1,889 research outputs found
Out-of-Band Radiation from Antenna Arrays Clarified
Non-linearities in radio-frequency (RF) transceiver hardware, particularly in
power amplifiers, cause distortion in-band and out-of-band. Contrary to claims
made in recent literature, in a multiple-antenna system this distortion is
correlated across the antennas in the array. A significant implication of this
fact is that out-of-band emissions caused by non-linearities are beamformed, in
some cases into the same direction as the useful signal.Comment: IEEE Wireless Communications Letters, 2018, to appea
Modeling and Analysis of Composite Antenna Superstrates Consisting on Grids of Loaded Wires
We study the characteristics and radiation mechanism of antenna superstrates
based on closely located periodical grids of loaded wires. An explicit
analytical method based on the local field approach is used to study the
reflection and transmission properties of such superstrates. It is shown that
as a result of proper impedance loading there exists a rather wide frequency
band over which currents induced to the grids cancel each other, leading to a
wide transmission maximum. In this regime radiation is produced by the magnetic
dipole moments created by circulating out-of-phase currents flowing in the
grids. An impedance matrix representation is derived for the superstrates, and
the analytical results are validated using full-wave simulations. As a
practical application example we study numerically the radiation
characteristics of dipole antennas illuminating finite-size superstrates.Comment: 9 pages, 11 figures. In the second version we have clarified the
analysis related to the prototype, and re-desinged the prototype antenn
Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions
Massive MIMO is a compelling wireless access concept that relies on the use
of an excess number of base-station antennas, relative to the number of active
terminals. This technology is a main component of 5G New Radio (NR) and
addresses all important requirements of future wireless standards: a great
capacity increase, the support of many simultaneous users, and improvement in
energy efficiency. Massive MIMO requires the simultaneous processing of signals
from many antenna chains, and computational operations on large matrices. The
complexity of the digital processing has been viewed as a fundamental obstacle
to the feasibility of Massive MIMO in the past. Recent advances on
system-algorithm-hardware co-design have led to extremely energy-efficient
implementations. These exploit opportunities in deeply-scaled silicon
technologies and perform partly distributed processing to cope with the
bottlenecks encountered in the interconnection of many signals. For example,
prototype ASIC implementations have demonstrated zero-forcing precoding in real
time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing
of 8 terminals). Coarse and even error-prone digital processing in the antenna
paths permits a reduction of consumption with a factor of 2 to 5. This article
summarizes the fundamental technical contributions to efficient digital signal
processing for Massive MIMO. The opportunities and constraints on operating on
low-complexity RF and analog hardware chains are clarified. It illustrates how
terminals can benefit from improved energy efficiency. The status of technology
and real-life prototypes discussed. Open challenges and directions for future
research are suggested.Comment: submitted to IEEE transactions on signal processin
On the Phase Response and Radiation Efficiency of the Complementary Strip-Slot as an Array Element
The complementary strip-slot element is a broadlymatched
microstrip radiator that has been used to design innovative
series-fed arrays. It consists of a microstrip series-fed slot
that have its complementary stub on the layer of the microstrip
and aligned to the slot. In this contribution, the influence of the
strip and slot geometry on its performance is studied through the
analysis of four different designs. The obtained results highlight
the possibility of controlling the radiation efficiency or the phase
response, without compromising the broad matching. Therefore,
potential series-fed arrays built with this element can exploit this
feature to set the magnitude and phase of the excitations with
certain flexibility.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work was supported by the Spanish Ministerio de
Ciencia e Innovaci ´on (Programa Consolider-Ingenio 2010)
under Grant CSD2008-00066, EME
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
Can Hardware Distortion Correlation be Neglected When Analyzing Uplink SE in Massive MIMO?
This paper analyzes how the distortion created by hardware impairments in a
multiple-antenna base station affects the uplink spectral efficiency (SE), with
focus on Massive MIMO. The distortion is correlated across the antennas, but
has been often approximated as uncorrelated to facilitate (tractable) SE
analysis. To determine when this approximation is accurate, basic properties of
the distortion correlation are first uncovered. Then, we focus on third-order
non-linearities and prove analytically and numerically that the correlation can
be neglected in the SE analysis when there are many users. In i.i.d. Rayleigh
fading with equal signal-to-noise ratios, this occurs when having five users.Comment: 5 pages, 3 figures, IEEE International Workshop on Signal Processing
Advances in Wireless Communications (SPAWC), 201
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