21,603 research outputs found
A Scalable Correlator Architecture Based on Modular FPGA Hardware, Reuseable Gateware, and Data Packetization
A new generation of radio telescopes is achieving unprecedented levels of
sensitivity and resolution, as well as increased agility and field-of-view, by
employing high-performance digital signal processing hardware to phase and
correlate large numbers of antennas. The computational demands of these imaging
systems scale in proportion to BMN^2, where B is the signal bandwidth, M is the
number of independent beams, and N is the number of antennas. The
specifications of many new arrays lead to demands in excess of tens of PetaOps
per second.
To meet this challenge, we have developed a general purpose correlator
architecture using standard 10-Gbit Ethernet switches to pass data between
flexible hardware modules containing Field Programmable Gate Array (FPGA)
chips. These chips are programmed using open-source signal processing libraries
we have developed to be flexible, scalable, and chip-independent. This work
reduces the time and cost of implementing a wide range of signal processing
systems, with correlators foremost among them,and facilitates upgrading to new
generations of processing technology. We present several correlator
deployments, including a 16-antenna, 200-MHz bandwidth, 4-bit, full Stokes
parameter application deployed on the Precision Array for Probing the Epoch of
Reionization.Comment: Accepted to Publications of the Astronomy Society of the Pacific. 31
pages. v2: corrected typo, v3: corrected Fig. 1
Applying autonomy to distributed satellite systems: Trends, challenges, and future prospects
While monolithic satellite missions still pose significant advantages in terms of accuracy and
operations, novel distributed architectures are promising improved flexibility, responsiveness,
and adaptability to structural and functional changes. Large satellite swarms, opportunistic satellite
networks or heterogeneous constellations hybridizing small-spacecraft nodes with highperformance
satellites are becoming feasible and advantageous alternatives requiring the adoption
of new operation paradigms that enhance their autonomy. While autonomy is a notion that
is gaining acceptance in monolithic satellite missions, it can also be deemed an integral characteristic
in Distributed Satellite Systems (DSS). In this context, this paper focuses on the motivations
for system-level autonomy in DSS and justifies its need as an enabler of system qualities. Autonomy
is also presented as a necessary feature to bring new distributed Earth observation functions
(which require coordination and collaboration mechanisms) and to allow for novel structural
functions (e.g., opportunistic coalitions, exchange of resources, or in-orbit data services). Mission
Planning and Scheduling (MPS) frameworks are then presented as a key component to implement
autonomous operations in satellite missions. An exhaustive knowledge classification explores the
design aspects of MPS for DSS, and conceptually groups them into: components and organizational
paradigms; problem modeling and representation; optimization techniques and metaheuristics;
execution and runtime characteristics and the notions of tasks, resources, and constraints.
This paper concludes by proposing future strands of work devoted to study the trade-offs of
autonomy in large-scale, highly dynamic and heterogeneous networks through frameworks that
consider some of the limitations of small spacecraft technologies.Postprint (author's final draft
A survey on OFDM-based elastic core optical networking
Orthogonal frequency-division multiplexing (OFDM) is a modulation technology that has been widely adopted in many new and emerging broadband wireless and wireline communication systems. Due to its capability to transmit a high-speed data stream using multiple spectral-overlapped lower-speed subcarriers, OFDM technology offers superior advantages of high spectrum efficiency, robustness against inter-carrier and inter-symbol interference, adaptability to server channel conditions, etc. In recent years, there have been intensive studies on optical OFDM (O-OFDM) transmission technologies, and it is considered a promising technology for future ultra-high-speed optical transmission. Based on O-OFDM technology, a novel elastic optical network architecture with immense flexibility and scalability in spectrum allocation and data rate accommodation could be built to support diverse services and the rapid growth of Internet traffic in the future. In this paper, we present a comprehensive survey on OFDM-based elastic optical network technologies, including basic principles of OFDM, O-OFDM technologies, the architectures of OFDM-based elastic core optical networks, and related key enabling technologies. The main advantages and issues of OFDM-based elastic core optical networks that are under research are also discussed
UDWDM-PON using low-cost coherent transceivers with limited tunability and heuristic DWA
A new Passive Optical Network (PON)
for access, making use of Ultra Dense Wavelength
Division Multiplexing (UDWDM) by densely spacing
channels at few GHz, and introducing the
“wavelength-to-the-user” concept, is proposed. The
key challenge will be developing low-cost coherent
transceivers, providing an excellent selectivity while
avoiding filters, and furnishing high sensitivity,
which will allow high splitting ratios, large number
of users and long distance reach. The Optical
Distribution Network (ODN) at the outside plant is
based on splitters and kept compatible with legacy
systems. Optical Network Unit (ONU) designs
realized with coherent transceivers using one or two
lasers are presented and the corresponding Optical
Line Terminal (OLT) architectures are introduced.
The ONUs at customer premises own lasers with
limited thermal tunability and their wavelengths are
randomly distributed in a band. By using heuristic
Dynamic Wavelength Assignment (DWA) schemes and
extending the original working band, the required
optical band is obtained and optimized. In activation
processes, ONU acceptances up to 99.9% are achieved.
Furthermore, in operation scenario under indoors
and also under outdoors environmental conditions,
ONU blocking probabilities below 0.1% and ONU
availability ratios (OARs) up to 99.9% are
demonstrated. The PON is dimensioned according to
the number of deployed users and system reach;
moreover, power safety and also fiber nonlinearities
constraints are evaluated, illustrating the
characteristics of the projected network. Finally, the
coexistence with legacy networks is discussed.Peer ReviewedPostprint (author's final draft
Dispersive Fourier Transformation for Versatile Microwave Photonics Applications
Abstract: Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an emerging technique for ultrafast signal generation and processing, and high-throughput real-time measurements, where the speed of traditional optical instruments falls short. In this paper, the principle and implementation methods of DFT are first introduced and the recent development in employing DFT technique for widespread microwave photonics applications are presented, with emphasis on real-time spectroscopy, microwave arbitrary waveform generation, and microwave spectrum sensing. Finally, possible future research directions for DFT-based microwave photonics techniques are discussed as well
Oxide Heterostructures from a Realistic Many-Body Perspective
Oxide heterostructures are a new class of materials by design, that open the
possibility for engineering challenging electronic properties, in particular
correlation effects beyond an effective single-particle description. This short
review tries to highlight some of the demanding aspects and questions,
motivated by the goal to describe the encountered physics from first
principles. The state-of-the-art methodology to approach realistic many-body
effects in strongly correlated oxides, the combination of density functional
theory with dynamical mean-field theory, will be briefly introduced. Discussed
examples deal with prominent Mott-band- and band-band-insulating type of oxide
heterostructures, where different electronic characteristics may be stabilized
within a single architectured oxide material.Comment: 19 pages, 9 figure
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