GSM by SherGill

7/26/2019 GSM by SherGill

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GSM manual prepared by AQEEL SHERGILL

SHerGill

Human exposure to radio frequency energy (PCS1900 only)

IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency ElectromagneticFields, !H" to ##$H"%

Power density (S)

&ower per unit area normal to the direction of propagation, usually expressed in units of watts per squaremetre '()m*+ or, for convenience, units such as mill watts per square centimeter 'm()cm*+%

For plane waves, power density, electric field strength 'E+ and magnetic field strength 'H+ are related ythe impedance of free space, -- ohms% In particular,

S.E'sq+ )-- . -- / H'sq+

Maximum permitted exposure ceilings

eryllium !ealt! and safety precautions

0eryllium '0e+, is a hard silver)white metal% It is stale in air, ut urns rilliantly in 1xygen%

Principles of Cellular "elecommunications

2 cellular telephone system lin!s moile station '3S+ suscriers into the pulic telephone system or toanother cellular system4s 3S suscrier%

#etwor$ Components

$S3 networ!s are made up of 3oile services Switching 5entres '3S5+, 0ase Station Systems'0SS+and 3oile Stations '3S+% 6hese three entities can e ro!en down further into smaller entities7such as, within the 0SS we have 0ase Station 5ontrollers, 0ase 6ransceiver Stations and 6ranscoders%

(ith the 3S5, 0SS and 3S we can ma!e calls, receive calls, perform illing etc, as any normal &S68networ! would e ale to do% 6he only prolem for the 3S is that not all the calls made or received arefrom other 3Ss% 6herefore, it is also necessary to connect the $S3 networ! to the &S68%

3oile Stations within the cellular networ! are located in 9cells:, these cells are provided y the 0SSs%Each 0SS can provide one or more cells, dependent on the manufacturers equipment% 6he cells arenormally represented y a hexagon, ut in practice they are irregular in shape%


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%requency Spectrum

6he frequency spectrum is very congested, with only narrow slots of andwidth allocated for cellularcommunications%

6he RF carrier in $S3 can support up to eight 6ime ;ivision 3ultiple 2ccess '6;32+ timeslots% 6hat is, in

theory, each RF carrier is capale of supporting up to eight simultaneous telephone calls, ut as we willsee later in this course although this is possile, networ! signalling and messaging may reduce theoverall numer from eight timeslots per RF carrier to six or seven timeslots per RF carrier%

3S4s% 1viously, not all of these 3S suscriers could ma!e a call at the same time, ut it is also unli!elythat all the 3S suscriers would want to ma!e a call at the same time% 6herefore, without !nowing it,3Ss share the same physical resources, ut at different times%

%requency &ange'SM 900

Receive 'uplin!+ ?@#A@=> 3H"

6ransmit 'downlin!+ @>A@B# 3H"

=*C 2solute radio frequency channels '2RF58+

'SM 900 Receive 'uplin!+ ??#A@=> 3H"

6ransmit 'downlin!+ @*>A@B# 3H"

=-C 2solute radio frequency channels '2RF58+

'SM 1*00 (+CS1*00) Receive 'uplin!+ =-=#A=-?> 3H"

6ransmit 'downlin!+ =?#>A=??# 3H"

-C 2solute radio frequency channels '2RF58+

PCS 1900 Receive 'uplin!+ =?>#A=@=# 3H"

6ransmit 'downlin!+ =@#A=@@# 3H"

*@@ 2solute radio frequency channels '2RF58+

,&%C#

0andwidth . *## DH" ? 6;32 timeslots

Cell Si-e

6he numer of cells in any geographic area is determined y the numer of 3S suscriers who will eoperating in that area, and the geographic layout of the area 'hills, la!es, uildings etc+%


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%requency &e.useStandard $S3 has a total of =*C frequencies availale for use in a networ!% 3ost networ! providers areunli!ely to e ale to use all of these frequencies and are generally allocated a small suset of the =*C%

xample2 networ! provider has een allocated C? frequencies to provide coverage over a large

area, let us ta!e for example $reat 0ritain%

2s we have already seen, the maximum cell si"e is approximately -# !m in diameter,thus our C? frequencies would not e ale to cover the whole of 0ritain%

6o overcome this limitation the networ! provider must reAuse the same frequencies overand over again, in what is termed a 9frequency reAuse pattern:%

(hen planning the frequency reAuse pattern the networ! planner must ta!e into accounthow often to use the same frequencies and determine how close together the cells are,otherwise coAchannel and)or adacent channel interference may occur% 6he networ!provider will also ta!e into account the nature of the area to e covered%

Co.c!annel /nterference

6his occurs when RF carriers of the same frequency are transmitting in close proximity toeach other, the transmission from one RF carrier interferes with the other RF carrier%

