[5G URLLC] Mini-Slot In 5GNR

(Source: https://medium.com/@jessica.chchuang)

Frame Structure In A Nutshell

1. Frame structure is a hierarchical structure to determine the transmission & receive of 5G data.
2. In general scenario:

• Minimum unit for data scheduling & resource allocation is — slot
• 1slot occupies 14OFDM symbols (normal cyclic prefix) & 12*OFDM symbols (extended cyclic prefix)
• slot-based scheduling is suitable for eMBB to a better spectrum efficiency

3. In low latency/unlicensed spectrum/mmWave band deployment scenario:

• Minimum unit for data scheduling & resource allocation can be — mini-slot (non-slot-based scheduling)
• 1mini-slot occupies 2, 4, or 7OFDM symbols
• Mini-slot based scheduling is suitable for URLLC for a shorter packet transmission duration.

Numbers

1frame = 2half-frame = 10*subframe

1slot = 14OFDM symbols (normal cyclic prefix)

1slot = 12OFDM symbols (extended cyclic prefix)

Slot/ per subframe:

• Subcarrier Spacing (SCS): 15 KHz >> 1*slot/ per subframe
• Subcarrier Spacing (SCS): 30 KHz >> 2*slot/ per subframe
• Subcarrier Spacing (SCS): 60 KHz >> 4*slot/ per subframe
• Subcarrier Spacing (SCS): 120 KHz >> 8*slot/ per subframe
• Subcarrier Spacing (SCS): 240 KHz >> 16*slot/ per subframe

1Resource Block (RB) = 12Subcarriers

Duration

1*frame duration = 10ms

1*subframe duration = 1ms

1*slot duration (normal cyclic prefix):

• Subcarrier Spacing (SCS): 15 KHz >> 1*slot duration = 1ms
• Subcarrier Spacing (SCS): 30 KHz >> 1*slot duration = 0.5ms
• Subcarrier Spacing (SCS): 60 KHz >> 1*slot duration = 0.25ms
• Subcarrier Spacing (SCS): 120 KHz >> 1*slot duration = 0.125ms
• Subcarrier Spacing (SCS): 240 KHz >> 1*slot duration = 0.0625ms

1*slot duration (extended cyclic prefix):

• Subcarrier Spacing (SCS): 60 KHz >> 1*slot duration = 0.25ms

Slot Format

The OFDM symbols in a slot format can be downlink symbols (D), uplink symbols (D), or flexible symbols (F or X).

• D: used for downlink transmission
• U: used for uplink transmission
• F: can be used for (1) uplink transmission & synchronization, or (2) downlink transmission & synchronization, or (3) guard period (GP), or (4). Reserved resource

(Source: 3GPP TS 38.213 V16.2.0)

Mini-Slot

Mini-slot is introduced in 5GNR in Release 15 as a minimum unit for data scheduling.

Mini-slot is used for the following scenario:

• Low latency for URLLC communications
• Unlicensed spectrum operating
• mmWave band deployment

Mini-slot is able to transmit data over a fraction of a slot (ie., data transmission is no need to start at a slot boundary), enabling faster data transmission & lower feedback latency time.

Mini-slot can occupy 2, or 4, or 7 OFDM symbols

In 3GPP TR 38.912, mini-slot with 1symbol is supported for Uplink at least above 6GHz, for downlink, and for URLLC scenario, at least 2Symbols are required.

[Reference]

TS 38.211

TS 38.213

TS 38.214

TR 38.912

5G Americas, Ultra-Reliable Low-Latency Communications

https://www.rfwireless-world.com/5G/5G-NR-Frame-Structure.html

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https://www.sharetechnote.com/html/5G/5G_MiniSlot.html