Download - Air Interface3
-
8/12/2019 Air Interface3
1/13
GSM PLMN NETWORK
-
8/12/2019 Air Interface3
2/13
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:
-
8/12/2019 Air Interface3
3/13
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*
-
8/12/2019 Air Interface3
4/13
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)
-
8/12/2019 Air Interface3
5/13
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$ice type and the serial number of the
equipment*
-
8/12/2019 Air Interface3
6/13
AIR INTERFACE
Physical channel: In GSM is defined by a frequency air f!r "L#$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
-
8/12/2019 Air Interface3
7/13
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
-
8/12/2019 Air Interface3
8/13
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.
-
8/12/2019 Air Interface3
9/13
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).
-
8/12/2019 Air Interface3
10/13
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+ and$!*n&in+ !in' '!
!in'
Ins'ruc' MS '! 'rans%i''in2!*er and f!r 'i%in2 ad5ance
Sends '(e si2na&
%easure%en' /s'ren2'( anqua&i'y0 !f i's ce&& and
nei2(b!rin2 ce&&s
Fas' Ass!cia'ed C!n'r!&C(anne&(FACCH)
"&in+ and$!*n&in+ !in' '!
!in'
Trans%i' (and !5er inf!r%a'i!nTrans%i' necessary (and
!5er inf!r%a'i!n in acces
burs'
-
8/12/2019 Air Interface3
11/13
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)
-
8/12/2019 Air Interface3
12/13
+'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
-
8/12/2019 Air Interface3
13/13
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)