,dacent C!annel /nterference

6his occurs when an RF source of a neary frequency interferes with the RF carrier%


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Site Sectori-ation


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Switc!ing and Control Having estalished radio coverage through the use of cells,oth omniAdirectional and directional 'sectored sites+, now consider what happens when the 3S is inmotion 'as 3Ss tend to e+%

2t some point the 3S will have to move from one cell4s coverage area to another cell4s coverage area%

Handovers from one cell to another could e for a numer of reasons 'e%g% the signal strength of the9serving cell: is less than the signal strength of a 9neighour cell:, or the 3S is suffering a quality prolemin the serving cell+ and y handing over to one of its neighours this may stop the quality prolem%

Regardless of the reason for a 9handover: it has to e controlled y some entity, and in$S3 that entity is the 3oile services Switching 5entre '3S5+%

6o perform a handover, the networ! must !now which neighour cell to hand the 3S over to% 6o ensurethat we handover to the est possile candidate the 3S performs measurements of its surroundingneighour cells and reports its findings to the networ!% 6hese are then analy"ed together with themeasurements that the networ! performs and a decision is made on a regular asis as to the need for ahandover% If a handover is required then the relevant signal protocols are estalished and the handover iscontrolled y the 3S5%

Handovers must e transparent to the 3S suscrier% 6hat is the suscrier should e unaware that ahandover has occurred%

#oteSome networ!s may allow certain handovers to e performed at the 0SS level% 6his would e dependenton the manufacturer4s equipment

%lexile Hando2er Processes


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'SM #etwor$ components

6he diagram opposite shows a simplified $S3 networ!% Each networ! component is illustrated onlyonce, however, many of the components will occur several times throughout a networ!%

Each networ! component is designed to communicate over an interface specified y the $S3 standards%

6his provides flexiility and enales a networ! provider to utili"e system components from differentmanufacturers% For example 3otorola 0ase Station System '0SS+ equipment may e coupled with anEricsson 8etwor! Switching System%6he principle component groups of a $S3 networ! are"!e Moile Station (MS)6his consists of the moile telephone, fax machine etc% 6his is the part of the networ! that the suscrierwill see%


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"!e ase Station System (SS)6his is the part of the networ! which provides the radio interconnection from the 3S to the landAasedswitching equipment%"!e #etwor$ Switc!ing System6his consists of the 3oile services Switching 5entre '3S5+ and its associated systemAcontrol dataasesand processors together with the required interfaces%6his is the part which provides for interconnection etween the $S3 networ! and the &ulic Switched6elephone 8etwor! '&S68+%"!e 3perations and Maintenance System6his enales the networ! provider to configure and maintain the networ! from acentral location

Moile station (MS) It consist of two parts, 3oile Equipment '3E+ and SI3%Moile quipment 6his is the hardware that the user actually have !nown as moilephone%

Suscrier /dentity Module (S/M)6he SI3 as mentioned previously is a 9smart card: which plugs into the 3E and contains informationaout the 3S suscrier hence the name Suscrier Identity 3odule%6he SI3 contains several pieces of information/nternational Moile Suscrier /dentity (/MS/)6his numer identifies the 3S suscrier% It is only transmitted over the air duringinitiali"ation%"emporary Moile Suscrier /dentity ("MS/)6his numer identifies the suscrier, it is periodically changed y the systemmanagement to protect the suscrier from eing identified y someoneattempting to monitor the radio interface%4ocation ,rea /dentity (4,/)Identifies the current location of the suscrier%Suscrier ,ut!entication 5ey (5i)

6his is used to authenticate the SI3 card%Moile Station /nternational Ser2ices +igital #etwor$ (MS/S+#)6his is the telephone numer of the moile suscrier% It is comprised of a countrycode, a networ! code and a suscrier numer%

ase Station System (SS)6he $S3 0ase Station System is the equipment located at a cell site% It comprises a comination ofdigital and RF equipment% 6he 0SS provides the lin! etween the 3S and the 3S5%6he 0SS communicates with the 3S over the digital air interface and with the 3S5 via * 3it)s lin!s%

6he 0SS consists of three maor hardware components"!e ase "ranscei2er Station 6 "S6he 06S contains the RF components that provide the air interface for a particular cell% 6his is the part of

the $S3 networ! which communicates with the 3S% 6he antenna is included as part of the 06S%"!e ase Station Controller 6 SC6he 0S5 as its name implies provides the control for the 0SS% 6he 0S5 communicates directly with the3S5% 6he 0S5 may control single or multiple 06Ss%"!e "ranscoder 6 7C+&6he 6ranscoder is used to compact the signals from the 3S so that they are more efficiently sent over theterrestrial interfaces% 2lthough the transcoder is considered to e a part of the 0SS, it is very oftenlocated closer to the 3S5%


