air interface3

8/12/2019 Air Interface3

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GSM PLMN NETWORK


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Mobile Stations Function :

They consist of two major component:

The Mobile Equipment (ME)

The Subscriber Identity Module (SIM)

Voice and data transmission

!requency and time synchroni"ation

Monitorin# of power and si#nal quality of the surroundin# cells for hando$er

%ro$ision of location updates

Equali"ation of multipath distortions

&isplay of short messa#es up to ' characters lon#

Timin# ad$ance*

Base Transciver Station Function(BTS):

+hannel codin#: To protect the transmission, incomin# information is pro$ided with parity chec-

and redundancy (con$olutional codin#) and spread in time o$er se$eral .! bursts (interlea$in#

+ipherin#*

/urst bloc- formation*

Modulation*

%ower +ontrol %+: +ontrol of the power le$el of the /TS and MS*

Timin# 0d$ance T0: +alculation of the distance of the MSs from the /TS the MSs are informe

necessary transmission ad$ance*

!requency .oppin#: a feature which enhances the reliability of information transfer*

Synchroni"ation: %ro$idin# of mobile stations with frequency and time synchroni"ation informat

Base Station controller Function:


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Inter1cell hando$er

2eallocation of frequencies amon# /TSs

%ower mana#ement of /TSs

Time and frequency synchroni"ation si#nals to /TSs

Time delay measurement of the recei$ed si#nals from MSs with respect to /TS

cloc-

+ontrols frequency hoppin#

MSC : Mobile services Switching Center Function:

Switchin# of user connections*

2outin# functionality (path selection)*

Si#nalin# with other MS+s and e3ternal networ- e3chan#es*

E$aluation of a$ailable si#nalin# information for destination routin#*

4e#al interception*

+opin# with abnormal si#nalin# conditions, e*#* loss of si#nalin# information*

Supplementary Ser$ice support*

%rocessin# of transmission path attributes, e*#* echo compensation*

+all super$ision*

5$erload protection*

+ontrol of priority calls, e*#* emer#ency call +har#in#**

Traffic measurement and traffic obser$ation*


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VLR : Visitor Location Register Function:

The Visitor 4ocation 2e#ister V42 is responsible to aid the MS+ with information on the subscriber,w

are temporarily in the MS+ ser$ice area*

Exa!les o" subscriber #ata in the VLR:

MSIS&6: Mobile Subscriber IS&6 number*

IMSI: International Mobile Subscriber Identity*

TMSI: Temporary Mobile Subscriber Identity*

.56: .ando$er 6umber*

MS26: Mobile Station 2oamin# 6umber*

Triples (0uthori"ation parameters)*

$LR : $oe Location Register Function:

The .ome 4ocation 2e#ister .42 is the main data base of the mobile subscriber* The .42 is

always associated with an 0uthentication +enter 0+*

The $LR !er"ors the "ollowing i!ortant tas%s:

It sends all necessary data to the V42*

It supports the call setup in case of Mobile Terminatin# +alls MT+*

2outin# information to the 7ateway MS+ (Interro#ation)*

It transmits the Triples from 0+ to V42 on request

&'C : &uthentication Center Function:

0n 0uthentication +enter 0+ contains all necessary means, -eys and 0l#orithms for the creation

of security related authori"ation parameters, the so1called Triples* The Triples are created on

V42 request and deli$ered $ia .42 to the V42* 0n 0+ is always associated with an .42*

Central in"oration containe# in the &C is:

IMSI: International Mobile Subscriber Identity

8i: Indi$idual 8ey (top secret mobile subscriber identity)


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0l#orithms for authentication and encryption: 09, 0*

ER : Eui!ent #entit* Register Function:

The Equipment Identity 2e#ister EI2 contains the Mobile Equipment identity: the International

Mobile Equipment Identity IMEI* 0n IMEI clearly identifies a unique Mobile Equipment ME and

contains information about the place of manufacture, de$ice type and the serial number of the

equipment*


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AIR INTERFACE

Physical channel: In GSM is defined by a frequency air f!r "L#$L and

a Ti%e S&!' TS !f '(e T$MA fra%e)

CH

3

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

CH124

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


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Kinds of frame

TDMA Frame:-

In GSM 8 TS form one TDMA frame (4.615ms), i.e. 8 physical channels are sin!

