Scheduling Request -
It is used to request the uplink resources. Suppose there is UL data from upper layer and UE does not have any resources for UL data transmission. So there should be some mechanism to inform the eNodeB like i have some data so please assign some resources.
There are two ways to request resources from eNodeB -
1. Using Rach procedure.
2. Scheduling Request.
Scheduling request is fast as compare to RACH as RACH make use of common resources whereas SR procedure make use of dedicated resources.
eNodeB configure the UE for SR resources, it not always mandatory for eNodeB to configure the SR resources, so in case there is no SR resources then there is only one option for resource request i.e. Rach procedure.
SR request can only be sent if UE is uplink time aligned means "TimeAlignmentTimer" is running.
If there is UL data but TimeAlignmentTimer has been expired then UE make use of RACH procedure.
SR parameter configuration -
It is used to request the uplink resources. Suppose there is UL data from upper layer and UE does not have any resources for UL data transmission. So there should be some mechanism to inform the eNodeB like i have some data so please assign some resources.
There are two ways to request resources from eNodeB -
1. Using Rach procedure.
2. Scheduling Request.
Scheduling request is fast as compare to RACH as RACH make use of common resources whereas SR procedure make use of dedicated resources.
eNodeB configure the UE for SR resources, it not always mandatory for eNodeB to configure the SR resources, so in case there is no SR resources then there is only one option for resource request i.e. Rach procedure.
SR request can only be sent if UE is uplink time aligned means "TimeAlignmentTimer" is running.
If there is UL data but TimeAlignmentTimer has been expired then UE make use of RACH procedure.
SR parameter configuration -
Scheduling request is separate message or piggybacked in some other messages.?
ReplyDeleteSR request is a separate message, no piggybacked concept is used here. Basically MAC trigger the SR procedure and then PHY layer will send it over the PUCCH provided that PUCCH resource are available. It is not mandatory always that PUCCH resource are available.
ReplyDelete