PUCCH (or PUSCH if there is UL traffic)
2. Scheduler at E-NodeB dynamically allocates resources to UE:
- UE reads PCFICH every subframe and finds out the number of OFDM symbols occupied by PDCCH
- UE finds about TX Mode and assigned resources (PRB and MCS) reading PDCCH
3. E-NodeB sends user data in PDSCH
4. UE attempts to decode the received packet and sends ACK/NACK using PUCCH (or PUSCH if there is UL traffic)
PDSCH Physical Downlink Shared Channel
PDCCH Physical Downlink Control Channel
PFICH Physical Format Indicator Channel
PUCCH Physical Uplink Control Channel
Basic Scheduler Operation:
- MAC in eNB includes a dynamic resource scheduler that allocate physical layer resources for the DL-SCH and UL-SCH transport channels
- Different schedulers operate on DL-SCH and UL-SCH
- The scheduler takes into account the traffic volume and the QoS requirements of each UE and associated radio bearers when sharing resources
between UEs
- DL Scheduler also assign resources taking into account the radio conditions as identified by the UE through reported measurements
- Radio resource allocations can be valid for one or multiple TTIs
- Resource assignment consists of physical resource blocks (PRB) and MCS
- Allocations for time periods longer than one TTI might also require additional information (allocation time, allocation repetition factor…).
- In the downlink, E-UTRAN can dynamically allocate resources (PRBs and MCS) to UEs at each TTI via the C-RNTI on L1/L2 control channel(s)
- A UE always monitors L1/L2 control channel(s) in order to find possible allocation when its downlink reception is enabled (activity governed by
DRX)
- In addition, E-UTRAN can allocate persistent downlink resources for the first HARQ transmissions to UEs. When required, retransmissions are
explicitly signalled via the L1/L2 control channel(s).
- In the sub-frames where the UE has persistent resource, if the UE cannot find its C-RNTI on the L1/L2 control channel(s), a downlink
transmission according to the persistent allocation that the UE has been assigned in the TTI is assumed.
- Otherwise, in the sub-frames where the UE has persistent resource, if the UE finds its C-RNTI on the L1/L2 control channel(s), the L1/L2 control
channel allocation overrides the persistent allocation for that TTI and the UE does not decode the persistent resources.