1.gsm overview.pdf

8/15/2019 1.GSM Overview.pdf

1/41

MobileComm Technologies India Pvt. Ltd

Dallas . Atlanta . Washington . LA . Sao Paulo . New Delhi . Toronto . M

GSM Overview

Ritesh Karan

P D F C r eat ed wi t h d es k P D F P D F

Wr i t er -T r i al : : h t t p: / / www.d oc ud es k .c om

http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/http://www.docudesk.com/


2/41

Copyright 2010 Mobile Comm Technologies India Pvt. Ltd.

All rights reserved

Mobile Comm is committed to providing our customers with quality instructor

Telecommunications Training.This documentation is protected by copyright. No part of the contents of thisdocumentation may be reproduced in any form, or by any means, without thMobile Comm Technologies .

Document Number: RK/CT/1/2010 This manual prepared by: Mobile Comm Technologies

MobileComm Technologies(India)Pvt. Ltd.424, First Floor, Udyog Vihar Phase -4,

Gurgaon-122002 Headquarter:

MobileComm Professionals Inc.1255 West 15th Street, Suite 440 Plano, TX, 75075 Tel: (972) 633-5100 Fax: (972) 633-5106

www.mcpsinc.com

Ritesh Karan




3/41

Module Objectives

Give an overview about GSM Channel

Describe the basic configuration i.e combined mode and no

Demonstrate speech coding and channel coding.

Give an overview about the Burst structure.

Ritesh Karan




4/41

Speech Flow in BSSSpeech,64 kbps

compression ChC

= red

Inteand

TDMAforma

GMSKmodulation

13kbit/s

33.8kbit/sAirInterface

MSC

TRAU TRAU BTS

CODING




5/41

S

Sourcdeco

Chandecod

De-in

Burst

Decip

Dem

equa

Digitizing andsource coding

Channel

coding

Modulation

Ciphering

Burst formatting

Interleaving

Step 1

Step 2

Step 3

Step 4

Transmission

Step 5

Step 6 Diver

From Speech to Radio TransmisP D F C r eat ed wi t h d es k P D F P D F



6/41

Speech Coding

BP A/D SPEECHENCODERCHCO

LP D/A SPEECHDECODERCHDE

BANDPASS

300 Hz -

3.4 kHZ

Every 125µ s value issampled from analog signaland quantised by 13 bitwordData rate = 13/125*10 -6

= 104 kbps

Every 20ms 160 samplestakenData rate = 160 * 13/20ms

= 104 kbps

Linear Predictive Coding & RegularPulse Excitation Analysis1. Generates 160 filter coeff2. These blocks sorted in 4 sequence

1,5,9,…37 / 2,6,10----38/3,7,11…39/8,12,16…40

3. Selects the sequence with most energy

So data rate = 104/4 = 26 kbps

Long term prediction analysis1. Previous sequences stored in memory2. Find out the correlation between the presentseq. And previous sequences3. Select the highest correlation sequence4. Find a value representing the differencebetween the two sequences.

Reduces data rate = 26 kbps/2 = 13 kbps

ie 260 bits in 20ms

50

1A

50 3

3 crc bits

378 code

Conv cod

456 57 x


Wr i t er -T r i al : : h t t p: / / www.d o

c ud es k .c om


7/41

C20 ms

A

A8

A7

A6

A5

B4

B3

B2

B1

B8

B7

B6

B5

57 bits

Information

1 1

CRL CRL

3

Tail

26 bits

Training

8 Bursts

8 Sub blocof 57 bits

Source coding

Channel coding

Interleaving

Normalburst

20 msB

456 bitsA 456 bitsB C

In

A8B4A7B3A6B2A5B1 B8C4B7C3B6C2B5C1

Speech blocks

Codec dependent Codec dependent

Channel Processing in GSMOverview for Full Rate




8/41


9/41

0 1 2 3 4 5 6 7 8 ... ... 452 453

0 1 2 3 4 5 6 78 9 10 11 12 13 14 15• • • • • • • •• • • • • • • •• • • • • • • •

448 449 450 451 452 453 454 455

Divide 456 bits in 8 sub-blocks

765432107654 0 1 2

b0 b1 b56 b1b0

Interleaving: TCH Full RateP D F C r eat ed wi t h d es k P D F P D F


c ud es k .c om


10/41

Bursts and time slots in the Air Interface

...

