Adaptive control of link adaptation for high speed downlink packet access (HSDPA) in W-CDMA

In HSDPA, a set of modulation and coding schemes (MCS) are applied in downlink data transmission. These MCS schemes are adaptively selected in response to channel propagation conditions. During the selection process, adaptive threshold values at the switching points are needed so that the maximum channel capacity is utilized in terms of bits/s/Hz. It has been suggested (see NEC and Telecom Modus, 3GPP TSG RAN WG1, Technical Document R1-01-0589, 2001) to use SIR as well as ACK/NACK information of the HARQ scheme to control threshold values that decide modulation and coding schemes. We further develop this algorithm to provide more stable, and hence higher, throughput results. In cooperation with ACK/NACK information of the HARQ scheme, the threshold values are only updated when the downlink SIR falls close (i.e. ±α dB) to one of the current threshold values of the received MCS level, otherwise the threshold value remains at its current level. Simulation results show that the proposed algorithm provides a significant increase of throughput performance in different radio propagation conditions.