What is Difference between ARQ and HARQ

ARQ (Automatic Repeat Request), which is used in UMTS, a package received in error will be discarded and a retransmission will be requested. If the retransmission is also erroneous, another retransmission will be requested.

Using HARQ, an erroneous package will be stored at the receiver and a retransmission will be requested. Even if the retransmission is faulty, the receiver attempts to combine the two erroneous packages to reproduce the original package.