11,265 research outputs found
Please Lower Small Cell Antenna Heights in 5G
In this paper, we present a new and significant theoretical discovery. If the
absolute height difference between base station (BS) antenna and user equipment
(UE) antenna is larger than zero, then the network capacity performance in
terms of the area spectral efficiency (ASE) will continuously decrease as the
BS density increases for ultra-dense (UD) small cell networks (SCNs). This
performance behavior has a tremendous impact on the deployment of UD SCNs in
the 5th-generation (5G) era. Network operators may invest large amounts of
money in deploying more network infrastructure to only obtain an even worse
network performance. Our study results reveal that it is a must to lower the
SCN BS antenna height to the UE antenna height to fully achieve the capacity
gains of UD SCNs in 5G. However, this requires a revolutionized approach of BS
architecture and deployment, which is explored in this paper too.Comment: Final version in IEEE: http://ieeexplore.ieee.org/document/7842150/.
arXiv admin note: substantial text overlap with arXiv:1608.0669
Models and optimisation methods for interference coordination in self-organising cellular networks
A thesis submitted for the degree of Doctor of PhilosophyWe are at that moment of network evolution when we have realised that our telecommunication systems should mimic features of human kind, e.g., the ability to understand the medium and take advantage of its changes. Looking towards the future, the mobile industry envisions the use of fully automatised cells able to self-organise all their parameters and procedures.
A fully self-organised network is the one that is able to avoid human involvement and react to the fluctuations of network, traffic and channel through the automatic/autonomous nature of its functioning. Nowadays, the mobile community is far from this fully self-organised kind of network, but they are taken the first steps to achieve this target in the near future. This thesis hopes to contribute to the automatisation of cellular networks, providing models and tools to understand the behaviour of these networks, and algorithms and optimisation approaches to enhance their performance.
This work focuses on the next generation of cellular networks, in more detail, in the DownLink (DL) of Orthogonal Frequency Division Multiple Access (OFDMA) based networks. Within this type of cellular system, attention is paid to interference mitigation in self-organising macrocell scenarios and femtocell deployments. Moreover, this thesis investigates the interference issues that arise when these two cell types are jointly deployed, complementing each other in what is currently known as a two-tier network. This thesis also provides new practical approaches to the inter-cell interference problem in both macro cell and femtocell OFDMA systems as well as in two-tier networks by means of the design of a novel framework and the use of mathematical optimisation. Special attention is paid to the formulation of optimisation problems and the development of well-performing solving methods (accurate and fast)
Ultra-Dense Networks: Is There a Limit to Spatial Spectrum Reuse?
The aggressive spatial spectrum reuse (SSR) by network densification using
smaller cells has successfully driven the wireless communication industry
onward in the past decades. In our future journey toward ultra-dense networks
(UDNs), a fundamental question needs to be answered. Is there a limit to SSR?
In other words, when we deploy thousands or millions of small cell base
stations (BSs) per square kilometer, is activating all BSs on the same
time/frequency resource the best strategy? In this paper, we present
theoretical analyses to answer such question. In particular, we find that both
the signal and interference powers become bounded in practical UDNs with a
non-zero BS-to-UE antenna height difference and a finite UE density, which
leads to a constant capacity scaling law. As a result, there exists an optimal
SSR density that can maximize the network capacity. Hence, the limit to SSR
should be considered in the operation of future UDNs.Comment: conference submission in Oct. 201
A novel risk assessment and optimisation model for a multi-objective network security countermeasure selection problem
Budget cuts and the high demand in strengthening the security of computer systems and services constitute a challenge. Poor system knowledge and inappropriate selection of security measures may lead to unexpected
financial and data losses. This paper proposes a novel Risk Assessment and Optimisation Model (RAOM) to solve a security countermeasure selection problem, where variables such as financial cost and risk may affect a final decision. A Multi-Objective Tabu Search (MOTS) algorithm has been developed to construct an efficient frontier of non-dominated solutions, which can satisfy organisational security needs in a cost-effective
manner
Pulse Shaping Diversity to Enhance Throughput in Ultra-Dense Small Cell Networks
Spatial multiplexing (SM) gains in multiple input multiple output (MIMO)
cellular networks are limited when used in combination with ultra-dense small
cell networks. This limitation is due to large spatial correlation among
channel pairs. More specifically, it is due to i) line-of-sight (LOS)
communication between user equipment (UE) and base station (BS) and ii)
in-sufficient spacing between antenna elements. We propose to shape transmit
signals at adjacent antennas with distinct interpolating filters which
introduces pulse shaping diversity eventually leading to improved SINR and
throughput at the UEs. In this technique, each antenna transmits its own data
stream with a relative offset with respect to adjacent antenna. The delay which
must be a fraction of symbol period is interpolated with the pulse shaped
signal and generates a virtual MIMO channel that leads to improved diversity
and SINR at the receiver. Note that non-integral sampling periods with
inter-symbol interference (ISI) should be mitigated at the receiver. For this,
we propose to use a fractionally spaced equalizer (FSE) designed based on the
minimum mean squared error (MMSE) criterion. Simulation results show that for a
2x2 MIMO and with inter-site-distance (ISD) of 50 m, the median received SINR
and throughput at the UE improves by a factor of 11 dB and 2x, respectively,
which verifies that pulse shaping can overcome poor SM gains in ultra-dense
small cell networks.Comment: Accepted to 17th IEEE International Workshop on Signal Processing
Advances in Wireless Communication
Study on Scheduling Techniques for Ultra Dense Small Cell Networks
The most promising approach to enhance network capacity for the next
generation of wireless cellular networks (5G) is densification, which benefits
from the extensive spatial reuse of the spectrum and the reduced distance
between transmitters and receivers. In this paper, we examine the performance
of different schedulers in ultra dense small cell deployments. Due to the
stronger line of sight (LOS) at low inter-site distances (ISDs), we discuss
that the Rician fading channel model is more suitable to study network
performance than the Rayleigh one, and model the Rician K factor as a function
of distance between the user equipment (UE) and its serving base station (BS).
We also construct a cross-correlation shadowing model that takes into account
the ISD, and finally investigate potential multi-user diversity gains in ultra
dense small cell deployments by comparing the performances of proportional fair
(PF) and round robin (RR) schedulers. Our study shows that as network becomes
denser, the LOS component starts to dominate the path loss model which
significantly increases the interference. Simulation results also show that
multi-user diversity is considerably reduced at low ISDs, and thus the PF
scheduling gain over the RR one is small, around 10% in terms of cell
throughput. As a result, the RR scheduling may be preferred for dense small
cell deployments due to its simplicity. Despite both the interference
aggravation as well as the multi-user diversity loss, network densification is
still worth it from a capacity view point.Comment: 6 pages, 7 figures, Accepted to IEEE VTC-Fall 2015 Bosto
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