Handover mechanisms in next generation heterogeneous wireless ...

TRUST ASSISTED HANDOVER ALGORITHM FOR RELIABLE HANDOVER
5.2), other handover deciding criteria such as bandwidth, network latency and so forth,
can be compared for the sake of better connection QoS.
Mathematically, � n is used to represent trust coefficient. The cost function of the
THOA is derived as follows:
f
n
n
�m �
i
i
C n i
� �
(Equation 5.5)
�
n
� w � N
�
in which C n represents the QoS evaluation part of the THOA, which takes into account
multiple handover metrics. The conditions of C n has been explained in (Equation 5.3).
A flow chart of the THOA process is demonstrated in Figure 5.3. In the network
discovery phase, the MH discovers all the available POAs. Thereafter, it retrieves their
corresponding trust coefficient values from its local network trust coefficient table.
Those networks having a positive non-zero entry in the table (with � � 0 ) are
regarded as within the MH’s circle of trust. The circle of trust is defined as a group of
networks that have established trust associations with the MH’s home network. In the
handover decision process, the discovered POAs within the circle of trust are selected
for handover. The handover cost of attaching to each POA within the circle of trust will
be calculated according to (Equation 5.5). Their handover costs are compared, and the
one having the minimum value of f n is selected as the next POA. If two POAs appear
to provide the same QoS as a result of the multicriteria cost evaluation (having the same
value of C n ), the one with the higher value of � n is selected. This justifies that home
network is always superior to foreign networks in regard to network selection when
their network conditions are the same.
- 91 -
n