page 2 gsm technology global system for mobile communications

GSM Technology

Global System for Mobile Communications

Analog and Digital

Speech Quality

Signal

Distance to the Transmitter

quality

Analog Signal

Digital Signal

SNR

r

BTS transmits

MS transmits

0 1 2 3 4 5 6 7 0 1 2 3

5 6 7 0 1 2 3 4 5 6 7 0

from: An Introduction to GSM© Artech House, Inc.

TDD - Time Division Duplex

GSM Technology

GSM Technology

TDMA frame and timeslot structure

0 1 2 3 4 5 6 7

4.615 ms

577 usec

3T

57Encrypted data

26Training Sequ.

1S

1S

57Encrypted data

3T

Burst Structures

T

3

148 Bit = 546.12 µs

Coded Data

57

S

1

Training Sequence

26

Coded Data

57

S

1

T

3

GP

8.25TypeNumber of Bits

T

8

88 Bit = 324.72 µs

GP

68.25

Type

Number of Bits

T

3

Synchronization Seq.

41

Coded Data

36

T

3

148 Bit = 546.12 µs

T

3

GP

8.25

Type

Number of Bits

fixed bit sequence

142

T

3

148 Bit = 546.12 µs

Coded Data

39

Synchronization Sequence

64

Coded Data

39

T

3

GP

8.25

Type

Number of Bits


FACCHFACCH

Logical Channels

SACCHSACCH

SCHSCH

TCHF/H

TCHF/H DCCHDCCH CCCHCCCH BCHBCH

RACHRACH

BCCHBCCH SCHSCH FCCHFCCH

AGCHAGCHPCHPCH

SDCCHSDCCH

Frame structure

Mapping of logical channels

F S CC -

D 0

D 0

D 1

D 1

D 2

D 2

D 3

D 3

D 4

D 4

D 5

D 5

D 6D 6

D 7

D 7

A 0

A 4

D 0

D 0

D 1

D 1

D 2

D 2

D 3

D 3

D 4

D 4

D 5

D 5

D 6

D 6

D 7

D 7

A 0

A 4

A 3A 1

A 5

A 2

A 6 A 7 --

- - -

-

--

- - -

-A 3A 1A 5

A 2

A 6 A 7

--

RD 3

D 3

D 0

D 0

D 1

D 1

D 2

D 2

A 0 A 1

A 3A 2F S

F SD 3D 2

D 3D 2F S

F S

D 1D 0

D 1D 0

A 2 A 3

A 1A 0

S:C:A:

F:B:D:R:

TDMA frame for frequency correction burstTDMA frame for BCCHTDMA frame for SDCCHTDMA frame for RACH

BCCH + CCCH(downlink)

BCCH + CCCH(uplink)

8 SDCCH/8(uplink)

8 SDCCH/8(downlink)

BCCH + CCCH4 SDCCH/4(downlink)

BCCH + CCCH4 SDCCH/4

(uplink)

TDMA frame for synchronization burstTDMA frame for CCCHTDMA frame for SACCH/C

51 fram es 235.38 m s»

R R R R R R R R R R R R R R R R R R R R R RR R R R R R R R R R R R R R R R R R R R R R R

RR R

RRR R

R

F S B C

F B CS

F S CC

F S CC

F S CCCCF SCCF SF S B C

R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R RR R R R R

Frequency Hopping and Adjacent Channel Monitoring

3

downlink (Base Station transmits)

uplink (Mobile Station transmits)

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

0 1 2 5 01234567 0 1 2 3 45 6 7 7640 1 2 3 45 6 7

30 1 2 5 01234567 0 1 2 3 45 6 7 7640 1 2 3 45 6 7

30 1 2 5 01234567 0 1 2 3 45 6 7 7640 1 2 3 45 6 7

F1

F2

F3

F3

F1

F2

0

Mobile Station monitors different neighboring cells

1

0

0

5

5

5

1

1

6

6

6


Burst Power-Time Template


dB

-1

-30

-70*

-6

+4+1

(147 bits)

