Gsm Radio if Kasera Ashish Apr04

8/17/2019 Gsm Radio if Kasera Ashish Apr04

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GSM Training: By Sumit Kasera and Ashish

Agenda

GSM Architecture

Entities

Interfaces

Protocol Architecture GSM Protocols

Um Protocols

Ais Protocols

A Interface Protocols

!" Protocols

#ther Protocols

GSM Procedures

Moility Management

!all $anding

Security Management Su%%lementary Ser&ices

!onclusion


2/60


Topics Covered

• GSM Air Interface

– Multiple Access Scheme

– Logical Channels

• Control channels

• Traffic Channels

– GSM Bursts

–GSM L1 unctionalit!


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Multiple Access Scheme "1#$%

• The radio interface is the interface &et'een the mo&ilestations and the BTS

• The Multiple Access Scheme defines ho' the GSM

radio fre(uenc! can &e shared &! differentsimultaneous communication &et'een different mo&ilestations

• GSM uses a mi) of re(uenc! *ivision Multiple Access"*MA% and Time *ivision Multiple Access "T*MA%

• +ach user is given a pair of fre(uencies "one for uplin,and one for do'nlin,% and a time slot during a timeframe


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re(uenc! Allocation "-#.%


5/60


*MA and T*MA "/#$%

• *MA divides the fre(uenc! spectrum into small slices

– Carrier Separation is -00 ,23 'hich provides4

– 1-5 pairs of carriers in the GSM 600 &and

– /.5 pairs of carriers in the GSM 1$00 &and – -66 pairs of carriers in the GSM 1600 &and3 etc7%

• T*MA divides each channel into $ timeslots such that each

carrier is shared &! $ users

• The &asic radio resource is a time slot 'ith a duration of8.. 9s

• $ Timeslots of 8.. µs constitutes a 57:18 ms T*MA rame


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*MA and T*MA "5#$%

• The start of a T*MA frame on uplin, is dela!ed &! a

fi)ed time "Three TS periods%

– The reason for this dela! is to allo' the same TSnum&er to &e used in &oth uplin, and do'nlin,

directions 'ithout re(uiring the MS to receive and

transmit simultaneousl!


7/60GSM Training: By Sumit Kasera and Ashish

Timeslot and T*MA rame "8#$%



• In a GSM s!stem3 ever! T*MA frame is assigned a fi)ed num&er3'hich repeats itself in a time period of / hours3 -$ minutes3 8/seconds3 and .:0 milliseconds7 This time period is referred to ash!perframe

• There are t'o t!pes of multiframes in the s!stem4

– -: frame multiframe 'ith a duration of 1-0 ms – Consists -: T*MA frames7

– ;sed to carr! the logical channels TC3 SACC andACC7

– 81 frame multiframe 'ith a duration of -/875 ms

– Consists 81 T*MA frames – ;sed to carr! the logical channels CC3 SC3 BCC3

CCC3 S*CC3 SACC etc7

!per3 Super < Multiframes ":#$%



• Superframe consists of 81 "-: frame Multiframes% or -: "81 frame

Multiframes% 'ith a duration of :71- seconds7

• A !perframe consists of -05$ superframes

• rame num&er is generated &! BTS7 BTS &roadcast current framenum&er 8 times in 81 frame multiframe

• The frame hierarch! is used for s!nchroni2ation &et'een BTS and

MS

!per3 Super < Multiframes ".#$%



!per3 Super < Multiframes "$#$%






• Control channels

• Traffic Channels

– GSM Bursts

– GSM L1 unctionalit!

