Telecom General Interview Question:

What is the structure of entire GSM?

Submitted by: Administrator

This diagram shows that the GSM system uses a single type of
radio channel. Each radio channel in the GSM system has a
frequency bandwidth of 200 kHz and a data transmission rate
of approximately 270 kbps. This example shows that each
radio communication channel is divided into 8 time slots (0
through 7). This diagram shows that a simultaneous two-way
voice communication session requires at least one radio
channel communicates from the base station to the mobile
station (called the forward channel) and one channel
communicates from the mobile station to the base station
(called the reverse channel). This example also shows that
some of the radio channel capacity is used to transfer voice
(traffic) information and some of the radio channel capacity
is used to transfer control messages.


Normal Burst Structures

This figure shows the field structures of the normal burst
used in the GSM system. This diagram shows that the field
structure is different for the normal burst, synchronization
burst, and the frequency correction bursts. The fields
transmitted during the normal burst include initial tail
bits (ramp-up time), training sequence, flag bits, user data
bits, final tail bits, and guard period. This diagram shows
that the first 3 bits of the time slot are dedicated to the
gradual increase of transmitter power level (ramp-up). For
the normal burst, this is followed by the information (user
data) bits. The flag bits indicate if the normal burst has
been replaced with FACCH signaling information. This diagram
shows that some of the bits in the center of the burst are
used as training bits (to allow equalizer training). At the
end of the transmitted burst there are tail bits (for error
protection) and 3 guard period bits that are used during the
gradual reduction of the RF transmitter signal (ramp-down).



Fast Associated Control Channel (FACCH) Signaling

This figure shows that GSM FACCH signaling replaces (steals)
speech frames and replaces them with control information.
This example shows the FACCH messages is divided and
transmitted over 8 sequential channel bursts and that the
speech information that would normally be transmitted is
discarded. When received, the FACCH message is reassembled
into its original message structure.
Submitted by: Administrator