Rate Adaptation of AMC/HARQ Systems with CQI Errors

We study the rate adaptation of a combined system with Adaptive Modulation and Coding (AMC) and Hybrid ARQ (HARQ) in the presence of Channel Quality Indicator (CQI) errors. An average BLock Error Rate (BLER) is imposed to maintain a target error rate. We formulate a generic average throughput expression that accommodates the possible CQI errors. The generic expression is adapted to different forms according to practical scenarios. According to our results, CQI errors can significantly degrade the average throughput of a pure AMC system, especially for the CQI errors generated by user mobility. Surprisingly, we found that it is harder to recover the loss by using HARQ when the CQI errors are caused by channel estimation errors. For the CQI errors generated by user mobility, most of the loss is recovered with simply one retransmission.