478 research outputs found
Democratization in the Middle East - A Comparative Case Study
One of the unsolved puzzles in democratization studies today is the prevalence of authoritarian regimes in the Middle East. Previous comparative studies have overlooked the region because it does not contain a single case of successful democratization. Middle Eastern scholars, on the other hand, tend to lack the theoretical tools on what it would take for this area to democratize. The purpose of this study is to elucidate the factors behind the level of (non-)democratization in the MENA-region. I will argue that democratization in the Middle East takes place on three different levels: international, national and societal. The study combines statistical data with process tracing analysis, in order to corroborate the evidence. Twelve variables, covering a wide range of democratization theories, are tested on four cases: Egypt, Iran, Saudi Arabia and Turkey. From this, I am able to confirm or discard certain theories, as well as establish the factors that are relevant for each case. Among other things, I am able to refute the claim that a Muslim population affects democratization negatively; to confirm the validity of the rentier state theory; to show that path dependency and political parties matter; and that FDI and aid can play a part in the future democratization of the Middle East
Random Access for Massive MIMO Systems with Intra-Cell Pilot Contamination
Massive MIMO systems, where the base stations are equipped with hundreds of
antenna elements, are an attractive way to attain unprecedented spectral
efficiency in future wireless networks. In the "classical" massive MIMO
setting, the terminals are assumed fully loaded and a main impairment to the
performance comes from the inter-cell pilot contamination, i.e., interference
from terminals in neighboring cells using the same pilots as in the home cell.
However, when the terminals are active intermittently, it is viable to avoid
inter-cell contamination by pre-allocation of pilots, while same-cell terminals
use random access to select the allocated pilot sequences. This leads to the
problem of intra-cell pilot contamination. We propose a framework for random
access in massive MIMO networks and derive new uplink sum rate expressions that
take intra-cell pilot collisions, intermittent terminal activity, and
interference into account. We use these expressions to optimize the terminal
activation probability and pilot length
Random Access Protocol for Massive MIMO: Strongest-User Collision Resolution (SUCR)
Wireless networks with many antennas at the base stations and multiplexing of
many users, known as Massive MIMO systems, are key to handle the rapid growth
of data traffic. As the number of users increases, the random access in
contemporary networks will be flooded by user collisions. In this paper, we
propose a reengineered random access protocol, coined strongest-user collision
resolution (SUCR). It exploits the channel hardening feature of Massive MIMO
channels to enable each user to detect collisions, determine how strong the
contenders' channels are, and only keep transmitting if it has the strongest
channel gain. The proposed SUCR protocol can quickly and distributively resolve
the vast majority of all pilot collisions.Comment: Published at the IEEE International Conference on Communications
(ICC), 2016, 6 pages, 6 figures. (c) 2016 IEEE. Personal use of this material
is permitte
Data-Intensive Modelling and Simulation in Life Sciences and Socio-economical and Physical Sciences
First paragraph: This special issue of the journal Data Science and Engineering is a result of the work fostered by the ICT COST Action IC1406 High-Performance Modelling and Simulation for Big Data Applications (cHiPSet), an EU-funded research network across 30+ European countries and overseas partners (http://chipset-cost.eu/).Output Type: Editoria
A Random Access Protocol for Pilot Allocation in Crowded Massive MIMO Systems
The Massive MIMO (multiple-input multiple-output) technology has great
potential to manage the rapid growth of wireless data traffic. Massive MIMO
achieves tremendous spectral efficiency by spatial multiplexing of many tens of
user equipments (UEs). These gains are only achieved in practice if many more
UEs can connect efficiently to the network than today. As the number of UEs
increases, while each UE intermittently accesses the network, the random access
functionality becomes essential to share the limited number of pilots among the
UEs. In this paper, we revisit the random access problem in the Massive MIMO
context and develop a reengineered protocol, termed strongest-user collision
resolution (SUCRe). An accessing UE asks for a dedicated pilot by sending an
uncoordinated random access pilot, with a risk that other UEs send the same
pilot. The favorable propagation of Massive MIMO channels is utilized to enable
distributed collision detection at each UE, thereby determining the strength of
the contenders' signals and deciding to repeat the pilot if the UE judges that
its signal at the receiver is the strongest. The SUCRe protocol resolves the
vast majority of all pilot collisions in crowded urban scenarios and continues
to admit UEs efficiently in overloaded networks.Comment: To appear in IEEE Transactions on Wireless Communications, 16 pages,
10 figures. This is reproducible research with simulation code available at
https://github.com/emilbjornson/sucre-protoco
Random Access Protocols for Massive MIMO
5G wireless networks are expected to support new services with stringent
requirements on data rates, latency and reliability. One novel feature is the
ability to serve a dense crowd of devices, calling for radically new ways of
accessing the network. This is the case in machine-type communications, but
also in urban environments and hotspots. In those use cases, the high number of
devices and the relatively short channel coherence interval do not allow
per-device allocation of orthogonal pilot sequences. This article motivates the
need for random access by the devices to pilot sequences used for channel
estimation, and shows that Massive MIMO is a main enabler to achieve fast
access with high data rates, and delay-tolerant access with different data rate
levels. Three pilot access protocols along with data transmission protocols are
described, fulfilling different requirements of 5G services
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