Radio Resource Managmen.doc

8/13/2019 Radio Resource Managmen.doc

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Version 1 Revision 0 O & M of GSM (Alcatel)

6 RADIO RESOURCE MANAGEMENT

OVERVIEW

6.1 OBJECTIVES

This lesson describes the different Radio resource manaement as!ects"

After com!letion of this lesson the student is able to#

$escribe all the Radio resource manaement functions#

This lesson is a!!licable to GSM%00' GSM%100 and GSM%100" hen the term *GSM+ is

mentioned' it includes GSM%00' GSM%100 or GSM ,100" -nless the. are referred to as

se!arate s.stems e/!licitl."

6.2 OVERVIEW OF RADIO RESOURCES MANAGEMENTRadio Resource manaement is a rou! of functions concerned ith the manaement of

transmission resources on the radio !ath (-m interface)" t must co!e ith limited radio

resources (and the corres!ondin terrestrial resources) and share them d.namicall. beteen

all demands"

The role of the Radio Resources manaement is to#

2stablish stable connections beteen the mobile stations and the 3S4 (3ase Station

4ontroller)

Maintain them des!ite user movement for the duration of a call"

Release the connections beteen the mobile stations and the 3S4"

6.2.1 FUNCTIONS PERFORMED BY BSC AND MS

The mobile station and the 3S4 mainl. !erform the functions of the Radio Resource

manaement"

Radio resources Manaement 5unctions

The Radio Resource manaement functions are#

6oer 4ontrol

7andover

$iscontinuous transmission

4all re%establishment

5re8uenc. ho!!in"

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6.3 POWER CONTROL6oer control enables the mobile station and the mobile station and the 3TS ado!t transmit!oer accordin to the 3S4 6oer 4ontrol commands"

6.3.1 MEASUREMENTS

hile a mobile station is active on a call' it has the res!onsibilit. of !rovidin measurement

data about the !erformance of the air%interface to its servin 3TS so that the servin 3S4 can

decide if a !oer control should be !erformed" Also the servin 3TS measures the

!erformance of the air%interface" hereas the mobile station measures the !erformance of the

donlin=' the 3TS measures the !erformance of the u!lin="

6.3.2 DOWNLINK MEASUREMENTSThe mobile station measures and re!orts the folloin measurements to the 3S4 reardin

the 6erformance of the donlin="

Strenth of the sinal bein receivin from its servin 3TS (in d3m)

?ualit. of the sinal bein received from its servin 3TS (in bit error rate)"

6.3.3 UPLINK MEASUREMENTS

The 3TS measures and re!orts the folloin measurements to the 3S4 reardin the

!erformance of the u!lin=#

Strenth of the sinal bein received from the mobile station"

?ualit. of the sinal bein received from the mobile station"

6.3.4 PERIODICALLY MEASURING

The mobile station measures !eriodicall. the !erformance of the donlin=' and sends the

Measurements in the SA447 (Slo Associated 4ontrol 4hannel) via the servin 3TS to the

3S4 ever. SA447 multi%frame" This corres!onds to the transmission of data ever. 10@

T$MA frames or @0 ms" The base station measures the 8ualit. of the u!lin=" Also' it

transfers the measurements in the SA447 to the 3S4 ever. @0ms"

6.3.5 SIGNAL STRENGTH

hen the 3S4 notices that the sinal strenth of a !articular radio lin= measured on the

u!lin= becomes belo the loer !re%defined threshold because the mobile station movesaa. from the 3TS' it sends a 6oer 4ontrol 4ommand to the mobile station to increase its

transmits !oer (MSTB6R) b. a !re%defined ste! (t.!icall. : d3)" The transmit !oer of

the mobile station can be increased until a ma/imum defined level is reached"

The 3S4 can also send a 6oer 4ontrol command to the mobile station to reduce transmits

!oer hen it notices that the sinal strenth measured becomes above the u!!er !re%defined

threshold"

The donlin= 6oer 4ontrol !rocess is similar to the u!lin= 6oer 4ontrol !rocess"

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The folloin fiure shos the u!lin= 6oer 4ontrol !rocess"

F! " 1

6.3.6 SIGNAL STRENGTH AND SIGNAL #UALITY

n the descri!tion of 6oer 4ontrol iven u! to this !oint' the reason for 6oer 4ontrol

is that the u!lin=


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The folloin fiure shos the o!timum area in the u!lin= 6oer 4ontrol !rocess"

