Basic GSM Training Material Introduction of GSM; GSM Network Architecture; Access Mode of GSM; Logical Channels in GSM; GSM Cell Structure; GSM Bands; Coding''s in GSM; Call Originating.
BASIC GSM Training Material Company Confidential Contents: v v v v v v v v Introduction of GSM GSM Network Architecture Access Mode of GSM Logical Channels in GSM GSM Cell Structure GSM Bands Coding's in GSM Call Originating Company Confidential INTRODUCTION OF GSM Company Confidential BASIC WIRELESS COMMUNICATION There are TWO major parts of wireless communication: TRANSMITTER (Tx) RECEIVER (Rx) Company Confidential TRANSMITTER MIC MODULATOR RF AMPLIFIER LOCAL OSC Company Confidential RECEIVER IF OUT BAND PASS FILTER MIXER DEMODULATOR LOCAL OSCILLATO R Company Confidential AUDIO AMPLIFIER TYPES OF CALLS MOBILE to LL Mobile - BTS - BSC - PSTN - LL LL to MOBILE LL - PSTN - BSC - BTS - Mobile MOBILE to MOBILE Mobile - BTS - BSC - BTS - Mobile ( If it is same Network) Mobile - BTS - BSC1 - PSTN - BSC2 - BTS - Mobile ( If it is different Network with same SP or different SP) Company Confidential GSM • • • • • • GSM means Global System for Mobile communications Developed in 1982 Most popular of cellular technologies GSM Only Handsets belong to 2G and 2.5G In GSM just like FM Radio channels users are identified by different frequencies, with assigned time slots Has mainly four frequency bands of operation (850/900/1800/1900) 8/2/16 TELECOM/MOBILE/MSS Company Confidential # * Mobile Technology Evolution 1st Generation Mobile Communication 2nd Generation Mobile Communication 2.5th Generation Mobile Communication 3rd Generation Mobile Communication 3G and above 8/2/16 TELECOM/MOBILE/MSS Company Confidential Emerging Technologies • 1GFirst Generation • ExampleAMPS • Analog • 2 way radio w/transmitter/receiver • Voice service only • FDM 8/2/16 10 TELECOM/MOBILE/MSS Company Confidential GSM speech coding AIR INTERFACE BASE TRANSCEIVER STATION MOBILE Company Confidential Transmit Path BS Side bit A-Law K sps to 13 bit Uniform RPE/LTP speech Encoder To Channel Coder 13Kbps RPE/LTP speech Encoder To Channel Coder 13Kbps MS Side LPF A/D K sps, Sampling Rate - 8K Encoding - 13 bit Encoding (104 Kbps) RPE/LTP - Regular Pulse Excitation/Long Term Prediction RPE/LTP converts the 104 Kbps stream to 13 Kbps Company Confidential GSM Speech Coding • • GSM is a digital system, so speech which is inherently analog, has to be digitized The method employed by current telephone systems for multiplexing voice lines over high speed trunks and is pulse coded modulation (PCM) The output stream from PCM is 64 kbps, too high a rate to be feasible over a radio link Company Confidential CODING IN GSM 8/2/16 100 TELECOM/MOBILE/MSS Company Confidential GMSK –Gaussian Minimum shift keying GMSK is a special type of digital FM modulation Ones and zeroes are represented by shifting the RF carrier by plus or minus 67.708 kHz Modulation techniques that use two frequencies to represent ones and zeroes are called frequency shift keying (FSK) In the case of GSM, the data rate of 270.833 kbps is chosen to be exactly four times the RF frequency shift This has the effect of minimizing the modulation spectrum and improving channel efficiency FSK modulation where the bit rate is exactly four times the frequency shift is called minimum shift keying (MSK) In GSM, the modulation spectrum is further reduced by applying a Gaussian premodulation filter This slows down the rapid frequency transitions, which would otherwise spread energy into adjacent channels Company Confidential BER Measurement GSM MS Tester Close_Loop_Comand Mic A/D Speech Coder Channel Coder GMSK Modulator Data Gen R F Control RF Speaker D/A Speech Decoder 64kbps Channel Decoder GMSK Demod 13kbps BER BER < 2.5% at -102dBm "GO/NOGO" 102 TELECOM/MOBILE/MSS Compare Company Confidential Receiver Testing GSM Receiver = Digital Data Receiver Rx Performance = Correct receipt of DATA No of Errored Bits Bit Error Rate (BER) % = Total No of Bits Sampled 103 TELECOM/MOBILE/MSS Company Confidential CALL ORIGINATING IN GSM Company Confidential Originated Call BS ORIGINATED CALL BS pages MS using the CCCH MS sends RACH MS ORIGINATED CALL MS responds with RACH BS assigns MS to SDCCH or TCH TCH Using the SDCCH, authentication, call setup, and TCH assignment Using the SACCH, BS commands MS to adjust 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 8/2/16 105 TELECOM/MOBILE/MSS Company Confidential MS transmits and receives speech on TCH Using the FACCH on TCH authentication & location update Location update from the mobile Company Confidential Call establishment from a mobile Company Confidential Call establishment to a mobile Company Confidential • Performance characteristics of GSM Communication − mobile, • • • • • wireless communication; support for voice and data services Total mobility − international access, chip-card enables use of access points of different providers Worldwide connectivity − one number, the network handles localization High capacity − better frequency efficiency, smaller cells, more customers per cell High transmission quality − high audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains) Security functions − access control, authentication via chip-card and PIN Company Confidential Disadvantages of GSM • • • • • • No full ISDN bandwidth of 64 kbit/s to the user Reduced concentration while driving Electromagnetic radiation Abuse of private data possible High complexity of the system Several incompatibilities within the GSM standards Company Confidential Thank You Company Confidential ... Introduction of GSM GSM Network Architecture Access Mode of GSM Logical Channels in GSM GSM Cell Structure GSM Bands Coding's in GSM Call Originating Company Confidential INTRODUCTION OF GSM Company Confidential... Company Confidential GSM • • • • • • GSM means Global System for Mobile communications Developed in 1982 Most popular of cellular technologies GSM Only Handsets belong to 2G and 2.5G In GSM just like... HandsetsMini ComputersHigh Power consumption 8/2/16 13 TELECOM/MOBILE/MSS Company Confidential GSM NETWORK ARCHIETECTURE Company Confidential GSM NETWORK ARCHITECTURE BTS BTS OS BSC * # BTS MS VLR BS MSC MSC EIR BTS