Bursts from Mobile StationsBursts from Mobile Stations

TDMA Time TDMA Time

TDMA FrameTDMA Frame




11/41

Burst

• The information format transmitted during one timframe is called a burst.

• Different Types of Bursts

– Normal Burst

– Random Access Burst

– Frequency Correction Burst – Synchronization Burst




12/41

NORMAL BURSTNORMAL BURST

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

57 bits 57 bits26 bits 11 3

FRAME1(4.615ms) FRAM

Training

sequenceData Data

Tail

Bits

Stealing

Bit

Guard

Period

0.577ms

Carries traffic channel and control channels BCCH, PCH,

SACCH and FACCH.

CHANNEL CONCEPTCHANNEL CONCEPT

Stealing

Bit




13/41

Data Data - Two blocks of 57 bits each. Carries speech, data or control info.

Tail bits - Used to indicate the start and end of each burst. Three bits always 0

Guard period Guard period - 8.25 bits long. The receiver can only receive and decode if the

timeslot designated for it .Since the MS are moving. Exact synchronizatio

practically. Hence 8.25bits corresponding to about 30us is available as guard p

error.

Stealing bits Stealing bits - This bit is used to indicate if the 57 bits data block is used as FA

Training SequenceTraining Sequence - This is a set sequence of bits known by both the transm

of BSIC). When a burst of information is received the equalizer searches for

The receiver measures and then mimics the distortion which the signal has bee

then compares the received data with the distorted possible transmitted sequ

likely one.

NORMAL BURSTNORMAL BURST





14/41

FREQUENCY CORRECTION BURSTFREQUENCY CORRECTION BURST

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


Fixed DataTail

Bits

0.577ms

Carries FCCH channel.

Made up of 142 consecutive zeros.

Enables MS to correct its local oscillator locking it to that





15/41

SYNCHRONISATION BURSTSYNCHRONISATION BURST

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


Synchronisation

Sequence

Tail

Bits

Encrypted

Bits Encrypte

BitsCarries SCH channel.Enables MS to synchronise its timings with the BTS.

Contains BSIC and TDMA Frame number.





16/41

DUMMY BURSTDUMMY BURST

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


Training

sequenceData Data

Tail

Bits

Ta

Bi

0.577ms

Transmitted on the unused timeslots of the BCCH

downlink.





17/41

AACCESS BURSTCCESS BURST

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


Tail

Bits

Tail

Bits

Guard

Period

0.577ms

Synchronisation

Sequence

Encrypted

Bits

Carries RACH.

Has a bigger guard period since it is used during initial

MS does not know how far it is actually from the BT





18/41

Time

TSL 1TSL 2TSL 3

TSL 4

TSL 5

TSL 6

TSL 7

Principle of Time Division Multiple Access (TDMA)



c ud es k .c om


19/41

1 9

8 s e a t s

i n e a c h v e h i c l e

L o g i s t i c a l p r o b l e m

PDF Created with deskPDF PDF Writer - Trial :: http://www.docudesk.com


20/41

Physical channel Physical channel - Each timeslot on a carrier is referred to as a phy

there are 8 physical channels.

Logical channel Logical channel - Variety of information is transmitted between the

different logical channels depending on the information sent. The logtypes

• Traffic channel

• Control channel

Downlink

Uplink

CHANNELSCHANNELS

CHANNEL CONCEPT



c ud es k .c om


21/41

FDMA

UPLINK DOWN

GSM900: 890 MHz - 915 MHz 935 M

GSM1800: 1710 MHz - 1785 MHz 1805

1 2 3 ...

Channel 1 - 124

1 - 374

200 kHz

1 2 3

Duplex frequency 45 MHz / 95 MHz



c ud es k .c om


22/41

01

23 4

5

76

01

23

4

5

76

01

23

4

200 kHz

Physical channel,e.g. allocated to one

subscriber with FR voice &no frequency hopping

frequen

t i m e

TDMA fram

TDMA




23/41

Physical channel:One timeslot of a TDMA-frame on one carrier is referred to as a phy

8 physical channels per carrier in GSM, channel 0-7(timeslot 0-7)

Logical channel:A great variety of information must be transmitted between BTS anddata and control signaling. Depending on the kind of information tradifferent logical channels. These logical channels are mapped on p

