URLLC use cases can have very stringent latency requirements, as low as 5 ms for end-to-end latency.
Considering the different components of the end-to-end network, the budget for the air interface delay can be very limited (for example, 1 ms or even less).
To achieve such low latency, every step of the data delivery needs to be optimized.
The latency components in each step of a downlink (DL) data transmission and the corresponding mechanisms to reduce the latency as below:
The Key techniques in the PHY/MAC layer to reduce the latency:
• Frequent transmission opportunities that minimize waiting time.
• Flexible transmission duration (short duration for both data and control channel).
• Short UE processing time.
• Short next-generation NodeB (gNB) processing time.
• Grant-free (or configured grant) UL transmission.
• Flexible frame structure for Time Division Duplexing (TDD).
Source: 5G Americas