2,401 research outputs found
A New SLNR-based Linear Precoding for Downlink Multi-User Multi-Stream MIMO Systems
Signal-to-leakage-and-noise ratio (SLNR) is a promising criterion for linear
precoder design in multi-user (MU) multiple-input multiple-output (MIMO)
systems. It decouples the precoder design problem and makes closed-form
solution available. In this letter, we present a new linear precoding scheme by
slightly relaxing the SLNR maximization for MU-MIMO systems with multiple data
streams per user. The precoding matrices are obtained by a general form of
simultaneous diagonalization of two Hermitian matrices. The new scheme reduces
the gap between the per-stream effective channel gains, an inherent limitation
in the original SLNR precoding scheme. Simulation results demonstrate that the
proposed precoding achieves considerable gains in error performance over the
original one for multi-stream transmission while maintaining almost the same
achievable sum-rate.Comment: 8 pages, 1 figur
Large System Analysis of Power Normalization Techniques in Massive MIMO
Linear precoding has been widely studied in the context of Massive
multiple-input-multiple-output (MIMO) together with two common power
normalization techniques, namely, matrix normalization (MN) and vector
normalization (VN). Despite this, their effect on the performance of Massive
MIMO systems has not been thoroughly studied yet. The aim of this paper is to
fulfill this gap by using large system analysis. Considering a system model
that accounts for channel estimation, pilot contamination, arbitrary pathloss,
and per-user channel correlation, we compute tight approximations for the
signal-to-interference-plus-noise ratio and the rate of each user equipment in
the system while employing maximum ratio transmission (MRT), zero forcing (ZF),
and regularized ZF precoding under both MN and VN techniques. Such
approximations are used to analytically reveal how the choice of power
normalization affects the performance of MRT and ZF under uncorrelated fading
channels. It turns out that ZF with VN resembles a sum rate maximizer while it
provides a notion of fairness under MN. Numerical results are used to validate
the accuracy of the asymptotic analysis and to show that in Massive MIMO,
non-coherent interference and noise, rather than pilot contamination, are often
the major limiting factors of the considered precoding schemes.Comment: 12 pages, 3 figures, Accepted for publication in the IEEE
Transactions on Vehicular Technolog
On Robustness of Massive MIMO Systems Against Passive Eavesdropping under Antenna Selection
In massive MIMO wiretap settings, the base station can significantly suppress
eavesdroppers by narrow beamforming toward legitimate terminals. Numerical
investigations show that by this approach, secrecy is obtained at no
significant cost. We call this property of massive MIMO systems `secrecy for
free' and show that it not only holds when all the transmit antennas at the
base station are employed, but also when only a single antenna is set active.
Using linear precoding, the information leakage to the eavesdroppers can be
sufficiently diminished, when the total number of available transmit antennas
at the base station grows large, even when only a fixed number of them are
selected. This result indicates that passive eavesdropping has no significant
impact on massive MIMO systems, regardless of the number of active transmit
antennas.Comment: 7 pages, 2 figures; To be presented in IEEE Global Communications
Conference (Globecom) 2018 in Abu Dhabi, UA
Achievable Rates of Multi-User Millimeter Wave Systems with Hybrid Precoding
Millimeter wave (mmWave) systems will likely employ large antenna arrays at
both the transmitters and receivers. A natural application of antenna arrays is
simultaneous transmission to multiple users, which requires multi-user
precoding at the transmitter. Hardware constraints, however, make it difficult
to apply conventional lower frequency MIMO precoding techniques at mmWave. This
paper proposes and analyzes a low complexity hybrid analog/digital beamforming
algorithm for downlink multi-user mmWave systems. Hybrid precoding involves a
combination of analog and digital processing that is motivated by the
requirement to reduce the power consumption of the complete radio frequency and
mixed signal hardware. The proposed algorithm configures hybrid precoders at
the transmitter and analog combiners at multiple receivers with a small
training and feedback overhead. For this algorithm, we derive a lower bound on
the achievable rate for the case of single-path channels, show its asymptotic
optimality at large numbers of antennas, and make useful insights for more
general cases. Simulation results show that the proposed algorithm offers
higher sum rates compared with analog-only beamforming, and approaches the
performance of the unconstrained digital precoding solutions.Comment: to be presented in IEEE ICC 2015 - Workshop on 5G & Beyond - Enabling
Technologies and Application
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