10 µs

*or -36dBm, whatever value is higher

8 µs 542.8 µs 8 µs10 µs 10 µs10 µs

Multipath Propagation

BTS

TSn TSn+1


Timing Advance and RF Power Control

AB

AB

long signal delay

high signal attenuation

short signal delay

small signal attenuation

BTS

TSn TSn+1


Handover from one BTS to another BTS

MSC BSC

BTS2

BTS1

MS

cell boundary

Handover of the MS fromBTS1 to BTS2 via the BSC


RF Power Levels for the MS - International GSM


Power Class Max Power of MS Max Power of BS

1 20 W (43 dBm) 320 W (55 dBm)2 8 W (39 dBm) 160 W (52 dBm)3 5 W (37 dBm) 80 W (49 dBm)4 2 W (33 dBm) 40 W (46 dBm)5 0.8 W (29 dBm) 20 W (43 dBm)6 10 W (40 dBm)7 5 W (37 dBm)8 2.5 W (34 dBm)

GSM Power Levels and Test Limits for the MS

Power Class Power Level Peak Power / Limits

1 0 43 dBm + - 2 dBm

1 1 41 dBm + - 3 dBm

1 2 2 39 dBm + - 3 dBm*)

1 2 3 3 37 dBm + - 3 dBm*)

1 2 3 4 35 dBm + - 3 dBm

1 2 3 4 533 dBm + - 3 dBm*)

1 2 3 4 6 31 dBm + - 3 dBm

1 2 3 4 5 7 29 dBm + - 3 dBm*)

1 2 3 4 5 8 27 dBm + - 3 dBm1 2 3 4 5 9 25 dBm + - 3 dBm1 2 3 4 5 10 23 dBm + - 3 dBm

1 2 3 4 5 11 21 dBm + - 3 dBm1 2 3 4 5 12 19 dBm + - 3 dBm

1 2 3 4 5 13 17 dBm + - 3 dBm

1 2 3 4 5 14 15 dBm + - 3 dBm1 2 3 4 5 15 13 dBm + - 3 dBm

*) +-2dBm if highestpower of a power class

Speech Processing in GSM

D

A

SPEECH

ENCODER

SPEECH

DECODER

MICROPHONE

LOUD-

SPEAKER

DA

COMFORT

NOISE

FUNCTION

VAD

VAD

SPEECH

ENCODER

SPEECH

DECODER

COMFORT

NOISE

FUNCTION

EXTRA

POLATION

EXTRA-

POLATION

13 BIT

LINEAR/

8 BIT

A-LAW

MOBILE-STATION

FIXED

NETWORK

RADIO TRANSMISSION

RADIO

TRANSMISSION


Full and Half Rate Speech Multiframes

T T T T T T T T T T T T T T T T T T T T T T T T S I 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

T = TCH, S = SACCH, I = idle

26 Frames = 120 ms

T T T T T T T T T T T T S 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

T = TCH1, S = SACCH1, t = TCH2, s = SACCH2

t s t t t t t t t t t t t


Authentication

A3

RAND RANDKi

SRESSRES

MS Network

= ?

yes/no?

(SRES)

Um Interface


Authentication - Create ciphering key

A8

RANDKi

Kc

MS

Start Ciphering

A5

Kc

MS Network

A5

Kc

DATA Ciphered

Ciphering

DATA

Command

DATA

Um Interface


A/ D Speech Conversion

t

t

t

000001010011100101

110111

0

12

34567

Filtered Input

Signal

Sampling

Signal

Sampled Signal

Quantization


Testing of Mobiles

Power Time Template, background informations

Noise floor

Cornerpoint (-x dBc @ y usec)

Time

Dynamic Range > 75 dBProgrammable CornerpointsZoom FunctionUser defined Power Time Template

Burstlength147 bits / 542 usec

next burst

Too fast rising edges create interference spectrumSlow edges overlap with neighbour burstsThe Power-Time- Template is the best compromise between both

PTT

Testing of Mobiles

Phase, Peak and RMS measurements:

Analysis of Transmitter Modulation Quality:

- Symbol “distance” of 90 degree only for GSM- Any TX phase error reduces this symbol “distance”- In real systems there is the sum of system noise and TX phase errors- Peak errors of >45 degree will confuse demodulators

Testing of Mobiles

10

00

01 11

area of confusion

Modulation principle Phase error + noise

Testing of Mobiles

Frequency error:

The ability to adjust to the base station frequency

Phase and Frequency Error

real phase trajectory from the received RF signal

90°

180°

-90°

-180°

calculated bit stream fromthe real phase trajectory(before differential encoding)

ideal, calculatedphase trajectory

90°

180°

-90°

calculated phase error and from this the resulting frequency errorphase error = deviation from the

correlation linefrequency error = inclination of the

correlation line

90°

180°

-90°

+1

-11 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 1816 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 181619

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 17 1816 19

-180°

-180°

1 2 3 4 5 6 7 9 10 11 12 13 14 15 17 1816 198

0°

0°

0°


Testing of Mobiles

BER Measurements:

Switch mobile to “Loop back”Transmit random but coded data to mobileReceive bit patterns from mobileMatch in/out data of bitstream: “round trip delay”

Unprotected bits: BER class IIProtected bits with Viterbi coding: BER class I

Testing a GSM Receiver with the 4400 (RX)

RX TX

DEC ENC

AUDIO

Combiner

LOOPBACK

Error

0010001001101

0010000001101

Bit Error Rate Test (BER)

Testing of Mobiles

Spectrum Measurements:

Risk for interference of neighbouring channels

ETSI:- Spectrum due to transients- Spectrum due to modulation

High performance analyser needed

Testing of Mobiles

Reports from the Mobile to the BS:

RXLEVEL: - (110 - Received Level in dBm) = RXLEV Report

RXQUAL:- Coded “BER” values ( = Viterbi activity)

RX - LEV Measurements by the Mobile Station

RX Level Level at MS Receiver (dBm)

012...............6263

Less than - 110- 110 to - 109- 109 to - 108

...

...

...

...

...- 49 to - 48above - 48

RX - QUAL Measurements by the Mobile Station

RX QualityRX-QUAL

Bit Error RateBER (%)

01234567

Below 0.20.2 to 0.40.4 to 0.80.8 to 1.61.6 to 3.23.2 to 6.46.4 to 12.8Above 12.8

Alignments

Different designs requires different alignments

The following are just brief examples!

Divided into 4 sections:•Why and what to align•Transmitter and Fref alignments•Receiver and logic alignments•Innovative vs conventional alignments

Divided into 4 sections:•Why and what to align•Transmitter and Fref alignments•Receiver and logic alignments•Innovative vs conventional alignments

Why and what to align

Different receiver architectures

Heterodyne Receiver - Basic theory

FrontEnd:

•Image rejection•LNA•Oscillator emmissions

1:st MF:

•Gain•Selectivity - adjacent channel suppression

2:nd MF:

•Improving selectivity•Reasonable sampling frequency

FrontEnd:

•Image rejection•LNA•Oscillator emmissions

1:st MF:

•Gain•Selectivity - adjacent channel suppression

2:nd MF:

•Improving selectivity•Reasonable sampling frequency

Homodyne Receiver - Basic theory

• Homodyne- The 1:st (and only) LO has the same frequency as received signal

• Frequency conversion directly to baseband - direct conversion- Frequency selectivity is made on the baseband

• Moves much of the complexity from the radio to the logic parts

• Was uptil recently too complex to build

• Homodyne- The 1:st (and only) LO has the same frequency as received signal

• Frequency conversion directly to baseband - direct conversion- Frequency selectivity is made on the baseband

• Moves much of the complexity from the radio to the logic parts

• Was uptil recently too complex to build


The problems…

• LO leakage- The LO:s frequency is same as the wanted

•DC offset- The LO-signal will be introcuced as a DC-level in the baseband signal

The problems…

• LO leakage- The LO:s frequency is same as the wanted

•DC offset- The LO-signal will be introcuced as a DC-level in the baseband signal


The Problems…continued

• AM detection- DC offset that varies in amplitude - hard to exlude in an algorithm- AM detection comes from several different sources:

- Selfmixing- Bad IP2 in the baseband- Bad IP3 in LNA/mixer (crossmodulation)- Bad IP3 in the basband (crossmodulation)

The Problems…continued

• AM detection- DC offset that varies in amplitude - hard to exlude in an algorithm- AM detection comes from several different sources:

- Selfmixing- Bad IP2 in the baseband- Bad IP3 in LNA/mixer (crossmodulation)- Bad IP3 in the basband (crossmodulation)


