495 research outputs found
Hybrid Beamforming for Large Antenna Arrays with Phase Shifter Selection
This paper proposes an asymptotically optimal hybrid beamforming solution for
large antenna arrays by exploiting the properties of the singular vectors of
the channel matrix. It is shown that the elements of the channel matrix with
Rayleigh fading follow a normal distribution when large antenna arrays are
employed. The proposed beamforming algorithm is effective in both sparse and
rich propagation environments, and is applicable for both point-to-point and
multiuser scenarios. In addition, a closed-form expression and a lower-bound
for the achievable rates are derived when analog and digital phase shifters are
employed. It is shown that the performance of the hybrid beamformers using
phase shifters with more than 2-bits resolution is comparable with analog phase
shifting. A novel phase shifter selection scheme that reduces the power
consumption at the phase shifter network is proposed when the wireless channel
is modeled by Rayleigh fading. Using this selection scheme, the spectral
efficiency can be increased as the power consumption in the phase shifter
network reduces. Compared to the scenario that all of the phase shifters are in
operation, the simulation results indicate that the spectral efficiency
increases when up to 50% of phase shifters are turned off.Comment: Accepted to Transactions on Wireless Communications, 201
Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs
With the congestion of the sub-6 GHz spectrum, the interest in massive
multiple-input multiple-output (MIMO) systems operating on millimeter wave
spectrum grows. In order to reduce the power consumption of such massive MIMO
systems, hybrid analog/digital transceivers and application of low-resolution
digital-to-analog/analog-to-digital converters have been recently proposed. In
this work, we investigate the energy efficiency of quantized hybrid
transmitters equipped with a fully/partially-connected phase-shifting network
composed of active/passive phase-shifters and compare it to that of quantized
digital precoders. We introduce a quantized single-user MIMO system model based
on an additive quantization noise approximation considering realistic power
consumption and loss models to evaluate the spectral and energy efficiencies of
the transmit precoding methods. Simulation results show that
partially-connected hybrid precoders can be more energy-efficient compared to
digital precoders, while fully-connected hybrid precoders exhibit poor energy
efficiency in general. Also, the topology of phase-shifting components offers
an energy-spectral efficiency trade-off: active phase-shifters provide higher
data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin
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