2 Channel Concepts

ORG010005 SiteMaster Introduction ISSUE 1.0.pptChannel Concepts In GSM System
GBSS Training Team
Copyright © 2006 Huawei Technologies Co., Ltd. All rights reserved.
After the completion of this course, the trainees should understand about:
Types of Channels in GSM
Different Burst and frame definition
BSS Feature Description
Chapter 1 Channel Concepts
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
2
3
0
1
6
7
4
5
2
3
0
1
slot is called a “burst”
Physical and Logical Channel
the information is carried: 200KHz and 0.577ms
The logical channel consists of the information
carried over the physical channels
Two types of Logical Channel
Traffic Channel (TCH) :
Control Channel (CCH) :
Traffic Channel (TCH)
TCH/9.6 Data Channel 9.6kb/s
TCH/4.8 Data Channel 4.8kb/s
TCH/2.4 Data Channel 2.4Kb/s
Traffic 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 TCH’s can share one physical channel, thus doubling the capacity of a cell.
FCCH
SCH
BCCH( Broadcast Control Channel )
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 )
Carries information for frame synchronization. Contains TDMA frame number and BSIC.
FCCH( Frequency Correction Channel )
Enables MS to synchronies to the frequency.
Also helps mobiles of the n cells to locate TS 0 of BCCH carrier.
BCH Channels
RACH( Random Access Channel )
AGCH( Access Grant Channel )
Downlink only
Used by the network to assign a signaling channel upon successful decoding of access bursts.
PCH( Paging Channel )
CCCH Channels
SDCCH( Standalone Dedicated Control Channel )
Uplink and Downlink
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.
Works by stealing traffic bursts.
DCCH Channels
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH
SDCCH
SACCH
FACCH
TCH/F
TCH/H
DCCH
TCH
DCH
How to use these channels?
Allocate signaling channel
Search for synchronous burst
Bursts
Burst:
Have finite duration
Sent in time and frequency windows ( Slots )
Burst Types:
Normal Burst
Frequency Correction
Synchronization Burst
Access Burst
Dummy Burst
Normal Burst
0.546ms
0.577ms
Carries traffic channel and control channels BCCH, PCH, AGCH, SDCCH, SACCH and FACCH.
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 period - 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.
Flag 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 is received 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
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Made up of 142 consecutive zeros.
Enables MS to correct its local oscillator locking it to that of the BTS.
Frequency Correction Burst
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Contains BSIC and TDMA Frame number.
Synchronisation Burst
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Used for Random and Handover access
Access Burst
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
3
3
FRAME1(4.615ms)
FRAME2
Training
sequence
Data
Data
Tail
Bits
Tail
Bits
Flag
Bit
Flag
Bit
Guard
Period
Guard
Period
0.546ms
0.577ms
Transmitted on the unused timeslots of the BCCH carrier in the downlink.
Dummy Burst
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.
GSM Multi-frames
TDMA Frames
GSM Multi-frames
TDMA Frames
0
1
0
1
2
2045
2046
2047
3h 28min 53s 760ms
1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes
1
2
3
49
48
47
50
0
1
24
25
0
1
2
23
24
25
0
48
1
2
49
50
2
3
4
5
6
7
6.12s
0
235.38ms
120ms
Basic Idea about various channels used in GSM.
Different types of bursts and frames.
Structure of bursts and frames.
Thank you

2 Channel Concepts

Documents

Transcript of 2 Channel Concepts