"he same fre#ency $an% $ein! cyclically

(&'ery 4.615 ms) alloca"e% "o a cer"ain ser applica"ion.

Multiframes:-

Multi-framesof physical channels alloca"e% for ser "raffic (Traffic

hannels T*) are repe"i"ion cycles of +6 TDMA frames.

Multi-framesof physical channels alloca"e% for si!nalin! %a"a (mos"ly

on one se'eral of "he TS of "he carrier of one cell) are repe"i"ion

cycles of 51 TDMA frames.

Superframe:-

51 Traffic Ml"i-frames.

+6 on"rol Ml"i-frames.

Time of Sper-frame 51/+6/4.615 6.1+ Sec

Hyperframe:-

+48 Sper-frame.

Time of *yper-frame +48/6.1+ 0.5 hors.

CH1

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

CH

2

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


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logical channels:Many "ypes of lo!ical channels eis"s, each %esi!ne% "o carry a %ifferen" messa!e "o or

from an MS. All informa"ion "o an% from an MS ms" $e forma""e% correc"ly,

2o!ical hannels can carry Traffic or con"rol si!nals.


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Traffic Channels:- 3nce call se"-p proce%res ha'e $een comple"e% on "he con"rol

physical channel, "he MS "nes "o a "raffic physical channel. I" ses "he Traffic hannel(T*) lo!ical channel. Traffic channels are "hs p lin an% %on lin.

There are two types of TCH:

Full rate (TCH) Transmi"s fll ra"e speech (10 $i"ss). A fll ra"e T*

occpies one physical channel.

Half rate (TCH/2) "ransmi"s half ra"e speech (6.5 $i"ss).


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Logical Channel Direction BTS info MS info

BroadcastChannel

Frequency C!rrec'i!nC(anne&(FCCH)

$!*n&in+ !in' '!%u&'i !in'

Trans%i's a carrier frequencyIden'ifies ,CC- carrier bcarrier frequency and 'une

'! '(e frequency

Sync(r!ni.a'i!n c(anne&

/SCH0

$!*n&in+ !in' '!

%u&'i !in'

Trans%i' inf!r%a'i!n ab!u'

T$MA fra%e s'ruc'ure in a ce&&and base1s'a'i!n iden'i'y /,SIC0

Sync(r!ni.e *i'( '(e fra%

s'ruc'ure *i'(in ar'icu&arce&&

,r!adcas' c!n'r!&c(anne& (BCCH)

$!*n&in+ !in' '!%u&'i !in'

,r!ad cas' s!%e 2enera& ce&&inf!r%a'i!n suc( as :

(LAI)&!ca'i!n area iden'i'y%a3 !u'u' !*er a&&!*ed in '(e

ce&& 4and '(e iden'i'y !f BCCHcarrier

Recei5es LAIand c!%ari' *i'( e3is'in2 !ne in '(eSIM4 MSse' '(e !u'u'

!*er based !ninf!r%a'i!n !f BCCH4

fina&&y MS s'!res BCCHcarriers '! assis' in bes'

(and !5er

Commoncontrol

channels

Pa2in2 c(anne&s (PCH)$!*n&in+ !in' '!

!in'

Trans%i' a a2in2 %essa2e '!indica'e an inc!%in2 ca&& 4 '(e

a2in2 %essa2e c!n'ains '(e

%!bi&e iden'i'y nu%ber !f '(e%!bi&e ne'*!r+ *is(es '!

c!n'ac'

If i's iden'ify MSIN '(en

'(e %!bi&e *i&& res!nd '!

'(e ne'*!r+

Rand!% Access C(anne&

(RACH)

$!*n&in+ !in' '!

