2G Radio Resource Allocation

8/13/2019 2G Radio Resource Allocation

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5.5 Radio Resource Allocation

This section describes the procedures enabling the assignment of radio resource to the mobileand in consequence the establishment of a TBF. These procedures correspond to the transitionfrom packet idle mode to packet transfer mode. The procedures used for the report ofmeasurements are also detailed.

As described in Chapter 3, two kinds of TBF can be established: plink TBF assigning uplink radio resource to the mobile with a downlink signaling channel! "ownlink TBF assigning downlink resources on shared #"C$s with an uplink signaling channel.Two simultaneous TBFs assigned to the same %& in opposite direction 'uplink and downlink( aresaid to be concurrent.

).).* plink TBF +stablishmentThe mobile triggers the establishment of an uplink TBF for three ma or reasons:

To perform an uplink data transfer! To answer a paging! To perform a -%% procedure 'e.g., A update procedure and -# & attach procedure(.

).).*.* AC$/# AC$ #hase

Access equest

The mobile triggers the establishment of an uplink TBF: B0 sending a C$A11+2 + +&T message on the AC$ when there is no #BCC$ in the cell! B0 sending a #AC4+T C$A11+2 + +&T message on the # AC$ if #BCC$ is present in the cell.

The mobile ma0 also request the establishment of an uplink TBF during a downlink TBF on#ACC$.

There are two codings for the #AC4+T C$A11+2 + +&T message. 5ne format allows thetransport of 6 bits information and the other one ** bits information. The C$A11+2 + +&Tmessage carries 6 bits of information.

The C$A11+2 + +&T message is used for both circuit7switched access and packet access. Thismessage contains 6 bits of information, allowing a limited number of uplink combinations. Assome of the combinations are reser8ed for -&% access, fewer combinations are a8ailable forpacket access.

5n # AC$, no circuit7switched access can occur. All the bit combinations of 6 or ** bits ofinformation within the access message are reser8ed for packet access onl0. Thus, access throughthe # AC$ allows the mobile to send more precise information on its capabilit0 and requirementsin order to establish as quickl0 as possible an uplink TBF.

Note On the RACH, the MS is unable to indicate its multislot capability in the CHANNELREQUEST messa e! "n o#de# to use its ma$imum capability, it %ill be necessa#y to establish a

T&' in t%o phases! The othe# possibility is to sta#t the uplin( t#ans)e# usin only one timeslot* once the mobile is identi)ied, the &SS can then #e+uest the mobile capabilities to theS SN and )inally e$tend the allocation %hen they %ill be #ecei-ed! E-en i) the multislotcapability o) the mobile is i-en to the net%o#( du#in the .RS attach p#ocedu#e, the &SSdoes not ha-e this in)o#mation %hen it #ecei-es the access #e+uest! This in)o#mation is onlya-ailable at the S SN side! The t%o/phase access p#ocedu#e is desc#ibed in the )ollo%insections!

As shown in Figure ).), the C$A11+2 + +&T and #AC4+T C$A11+2 + +&T messages arecomposed of two parts:

5ne establishment cause! 5ne random reference.


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Figure ).): Channel request and packetchannel request format.

The random reference length is from 9 to ) bits depending on the establishment cause.

The random reference reduces the probabilit0 that two %&s requiring the establishment of a TBFsend e actl0 the same message in the same AC$ or # AC$ occurrence. This could happen, butthe problem is sol8ed b0 the contention resolution procedure described later.

;hen the %& requests the establishment of an uplink TBF, it randoml0 chooses the few bits thatare sent within the random reference field of the access request message. ;hen the networkassigns the resources to the mobile it returns the request reference 'random reference,establishment cause, and F1 in which the AB was recei8ed( in order for the %& to correlate theassignment and the request.


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Access #ersistence Control on # AC$


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Figure ). : 5ne7phase access establishment scenario on CCC$.

The %& initiates this procedure b0 sending a C$A11+2 + +&T message on the AC$. The

C$A11+2 + +&T message contains the establishment cause and the random 8alue asdescribed in the pre8ious section. The establishment cause for this procedure is one7phaseaccess.

1ote that the network does not ha8e to respect the one7phase access request of the mobile andma0 force a two7phase access procedure.

pon reception of the C$A11+2 + +&T message, the B&& sends an


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1ote that the network ma0 request the sending of a #AC4+T C51T 52 AC415;2+"-%+1Tmessage in order to be sure that the mobile has recei8ed the uplink assignment and to a8oid theallocation of uplink resources that will not be used, particularl0 in case of d0namic allocation.

At the end of the assignment procedure, the mobile enters into contention resolution phase. Thisprocedure is described later in this chapter.

Two7#hase Access #rocedure on CCC$The mobile must initiate a two7phase access procedure when it wants to establish a TBF in 2Cunacknowledged mode. This procedure ma0 be requested in other cases not specified in the -&%standard 'e.g., if the mobile wants to establish an uplink TBF with multislot allocated on CCC$(.

1ote that when a two7phase access is requested b0 the mobile, the network must use thisprocedure to establish the uplink TBF.

