436 research outputs found
Performance Comparison of Dual Connectivity and Hard Handover for LTE-5G Tight Integration in mmWave Cellular Networks
MmWave communications are expected to play a major role in the Fifth
generation of mobile networks. They offer a potential multi-gigabit throughput
and an ultra-low radio latency, but at the same time suffer from high isotropic
pathloss, and a coverage area much smaller than the one of LTE macrocells. In
order to address these issues, highly directional beamforming and a very
high-density deployment of mmWave base stations were proposed. This Thesis aims
to improve the reliability and performance of the 5G network by studying its
tight and seamless integration with the current LTE cellular network. In
particular, the LTE base stations can provide a coverage layer for 5G mobile
terminals, because they operate on microWave frequencies, which are less
sensitive to blockage and have a lower pathloss. This document is a copy of the
Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr.
Marco Mezzavilla and Prof. Michele Zorzi. It will propose an LTE-5G tight
integration architecture, based on mobile terminals' dual connectivity to LTE
and 5G radio access networks, and will evaluate which are the new network
procedures that will be needed to support it. Moreover, this new architecture
will be implemented in the ns-3 simulator, and a thorough simulation campaign
will be conducted in order to evaluate its performance, with respect to the
baseline of handover between LTE and 5G.Comment: Master's Thesis carried out by Mr. Michele Polese under the
supervision of Dr. Marco Mezzavilla and Prof. Michele Zorz
Load balancing in hybrid LiFi and RF networks
The increasing number of mobile devices challenges the current radio frequency (RF) networks.
The conventional RF spectrum for wireless communications is saturating, motivating
to develop other unexplored frequency bands. Light Fidelity (LiFi) which uses more than 300
THz of the visible light spectrum for high-speed wireless communications, is considered a
promising complementary technology to its RF counterpart. LiFi enables daily lighting infrastructures,
i.e. light emitting diode (LED) lamps to realise data transmission, and maintains the
lighting functionality at the same time. Since LiFi mainly relies on line-of-sight (LoS) transmission,
users in indoor environments may experience blockages which significantly affects
users’ quality of service (QoS). Therefore, hybrid LiFi and RF networks (HLRNs) where LiFi
supports high data rate transmission and RF offers reliable connectivity, can provide a potential
solution to future indoor wireless communications.
In HLRNs, efficient load balancing (LB) schemes are critical in improving the traffic performance
and network utilisation. In this thesis, the optimisation-based scheme (OBS) and the
evolutionary game theory (EGT) based scheme (EGTBS) are proposed for load balancing in
HLRNs. Specifically, in OBS, two algorithms, the joint optimisation algorithm (JOA) and the
separate optimisation algorithm (SOA) are proposed. Analysis and simulation results show
that JOA can achieve the optimal performance in terms of user data rate while requiring high
computational complexity. SOA reduces the computational complexity but achieves low user
data rates. EGTBS is able to achieve a better performance/complexity trade-off than OBS and
other conventional load balancing schemes. In addition, the effects of handover, blockages,
orientation of LiFi receivers, and user data rate requirement on the throughput of HLRNs are
investigated. Moreover, the packet latency in HLRNs is also studied in this thesis. The notion
of LiFi service ratio is introduced, defined as the proportion of users served by LiFi in
HLRNs. The optimal LiFi service ratio to minimise system delay is mathematically derived
and a low-complexity packet flow assignment scheme based on this optimum ratio is proposed.
Simulation results show that the theoretical optimum of the LiFi service ratio is very close to the
practical solution. Also, the proposed packet flow assignment scheme can reduce at most 90%
of packet delay compared to the conventional load balancing schemes at reduced computational
complexity
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