Cont... ➢
GSM frame structure is used to transmit the data.
➢
The GSM frame structure establishes schedules for the predetermined use of time slots.
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By the use of a frame structure, both the mobile and the base station are able to communicate.
By using GSM frame structure ➢
The voice data and signaling information is passed.
➢
What types of information are being transmitted.
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The GSM frame structure provides the basis for the various physical channels used within GSM.
➢
t is at the heart of the overall ov erall system.
Basic GSM frame structure ➢
The basic element in the GSM frame structure is the frame itself.
➢
!ight slots, each used for different users within the T"M# system.
➢
The slots for transmission and reception for a given mobile are offset in time so that the mobile does not transmit and receive at the same time.
Cont...... ➢
The BS transmits two types of channel.
➢
Traffic and Control.
➢
Traffic$%one for the traffic on the main traffic carrier fre&uency.
➢
Control$%The 'nd for the control on the beacon fre&uency.
Time Slot Structure ➢
Time slots are the smallest division of a communication channel.
➢
t is assigned to particular users in a communication system.
➢
Time slots can be combined for a single user to increase the total data transfer rate available to that user.
➢
n some systems, time slots are assigned dynamically (G)*S+.
Cont... ➢
Slot structure is the division of a time slot into different fields (information+parts.
➢
Slot structure fields typically include
%$➢
# preamble for synchroniation.
➢
Control header (e.g. address information+.
➢
-ser data, and error detection.
Cont.... ➢
The no of data bits in a ts depending on the type of the user data.
➢
The structure of the time slot can vary.
➢
f the ts is on the - or " radio channel ,!ach normal time slot contains /01 bits of information.
➢
Some time slot data bits are used for user data and other bits are dedicated for control.
Cont... ➢
2or voice communication, users have a fi3ed assignment of particular time slots.
➢
2or pac4et data transmission (such as G)*S+, time slots are dynamically assigned.
Cont... ➢
Time slots include ramp up and ramp down periods to minimie rapid changes in radio transmitter power.
➢
The ramp up and ramp down time is used to reduce unwanted radio emissions that occur from rapidly changing signals.
➢
# single time slot transmission is called a radio burst.
➢
5 types of radio bursts are defined in the GSM system,Such as 2CB,SB,#B,"B,6B
GSM multi frame ➢
The GSM frames are grouped together to form multi frames.
➢
There are two type GSM multi frame structures$Such as
➢
Traffic multi frame 7Control multi frame
Traffic multi frame ➢
The Traffic Channel frames are organied into multi frames consisting of '8 bursts.
➢
t ta4ing /'9 ms.
➢
n a traffic multi frame,'0 bursts are used for traffic.
Cont... ➢
These are numbered 9 to // 7 /: to '0.
➢
;ne of the remaining bursts is then used to accommodate the S#CC<.
➢
the remaining frame ('5+ is idle.
➢
The actual position used alternates between position /' and '5.
Control multi frame ➢
the Control Channel multi frame that comprises 5/ bursts.
➢
t ta4ing ':5.0 ms.
➢
t always occurs on the beacon fre&uency in time slot ero.
➢
t may also occur within slots ', 0 and 8 of the beacon fre&uency as well.
➢
This multi frame is subdivided into logical channels.
Cont... ➢
The logical channels are following
%$➢
2re&uency correction burst.
➢
Synchroniation burst.
➢
Broadcast channel (BC<+.
➢
)aging and #ccess Grant Channel ()#CC<+
➢
Stand #lone "edicated Control Channel (S"CC<+.
Super frame ➢
# super frame is a multi frame se&uence that combines the period of a 5/multiframe with '8 multi frames.
➢
t ta4ing 8./' seconds.
➢
The use of the super frame time period allows all mobile devices to scan all the different time frame types at least once
# hyper frame is a multi frame se&uence that is composed of '901 super%frames.
➢
t is the largest time interval in the GSM system.
➢
t ta4ing : hours, '1 minutes, 5: seconds.
➢
The hyper frame allows to synchronie fre&uency hopping se&uence 7 encryption processes for voice privacy of subscribers= conversations.
The 5/%frame Control Channel Multi frame (BCC<>CCC<+ ➢
The BCC<>CCC< 5/%frame structure will apply at TS 9 for each T"M# frame on the ?BCC< carrier.
➢
The *2 carrier fre&uency to which BCC< is assigned on a per cell basis.
➢
one T"M# frame with the first repetition (numbered 9+ at the bottom.
Cont..... ➢
- (MS@BSS+ all time slot 9s are allocated to *#C<.
➢
Because *#C< is the only control channel in the BCC<>CCC< group which wor4s in the - direction.
➢
" (BSS@MS+, the arrangement is more interesting.
➢
Starting at frame 9 of the 5/%frame structure, the first time slot 9 is occupied by a fre&uency burst (2B+.
➢
The second by a synchroniing burst (?S=+ and then the following four repetitions of time slot 9 by BCC< data (B+ .
Beacon 2re&uency Channel ➢
t is at Slot A 9 channel (T"M# Channel 9+.
➢
t is formatted as 5/%multi frame.
➢
/st (Slot A 9 of the multi frame+ is 2CC<.
➢
The ne3t one is SC<.
➢
This pair (2CC< 7 SC<+ repeats 53 in a multi frame.
➢
BCC< channel 0 slots long appears once per 5/multi frame and it ta4es Slot A ' to 0 (:rd,0th,5th7 8th slots+.
Cont.... ➢
The remaining slots care common control channels or CCC< ()C< and #GC<+
➢
BCC<, CCC<, S"CC<, S#CC< and 2#CC<, form a message of 0 slots long.
➢
The beacon is a down lin4 channel.
➢
GSM always has a pair of fre&uencies (up and down lin4s+ per #*2C6.
➢
up lin4 contains *#C< channel.
