hybrid automatic repeat request (HARQ)

Hybrid Automatic Repeat Request (HARQ) is used with High Speed Downlink Packet Access(HSDPA) and with Mobile WiMAX to increase efficiency.

HARQ technology is used for error-free transmission of data packets and can request faulty data packets again. In this process, the data packet detected as erroneous is stored and after retransmission it is decoded and viewed in conjunction with the previously received packet copies.

HARQ operates in a stop-and-wait mechanism based on acknowledgements( CONF) and negative acknowledgements( NAK), where the receiving station communicates with the transmitting station through a channel. In the case of High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access( HSUPA), it is the E-HICH channel over which the sending station communicates with the receiving station.

To increase the round trip time( RTT), the repeated transmission of data packets takes place on the physical layer.