OMF000001 Um interface and radio channels ISSUE1.4
Wireless Training Department
Contents
Overview Processing of voice signal Radio channel
Contents
Overview Processing of voice signal Radio channel
Radio Interface
PSTN ISDN
Another MSC
Um BSC BTS MS
A-bis interface
A interface
Um
MSC
MAP interface
HLR/AUC/LR MS
OMC
Um interface
SMC
Hierarchical Structure of Um Interface
Communication management (CM) Network application layer (L3) Mobility and security management (MM) Radio resources management (RR)
Data link layer (L2)
RACH
Integrated management
BCCH
AGCH/PCH A GCH/PCH
SDCCH SDCC H
TCH0 TCH1 TCH2
SACCH
SACCH
Physical link layer (L1) Multiframe
TCH
TCH23 IDL
FACCH
Radio Access Technology
Time
Time
TDMA
FDMA
Frequency
Frequency
Time CDMA Code
Frequency
Radio Access Technology
Time
Time
TDMA
FDMA
Frequency
Frequency
Time CDMA Code
Frequency
Contents
Overview Processing of voice signal Radio channel
Voice Signal Processing
20ms A/D
Voice
8KHz
13bit
Segme ntation
Speech coding
13kbit/s
Channel coding
22.8kbit/s
33.8kbit/s Interleaving
Encryption
Burst formatting
Modulation
Transmission
Speech Coding
The coding mode is called Regular Pulse Excited-Long Term Prediction (RPE-LTP). It works as follow: 8KHZ of sampling is performed first, then divided into frames with 20ms; every frame has 4 sub-frames; the duration of every sub-frame is 5ms; and the pure bit rate is 13kbit/s.
Channel Coding
+3 50bit
132bit
78bit
*2+4
Block coder Excited coder
456bit
Interleaving B 1 2 3 4 5 6 7 8 ...
First interleaving:
....
... 452 453 454 455 456
B0
B1 B2
B3 B4 B5
B6 B7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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449
450
451
452
453
454
455
456
....
Second interleaving:
{A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1}
{B6,C2}
{B7,C3}
Interleaving B 1 2 3 4 5 6 7 8 ...
First interleaving:
....
... 452 453 454 455 456
B0
B1 B2
B3 B4 B5
B6 B7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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449
450
451
452
453
454
455
456
....
Second interleaving:
{A4,B0} {A5,B1} {A6,B2} {A7,B3} {B4,C0} {B5,C1}
{B6,C2}
{B7,C3}
Voice Burst
3
57
1
26
1
57
3
Timing Advance (TA)
The mobile phone should send the signal in advance!!
TA Transmission delay t
Transmission delay t
Timing Advance (TA)
The mobile phone should send the signal in advance!!
TA Transmission delay t
Transmission delay t
Frequency Hopping Frequency
f0 f1 f2 f3 f4 Frame Time
Frequency Hopping Frequency
f0 f1 f2 f3 f4 Frame Time
DTX
DTX: Discontinuous Transmission
Shut off the transmission at voice intervals;
Only transmit SID frames’
The transcoder at the RX terminal produces comfortable noise.
VAD: Voice Activity Detection
Implemented by the transcoder.
Prolong battery life and reduce interference
DTX
DTX: Discontinuous Transmission
Shut off the transmission at voice intervals;
Only transmit SID frames’
The transcoder at the RX terminal produces comfortable noise.
VAD: Voice Activity Detection
Implemented by the transcoder.
Prolong battery life and reduce interference
Power Control
Prolong battery life
Reduce network interference
Include both uplink power control and downlink power control
Level and quality are taken into account
BSC is the final adjudicator Signal level Target level value: e.g. -85 dm BCCH Carrier is not involved in power control.
