Optimization of E-DCH Channel Power Ratios to Maximize Link Level Efficiency

For the WCDMA/HSUPA concept, a key to ensuring high spectral efficiency is to correctly adjust the transmission power ratios among the data and control channels. This paper provides optimal values for the power ratio between the enhanced-dedicated physical data channel (E-DPDCH) and the dedicated physical control channel (DPCCH) from a Link Efficiency (LE) point of view. LE has been defined as the ratio between the average number of correctly received bits per second and the average total transmitted power. The optimization was carried out by testing different E-DPDCH to DPCCH power ratios in an HSUPA link level simulator for different bit rates. This simulator includes hybrid ARQ (HARQ) and optimal power ratios are extracted for different retransmission sequence number (RSN) targets. For vehicular-A 30 km/h conditions, the optimal power ratios per code show only minor dependency on the bit rate (typical values ranging from 8.1 to 9.9 dB) and the RSN target (maintaining or decreasing their value as the target increases). These results show that it is more link efficient to increase the DPCCH transmission power with the bit rate (and the E-DPDCH's by applying the power ratio) than to maintain a constant DPCCH transmission power and just increase the E-DPDCH to DPCCH power ratio.