621 research outputs found
Quantifying Potential Energy Efficiency Gain in Green Cellular Wireless Networks
Conventional cellular wireless networks were designed with the purpose of
providing high throughput for the user and high capacity for the service
provider, without any provisions of energy efficiency. As a result, these
networks have an enormous Carbon footprint. In this paper, we describe the
sources of the inefficiencies in such networks. First we present results of the
studies on how much Carbon footprint such networks generate. We also discuss
how much more mobile traffic is expected to increase so that this Carbon
footprint will even increase tremendously more. We then discuss specific
sources of inefficiency and potential sources of improvement at the physical
layer as well as at higher layers of the communication protocol hierarchy. In
particular, considering that most of the energy inefficiency in cellular
wireless networks is at the base stations, we discuss multi-tier networks and
point to the potential of exploiting mobility patterns in order to use base
station energy judiciously. We then investigate potential methods to reduce
this inefficiency and quantify their individual contributions. By a
consideration of the combination of all potential gains, we conclude that an
improvement in energy consumption in cellular wireless networks by two orders
of magnitude, or even more, is possible.Comment: arXiv admin note: text overlap with arXiv:1210.843
Uplink Performance of Time-Reversal MRC in Massive MIMO Systems Subject to Phase Noise
Multi-user multiple-input multiple-output (MU-MIMO) cellular systems with an
excess of base station (BS) antennas (Massive MIMO) offer unprecedented
multiplexing gains and radiated energy efficiency. Oscillator phase noise is
introduced in the transmitter and receiver radio frequency chains and severely
degrades the performance of communication systems. We study the effect of
oscillator phase noise in frequency-selective Massive MIMO systems with
imperfect channel state information (CSI). In particular, we consider two
distinct operation modes, namely when the phase noise processes at the BS
antennas are identical (synchronous operation) and when they are independent
(non-synchronous operation). We analyze a linear and low-complexity
time-reversal maximum-ratio combining (TR-MRC) reception strategy. For both
operation modes we derive a lower bound on the sum-capacity and we compare
their performance. Based on the derived achievable sum-rates, we show that with
the proposed receive processing an array gain is achievable. Due
to the phase noise drift the estimated effective channel becomes progressively
outdated. Therefore, phase noise effectively limits the length of the interval
used for data transmission and the number of scheduled users. The derived
achievable rates provide insights into the optimum choice of the data interval
length and the number of scheduled users.Comment: 13 pages, 6 figures, 2 tables, IEEE Transactions on Wireless
Communications (accepted
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
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