Lecture no: 11 (Brief) history of mobile telephony Global System - PowerPoint PPT Presentation

RADIO SYSTEMS – ETI 051 Contents Lecture no: 11 • (Brief) history of mobile ”telephony” • Global System for Mobile Communications (GSM) • Wide-band Code-Division Multiple Access (WCDMA) GSM and WCDMA Ove Edfors, Department of Electrical and Information Technology Ove.Edfors@eit.lth.se 2010-05-11 Ove Edfors - ETI 051 1 2010-05-11 Ove Edfors - ETI 051 2 HISTORY The short version 1959 - First automatic mobile telefony system in Stockholm. ’The Phone’ weighs 40 kg and costs as much as a car. 1981 - NMT (Nordic Mobile Telephony) starts in the nordic countries HISTORY OF MOBILE ”TELEPHONY” and Saudi Arabia. 1989 - First GSM-system (Global System for Mobile Telephony) starts in Germany. 2001 - First WCDMA-system (Wide-band Code-division Multiple Access) starts in Japan. 2010-05-11 Ove Edfors - ETI 051 3 2010-05-11 Ove Edfors - ETI 051 4

HISTORY Generations Analog technology. No data communication. Examples are NMT in the nordic countries and AMPS in North America. Digital technology. Slow data communication. GLOBAL SYSTEM FOR MOBILE Examples are GSM (first in Europe) New enhancements have and CdmaOne in North America. increased datarate to COMMUNICATIONS (GSM) 50-100 kbit/sec. Still evolving! Digital technology. Focus on both speech and data/ Examples are WCDMA (Europe) multimedia. and Cdma2000 (North America). Initially up to 2 Mbit/sec. Evolving towards higher data rates! 2010-05-11 Ove Edfors - ETI 051 5 2010-05-11 Ove Edfors - ETI 051 6 GSM GSM Simplified system overview Simplified block diagram BTS Speech Channel Burst Modulator/ BSC BTS coder encoder formatting transmitter VLR BTS MSC BSS EIR BTS AUC bits BSC BTS HLR MSC Speech Viterbi Viterbi BSS VLR Receiver Interface to decoder decoder equalizer other networks quality info. BTS Base Transceiver Station VLR Visitor Location Register BSC Base Station Controller EIR Equipment Identity Register BSS Base Station Sub-system AUC AUthentication Center MSC Mobile Switching Center HLR Home Location Register (Encryption not included in figure) 2010-05-11 Ove Edfors - ETI 051 7 2010-05-11 Ove Edfors - ETI 051 8

GSM GSM Some specification parameters GMSK modulation (initial specification) 2010-05-11 Ove Edfors - ETI 051 9 2010-05-11 Ove Edfors - ETI 051 10 GSM GSM Power spectrum TDMA/FDMA structure ARFCN Absolute Radio Frequency Channel Number 2010-05-11 Ove Edfors - ETI 051 11 2010-05-11 Ove Edfors - ETI 051 12

GSM GSM Frames and multiframes Up/down-link time slots Time slot index . 6 1 2 s 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 ARFCN Super frame 51 Multiframes Downlink Uplink 45 MHz 1 m s Multiframe 2 0 26 Frames ARFCN 0 1 2 3 4 5 6 7 0 1 s 4 . 5 m 61 Frame Time slot index Frame 8 Timeslots The MS transmits to the BS three time-slots after it receives a transmission from the BS. 576.92 μs Using this strategy, the duplex scheme is a combination Timeslot 156.25 Bits of TDD and FDD, and the MS avoids simultaneous transmission and reception. 2010-05-11 Ove Edfors - ETI 051 13 2010-05-11 Ove Edfors - ETI 051 14 GSM GSM Some of the time slots Viterbi equalizer Normal 3 start 58 data bits 26 training 58 data bits 3 stop 8.25 bits bits (encrypted) bits (encrypted) bits guard period FCCH burst 3 start 3 stop 8.25 bits 142 zeros bits bits guard period SCH burst 3 start 39 data bits 64 training 39 data bits 3 stop 8.25 bits bits (encrypted) bits (encrypted) bits guard period RACH burst 8 start 36 data bits 3 stop 41 synchronization 68.25 bits extended bits bits bits (encrypted) guard period FCCH Frequency Correction CHannel SCH Synchronization CHannel RACH Random Access CHannel 2010-05-11 Ove Edfors - ETI 051 15 2010-05-11 Ove Edfors - ETI 051 16