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SS Configurations

2s we have mentioned, a 0S5 may control several 06Ss, the maximum numer of 06Ss which may econtrolled y one 0S5 is not specified y $S3% Individual manufacturer4s specifications may vary greatly%

6he 06Ss and 0S5 may either e located at the same cell site 9coAlocated:, or located at different sites9Remote:% In reality most 06Ss will e remote, as there are many more 06Ss than 0S5s in a networ!%

2nother 0SS configuration is the daisy chain% 2 06S need not communicate directly with the 0S5 whichcontrols it, it can e connected to the 0S5 via a chain of 06Ss%

;aisy chaining reduces the amount of caling required to set up a networ! as a 06S can e connected to

its nearest 06S rather than all the way to the 0S5%

&rolems may arise when chaining 06Ss, due to the transmission delay through the chain% 6he length ofthe chain must, therefore, e !ept sufficiently short to prevent the round trip speech delayecoming too long%

1ther topologies are also permitted, including stars and loops% Loops are used to introduce redundancyinto the networ!, for example if a 06S connection was lost, the 06S may still e ale to communicatewith the 0S5 if a second connection is availale%


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SS Configurations

"ranscoder (7C+&)

6he 6ranscoder 'G5;R+ is required to convert the speech or data output from the 3S5 'BC !it)s &53+,into the form specified y $S3 specifications for transmission over the air interface, that is, etween the0SS and 3S 'BC !it)s to =B !it)s and vice versa+%

6he BC !it)s &ulse 5ode 3odulation '&53+ circuits from the 3S5, if transmitted on the air interfacewithout modification, would occupy an excessive amount of radio andwidth%6his would use the availale radio spectrum inefficiently%

In the =B Dits)s of data the Dits)s are for control data which is !nown as 6R2< ' 6ranscoder rateadaption unit + and the remaining = Dits)s are for speech data%


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#etwor$ Switc!ing System6he 8etwor! Switching System includes the main switching functions of the $S3 networ!% It alsocontains the dataases required for suscrier data and moility management% Its main function is tomanage communications etween the $S3 networ! and other telecommunications networ!s%

6he components of the 8etwor! Switching System are listed elow

Moile Ser2ices Switc!ing Centre 6 MSCHome 4ocation &egister 6 H4&8isitor 4ocation &egister 6 84&quipment /dentity &egister 6 /&,ut!entication Centre 6 ,C/nterwor$ing %unction 6 /:%c!o Canceller 6 C


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Moile Ser2ices Switc!ing Centre (MSC)6he 3S5 is included in the $S3 system for callAswitching% Its overall purpose is the same as that of anytelephone exchange%However, ecause of the additional complications involved in the control and security aspects of the $S3cellular system and the wide range of suscrier facilities that it offers, the 3S5 has to e capale offulfilling many additional functions%

6he 3S5 will carry out several different functions depending upon its position in the networ!% (hen the3S5 provides the interface etween the &S68 and the 0SSs in the $S3 networ! it will e !nown as a$ateway 3S5%Each 3S5 provides service to 3Ss located within a defined geographic coverage area, the networ!typically contains more than one 3S5% 1ne 3S5 is capale of supporting a regional capital withapproximately one million inhaitants% 2n 3S5 of this si"e will e contained in aout half a do"en rac!s%

6he functions carried out y the 3S5 are listed elowCall ProcessingIncludes control of data)voice call setup, interA0SS and interA3S5 handovers and control of moilitymanagement 'suscrier validation and location+%3perations and Maintenance SupportIncludes dataase management, traffic metering and measurement, and a manmachine interface%

/nternetwor$ /nterwor$ing3anages the interface etween the $S3 networ! and the &S68%illing5ollects call illing data%

Home 4ocation &egister (H4&)6he HLR is the reference dataase for suscrier parameters%arious identification numers and addresses are stored, as well as authentication parameters% 6hisinformation is entered into the dataase y the networ! provider when a new suscrier isadded to the system%6he parameters stored in the HLR are listed opposite6he HLR dataase contains the master dataase of all the suscriers to a $S3 &L38%6he data it contains is remotely accessed y all the 3S5s and the LRs in the networ! and, although the

networ! may contain more than one HLR, there is only one dataase record per suscrier A each HLR istherefore handling a portion of the total suscrier dataase% 6he suscrier data may e accessed yeither the I3SI or the 3SIS;8 numer%

8isitor 4ocation &egister (84&)6he LR contains a copy of most of the data stored at the HLR% It is, however, temporary data whichexists for only as long as the suscrier is 9active: in the particular area covered y the LR% 6he LRdataase will therefore contain some duplicate data as well as more precise data relevant to thesuscrier remaining within the LR coverage%