Channel concept




24/41

Logical Channels on Air interface

LOGICAL

CHANNELS

COMMON

CHANNELS

DEDICAT

CHANNE

BROADCAST

CHANNELS

COMMON

CONTROL

CHANNELS

DEDICATED

CONTROL

CHANNELS

FCCH BCCHSCH SDCCH SACCH FAC

PCH AGCHRACH TCH/F




25/41

FACCH

BTS

0 1 2 3 4 5 6 7TS

FCCH

SCH

BCCH

PCH

AGCH

CBCH

SDCCH

SACCH

TCH

TCH

FACCH

SDCCHSACCH

FCCH

SCH

BCCH

RACH

PCH

AGCH

RACH

CBCH

Synchronization

Frequency correction

Broadcast control

Access request

Subscriber paging

Answer to Access request

Broadcast info

Dedicated Signaling

Sys InFo 5, 6 + SMS

Traffic (speech data)

Associated Signaling

A

T

R

D

B

M

A

S

A

The Logical Channels on Radio Interface




26/41

Full Rate - Downlink & Uplink

T : TCH A : SACCHTi: TCH

sub-channel no. i

Ai

: SACCH

sub-channel no. i

26 frames = 120 ms

T0

A0

T0

T0 T0

T0

T0

T0

T0

T0

T0

T 1

T 1

T 1

T 1

T 1

T 1

T 1

T 1

T 1

T 1

Half Rate - Downlink & Uplink

T AT T T T T T T T TT T T T T T T T T T

T

26 frames = 120 ms

Logical Channel Mapping-TCH




27/41

Configuration of Signalling Channels

0 7

Non-combined Configuration

Combined Configuration

0 7

ts0=bcch + pch + agch ts1=sdcch/8

ts0=bcch + sdcch/4 + pch + agc

1




28/41

BCCH/CCCH Multiframe

f s bb bb c fc fc sc cc c cc c c fc fsc cc c cc cc f fc ccc cc c cs

r r rr r r r fr rr r r r r r rr r r rr fr r r r r rr r r r fr r r r rr r r rr

Downlink

Uplink

CHANNELS: f = FCCH b = BCCH r = RACHs = SCH c = CCCH = PCH/AGC

51 TDMA frames = 235 ms

0

Non-Combined ModeP D F C r eat ed wi t h d es k P D F P D F


c ud es k .c om


29/41

SDCCH/8 Multiframe

t t tt t t t ft tt t t t t t tt t t tt ft t t t t tt t t t fs s s s ss s s

ss ss s ss fs ss s t tt t t ts ft t t t t tt t t t ft t t t tt t tt

Downlink

Uplink

CHANNELS: t = SDCCH/8 s = SACC

t


1. 2. 3. 5. 6. 7. 8.4.

0

iii

Non-Combined ModeP D F C r eat ed wi t h d es k P D F P D F


c ud es k .c om


30/41

Combined BCCCH + SDCCH/4 Multiframe

f s bb bbc fc fc scc cc cc cc fc fs t t t t tt t t f ft t t t tt t ts

t t tt r r s fs ss s s sr r rr r r rs fr r r r r rr r r r fr r r r tr t tr

Downlink

Uplink

CHANNELS: f then s = FCCH then SCH b = BCCH

ssss = SACCH c = CCCH t = SDCC


0

1. 2. 3. 4.

BTS Physical ChannelARFCN (n) TS (s)FCCH

SCH BCCH

PCH/AGCH

Combined Mode



c ud es k .c om


31/41

00

11

00

11

22

20452045

1 Hyperframe = 2048 superframes = 2,715,648 TDM3h 28min 53s 760ms

1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes

11 2 33 4

00

11

0

0

1

1

2

2

23

23

24

24

25

25

0

0

1

1

2

2

22

33

44

55

66

77

6.12s

0

235.3120ms

Control 51 -Traffic 26 - Frame Multiframe

4.615ms

TDMA Fr

HYPERFRAME AND SUPERFRAME STRUCTUREHYPERFRAME AND SUPERFRAME STRUCTURE



c ud es k .c om


32/41

•FCCH•SCH

•BCCH•BCCH•BCCH•BCCH

•PCH

•AGCH

•0•1•2•3•4•5

•50 •IDLE

•0 •1 •2 •3 •4 •5

• 5 1 - F r a m e M

u l t i f r a m e

• 5 1 - F r a m e M

u l t i f r a m e

•TCH/F•TCH/F•TCH/F•TCH/F

•TCH/F•SACCH•TCH/F

•IDLE

•0•1•2•3

•11

• 2 6 - F r a m e M

u l t i f r a m e

• 2 6 - F r a m e M

u l t i f r a m e

•12•13

•25•TCH/F•24

•FCCH

•SCH

•SDCCH

•SACCH

• . . .

