3,327 research outputs found
Digital Predistortion in Large-Array Digital Beamforming Transmitters
In this article, we propose a novel digital predistortion (DPD) solution that
allows to considerably reduce the complexity resulting from linearizing a set
of power amplifiers (PAs) in single-user large-scale digital beamforming
transmitters. In contrast to current state-of-the art solutions that assume a
dedicated DPD per power amplifier, which is unfeasible in the context of large
antenna arrays, the proposed solution only requires a single DPD in order to
linearize an arbitrary number of power amplifiers. To this end, the proposed
DPD predistorts the signal at the input of the digital precoder based on
minimizing the nonlinear distortion of the combined signal at the intended
receiver direction. This is a desirable feature, since the resulting emissions
in other directions get partially diluted due to less coherent superposition.
With this approach, only a single DPD is required, yielding great complexity
and energy savings.Comment: 8 pages, Accepted for publication in Asilomar Conference on Signals,
Systems, and Computer
Minimum BER Precoding in 1-Bit Massive MIMO Systems
1-bit digital-to-analog (DACs) and analog-to-digital converters (ADCs) are
gaining more interest in massive MIMO systems for economical and computational
efficiency. We present a new precoding technique to mitigate the
inter-user-interference (IUI) and the channel distortions in a 1-bit downlink
MUMISO system with QPSK symbols. The transmit signal vector is optimized taking
into account the 1-bit quantization. We develop a sort of mapping based on a
look-up table (LUT) between the input signal and the transmit signal. The LUT
is updated for each channel realization. Simulation results show a significant
gain in terms of the uncoded bit-error-ratio (BER) compared to the existing
linear precoding techniques.Comment: Presented in IEEE SAM 2016, 10th-13th July 2016, Rio De Janeiro,
Brazi
On the Impact of Hardware Impairments on Massive MIMO
Massive multi-user (MU) multiple-input multiple-output (MIMO) systems are one
possible key technology for next generation wireless communication systems.
Claims have been made that massive MU-MIMO will increase both the radiated
energy efficiency as well as the sum-rate capacity by orders of magnitude,
because of the high transmit directivity. However, due to the very large number
of transceivers needed at each base-station (BS), a successful implementation
of massive MU-MIMO will be contingent on of the availability of very cheap,
compact and power-efficient radio and digital-processing hardware. This may in
turn impair the quality of the modulated radio frequency (RF) signal due to an
increased amount of power-amplifier distortion, phase-noise, and quantization
noise.
In this paper, we examine the effects of hardware impairments on a massive
MU-MIMO single-cell system by means of theory and simulation. The simulations
are performed using simplified, well-established statistical hardware
impairment models as well as more sophisticated and realistic models based upon
measurements and electromagnetic antenna array simulations.Comment: 7 pages, 9 figures, Accepted for presentation at Globe-Com workshop
on Massive MIM
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