Heterogeneous wireless networks (HWNs) provide flexible and diversified
wireless network access (e.g., cellular, IEEE 802.11) by integrating cellular networks,
wireless LANs, and ad hoc networks with the Internet. It has been
emerging as a promising solution to offer a variety of exciting applications,
anytime and anywhere. The flexibility and benefits of the HWN, for example,
is to extend the service coverage of the existing cellular and WLAN infrastructure,
to improve the communication throughput, and reduce packet
transmission latency, based on availability of different types of radio network
in the roaming area (cellular, WLAN, or others). In the study, we answer some
fundamental questions in the design and deployment of a HWN. The first is
how to effectively operate a mobile terminal in ad hoc mode to access the
Internet through a cellular network, WLAN or other underlying wireless access
networks. The second is how to design ubiquitous seamless mobility support
for a roaming user, allowing ubiquitous and bi-directional Internet accessibility,
connectivity, and mobility. Finally, it answers the questions that what
is the security threats for a mobile terminal that is operating in the ad hoc
mode, and how to provide information confidentiality for a continuously moving
mobile terminal.