gsm air interface and physical layer - linköping · pdf filegsm air interface and...

GSM AIR INTERFACEAND

PHYSICAL LAYER

Andreas Bergström

Ericsson Research, Linköping

Lecture FOR TSKS05 Kommunikationssystem CDIO

2012-09-13

Ericsson Internal | 2012-09-09 |

Agenda› About me› GSM BASICS

– GERAN Network Overview– FREQUENCY BANDS– GSM LOGICAL CHANNELS

› RADIO NETWORK DEPLOYMENT - DIVIDING THE RESOURCES- Frequency reuse CONCEPTS- Frequency reuse PATTERNS- OTHER IMPORTANT ASPECTS

› GSM RADIO INTERFACE (UM)– RADIO INTERFACE STRUCTURE– TDMA Frame Structure AND Burst Types– MAPPING OF LOGICAL TO PHYSICAL CHANNELS– RADIO INTERFACE EXAMPLE

› GPRS/EDGE – Packet data in gsm– Modulation and CODING SCHEMES– EGPRS LINK QUALITY CONTROL– GMSK AND 8PSK POWER

› GSM PHYSICAL LAYER– Transmission and reception (TX/RX CHAIN)– Channel coding AND INTERLEAVING– Modulation– Demodulation– AIR INTERFACE (UM)– Deinterleaving– Channel decoding

› Recent/Future GSM Development- EDGE EVOLUTION- VAMOS- OTHER 3GPP activities

› QUESTIONS? COMMENTS?


› Currently at Ericsson Research Linköping since Oct 2011:

– LTE/LTE-Advanced and beyond…– HetNet SON (Self-Optimizing Networks)– Simulations, Simulator Development etc.– …

› Previously at GSM Systems department at Ericsson 2005-2011:

– Research, Analysis, Simulations, Simulator development and Standardization.

– Main topics: GSM Packet Data specifics: EGPRS/EDGE, EDGE Evolution, M2M, smartphone enhancements etc…

› Education:

– M.Sc. in Applied Physics & E.E. (Y) (1999-2005)– Thesis work at E/// Research HT04-VT05 (HSDPA Flow control)– …

› Personal:– From Sundsvall, now live in Västerlösa. – Married, 1 daughter Kerstin (2 years old) + another on the way…

› Hobbies– Triathlon - both full-distance Ironman (3.8km swim + 180km bike +

42km run) as well as shorter distances. Also done numerous “Svensk Klassiker”, marathons etc…

– Also co-founder and president of the local triathlon club (“LinköpingsTriathlonklubb”)

ABOUT MEAndreas BergstrÖm

GSM BASICS

GERAN Network Overview

FREQUENCY BANDS

GSM LOGICAL CHANNELS


GERAN network overview(GERAN = GSM/EDGE RADIO ACCESS NETWORK)

BTS

BSC SGSN GGSN

MSC/VLR HLR/AUC

PSTN

”Internet”

Radio network

(GERAN)

Core Network

Radio interface (Um)


GSM FREQUENCY BANDS


GSM LOGICAL CHANNELS

GSM (E)GPRS

+

RADIO NETWORK DEPLOYMENT

- DIVIDING THE RESOURCES

- Frequency reuse CONCEPTS

- Frequency reuse PATTERNS

- OTHER IMPORTANT ASPECTS


DIVIDING THE RESOURCESES

› Among operators

– Done by dividing the spectrum.

› Duplex communication

– Half/Full Duplex, TDD/FDD

› Multiple access

– FDMA, TDMA, CDMA, SDMA, …

› Cellular planning

– Neighbouring cells can not use the same resources. Or can they? ☺


FREQUENCY reuse CONCEPTS

Frequency reuse = Using same frequencies in different cells separated by “sufficient” distance to cause minimal

interference with each other. The frequency reuse possible is dependent on many factors such as real world propagation environment, technology etc.

Frequency plan= Assignment of radio frequencies to radio transmission sites (cell sites) that are located within a defined geographic area. The frequency plan may use ratios that are different dependent on the number of

transmitting sites to the number of antennas (sectors) on each site.


FRECUENCY REUSE PATTERNS (1/3)

Example of looser reuse Example of tighter reuse

›In GSM typically k = 3, 7 or 12.


FRECUENCY REUSE PATTERNS (2/3)› In the GSM 900-band (2x25MHz wide), we can have 124 carriers á

200kHz.

