3,162 research outputs found
Improving public spaces in Helsinki during wintertime
This thesis is about public spaces in Helsinki, focusing on cultivating urban life during the winter months. Unlike the vibrant public life present during the summer, public spaces in winter are mostly unavailable and consequently, public life is highly limited. Through a literature review, the study of public life is explained, and its historical background, methods, and primary focus are elaborated. Through observational research, how public spaces in winter Helsinki, particularly around the Helsinki central railway station, are used by the public is described. The research findings revealed that the streets and commercial places are the most frequently used public spaces in winter. The key argument is that because of the long wintertime, it needs to be considered thoughtfully how public life in winter has developed and how it can be improved. Through further discussion of these aspects, design ideas to help promote public life on the street and in commercial areas are suggested.Chun, Ji
On Modeling Heterogeneous Wireless Networks Using Non-Poisson Point Processes
Future wireless networks are required to support 1000 times higher data rate,
than the current LTE standard. In order to meet the ever increasing demand, it
is inevitable that, future wireless networks will have to develop seamless
interconnection between multiple technologies. A manifestation of this idea is
the collaboration among different types of network tiers such as macro and
small cells, leading to the so-called heterogeneous networks (HetNets).
Researchers have used stochastic geometry to analyze such networks and
understand their real potential. Unsurprisingly, it has been revealed that
interference has a detrimental effect on performance, especially if not modeled
properly. Interference can be correlated in space and/or time, which has been
overlooked in the past. For instance, it is normally assumed that the nodes are
located completely independent of each other and follow a homogeneous Poisson
point process (PPP), which is not necessarily true in real networks since the
node locations are spatially dependent. In addition, the interference
correlation created by correlated stochastic processes has mostly been ignored.
To this end, we take a different approach in modeling the interference where we
use non-PPP, as well as we study the impact of spatial and temporal correlation
on the performance of HetNets. To illustrate the impact of correlation on
performance, we consider three case studies from real-life scenarios.
Specifically, we use massive multiple-input multiple-output (MIMO) to
understand the impact of spatial correlation; we use the random medium access
protocol to examine the temporal correlation; and we use cooperative relay
networks to illustrate the spatial-temporal correlation. We present several
numerical examples through which we demonstrate the impact of various
correlation types on the performance of HetNets.Comment: Submitted to IEEE Communications Magazin
Active-IRS Aided Wireless Network: System Modeling and Performance Analysis
Active intelligent reflecting surface (IRS) enables flexible signal
reflection control with \emph{power amplification}, thus effectively
compensating the product-distance path-loss in conventional passive-IRS aided
systems. In this letter, we characterize the communication performance of an
active-IRS aided single-cell wireless network. To this end, we first propose a
\emph{customized} IRS deployment strategy, where the active IRSs are uniformly
deployed within a ring concentric with the cell to serve the users far from the
base station. Next, given the Nakagami- fading channel, we characterize the
cascaded active-IRS channel by using the \emph{mixture Gamma distribution}
approximation and derive a closed-form expression for the mean signal-to-noise
ratio (SNR) at the user averaged over channel fading. Moreover, we numerically
show that to maximize the system performance, it is necessary to choose a
proper active-IRS density given a fixed number of total reflecting elements,
which significantly differs from the passive-IRS case for which the centralized
IRS deployment scheme is better. Furthermore, the active-IRS aided wireless
network achieves higher spatial throughput than the passive-IRS counterpart
when the total number of reflecting elements is small
A Stochastic Geometric Analysis of Device-to-Device Communications Operating over Generalized Fading Channels
Device-to-device (D2D) communications are now considered as an integral part
of future 5G networks which will enable direct communication between user
equipment (UE) without unnecessary routing via the network infrastructure. This
architecture will result in higher throughputs than conventional cellular
networks, but with the increased potential for co-channel interference induced
by randomly located cellular and D2D UEs. The physical channels which
constitute D2D communications can be expected to be complex in nature,
experiencing both line-of-sight (LOS) and non-LOS (NLOS) conditions across
closely located D2D pairs. As well as this, given the diverse range of
operating environments, they may also be subject to clustering of the scattered
multipath contribution, i.e., propagation characteristics which are quite
dissimilar to conventional Rayeligh fading environments. To address these
challenges, we consider two recently proposed generalized fading models, namely
and , to characterize the fading behavior in D2D
communications. Together, these models encompass many of the most widely
encountered and utilized fading models in the literature such as Rayleigh, Rice
(Nakagami-), Nakagami-, Hoyt (Nakagami-) and One-Sided Gaussian. Using
stochastic geometry we evaluate the rate and bit error probability of D2D
networks under generalized fading conditions. Based on the analytical results,
we present new insights into the trade-offs between the reliability, rate, and
mode selection under realistic operating conditions. Our results suggest that
D2D mode achieves higher rates over cellular link at the expense of a higher
bit error probability. Through numerical evaluations, we also investigate the
performance gains of D2D networks and demonstrate their superiority over
traditional cellular networks.Comment: Submitted to IEEE Transactions on Wireless Communication
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