Hybrid ARQ and adaptive modulation and coding schemes for high speed downlink packet access

A major evolution of the UMTS standard is the so-called high speed downlink packet access (HSDPA) mode, which provides peak data rates of 10.8 Mbps. Key enabling technologies include fast scheduling, adaptive modulation and coding (AMC), as well as hybrid automatic repeat request (HARQ). The paper gives a general overview of the current HSDPA standard. Special focus is put on the implementation and performance of the AMC and HARQ functions, as well as on their interworking. The performance of different HARQ schemes are compared for QPSK and 16-QAM and varying code rates. Subsequently, link-level throughput is simulated. It is shown that the throughput gains offered by advanced HARQ schemes depend on the performance of the AMC function. In particular, the gain offered by incremental redundancy techniques increases with increasing errors in selecting the appropriate modulation and code rate.