!in'

Recei5es a si2na& fr!% %!bi&e

s'a'i!n f!r si2na&in2 c(anne&

Ans*er a a2in2 %essa2eby reques' a si2na&in2

c(anne&

Access Gran' C(anne&

(AGCH)

$!*n&in+ !in' '!!in'

Assi2ns a si2na&in2 c(anne&SDCCH'! MS

Recei5es si2na& c(anne&assi2n%en' SDCCH

DedicatedControlChannels

DedicatedControlChannels

S'anda&!ne $edica'ed

C!n'r!& C(anne& /SDCCH0

"&in+ and$!*n&in+ !in' '!

!in'

T(e ,TS s*i'c(es '! '(e

assi2nedSDCCH '(e ca&& se'ur!cedure is erf!r%ed in id&e

%!de 4a&s! used '! 'rans%i' 'e3'

%essa2es and s%s

T(e MS s*i'c(es '! '(eassi2nedSDCCHT(e M

Recei5es TC- assi2n%eninf!r%a'i!n

S&!* Ass!cia'ed C!n'r!&C(anne&(SACCH)


!in'

Ins'ruc' MS '! 'rans%i''in2!*er and f!r 'i%in2 ad5ance

Sends '(e si2na&

%easure%en' /s'ren2'( anqua&i'y0 !f i's ce&& and

nei2(b!rin2 ce&&s

Fas' Ass!cia'ed C!n'r!&C(anne&(FACCH)


!in'

Trans%i' (and !5er inf!r%a'i!nTrans%i' necessary (and

!5er inf!r%a'i!n in acces

burs'


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Ta!le" Ill#strate the Logical Control Channels

RA$IO TRANSMISSION PRO,LEMS

Intro"

A %!bi&e c!%%unica'i!n en5ir!n%en' suffers fr!% %any r!b&e%s re&a'ed '! radi!

'rans%issi!n4 *(ic( %ay cause unacce'ab&e de2rada'i!n !f '(e ser5ice qua&i'y)

Ra$io Trans%ission Pro!le%s"

Fa#ing !ro!le:Fadin2 %eans '(a' '(e si2na& s'ren2'( recei5ed f&uc'ua'es ar!und a %ean 5a&ue *(i&e

c(an2in2 '(e %!bi&e !si'i!n)

&'Slo Fa$ing Log *or%al Fa$ing Sha$oing "'

T(e reas!n f!r s(ad!*in2 is '(e resence !f !bs'ac&es &i+e &ar2e bui&din2s !r (i&&s in '(e a'( be'*een

'(e si'e and '(e %!bi&e) T(e dis'ance be'*een fadin2 dis /%ini%u% 5a&ues !f si2na& s'ren2'(0 is fr!%67 '! 87 %e'ers)

Sol#tion For The Slo Fa$ing"'

T! !5erc!%e '(e fadin2 r!b&e%s4 '(e fadin2 %ar2in s(!u&d be &ar2e en!u2( '(a' '(e &!*es' fadin2

di is s'i&& (i2(er '(an '(e recei5er sensi'i5i'y)


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+'Fast Fa$ing Rayleigh Fa$ing M#lti,ath Fa$ing"'

T(is !ccurs *(en a si2na& 'a+es %!re '(an !ne a'( be'*een '(e MS and ,TS an'ennas)4 T(e Si2na& is

ref&ec'ed !ff bui&din2s4 f!r e3a%&e4 and is recei5ed fr!% se5era& differen' indirec' a'(s) Ray&ei2( fadin2!ccurs *(en '(e !bs'ac&es are c&!se '! '(e recei5in2 an'enna) T(e recei5ed si2na& is '(e su% !f %any

iden'ica& si2na&s '(a' differ !n&y in (ase /and '! s!%e e3'en' a%&i'ude0)

Sol#tion of Rayleigh Fa$ing"'

& Antenna (S,ace) Di-ersity"'

T(e ce&& 'ranscei5er *i&& use '*! recei5in2 an'ennas ins'ead !f !ne) A

dis'ance !f ab!u' 9 %e'ers *i&& seara'e '(e%4 and '(ey *i&& recei5e

radi! si2na&s indeenden'&y4 s! '(ey *i&& be affec'ed differen'&y by '(e

fadin2 dis and '(e be''er si2na& recei5ed *i&& be se&ec'ed)

+ Fre.#ency Ho,,ing "'

T(e fadin2 effec' %ay n!' be '(e sa%e f!r a&& !f '(e frequencies4 s!

