Handover mechanisms in next generation heterogeneous wireless ...

TRUST ASSISTED HANDOVER ALGORITHM FOR RELIABLE HANDOVER
with each other. As such, mobile terminals need to deal with both the heterogeneities of
networking technologies and the multiplicities of network operators. Network selection
coupled with trust relationship would become a prominent issue for roaming mobile
users.
The network selection issue in heterogeneous wireless networks has raised a lot of
concerns in the 3GPP specifications [72, 91] for Public Land Mobile Network (PLMN)
and WLAN interworking. In 3GPP, it is proposed that network identity lists that are
either user controlled or operator controlled can be used for network selection by mobile
users. However, the 3GPP solutions provide very limited support to the multiplicity of
network operators in NG wireless networks. State-of-the-art handover algorithms such
as the MHOA, aims at optimising QoS by mitigating technology heterogeneity caused
by the interworking. Unfortunately, they have not taken into account complex network
trust relationships between multiple network operators, and thus are ineffective in
resolving the multiplicity problem.
Handover failure occurs in two possible cases when a mobile user attempts to attach to
its selected network in a handover. In the first case (Case A), handover authentication
can fail in the absence of roaming agreements between the selected access network and
the home network of the roaming user. This can be promptly detected by the AAA
functions at visited networks. In contrast, in the second case (Case B), the HAAA may
refuses access to the user-selected network, especially if a fine-grained AAA policy is
applied for security reasons. In this case, a long AAA delay would be expected because
the HAAA is involved in the validation. In both cases, the mobile user would be forced
to reselect another network for roaming related access. Obviously, the mobile user
would likely have missed the best time for triggering handover. Long interruption in
connections would incur as a consequence.
Generally, for the mobile-controlled handover, the unawareness of the network trust
relationship between a candidate network and the home network can cause unnecessary
handover attempts. This inevitably increases signalling overheads and results in a long
latency in a handover. Thus, the MHOA may become inefficient and has limited
scalability in a multi-technology and multi-operator environment. Current handover
approaches take into account the heterogeneities of access technologies of interworking
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