Handover mechanisms in next generation heterogeneous wireless ...

Chapter 1
INTRODUCTION
New access technologies such as IEEE 802.11 Wireless Local Area Network (WLAN)
are emerging as an effective means of public wireless access. The IEEE 802.11 standard,
also known by its commercial trademark Wi-Fi, can provide high speed data services of
up to 54Mbps with a radio range of less than 1km. Small radio coverage of such access
technologies is due to several reasons, e.g. limitations of radio transmit power on using
public unlicensed bands. In contrast, cellular networks can cover much wider areas.
Current public wireless infrastructure is mainly built based on cellular network
technologies such as the Third Generation (3G) Universal Mobile Telecommunications
System (UMTS). Relying on Wideband Code Division Multiple Access (W-CDMA)
techniques for radio access, UMTS supports wide radio coverage but at a relative low
data rate of up to 384Kbps. Although more advanced standards such as High-Speed
Downlink Packet Access (HSDPA) may achieve a data rate of up to 14.4Mbps in the
downlink connection (as specified in the 3rd Generation Partnership Project (3GPP)
release 5), it may be insufficient for many multimedia applications.
The growing demand for high speed data access at anytime, anywhere and on any
device necessitates a new direction in the design of the Next Generation Wireless
Networks. From a mobile user’s viewpoint, some key features of the Next Generation
Wireless Networks include high bandwidth, low latency, and ubiquitous coverage.
However, none of the current wireless technologies can simultaneously satisfy these
needs at low cost. Intuitively, the “high bandwidth” and “ubiquitous coverage” needs of
a mobile user are best satisfied if it can freely hand over to any discovered networks to
maintain its services at all times. The interworking of the current wireless technologies
including 3G UMTS and WLAN, and other future technologies thus becomes an
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