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

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

TRUST ASSISTED HANDOVER ALGORITHM FOR RELIABLE HANDOVER<br />

users of HPLMN, because no trust association with HPLMN can be found. QoS-driven<br />

network selection schemes may <strong>in</strong>itially choose WLAN#2 as the best candidate, but<br />

later realise that mobile users are not allowed to access the selected doma<strong>in</strong>s.<br />

Accord<strong>in</strong>g to the above analysis, the handover requirements <strong>in</strong> a NG multi-technology<br />

and multi-operator network are summarised as follows. Firstly, handover algorithms<br />

process should not depend on underly<strong>in</strong>g access technologies to deal with their<br />

heterogeneities <strong>in</strong> the <strong>in</strong>terwork<strong>in</strong>g. <strong>Handover</strong> algorithms should be scalable over a<br />

variety of access technologies and allow the <strong>in</strong>troduction of new access technologies.<br />

Secondly, network trust relationship between a candidate access network and a mobile’s<br />

home network is the prerequisite for successful handover. Therefore, <strong>in</strong> a multi-operator<br />

environment, it should be checked with network selection before any handover decision<br />

is made. Thirdly, handover algorithms should be capable of accommodat<strong>in</strong>g various<br />

handover metrics such as signal strength, network conditions and so forth so as to<br />

guaranteee QoS.<br />

5.4 Trust-Assisted <strong>Handover</strong> Decision Algorithm<br />

Chapter 4 has presented a neighbour network trust <strong>in</strong>formation retriev<strong>in</strong>g scheme<br />

(named as Neighbour Trust Correlation, NTC), which is based on the analysis of a large<br />

number of mobiles’ handover history. With the NTC scheme, the network trust<br />

<strong>in</strong>formation of neighbour<strong>in</strong>g candidate networks to a mobile’s home network can be<br />

made available to an access network. Thus, it is assumed that Po<strong>in</strong>ts of Attachment<br />

(POA) at access networks have knowledge of their neighbour network trust patterns.<br />

In this section, with the <strong>in</strong>put from the NTC scheme, a Trust-Assisted <strong>Handover</strong><br />

Decision Algorithm (THOA) is proposed for mak<strong>in</strong>g handover decision <strong>in</strong> a multioperator<br />

and multi-technology environment. The proposed THOA algorithm uses the<br />

NTC data of the candidate POAs as an additional <strong>in</strong>put, and is expected to be used at<br />

the mobile term<strong>in</strong>als. Because it can learn related network trust <strong>in</strong>formation before<br />

conduct<strong>in</strong>g network selection, a mobile user is able to check whether it is possible to<br />

access a candidate network before select<strong>in</strong>g that network and <strong>in</strong>itiat<strong>in</strong>g the handover.<br />

This would avoid unnecessary handover attempts <strong>in</strong> the NG multi-technology and<br />

multi-operator network. The basic ideas beh<strong>in</strong>d the THOA are as follows. The serv<strong>in</strong>g<br />

- 89 -

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

Saved successfully!

Ooh no, something went wrong!