channel concepts.ppt
TRANSCRIPT
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Copyright 2006 Huawei Technologies Co., Ltd. All rights reserved.
Channel Concepts
In GSM System
GBSS Training Team
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After the completion of this
course, the trainees should
understand about:
Types of Channels in GSM
Different Burst and frame
definition
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BSS Feature Description
BSS Signaling Analysis Manual
BSC Technical Manual
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Chapter 1 Channel Concepts
Chapter 2 Bursts
Chapter 3 Frames
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Physical channel- Each timeslot on a carrier is referred to as a physical channel.
Per carrier there are 8 physical channels.
Logical channel- Variety of information is transmitted between the MS and BTS.There are different logical channels depending on the information sent. The logical
channels are of two types
Traffic channel
Control channel
Downlink
Uplink
Channel Concepts
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2 30 16 74 52 30 1
TDMA FRAME
Timeslot The information carried in one timeslot is called a burst
Physical and Logical Channel
TDMA FRAME
The physical channel is the medium over which
the information is carried: 200KHz and 0.577ms
The logical channel consists of the information
carried over the physical channels
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Two types of Logical Channel
Traffic Channel (TCH) :
Transmits traffic information, include data and
speech.
Control Channel (CCH) :
Or Signaling Channel, transmits all kinds of
control information.
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Traff ic Channel (TCH)
TCH
Traffic Channels
Speech
TCH/FS
Data
TCH/HSTCH/9.6 TCH/2.4
TCH/4.8
TCH Traffic ChannelTCH/FS Full rate Speech Channel
TCH/HS Half rate Speech Channel
TCH/9.6 Data Channel 9.6kb/s
TCH/4.8 Data Channel 4.8kb/s
TCH/2.4 Data Channel 2.4Kb/s
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Traff ic Channel (TCH)
User Data Transmission:
Speech and data (not SMS) are transmitted using traffic
channel (TCH).
Full Rate (TCH):Transmits full rate speech
(13Kbits/sec). A full rate TCH occupies one physical
channel.
Half Rate (TCH/2):Transmits half rate speech
(6.5Kbits/sec). Two half rate TCHs can share one
physical channel, thus doubling the capacity of a cell.
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FCCHSCH
CCH (Control Channels)
DCCH
SDCCH
BCH
BCCH Synch. CH.ACCH
SACCHFACCH CCCH
RACH CBCH
PCH/AGCH
Broadcast Control Channel BCCH
Common Control Channel CCCH
Dedicated Control Channel DCCH
Associated Control Channel ACCH
Control Channel (CCH)
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BCCH( Broadcast Control Channel ) Downlink only Broadcasts general information of the serving cell called System
Information
BCCH is transmitted on timeslot zero of BCCH carrier Read only by idle mobile at least once every 30 sec.
SCH( Synchronization Channel )
Downlink only Carries information for frame synchronization. Contains TDMA
frame number and BSIC.
FCCH( F requency Correction Channel )
Downlink only. Enables MS to synchronies to the frequency. Also helps mobiles of the n cells to locate TS 0 of BCCH carrier.
BCH Channels
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RACH( Random Access Channel )
Uplink only Used by the MS to access the Network.
AGCH ( Access Grant Channel )
Downlink only Used by the network to assign a signaling channel upon
successful decoding of access bursts.
PCH( Paging Channel )
Downlink only. Used by the Network to contact the MS.
CCCH Channels
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SDCCH ( Standalone Dedicated Control Channel )
Uplink and Downlink Used for call setup, location update and SMS.
SACCH ( Slow Associated Control Channel )
Used on Uplink and Downlink only in dedicated mode. Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info.
FACCH ( Fast Associated Control Channel )
Uplink and Downlink. Associated with TCH only. Is used to send fast messages like handover messages. Works by stealing traffic bursts.
DCCH Channels
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RACH CCCHCCH
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH
Uplink Logical channel
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FCCH
SCH
BCCH
PCH
AGCH
BCCH
CCCH
CCH
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH
Downlink Logical channel
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Allocate signaling channel
Power-off
Idle mode
Dedicated mode
Idle mode
How to use these channels?
