Chapter 4
EDGE Call Mode Operation
EGPRS basics
4460 GSM System Option and 4468 EDGE System Option
Version 12.20
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EGPRS basics
This section covers information on mobile phone testing in EGPRS synchronous
mode. Read this section to learn of EGPRS test prerequisites and modes before
starting a test using the Willtek 4468 EDGE System Option.
Why EGPRS tests?
EGPRS (Enhanced General Packet Radio Service) is an extension of GPRS for
higher data rates. These are achieved using a new modulation format: 8-PSK.
EDGE offers a choice between the two modulation formats GMSK and 8-PSK. The
latter transmits 3 bits per symbol, in contrast to GMSK modulation where only
1 bit per symbol is transmitted.
The amplitude of the signals transmitted by the mobile phone is no longer
constant because it is not rotating on a circle as it does for GMSK. It can actually
change from one phase state to any of the eight phase states, having the effect
that the amplitude may cross near the origin of the I/Q plane. In order to avoid
this, the whole I/Q plane is rotating by 22.5° per symbol, which ensures that the
signal never reaches the origin.
This effect has an impact on the type of amplifier that can be used and may result
in separate TX paths for GMSK and 8PSK. Depending on the type of amplifier
being used, the battery life will be constrained as well.
Like GPRS, EGPRS uses different coding schemes, combined with either GMSK or
8-PSK modulation. This allows to maintain the connection at reduced data rates
under bad radio conditions. The following table shows the different Modulation
and Coding Schemes (MCS) for EDGE.
Table 1
Modulation and Coding Schemes
MSC
Modulation
Data rate
MCS-1
GMSK
8.8 kbps
MCS-2
GMSK
11.2 kbps
MCS-3
GMSK
14.8 kbps
MCS-4
GMSK
17.6 kbps
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