• . . .

• . . . •

. . .

• . . .

• . . .

• . . .

• . . .

• . . .

• . . .

• . . .

• . . .

•...

Logical channels in TDMA fraP D F C r eat ed wi t h d es k P D F P D F


c ud es k .c om


33/41

List of the frequencies of the

selected PLMN

IMSI Attach

Look for the cell with the best C1 in the

suitable cells list

Eligible cell?

YesNo

C1

for eligible cell

Computation s

Suitable cell?

YesNo

Initial Cell Selection

PLMN

End of Cell Selection

No

Eligible cell

Suitable cell:

- cell of the selected PLMN

- cell not barred- C1 > 0

Rejected?




34/41

IDLE MODE--Cell Selection

Path loss criterion parameter C1 used for cell selection and reselection

is defined by:

C1 = (A - Max(B,0))

where

A = Received Level Average - rxLevAccessMin

B = msTxPwrMaxCCH P

Where,

rxLevAccessMin = Minimum received level at the MS required for

access to the system.

msTxPwrMaxCCH = Maximum TX power level an MS may use when

accessing the system until otherwise commanded.

P = Maximum RF output power of the MS.




35/41

Example:

C1(cell_A) =AV_RXLEV rxLevAccessMin-Max(0, msTxPwrMaxCCH max outpu

MS)

C1(cell_A) = -80dBm (-100dBm) max(0, 36dBm 33dBm)

C1(cell_A) = 17 > 0

C1(cell_B) = -82dBm (-105dBm) max(0, 33dBm 33dBm)

C1(cell_B) = 23 > C1(cell_A)

Thus MS camps on cell_B




36/41

Cell Reselect Hysteresis

• Cell reselection on the border of two location areas result in a lan MS moves on the border of two location areas lots of locatioTo avoid these ping pong location updates, the reselect hystere

Cell1

LA1

RX LevelCell1

RX Cell

A B C




37/41

Idle Mode--Cell Re-selection

Why C2?Cell Prioritisation

As a means of encouraging MSs to select some suitable

cells in preference to others Example:

"In dualband network--to give different priorities for different ban

"In multilayer--to give priority to microcell for slow moving traff

"Any other special case where specific cell required higher priorit

rest




38/41

Pathloss Criterion C2

C1 + CELL_RESELECT_OFFSET – TEMPORARY OFFSET * H(PENAL

for PC1 - CELL_RESELECT_OFFSET for P

C2 =

0 .. 126 dBstep size: 2 dB

0, 10, 20, 30,40, 50, 60, ∞

dB

PENALTY_TIME

TEMPORAR

CELL_

C2

new candidate= formerly non-

serving cell

CELL_

C2no TEMPORARY OFFSET



c ud es k .c om


39/41

Cell Reselection Events

When shall Iselect a new cell?

Pathloss Criterion C1C1 ≤ 0 for a period of 5 s

Pathloss Criterion C2• neighbour‘s C2 value >

current cell‘s C2 value (sameLA)

• neighbour‘s C2 value + CRH >current cell‘s C2 value (new LA)

for a period of 5 s. Downlink SigDS

RACH FailureMAX RETRANS + 1 times

RACH FailureMAX RETRANS + 1 times

Authennotificatio

Cell has bCELL_BAR_ACCESS &

Cell has bCELL_BAR_ACCESS &




40/41

Downlink Signalling Failure

B C C H

( ..., B S_ PA

MS

Downlink radio link

failure detected!

DSCinit

:= roundBS_PA_MFRMS

90

paging

message successfully

decoded?

DSC ≤≤≤≤ 0

DSC := min (DSC+1, DSCinit

) DSC := DSC - 4

yes no

yes

no

DSC = Downlink Signalling failure Counter

DSC := DSCinit




41/41

4 1

1.gsm overview.pdf

Documents