6he additional data stored in the LR is listed elow

3oile status 'usy)free)no answer etc%+%

Location 2rea Identity 'L2I+%

6emporary 3oile Suscrier Identity '63SI+%

3oile Station Roaming 8umer '3SR8+%


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quipment /dentity &egister (/&)6he EIR contains a centrali"ed dataase for validating the International 3oileEquipment Identity 'I3EI+%

6he EIR dataase consists of lists of I3EIs 'or ranges of I3EIs+ organi"ed as follows:!ite 4ist

5ontains those I3EIs which are !nown to have een assigned to valid 3S equipment%lac$ 4ist5ontains I3EIs of 3S which have een reported stolen or which are to e deniedservice for some other reason%'rey 4ist5ontains I3EIs of 3S which have prolems 'for example, faulty software+%

,ut!entication Centre (,C)

6he 2


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3perations and Maintenance Centre (3MC)

6he 135 provides a central point from which to control and monitor the other networ! entities 'i%e% asestations, switches, dataase, etc+ as well as monitor the quality of service eing provided y the networ!%

6here are two types of 135 these are3MC (&)135 controls specifically the 0ase Station System%3MC (S)135 controls specifically the 8etwor! Switching System%


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'SM #etwor$ Components


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Modulation "ec!niques

6here are three methods of modulating a signal so that it may e transmitted over the air,mplitude Modulation (,M)

2mplitude 3odulation is very simple to implement for analogue signals ut it is prone to noise%%requencyModulation(%M)

Frequency 3odulation is more complicated to implement ut provides a etter tolerance to noise%P!ase Modulation (PM)&hase 3odulation provides the est tolerance to noise ut it is very complex to implement for analoguesignals and therefore is rarely used%

P!ase S!ift 5eying (PS5)&hase modulation provides a high degree of noise tolerance% However, there is a prolem with this formof modulation% (hen the signal changes phase aruptly, high frequency components are produced, thusa wide andwidth would e required for transmission%$S3 has to e as efficient as possile with the availale andwidth% 6herefore, it is not this technique, uta more efficient development of phase modulation that is actually used y the $S3 air interface, it iscalled $aussian 3inimum Shift Deying '$3SD+%'aussian Minimum S!ift 5eying ('MS5)

(ith $3SD, the phase change which represents the change from a digital J=4 or a J#4 does not occurinstantaneously as it does with 0inary &hase Shift Deying '0&SD+%Instead it occurs over a period of time and therefore the addition of high frequency components to thespectrum is reduced%(ith $3SD, first the digital signal is filtered through a $aussian filter% 6his filter causes distortion to thesignal, the corners are rounded off% 6his distorted signal is then used to phase shift the carrier signal%6he phase change therefore is no longer instantaneous ut spread out%


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'SM control c!annel groups

CCH 'roup6he 0roadcast 5ontrol 5hannels are downlin! only '0SS to 3S+

CCCH 'roup

6he 5ommon 5ontrol 5hannel $roup wor!s in oth uplin! and downlin! directions%

+CCH 'roup;edicated 5ontrol 5hannels are assigned to a single 3S for call setup and suscrier validation%

roadcast Control C!annel (CCH)6he 0roadcast 5ontrol 5hannel is transmitted y the 06S at all times% 6he RF carrier used to transmitthe 055H is referred to as the 055H carrier% 6he information carried on the 055H is monitored y the3S periodically 'at least every # secs+, when it is switched on and not in a call%

0roadcast 5ontrol 5hannel '055H+ 5arries the following information 'this is only a

partial list+ 4ocation ,rea /dentity (4,/);

4ist of neig!oring cells w!ic! s!ould e monitored y t!e MS;

4ist of frequencies used in t!e cell;

Cell identity;

Power control indicator;

+"7 permitted;

,ccess control (for example< emergency calls< call arring);

CCH description;

%requency Correction C!annel (%CCH)6his is transmitted frequently on the 055H timeslot and allows the moile to

synchroni"e its own frequency to that of the transmitting ase site%

Sync!roni-ation C!annel (SCH)6he S5H carries the information to enale the 3S to synchroni"e to the 6;32 frame structure and !nowthe timing of the individual timeslots% 6he following parameters are sent

Frame numer% 0ase Site Identity 5ode '0SI5+%6he 3S will monitor 055H information from surrounding cells and store the information from the est sixcells% 6he S5H information on these cells is also stored so that the 3S may quic!ly resynchroni"e whenit enters a new cell%

Common Control C!annels (CCCH)

6he 5ommon 5ontrol 5hannel '555H+ is responsile for transferring control information etween allmoiles and the 06S% 6his is necessary for the implementation of 9call origination: and 9call paging:functions%It consists of the following&andom ,ccess C!annel (&,CH)


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GSM by SherGill

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