Abstract:
Wireless local area networks (WLANs) have emerged to provide mobility or
roaming capability to its nodes/terminals and have permitted connectivity to the
Internet at a cheap rate using wireless access points. On the other hand, due to the
recent technological achievements in cellular mobile communications, a mobile
station (MS) may now be used to get connected to the Internet using CDMA 2000.
Roaming of nodes/terminals between adjacent WLANs and that of an MS
between CDMA 2000 networks are possible using the respective handover
schemes already available. However, it would be a novel initiative for a mobile
node (such as a laptop PC or an MS) to switch between WLAN and CDMA 2000
network, and vice versa, for ensuring a continuous on-line connectivity with the
Internet. In this work, an investigation has been carried out into the existing
interworking protocols of different OSI layers in order for them to be modified for
interworking between WLAN and CDMA 2000.
As part of the current research a new roaming technique have been developed
modifying the existing handover schemes. To comprehend the actual practical
scenario and explore the conditions of handover, two cases have been studied,
namely, WLAN to WLAN handover and CDMA to CDMA handover. Drive tests
have been performed in this regard, and the relevant information and data
collected from the drive tests have been scrutinized and analyzed very carefully.
Some logics and underlying operating principles have been comprehended from
the practical drive test data. The main challenge was to ensure how mobile
Internet users would get connected to the WLAN within the hot-spots and switch
to CDMA 2000 network when WLAN is not accessible. The core idea is that the
mobile device (a laptop, for example) will have two interface cards installed: one
for the wireless LAN interface card and another for the CDMA 2000. Both cards
need to be powered on for all the time; but as long as the laptop is under any
access point coverage area of a WLAN, the CDMA card remains inactive.
Following the data collection, appropriate simulation analysis has been performed
using the Matlab toolbox. A software named ‘WLAN-CDMA handover’ has been
developed, to manage the handover between WLAN and CDMA 2000 and vice
versa, using the C Sharp programming language. The developed software
measures the received signal strength of the wireless LAN access point through its
interface card. As soon as it detects the signal strength below a pre-defined
threshold value, it activates the CDMA card and data traffic is re-routed through
the CDMA network. Finally, a test bed has been developed for testing the
handover between WLAN and CDMA for a simple scenario. The test confirms
that the algorithm can initiate and complete successful handover as and when
needed.
The advantage of a WLAN network is lower cost and higher data rate compared to
a CDMA 2000 network. The mobility of WLAN is low with only over small
areas, whereas CDMA 2000 offers relatively lower date rates but much higher
mobility with a reliable nationwide coverage. The proposed technique, which is
the combination of the two, would now result in a low cost high data rate Internet
connectivity within certain hot-spots under the WLAN environment, while still
obtaining reliable connection outside the hot-spots under the CDMA 2000
environment.
