7,112 research outputs found
A software definable MIMO testbed: architecture and functionality
Following the intensive theoretical studies of recently emerged MIMO technology, a variety of performance measures become important to investigate the challenges and trade-offs at various levels throughout MIMO system design process. This paper presents a review of the MIMO testbed recently set up at King’s College London. The architecture that distinguishes the testbed as a flexible and reconfigurable system is first preseneted. This includes both the hardware and software aspects, and is followed by a discussion of implementation methods and evaluation of system research capabilities
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
Hybrid Beamforming via the Kronecker Decomposition for the Millimeter-Wave Massive MIMO Systems
Despite its promising performance gain, the realization of mmWave massive
MIMO still faces several practical challenges. In particular, implementing
massive MIMO in the digital domain requires hundreds of RF chains matching the
number of antennas. Furthermore, designing these components to operate at the
mmWave frequencies is challenging and costly. These motivated the recent
development of hybrid-beamforming where MIMO processing is divided for separate
implementation in the analog and digital domains, called the analog and digital
beamforming, respectively. Analog beamforming using a phase array introduces
uni-modulus constraints on the beamforming coefficients, rendering the
conventional MIMO techniques unsuitable and call for new designs. In this
paper, we present a systematic design framework for hybrid beamforming for
multi-cell multiuser massive MIMO systems over mmWave channels characterized by
sparse propagation paths. The framework relies on the decomposition of analog
beamforming vectors and path observation vectors into Kronecker products of
factors being uni-modulus vectors. Exploiting properties of Kronecker mixed
products, different factors of the analog beamformer are designed for either
nulling interference paths or coherently combining data paths. Furthermore, a
channel estimation scheme is designed for enabling the proposed hybrid
beamforming. The scheme estimates the AoA of data and interference paths by
analog beam scanning and data-path gains by analog beam steering. The
performance of the channel estimation scheme is analyzed. In particular, the
AoA spectrum resulting from beam scanning, which displays the magnitude
distribution of paths over the AoA range, is derived in closed-form. It is
shown that the inter-cell interference level diminishes inversely with the
array size, the square root of pilot sequence length and the spatial separation
between paths.Comment: Submitted to IEEE JSAC Special Issue on Millimeter Wave
Communications for Future Mobile Networks, minor revisio
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