A study of adaptive transmission in HSDPA

The increasing usage of 3G CDMA systems has led to many developments aimed at improving the system efficiency. The HSDPA feature of the Wideband CDMA improves the system efficiency by sharing the base station resources among several users. It employs a common downlink channel having shorter sub-frames which can be allocated to users dynamically. This report presents a scheduling policy for a single user that changes the rate of transmission based on the SNR feedback received from the user about the channel conditions. A theoretical model for analysing the throughput achievable using the scheduling policy at the base station has been developed. The theoretical bounds of achievable throughput for the single-path and multi-path channels are computed. A comparison of the throughput obtained by employing the adaptive rate scheme and the fixed rate transmission is presented. The simulation results achieved using a RAKE receiver are compared with the theoretical estimates.