We consider single cell multi-user OFDMA downlink resource allocation on aflat-fading channel such that average supply power is minimized whilefulfilling a set of target rates. Available degrees of freedom are transmissionpower and duration. This paper extends our previous work on power optimalresource allocation in the mobile downlink by detailing the optimal powercontrol strategy investigation and extracting fundamental characteristics ofpower optimal operation in cellular downlink. We find that only a system wideallocation of transmit powers is optimal rather than on link level. Theallocation strategy that minimizes overall power consumption requires thetransmission power on all links to be increased if only one link degrades.Furthermore, we show that for mobile stations with equal channels but differentrate requirements, it is power optimal to assign equal transmit powers withproportional transmit durations. To relate the effectiveness of power controlto live operation, we take the power model into consideration which mapstransmit power to supply power. We show that due to the affine mapping, thesolution is independent of the power model. However, the effectiveness of powercontrol measures is completely dependent on the underlying hardware and theload dependence factor of a base station (instead of absolute consumptionvalues). Finally, we conclude that power control measures in base stations aremost relevant in macro stations which have load dependence factor of more than50%.
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