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Kinds of frame
TDMA Frame:-In GSM 8 TS form one TDMA frame (4.615ms), i.e. 8
physical channels are using the
same frequency band being cyclically(Every 4.615 ms) allocated
to a certain user / application.
Multiframes:- Multi-framesof physical channels allocated for
user traffic (Traffic
Channels TCH) are repetition cycles of 26 TDMA frames.
Multi-framesof physical channels allocated for signaling data
(mostly onone / several of the TS0 of the carrier of one cell) are
repetition cycles of 51
TDMA frames.
Superframe:- 51 Traffic Multi-frames. 26 Control
Multi-frames.
Time of Super-frame = 51*26*4.615 = 6.12 Sec
Hyperframe:-2048 Super-frame.
Time of Hyper-frame = 2048*6.12 = 3.5 hours.
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logical channels:Many types of logical channels exists, each
designed to carry a different message to or from
an MS. All information to and from an MS must be formatted
correctly,
Logical Channels can carry Traffic or control signals.
Traffic Channels:-Once call set-up procedures have been
completed on the control
physical channel, the MS tunes to a traffic physical channel. It
uses the Traffic Channel (TCH)logical channel. Traffic channels are
thus up link and down link.
There are two types of TCH:
Full rate (TCH) Transmits full rate speech (13 Kbits/s). A full
rate TCH occupiesone physical channel.
Half rate (TCH/2) transmits half rate speech (6.5 Kbits/s).
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Table: Illustrate the Logical Control Channels
Logical Channel Direction BTS info MS info
BroadcastChannel
Frequency Correction
Channel(FCCH)
Downlink point to
multi point
Transmits a carrier frequencyIdentifies BCCH carrier b
carrier frequency and
tune to the frequency
Synchronization channel
(SCH)
Downlink point to
multi point
Transmit information about
TDMA frame structure in a cell
and base-station identity(BSIC)
Synchronize with the
frame structure within
particular cell
Broadcast control
channel (BCCH)
Downlink point to
multi point
Broad cast some general cell
information such as :
(LAI)location area identity
max output power allowed in
the cell ,and the identity of
BCCHcarrier
Receives LAIand
compare it with existing
one in the SIM, MSset th
output power based on
information of BCCH,
finally MS stores BCCH
carriers to assist in best
hand over
Commoncontrolchannels
Paging channels (PCH)Downlink point to
point
Transmit a paging message toindicate an incoming call , the
paging message contains the
mobile identity number of the
mobile network wishes to
contact
If its identify MSIN then
the mobile will respond
to the network
Random Access Channel
(RACH)
Downlink point to
point
Receives a signal from mobile
station for signaling channel
Answer a paging messag
by request a signaling
channel
Access Grant Channel
(AGCH)
Downlink point to
point
Assigns a signaling channel
SDCCHto MS
Receives signal channel
assignment SDCCH
Dedicat
edControlChannels
Standalone Dedicated
Control Channel (SDCCH)
Uplink and
Downlink point to
point
The BTS switches to the
assignedSDCCH. the call setup
procedure is performed in idle
mode ,also used to transmit
text messages and sms
The MS switches to the
assignedSDCCH.The MS
Receives TCH assignmen
information
Slow Associated Control
Channel(SACCH)
Uplink and
Downlink point to
point
Instruct MS to transmitting
power and for timing advance
Sends the signal
measurement (strength
and quality) of its cell an
neighboring cells
Fast Associated Control
Channel(FACCH)
Uplink and
Downlink point to
point
Transmit hand over
information
Transmit necessary hand
over information in
access burst
