1,604 research outputs found
VADER - A Satellite Mission Concept For High Precision Dark Energy Studies
We present a satellite mission concept to measure the dark energy equation of
state parameter w with percent-level precision. The Very Ambitious Dark Energy
Research satellite (VADER) is a multi-wavelength survey mission joining X-ray,
optical, and IR instruments for a simultaneous spectral coverage from 4microns
(0.3eV) to 10keV over a field of view (FoV) of 1 square degree. VADER combines
several clean methods for dark energy studies, the baryonic acoustic
oscillations in the galaxy and galaxy cluster power spectrum and weak lensing,
for a joint analysis over an unrivalled survey volume. The payload consists of
two XMM-like X-ray telescopes with an effective area of 2,800cm^2 at 1.5keV and
state-of-the-art wide field DEPFET pixel detectors (0.1-10keV) in a curved
focal plane configuration to extend the FoV. The X-ray telescopes are
complemented by a 1.5m optical/IR telescope with 8 instruments for simultaneous
coverage of the same FoV from 0.3 to 4 microns. The 8 dichroic-separated bands
(u,g,r,z,J,H,K,L) provide accurate photometric galaxy redshifts, whereas the
diffraction-limited resolution of the central z-band allows precise shape
measurements for cosmic shear analysis.
The 5 year VADER survey will cover a contiguous sky area of 3,500 square
degrees to a depth of z~2 and will yield accurate photometric redshifts and
multi-wavelength object parameters for about 175,000 galaxy clusters, one
billion galaxies, and 5 million AGN. VADER will not only provide unprecedented
constraints on the nature of dark energy, but will additionally extend and
trigger a multitude of cosmic evolution studies to very large (>10 Gyrs)
look-back times.Comment: 14 pages, 7 figures, accepted for publication in the SPIE conference
proceeding
Improving the system capacity of broadband services using multiple high-altitude platforms
A method of significantly improving the capacity of high-altitude platform (HAP) communications networks operating in the millimeter-wave bands is presented. It is shown how constellations of HAPs can share a common frequency allocation by exploiting the directionality of the user antenna. The system capacity of such constellations is critically affected by the minimum angular separation of the HAPs and the sidelobe level of the user antenna. For typical antenna beamwidths of approximately 5/spl deg/ an inter-HAP spacing of 4 km is sufficient to deliver optimum performance. The aggregate bandwidth efficiency is evaluated, both theoretically using the Shannon equation, and using practical modulation and coding schemes, for multiple HAP configurations delivering either single or multiple cells. For the user antenna beamwidths used, it is shown that capacity increases are commensurate with the increase in the number of platforms, up to 10 HAPs. For increases beyond this the choice of constellation strategy becomes increasingly important
Revolutionizing Future Connectivity: A Contemporary Survey on AI-empowered Satellite-based Non-Terrestrial Networks in 6G
Non-Terrestrial Networks (NTN) are expected to be a critical component of 6th
Generation (6G) networks, providing ubiquitous, continuous, and scalable
services. Satellites emerge as the primary enabler for NTN, leveraging their
extensive coverage, stable orbits, scalability, and adherence to international
regulations. However, satellite-based NTN presents unique challenges, including
long propagation delay, high Doppler shift, frequent handovers, spectrum
sharing complexities, and intricate beam and resource allocation, among others.
The integration of NTNs into existing terrestrial networks in 6G introduces a
range of novel challenges, including task offloading, network routing, network
slicing, and many more. To tackle all these obstacles, this paper proposes
Artificial Intelligence (AI) as a promising solution, harnessing its ability to
capture intricate correlations among diverse network parameters. We begin by
providing a comprehensive background on NTN and AI, highlighting the potential
of AI techniques in addressing various NTN challenges. Next, we present an
overview of existing works, emphasizing AI as an enabling tool for
satellite-based NTN, and explore potential research directions. Furthermore, we
discuss ongoing research efforts that aim to enable AI in satellite-based NTN
through software-defined implementations, while also discussing the associated
challenges. Finally, we conclude by providing insights and recommendations for
enabling AI-driven satellite-based NTN in future 6G networks.Comment: 40 pages, 19 Figure, 10 Tables, Surve
A satellite-based personal communication system for the 21st century
Interest in personal communications (PCOMM) has been stimulated by recent developments in satellite and terrestrial mobile communications. A personal access satellite system (PASS) concept was developed at the Jet Propulsion Laboratory (JPL) which has many attractive user features, including service diversity and a handheld terminal. Significant technical challenges addressed in formulating the PASS space and ground segments are discussed. PASS system concept and basic design features, high risk enabling technologies, an optimized multiple access scheme, alternative antenna coverage concepts, the use of non-geostationary orbits, user terminal radiation constraints, and user terminal frequency reference are covered
Proceedings of the Fifth International Mobile Satellite Conference 1997
Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments
Millimeter-wave Evolution for 5G Cellular Networks
Triggered by the explosion of mobile traffic, 5G (5th Generation) cellular
network requires evolution to increase the system rate 1000 times higher than
the current systems in 10 years. Motivated by this common problem, there are
several studies to integrate mm-wave access into current cellular networks as
multi-band heterogeneous networks to exploit the ultra-wideband aspect of the
mm-wave band. The authors of this paper have proposed comprehensive
architecture of cellular networks with mm-wave access, where mm-wave small cell
basestations and a conventional macro basestation are connected to
Centralized-RAN (C-RAN) to effectively operate the system by enabling power
efficient seamless handover as well as centralized resource control including
dynamic cell structuring to match the limited coverage of mm-wave access with
high traffic user locations via user-plane/control-plane splitting. In this
paper, to prove the effectiveness of the proposed 5G cellular networks with
mm-wave access, system level simulation is conducted by introducing an expected
future traffic model, a measurement based mm-wave propagation model, and a
centralized cell association algorithm by exploiting the C-RAN architecture.
The numerical results show the effectiveness of the proposed network to realize
1000 times higher system rate than the current network in 10 years which is not
achieved by the small cells using commonly considered 3.5 GHz band.
Furthermore, the paper also gives latest status of mm-wave devices and
regulations to show the feasibility of using mm-wave in the 5G systems.Comment: 17 pages, 12 figures, accepted to be published in IEICE Transactions
on Communications. (Mar. 2015
Role of satellite communications in 5G ecosystem: perspectives and challenges
The next generation of mobile radio communication systems – so-called 5G – will
provide some major changes to those generations to date. The ability to cope with huge
increases in data traffic at reduced latencies and improved quality of user experience
together with a major reduction in energy usage are big challenges. In addition,
future systems will need to embody connections to billions of objects – the so-called
Internet of Things (IoT) which raises new challenges.Visions of 5G are now available
from regions across the world and research is ongoing towards new standards. The
consensus is a flatter architecture that adds a dense network of small cells operating in
the millimetre wave bands and which are adaptable and software controlled. But what
is the place for satellites in such a vision? The chapter examines several potential
roles for satellites in 5G including coverage extension, IoT, providing resilience,
content caching and multi-cast, and the integrated architecture. Furthermore, the
recent advances in satellite communications together with the challenges associated
with the use of satellite in the integrated satellite-terrestrial architecture are also
discussed
- …