562 research outputs found
Channel Estimation for Millimeter-Wave Massive MIMO with Hybrid Precoding over Frequency-Selective Fading Channels
Channel estimation for millimeter-wave (mmWave) massive MIMO with hybrid
precoding is challenging, since the number of radio frequency (RF) chains is
usually much smaller than that of antennas. To date, several channel estimation
schemes have been proposed for mmWave massive MIMO over narrow-band channels,
while practical mmWave channels exhibit the frequency-selective fading (FSF).
To this end, this letter proposes a multi-user uplink channel estimation scheme
for mmWave massive MIMO over FSF channels. Specifically, by exploiting the
angle-domain structured sparsity of mmWave FSF channels, a distributed
compressive sensing (DCS)-based channel estimation scheme is proposed.
Moreover, by using the grid matching pursuit strategy with adaptive measurement
matrix, the proposed algorithm can solve the power leakage problem caused by
the continuous angles of arrival or departure (AoA/AoD). Simulation results
verify that the good performance of the proposed solution.Comment: 4 pages, 3 figures, accepted by IEEE Communications Letters. This
paper may be the first one that investigates the frequency selective fading
channel estimation for mmWave massive MIMO systems with hybrid precoding. Key
words: Millimeter-wave (mmWave) massive MIMO, frequency-selective fading,
channel estimation, compressive sensing, hybrid precodin
On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming
This paper considers hybrid beamforming (HB) for downlink multiuser massive
multiple input multiple output (MIMO) systems with frequency selective
channels. For this system, first we determine the required number of radio
frequency (RF) chains and phase shifters (PSs) such that the proposed HB
achieves the same performance as that of the digital beamforming (DB) which
utilizes (number of transmitter antennas) RF chains. We show that the
performance of the DB can be achieved with our HB just by utilizing RF
chains and PSs, where is the rank of the
combined digital precoder matrices of all sub-carriers. Second, we provide a
simple and novel approach to reduce the number of PSs with only a negligible
performance degradation. Numerical results reveal that only PSs per RF
chain are sufficient for practically relevant parameter settings. Finally, for
the scenario where the deployed number of RF chains is less than ,
we propose a simple user scheduling algorithm to select the best set of users
in each sub-carrier. Simulation results validate theoretical expressions, and
demonstrate the superiority of the proposed HB design over the existing HB
designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision
Low-Complexity Hybrid Beamforming for Massive MIMO Systems in Frequency-Selective Channels
Hybrid beamforming for frequency-selective channels is a challenging problem
as the phase shifters provide the same phase shift to all of the subcarriers.
The existing approaches solely rely on the channel's frequency response and the
hybrid beamformers maximize the average spectral efficiency over the whole
frequency band. Compared to state-of-the-art, we show that substantial sum-rate
gains can be achieved, both for rich and sparse scattering channels, by jointly
exploiting the frequency and time domain characteristics of the massive
multiple-input multiple-output (MIMO) channels. In our proposed approach, the
radio frequency (RF) beamformer coherently combines the received symbols in the
time domain and, thus, it concentrates signal's power on a specific time
sample. As a result, the RF beamformer flattens the frequency response of the
"effective" transmission channel and reduces its root mean square delay spread.
Then, a baseband combiner mitigates the residual interference in the frequency
domain. We present the closed-form expressions of the proposed beamformer and
its performance by leveraging the favorable propagation condition of massive
MIMO channels and we prove that our proposed scheme can achieve the performance
of fully-digital zero-forcing when number of employed phase shifter networks is
twice the resolvable multipath components in the time domain.Comment: Accepted to IEEE Acces
A Generalized Framework on Beamformer Design and CSI Acquisition for Single-Carrier Massive MIMO Systems in Millimeter Wave Channels
In this paper, we establish a general framework on the reduced dimensional
channel state information (CSI) estimation and pre-beamformer design for
frequency-selective massive multiple-input multiple-output MIMO systems
employing single-carrier (SC) modulation in time division duplex (TDD) mode by
exploiting the joint angle-delay domain channel sparsity in millimeter (mm)
wave frequencies. First, based on a generic subspace projection taking the
joint angle-delay power profile and user-grouping into account, the reduced
rank minimum mean square error (RR-MMSE) instantaneous CSI estimator is derived
for spatially correlated wideband MIMO channels. Second, the statistical
pre-beamformer design is considered for frequency-selective SC massive MIMO
channels. We examine the dimension reduction problem and subspace (beamspace)
construction on which the RR-MMSE estimation can be realized as accurately as
possible. Finally, a spatio-temporal domain correlator type reduced rank
channel estimator, as an approximation of the RR-MMSE estimate, is obtained by
carrying out least square (LS) estimation in a proper reduced dimensional
beamspace. It is observed that the proposed techniques show remarkable
robustness to the pilot interference (or contamination) with a significant
reduction in pilot overhead
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