Handover mechanisms in next generation heterogeneous wireless ...

DYNAMIC NEIGHBOUR TRUST INFORMATION RETRIEVAL FOR GLOBAL ROAMING
size of the simulated region was changed from 4 to 18 rings. Figure 4.13 shows the
simulation results. Basically, when a region grows in size, less mobile users would be
needed on a cell basis. For example, a region consisting of 6 rings needs a minimum of
2.5 mobile users per cell to establish complete network trust pattern. In contrast, when a
region includes more than 12 rings of cells, a mobile user per cell would be sufficient.
This demonstrates that the overheads of making use of mobile users for building
network trust information can be easily controlled when the networks are expanded in
scale.
Figure 4.13 Size of rings vs. Number of mobile users required per cell [MCRT=30mins]
Since the proposed NTC distribution needs additional transmissions of data packets
from the HAAA to access networks, its signalling costs are a great concern. In the
simulation, the signalling cost of the handover plus the NTC distribution (NTC HO)
was compared with that of the standard handover process (Std HO). It is assumed that a
standard handover involves the re-authentication procedure as described in [74]. The
NTC distribution is performed during every handover. Alternatively, the intelligence
can be introduced: the NTC distribution is executed when no valid NTC data is
- 76 -