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Handover mechanisms in next generation heterogeneous wireless ...

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DYNAMIC NEIGHBOUR TRUST INFORMATION RETRIEVAL FOR GLOBAL ROAMING<br />

NTC exchanges that have been performed between the adjacent networks. As proved<br />

earlier, a group of mobile users are required to participate <strong>in</strong> the NTC distribution to<br />

obta<strong>in</strong> complete network trust pattern. For practical implementation, it is assumed that a<br />

NTC EFR of 95% is a good <strong>in</strong>dicator that the network trust pattern <strong>in</strong> a region has been<br />

effectively formed. In this simulation, the size of r<strong>in</strong>gs as shown <strong>in</strong> Figure 4.7 was<br />

varied to get a comparative result. The experimental results show that the m<strong>in</strong>imum<br />

number of mobile users required for establish<strong>in</strong>g network trust pattern for the region <strong>in</strong><br />

size: 4, 8, 12 (r<strong>in</strong>gs) is 132, 169 and 196 respectively. Figure 4.11 shows that the NTC<br />

EFR tends to stabilise at a certa<strong>in</strong> value no matter how long the observation on the NTC<br />

exchange has lasted. The stabilisation of the NTC EFR under a fixed number of mobile<br />

users can be expla<strong>in</strong>ed by the rationale beh<strong>in</strong>ds Figure 4.9 and Figure 4.10 that the<br />

contribution of s<strong>in</strong>gle mobile user to the NTC distribution is very limited. By compar<strong>in</strong>g<br />

the NTC EFRs under the different numbers (2, 5, 10) of mobile users, it is found that an<br />

effective way of <strong>in</strong>creas<strong>in</strong>g the NTC EFR is to get more mobile users participate <strong>in</strong> the<br />

NTC distribution. More mobile users are <strong>in</strong>volved, higher the NTC EFR is.<br />

Figure 4.11 NTC exchange f<strong>in</strong>ish ratio vs. time [Size of r<strong>in</strong>gs=6, MCRT=30m<strong>in</strong>s]<br />

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