<p>Wireless handsets are becoming increasingly multi-modal, supporting both cellular
and wireless LAN air interfaces. When such a handset roams from one network to
another during an active voice call, the call must be re-routed into the new network.
The process of re-routing calls in this manner is referred to as a vertical handover.</p> <p>Achieving seamless WLAN-to-cellular handover can be very difficult due to the
fact that WLAN coverage can often be lost long before a cellular call leg replacement
can be established. A possible worse-case scenario occurs when mobile users walk
from indoor building WLAN coverage to outdoors during voice connections. In this
thesis, results from a measurement-based study of dual-mode handover are given.
The presented results come from extensive IEEE 802.11 measurements that were
made on the McMaster University campus. These results give important insights
into the difficulty of this problem, and relate to various system parameters such as
WiFi deployment type and link loss threshold. The results show that it is almost
impossible to successfully complete the handover unless the WLAN deployment has
been carefully engineered. In WLAN deployments which would ordinarily restrict
the use of lower data rates, the results also suggest that a "limited data rate use"
(LDU) algorithm can greatly improve the probability of seamless handover. This can
be done without adversely affecting the capacity of the WLAN network. </p> <p>Vertical handover can be performed using enterprise voice gateways which support
basic conference bridging. This feature can be used to achieve soft handover, since
a new leg of the call can be established to the conference bridge while the existing
media stream path is active. Unfortunately this requires that all intra-enterprise calls
be routed through the gateway when the call is established. In this work we consider
a SIP based architecture to perform conferenced dual-mode handover and propose a
much more scalable mechanism for short-delay environments, whereby active calls are
handed off into the conference bridge prior to the initiation of the vertical handover.
Results are presented which are taken from a dual-mode handset testbed, from analytic
models, and from simulations which characterize the scalability of the proposed
mechanism. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/16743 |
| Date | 04 1900 |
| Creators | Smadi, Mohammed N. |
| Contributors | Todd, Terence D., Electrical and Computer Engineering |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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