Time
Contents
Overview Processing process of voice channel Radio channel
Frame and Channel
Frequency
200kHz
Time
BP 15/26ms
Slit
Frame 1 hyper frame=2048 super-frames=2715648TDMA frames (3 hours, 28 minutes, 53 seconds and 760 milliseconds) 0
TCH SACCH/T FACCH
1
2
3
2045
2044
2046
BCCH CCCH SDCCH
1 super-frame=1326TDMA frames (6.12 seconds) 1
0
2
0
3
47
48
1
49
24
1 multiframe=26TDMA frames (120ms) 0
1
2047
50 25
1 multiframe=51TDMA frames (3060/13ms)
24
25
1
0
49
50
1TDMA frame=8 timeslots (120/26=4.615ms) 0
2
1
3
4
5
6
7
1 timeslot=156.25 bit duration (15/26=0.577ms) (1 bit duration: 48/13=3.68us) Normal burst (NB)
Frequency correction burst (FB) Synchronous burst (SB) Access burst (AB)
TB 3
58 information bits
26 training sequences
TB 3 TB 3
58 information bits
TB GP 3 8.25
Constant bit 142 Information bit 39
TB GP 3 8.25
GP Extended training sequence 64Information bit 39 TB 3 8.25
TB Synchronous sequence 41 3
TB Information bit 36 3
GP 68.25
TB: Tail bit GP: Guard period
Frame 1 hyper frame=2048 super-frames=2715648TDMA frames (3 hours, 28 minutes, 53 seconds and 760 milliseconds) 0
TCH SACCH/T FACCH
1
2
3
2045
2044
2046
BCCH CCCH SDCCH
1 super-frame=1326TDMA frames (6.12 seconds) 1
0
2
0
3
47
48
1
49
24
1 multiframe=26TDMA frames (120ms) 0
1
2047
50 25
1 multiframe=51TDMA frames (3060/13ms)
24
25
1
0
49
50
1TDMA frame=8 timeslots (120/26=4.615ms) 0
2
1
3
4
5
6
7
1 timeslot=156.25 bit duration (15/26=0.577ms) (1 bit duration: 48/13=3.68us) Normal burst (NB)
Frequency correction burst (FB) Synchronous burst (SB) Access burst (AB)
TB 3
58 information bits
26 training sequences
TB 3 TB 3
58 information bits
TB GP 3 8.25
Constant bit 142 Information bit 39
TB GP 3 8.25
GP Extended training sequence 64Information bit 39 TB 3 8.25
TB Synchronous sequence 41 3
TB Information bit 36 3
GP 68.25
TB: Tail bit GP: Guard period
Burst • Access burst (AB): Used in MS initial access Tail bit
8bit
Data 41 synchronous bits
Tail bit
36 encrypted bits
3bit
Guard interval
68.25bit
• Frequency correction burst (FB): Used in frequency synchronization between MS and BTS Tail bit
Data
3bit
142bit
Tail bit
Guard interval
3bit
8.25bit
• Synchronous burst (SB): Used in timing synchronization between MS and BTS Tail bit
3bit
Data
Data 39 encrypted bits
64 synchronous bits
Tail bit
39 encrypted 3bit bits
Guard interval
8.25bit
Burst
• Normal burst (NB): Used to carry the information of the traffic channel and the control channel except for RACH Tail bit
Data
3bit
57 encrypted bits
Training sequence
1 26bit 1
Data 57 encrypted bits
Tail bit
Guard interval
3bit
8.25bit
Frame stealing flag
• Dummy burst (DB): Used in transmission of filling frames by BTS at timeslots when there is no information delivered Tail bit
3bit
Tail bit 142 modulation bits
3bit
Guard interval
8.25bit
Logical Channel Type
GSM900 and DCS1800 have the same logical channel category Logical channel
Common channel (CCH)
Broadcast control channel (BCCH)
FCH
SCH
Dedicated channel (DCH)
Common control channel (CCCH)
BCCH PCH (system information)
AGCH
RACH
Voice channel (TCH)
Control channel
SDCCH
FACCH
SACCH
TCH/F
TCH/H
TCH/9.6F TCH/ 4.8F, H TCH/ 2.4F, H
Downlink Logical Channel
FCCH Common Channel
BCCH
SCH BCCH
CCCH
PCH AGCH
SDCCH
Dedicated Channel
DCCH
SACCH FACCH
TCH
TCH/F TCH/H
Downlink Logical Channel
FCCH Common Channel
BCCH
SCH BCCH
CCCH
PCH AGCH
SDCCH
Dedicated Channel
DCCH
SACCH FACCH
TCH
TCH/F TCH/H
Uplink Logical Channel
RACH
CCCH
Common channel
SDCCH SACCH
DCCH
FACCH TCH/F TCH/H
TCH
Dedicated channel
Uplink Logical Channel
RACH
CCCH
Common channel
SDCCH SACCH
DCCH
FACCH TCH/F TCH/H
TCH
Dedicated channel
Use of Logical Channels
“off” state
Search for frequency correction burst Search for synchronization sequence Read system information
idle mode
Listen paging message Send access burst Wait for signaling channel allocation
dedicated mode
Call setup Assign traffic channel Conversation Call release
idle mode
FCCH SCH BCCH PCH RACH AGCH SDCCH SDCCH TCH FACCH
Physical Combination of Logical Channel
26-frame multiframe TCH/F+FACCH/F+SACCH/TF (full-rate TCH) TCH/H+FACCH/H+SACCH/TH (half-rate TCH)
