1.1 Wireless Communication Systems
Wireless communication has experienced tremendous growth in the last decade. In
1991 less than 1% of the world’s population had access to a mobile phone. By the
end of 2001, an estimated one in every six people had a mobile phone [1]. During the
same period the number of countries worldwide having a mobile network increased
from just three to over 90%. In fact the number of mobile subscribers overtook the
number of fixed-line subscribers in 2002, as shown in Figure 1.1. It is predicted that
this growth will continue to rise, and by 2010 there will be more than 1700 million
mobile subscribers worldwide [2].
Apart from mobile telephone communications, Wireless Local Area Networks
(WLANs), which came on the scene less than a decade ago (1997), have also
experienced phenomenal growth. The rapid proliferation of WLAN hotspots in public
places, such as airport terminals has been astounding. In fact WLANs have now
made their way into homes, riding on the back of xDSL and cable access modems,
which are now integrated with WLAN Radio Access Points (RAPs). As a result, the
number of wireless Internet subscribers is expected to overtake the number of wired
internet users quite soon, as shown in Figure 1.1. The growth of wireless data
systems is also seen in the many new standards which have recently been developed
or are currently under development (see Section 1.2).
The rapid growth of wireless communications is mainly attributed to their ease of
installation in comparison to fixed networks [1]. However, technological
advancement, and competition among mobile operators have also contributed to the
growth. So far there have been three mobile telephone standards, launched in
succession approximately every decade. The first-generation (1G) mobile systems
were analogue, and were commissioned in the 1980s. In the 1990s, second-generation
(2G) digital mobile systems such as the Global System for Mobile communications
(GSM) came on the scene. The GSM standard has been extremely successful,
providing not only national, but international coverage as well. Thus, GSM is
currently the mainstream mobile communication system.
Both 1G and 2G systems were designed primarily to provide voice applications, and
to support circuit-switched services [4]. However, GSM does offer data
communication services to users, although the data rates are limited to just a few tens
of kbps. In contrast, WLANs originally designed to provide fixed data network
extension, support Mbps data transmission rates. The WLAN standard – IEEE
802.11, also known as Wi-Fi, was first commissioned in 1997 and offered 2 Mbps.
Since then, the standard has evolved several times responding to the sustained user
demand for higher bit-rates as shown in Table 1.1. Currently, WLANs are capable of
offering up-to 54 Mbps for the IEEE 802.11a/g, and HiperLAN2 standards operating


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