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Handover mechanisms in next generation heterogeneous wireless ...

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CONCLUSIONS AND FUTURE RESEARCH WORK<br />

presented. In the Active Operation Mode NTC (AOMN) solution, a mobile user<br />

carry<strong>in</strong>g active sessions is <strong>in</strong>volved <strong>in</strong> the NTC process. The AOMN solution relies on<br />

actual handover event and can produce the most accurate <strong>in</strong>formation about neighbours’<br />

trust relationships. In contrast, the Power Save Mode NTC (PSMN) approach takes<br />

advantage of the location update and pag<strong>in</strong>g process of a mobile user <strong>in</strong> a dormant state<br />

to trigger the NTC process. The PSMN derives neighbours’ trust relationships from<br />

analys<strong>in</strong>g location update records of mobile users <strong>in</strong>volved <strong>in</strong> the NTC process.<br />

To evaluate the performance of the proposed scheme, a hexagonal random walk model<br />

with the Markov transition probabilities was used to simulate a multi-operator<br />

environment, <strong>in</strong> which a group of mobile users performed handover between networks.<br />

A series of simulations were conducted on a number of parameters. The simulation<br />

results showed that the proposed trust <strong>in</strong>formation retrieval scheme can function <strong>in</strong> a<br />

cost-effective manner, generat<strong>in</strong>g 3.7% additional signall<strong>in</strong>g overhead on networks<br />

compared with the standard handover signall<strong>in</strong>g cost. Moreover, it was shown that one<br />

mobile user per network would be sufficient to establish a complete network trust<br />

pattern <strong>in</strong> most cases when the proposed scheme is widely deployed <strong>in</strong> networks. From<br />

the perspective of real deployment, this makes sure that the implementation of the<br />

proposed NTC scheme would not be a burden for operational networks. It was found<br />

that the time taken for construct<strong>in</strong>g neighbour trust pattern can be speeded up by<br />

<strong>in</strong>creas<strong>in</strong>g the number of mobile users <strong>in</strong>volved.<br />

8.1.2 Trust Assisted <strong>Handover</strong> Algorithm for Reliable <strong>Handover</strong><br />

In Chapter 5, a Trust assisted <strong>Handover</strong> Algorithm (THOA) was presented to deal with<br />

the coexistence of multiple network operators, which has not been addressed <strong>in</strong> current<br />

handover approaches. A THOA cost function that can take <strong>in</strong>to account network trust<br />

relationship along with multiple handover metrics was proposed. The proposed THOA<br />

cost function works with a trust coefficient model that normalises the NTC data <strong>in</strong> order<br />

to have networks hold<strong>in</strong>g different trust values accurately weighed <strong>in</strong> network selection.<br />

To implement the proposed algorithm at the mobile end, the thesis presented an<br />

optimised network selection process that is designed to provide build-<strong>in</strong> trust awareness.<br />

The optimised network selection process along with the THOA can guarantee more<br />

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