HARQ process in 5G NR

Hybrid ARQ Fundamentals

HARQ combines forward error correction with automatic retransmission to maximize decoding success while minimizing wasted air-interface resources. When the receiver attempts to decode a transport block and fails, it sends a NACK and retains the corrupted soft bits in a buffer rather than discarding them. The transmitter then retransmits the same data using a different redundancy version, and the receiver combines the original reception with the retransmission through soft combining. This merged data has significantly better decoding probability than either individual reception because the…