1. Agenda . GSM900/DCS1800 . The GSM Network & Air Interface
. Technical Basics
. Speech Coding
. Types of Channel
. Making a Phone Call

2. ( Groupe Special Mobile )
Global System for Mobile
G S M

3. GSM Development History
1982 Groupe Special Mobile?is created within CEPT
1986 A Permanent Nucleus is set up
1987 Main radio transmission techniques are chosen, based on prototype evalution (1986)
1989 GSM becomes an ETSI technical committe
1990 The phase 1 GSM 900 specifications are finalized
1991 First systems are running
1992 All major European GSM 900 operators begin commercial operator

4. GSM / DCS1800 Functionalities
Speech Services
Data Services
Short Message Services (SMS)
Supplementary Services
Subscriber Identity Module (SIM)
Security Function

5. RF Aspects TDMA 0.3GMSK Modulation Burst Power Transmission
Neighbour Cells Measurement
Hopping
Uplink / Downlink DTx
BER & Receiver Testing

6. GSM900/DCS1800/PCS1900

7. GSM Frequency Range
MHz Uplink / MS Transmit
MHz Downlink / BS Transmit
Duplex Offset 45 MHz
Channel Spacing 200kHz
Channel numbering
Transmission Speed 270 Kbits

8. DCS1800 Frequency Range
MHz Uplink / MS Transmit
MHz Downlink / BS Transmit
Duplex Offset 95 MHz
Channel Spacing 200kHz
Channel numbering
Transmission Speed 270 Kbits

9. Uplink ( Mobile to Base ) Downlink ( Base to Mobile )
GSM Primary Band
45 MHz
890
900
910
920
930
940
950
960
Freq
Uplink ( Mobile to Base )
Downlink ( Base to Mobile )

10. Uplink ( Mobile to Base ) Downlink ( Base to Mobile )
DCS1800 Primary Band
95 MHz
1710
1735
1760
1785
1800
1825
1850
1875
Freq
Uplink ( Mobile to Base )
Downlink ( Base to Mobile )

11. Carriers at the border of the GSM band
Freq
890.2
890.4
890.6
890.8
200 kHz
GSM band

12. Carriers at the border of the DCS1800 band
Freq
1710.2
1710.4
1710.6
1710.8
200 kHz
DCS1800 band

13. GSM Networks MS ADC NMC OMC OMC BTS BSC BTS MSC VLR EIR BTS BSS AUC
HLR
BTS
VLR
BTS
Interface to other
network
BSS

14. GSM Networks Terminology: MS- Mobile Station (移动台)
BSS- Base Station System (基站系统)
BTS- Base Transceiver Station (基站收发台)
BSC- Base Station Controller (基站控制器)
MSC- Mobile Switching Centre (移动业务交换中心)
OMC- Operations and Maintenance Centre
(操作与维护中心)
NMC- Network Management Centre (网络管理中心)
AUC- Authentication Centre (鉴权中心)
HLR- Home Location Register (归属位置寄存器)
VLR- Visitors Location Register (来访位置寄存器)
EIR- Equipment Identity Register (设备标识寄存器)

15. GSM Interface Air Interface Abis Interface SS#7 SS#7 BTS BSC BTS BSC
MSC
PSTN MS
BTS
BSC

16. GMSK Modulation
PSK 1 1 1 1 1 1
Guassian Filter
Spectrum < 200kHz

17. Modulation Fc Fc + 67.708KHz +67.708KHz -67.708KHz Data Type ?0

18. TDMA and FDMA Physical Channel is an ARFCN and Timeslot Amplitude7 6 5
Amplitude 4
Timeslot 3 2
Frequency 1
ARFCN 4 1 2 3 4 5 6

19. TDMA and FDMA Terminology: FDMA - Frequency Division Multiple Access
TDMA Time Division Multiple Access
ARFCN Absolute RF Channel Number
TS Timeslot
Physical - The Combination of a TS number
Channels and ARFCN.
Logical Are Mapped on Physical Channels
Channels

20. GSM TDMA Power Burst +4dB Tol +1.0dB Tol -1.0dB -6dB -6dB
147 Useful Bits
-30dB
542.8us
-70dB
-70dB
148 Active Bits, us
10us
8us
10us
10us
8us
10us 3 57 1 26 1 57 3

21. Power Time Template Power Upper Limit dB Actual Lower Limit -70 us
Lower Limit
-70 us
Time 10 8 10
542.8 us / 147 Bits 10 8 10
Normal Burst

22. Power Time Template Upper Limit Power dB Actual Lower Limit 87 bits
Lower Limit
87 bits
-70 us
Time 10 8 10
us / 87 Bits 10 8 10
Access Burst

23. Uplink & Downlink Downlink / MS Receive Uplink / MS Transmit 1 2 3 4 51 2 3 4 5 6 7 1 2 3 4 5 6 7 5 6 7 1 2 3 4 5 6 7 1 2 3 4
Uplink / MS Transmit