F! " 2

6.3.$ GSM FEATURE

6oer 4ontrol is a GSM feature that can be enabled or disabled on a !er cell basis" f !oer

4ontrol is disabled for the mobile stations' the mobile stations ill ala.s transmit at

ma/imum !oer level" The same is a!!licable for the 3TS# if 6oer 4ontrol is disabled for

the 3TS" t ill ala.s transmit at ma/imum !oer level"

6.3.% REASONS FOR POWER CONTROL

One reason to enable 6oer 4ontrol is to save mobile station batter. !oer" 7oever' the

main reason for 6oer 4ontrol is im!rovin the carrier%to%interference ratio ithin the

cellular netor=' reducin !oer on the 3TS or the mobile station' hile =ee!in similar

sinal 8ualit. received' and decrease interference caused on the other calls in the surroundin

area"

6.3.& HANDOVER

7andover is the !rocess of automaticall. sitchin a call in !roress from one traffic channel

to another to neutraliHe the adverse effects of user movements" The sitch can be made eitherto a T47 ithin the same cell or in another cell"

-suall.' handovers ta=e !lace on the T47' hen the call is in the s!eech stae" 7oever' in

rare cases it ma. be necessar. to !erform a handover hen' for e/am!le' the call is still in

build u! stae" n that case the S$447 ill be handed over to another fre8uenc. or time slot"

This t.!e of handover is more li=el. to ta=e !lace durin transmission of short messaes b.

the !oint%to%!oint Short Messae Service (SMS)

Cote that the handover !rocess ill normall. onl. be started if !oer control is not hel!ful

an.more"

The folloin fiure shos the handover !rocess"

3R3RATT' 9abal!ur' ssued in 9une%:00; @


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F! " 3

6.3.1' MEASUREMENTS

To decide if a handover should be !erformed' the 3S4 receives measurements data about the

!erformance of the air interface from its servin 3TSs and mobile stations" The 3S4 uses the

same measurements are those used in the !oer control !rocess"

6.3.11 DOWNLINK MEASUREMENTS

?ualit. of the sinal bein received from its servin 3TS (in bit error rate)

Sinal strenth of the I best neihborin 3TS donlin= control channels (candidate list)"

6.3.12 UPLINK MEASUREMENTS

The 3TS measures and re!orts the folloin measurements to the 3S4 reardin the

!erformance of the u!lin=#

Strenth of the sinal bein receivin from the mobile station'

?ualit. of the sinal bein received from the mobile station"

$istance beteen the servin 3TS and the mobile station (in meters)

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6.3.13HANDOVER PROCESS

As a mobile station moves aa. from its servin 3TS toards the coverae area of

neihborin 3TSs' the mobile station measurement re!orts ill sho a radual decrease in

sinal strenth from its servin 3TS hile shoin an increase in measured sinal strenth

from one or more neihborin 3TSs"t is the res!onsibilit. of the servin 3S4 to anal.He the measurement re!orts from the

mobile station and to decide hen a handover should be !erformed" f it is determined that

there is a better 3TS to serve the call' the servin 3S4 initiates the handover !rocedure"

6.3.14HANDOVER TYPES

The t.!es of handover !rocedure e/ecuted de!ends on hat level of sitchin must be

!erformed in order to move the call from the servin 3TS to the ne candidate 3TS"

There are basicall. four t.!es of handovers#

nternal or intra%3SS handover' hich can be#

ntra ,cell handover

nter%cell handover"

2/ternal or inter%3SS handover' hich can be#

ntra%MS4 handover"

nter%MS4 handover"

f the servin and candidate 3TSs reside ithin the same 3SS' the 3S4 for the 3SS can

!erform the handover ithout the involvement of the MS4 thus termed internal or intra 3SS

handover" This t.!e of handover can also be sub%divided into intra%cell and inter%cell

handovers" An intra%cell handover is an intra%3SS handover ithin the same 3TS" An inter%

cell handover is a handover beteen different 3TSs"

f the servin and candidate 3TSs do not reside ithin the same 3SS' then an inter%3SS

handover is !erformed' hich re8uires the MS4 to servin 3TS and the candidate 3TS" Thist.!e of handover can also be divided into intra%MS4 and inter%MS4 handovers"

6.3.15 E(AMPLES OF DIFFERENT HAND OVER TYPES

$ifferent t.!es of handover are e/!lained usin the e/am!les of a s.stem consistin of to

MS4s and three 3SSs" Also de!icted is cell coverae

Areas ith e/am!le 4ell Global dentification codes for each 3SS"

Assume that the mobile and land stations are active in a cell' the call is bein controlled b.

