A system and method for determining a downlink transmit power level for a downlink signaling channel such as the E-DCH HARQ Indicator Channel (E-HICH) in a cellular radio communication network, wherein the transmit power level is calculated to achieve a desired signaling message error rate. The base station determines a diversity order of an uplink control channel from a mobile station, and sets the downlink E-HICH transmit power based on the desired signaling message error rate and the diversity order of the uplink control channel. Optionally, the base station may first determine whether the cell transmitting the E-HICH is the serving cell for the High-Speed Downlink Shared Channel (HS-DSCH). If so, the base station determines the downlink transmit power level for the downlink signaling channel as an offset from the reported Channel Quality Indicator (CQI) value.