Chapter 1 11
Understanding EDGE (with GSM)
What Is EDGE (with GSM)?
What Is an ARFCN?
An ARFCN is the Absolute Radio Frequency Channel Number used in
the EDGE (with GSM) system. Each RF channel is shared by up to
eight mobile stations using Time Division Multiple Access (TDMA). The
ARFCN is an integer (in a range dependent on the chosen standard,
refer to Table 1-1) which designates the carrier frequency.
What are Timeslots?
EDGE (with GSM) utilizes Time Division Multiple Access (TDMA) with
eight time slots per RF channel which allows eight users to use a single
carrier frequency simultaneously. Users avoid one another by
transmitting in series. The eight users can transmit once every 4.62 ms
for 1 timeslot which is 577 µs long. The eight user timeslots are
numbered from 0 to 7.
Typically, each 577 µs timeslot has a length of 156.25 bit periods, which
consists of 148 data bits and 8.25 guard bits. The 4.62 ms required to
cycle through eight timeslots is called a frame. In a TDMA system, the
shape of each transmitted burst must be controlled carefully to avoid
over-lapping bursts in time.
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