1. Mini-Slot Scheduling Mini-Slot transmission in the downlink path mainly involves PDSCH (Physical Downlink Shared Channel) that carries user data. By scheduling Mini-Slot, the system can quickly transmit data to reduce latency.
2. Scheduling Principle Mini-Slot can be scheduled at any time in a time slot, that is, once the gNB (5G base station) is ready, it will use 2, 4 or 7 OFDM symbols to send data immediately (depending on the data size and required latency). The terminal (UE) side will pay close attention to the specific search area to find the Mini-Slot allocation and decode the data as needed.
In the figure above: the PDSCH on the left is presented in the form of 2 OFDM symbol Mini-Slot in time slot #n. The PDSCH on the right is presented in the form of 4 OFDM symbol Mini-Slot in time slot #1; this highlights how 5G (NR) can adapt to time-sensitive traffic through flexible scheduling.
3. Parameter Sets and Mini-Slot Transmission Mini-Slot operation is closely related to the 5G (NR) parameter set, which defines the subcarrier spacing (SCS) and mini-slot duration. A larger subcarrier spacing reduces the mini-slot duration, further reducing latency. The relationship between these two parameters is as follows:
As shown in the figure above, the capacity of all subcarrier spacings in the frame, subframe, and slot structures of different parameter sets, measured in bits per Hz, is the same. As the parameter set increases, the subcarrier spacing increases, but the number of symbols per unit time also increases. The figure above only illustrates the cases of 15kHz and 30kHz subcarrier spacing, where the number of subcarriers is halved, but the number of slots per symbol per unit time doubles.
The relationship between a typical mini-slot and its duration (2 OFDM symbols) is as follows:
μ = 0/15kHz/1ms to 0.14ms
μ = 1/30kHz/0.5ms to 0.07ms
μ = 2/60kHz/0.25ms to 0.035ms
μ = 3/120kHz/0.125ms to 0.018ms
The above equations illustrate how a larger subcarrier spacing (SCS) and shorter slots work together with mini-slot transmission to help achieve the ultra-low latency goals of 5G (NR).