MS4 A' and the mobile station is currentl. in cell area :@%01%100%J1"

6.3.16INTRA)BSS INTRA CELL HANDOVER5or this t.!e of handover' the mobile station is handed over to a different radio channel

ithin the same cell area# :@%01%100%J1" This is actuall. an unusual t.!e of handover' since

it is not triered b. !oor sinal strenth (if it as' the candidate base station ould be

different from the servin base station)" A !robabl. cause for this t.!e of handover ould be

!oor sinal 8ualit. (not strenth)' !ossibl. due to co%channel interference" 5or this t.!e of

handover' 3S4: ould allocate a ne radio channel and instruct the mobile station to retune"

6.3.1$ INTRA)BSS* INTER ) CELL HANDOVER

The mobile station moves from area :@%01%100%J1 toards area :@%01%100%J:" At some

!oint in time' 3S4 : ill determine from the sinal strenth measurement re!orts that the

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base station res!onsible for cell area :@%01%100%J: can better serve the call" Since the

candidate base station is also connected to 3S4%:' the handover can be coordinated b. 3S4 :

ithout the involvement of MS4 A" in this situation' 3S4 : reserves an available radio

channel from cell area :@%01%100%J: and instructs the mobile station to retune to the ne

radio channel' 3S4 : is also res!onsible for sitchin the voice !ath beteen MS4 A andthe old radio channel to the ne radio channel"

The folloin fiure shos four t.!es of handovers"

F! " 4

6.3.1% INTER)BSS INTRA) MSC HANDOVER

The mobile station moves from area :@%01%100% J1 toards area :@%01%100%JJ" At some

!oint in time' 3S4 : ill determine from the sinal strenth measurement re!orts that the

base station res!onsible for cell are :@%01%100%JJ can better serve the call" 3S4 : ill then

determine that there are no base states connected to it that serves area :@%01%100%JJ and ill

re8uest MS4 A to arrane the handover to the candidate base station" MS4 A ill determine

that 3S4 is res!onsible for cell area :@%01%100%JJ and re8uest it to reserve a free radio

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channel for a handover" MS4 A ill rela. the ne radio channel information bac= to 3S4:"

3S4 : ill then as= the mobile to retune to the ne channel" At the same time' MS4 A ill

sitch voice !aths beteen the 6ublic Sitched Tele!hone Cetor= (6STC) and the old

3S4 (3S4 :) to the ne 3S4"

6.3.1& BSS* INTER)MSC HANDOVER

The mobile station moves from area :@%01%100%J1 toards area :@%01%0%:1" Similar to

!revious scenario' 3S4 : ill as= MS4 A to coordinate the handover to :@%01%0%:1"

MS4 A ill determine that it has no base stations under its control res!onsible for the

identified cell area" MS4 A then needs to determine hich neihborin MS4 is res!onsible

for the cell area' in this case MS4 3" and ill as= it to receive a handover"

6.3.2' MS UNAWARE OF HANDOVER

5rom the mobile stationFs reference !oint' it is unaare of the @ level of handover" The

mobile station has to handover related res!onsibilities !rovide !erformance measurements

to its servin base station and to retune to a ne radio channel hen ordered to do so"

6.3.21 INTER)PLMN HANDOVER

The GSM s!ecification does not describe the handover beteen cells of different 6KMS"

6.4 INTRA)BSS* INTER)CELL HANDOVER PHASESThe folloin fiure shos the lobal !hases in an intra%3SS' inter%cell handover"

F! " 5

6.4.1 SCENARIO

The handover scenario consists of#

" The MS is continuousl. listenin to the broadcast channel' measurin the strenth of

the currentl. used radio channel and the neihborin channels and re!ortin the resultto the 3SS"

" The 3S4 allocates a ne radio channel and instructs the MS to re%tune to it"

" The MS tunes to the ne radio channel' and sends a 7andover 4om!lete to the 3SS"

V" The 3SS informs the MS4 about the ne location of the MS"