Search for frequency correction burst
Search for synchronous burst
Extract system information
Monitor paging message
Send access burst
Set up the call
Allocate voice channel
Conversation
Release the call
SCH
FCCH
BCCH
PCH
RACH
AGCH
SDCCH
SDCCH
TCH
FACCH
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Chapter 1 Channel Concepts
Chapter 2 Bursts
Chapter 3 Frames
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Bursts
Burst:
Unit of transmission ( about hundred modulated bits )
Have finite duration
Occupy a finite number of spectrum
Sent in time and frequency windows ( Slots )
Burst Types:
Normal Burst
Frequency Correction
Synchronization Burst Access Burst
Dummy Burst
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Normal Burst
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
57 bits 57 bits26 bits 33
FRAME1(4.615ms) FRAME2
Training
sequenceData Data
Tail
Bits
Tail
Bits
Flag
Bit
Flag
Bit
Guard
Period
Guard
Period(8.25 bits)
0.546ms0.577ms
Carries traffic channel and control channels BCCH, PCH, AGCH, SDCCH, SACCH and
FACCH.
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Data- Two blocks of 57 bits each. Carries speech, data or control info.
Tail bits - Used to indicate the start and end of each burst. Three bits always 000.
Guard per iod- 8.25 bits long. The receiver can only receive and decode if the
burst is received within the timeslot designated for it.Since the MS are moving.
Exact synchronization of burst is not possible practically. Hence 8.25bits
corresponding to about 30us is available as guard period for a small margin of
error.
F lag bits- This bit is used to indicate if the 57 bits data block is used as FACCH.
Training Sequence - This is a set sequence of bits known by both the
transmitter and the receiver( BCC of BSIC). When a burst of information isreceived the equalizer searches for the training sequence code. The receiver
measures and then mimics the distortion which the signal has been subjected to.
The receiver then compares the received data with the distorted possible
transmitted sequence and chooses the most likely one.
Normal Burst
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
142 bits 33
FRAME1(4.615ms) FRAME2
Fixed Data
Tail
Bits
Tail
Bits
Guard
Period
Guard
Period(8.25 bits)
0.546ms0.577ms
Carries FCCH channel. Made up of 142 consecutive zeros. Enables MS to correct its local oscillator locking it to that of the BTS.
Frequency Correction Burst
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
39 bits 33
FRAME1(4.615ms) FRAME2
Synchronisation
Sequence
Tail
Bits
Tail
Bits
Guard
Period
Guard
Period(8.25 bits)
0.546ms0.577ms
64 bits 39 bits
Encrypted
Bits
Encrypted
Bits
Carries SCH channel. Enables MS to synchronies its timings with the BTS. Contains BSIC and TDMA Frame number.
Synchronisation Burst
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
41 bits8
FRAME1(4.615ms) FRAME2
Encrypted
Sequence
Tail
Bits
Guard
Period GuardPeriod
0.577ms
36 bits 68.25 bits
Synchronization
Bits
Carries RACH and FACCH channels. Used for Random and Handover access
Access Burst
3
Tail
Bits
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0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
57 bits 57 bits26 bits 33
FRAME1(4.615ms) FRAME2
Training
sequenceData Data
Tail
Bits
Tail
Bits
Flag
Bit
Flag
Bit
Guard
Period
Guard
Period
0.546ms0.577ms
Transmitted on the unused timeslots of the BCCH carrier in the downlink.
Dummy Burst
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Chapter 1 Channel Concepts
Chapter 2 Bursts
Chapter 3 Frames
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Frames
26 TDMA frame multiframe: Used to carry
traffic channels. TCH,SACCH and FACCH.
51 TDMA frame multiframe: Used to carry
control channels BCCH,CCCH,SDCCH and
SACCH.
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TDMA Frames
0 1
0 1 2 43 46 47 48 5049
51Frame Multi-frames
0 1 10
CONTROL CHANNELS
2 3 4 5 6 7 2 3 5 764
GSM Multi-frames
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GSM Multi-frames
TDMA Frames
0 1
0 1 2 43 21 22 23 2524
26Frame Multi-frames
0 1 10
TRAFFIC CHANNELS
2 3 4 5 6 7 2 3 5 764
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0 1
0 1 2 2045 2046 2047
1 Hyperframe = 2048 superframes = 2,715,648 TDMA frames3h 28min 53s 760ms
1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes
1 2 3 494847 50
0 1 24 25
0 1 2 23 24 25 0 481 2 49 50
2 3 4 5 6 7
6.12s
0
235.38ms120ms
Control 51 - Frame MultiframeTraffic 26 - Frame Multiframe
4.615ms
TDMA Frame
Hyperframe and Superframe Structure
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Basic Idea about various channels used
in GSM.
Different types of bursts and frames.
Structure of bursts and frames.
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