02.11.2012 Views

Handover mechanisms in next generation heterogeneous wireless ...

Handover mechanisms in next generation heterogeneous wireless ...

Handover mechanisms in next generation heterogeneous wireless ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

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

The NTC distribution process beg<strong>in</strong>s once the identity of the MH is successfully<br />

verified by the HAAA. Because the NTC distribution to the nPOA ( C<br />

hn ) can be<br />

<strong>in</strong>cluded <strong>in</strong> the EAP-AKA notification sent by the HAAA, it would avoid any additional<br />

costs. Thus, the NTC distribution part signall<strong>in</strong>g cost ( C N ) is equal to the transmission<br />

cost ( C ho ) of the one-way NTC data to the oPOA. Thus, we can get:<br />

where<br />

� j�<br />

� � � � � h � j��<br />

CN � Cbh<br />

� Cob<br />

� � � hob<br />

2 ob<br />

(Equation 4.4)<br />

hob �j� denotes the trust association hops that an AAA message has to pass<br />

through from the HAAA to the oPOA FAAA.<br />

From Equation 4.3 and 4.4, total signall<strong>in</strong>g cost related to the NTC retrieval and<br />

distribution process is<br />

H<br />

N<br />

mf<br />

�10 � 4hnb<br />

�i� � hob<br />

� j��<br />

� am<br />

ah<br />

C � C � C � 5C � � �<br />

� 2 (Equation 4.5)<br />

4.4.2 Power Save Mode NTC<br />

With the appropriate operator policies <strong>in</strong> place, the active operation mode NTC, AOMN<br />

process can be implemented to trigger the NTC exchange <strong>in</strong> a timely manner. This<br />

makes sure that a network can obta<strong>in</strong> an accurate picture of its neighbour<strong>in</strong>g networks’<br />

network trust <strong>in</strong>formation. However, the disadvantages of the AOMN are that it requires<br />

the <strong>in</strong>volvement of a mobile user carry<strong>in</strong>g active user sessions which may result <strong>in</strong><br />

compromised QoS.<br />

For this reason, an alternative method named as Power Save Mode NTC (PSMN)<br />

process was proposed. The PSMN makes use a group of mobile users <strong>in</strong> power save<br />

mode to trigger the NTC exchange between neighbour<strong>in</strong>g networks. Instead of rely<strong>in</strong>g<br />

on actual handover, Location Update (LU) and Pag<strong>in</strong>g (PA) procedures of mobile<br />

term<strong>in</strong>als <strong>in</strong> power save mode are utilised. Location update LU has been proposed to<br />

keep track of a mobile user’s locations by register<strong>in</strong>g to the network about the current<br />

location of the mobile user. The accuracy of location data obta<strong>in</strong>ed dur<strong>in</strong>g the LU is<br />

determ<strong>in</strong>ed by the def<strong>in</strong>ed update <strong>in</strong>terval [76]. Therefore, theoretically, if a f<strong>in</strong>egra<strong>in</strong>ed<br />

LU scheme is applied, a mobile user <strong>in</strong> power save mode is able to perform the<br />

- 66 -

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!