Topics Covered



Logical Channels

• Tas,s performed in GSM are supported &! num&er of

functional channels ,no'n as logical channels

• *ifferent logical channels are mapped in either

direction on =h!sical Channels

• The logical channels carr!ing control information are

generall! mapped on to one or t'o timeslots of one

carrier ">no'n as BCC re(uenc!% in a cell

• The remaining ?logical channels? are used to carr!

traffic



LOGICAL CHANNELS

SIGNALLING

FULL RATE

22.8 Kb/S

HALF RATE

11.4 Kb/S

BROADCAST COMMON CONTROL DEDICATED CONTROL

FCCH SCH BCCH

PCHRACH

AGCH

SDCCH SACCH FACCH

FCCH -- FREQUENCY CORRECTION CHANNEL

SCH -- SYNCHRONISATION CHANNELBCCH -- BROADCAST CONTROL CHANNEL

PCH -- PAGING CHANNEL

RACH -- RANDOM ACCESS CHANNEL

AGCH -- ACCESS GRANTED CHANNEL

SDCCH -- STAND ALONE DEDICATED CONTROL CHANNEL

SACCH -- SLOW ASSOCIATED CONTROL CHANNEL

FACCH -- FAST ASSOCIATED CONTROL CHANNEL

DOWN LINK ONLY

UPLINK ONLY

BOTH UP

DOWNLINKS

TRAFFIC


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Broadcast Channels "1#:%

L!"#$%& $'%(()&*

T+%,,#$ $'%(()&*C!(+!& $'%(()&*

BCH

FCCH BCCH SCH


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Broadcast Channels "-#:%

• re(uenc! correction channel @ CC

– ne 'a! channel operating in for'ard direction and

using fre(uenc! correction &urst format

– Bears information for re(uenc! S!nchroni2ation – 15- all 0 &its in this &urst causes GMS> modulator to

deliver an unmodulated carrier for the entire duration

of the timeslot

• ;pon detecting this sine 'ave the MS can adust itsfre(uenc! reference appropriatel!


16/60


Broadcast Channels "/#:%

• S!nchroni2ation channel "SC%

– ne 'a! channel operating in for'ard direction and usingthe s!nchroni2ation &urst format

– Contains information for timing s!nchroni2ation "rame

um&er% and BTS Identification – Da' *ata information for SC is of $6 &its

• :5 &its are same for each cell and helps them toachieve timing s!nchroni2ation7 These are mapped ontothe s!nchroni2ation field of s!nchroni2ation &urst format

• : &its are for the identification of BTS and mapped onBSIC

• 16 &its represent the T*MA frame num&er


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D%% F#)&8 b#

+%0*"

CRC

E($!)+

13 b#* C!(!&5#

!(E($!)+

67

8

94

S:($'+!(#;%#!(

,#)&


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• Broadcast control channel "BCC%

– ne 'a! channel operating in the for'ard direction andusing the normal &urst format

– BCC ccur in timeslot 0 of some specific carriers

,no'n as BCC carriers – After loc,ing on to the fre(uenc! and frame structure in

the cell3 MS needs some more general information&roadcast on the BCC for call setup purposes

• Cell Identit!

• et'or, Identit!• Control Channel structure

• BCC re(uencies of neigh&oring cells


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Broadcast Channels ":#:%

• Da' *ata information for BCC is of 1$5 &its3protected &! an error correcting &loc, code "'hichmeans adding 50 more &its%

• --5 &its are convolution encoded !ielding 58: &its

•58: &its are split into 5)115 &its and sent in 5 timeslots

D%% F#)&184 b#

+%0 *"

,#+)

E($!)+


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Common Control Channels "1#5%

C!(+!& $'%(()&*

CCCHBCH

DCCH

PCH RACH AGCH


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Common Control Channels "/#5%

• Dandom access channel – DAC

– ne 'a! channel operating in the reverse directionand using the access &urst format

– Ehen MS 'ants to initiate dialogue 'ith net'or,3this channel is used to send re(uest to net'or, fora dedicated resource

– The actual communication &et'een the MS andthe net'or, 'ill ta,es place later on the dedicated

channel7 – If the re(uest is not granted 'ithin a specific time

period3 the MS repeats the re(uest on DAC7


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Common Control Channels "5#5%

