Scheduling — Who gets the grid, this slot
Procedures over time
Where it sits
What it is
What it is. Deciding, every slot, which devices get which resources. The one thing 3GPP deliberately does not specify.
What is specified is the vocabulary: what a grant looks like (PDSCH §8), where a device must look for one (search space), how it acknowledges (PUCCH), and how the device prioritises among its own logical channels (TS 38.321 clause 5.4).
What is not specified is the policy — which device to serve when several are waiting. Round robin, proportional fair, delay-sensitive, or anything else. That is where vendors compete, and leaving it open is deliberate.
Three flavours of allocation exist:
- Dynamic — a DCI per transmission. Maximum flexibility, one PDCCH each time.
- Semi-persistent scheduling (SPS) — an allocation activated once by a DCI with CS-RNTI, then recurring on a period without further control. For predictable traffic, chiefly voice.
- Configured grants — the uplink counterpart.
SPS is control overhead traded against flexibility. A voice packet every 20 ms does not need a fresh grant each time, and the PDCCH it would consume is a scarce resource (aggregation levels). The cost is that the allocation cannot follow the channel.
Read on
This concept was first written up in ref-system, which reads the whole group as one argument.
Before this concept, the hierarchy says to learn the following — the full chain, in order: