Performance of hybrid ARQ techniques for WCDMA high data rates

Hybrid ARQ is being considered as a potential method for improving the performance of WCDMA in UMTS. We compare different hybrid ARQ techniques, namely the incremental redundancy type II hybrid ARQ schemes and type I hybrid ARQ schemes with and without soft combining. The emphasis is at high data rates and downlink shared channel (DSCH). Both link and system simulations are used for comparison. The hybrid ARQ schemes are shown to achieve higher throughput and capacity than the conventional ARQ schemes currently specified in the 3GPP WCDMA standard. Also, the combining of packets can cut the tail of the delay distribution which reduces the required maximum number of transmissions. However, the complexity increase due to physical layer buffering in the mobile station is too high if the round trip delay is large.