitted to IEEE Transactions on Wireless Communication
Frequency Selective Hybrid Precoding for Limited Feedback Millimeter Wave Systems
Hybrid analog/digital precoding offers a compromise between hardware
complexity and system performance in millimeter wave (mmWave) systems. This
type of precoding allows mmWave systems to leverage large antenna array gains
that are necessary for sufficient link margin, while permitting low cost and
power consumption hardware. Most prior work has focused on hybrid precoding for
narrowband mmWave systems, with perfect or estimated channel knowledge at the
transmitter. MmWave systems, however, will likely operate on wideband channels
with frequency selectivity. Therefore, this paper considers wideband mmWave
systems with a limited feedback channel between the transmitter and receiver.
First, the optimal hybrid precoding design for a given RF codebook is derived.
This provides a benchmark for any other heuristic algorithm and gives useful
insights into codebook designs. Second, efficient hybrid analog/digital
codebooks are developed for spatial multiplexing in wideband mmWave systems.
Finally, a low-complexity yet near-optimal greedy frequency selective hybrid
precoding algorithm is proposed based on Gram-Schmidt orthogonalization.
Simulation results show that the developed hybrid codebooks and precoder
designs achieve very good performance compared with the unconstrained solutions
while requiring much less complexity.Comment: 42 pages, 8 figures, IEEE Transactions on Communications (Invited
Paper) [Some typos are fixed in this version
Multi-User Hybrid Precoding for Dynamic Subarrays in MmWave Massive MIMO Systems
Dynamic subarray achieves a compromise between sum rate and hardware
complexity for millimeter wave (mmWave) massive multiple-input multiple-output
(MIMO) systems in which antenna elements are dynamically partitioned to radio
frequency (RF) chain according to the channel state information.} However,
multi-user hybrid precoding for the dynamic subarray is intractable to solve as
the antenna partitioning would result in the user unfairness and multi-user
interference (MUI). In this paper, a novel multi-user hybrid precoding
framework is proposed for the dynamic subarray architecture. Different from the
existing schemes, the base station (BS) firstly selects the multi-user set
based on the analog effective channel. And then the antenna partitioning
algorithm allocates each antenna element to RF chain according to the maximal
increment of the signal to the interference noise ratio (SINR). Finally, the
hybrid precoding is optimized for the dynamic subarray architecture. By
calculating SINRs on the analog effective channels of the selected users, the
antenna partitioning can greatly reduce computation complexity and the size of
the search space. Moreover, it also guarantees the user fairness since each
antenna element is allocated to acquire the maximal SINR increment of all
selected users. \textcolor{blue}{Extensive simulation results demonstrate that
both the energy efficiency and sum rate of the proposed solution obviously
outperforms that of the fixed subarrays, and obtains higher energy efficiency
with slight loss of sum rate compared with the fully-connected architecture
Channel Tracking and Hybrid Precoding for Wideband Hybrid Millimeter Wave MIMO Systems
A major source of difficulty when operating with large arrays at mmWave
frequencies is to estimate the wideband channel, since the use of hybrid
architectures acts as a compression stage for the received signal. Moreover,
the channel has to be tracked and the antenna arrays regularly reconfigured to
obtain appropriate beamforming gains when a mobile setting is considered. In
this paper, we focus on the problem of channel tracking for frequency-selective
mmWave channels, and propose two novel channel tracking algorithms that
leverage prior statistical information on the angles-of-arrival and
angles-of-departure. Exploiting this prior information, we also propose a
precoding and combining design method to increase the received SNR during
channel tracking, such that near-optimum data rates can be obtained with
low-overhead. In our numerical results, we analyze the performance of our
proposed algorithms for different system parameters. Simulation results show
that, using channel realizations extracted from the 5G New Radio channel model,
our proposed channel tracking framework is able to achieve near-optimum data
rates
Channel Estimation and Hybrid Precoding for Distributed Phased Arrays Based MIMO Wireless Communications
Distributed phased arrays based multiple-input multiple-output (DPA-MIMO) is
a newly introduced architecture that enables both spatial multiplexing and
beamforming while facilitating highly reconfigurable hardware implementation in
millimeter-wave (mmWave) frequency bands. With a DPA-MIMO system, we focus on
channel state information (CSI) acquisition and hybrid precoding. As benefited
from a coordinated and open-loop pilot beam pattern design, all the sub-arrays
can perform channel sounding with less training overhead compared with the
traditional orthogonal operation of each sub-array. Furthermore, two sparse
channel recovery algorithms, known as joint orthogonal matching pursuit (JOMP)
and joint sparse Bayesian learning with reweighting (JSBL-),
are proposed to exploit the hidden structured sparsity in the beam-domain
channel vector. Finally, successive interference cancellation (SIC) based
hybrid precoding through sub-array grouping is illustrated for the DPA-MIMO
system, which decomposes the joint sub-array RF beamformer design into an
interactive per-sub-array-group handle. Simulation results show that the
proposed two channel estimators fully take advantage of the partial coupling
characteristic of DPA-MIMO channels to perform channel recovery, and the
proposed hybrid precoding algorithm is suitable for such array-of-sub-arrays
architecture with satisfactory performance and low complexity.Comment: accepted by IEEE Transactions on Vehicular Technolog
Beamforming Algorithm for Multiuser Wideband Millimeter-Wave Systems with Hybrid and Subarray Architectures
We present a beamforming algorithm for multiuser wideband millimeter wave
(mmWave) communication systems where one access point uses hybrid
analog/digital beamforming while multiple user stations have phased-arrays with
a single RF chain. The algorithm operates in a more general mode than others
available in literature and has lower computational complexity and training
overhead. Throughout the paper, we describe: i) the construction of novel
beamformer sets (codebooks) with wide sector beams and narrow beams based on
the orthogonality property of beamformer vectors, ii) a beamforming algorithm
that uses training transmissions over the codebooks to select the beamformers
that maximize the received sumpower along the bandwidth, and iii) a numerical
validation of the algorithm in standard indoor scenarios for mmWave WLANs using
channels obtained with both statistical and raytracing models. Our algorithm is
designed to serve multiple users in a wideband OFDM system and does not require
channel matrix knowledge or a particular channel structure. Moreover, we
incorporate antenna-specific aspects in the analysis, such as antenna coupling,
element radiation pattern, and beam squint. Although there are no other
solutions for the general system studied in this paper, we characterize the
algorithm's achievable rate and show that it attains more than 70 percent of
the spectral efficiency (between 1.5 and 3 dB SNR loss) with respect to ideal
fully-digital beamforming in the analyzed scenarios. We also show that our
algorithm has similar sum-rate performance as other solutions in the literature
for some special cases, while providing significantly lower computational
complexity (with a linear dependence on the number of antennas) and shorter
training overhead
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
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