3

Table 1. Key differences in GSM, EDGE, and EDGE Evolution standards

GSM

EDGE

EDGE Evolution (EGPRS2)

Level A (EGPRS2-A)

Level B (EGPRS2-B)

Modulation

GMSK

3π/8 shift 8PSK

GMSK

3π/8 shift 8PSK,

+π/4 shift 16QAM,

–π/4 shift 32QAM

3π/8 shift QPSK,

+π/4 shift 16QAM,

–π/4 shift 32QAM

Bits per symbol

1

3

1, 3, 4, 5

2, 4, 5

Payload per timeslot

114 bits (57+57)

348 bits (174+174)

114 bits (57+57)

348 bits (174+174)

464 bits (232+232)

580 bits (290+290)

276 bits (138+138)

552 bits (276+276)

690 bits (345+345)

Symbol rate

270.833 ksps

270.833 ksps

270.833 ksps

325 ksps

Amplitude modulation

No

Yes

Yes

Yes

Filter

Gaussian

Linearlized Gaussian

(EDGE)

Linearlized Gaussian

(EDGE)

Narrow or wide pulse

shaping filter

BT

0.3

0.3

0.3

–

The global system for mobile communications (GSM) digital

cellular standard is a time division multiple access (TDMA)

channel access scheme that uses Gaussian minimum shift

keying (GMSK) modulation. It uses 200 kHz RF channels, time

division multiplexed, to enable up to eight users to access

each carrier.

Enhanced data rates for GSM evolution (EDGE) technology

is an upgrade to the GSM standard, providing higher data

rates in the same frequency spectrum by using higher density

modulation, 3π/8 rotating 8PSK modulation. The rotation

prevents symbol transitions through the origin, reducing the

peak-to-average power, thereby minimizing spectral re-growth

and improving power efficiency. The 3π/8 rotating 8PSK

is not a constant amplitude modulation; hence a standard

Gaussian filter (non-linear) will distort the signal. Therefore,

EDGE uses a special “linearized” version of the Gaussian

filter from GSM resulting in a spectrum that is very similar

to that of GSM, while minimizing non-linear distortion in the

baseband signal.

EDGE Evolution or EGPRS2 is a technology to offer near-

UMTS (universal mobile telecommunications system)

level data throughput with more than double the spectrum

efficiency. For a higher data rate, the EDGE Evolution signal

configuration has normal burst (NB) and higher symbol rate

(HSR) burst including new modulation formats such as QPSK,

16QAM, and 32QAM. New pulse shaping filters are defined as

narrow and wide filters for HSR. This is necessary to adjust

the HSR spectrum with normal EDGE mask tests because

GSM, EDGE, and EDGE Evolution will coexist in commercial

services.

Now included in 3GPP Release 9 is voice services over adap-

tive multi-user channels on one slot (VAMOS). VAMOS can

double the channel number assignment capacity of existing

GSM networks by sending two sub channels on one slot. It

utilizes adaptive QPSK (AQPSK), which is PSK with four state

points whose positions are adjustable via a parameter Alpha.

GSM/EDGE Technology Overview