The folloin fiure shos an intra%3SS' inter%cell handover

3R3RATT' 9abal!ur' ssued in 9une%:00;

MS 3SSMS4

Sinal StrenthMeasurements

SA447

5A447

7andover 4ommand

7andover 6erformed

5A447

7andover Access

5A447

7andover 4ommand


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F! " 6

6.4.2 INTER)BSS* INTRA)MSC HANDOVER PHASES"

The table belo lists the to staes in an inter%3SS' intra%MS4 handover"

S+,!- D-/0+

1 MS served by old BSS: the MS detects that there is a better 3SS

candidate and re8uests the MS4 (via the old 3SS) to be connected to

this 3SS" The MS4 then allocates resources to the ne 3SS"

: MS served by new BSS: the MS tunes to the ne 3SS and uses the

nel. allocated resources" The resources to the old 3SS are released"

The folloin fiure shos the !hases in an inter%3SS' intra%MS4 handover"

3R3RATT' 9abal!ur' ssued in 9une%:00;

b" Allocate ne resources

MSC

VLR A

a" Re8uest to handover

Old 3SS

MSC

VLR ACe 3SS

MS -0- 78 9 BSS"

MS -0- 78 -: BSS"

MS

MSC

VLR A

b" Release of old resources

Old 3SS

MSC

VLR ACe 3SS

a" 7and over e/ecution

MS

L Voice !ath L 4onnection


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F! " $

" The MS is continuousl. listenin to the broadcast channel' measurin the strenthof the currentl. used radio channel and the neihborin channels

" hen the old 3SS' currentl. su!!ortin the MS' determines that the MS re8uires to

be handed over it ill send a 7andover re8uired messae to the MS4 ith a list of

cells to hich the MS can be handed over"

" On receivin the 7andover re8uired messae' the MS4 beins the !rocess of

handin over the MS to the ne 3SS" The MS4 sends a 7andover Re8uest messae

to the selected 3SS (ne 3SS)



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V" The ne 3SS ta=es the necessar. actions to allo the MS to access the ne radio

resources and then sends the , ac=noledement (7andover Re8uest%A4 messae

to the MS4 containin the 7andover Reference Cumber (hrn))

V" The MS4 informs the old 3SS that the handover can ta=e !lace

V" The old 3SS sends a command to the MS to tune to the ne radio channel

V" The MS accesses the ne radio resource b. sendin the messae 7andover Access

containin the hrn" The hrn is chec=ed b. the ne 3SS to ensure it is as e/!ected

and the correct MS has been ca!tured"

V" f this is the correct MS the ne 3SS sends a handover $etect messae to the MS4

B" hen the MS is successfull. communicatin ith the ne 3SS it sends to it a

7andover 4om!lete messae"

B" The ne 3SS forards this messae to the MS4"

B" The MS is no served b. a ne 3SS' the trun= reserved for the communication

beteen the MS4 and the old 3SS can no be released"

B" 4onse8uentl. the radio traffic channel is released"

6.4.3 SCENARIO

The inter%3SS' intra%MS4 handover scenario consists of#

The folloin fiure shos an inter%3SS' intra%MS4 handover



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F! " %

3R3RATT' 9abal!ur' ssued in 9une%:00; 1:


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6.5 INTER)BSS* INTER)MSC HANDOVER PHASES

The fiure belo shos the !hases of an nter%3SS' nter%MS4 handover" MS served b. old

3SS' MS served b. ne 3SS"

F! " &


b" Allocate ne resources

MSC VLR A

a" Re8uest to handover

Old 3SS

MSC

VLR ACe 3SS

MS -0- 78 9 BSS"

MS -0- 78 -: BSS"

MS

MSC

VLR A

b" Release of old resources

Old 3SS

MSC

VLR ACe 3SS

a" 7and over e/ecution

MS

L Voice !ath L 4onnection


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T;-


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BV" f this is the correct MS 3SS%3 sends a 7andover $etect messae to the MS4%3

BV" hen the MS is successfull. communicatin ith the 3SS%3 it sends to it a handover

4om!lete messae

BV" The 3SS%3 forards this messae to the MS4%3

BV" 3. com!letion of the handover' MS4%3 informs MS4%A that the connection can be

ended

BV" MS4%A ac=nolede the recei!t of this messae

BB" The radio traffic channel used earlier b. the MS can be released

BB" The 3SS%A ac=noleded this messae to the MS4%A

BB" The trun= used for the communication beteen MS4%A and the 3SS to serve the MSis no loner needed and can be released" MS4%A informs MS4%3 that the old

resources used b. the MS are released"

