22,650 research outputs found
Massive MIMO is a Reality -- What is Next? Five Promising Research Directions for Antenna Arrays
Massive MIMO (multiple-input multiple-output) is no longer a "wild" or
"promising" concept for future cellular networks - in 2018 it became a reality.
Base stations (BSs) with 64 fully digital transceiver chains were commercially
deployed in several countries, the key ingredients of Massive MIMO have made it
into the 5G standard, the signal processing methods required to achieve
unprecedented spectral efficiency have been developed, and the limitation due
to pilot contamination has been resolved. Even the development of fully digital
Massive MIMO arrays for mmWave frequencies - once viewed prohibitively
complicated and costly - is well underway. In a few years, Massive MIMO with
fully digital transceivers will be a mainstream feature at both sub-6 GHz and
mmWave frequencies. In this paper, we explain how the first chapter of the
Massive MIMO research saga has come to an end, while the story has just begun.
The coming wide-scale deployment of BSs with massive antenna arrays opens the
door to a brand new world where spatial processing capabilities are
omnipresent. In addition to mobile broadband services, the antennas can be used
for other communication applications, such as low-power machine-type or
ultra-reliable communications, as well as non-communication applications such
as radar, sensing and positioning. We outline five new Massive MIMO related
research directions: Extremely large aperture arrays, Holographic Massive MIMO,
Six-dimensional positioning, Large-scale MIMO radar, and Intelligent Massive
MIMO.Comment: 20 pages, 9 figures, submitted to Digital Signal Processin
Engine performance characteristics and evaluation of variation in the length of intake plenum
In the engine with multipoint fuel injection system using electronically controlled fuel injectors has an intake manifold in which only the air flows and, the fuel is injected into the intake valve. Since the intake manifolds transport mainly air, the supercharging effects of the variable length intake plenum will be different from carbureted engine. Engine tests have been carried out with the aim of constituting a base study to design a new variable length intake manifold plenum. The objective in this research is to study the engine performance characteristics and to evaluate the effects of the variation in the length of intake plenum. The engine test bed used for experimental work consists of a control panel, a hydraulic dynamometer and measurement instruments to measure the parameters of engine performance characteristics. The control panel is being used to perform administrative and management operating system. Besides that, the hydraulic dynamometer was used to measure the power of an engine by using a cell filled with liquid to increase its load. Thus, measurement instrument is provided in this test to measure the as brake torque, brake power, thermal efficiency and specific fuel consumption. The results showed that the variation in the plenum length causes an improvement on the engine performance characteristics especially on the fuel consumption at high load and low engine speeds which are put forward the system using for urban roads. From this experiment, it will show the behavior of engine performance
Demonstration of efficient nonreciprocity in a microwave optomechanical circuit
The ability to engineer nonreciprocal interactions is an essential tool in
modern communication technology as well as a powerful resource for building
quantum networks. Aside from large reverse isolation, a nonreciprocal device
suitable for applications must also have high efficiency (low insertion loss)
and low output noise. Recent theoretical and experimental studies have shown
that nonreciprocal behavior can be achieved in optomechanical systems, but
performance in these last two attributes has been limited. Here we demonstrate
an efficient, frequency-converting microwave isolator based on the
optomechanical interactions between electromagnetic fields and a mechanically
compliant vacuum gap capacitor. We achieve simultaneous reverse isolation of
more than 20 dB and insertion loss less than 1.5 dB over a bandwidth of 5 kHz.
We characterize the nonreciprocal noise performance of the device, observing
that the residual thermal noise from the mechanical environments is routed
solely to the input of the isolator. Our measurements show quantitative
agreement with a general coupled-mode theory. Unlike conventional isolators and
circulators, these compact nonreciprocal devices do not require a static
magnetic field, and they allow for dynamic control of the direction of
isolation. With these advantages, similar devices could enable programmable,
high-efficiency connections between disparate nodes of quantum networks, even
efficiently bridging the microwave and optical domains.Comment: 9 pages, 6 figure
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