What Is 5G NR Mini-Slot | Function Of Mini-Slot In 5G NR

 

What Is 5G NR Mini-Slot | Function Of Mini-Slot In 5G NR

This page mentions 5G NR Mini-slot basics including function of Mini-slot. The difference between slot and mini-slot in 5G NR is also mentioned.

Introduction:
As shown in the figure-1, a frame in 5G NR consists of 10 ms duration. A frame consists of 10 subframes with each having 1ms duration similar to LTE. Each subframe consists of 2μ slots. Each slot can have either 14 (normal CP) or 12 (extended CP) OFDM symbols.

Slot is typical unit for transmission used by scheduling mechanism. NR allows transmission to start at any OFDM symbol and to last only as many symbols as required for communication. This is known as "mini-slot" transmission. This facilitates very low latency for critical data communication as well as minimizes interference to other RF links. Mini-slot helps to achieve lower latency in 5G NR architecture. Table below mentions typical fixed slots used in a 5G NR frame structure.

Μ, (Subcarrier Spacing)	Slots/Slot	Slots/Subframe	Slots/Frame	Slot Duration
0 (15 KHz)	14	1	10	1 ms
1 (30 KHz)	14	2	20	500 µs
2 (60 KHz), normal CP	14	4	40	250 µs
2 (60 KHz), Extended CP	12	4	40	250 µs
3 (120 KHz)	14	8	80	125 µs
4 (240 KHz)	14	16	160	62.5 µs

Unlike slot, mini-slots are not tied to the frame structure. It helps in puncturing the exising frame without waiting to be scheduled.

Difference Between Slot And Mini-Slot In 5G NR

➤As mentioned normal slot occupies either 14 (normal CP) or 12 (Extended CP) OFDM symbols. It enables slot based scheduling. One slot is the possible scheduling unit and slot aggregation is also allowed. Slot length scales with subcarrier spacing.
• Slot length = 1 ms/2μ,
➤Mini-slot occupies 2, 4 or 7 OFDM symbols. It enables non-slot based scheduling. It is minimum scheduling unit used in 5G NR. As mentioned mini-slots can occupy as little as 2 OFDM symbols and are variable in length. They can be positioned asynchronously with respect to the beginning of a standard slot.