Iterative Soft Multipath Interference Cancellation Assisted by Hybrid ARQ with Constellation Rearrangement for HSDPA System

High speed downlink packet access (HSDPA) is the major evolution of UMTS downlink. It provides peak data rates up to 10.8 Mbps. This is reached by radio link adaptivity, which includes fast scheduling, adaptive modulation and coding (AMC), and hybrid automatic repeat request (HARQ). The performance of AMC suffers from multipath interference introduced by the channel especially when using 16-QAM modulation. This is because of the variation in bit reliabilities caused by the bit-mapping onto the signal constellation. In this paper, we present a soft iterative multipath interference canceller (MPIC) for suppressing the multipath interference. We also propose to use HARQ Chase combining with the constellation rearrangement technique in joint application with MPIC. This can equalize the variation of bit reliabilities by using different mapping rules over HARQ transmissions. It is proven that the performance of adaptive modulation and coding is significantly improved after only two HARQ transmissions.