'(e 'i%e s&!' !f '(e subscriber *i&& u% !r ;(!< be'*een '(e

FadingMargin

ReceiverSensitivity

dB

Time


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frequencies !f '(e ce&& *(en i' is reea'ed in eac( T$MA fra%e) If

!n&y !ne !f '(e frequencies is affec'ed se5ere&y by fadin24 a s%a&&

frac'i!n !f '(e si2na& *i&& be &!s') T(e (!in2 sequence %i2(' be

cyc&ic !r rand!%)

Ti%e $elay ,ro!le%"

Eac( MS !n a ca&& is a&&!ca'ed a 'i%e s&!' !n a T$MA fra%e) T(is is an a%!un' !f 'i%e durin2 *(ic( '(e

MS 'rans%i's inf!r%a'i!n '! '(e ,TS) T(e inf!r%a'i!n %us' a&s! arri5e a' '(e ,TS *i'(in '(a' 'i%e s&!')

T(e 'i%e a&i2n%en' r!b&e% !ccurs *(en ar' !f '(e inf!r%a'i!n 'rans%i''ed by an MS d!es n!' arri5e

*i'(in '(e a&&!ca'ed 'i%e s&!') Ins'ead4 '(a' ar' %ay arri5e durin2 '(e ne3' 'i%e s&!'4 and %ay in'erfere *i'(

inf!r%a'i!n fr!% an!'(er MS usin2 '(a' !'(er 'i%e s&!') A &ar2e dis'ance be'*een '(e MS and '(e ,TS

causes 'i%e a&i2n%en') Effec'i5e&y4 '(e si2na& cann!' 'ra5e& !5er '(e &ar2e dis'ance *i'(in '(e 2i5en 'i%e)

Sol#tion of Ti%e Delay"'

Ti%in2 ad5ance is a s!&u'i!n secifica&&y desi2ned '! c!un'erac' '(e r!b&e% !f 'i%e a&i2n%en') I' *!r+s

by ins'ruc'in2 '(e %isa&i2ned MS '! 'rans%i' i's burs' ear&ier !r &a'er '(an i' n!r%a&&y *!u&d) In GSM4 '(e

'i%in2 ad5ance inf!r%a'i!n re&a'es '! bi' 'i%es) Ma3i%u% => bi' 'i%es can be used in GSM sys'e%s)

Interference ,ro,le%"

&) Co'channel interference"'

Is Caused ,y use !f a frequency c&!se '! '(e e3ac' sa%e frequency) T(e f!r%er *i&& in'erfere *i'( '(e

&a''er4 &eadin2 '! '(e 'er%s in'erferin2 frequency /I0 and carrier frequency /C0)

Sol#tion"'

60 T(e GSM secifica'i!n rec!%%ends '(a' '(e carrier1'!1in'erference /C#I0 ra'i! is 2rea'er '(an ? decibe&s

/d,0)

80 Sec'!ri.a'i!n !f Ce&&s)

+) A$/acent Channel Interference"'Adacen' frequencies /A04 '(a' are frequencies s(if'ed 877+-. fr!% '(e carrier frequency /C04 %us' be

a5!ided in '(e sa%e ce&& and referab&y in nei2(b!rin2 ce&&s a&s!) A&'(!u2( adacen' frequencies are a'

differen' frequencies '! '(e carrier frequency '(ey can s'i&& cause in'erference and qua&i'y r!b&e%s)

Sol#tion"'

60 Sec'!ri.a'i!n !f Ce&&s)

air interface3

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