Interference from DC offset and AM detectioncan be many times higher than wanted signal

Conventional AGC can not be used => High dynamic ADC (24 bits or more)

Interference from DC offset and AM detectioncan be many times higher than wanted signal

Conventional AGC can not be used => High dynamic ADC (24 bits or more)

I

Q

DC/AM

Wanted signal

Homodyne - Heterodyne Conclusion

Pro’s:•Choice of components•Well-known design

Con’s:•Requires large chip space

•(MF-filters, mixers, LO)•Expensive components•High current consumption

Pro’s:•Choice of components•Well-known design

Con’s:•Requires large chip space

•(MF-filters, mixers, LO)•Expensive components•High current consumption

Superheterodyne Homodyne

Pro’s:•Cheap•Small chip space•Low current consumption

Con’s:•Harder to protect from noise•LO leakage•DC offset•AM detection

Pro’s:•Cheap•Small chip space•Low current consumption

Con’s:•Harder to protect from noise•LO leakage•DC offset•AM detection

Output power and PTT (1)

Spectrum due to switching derives from PTT

dB

-1

-30

-70*

-6

+4+1

(147 bits)

10 µs

*or -36dBm, whatever value is higher

8 µs 542.8 µs 8 µs10 µs 10 µs10 µs

Output power and PTT (2)

Power Class Power Level Peak Power / Limits

1 0 43 dBm + - 2 dBm

1 1 41 dBm + - 3 dBm

1 2 2 39 dBm + - 3 dBm*)

1 2 3 3 37 dBm + - 3 dBm*)

1 2 3 4 35 dBm + - 3 dBm

1 2 3 4 5 33 dBm + - 3 dBm*)

1 2 3 4 6 31 dBm + - 3 dBm

1 2 3 4 5 7 29 dBm + - 3 dBm*)

1 2 3 4 5 8 27 dBm + - 3 dBm1 2 3 4 5 9 25 dBm + - 3 dBm1 2 3 4 5 10 23 dBm + - 3 dBm

1 2 3 4 5 11 21 dBm + - 3 dBm1 2 3 4 5 12 19 dBm + - 3 dBm

1 2 3 4 5 13 17 dBm + - 3 dBm

1 2 3 4 5 14 15 dBm + - 3 dBm1 2 3 4 5 15 13 dBm + - 3 dBm

Output power and PTT (3)Output power and PTT (3)

Competitorsinaccuracy

Alignmentwindow

ExtendedAlignmentWindow

4400M

loweralignment

point+/- 2dB

35dB

31dB

0,5dB 0,15dB

1dB 1,7dB

Specification limit

Specification limit

Lower power consumptionExtended alignment window

Lower power consumptionExtended alignment window31,15dBm vs 31,5dBm

=> ~ 8,5% higher power consumption during burst

31,15dBm vs 33dBm => ~ 53,5% higher power consumption during burst

31,15dBm vs 31,5dBm => ~ 8,5% higher power consumption during burst

31,15dBm vs 33dBm => ~ 53,5% higher power consumption during burst

Spectrum due to switching

dB

t100%90%Averaging

period

50%

midamble

Useful part of the burst

0%

Switching transients

Max-hold level = peak of switching transients

Video average level= spectrum due to

modulation

Power level Maximum level for various offsets from carrierfrequency

400 kHz 600 kHz 1200 kHz 1800 kHz39 dBm -13 dBm -21 dBm -21 dBm -24 dBm37 dBm -15 dBm -21 dBm -21 dBm -24 dBm35 dBm -17 dBm -21 dBm -21 dBm -24 dBm33 dBm -19 dBm -21 dBm -21 dBm -24 dBm31 dBm -21 dBm -23 dBm -23 dBm -26 dBm29 dBm -23 dBm -25 dBm -25 dBm -28 dBm27 dBm -23 dBm -26 dBm -27 dBm -30 dBm25 dBm -23 dBm -26 dBm -29 dBm -32 dBm23 dBm -23 dBm -26 dBm -31 dBm -34 dBm

<= +21 dBm -23 dBm -26 dBm -32 dBm -36 dBm

-24dBm-21dBm

-19dBm

+33dBm

-52dBc @ 400kHz

Spectrum due to modulation

dB

t100%90%Averaging

period

50%

midamble

Useful part of the burst

0%

Switching transients

Max-hold level = peak of switching transients

Video average level= spectrum due to

modulation

-60dBc

-30dBc

+0,5dBc

power levels in dB relative to themeasurement at FT

Power level Frequency offset(kHz)

(dBm) 0-100 200 250 400 600 to <180039 +0,5 -30 -33 -60 -6637 +0,5 -30 -33 -60 -6435 +0,5 -30 -33 -60 -62

<= 33 +0,5 -30 -33 -60 -60The values above are subject to the minimum absolute levels (dBm)below.

