Handover mechanisms in next generation heterogeneous wireless ...

TRUST ASSISTED HANDOVER ALGORITHM FOR RELIABLE HANDOVER
remain low. This will make those networks having close trust relationship with the
MH’s home network remain competitive in network selection. As soon as h n reaches a
predefined TAH threshold, � n should drop rapidly to zero and thus exclude network n
as a candidate for handover. This is justified by the fact that too many third parties
involving in intermediating AAA messages may become inefficiency and weaken the
reliability of handover. The predefined TAH threshold is denoted as Effective TAH
Scope (ETS, H eff ). The ETS indicates how network trust relationship may have an
impact on handover related AAA. Based on the above analysis, it was found that the
reciprocal of inverse tangent function can provide the logic for the trust coefficient
function. Figure 5.4 shows the curves of the proposed trust coefficient function,
compared with a reciprocal of an exponential function.
Figure 5.4 Trust coefficient function (with H � 6)
The trust coefficient function is represented as follows:
5.6)
H effective
1
� n � hn
e
Effective scope of TAH
� �hn�H��� gradient of the
curve at P
��
� n � d �
�
� arctan
eff
(Equation
� 2
- 93 -
(3)
gradient of the
curve at Q
eff