› Diving these into groups of 12 frequencies gives 10 such groups where

one cell can thus be covered by 10 carriers where each carrier can have

8 TDMA timeslots. Hence in total 80 Timeslots = e.g. 80 FR CS calls.

› These resources need to be shared between operators on this band.


FRECUENCY REUSE PATTERNS (3/3)

Loose (4x3) Frequency Reuse Pattern for BCCH(giving less interference and capacity)

Tighter (3x3) Frequency Reuse Pattern for TCH(giving more interference and capacity)

<Cluster Size> x <Sectors per Site>


OTHER IMPORTANT ASPECTS

› Power Control

› Frequency Hopping

GSM RADIO INTERFACE (UM)

RADIO INTERFACE STRUCTURE

TDMA Frame Structure AND Burst Types

MAPPING OF LOGICAL TO PHYSICAL CHANNELS

RADIO INTERFACE example


Radio interface structure Multiple access: TDMA+FDMA Duplex: FDD (+TDD)

Time

frequ

ency

880

915

925

960

TDMA frame

do

wnlin

kuplin

k

...

...

...

...

...

...

200 kHz carrier


TDMA FRAME STRUCTURE AND BURST TYPES


MAPPING OF LOGICAL TO PHYSICAL CHANNELS

26-TDMA Multiframe Example

(TCH+SACCH)

51-TDMA Multiframe Example

(CCCH)


Radio interface example (1/4)Speech channel (note TDD structure)

Time

frequ

ency

880

915

925

960

TDMA frame

do

wnlin

kuplin

k

...

...

...

...

...

...

200 kHz carrier


Radio interface EXAMPLE (2/4)Packet data channel (5+1)

Time

frequ

ency

880

915

925

960

TDMA frame

do

wnlin

kuplin

k

...

...

...

...

...

...

200 kHz carrier



Time

frequ

ency

880

915

925

960

TDMA frame

do

wnlin

kuplin

k

...

...

...

...

...

...

200 kHz carrier

(E)GPRS/EDGE PACKET DATA IN GSM

Modulation and CODING SCHEMES

EGPRS LINK QUALITY CONTROL

GMSK AND 8PSK POWER


MODULATION AND CODING SCHEMES› The radio block is the basic unit

of transmission

› Channel coding/interleaving over

one radio block

› Nine modulation/coding schemes (MCS) defined

TDMA frame (~4.6 ms)

Tim

e a

xis

120 m

s


EGPRS LINK QUALITY CONTROl› Link Adaptation (LA)

– Extensive set of modulation and coding schemes

› Incremental Redundancy (IR)– Code combining of transmission

attempts

› LA and IR can be combined


GMSK and 8PSK power

P0

GMSK 8PSK

0 dB

-2 dB

-4 dB

-6 dB

Average

power

reduction

P1

P2

P3

P0,P1

P2

P3

-3.3 dB

Peaks up

to 3.3 dB

higher

GSM PHYSICAL LAYER

Transmission and reception (TX/RX CHAIN)Channel coding AND INTERLEAVINGModulationDemodulationDeinterleavingChannel decoding


Transmission and reception (TX/RX CHAIN)

ModulatorBurst

Mapping

Insertion of TS

Tx pulse shaping

Radio transmitter

Radiochannel

Radioreceiver

Rxfilter

t

t

t

Eq./Demod

analogdigital

RF

InterleaverData+Header

Channel Encoder

Channel Decoder

De-Interleaver

Binary datafor

Transmission

ReceivedBinary data

From Higher Protocols

To Higher Protocols

0 1 0 … 0 0 1 1 0 0.. 0 1 1 0..

00

1

1010

110

0

z1 + w1i,

z2 + w2i,

….

20.34,

-15.65,

-34.32,

…

20.34,9.54

20.3

4,-1

5.6

5

20.34,

9.54,

…0 1 0 …

Ch. Est

x1 + y1i,

x2 + y2i,

….


Channel codingAND INTERLEAVING

Ch. Enc Int Mod

Ch. Dec Deint Dem

› Uncoded bits are coded in the channel encoder.

› In EGPRS a 1/3 convolutional code is used (EGPRS2 DL uses a

Turbo Encoder).

0 1 0 0 0 1 0 0 1 1 1 0 0 1 0 1

› To reach the desired code rate of the MCS used, the code word is

punctured0 1 0 0 1 1 1 0 0 1 0 1

1 0 1 1 1 1 1 0 1 1 1 0

0 0 0 1 1 1 0 1 0

R=4/9

› The punctured code word is interleaved to avoid bursty errors at the

receiver.

