The Evolution Generation (2.5G) What Is 2.5G?

As the question implies, just what is 2.5 Generation (2.5G)? Well, 2.5G, or the
next generation transitional technology, is the method or methodology from
which existing cellular and Personal Communications Service (PCS) operators
are migrating to the next generation wireless technology referenced in
the International Mobile Telecommunications-2000 (IMT-2000) specification.
2.5G enables the wireless operators whether they utilize in cellular, PCS, or
Universal Mobile Telecommunications System (UMTS) spectrum to deploy
digital packet services prior to the availability of 3G platforms. The specific
technology and implementation path that each operator must make or has
made follows a similar decision path. The decision path that is followed is
driven largely based on the existing infrastructure that has been previously
deployed, the spectrum that is available and will be available, the growth
rate, and of course the expected services being offered.
Obviously, the decision on which platform to utilize involves guesswork
and decisions based on a fundamental belief that particular technology
platforms will enable services that are yet to be developed. The 2.5G platforms
are meant to provide the bridge between the existing 2G systems
that have already been deployed and those envisioned for 3G.
Several platforms are leading the 2.5G effort; they are as follows:
■ General Packet Radio Service (GPRS)/High Speed Circuit Switched
Data (HSCSD)
■ Enhanced Data Rates for Global Evolution (EDGE)
■ Code Division Multiple Access (CDMA2000) (phase 1)
The 2.5G platform chosen for the operating system needs to involve the
following fundamental issues independent on the technology platform:
■ The underlying technology platform in existence
■ The overlay approach (only for existing wireless operators)
■ The introduction of packet data services
■ The new user devices required
■ New modifications to existing infrastructure
This chapter will attempt to cover the vast array of 2.5G issues that an
operator needs to factor in to the decision process. Obviously, not all the
issues that need to be addressed by a wireless operator can or will be covered
in this chapter. Because the practical design issues for a 3G system are
interrelated with 2.5G systems, the design examples are included in Chapters
12, “UMTS System Design,” for UMTS, and Chapter 13, “CDMA2000
System Design,” for CDMA2000. However, having a fundamental understanding
of the major platforms being deployed will help proper technological
and business decisions to be made that can exploit the advantages of
each of the infrastructure platforms.
Some of the key concepts that need to be kept in mind when establishing
a wireless technology transition plan from 2G to 3G is the methodology
associated with the realization of the transition itself. The key concepts
associated with a 2.5G transition are as follows:
■ Existing wireless and fixed network access platforms.
■ Transition platforms required.
■ Overlay implementation.
■ No one specific standard chosen for transition.
■ New user devices required.
■ 2.5G is primarily a data-play only.
■ Additional base station and support infrastructure required.
■ 2.5G is an application enabler only and can support a host of
applications offered of which few, if any, are defined.