1,644 research outputs found
A New Look at MIMO Capacity in the Millimeter Wave
In this paper, we present a new theoretical discovery that the multiple-input
and multiple-output (MIMO) capacity can be influenced by atmosphere molecules.
In more detail, some common atmosphere molecules, such as Oxygen and water, can
absorb and re-radiate energy in their natural resonance frequencies, such as
60GHz, 120GHz, and 180GHz, which belong to the millimeter wave (mmWave)
spectrum. Such phenomenon can provide equivalent non-line-of-sight (NLoS) paths
in an environment that lacks scatterers, and thus greatly improve the spatial
multiplexing and diversity of a MIMO system. This kind of performance
improvement is particularly useful for most mmWave communications that heavily
rely on line-of-sight (LoS) transmissions. To sum up, our study concludes that
since the molecular re-radiation happens at certain mmWave frequency bands, the
MIMO capacity becomes highly frequency selective and enjoys a considerable
boosting at those mmWave frequency bands. The impact of our new discovery is
significant, which fundamentally changes our understanding on the relationship
between the MIMO capacity and the frequency spectrum. In particular, our
results predict that several mmWave bands can serve as valuable spectrum
windows for high-efficiency MIMO communications, which in turn may shift the
paradigm of research, standardization, and implementation in the field of
mmWave communications.Comment: arXiv admin note: text overlap with arXiv:1710.0903
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
Exact MIMO Zero-Forcing Detection Analysis for Transmit-Correlated Rician Fading
We analyze the performance of multiple input/multiple output (MIMO)
communications systems employing spatial multiplexing and zero-forcing
detection (ZF). The distribution of the ZF signal-to-noise ratio (SNR) is
characterized when either the intended stream or interfering streams experience
Rician fading, and when the fading may be correlated on the transmit side.
Previously, exact ZF analysis based on a well-known SNR expression has been
hindered by the noncentrality of the Wishart distribution involved. In
addition, approximation with a central-Wishart distribution has not proved
consistently accurate. In contrast, the following exact ZF study proceeds from
a lesser-known SNR expression that separates the intended and interfering
channel-gain vectors. By first conditioning on, and then averaging over the
interference, the ZF SNR distribution for Rician-Rayleigh fading is shown to be
an infinite linear combination of gamma distributions. On the other hand, for
Rayleigh-Rician fading, the ZF SNR is shown to be gamma-distributed. Based on
the SNR distribution, we derive new series expressions for the ZF average error
probability, outage probability, and ergodic capacity. Numerical results
confirm the accuracy of our new expressions, and reveal effects of interference
and channel statistics on performance.Comment: 14 pages, two-colum, 1 table, 10 figure
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