Priority-base retransmission scheduling for Automatic Repeat Request over wireless networks

When data is transmitted over error-prone channels, portions of data may be corrupted due to many reasons, including multipath fading, interference, signal attenuation, and shadowing. Even if there is only one bit uncorrectable, the data block or packet will be considered as invalid, and will be discarded. The Automatic Repeat reQuest (ARQ) is an important mechanism to recover lost packets transmitted over either unstable or congested networks. An ARQ mechanism is also implemented in the 4G wireless networks on the link layer, where a receiver can request its sender to retransmit invalid packets. However, retransmission requires additional bandwidth, and it can result in longer delay. For some applications, such as layered video streaming, the utility of each packet of a stream can be different. The QoS requirements of different flows can vary as well. In this paper, a priority-based scheduling method for retransmission is proposed for wireless channels with limited bandwidth resources. For intra-flow traffic, which can be treated as several link-layer flows, the priorities can be assigned to the flows using different QoS classes. A dynamic utility function is developed for the scheduling of invalid packets such that the overall utility can be improved. The amount of resources for retransmission is also regulated dynamically such that each flow can occupy reasonable bandwidth. The improved performance is verified with simulation results.