Applications
HARQ is used in HSDPA and HSUPA which provide high speed data transmission (on downlink and uplink, respectively) for mobile phone networks such as UMTS, and in the IEEE 802.16-2005 standard for mobile broadband wireless access, also known as "mobile WiMAX". It has also been used in 3GPP Long Term Evolution (LTE).
Type I Hybrid ARQ is used in ITU-T G.hn, a high-speed Local area network standard that can operate at data rates up to 1 Gbit/s over existing home wiring (power lines, phone lines and coaxial cables). G.hn uses CRC-32C for Error Detection, LDPC for Forward Error Correction and Selective Repeat for ARQ.
HARQ is generally implemented in hardware, rather than in software.
Read more about this topic: Hybrid Automatic Repeat Request