Type-II hybrid ARQ protocol and its applications in slotted Aloha DS-CDMA

In spread spectrum communication systems where the channel state temporarily changes, it is preferable to change error-correcting capability in the hybrid ARQ scheme according to the channel state. The type-II hybrid ARQ (ARQ-II) protocol in the slotted CDMA network is analyzed. The performance of ARQ-II in slotted DS-CDMA is obtained using a simplified Gaussian approximation. Comparisons of type-I hybrid ARQ (ARQ-I) and ARQ-II in slotted Aloha DS-CDMA (SSA) are performed and results are given. It is shown that ARQ-II can be regarded as a multirate strategy that performs an information rate adaptation at the DLC (data link control) layer.