5 research outputs found
On Out-of-Band Emissions of Quantized Precoding in Massive MU-MIMO-OFDM
We analyze out-of-band (OOB) emissions in the massive multi-user (MU)
multiple-input multiple-output (MIMO) downlink. We focus on systems in which
the base station (BS) is equipped with low-resolution digital-to-analog
converters (DACs) and orthogonal frequency-division multiplexing (OFDM) is used
to communicate to the user equipments (UEs) over frequency-selective channels.
We demonstrate that analog filtering in combination with simple
frequency-domain digital predistortion (DPD) at the BS enables a significant
reduction of OOB emissions, but degrades the
signal-to-interference-noise-and-distortion ratio (SINDR) at the UEs and
increases the peak-to-average power ratio (PAR) at the BS. We use Bussgang's
theorem to characterize the tradeoffs between OOB emissions, SINDR, and PAR,
and to study the impact of analog filters and DPD on the error-rate performance
of the massive MU-MIMO-OFDM downlink. Our results show that by carefully tuning
the parameters of the analog filters, one can achieve a significant reduction
in OOB emissions with only a moderate degradation of error-rate performance and
PAR.Comment: Presented at the 2017 Asilomar Conference on Signals, Systems, and
Computers, 6 page
Reconsidering Linear Transmit Signal Processing in 1-Bit Quantized Multi-User MISO Systems
In this contribution, we investigate a coarsely quantized Multi-User
(MU)-Multiple Input Single Output (MISO) downlink communication system, where
we assume 1-Bit Digital-to-Analog Converters (DACs) at the Base Station (BS)
antennas. First, we analyze the achievable sum rate lower-bound using the
Bussgang decomposition. In the presence of the non-linear quanization, our
analysis indicates the potential merit of reconsidering traditional signal
processing techniques in coarsely quantized systems, i.e., reconsidering
transmit covariance matrices whose rank is equal to the rank of the channel.
Furthermore, in the second part of this paper, we propose a linear precoder
design which achieves the predicted increase in performance compared with a
state of the art linear precoder design. Moreover, our linear signal processing
algorithm allows for higher-order modulation schemes to be employed
Quantized Constant Envelope Precoding with PSK and QAM Signaling
Coarsely quantized massive Multiple-Input Multiple-Output (MIMO) systems are
gaining more interest due to their power efficiency. We present a new precoding
technique to mitigate the Multi-User Interference (MUI) and the quantization
distortions in a downlink Multi-User (MU) MIMO system with coarsely Quantized
Constant Envelope (QCE) signals at the transmitter. The transmit signal vector
is optimized for every desired received vector taking into account the QCE
constraint. The optimization is based on maximizing the safety margin to the
decision thresholds of the receiver constellation modulation. Simulation
results show a significant gain in terms of the uncoded Bit Error Ratio (BER)
compared to the existing linear precoding techniques