Figure ).6 describes the scenario for two7phase access uplink establishment on CCC$.

Figure ).6: Two7phase access establishment scenario on CCC$.

The mobile initiates the two7phase access procedure b0 sending a C$A11+2 + +&T messageon AC$ requesting a single7block packet access. pon receipt of the C$A11+2 + +&Tmessage, the network sends an


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TLLI. This parameter uniquel0 identifies the mobile. Access t#pe. This indicates the reason for requesting the access 'in this e ample, two7phase

access(. Channel request description. This indicates the peak throughput class for the #"# conte t of the

22C #" , the radio priorit0, the 2C mode, the t0pe of the first 22C #" , and the number of 2Cdata octets of the requested TBF.

!$ radio access capabilit#. This indicates the mobile capabilities in terms of multislot class and

F power for the different frequenc0 bands that are supported b0 the mobile.;ith all this information, the network is able to allocate uplink resources in a more efficient wa0.The requested TBF properties are used b0 the network to select the multiple ing le8el matching."epending on the o& parameters, more or less bandwidth will be allocated to the mobile. Themobile that will share the same uplink #"C$s as other mobiles will ha8e more or less uplinkresources depending on these parameters. The radio access capabilit0 parameters are used totake ma imum ad8antage of the mobile capabilities. The allocated #"C$s can be in an0frequenc0 band that is supported b0 the mobile.

1ote that if the mobile indicates for the number of 2C data octets that ha8e to be transferred,the network interprets the TBF as an open7ended TBF.


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Figure ).I: 5ne7phase access establishment scenario on #CCC$.

1ote that despite the request of the mobile, the network can force a two7phase access procedurewhen a one7phase access is requested.

The #AC4+T C$A11+2 + +&T message contains either 6 or ** bits of information dependingon the ACC+&&>B &T>TG#+ parameter, which is broadcast on #BCC$. The establishment causeof the #AC4+T C$A11+2 + +&T message contains the multislot class of the mobile. %oreo8er,if the message is sent in the **7bit format, it also contains the radio priorit0 of the TBF. Thenetwork is then able to assign uplink resources matching the multislot capabilit0 of the mobile.

The radio priorit0 parameter, if a8ailable, can be used b0 the network to prioritiHe the request inrelation to others recei8ed from other mobiles. The network sends the #AC4+T #2


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Figure ).* : Two7phase access establishment scenario on #CCC$.

The %& requests the establishment of a TBF in two7phase access b0 sending a #AC4+T C$A11+2+ +&T message on # AC$. The establishment cause within the #AC4+T C$A11+2 + +&T

message indicates two7phase access.

1ote that the network must respect the request of the mobile.


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Figure ).**: #acket queuing notification procedure.

The mobile requests the establishment of a TBF b0 sending a #AC4+T C$A11+2 + +&Tmessage on # AC$. Because of congestion or other reasons, the network is unable to satisf0 therequest. A #AC4+T +


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the two7phase access procedure on CCC$.

;hen the network detects the channel request description within a #AC4+T "5;12


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).).*. Contention esolution #rocedure


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was recei8ed in the uplink 2C data block. At this time, the contention resolution is completed atnetwork side.


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TLLI. This indicates the identit0 of the mobile for which the message is intended. (o nlink TFI. This is the identifier of the downlink TBF. Po er control parameters. These indicate the downlink power control mode and the uplink power

control parameters. Packet channel description. This indicates the allocated T1, the T& code, and the frequenc0

parameters. RLC mode. This indicates whether the TBF is in 2C acknowledged mode or 2C unacknowledged

mode. TA parameters. These include the TA inde and the TA T1 if continuous TA is implemented b0 the

network. The initial TA ma0 not be present, as the network has no information on it e ceptperhaps from a pre8ious TBF.;ithin the


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).).9.9 "ownlink TBF +stablishment on #CCC$

Figure ).*6 describes an e ample of downlink TBF establishment on #CCC$ when the mobile is inpacket idle mode.

Figure ).*6: + ample of downlink TBF establishment on #CCC$.

;hen the network recei8es a downlink 22C #" to transmit to the mobile, it initiates theestablishment of a downlink TBF b0 sending a #AC4+T "5;12


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Figure ).*I: #acket downlink establishment on the #ACC$.

The B&& sends a #AC4+T T


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single uplink block to the mobile. The mobile sends a #AC4+T %+A& +%+1T +#5 T messagein this occurrence. The information that is pro8ided to the mobile in the assignment message isthe same as that in the first assignment message during the two7phase access on CCC$. Figure).9 describes the measurement report procedure on CCC$.

Figure ).9 : %easurement report procedure on CCC$ in packet idle mode.

).).3.9 %easurement eport #rocedure on #CCC$

5n #CCC$, the mobile initiates the measurement report procedure b0 sending a #AC4+TC$A11+2 + +&T message indicating Ksingle block without TBF establishmentK as theestablishment cause.

The B&& allocates one uplink block occurrence b0 sending a #AC4+T #2

2G Radio Resource Allocation

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