347 research outputs found
Spectral Efficiency and Energy Efficiency Tradeoff in Massive MIMO Downlink Transmission with Statistical CSIT
As a key technology for future wireless networks, massive multiple-input
multiple-output (MIMO) can significantly improve the energy efficiency (EE) and
spectral efficiency (SE), and the performance is highly dependant on the degree
of the available channel state information (CSI). While most existing works on
massive MIMO focused on the case where the instantaneous CSI at the transmitter
(CSIT) is available, it is usually not an easy task to obtain precise
instantaneous CSIT. In this paper, we investigate EE-SE tradeoff in single-cell
massive MIMO downlink transmission with statistical CSIT. To this end, we aim
to optimize the system resource efficiency (RE), which is capable of striking
an EE-SE balance. We first figure out a closed-form solution for the
eigenvectors of the optimal transmit covariance matrices of different user
terminals, which indicates that beam domain is in favor of performing RE
optimal transmission in massive MIMO downlink. Based on this insight, the RE
optimization precoding design is reduced to a real-valued power allocation
problem. Exploiting the techniques of sequential optimization and random matrix
theory, we further propose a low-complexity suboptimal two-layer
water-filling-structured power allocation algorithm. Numerical results
illustrate the effectiveness and near-optimal performance of the proposed
statistical CSI aided RE optimization approach.Comment: Typos corrected. 14 pages, 7 figures. Accepted for publication on
IEEE Transactions on Signal Processing. arXiv admin note: text overlap with
arXiv:2002.0488
Energy Efficiency Optimization for Downlink Massive MIMO With Statistical CSIT
We investigate energy efficiency (EE) optimization for single-cell massive
multiple-input multiple-output (MIMO) downlink transmission with only
statistical channel state information (CSI) available at the base station. We
first show that beam domain transmission is favorable for energy efficiency in
the massive MIMO downlink, by deriving a closed-form solution for the
eigenvectors of the optimal transmit covariance matrix. With this conclusion,
the EE optimization problem is reduced to a real-valued power allocation
problem, which is much easier to tackle than the original large-dimensional
complex matrix-valued precoding design problem. We further propose an iterative
water-filling-structured beam domain power allocation algorithm with low
complexity and guaranteed convergence, exploiting the techniques from
sequential optimization, fractional optimization, and random matrix theory.
Numerical results demonstrate the near-optimal performance of our proposed
statistical CSI aided EE optimization approach.Comment: 32 pages, 6 figures. Accepted for publication in the IEEE
Transactions on Wireless Communication
Rate Splitting for MIMO Wireless Networks: A Promising PHY-Layer Strategy for LTE Evolution
MIMO processing plays a central part towards the recent increase in spectral
and energy efficiencies of wireless networks. MIMO has grown beyond the
original point-to-point channel and nowadays refers to a diverse range of
centralized and distributed deployments. The fundamental bottleneck towards
enormous spectral and energy efficiency benefits in multiuser MIMO networks
lies in a huge demand for accurate channel state information at the transmitter
(CSIT). This has become increasingly difficult to satisfy due to the increasing
number of antennas and access points in next generation wireless networks
relying on dense heterogeneous networks and transmitters equipped with a large
number of antennas. CSIT inaccuracy results in a multi-user interference
problem that is the primary bottleneck of MIMO wireless networks. Looking
backward, the problem has been to strive to apply techniques designed for
perfect CSIT to scenarios with imperfect CSIT. In this paper, we depart from
this conventional approach and introduce the readers to a promising strategy
based on rate-splitting. Rate-splitting relies on the transmission of common
and private messages and is shown to provide significant benefits in terms of
spectral and energy efficiencies, reliability and CSI feedback overhead
reduction over conventional strategies used in LTE-A and exclusively relying on
private message transmissions. Open problems, impact on standard specifications
and operational challenges are also discussed.Comment: accepted to IEEE Communication Magazine, special issue on LTE
Evolutio
MMSE precoder for massive MIMO using 1-bit quantization
We propose a novel linear minimum-mean-squared-error (MMSE) precoder design
for a downlink (DL) massive multiple-input-multiple-output (MIMO) scenario. For
economical and computational efficiency reasons low resolution 1-bit
digital-to-analog (DAC) and analog-to-digital (ADC) converters are used. This
comes at the cost of performance gain that can be recovered by the large number
of antennas deployed at the base station (BS) and an appropiate precoder design
to mitigate the distortions due to the coarse quantization. The proposed
precoder takes the quantization non-linearities into account and is split into
a digital precoder and an analog precoder. We formulate the two-stage precoding
problem such that the MSE of the users is minimized under the 1-bit constraint.
In the simulations, we compare the new optimized precoding scheme with
previously proposed linear precoders in terms of uncoded bit error ratio (BER).Comment: Presented in ICASSP 2016, 20-25 March 2016, Shanghai, Chin
MMSE precoder for massive MIMO using 1-bit quantization
We propose a novel linear minimum-mean-squared-error (MMSE) precoder design
for a downlink (DL) massive multiple-input-multiple-output (MIMO) scenario. For
economical and computational efficiency reasons low resolution 1-bit
digital-to-analog (DAC) and analog-to-digital (ADC) converters are used. This
comes at the cost of performance gain that can be recovered by the large number
of antennas deployed at the base station (BS) and an appropiate precoder design
to mitigate the distortions due to the coarse quantization. The proposed
precoder takes the quantization non-linearities into account and is split into
a digital precoder and an analog precoder. We formulate the two-stage precoding
problem such that the MSE of the users is minimized under the 1-bit constraint.
In the simulations, we compare the new optimized precoding scheme with
previously proposed linear precoders in terms of uncoded bit error ratio (BER).Comment: Presented in ICASSP 2016, 20-25 March 2016, Shanghai, Chin
Multiple Access in Aerial Networks: From Orthogonal and Non-Orthogonal to Rate-Splitting
Recently, interest on the utilization of unmanned aerial vehicles (UAVs) has
aroused. Specifically, UAVs can be used in cellular networks as aerial users
for delivery, surveillance, rescue search, or as an aerial base station (aBS)
for communication with ground users in remote uncovered areas or in dense
environments requiring prompt high capacity. Aiming to satisfy the high
requirements of wireless aerial networks, several multiple access techniques
have been investigated. In particular, space-division multiple access(SDMA) and
power-domain non-orthogonal multiple access (NOMA) present promising
multiplexing gains for aerial downlink and uplink. Nevertheless, these gains
are limited as they depend on the conditions of the environment. Hence, a
generalized scheme has been recently proposed, called rate-splitting multiple
access (RSMA), which is capable of achieving better spectral efficiency gains
compared to SDMA and NOMA. In this paper, we present a comprehensive survey of
key multiple access technologies adopted for aerial networks, where aBSs are
deployed to serve ground users. Since there have been only sporadic results
reported on the use of RSMA in aerial systems, we aim to extend the discussion
on this topic by modelling and analyzing the weighted sum-rate performance of a
two-user downlink network served by an RSMA-based aBS. Finally, related open
issues and future research directions are exposed.Comment: 16 pages, 6 figures, submitted to IEEE Journa
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