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Introduction
EDGE
is the next step in the evolution of GSM and IS- 136. The objective of the new
technology is to increase data transmission rates and spectrum efficiency and
to facilitate new applications and increased capacity for mobile use. With the
introduction of EDGE in GSM phase 2+, existing services such as GPRS and high-speed
circuit switched data (HSCSD) are enhanced by offering a new physical layer. The
services themselves are not modified. EDGE is introduced within existing specifications
and descriptions rather than by creating new ones. This paper focuses on the packet-switched
enhancement for GPRS, called EGPRS. GPRS allows data rates of 115 kbps and, theoretically,
of up to 160 kbps on the physical layer. EGPRS is capable of offering data rates
of 384 kbps and, theoretically, of up to 473.6 kbps. A
new modulation technique and error-tolerant transmission methods, combined with
improved link adaptation mechanisms, make these EGPRS rates possible. This is
the key to increased spectrum efficiency and enhanced applications, such as wireless
Internet access, e-mail and file transfers.
GPRS/EGPRS
will be one of the pacesetters in the overall wireless technology evolution in
conjunction with WCDMA. Higher transmission rates for specific radio resources
enhance capacity by enabling more traffic for both circuit- and packet-switched
services. As the Third-generation Partnership Project (3GPP) continues standardization
toward the GSM/EDGE radio access network (GERAN), GERAN will be able to offer
the same services as WCDMA by connecting to the same core network. This is done
in parallel with means to increase the spectral efficiency. The goal is to boost
system capacity, both for real- time and best-effort services, and to compete
effectively with other third-generation radio access networks such as WCDMA and
cdma2000.
Technical
differences between GPRS and EGPRS
Introduction
Regarded
as a subsystem within the GSM standard, GPRS has introduced packet-switched data
into GSM networks. Many new protocols and new nodes have been introduced to make
this possible. EDGE is a method to increase the data rates on the radio link for
GSM. Basically, EDGE only introduces a new modulation technique and new channel
coding that can be used to transmit both packet-switched and circuit-switched
voice and data services. EDGE is therefore an add-on to GPRS and cannot work alone.
GPRS has a greater impact on the GSM system than EDGE has. By adding the new modulation
and coding to GPRS and by making adjustments to the radio link protocols, EGPRS
offers significantly higher throughput and capacity. GPRS
and EGPRS have different protocols and different behavior on the base station
system side. However, on the core network side, GPRS and EGPRS share the same
packet-handling protocols and, therefore, behave in the same way. Reuse of the
existing GPRS core infrastructure (serving GRPS support node/gateway GPRS support
node) emphasizes the fact that EGPRS is only an "add-on" to the base
station system and is therefore much easier to introduce than GPRS . In addition
to enhancing the throughput for each data user, EDGE also increases capacity.
With EDGE, the same time slot can support more users. This decreases the number
of radio resources required to support the same traffic, thus freeing up capacity
for more data or voice services. EDGE makes it easier for circuit-switched and
packet-switched traffic to coexist, while making more efficient use of the same
radio resources. Thus in tightly planned networks with limited spectrum, EDGE
may also be seen as a capacity booster for the data traffic.
EDGE
technology
EDGE leverages the knowledge gained
through use of the existing GPRS standard to deliver significant technical improvements.
Figure 2 compares the basic technical data of GPRS and EDGE. Although GPRS and
EDGE share the same symbol rate, the modulation bit rate differs. EDGE can transmit
three times as many bits as GPRS during the same period of time. This is the main
reason for the higher EDGE bit rates. The differences between the radio and user
data rates are the result of whether or not the packet headers are taken into
consideration. These different ways of calculating throughput often cause misunderstanding
within the industry about actual throughput figures for GPRS and EGPRS. The data
rate of 384 kbps is often used in relation to EDGE.
The International Telecommunications
Union (ITU) has defined 384 kbps as the data rate limit required for a service
to fulfill the International Mobile Telecommunications-2000 (IMT-2000) standard
in a pedestrian environment. This 384 kbps data rate corresponds to 48 kbps per
time slot, assuming an eight-time slot terminal.
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