51-frames multiframe FCCH+SCH+BCCH+CCCH (main BCCH) FCCH+SCH+BCCH+CCCH+SDCCH/4+SACCH/C4 (combined BCCH) BCCH+CCCH (extended BCCH) SDCCH/8+SACCH/C8 (main SDCCH)
Structure of Logical Channel Combination Frame-Main BCCH 1 multi-frame (51TDMA Frames) 235.38ms Downlink Group3,4
Group
Group1
Group2
(same as
Grpup5
Group2)
Channel Frame
F
S
BX4
CX4
F
S
CX4
CX4
……
F
S
CX4
CX4
I
0
1
2-5
6-9
10
11
12-15
16-19
20-39
40
41
42-45
46-49
50
Number
1 multi-frame (51TDMA Frames) 235.38ms Uplink
Channel
Frame
R
R
R
R
R
R
R
R
R
R
R
R
R
R……R
R
R
R
R
0
1
2
3
4
5
6
7
8
9
10
11
12
13-46
47
48
49
50
Number
F:FCCH; S:SCH; B:BCCH; C:CCCH; I:IDLE; R:RACH
Structure of Logical Channel Combination Frame-Combined BCCH 1 multi-frame (51TDMA Frames) 235.38ms Downlink Group
Group1 B
Channel
Channel
Frame Number
F
F
0
Group2 C
S
C F
C
D0
S
F
Group4 D1
S
Grpup5
D2 F
D3
S
A0 F
A1
S
I
4
4
4
4
4
4
4
4
4
4
B
C
C
C
D0
D1
D2
D3
A2
A3
S
F
1
Group3
4
4
2-5
6-9
S
10
F
11
4
4
12-
16-
15
19
S
20
21
F 4
4
22-
26-
25
29
1 multi-frame (51TDMA Frames) 235.38ms
30
S
31
F 4
4
32-
36-
35
39
S
40
41
I 4
4
42-
46-
45
49
50
Uplink
Channel
D3
4
R
R
A2
4
A3 4
R……R
D0 4
D1
4
R
R
D2
4
Channel
D0
4
R
R
A0
4
A1
R……R
D0
D1
4
R
R
D2
4
4
5
41-44
45
46
Frame Number
0-3
6-9
4
10-13
14-36
4
37-40
F:FCCH; S:SCH; B:BCCH; C:CCCH; I:IDLE; R:RACH
47-50
Structure of Logical Channel Combination Frame-Main SDCCH 1 multi-frame (51TDMA Frames) 235.38ms Downlink
Channel
Channel
Frame
Number
D0
D1
D2
D3
D4
D5
D6
D7
A0
A1
A2
A3
4
4
4
4
4
4
4
4
4
4
4
4
D0
D1
D2
D3
D4
D5
D6
D7
A4
A5
A6
A7
4
4
4
4
4
4
4
4
4
4
4
4
0-3
4-7
8-11
12-15
16-19
20-23
24-27
28-31
32-35
36-39
40-43
44-47
I
I
I
I
I
I
48
49
50
1 multi-frame (51TDMA Frames) 235.38ms Uplink
Channel
Channel
Frame
Number
A5
A6
A7
4
4
4
A1
A2
A3
4
4
4
4-7
8-11
0-3
I
I
I
I
I
I
12
13
14
D0
D1
D2
D3
D4
D5
D6
D7
A0
4
4
4
4
4
4
4
4
4
D0
D1
D2
D3
D4
D5
D6
D7
A4
4
4
4
4
4
4
4
4
4
31-34
35-38
39-42
43-46
47-50
15-
19-
18
22
23-26
27-
30
F:FCCH; S:SCH; B:BCCH; C:CCCH; I:IDLE; R:RACH
Structure of Logical Channel Combination Frame-TCH
1 multi-frame (26TDMA Frames) 120ms
Channel
T
T
T
T
T
T
T
T
T
T
T……T
T
T
T
T
I
Frame Number
0
1
2
3
4
5
6
7
8
9
10
21
22
23
24
25
T:TCH; I:IDLE
20
Configuration of Common Control Channel
Downlink CCCH
PCH
Uplink CCCH
AGCH
RACH
How to determine the total CCCH resources of the cell? How to allocate AGCH and PCH reasonably?
CCCH Grouping
The GSM system supports various kinds of channel combinations (GPRS not taken into account), in which the main BCCH, extended BCCH, combined BCCH, and the BCCH+CBCH combination contain the CCCH, i.e. all of the four combinations support the MS access. The MS are distributed to different CCCH groups based on this fact.
CCCH Grouping
The GSM specifies that the CCCH can be mapped to timeslots 0, 2, 4 and 6 but the extended BCCH combination can only be mapped to timeslots 2, 4 and 6 because it does not contain FCCH and SCH. Therefore, all MS synchronize with the base station at timeslot 0 and access the network via different CCCH.
Paging Group
The GSM system supports a maximum of 9 9=81 paging groups. the MS can be divided into 81 sub-groups at most from the opinion of the paging group. No matter what combination mode is adopted, the number of blocks used for paging in every 51 multi-frame does not exceed 9. The system enables the 51 multi-frame to cycle again , with a quantity of “BS-PA-MFRAMS” (number of frames of the same paging) of
51 multi-frames as a period.
Paging Group
In GSM terms, the paging block in any 51 multiframe is called a paging super-group. Therefore, the number of paging superframes in the system is the “number of frames of the same paging”. The number of paging groups in each super-group is
9 or 3 – “number of access granted reserved blocks”.
Calculation of CCCH and Paging Group
CCCH group number of MS=[(IMSI mod 1000) mod (BS_CC_CHANS x N)] div N
Paging group number of MS=[(IMSI mod 1000) mod (BS_CC_CHANS x N)] mod N
In the formula: N = Number of paging groups x BS-PA-MFRAMS IMSI = IMSI number of the mobile phone mod = Modulo calculation div = Divide exactly
Questions
What’s the rate of voice coding ?
What
are
the
advantages
of
discontinuous transmission (DTX)?
What types of logical channels are there?