BB" The netor= connection beteen MS4%A and MS4%3 is released

BB" The hrn that as used for the routin of the connection beteen MS4%A and MS4%3

is no more needed and can be de%allocated"

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The folloin fiure shos the nter%3SS' nter%MS4 7andover Scenario (1)"

F! " 1'

3R3RATT' 9abal!ur' ssued in 9une%:00; 1I

MS4 it is not an ambiuous identification of a base station"

Man. cells bear the same 3S4" The scheme of 3S4 values to be used is normall. laid don

in a bilateral areement beteen the concerned 6KMC o!erators to !revent that the same

3S4 is used in adNacent 6KMCs"

6.% DISCONTINUOUS TRANSMISSIOND-


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lo rate flo is sufficient to encode the bac=round noise' hich is re%enerated to ensure

that the listener does not thin= that the connection is bro=en (comfort noise)"

At the transmission side' the voice activit. detection function detects hether s!eech ill be

transmitted on a !articular radio lin= or not" hen it detects that no s!eech has to be

transmitted' transmission ill cease after a defined !eriod of time after s!eech activit. hassto!!ed"

The transmitter ill !eriodicall. send a sinal called a Silence ndicator 3loc= ever. certain

!eriod of time" The Silence ndicator 3loc= !rovides the comfort noise level information to

the mobile station or 3TS"

6.%.2 REASONS FOR DT(

hen $TB is a!!lied' actual transmission on the radio !ath is reduced" This ill cause a

decrease of the interference level in co%channel cells (usin the same fre8uenc.)" Another

advantae ill a!!ear hen usin $TB in the u!lin= mode# it saves batter. !oer for the

mobile station" 7oever' a disadvantae of the $TB mode is that it slihtl. deteriorates the

8ualit. of transmission"

Cote that transmittin in $TB mode does not save timeslots on the air%interface"

6.& CALL RE)ESTABLISHMENTD-


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6.1'.1 FOR FRE#UENCY HOPPING

The reasons of usin 5re8uenc. 7o!!in are#

$ecreasin the !robabilit. of interference

5re8uenc. 7o!!in ill s!read the anno.ance of interference over different mobile

stations in a !articular cell"

Su!!ressin the effect of Ra.leih fadin

Ra.leih fadin (or multi!ath fadin) is caused b.%different !aths folloed b. the radio

sinal" Ra.leih fadin can cause coverae holes"

Ra.leih fadin is location and fre8uenc. de!endent" hen the mobile station is stationar. or

moves at a slo s!eed" 5re8uenc. 7o!!in ill sinificantl. im!rove the level of the air%

interface !erformance" 7oever' hen the mobile station moves at a hih s!eed" 5re8uenc.

7o!!in does not harm' but does not hel! much either" The more fre8uencies are used in a

!articular cell' the more 5re8uenc. 7o!!in can ain in su!!ressin the effect of Ra.leihfadin"

6.1'.2 FRE#UENCY HOPPING PROCESS

The reular !attern' b. hich a radio lin= chanes carrier fre8uenc.' is described b. the

ho!!in se8uence" The ho!!in se8uence can have a c.clic !attern or a !seudo%random

!attern"

5olloin fiure shos the 4.clical 5re8uenc. 7o!!in Scheme

F! " 13

n order to calculate the ho!!in se8uence' a function issued hich ma!s a !articular T$MA

frame to a radio fre8uenc. ithin the set of fre8uencies' usin !arameters such as T$MA

frame number and number of fre8uencies in the set of fre8uencies" 3oth the u!lin= and the

donlin= use the same ho!!in se8uence" 5or this !ur!ose the !arameters used to calculate

the ho!!in se8uences are also transferred from the 3TS to the mobile station"

There is an e/ce!tion for the fre8uenc. ho!!in se8uence" This e/ce!tion is a!!licable to

timeslots bearin the common channels (3447' 5447' S47' 6AG47 and RA47) in

timeslot number 0 of the loest radio fre8uenc." To reduce com!le/it. of the GSM s.stem'

the common channels do not ho! (the. are fi/ed)"

3R3RATT' 9abal!ur' ssued in 9une%:00; :1

Radio Resource Managmen.doc

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