Enhanced Data Rates for Global Evolution (EDGE)

EDGE once stood for the term ‘Enhanced Data Rates for GSM Evolution.’
Not long after the technology was proposed, however, it was also suggested
that it be used as part of the evolution of IS-136 TDMA networks. In fact,
for a while, the accepted evolution path for IS-136 networks was IS-136 to
EDGE to something called UWC-136, a wideband TDMA technology. More
recently, however, some of the world’s largest IS-136 network operators
have abandoned that migration path and have opted to move towards
UMTS. In fact, those same operators are in the process of complementing
and/or replacing their existing networks with GSM/GPRS as a stepping stone towards UMTS. Consequently, UWC-136 is unlikely to be widely
deployed. Moreover, the deployment of EDGE with IS-136 will certainly not
happen on the scale once envisaged, if at all.Thus, although the G in EDGE
still officially means Global, it may well be that it will only ever be associated
with GSM. In this chapter, we focus only on the use of EDGE in a GSM
environment.
The basic goal with EDGE is to enhance the data throughput capabilities
of a GSM/GPRS network. In other words, the objective is to squeeze more
bits per second out of the same 200-kHz carrier and eight-timeslot TDMA.
This is done primarily by changing the air interface modulation scheme
from Gaussian Minimum Shift Keying (GMSK), as used in GSM, to 8 Phase
Shift Keying (8-PSK). The result is that EDGE can theoretically support
speeds of up to 384 Kbps. Thus, it is clearly more advanced than GPRS, but
still does not meet the requirements for a true 3G system (which should
support speeds of up to 2 Mbps). Consequently, one might call EDGE a
2.75G technology.
Whether EDGE will see widespread deployment is a matter of some
debate—a debate that revolves around timing, user demand for high-speed
data services, the availability of EDGE-capable terminals, and cost. From a
timing perspective, the development of EDGE and UMTS technologies are
occurring in the same timeframe. In fact, the specification of EDGE standards
is done within the Third Generation Partnership Project (3GPP) as
part of a set of specifications known as 3GPP Release 1999—the same set
of specifications that includes UMTS. From a user-demand perspective, it is
still unclear as to exactly what the killer applications will be for wireless
data and whether the speeds afforded by UMTS will really be required, or
whether EDGE speeds will be sufficient.
Then there is the issue of cost. To deploy a UMTS network, one first
requires the acquisition of UMTS spectrum. In some countries, this spectrum
has been auctioned to the highest bidder, with billions of dollars committed
by network operators simply for the right to use a certain amount of
UMTS spectrum. Once the spectrum is acquired, one then has to build a
completely new radio access network—something which can cost billions of
dollars more. To deploy EDGE instead does not require a new spectrum (at
least not in the bands set aside for UMTS) and does not require as drastic
changes to the network. Consequently, EDGE can be deployed at far less
cost than UMTS. It remains to be seen whether EDGE will be widely
deployed as a psuedo-3G system, as a stepping stone towards UMTS, or
whether operators will decide to leapfrog EDGE and move directly from
GPRS to UMTS.