• Access grant channel @ AGC

– AGC is a one 'a! channel operating in for'ard

direction and using the normal &urst format

– In response to re(uests from different MS onDAC3 the net'or, allocates a specific dedicated

signaling channel "S*CC% against each re(uest

for further communication7

– The response to the re(uest is sent on AGC7 – ;ses same coding scheme as used for BCC


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*edicated Control Channels "1#8%

C!(+!& $'%(()&*

CCCH BCHDCCH

SDCCH SACCHFACCH


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*edicated Control Channels "-#8%

• Stand alone@dedicated control channel @ S*CC

– T'o 'a! channel using normal &urst format

– As per the allocation conve!ed over the AGC3

&oth the MS < the BTS s'itch over to theassigned S*CC for a further communication

– The ollo'ing tas,s re(uire the use of S*CC

– Location ;pdates

– Call Setup

– SMS

– ;ses the same coding scheme as used &! BCC


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*edicated Control Channels "/#8%

• Slo' associated control channel @ SACC

– T'o 'a! channel using normal &urst format

– SACC is al'a!s associated 'ith TC or S*CC

– Ehen associated 'ith a TC3 the SACC occursin 1- or -8 frame of each -:@frame multi frame

– +ach message comprises of 58: &its so 5

multi frames are re(uired to transmit a

message


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• ;sed to conve! the periodic carrier@signal strengthmeasurements to the net'or,

– Ehile an MS is &us! on a call over a trafficchannel "TC% or in communication 'ith MSC onthe S*CC3 MS ta,es periodic carrier@signalstrength measurements on o'n &ase station <neigh&oring &ase stations7

• Based on the anal!sis of measurements ta,en &!

BTS < the MS3 the BSC conve!s information ontiming advance < MS transmitter po'er control

• ;ses the same coding scheme as used &! BCC


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• ast associated control channel @ ACC

– ACC is a t'o 'a! channel using normal &urstformat

– ACC can &e associated 'ith S*CC or TC – ACC 'or,s on the principle of stealing "The

&urst of speech is replaced &! ACC signaling%

– ACC is used to conve!

– andover information

– ;ses the same coding scheme as used &! BCC


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Traffic Channels

• There are t'o t!pe of Traffic Channels – ull Date Traffic Channel

• This channel carries information at rate of 22.8 Kbps

– alf Date Traffic Channel

• This channel carries information at rate of 11.4 Kbps


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Mapping of logical Channels

• Generall! t'o configurations are mainl! used

– CC F SC F BCC F CCC

– Addresses a channel configuration in 'hich no S*CCare availa&le on TS 07

– In this case S*CC su& channels are defined on TS 1 – Dest of the TS are used &! Traffic channels

– CC F SC F BCC F CCC F S*CC#5

– addresses a channel configuration in 'hich all controlchannels are assigned to TS 0

– In this case TS1 is also availa&le for Traffic channels


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Mapping of logical Channels

• The do'nlin, direction of TS 0 of the BCC@TD isused &! various channels7

– CC

– SC

– BCC

– our S*CC su& channels "optional%H

– CCC

• This use is possi&le &ecause the logical channels can

time@share TS 0 in different T*MA frames of 81 frameMulti frame


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Mapping of Broadcast and Common

Control Channels

3 1 2 6 4 7 9

TDMA ,+%) - 4.917 *

3 1 2 6 4 7 9

TDMA ,+%) - 4.917 *

3 1

BF S

CF S

C CIF S

C C

Multiplexing of Broadcast and Common Control Channel on TS of radio fre!uenc" C #$o%nlin&'

