radio systems – etin15 lecture no: 11 - lth · radio systems – etin15 lecture no: 11 gsm and...
TRANSCRIPT
2015-05-12 Ove Edfors - ETIN15 1
Ove Edfors, Department of Electrical and Information [email protected]
RADIO SYSTEMS – ETIN15
Lecture no: 11
GSM and WCDMA
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Contents
• (Brief) history of mobile ”telephony”• Global System for Mobile Communications (GSM)• Wide-band Code-Division Multiple Access (WCDMA)
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HISTORY OF MOBILE ”TELEPHONY”
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HISTORYThe 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 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.
2009 - First LTE (Long-term Evolution) service launched in Stockholm and Oslo.
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HISTORYGenerations
Analog technology.Examples are NMT in the nordiccountries and AMPS in North America.
No data communication.
Digital technology.Examples are GSM (first in Europe) and CdmaOne in North America.
Slow data communication.New enhancements haveincreased datarate to50-100 kbit/sec.
Digital technology.Examples are WCDMA (Europe) and Cdma2000 (North America).
Focus on both speech and data/multimedia.Initially up to 2 Mbit/sec. Usuallyup to 10-15 Mbit/sec.
Digital technology.LTE (Advanced). Early versionssometimed called 3.9 G
Focus on data and multimedia.Initial datarates up to 100Mbit/sec. Evolving to 1 Gbit/sec.
We focus on these here
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GLOBAL SYSTEM FOR MOBILECOMMUNICATIONS (GSM)
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GSMSimplified system overview
BSS
BSS
AUC
HLR
EIR
VLR
VLRBSC
MSC
BTS
BTS
BTS
BTS
BTS
MSC
BSC
Interface toother networks
BTS Base Transceiver StationBSC Base Station ControllerBSS Base Station Sub-systemMSC Mobile Switching Center
VLR Visitor Location RegisterEIR Equipment Identity RegisterAUC AUthentication CenterHLR Home Location Register
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GSMSimplified block diagram
Speechcoder
Channelencoder
Burstformatting
Modulator/transmitter
ReceiverViterbiequalizer
Viterbidecoder
Speechdecoder
bits
quality info.
(Encryption not included in figure)
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GSMSome specification parameters
(initial specification)
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GSMGMSK modulation
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GSMPower spectrum
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GSMTDMA/FDMA structure
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GSMFrames and multiframes
Super frame 51 Multiframes
Timeslot 156.25 Bits
576.92 μs
Frame 8 Timeslots4.615ms
Multiframe 26 Frames120ms
6.12s
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GSMUp/down-link time slots
2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1
2 3 4 5 6 7 0 110
ARFCN
ARFCN
45
MH
z
Time slot index
Time slot index
Frame
Dow
nlink
Upl
ink
The MS transmits to the BS three time-slots after itreceives a transmission from the BS.
Using this strategy, the duplex scheme is a combinationof TDD and FDD, and the MS avoids simultaneous transmissionand reception.
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GSMSome of the time slots
RACH burst41 synchronization
bits36 data bits(encrypted)
3 stopbits
68.25 bits extendedguard period
SCH burst
FCCH burst
142 zeros
3 startbits
3 startbits
3 startbits
8 startbits
Normal26 training
bits
64 trainingbits
58 data bits (encrypted)
39 data bits (encrypted)
3 stopbits
3 stopbits
3 stopbits
8.25 bitsguard period
8.25 bitsguard period
8.25 bitsguard period
58 data bits(encrypted)
39 data bits(encrypted)
FCCH Frequency Correction CHannelSCH Synchronization CHannelRACH Random Access CHannel
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GSMViterbi equalizer
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GSMChannel coding of speech
The speech code bits are in three categories, with different levelsof protection against channel errors.
Type 1a50 bits
Type 1b132 bits
Type 278 bits
378
Rate 1/2 convolutional code doublingthe number of bits
Block code adding 3
parity bits
50 3
Copy the Type 1b bitsTail
132 4
78
CopyType 2
bits
Coded 20 ms speech frame378 + 78 = 456 bits
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GSMEncryption
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GSMGPRS and EDGE
GSM has evolved into a high-speed packet radio system in two steps
GPRS General Packet Radio Serviceswhere empty time slots can be usedto transmit data packets.Four new coding schemes are used(CS-1, ..., CS-4) with different levelsof protection.
EDGE Enhanced Data-rate for GSM Evolutionwhere, in addition to GPRS, a new8PSK modulation is introduced.Eight new modulation and coding schemesare used (MCS-1, ..., MCS-8) withdifferent levels of protection.
Up to 115 kbit/sec
Up to 384 kbit/sec
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GSMGPRS network
SGSN Serving GPRS Support NodeGGSN Gateway GPRS Support NodeISP Internet Service Provider
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GSMEDGE 8PSK modulation
38
2×38 3×
38
Linear 8-PSK ... but with rotation of signal constellation for each symbol
We avoid transitionsclose to origin, thusgetting a lower amplitudevariation!