0 0 0 1 1 1 0 1 0

0 1 2 3 4 5 6 7 8mod(3k,9) 0 0 1 0 0 0 1 1 1

0 2 4 6 8 1 3 5 7


Modulation (1/2)Ch. Enc Int Mod

Ch. Dec Deint Dem

› The modulation consists of

– Modulating the bits onto symbols

– Modulating the symbols onto a transmit pulse

0 0 1 0 0 0 1 1 1

› Possible modulations:

– For GSM/GPRS: GMSK

– For EGPRS/EDGE: GMSK and 8PSK

– For EGPRS2: GMSK, QPSK, 8PSK, 16QAM, 32QAM (see later slide)

Mod.

I

Q

000

001011

010

110

111

101

100

s1 = I1+Q1j

s2 = I2+Q2j

s3 = I3+Q3js1 s2 s3


MODULATION (2/2)Ch. Enc Int Mod

Ch. Dec Deint Dem

› Pulse modulation

– To transmit the information over the air

interface and keep it within the carrier

spectrum mask, a transmit pulse is

needed.

s1

s2

s3

*

*

*

+

+

Ts

|s|

Burst sample (4xoversampling)


AIR INTERFACE (UM)Ch. Enc Int Mod

Ch. Dec Deint Dem

› See earlier slides.... ☺


DemodulationCh. Enc Int Mod

Ch. Dec Deint Dem

› The demodulation consist of two major tasks:

1. Channel estimation

2. Signal demodulation

r

Ch. est

Dem.

The channel estimator uses the known

training sequence code (TSC) to estimate the channel.

TSC Tail

Tail

+ Intf./Noise

s

-5,-1, 1 …

The demodulator returns soft bit values. The larger absolut

value, the larger confident from the demodulator.


deinterleaving› The deinterleaver performs the reverse operation of the

interleaver.

The quality of the code word is spread out

Ch. Enc Int Mod

Ch. Dec Deint Dem

mod(3k,9)-1

0 0 1 0 0 0 1 1 1

0 2 4 6 8 1 3 5 7

-5 -1 1 2 -50 73 62 100 88

+1

-0

Soft value

sign

Bin

Qualit

y

(Transmitted

Int. bit pos

Soft val.

0 0 1 0 0 0 1 1 1)

0 1 2 3 4 5 6 7 8

-5 73 -1 62 1 100 2 88 -50

Qualit

y


Channel decoding› The soft bits are depunctured with the same puncturing

scheme used in the transmitter.

› A Viterbi decoder is used in the decoding.

Ch. Enc Int Mod

Ch. Dec Deint Dem

-5 0 73 -1 62 1 100 0 2 88 -50 0

1 0 1 1 1 1 1 0 1 1 1 0

0s (= no confidence on whether it’s a 0 or 1) is inserted in

the punctured bit positions as soft value

Viterbi dec.

0 1 0 0

› In case Incremental Redundancy, IR, is used, the soft values

are combined before Viterbi decoding

-5 0 73 -1 62 1 100 0 2 88 -50 0

-5 10 0 0 12 10 1 -30 5 28 -23 58

+

Prev. Trans.

Curr. Trans.Viterbi dec.

0 1 0 0

RECENT/FUture GSM development

- EDGE EVOLUTION- VAMOS

- OTHER 3GPP activities


EDGE Evolution (1/7)

Dual carrier DL1.0 Mbpswith 32QAM & 10 TS

10 ms TTI80 ms e2e latency

Higher symbol rate UL/DL+20% bitrate per carrier/timeslot

16/32-QAM & Turbo codes DL&

100 kbps pertimeslot

32-QAM UL100 kbps per timeslot&

Dual-antenna terminals3 - 8 dB link improvement

16-QAM UL &80 kbps pertimeslot

Fast Ack/Nack

EGPRS 2 (Next Slides...)

EGPRS 2 (Next Slides...)


