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

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

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

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

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

GSM900/DCS1800/PCS1900

GSM Frequency Range 890 - 915 MHz Uplink / MS Transmit 935 - 960 MHz Downlink / BS Transmit Duplex Offset 45 MHz Channel Spacing 200kHz Channel numbering 1 - 124 Transmission Speed 270 Kbits

DCS1800 Frequency Range 1710 - 1785 MHz Uplink / MS Transmit 1805 - 1880 MHz Downlink / BS Transmit Duplex Offset 95 MHz Channel Spacing 200kHz Channel numbering 512 - 885 Transmission Speed 270 Kbits

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 )

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 )

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

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

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

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)

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

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

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

TDMA and FDMA Physical Channel is an ARFCN and Timeslot Amplitude 7 6 5 Amplitude 4 Timeslot 3 2 Frequency 1 ARFCN 4 1 2 3 4 5 6

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

GSM TDMA Power Burst +4dB Tol +1.0dB Tol -1.0dB -6dB -6dB 147 Useful Bits -30dB 542.8us -70dB -70dB 148 Active Bits, 546.42us 10us 8us 10us 10us 8us 10us 3 57 1 26 1 57 3

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

Power Time Template Upper Limit Power dB Actual Lower Limit 87 bits Lower Limit 87 bits -70 us Time 10 8 10 321.23 us / 87 Bits 10 8 10 Access Burst

Uplink & Downlink Downlink / MS Receive Uplink / MS Transmit 1 2 3 4 5 1 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

Uplink & Downlink . Uplink Lags Downlink by 3 Timeslot periods 1 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)

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

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

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

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

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

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

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

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

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

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