GSM GSM Channel coding of speech Encryption The speech code bits are in three categories, with different levels of protection against channel errors. Block code Uncoded 2010-05-11 Ove Edfors - ETI 051 17 2010-05-11 Ove Edfors - ETI 051 18 GSM GSM GPRS and EDGE GPRS network GSM has evolved into a high-speed packet radio system in two steps GPRS General Packet Radio Services where empty time slots can be used Up to 115 kbit/sec to transmit data packets. Four new coding schemes are used (CS-1, ..., CS-4) with different levels of protection. EDGE Enhanced Data-rate for GSM Evolution where, in addition to GPRS, a new Up to 384 kbit/sec 8PSK modulation is introduced. Eight new modulation and coding schemes are used (MCS-1, ..., MCS-8) with SGSN Serving GPRS Support Node different levels of protection. GGSN Gateway GPRS Support Node ISP Internet Service Provider 2010-05-11 Ove Edfors - ETI 051 19 2010-05-11 Ove Edfors - ETI 051 20

GSM EDGE 8PSK modulation Linear 8-PSK ... but with rotation of signal constellation for each symbol 2 × 3  3 × 3  3  8 8 8 WIDE-BAND CODE-DIVISION MULTIPLE ACCESS (WCDMA) We avoid transitions close to origin, thus getting a lower amplitude variation! 2010-05-11 Ove Edfors - ETI 051 21 2010-05-11 Ove Edfors - ETI 051 22 WCDMA WCDMA Some parameters Direct-Sequence CDMA What we learned during Lecture 9: data spread spectrum signal Users/channels Carrier spacing 5 MHz are separated by spreading Chip rate 3.84 Mchips/sec different codes. code Uplink spreading factor 4 to 256 Downlink spreading factor 4 to 512 In WCDMA we do this a bit different: Like we discussed during Lecture 9, all cells use data spread spectrum signal the same frequency band! The total spreading is a spreading scrambling combination of code spreading and scrambling. 2010-05-11 Ove Edfors - ETI 051 23 2010-05-11 Ove Edfors - ETI 051 24

WCDMA WCDMA Channelization and scrambling Orthogonal Variable Spreading Factor The OVSF codes used for variable rate spreading can be viewed as a code tree. data spread spectrum signal channelization scrambling code The different Scrambling makes the channelization/spreading total spreading codes are orthogonal (spreading + and have different scrambling) unique spreading factors between different between 4 and 512. sources. We can create several orthogonal channels by picking spreading codes from different branches of the tree. 2010-05-11 Ove Edfors - ETI 051 25 2010-05-11 Ove Edfors - ETI 051 26 WCDMA WCDMA Downlink Uplink 2010-05-11 Ove Edfors - ETI 051 27 2010-05-11 Ove Edfors - ETI 051 28

WCDMA WCDMA Spectrum mask Data rate and spreading factor Data rate Time We always spread Spreading factor to the full bandwidth. Time Transmit power Transmit power and generated interference to others vary accordingly. Time 2010-05-11 Ove Edfors - ETI 051 29 2010-05-11 Ove Edfors - ETI 051 30 WCDMA WCDMA Data rate and interference Soft handover Since all base stations used the same frequency band, a terminal In simple words, with a limited interference allowed, we can have close to the cell boundary can receive “the same” signal from more than many low data-rate channels or a few high data-rate channels. one base station and increase the quality of the received signal. Interference y r a d n u o The interference b l l e C level also varies with propagation loss, which makes MS 3 BS 1 BS 2 power control important! MS 2 MS 1 Time 2010-05-11 Ove Edfors - ETI 051 31 2010-05-11 Ove Edfors - ETI 051 32