B

• Multiple)ing of CC F SC F BCC F CCC on TS

0 of radio fre(uenc! C0 "81 rame Multiframe%

• C!cle of 81 T*MA frame "0@80%3 The structure isrepeated after I*L+ frame

• It contains one &loc, of 5 frames for BCC and 6

Bloc,s of 5 frames for CCC "AGC#=C%


33/60


Mapping of DAC on ;plin,

3 1 2 6 4 7 9

TDMA ,+%) - 4.917 *

3 1 2 6 4 7 9

TDMA ,+%) - 4.917 *

3 1

T#)*&! 3> C3> 5?(@

(ach burst on the uplin& is a )*C+

• In the ;plin, direction TS0 on carrier fre(uenc! C0 is

used to access the net'or,• nl! DAC is sent on this timeslot in uplin, direction


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Mapping of *edicated Control Channels

3 1 2 6 4 7 9 TDMA ,+%) - 4.917 *

3 13 1 2 6 4 7 9 TDMA ,+%) - 4.917 *

D3 D IA3 A6

D3 D IA4 A

IA7 A

IA1 A6

D3 D A3

D3 D A4

Multiplexing of $edicated Control Channel on TS 1 of radio fre!uenc" C

• "S*CC#$ F SACC#$% The Structure is c!clic over 10- frames

• ;plin, and do'nlin, patterns are time shifted so that S*CC su&

channel 0 is sent in frames 0@/ in do'nlin, and in frames18@1$ inuplin,

• To give sufficient time to MS to calculate ans'ers to the re(uest

received on do'nlin,

• $ MS can share this timeslot simultaneousl!


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Mapping of TC on Timeslots

TDMA ,+%) - 4.917 *

3 1 2 6 4 7 9

TDMA ,+%) - 4.917 *

3 1 2 6 4 7 9

TDMA ,+%

3 1 2 6

Multiplexing of $edicated Control Channel on TS 2 of radio fre!uenc" C

AT T T IT T T

• "TC# F SACC#T F ACC#% The Structure is

c!clic over -: frames

• TC are mapped together 'ith SACC

• ACC is also used together 'ith TC#7

• ACC 'or,s in stealing mode "The speech &urst

are replaced &! ACC signaling%


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• Control channels• Traffic Channels

– GSM Bursts


Topics Covered


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GSM Bursts

• Burst define a format in 'hich a particular information istransmitted on TS "The ph!sical content of TS is called a&urst%

• The time interval of a TS corresponds to 18:7-8 &its

• These &its are divided into different parts depending onthe t!pe of &urst

• There are 8 t!pes of &ursts in GSM

– ormal Burst

– re(uenc! Correction Burst

– S!nchroni2ation Burst

– Access Burst

– *umm! Burst


39/60


ormal Burst

• ;sed to carr! Traffic or control information

• Tail &its are se(uence of 2ero &its to indicate the start and the

end of &urst

• *ata &its carries Traffic or control information

• Training &its carries a training se(uence used &! adaptive

e(uali2er to estimate the channel

• lag &it indicates t!pe of information &eing transmitted ";serinfo#signaling info "TC or ACC%

• Guard &its are used to avoid overlapping &et'een adacent

timeslots

Tail'

(ata)*

+lag,

Training-.

+lag,

(ata)*

Tail'

Guard/0-)

"ormal Burst


40/60


re(uenc! Correction Burst

Tail

'

All 1eros

,2-

Tail

'

Guard

/0-)

+re3uency !orrection Burst

• This &urst format is used in do'nlin, direction on

CC for fre(uenc! s!nchroni2ation of MS

• Contains a se(uence of 15- 2eros

• After modulation the resulting signal is pure sine 'ave• Tail &its are se(uence of 2ero &its to indicate the start

and the end of &urst


41/60


S!nchroni2ation Burst

• This &urst format is used in do'nlin, direction on SC

for time s!nchroni2ation of MS

• Carries BSIC and in data field

• Contains a long Training se(uence "s!nchroni2ationfield%

Tail

'

(ata

'4

Synchroni1ation

.2

(ata

'4

Tail

'

Guard

/0-)

Synchroni1ation Burst


42/60


Access Burst

• This &urst format is used in ;plin, direction on DAC to

access the net'or,

• Long guard period ensures that the mo&ile

transmissions from all parts of the cell arrive at the BTS

'ithin the duration of the &urst

Tail

/

Synchroni1ation

2,

Tail

'

Guard

./0-)

Access Burst

(ata

'.


