Optimization of Soft Handover for Addis Ababa UMTS Radio Access Network
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Date
2020-02
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Addis Ababa University
Abstract
Handover is an essential radio management technique of mobile communication to
enable seamless communication while users move from one cell to another one. To
mitigate impacts of interference on cell-edge users, third Generation (3G) supports soft
handover where users can be simultaneously served by two or more cells, in addition to
hard handover, where a user is served by only one cell. The number of soft handover
users and their active cells determine the degree of soft handover overhead. The soft
handover overhead data for the year 2018 of Addis Ababa 3G network is 87% average
overhead, which is considerably beyond the maximum recommended value. This figure
indicates the requirement to optimize the soft handover overhead using the soft
handover related network parameters’ configurations.
In this thesis, soft handover overhead performance of the Addis Ababa 3G network is
analyzed. The spatial distribution of the overhead is visualized using data collected from
the network management system. Furthermore, optimization of soft handover overhead
is done through fine-tuning window add, pilot power, and electrical antenna down tilt.
We apply a heuristic algorithm for the optimization considering potential sets of values
for the optimization variables. Moreover, obtained results are compared with a result
obtained using existing default network configuration parameters. For the sample 3G
sites network simulation, we use WinProp while we also use MATLAB and Google Earth
for soft handover performance analysis and visualization.
Soft handover overhead performance analysis of 5 Radio Network controllers (RNCs)
shows that the Addis Ababa network is within the range of 111 to 115% for the 90
th
percentile. Sites in RNC4 using carrier three are selected for the simulation and
optimization as 5 to 21 more number of radio links used comparing with the other three carriers. After optimization, results show that soft handover overhead and network
capacity are considerably improved by fine-tuning the window add, pilot power, and
antenna tilt parameters. For instance, soft handover overhead is reduced from 85.4 % to
57.7% and network capacity gain by 3.76% when using window add of 2 dB, pilot power
of 7.5%, and electrical antenna down tilt by 2 degrees. Soft handover overhead is reduced
from 85.4 % to 46.6% and network capacity gain by 5.72% when using window add of 1.5
dB, pilot power of 5% and electrical antenna down tilt by 3 degrees.
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Keywords
Soft handover, pilot power, antenna down tilt, window add, soft handover overhead, 3G, Addis Ababa, optimization