24. Uplink & Downlink . Uplink Lags Downlink by 3 Timeslot periods1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7
ARFCN
DOWNLINK
45MHz
UPLINK
ARFCN 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 3 4 5 6 7 1 2 3 4 5
. Uplink Lags Downlink by 3 Timeslot periods
. Uplink and Downlink use same Timeslot Number
. Uplink and Downlink use same Channel Number (ARFCN)
. Uplink and Downlink use different bands(45MHz apart for GSM900)

25. Frequency Hopping Control Uplink BS 1 BS 2 Monitoring RX Lev RX QualD
Coupler
Switch
Synth
Register
Control
Uplink
BS 1
BS 2
Monitoring
RX Lev
RX Qual
Downlink 1 65
124
Home BS

26. Speech Coder . RELP and LTP Coder . Converts Speech to Low Data Rate
RELP- Residual-Excited Linear
Prediction Coder
LTP- Long Term Prediction
. Converts Speech to Low
Data Rate
. 20ms Speech makes 260Bits
. Output 13kbit/s
20ms Blocks
Speech Coder
260 Bits
Bits Ordered
260 Bits 50
132 78
Very Important Bits
Important Bits
Other Bits

27. Error Correction
Type Ia 50
Type Ib 132
Type II 78 In
Block Code
Type Ia
CRC
Type Ib
Type II
262 Bits 50 3
132 78
Re-ordering
Type Ia
Type Ib
CRC
Type Ib
Type Ia
Tail
Type II
Out 25 66 3 66 25 4 78
456 Bits
Half rate convolutional code
378 78
456 Bits from 20ms of Speech

28. Diagonal Interleaving
456 Bits from 20ms of Speech
456 Bits from 20ms of Speech 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57 57
TCH 57 57 57 57 57 57 57 57 57 57 57 57
Traffic Channel (TCH) Bursts Carry Two 57 Bits Blocks (114) Each
120ms of Speech = 456x6 = 2736 bits
2736/114 = 24 bursts I.e. 24frames(mobile transmits once per frame)
Multiframe has 26 frames in 120ms
There are 2 spare frames厖 One SACCH, one Idle

29. Speech to Radio / Radio to Speech
Digitizing and
Source coding
Source
decoding
Channel
coding
Channel
decoding
Interleaving
De-interleaving
Burst
formatting
Burst
formatting
Ciphering
Deciphering
Modulation
Demodulation

30. MS camped on - listens for page, can request service
MS Camp on Flow Chart
MS Turn On
MS searches channels
and orders by signal
strength
MS goes to the assigned
SDCCH ( Freq., timeslot, ... )
for authentication + location Update MS
Stongest
BCCH NO MS
Next Stongest
BCCH NO
Using SACCH - adjust
power, TA & report RX Qual
etc
YES
YES
FCCH on BCCH and adjusts timebase
BS assigns SDCCH to MS
using the CCCH
MS camped on - listens for page, can request service
SCH on BCCH and fine tunes timebase & timing
YES
Decode BCCH & store info
Location =
Previous Location?
MS sends
RACH
Is BCCH
in PLMN ? NO
YES

31. Orignated Call BS ORIGINATED CALL MS ORIGINATED CALL TCH MS sends RACH
BS pages MS using
the CCCH
MS sends RACH
MS ORIGINATED CALL
MS responds with
RACH
BS assigns
MS to SDCCH
or TCH
TCH
MS transmits and
receives speech on
TCH
Using the SDCCH, authentication,
call setup, and TCH assignment
Using the FACCH on
TCH authentication &
location update
Using the SACCH, BS commands
MS to adust power + timing, MS
reports power + Rx quality of BCCH + adjacent BCCH
MS transmits + receives speech
on TCH
During inactive timeslots, MS
measures adjacent cells, BCCH
Using the SACCH on TCH, MS
reports power + Rx quality , BS
commands MS to adjust power ,TA
Call disconnected by MS or BS

32. Subscriber Identity Module ( SIM )
SIM contains ( at least ) following information :
IMSI (International Mobile Subscriber Identification)
MCC & MNC (Mobile Country Code and mobile Network Code)
Any other user specific information

33. International Mobile Subscriber Identity ( IMSI )
NMSI
IMSI =
MCC +
MNC +
MSIN
3 digits
2 digits
Not more than 15 digits
IMSI = International Mobile Subscriber Identity
MCC = Mobile Country Code
MNC = Mobile Network Code
MSIN = Mobile Station Identification Number
NMSI = National Mobile Subscriber Identity

34. International Mobile Equipment Identity ( IMEI )=
TAC +
FAC +
SNR + SP
6 digits
2 digits
6 digits
1digit
IMEI = International Mobile Equipment Identity
TAC = Type Approval Code
FAC = Final Assembly Code
SNR = Serial Number
SP = Spare