On the Performances of User Association Enhancements in Dense Wireless Heterogeneous Networks
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Date
2023-03
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Addis Ababa University
Abstract
User Association (UA) plays a signi cant role in radio resource management of wireless
communication systems. Currently, network densi cation and heterogeneity have already
been identi ed as a feasible solution for the exponentially expanding data service demand.
Hence, UA methods must meet di erent requirements in dense and ultra dense
Heterogeneous Networks (HetNets). The load-imbalance due to transmit power di erence
between tiers and interference coordination challenges, the e ect of serving node intensity
on load sharing and achievable throughputs and the e ort to satisfy certain users with
high data rate demands are a few problems. Furthermore, the interconnected and complicated
problems of service delivery are posed by the spatio-temporal dynamics in service
demand and the mobility of User Equipment (UE).
This thesis takes a step-by-step approach to solving UA problems in dense and ultra
dense HetNets. This research uses stochastic geometry tools, system level simulations, and
realistic test case deployment simulations. Models were created for each scenario based
on the load balancing, interference coordination, varied densi cation levels, heterogeneity,
and user mobility.
The work's rst contribution is a solution to the problem of load imbalance and interference
coordination. The proposed method is simple to integrate into an existing HetNets
network, and the results demonstrate e ective load-aware association and adaptive interference
coordination. A cell clustering-based load-aware o setting and an adaptive Low
Power Subframe (LPS) approach was developed. The solution allows the separation of UA
functions at the UE and network server such that users can make a simple cell-selection
decision similar to that in the Maximum Received Signal Strength (max-RSS) based UA
scheme, where the network server computes the load-aware o setting and required LPS
periods based on the load conditions of the system. The proposed solution was evaluated
using system level simulations wherein the results correspond to performance changes in
di erent service regions. Results show that the method e ectively solves the o oading
and interference coordination problems in dense HetNets.
The second contribution of the research is on the coupled and decoupled User Association.
It can be used as a guide for network operators to select the appropriate UA
scheme for their network. The concepts of Poisson random networks were used to analytiv ically obtain the relative densi cation levels for which we need the o oading, decoupled
or coupled UA and validate the analysis with numerical and system level simulation of
realistic network. The association window, where users choose to use decoupled association
in terms of the relative intensity, transmit powers at each tiers and the Path Loss
Exponent (PLE) of the propagation environment, is derived. Further, the ergodic rate
expressions in order to study throughput performances in di erent densi cation regions,
which can be computed numerically, are formulated . To validate the theoretical analysis,
numerical, system level simulation and realistic network analysis were used. The analytical,
simulation, and realistic test case results provide insights for the operators about the
densi cation ranges, where to use coupled or decoupled association.
Finally, the research work focused on solutions for UEs with high data rate demands
and mobility management. With Multiple Association (MA), user-centric clustering, control,
and user-plane split usages were designed and investigated. Mobility management
approaches in Long Term Evolution Advanced (LTE-A)/Fifth Generation (5G) and MA
were used. The scheme attempts to separately treat UEs based on their speed by setting
some prede ned thresholds. In addition, a clustering approach, which produce virtual
cells with which UEs gets associated was developed. Combining of MA with clustering
enhances cooperation between most appropriate cells to serve a given UE. The ndings
indicate that the issues were addressed in an e cient and e ective manner.
Description
Keywords
LTE/LTE-A, 5G, user association, load balancing, HetNets, cell densi- cation, service demand, cell range expansion, almost-blank subfram, inter-cell interference, clustering, downlink and uplink decoupling, multiple association, mobility management