Wireless local area networks (WLANs) are subjected to interference because of their operation in the unlicensed spectrum. WLANs' coverage ranges from about 30 to 300 m. Therefore, they are suitable only in high-density areas and thus not able to provide ubiquitous coverage.
WLAN technology is relatively inexpensive and quick to deploy. Although WLANs were originally designed to extend LANs in corporate environments, they are becoming increasingly popular to provide IP connectivity in residential, small office home office (SOHO), and campus environments. A new phenomenon in populated areas has emerged to deploy WLANs in public hotspots including airports, coffee houses, convention centers, hotels, and other public areas with a high demand for wireless data.
Both WLANs and 3G are capable of providing higher-speed wireless connections that cannot be offered by earlier 2G cellular technologies. Therefore, they seem to compete. However, each technology has niche market applications.
WLANs can cover only a small area and allow limited mobility, but provide higher data rates. Therefore, WLANs are well suited to hotspot coverage where there is a high density of demand for high-data-rate wireless services requiring limited mobility. On the other hand, 3G wireless networks, with their well-established voice support, wide coverage, and high mobility, are more suited to areas with moderate or low-density demand for wireless usage requiring high mobility. Therefore, WLANs and 3G are complementary.
The integration of 3G wireless and WLANs is highly significant to make wireless multimedia and other high-data-rate services a reality for a large population. A multimedia 3G/WLAN terminal can access high-bandwidth data services where WLAN coverage is offered, while accessing wide area networks using 3G at other places. However, this approach alone will only allow limited multi-access functionality.
To make multi-access solutions effective, we need an integrated solution to provide seamless mobility between access technologies, allowing continuity of existing sessions. 3G/WLAN integration promises to offer these capabilities seamlessly [1,2,11–13].
In the standard arena, work is going on both in the 3G partnership project (3GPP) and 3GPP2 on 3G/WLAN integration. 3GPP has specified an interworking architecture that enables users to access their 2G and 3G data services from WLANs. 3GPP2 has been initiated to examine the issues of 3G/WLAN interworking. They are finalizing stage 1 specifications of the interworking system and in the near future will start the architectural activities.
Several WLAN standardization organizations (in particular ETSI BRAN, IEEE 802.11, IEEE 802.15 and multimedia access communication (MMAC)) have agreed to set up a joint wireless interworking group (WIG) to deal with the interworking between WLANs and cellular networks. This activity is being driven primarily from Europe by ETSI BRAN.
In this chapter we focus on interworking issues of WLANs and wireless wide-area networks (WWANs). We also discuss the local multipoint distribution system (LMDS) and the multichannel multipoint distribution system (MMDS).