SBFD Ultra-Low HARQ Latency

Technical Explanation

In traditional TDD with a 4:1 DL:UL ratio, a UE receiving a downlink packet may have to wait 3 to 4 milliseconds for the next uplink slot to transmit its HARQ ACK/NACK. SBFD provides continuous uplink transmission opportunities on the UL subband, allowing UEs to send HARQ feedback in the very next symbol, reducing round-trip latency from 4 ms down to under 1 ms.

Key Functions

• Eliminates TDD slot waiting times for downlink packet acknowledgment
• Enables sub-1 ms round-trip layer-1 retransmission cycles in TDD spectrum
• Critical for mission-critical industrial robotics, cloud gaming, and XR streams
• Maintains high TCP throughput by eliminating ACK serialization delays