2,725 research outputs found
Wideband Channel Estimation for Hybrid Beamforming Millimeter Wave Communication Systems with Low-Resolution ADCs
A potential tremendous spectrum resource makes millimeter wave (mmWave)
communications a promising technology. High power consumption due to a large
number of antennas and analog-to-digital converters (ADCs) for beamforming to
overcome the large propagation losses is problematic in practice. As a hybrid
beamforming architecture and low-resolution ADCs are considered to reduce power
consumption, estimation of mmWave channels becomes challenging. We evaluate
several channel estimation algorithms for wideband mmWave systems with hybrid
beamforming and low-resolution ADCs. Through simulation, we show that 1)
infinite bit ADCs with least-squares estimation have worse channel estimation
performance than do one-bit ADCs with orthogonal matching pursuit (OMP) in an
SNR range of interest, 2) three- and four-bit quantizers can achieve channel
estimation performance close to the unquantized case when using OMP, 3) a
receiver with a single RF chain can yield better estimates than that with four
RF chains if enough frames are exploited, and 4) for one-bit ADCs, exploitation
of higher transmit power and more frames for performance enhancement adversely
affects estimation performance after a certain point.Comment: 6 pages, 8 figures, submitted to ICC 201
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
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
Wideband mmWave Channel Estimation for Hybrid Massive MIMO with Low-Precision ADCs
In this article, we investigate channel estimation for wideband
millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) under
hybrid architecture with lowprecision analog-to-digital converters (ADCs). To
design channel estimation for the hybrid structure, both analog processing
components and frequency-selective digital combiners need to be optimized. The
proposed channel estimator follows the typical linear-minimum-mean-square-error
(LMMSE) structure and applies for an arbitrary channel model. Moreover, for
sparsity channels as in mmWave, the proposed estimator performs more
efficiently by incorporating orthogonal matching pursuit (OMP) to mitigate
quantization noise caused by low-precision ADCs. Consequently, the proposed
estimator outperforms conventional ones as demonstrated by computer simulation
results
Hybrid Analog-Digital Channel Estimation and Beamforming: Training-Throughput Tradeoff
This paper designs hybrid analog-digital channel estimation and beamforming
techniques for multiuser massive multiple input multiple output (MIMO) systems
with limited number of radio frequency (RF) chains. For these systems, first we
design novel minimum mean square error (MMSE) hybrid analog-digital channel
estimator by considering both perfect and imperfect channel covariance matrix
knowledge cases. Then, we utilize the estimated channels to enable beamforming
for data transmission. When the channel covariance matrices of all user
equipments (UEs) are known perfectly, we show that there is a tradeoff between
the training duration and throughput. Specifically, we exploit that the optimal
training duration that maximizes the throughput depends on the covariance
matrices of all UEs, number of RF chains and channel coherence time (). We
also show that the training time optimization problem can be formulated as a
concave maximization problem {for some system parameter settings} where its
global optimal solution is obtained efficiently using existing tools. In
particular, when the base station equipped with antennas and RF chain
is serving one single antenna UE, symbol periods () and signal
to noise ratio of dB, we have found that the optimal training durations are
and for highly correlated and uncorrelated Rayleigh fading
channel coefficients, respectively. The analytical expressions are validated by
performing numerical and extensive Monte Carlo simulations.Comment: IEEE Transactions on Communication (To appear
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
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
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
Wideband Hybrid Precoding for Next-Generation Backhaul/Fronthaul Based on mmWave FD-MIMO
Millimeter-wave (mmWave) communication is considered as an indispensable
technique for the next-generation backhaul/fronthaul network thanks to its
large transmission bandwidth. Especially for heterogeneous network (HetNet),
the mmWave full-dimension (FD)-MIMO is exploited to establish the
backhaul/fronthaul link between phantom-cell base stations (BSs) and macro-cell
BSs, where an efficient precoding is prerequisite. Against this background,
this paper proposes a principle component analysis (PCA)-based hybrid precoding
for wideband mmWave MIMO backhaul/fronthaul channels. We first propose an
optimal hybrid precoder by exploiting principal component analysis (PCA),
whereby the optimal high dimensional frequency-selective precoder are projected
to the low-dimensional frequency-flat precoder. Moreover, the combiner is
designed by leveraging the weighted PCA, where the covariance of received
signal is taken into account as weight to the optimal minimum mean square error
(MMSE) fully-digital combiner for further improved performance. Simulations
have confirmed that the proposed scheme outperforms conventional schemes in
spectral efficiency (SE) and bit-error-rate (BER) performance.Comment: This paper has been accepted by 2018 GLOBECOM worksho
Frequency-domain Compressive Channel Estimation for Frequency-Selective Hybrid mmWave MIMO Systems
Channel estimation is useful in millimeter wave (mmWave) MIMO communication
systems. Channel state information allows optimized designs of precoders and
combiners under different metrics such as mutual information or
signal-to-interference-noise (SINR) ratio. At mmWave, MIMO precoders and
combiners are usually hybrid, since this architecture provides a means to
trade-off power consumption and achievable rate. Channel estimation is
challenging when using these architectures, however, since there is no direct
access to the outputs of the different antenna elements in the array. The MIMO
channel can only be observed through the analog combining network, which acts
as a compression stage of the received signal. Most of prior work on channel
estimation for hybrid architectures assumes a frequency-flat mmWave channel
model. In this paper, we consider a frequency-selective mmWave channel and
propose compressed-sensing-based strategies to estimate the channel in the
frequency domain. We evaluate different algorithms and compute their complexity
to expose trade-offs in complexity-overhead-performance as compared to those of
previous approaches
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