43/60


*umm! Burst

Tail

'

Mi5ed

)/

Training

-.

Mi5ed

)/

Tail

'

Guard

/0-)

(ummy Burst

• BTS al'a!s transmit on C0 "BCC fre(uenc! in the cell%

to ena&le MS to perform po'er measurementscontinuousl!

• The po'er measurements are useful to select the BTS

for initial access or for andover

• In order to achieve this dumm! &urst are transmitted onC0 'hen no other &urst is transmitted on C0

• *umm! Bursts are transmitted 'ith a pre@defined

se(uence of fi)ed &its


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• Control channels• Traffic Channels

– GSM Bursts


Topics Covered


45/60


La!er 1 unctionalit! "1#-%

• unctions that are necessar! to transfer &it streams

on ph!sical media "I7e7 the air interface%

– Step 14 oice +ncoding

– Step -4 Channel Coding "&loc,3 conv7%

– Step /4 Interleaving and Burst Generation

– Step 54 Ciphering

– Step 84 Modulation and Amplification


46/60


La!er 1 unctionalit! "-#-%

,nformation bits -

receie

*ir

,nterface

#/'

#0'

Dec7 05.02

#4'

Info &itstransmit

Dec7 05.03

#2'#1'Code 1

#bloc&'Code 2

#con'

)eorderingand

partitioning

#',nter-

leaing

(ncr"ption

unit

Burst

building

Burst

multiplex

Dec7 05.04

$ifferential

encoding

MSK

Modulation

Dec7 05.05

*ntenna

Transmitter

Transmitter


47/60


Step14 Speech +ncoding

• GSM is a digital s!stem3 so speech 'hich is inherentl!analog3 has to &e digiti2ed7

• The method emplo!ed &! current telephone s!stems for

multiple)ing voice lines over high speed trun,s is pulse

coded modulation "=CM%7• The output stream from =CM is :5 ,&ps3 too high a rate to &e

feasi&le over a radio lin,7

• Speech is divided into -0 millisecond samples3 each of 'hich

is encoded as -:0 &its3 giving a total &it rate of 1/ ,&ps7

– The speech coding algorithm used is called the Degular

pulse e)cited @@ linear predictive coder "D=+@@L=C% 'ith a

long term predictor loop7 "GSM 0:710%


48/60


• Channel coding is used to detect and correct &it errors in thereceived &it stream7 That is3 it reduces the Bit +rror Date "B+D%7In order to achieve this3 redundanc! is added to the information7

• Coding means adding some redundant information calculatedfrom the information source7

• *uring decoding3 the redundanc! is used to detect the presenceof errors7

• +rrors are detected 'hen transmitted redundanc! is differentfrom the one calculated 'ith received data7

• T'o forms of channel coding schemes are used in GSM4

– Bloc, coding

– Convolution coding

Step -4 Channel Coding


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Step -a4 Bloc, Coding

• or &loc, codes3 the information is divided into &loc,sof e(ual length7 According to a specific algorithm anum&er of redundant &its are added to these &loc,s7

• The &loc, code used for full rate speech coding in theGSM s!stems uses / redundant &its and can detectan! single &it error in each &loc, of 80 information&its7


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Step -&4 Convolution Coding

• In Convolution coding3 the data is divided into much smaller

&loc,s that are called information frames7

• The information frames t!picall! contain no more than a fe'

s!m&ols3 'hich are encoded into code 'ord frames7

•This procedure results in successive code 'ord frames coupledtogether &! the encoding procedure7 The codes that are

o&tained in this 'a! are called tree codes7

• The most important tree codes are ,no'n as convolution codes7

Convolution codes are tree codes that satisf! certain additional

linearit! and time invariance properties7


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Step /4 Interleaving

• Channel coding and particularl! convolution coding ismost effective in detecting and correcting singlerandom errors7

