GSM CHHANELS
What is GSM?
GSM stands for Global System
for Mobile Communication.
GSM is an open and digital
cellular technology used for mobile
communication.
It uses 4 different frequency bands
of 850 MHz, 900 MHz, 1800 MHz
and 1900 MHz .

Types:
There are two types of GSM
channels:
Logical channels
the logical channels are
determined by the
information carried within
the physical channel.
Physical channels
• The Physical channels are
determined by the timeslot,
( a time when something
can happen or is planned
to happen, especially when
it is one of several possible
times).

There are two types of logical channels:
• Control channels
• Traffic channels

BTS
A base transceiver station (BTS) is a fixed radio transceiver in any mobile network.
The BTS connects mobile devices to the network.
 It sends and receives radio signals to mobile devices and converts them to digital signals.
It is in the mid of mobile and radio station.

Control channel:
It is most often used in the context of a trunked radio
system, where the control channel sends various data which
coordinates users in talkgroups.
In radio communication, a control channel is a central
channel that controls other constituent radios by handling
data streams.

Types OF CONTROL CHANNELS
Broadcast
channels
To connect or
work with
network
Types: FCCH SCH BCCH
To make or
receive a call:
Common
control channels
Types: PCH RACH ACCH
MS and BSS[Base-Station
Subsystem (BSS); Mobile
station (MS) ] are ready to
begin call setup procedure:
Dedicated control
channels
Types: SDCCH CBCH SACCH FACCH

TRAFFIC CHANNELS:
The traffic channel is used to transmit data to the multiple users in a TDM
fashion(Time-division multiplexing (TDM) is a method of putting multiple
data streams in a single signal by separating the signal into many
segments, each having a very short duration).

1- Full Rate TCH:
2- Half Rate TCH/2:
• It transmits half rate speech
• Its speed is 6.5kb/s.
• It can share one physical channel.
• It transmits full rate speech.
• Its speed is 13kb/s.
• A full rate TCH occupies one physical
channel.

Broadcast Channel in GSM Channels
Broadcast control channels are transmitted in downlink direction only i.e. only transmitted by
BTS.
-The broadcast channels are used to broadcast synchronization and general network
information to all the MSs within a cell.
-They are essential so that a mobile station finds a network ,synchronize it and connects with
it.

Types:
. .a. FREQUENCY CORRECTION CHANNEL (FCCH):
. Used for the frequency correction / synchronization of a mobile station.
. The repeated (every 10 sec) transmission of Frequency Bursts is called FCCH.
It uses 51 multiframe structure.
b. SYNCHRONISATION CHANNEL (SCH):
. Allows the mobile station to synchronize time wise with the BTS.
. Repeated broadcast (every 10 frames) of Synchronization Bursts is called (SCH).
It is carried in 51 multi frame structure.
c. BROADCAST CONTROL CHANNEL (BCH):
. The BROADCAST CONTROL CHANNEL (BCCH) is used to broadcast control information to every MS within a cell.
It is carried in 51 multi frame structure.

SLOW ASSOCIATED CONTROL CHANNEL(SACCH)

GSM SACCH(Slow Associated Control
Channel)
Slow Associated Control Channel is called as "associated" as this channel is always associated with either TCH or
SDCCH. It also maps on the same physical channel(T0,F0) as TCH/SDCCH. T0 is time slot and F0 is frequency.

In the downlink, SACCH is used to convey transmit power level control instructions
and timing advance information to the GSM mobile.
In the uplink, SACCH carries received signal strength, TCH quality information and
measurement report of neighboring cells etc. GSM mobile carry signaling
information using SACCH, while being connected with BTS during call flow

STAND-ALONE DEDICATED CHANNEL(SDCCH)

Stand-alone Dedicated Control Channel (SDCCH):
SACCH is transmitted on both up and downlink,MS TO BTS
just before call is connected, SACCH ensures that MSremain connected to BTS during MS
authentication
On the uplink,MS sends averaged meaursements on own BTS(signal strenght and quality) and
neighboring BTS(signal strength).
On the downlink the MS recieves system information, which transmitting power and what timing
advance to use.

GSM FACCH(Fast Associated Control Channel)

Fast Associated Control Channel:
In GSM, FACCH is used to exchange information between GSM Mobile Station(MS) and Base Transceiver
Station(BTS) more quickly than possible with SACCH.
FACCH information message can easily be transmitted in 20 ms duration, as used by traffic channel(TCH).
SACCH usually is trasmitted once every 26 frame and hence if fast information to be conveyed than FACCH is
employed. One signalling block of FACCH replace one TCH speech block. In case higher data rate is required, TCH
time slot is usually stolen to be used by FACCH.
FACCH is used both in uplink as well as downlink.

Channel signaling:
Channel signaling is signaling in which one channel in each Link is used for
signaling to control account for manage traffic on All channels of the link. Channels
used for common channel signaling does not carry user information.signals are
carried by separate network consisting of signy data links and signaling transfer
points to transfer digital signaling messages between exchanges.

Features of channel signaling:

Advantage of channel signaling:

Disadvantage of channel signaling:

GSM channels wireless