-36 -36 -36 -36 -51

Modulator alignment

Phase balanceAmplitude balance=> Low Fc feedthrough=> Desired Sideband suppression

Peak phase derives from oscillator noise

RES BW 10 kHz VBW 10 kHz SWP 30.0 msec

AT 30 dBREF 21.0 dBm

LOG

10dB/

CENTER 1.879800 GHz SPAN 1.000 MHz

-24.09 dBMKR -268 kHz

PG -6.8 dBPEAK

WA SB

SC FS

CORR

COPY DEV

PRNT PLT

Plot

Config

Print

Config

Time

Date

Change

Prefix

More

1 of 3

-6 7 ,7 0 8 k H z

+ 6 7 ,7 0 8 k H z

-x x d B

F C + 6 7 ,7 0 8 k H z (m o d u la t io n fre q u e n c y )

F C

T X b a la n c e

3 :e M F

2 :a M F

4 :e M F

-1 3 5 ,4 2 k H z

-2 0 3 ,1 2 k H z

-2 7 0 ,8 3 k H z

~~

~~

+

I

Q

Master Clock alignment

3 reasons:Absolute freqStep sizePulling range

3 reasons:Absolute freqStep sizePulling range

Ch freq.DAC

Freq.

Pulling range

Step size:Kp=*((y2-y1)/(x2-x1))

x1,y1

x2,y2

Transmitter VCO alignment

Pushing marginPulling marginLocking time on all channelsCatch-and-hold ranges….in temperature

Pushing marginPulling marginLocking time on all channelsCatch-and-hold ranges….in temperature

VCOTo PA

Modulator

PHD

Fsynth

Vcc

DAC

PHD has a comparator output

PHD has a comparator output

Sweepgen.

VccHow to get into thecatch range of PHD?

How to get into thecatch range of PHD?Same locking timeon all channels?

Same locking timeon all channels?

PushingPulling

Handover test

Different TX VCO’s for different bands

Often common up-converter

Different TX VCO’s for different bands

Often common up-converter

Different LO VCO’s for different bands

Often the same mixers

Different LO VCO’s for different bands

Often the same mixers

Receiver and logic alignments

RSSIIQ Tuning RXCurrent/voltage alignmentTemperature sensorRTC

RSSIIQ Tuning RXCurrent/voltage alignmentTemperature sensorRTC

RSSI alignment

Learn input power versus ADC response -> RXLev

Learn input power versus ADC response -> RXLev

Phone

Calibration equipment

Radiosignal (-50 dBm)Radiosignal (-50 dBm)

Measure signalMeasure signal The ADC respone points to

a specific EEPROM value

The ADC respone points to a specific EEPROM value

Send amplitude value of the injected signalSend amplitude value of the injected signal

Write amplitude value into EEPROMWrite amplitude value into EEPROM

EEPROM-address Value12 -50 dBm3456789

10

Compensation tableEEPROM-address Value

12 -50 dBm3456789

10

Compensation tableCompensation table

IQ tuning RX alignment

Align the amplitude (and phase) relationship between the I&Q signals to achieve suppression of unwanted signals

Make sure that sufficient AM suppression is reached!

Homodyne receiversDouble-balanced quadrature mixers

Homodyne receiversDouble-balanced quadrature mixers

BER testing

Current/Voltage alignment

Current/voltage alignment

• Charging algorithm (Li-Ion)• Power off decision• ADC reference voltage

CHARGER IN

RTC alignment/test

RTC - Real Time Clock• Can often be checked against the master clock• Separate oscillator to save power

RTC - Real Time Clock• Can often be checked against the master clock• Separate oscillator to save power

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