ABSTRACT
As the wireless Internet rolls out over the next several years, there will be an increasing demand for new mobile devices (e.g., new cellular phones, PDAs, laptop and palmtop computers), services (e.g., m-commerce, wireless Web, high-quality wireless multimedia), and technologies (e.g., W-CDMA, Wi-Fi, WiMax) that can meet the needs of mobile users. Recent trends indicate that a wide variety of mobile devices will be available, each requiring specialized services and protocols. Connectivity between mobile devices and emerging diverse wireless service providers is likely to hinge on the capability of each provider’s infrastructure to support a variety of mobile devices as well as the capability of mobile devices to connect to heterogeneous access networks. Today, the incompatibility of signaling systems and physical-layer radio technologies prevents mobile devices from roaming between heterogeneous wireless networks. Such factors limit the vision of seamless mobility. For example, a CDMA-based cellular phone cannot be easily connected to an IEEE 802.11-based wireless local area network (WLAN). Although a variety of handoff algorithms have been proposed and investigated in the past, these algorithms are mostly tailored toward the needs of some specific type of mobile device or access network. The diversity in signaling systems that characterize wireless access network architectures poses a challenge in realizing intersystem handoff. Furthermore, access network protocols make specific assumptions about the capability of mobile devices; for example, many Mobile IP-based approaches assume that handoff control is located at the mobile device. Such mobile-controlled handoff schemes may not be suitable for many low-power devices that are incapable of continuously monitoring channel quality measurements.
