3G: W-CDMA for IMT-2000

3G: W-CDMA for IMT-2000
The motivation for migrating to 3G technologies was to develop an international
standard combining and gradually replacing 2G digital cellular, PCS, and mobile data services. The 3G systems were expected to improve voice quality, expand network
capacity, and increase the data rates of wireless data services. The primary standard
for 3G systems is referred to as International Mobile Telecommunications Beyond the
Year 2000 (IMT-2000).
Among the several radio transmission technology (RTT) proposals submitted to
the International Telecommunications Union (ITU), most were based on the use
of CDMA. Given the experience gained with 2G cellular systems, it was recognized
that CDMA systems provide voice quality superior to that of other systems. Furthermore,
CDMA provides a very flexible air-interface design amenable to customization
for higher-rate multimedia applications.
Two Approaches for IMT-2000. In the deliberations on RTT proposals for IMT-2000,
there were two major overall approaches: (1) wideband CDMA (W-CDMA) based on
the UMTS Terrestrial Radio Access (UTRA) FDD and TDD proposals, and (2) the
cdma2000 proposal, which is backwardly compatible with the IS-95 standard. The
first approach is intended to build on the success of the installed GSM infrastructure
(UMTS/IMT-2000); the second approach is intended to build on the experience
with cdmaOne (cdma2000/IMT-2000). The distinctions between these two overall
approaches lie mainly in chip-rate selection, synchronous-versus-asynchronous base
station operation, and pilot structure [Zen00].
3G Perspective on Wireless Access Methods. Figure 2.2 provides an overview of current
wireless access methods. The horizontal axis shows user bit rates in Mb/s, and
the vertical axis gives an indication of relative user mobility for various categories of
networks. For wide-area networks, in the low-bit-rate region, we see 2G cellular systems
with bit rates limited to about 50 kb/s but with a wide range of mobility options.
The 3G cellular systems provide the same mobility characteristics and offer data rates
up to about 1 Mb/s. WLANs provide even higher data rates, 10 Mb/s and higher, but
with more restricted user mobility. Wireless personal area networks (WPANs) provide data rates comparable to those of 3G cellular systems but are designed to enable connectivity
between wireless devices over relatively short distances. Of course, a major
distinction between the WANs, on the one hand, and WLANs and WPANs, on the
other, is licensed versus unlicensed operation, respectively.
Just as was the case for the 2G market, it is useful to distinguish two sectors of the
3G market, but here the two sectors must be defined somewhat differently to reflect the
changes that have taken place in the evolution from 2G to 3G. First, we can identify
a 3G market sector characterized as a voice-oriented cellular market that integrates
cellular, PCS, and mobile data systems and services. The 3G IMT-2000 standards
harmonization process will provide the underlying access methods in these systems.
These systems will all operate in licensed bands subject to frequency administration
and regulation.
Second, we have a data-oriented market sector characterized by broadband and ad
hoc wireless systems. This sector includes traditional WLAN products operating in
unlicensed bands providing wireless Internet access as well as newer WPANS and
emerging ad hoc networks providing wireless connectivity between consumer devices.