On optimal hybrid ARQ control schemes for HSDPA with 16QAM

We consider several hybrid ARQ (H-ARQ) control schemes for high speed downlink packet access (HSDPA) with 16 symbols quadrature amplitude modulation (16QAM). These schemes consist of a sequence of values for the X_rv parameter to be used at sequential retransmissions when a block is not decoded correctly. A choice of an H-ARQ control scheme influences two parameters: quality of service (QoS) and user equipment (UE) buffer requirements. Based on several link level simulations, we propose an optimal control scheme using maximum space, as well as two slightly suboptimal ones that allow to reduce the UE buffer size.