5G(NR): Scheduling Request

 

5G(NR): Scheduling Request:

This Blog will explain about the NR scheduling request mechanism which is applicable between UE and gNodeB. 

The Scheduling Request is triggered when UE is in uplink sync with gNodeB and It is not having and up-link (PUSCH/PUCCH) resource allocated for transmission of  new user plane or control plane data. 

 

The Scheduling Request (SR) is used for requesting UL-SCH resources( up-link grant ) for new transmission on PUCCH channel. 

 

Network (gNodeB) replies the UE with uplink grant in DCI 0_0 or DCI 0_1 messages on PDCCH channel.  

 

 

Configuration:

 

RRC connection setup or RRC reconfiguration request are used to configure the scheduling request related parameters. 

 

 

-MAC is controling the SR and the IE MAC-CellGroupConfig is used to configure MAC parameters for a cell group.

 

MAC-CellGroupConfig ::= SEQUENCE {  

      drx-Config SetupRelease { DRX-Config } OPTIONAL, -- Need M 

      schedulingRequestConfig

       bsr-Config

       tag-Config     

       phr-Config

       skipUplinkTxDynamic BOOLEAN,  

... }

-The IE SchedulingRequestConfig is used to configure the parameters, for the dedicated scheduling request (SR) resources. 

 

SchedulingRequestConfig ::= SEQUENCE {

    schedulingRequestToAddModList       SEQUENCE

                                               SchedulingRequestToAddMod  OPTIONA,

    schedulingRequestToReleaseList      SEQUENCE

                                               SchedulingRequestId  OPTIONAL -- Need N

}

 

SchedulingRequestToAddMod ::= SEQUENCE {

    schedulingRequestId                 SchedulingRequestId,

    sr-ProhibitTimer                    ENUMERATED {ms1, ms2, ms4, ms8, ms16,

                                                    ms32, ms64, ms128}

    sr-TransMax                         ENUMERATED {n4, n8, n16, n32, n64,

                                                    spare3, spare2, spare1}

}

 

- The IE "SchedulingRequestId" is used to identify a Scheduling Request instance in the MAC layer.

 

 SchedulingRequestId ::= INTEGER (0..7)

 

 

Each SR configuration corresponds to one or more logical channels. Each logical channel may be mapped to zero or one SR configuration, which is configured by RRC. 

 RRC configures the following parameters for the scheduling request procedure:  

- sr-ProhibitTimer (per SR configuration);  

- sr-TransMax (per SR configuration).

 

 SR will NOT be transmitted if:

1. SR opportunity falls in measurement gap interval or
2. another SR-Prohibit timer is running or
3. DL PDCCH with UL resources is received.