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.