EDGE Evolution (2/7)EGPRS2 Coding schemes uplink

Uplink Level A

8.8

11.2

14.8

17.6

22.4

29.6

44.8

51.2

59.2

67.2

76.8

Bitrate (kbps)

NSR

Symbol Rate

GMSKMCS-1

GMSKMCS-2

GMSKMCS-3

GMSKMCS-4

8PSKMCS-5

8PSKMCS-6

16QAM

16QAM

16QAM

16QAM

16QAM

Modulation

UAS-10

UAS-7

UAS-8

UAS-9

UAS-11

MCS

8.8

11.2

14.8

17.6

22.4

29.6

44.8

59.2

67.2

88.8

108.8

118.4

Bitrate (kbps)

NSR

HSR

Symbol Rate

32QAMUBS-12

GMSKMCS-1

GMSKMCS-2

GMSKMCS-3

GMSKMCS-4

QPSKUBS-5

QPSKUBS-6

16QAM

16QAM

16QAM

32QAM

32QAM

Modulation

UBS-10

UBS-7

UBS-8

UBS-9

UBS-11

MCS

Uplink Level B

› Level A: Adding 16QAM

› Level B: Adding 16QAM+32QAM+Higher symbol rate


Downlink Level A

98.432QAMDAS-12

8.8

11.2

14.8

17.6

22.4

27.2

32.8

44.8

54.4

65.6

81.6

Bitrate (kbps)

NSR

Symbol Rate

GMSKMCS-1

GMSKMCS-2

GMSKMCS-3

GMSKMCS-4

8PSKDAS-5

8PSKDAS-6

8PSK

16QAM

16QAM

32QAM

32QAM

Modulation

DAS-10

DAS-7

DAS-8

DAS-9

DAS-11

MCS

8.8

11.2

14.8

17.6

22.4

29.6

44.8

59.2

67.2

88.8

108.8

118.4

Bitrate (kbps)

NSR

HSR

Symbol Rate

32QAMDBS-12

GMSKMCS-1

GMSKMCS-2

GMSKMCS-3

GMSKMCS-4

QPSKDBS-5

QPSKDBS-6

16QAM

16QAM

16QAM

32QAM

32QAM

Modulation

DBS-10

DBS-7

DBS-8

DBS-9

DBS-11

MCS

Downlink Level B

Level A: Adding 16QAM+32QAM+turbo codes

Level B: Adding QPSK+16QAM+32QAM+turbo

codes+Higher symbol rate

EDGE Evolution (3/7)EGPRS2 Coding schemes Downlink


EDGE Evolution (4/7)EGPRS2 Link performanceDownlink throughput per timeslot (no IRC/MSRD)

Downlink, no IRC

0

20

40

60

80

100

120

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

C/I

Rad

io L

ink B

itra

te (

kb

ps)

EGPRS

EGPRS2-A

EGPRS2-B

DW4

DW4 Detta är fyra figurer som man vill jämföra, tror du inte det blir bättre att ha dem i en 2x2 ruta?Daniel Widell; 2012-09-12

Ericsson Internal | 2012-09-09 | Page 41

EDGE Evolution (5/7)EGPRS2 Link performanceDownlink throughput per timeslot (with IRC/MSRD)

Downlink, with IRC

0

20

40

60

80

100

120

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

C/I

Rad

io L

ink B

itra

te (

kb

ps)

EGPRS

EGPRS2-A

EGPRS2-B


EDGE Evolution (6/7)EGPRS2 Link performanceUplink throughput per timeslot (no IRC)

Uplink, no IRC

0

20

40

60

80

100

120

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

C/I

Rad

io L

ink B

itra

te (

kb

ps)

EGPRS

EGPRS2-A

EGPRS2-B


EDGE Evolution (7/7)EGPRS2 Link performanceUplink throughput per timeslot (with IRC)

Uplink with IRC

0

20

40

60

80

100

120

-4 -2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46

C/I

Rad

io L

ink B

itra

te (

kb

ps)

EGPRS

EGPRS2-A

EGPRS2-B


VAMOS (Voice services over Adaptive Multi-user CHannels on One Slot)

Full rate (FR), half rate (HR), VAMOS FR (VFR) and VAMOS HR (VHR) allocations on a single time slot

One Timeslot

VAMOS downlink air interface. The RBS is transmitting a single AQPSK modulated signal to a pair of VAMOS mobiles

Two examples of the AQPSK constellation. The subchannel power distribution is illustrated by the length of the colored vectors

VAMOS uplink air interface. Two mobiles simultaneously transmit GMSK modulated signals on the same carrier frequency

Cell capacity as a function of the number of TCH TRXs


OTHER 3GPP activities(AFFECTING THE GSM UM)

› M2M/Smartphone improvements:

– Handle more users with smaller transactions per user.

› Introdution of OFDM in GSM

– A.k.a SPEED – Single Precoded Enhanched EGPRS Downlink)

› Multi-Carrier Downlink

– Up to 4 carriers i DL to one UE

› MIMO for GSM

› ...

Questions?

COMMENTS?

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