• Bit errors often occur in groups "&urst errors%7 This is

especiall! true in a mo&ile telephon! s!stem 'herelong fading dips affect several consecutive &its7

• The interleaving method deals 'ith this pro&lem7

• It separates consecutive &its of a message3 so that the

&its can &e sent in a non@consecutive 'a!7• If a &urst of errors occurs in this non@consecutive

se(uence3 it leads to separated single errors after the&urst is reordered7


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Step /4 Interleaving

• Ta,e a message &loc, consisting of four names each containingfour letters7This information is read into a matri) of four ro's andfour columns7 Ehen the information is read out3 it is organi2ed &!

columns so that the first letter in ever! name is transmitted first3 thesecond letter is transmitted second3 etc7 *uring the transmission3frame - for e)ample is lost7 Eithout interleaving3 the entire name'ould &e lost7 Eith interleaving3 onl! one letter in each name is lost7The channel decoder can then correct this one error7


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Channel Coding of Speech "1#/%

• The full rate speech coder delivers a &loc, of -:0 &its ever!

-0 ms to the channel coder7

• The -:0 &its are divided into three classes7 This division is

made according to the importance of the &its4

– Class Ia 80 &its @ most sensitive to &it errors7

– Class I& 1/- &its @ moderatel! sensitive to &it errors7

– Class II .$ &its @ least sensitive to &it errors7

• Class Ia &its have a / &it c!clic redundanc! code added for

error detection J 80F/ &its7


54/60


Channel Coding of Speech "-#/%

• 1/- class I& &its 'ith 5 &it tail se(uence J 1/- F 5 J1/:7

• Class Ia F class I& J 8/F1/:J1$63 input into a 1#-rate convolution encoder

• The convolution encoder thus outputs /.$ &its3 to'hich are added the .$ remaining class II &its

• Thus ever! -0 ms speech sample -:0&its of actualinformation is encoded as 58: &its3 giving a &it rate of

--7$ ,&ps


55/60


Channel Coding of Speech "/#/%

Prioriti1ation of S%eech Information

C!(!&5#!(

$!)+


56/60


Interleaving of Speech "1#/%

• The 58: coded &its are reordered < interleaved over $half &ursts7

• +ach alf &urst contains 8. &its

8 *)")(* !, 7 b#* )%$'

1

1

27

.

.

.

.

..

441

44

2

13

18

29

.

.

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..

442

473

6

11

1

2

.

.

.

.

..

446

471

4

12

23

28

.

.

.

.

..

444

472

7

16

21

2

.

.

.

.

..

447

476

9

14

22

63

.

.

.

.

..

449

474

8

19

24

62

.

.

.

.

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448

479

17

26

61

.

.

.

.

..

44

477

+irst 6e&el #f Interlea&ing


57/60


Interleaving of Speech "-#/%

• The second level of interleaving is performed &! interleavingt'o &loc,s of -0 ms of speech

• +ach -0 ms &loc, !ields 58: coded &its3 ordered in $ su&@&loc,s of 8. &its7

• The first su&@&loc, from &loc, B is then interleaved in thesame &urst as the fifth su&@&loc, from &loc, A7

• This interleaving is made on a per &it &asis3 The &its from&loc, B1 occup! all odd num&ered positions in the t'o half

&ursts3 and the &its from A8 occup! all even num&eredpositions


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Interleaving of Speech "/#/%


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Modulation

• GSM ;ses GMS> "Gaussian =hase Shift >e!ing%modulation scheme

• Defer GSM Spec 08705 for details


60/60

Deferences

• GSM 08701 "General *escription and concepts%

• GSM 0870- "*escri&es logical channels%

• GSM 0870/ "+rror detection and correction%

• GSM 08705 "GSM> Modulation#demodulation%

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Gsm Radio if Kasera Ashish Apr04

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