17,146 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
System level analysis of heterogeneous networks under imperfect traffic hotspot localization
We study, in this paper, the impact of imperfect small cell positioning with
respect to traffic hotspots in cellular networks. In order to derive the
throughput distribution in macro and small cells, we firstly perform static
level analysis of the system considering a non-uniform distribution of user
locations. We secondly introduce the dynamics of the system, characterized by
random arrivals and departures of users after a finite service duration, with
the service rates and distribution of radio conditions outfitted from the first
part of the work. When dealing with the dynamics of the system, macro and small
cells are modeled by multi-class processor sharing queues. Macro and small
cells are assumed to be operating in the same bandwidth. Consequently, they are
coupled due to the mutual interferences generated by each cell to the other. We
derive several performance metrics such as the mean flow throughput and the
gain, if any, generated from deploying small cells to manage traffic hotspots.
Our results show that in case the hotspot is near the macro BS (Base Station),
even a perfect positioning of the small cell will not yield improved
performance due to the high interference experienced at macro and small cell
users. However, in case the hotspot is located far enough from the macro BS,
performing errors in small cell positioning is tolerated (since related results
show positive gains) and it is still beneficial in offloading traffic from the
congested macrocell. The best performance metrics depend also on several other
important factors such as the users' arrival intensity, the capacity of the
cell and the size of the traffic hotspot.Comment: This paper is already published in IEEE Transactions on Vehicular
Technology 201
Visible Light Communications towards 5G
5G networks have to offer extremely high capacity for novel streaming applications. One of the most promising approaches is to embed large numbers of co-operating small cells into the macro-cell coverage area. Alternatively, optical wireless based technologies can be adopted as an alternative physical layer offering higher data rates. Visible light communications (VLC) is an emerging technology for future high capacity communication links (it has been accepted to 5GPP) in the visible range of the electromagnetic spectrum (~370–780 nm) utilizing light-emitting diodes (LEDs) simultaneously provide data transmission and room illumination. A major challenge in VLC is the LED modulation bandwidths, which are limited to a few MHz. However, myriad gigabit speed transmission links have already been demonstrated. Non line-of-sight (NLOS) optical wireless is resistant to blocking by people and obstacles and is capable of adapting its’ throughput according to the current channel state information. Concurrently, organic polymer LEDs (PLEDs) have become the focus of enormous attention for solid-state lighting applications due to their advantages over conventional white LEDs such as ultra-low costs, low heating temperature, mechanical flexibility and large photoactive areas when produced with wet processing methods. This paper discusses development of such VLC links with a view to implementing ubiquitous broadcasting networks featuring advanced modulation formats such as orthogonal frequency division multiplexing (OFDM) or carrier-less amplitude and phase modulation (CAP) in conjunction with equalization techniques. Finally, this paper will also summarize the results of the European project ICT COST IC1101 OPTICWISE (Optical Wireless Communications - An Emerging Technology) dealing VLC and OLEDs towards 5G networks
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