Nick W. Whinnett

Power control of the high speed shared control channel

In High Speed Downlink Packet Access (HSDPA) system, the High Speed Shared Control Channel (HS-SCCH) carries downlink signalling information essential to the operations of the high-speed mobile broadband access system. In this paper, power control of the HS-SCCH is considered. Two algorithms - traditional power control and channel quality indicator (CQI) based power control are analyzed. The traditional power control algorithm couples the HS-SCCH transmit power to the power of the dedicated control channel and performs well when the mobile is not in soft-handoff. However, in soft-handoff HS-SCCH performance degrades significantly since power control decisions are now based on the received powers of all base stations in soft-handoff rather than just from the HSDPA serving base station. On the other hand, CQI-based power control decouples HS-SCCH power control from that of the dedicated control channel and thus is not affected by mobile handoff state. However, CQI reports are infrequent, and, as a result, performance suffers when the reporting frequency is inadequate in tracking the propagation channel. This is alleviated by using prediction to fill in gaps between CQI reports. Our simulation results show that performance of the CQI-based power control algorithm is comparable to the traditional algorithm when the mobile is not in soft-handoff, and significantly better than the traditional algorithm under soft-handoff.