Study of channel quality feedback in UMTS HSDPA

As UMTS enhancement function, high speed downlink packet access (HSDPA) was specified in 3GPP in year 2002. This enhanced system supplies higher packet data rate on the downlink. One of the key techniques supporting HSDPA is adaptive modulation and coding (AMC) that the modulation scheme and the coding rate for error correction are adaptively changed according to the radio channel condition. Therefore, the channel quality information dominates the accuracy of AMC and affects the system performance. In current 3GPP specification release 5, periodic channel quality feedback by the UE is defined. However, the coexistence of high throughput and low uplink interference is not easy. This paper proposes the additional feedback scheme in addition to current scheme to aim at the coexistence of such system performance. After the description of this proposal, the throughput performance on the downlink, the interference situation on the uplink and the error probability of the retransmission are shown. This proposal scheme has been proposed as further enhancement technique of HSDPA for specification release 6.