Optimizing the Target Error Rate for Link Adaptation

Wireless link adaptation configures the physical layer of the transmitter in the presence of dynamic channel conditions to maximize link performance under error rate reliability constraints. Typically, error rate reliability targets are defined externally and remain fixed, regardless of the physical layer configuration. In this paper, we allow link adaptation to define its own error rate reliability target. We derive a closed form expression for the optimal target block error rate (BLER) that maximizes the throughput with hybrid automatic repeat request (HARQ). This expression shows that the optimal BLER target is inversely proportional to the SINR. We conduct LTE simulations with link adaptation that exploits the optimal BLER target to reinforce the utility of our derived BLER target expression and to showcase that a performance improvements of up to 30% in throughput can be obtained through dynamic BLER targets for link adaptation.