4,252 research outputs found
System Concepts for Bi- and Multi-Static SAR Missions
The performance and capabilities of bi- and multistatic spaceborne synthetic aperture radar (SAR) are analyzed. Such systems can be optimized for a broad range of applications like frequent monitoring, wide swath imaging, single-pass cross-track interferometry, along-track interferometry, resolution enhancement or radar tomography. Further potentials arises from digital beamforming on receive, which allows to gather additional information about the direction of the scattered radar echoes. This directional information can be used to suppress interferences, to improve geometric and radiometric resolution, or to increase the unambiguous swath width. Furthermore, a coherent combination of multiple receiver signals will allow for a suppression of azimuth ambiguities. For this, a reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of non-optimum receiver aperture displacements leading to a non-uniform sampling of the SAR signal. This algorithm has also a great potential for systems relying on the displaced phase center (DPC) technique, like the high resolution wide swath (HRWS) SAR or the split antenna approach in the TerraSAR-X and Radarsat II satellites
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
Advanced Synthetic Aperture Radar Based on Digital Beamforming and Waveform Diversity
This paper introduces innovative SAR system
concepts for the acquisition of high resolution radar images with
wide swath coverage from spaceborne platforms. The new concepts
rely on the combination of advanced multi-channel SAR front-end
architectures with novel operational modes. The architectures
differ regarding their implementation complexity and it is shown
that even a low number of channels is already well suited to
significantly improve the imaging performance and to overcome
fundamental limitations inherent to classical SAR systems. The
more advanced concepts employ a multidimensional encoding of
the transmitted waveforms to further improve the performance
and to enable a new class of hybrid SAR imaging modes that are
well suited to satisfy hitherto incompatible user requirements for
frequent monitoring and detailed mapping. Implementation
specific issues will be discussed and examples demonstrate the
potential of the new techniques for different remote sensing
applications
Interference Mitigation for Cognitive Radio MIMO Systems Based on Practical Precoding
In this paper, we propose two subspace-projection-based precoding schemes,
namely, full-projection (FP)- and partial-projection (PP)-based precoding, for
a cognitive radio multiple-input multiple-output (CR-MIMO) network to mitigate
its interference to a primary time-division-duplexing (TDD) system. The
proposed precoding schemes are capable of estimating interference channels
between CR and primary networks, and incorporating the interference from the
primary to the CR system into CR precoding via a novel sensing approach. Then,
the CR performance and resulting interference of the proposed precoding schemes
are analyzed and evaluated. By fully projecting the CR transmission onto a null
space of the interference channels, the FP-based precoding scheme can
effectively avoid interfering the primary system with boosted CR throughput.
While, the PP-based scheme is able to further improve the CR throughput by
partially projecting its transmission onto the null space.Comment: 12 pages, 4 figures, submitted to the IEEE Trans. Wireless
Communications in April 201
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