LTE E-UTRA DL Scheduling Principles

Dynamic Scheduling: E-UTRAN dynamically allocates resources (PRBs and MCS) to UEs at each TTI via the C-RNTI on PDCCH(s)
• UE monitors the PDCCH(s) in order to find possible allocation when its downlink reception is enabled (activity governed by DRX when configured) Semi-persistent Scheduling: Initially PDCCH indicates if the DL grant can be implicitly reused in the following TTIs according to the periodicity defined by RRC
• RRC defines the periodicity of the semi-persistent DL grant
– Characterized by a start frame number, periodicity and packet format (one or more may be defined)
• Retransmissions are explicitly signalled via the PDCCH(s).

For persistent assignments
􀁺 In the sub-frames where the UE has semi-persistent downlink resource, if the UE cannot find
its C-RNTI on the PDCCH(s), a downlink transmission according to the semi-persistent
allocation that the UE has been assigned in the TTI is assumed.
􀁺 in the sub-frames where the UE has semi-persistent downlink resource, if the UE finds its CRNTI
on the PDCCH(s), the PDCCH allocation overrides the semi-persistent allocation for
that TTI and the UE does not decode the semi-persistent resources.