Until now, {HEAD ~ the transmission power} has been controlled exclusively by varying {TAIL ~ the gain} of the power amplifier 
controlled exclusively by varying
Until now , { HEAD ~ the transmission power } has been controlled exclusively by varying { TAIL ~ the gain } of the power amplifier
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH