SHARQ: Scheduled HARQ for Time- and Loss-Rate-Sensitive Networks

5G networks provide high reliability and low delay thanks to Hybrid Automatic Repeat reQuest (HARQ). However, HARQ does not provide predictability for either reliability or delay and residual losses -mostly due to feedback losses and the non-adaptivity of the redundency versions- need to be compensated by the upper layers. We explore the possibility of extending HARQ to the transport layer with a cross-layer implementation that obtains the requirements from the application layer and the channel state information from the lower layers. We propose Scheduled HARQ (SHARQ), a capacity-approaching scheme that uses a graph-based algorithm to find the best repair schedule in polynomial time, thereby approaching the channel capacity much better than unscheduled codes.