use envelope tracking. This is achieved by generating a 'tracking control voltage' to modify the supply voltage to the PA transistor. A DC-to-DC buck/boost converter is used both as a control function of the supply and to raise the voltage to greater than 5 V. Additionally, the PA drive is produced at very low output power levels in order to assist the tracking process through the area where the PA transfer function is extremely nonlinear. Using this technique ideally results in a relatively constant PAE over a widely varying PAPR. The control voltage function is reconstructed from digital baseband information and due to the PA device variation will require calibration at handset assembly stage. The assump- tion is that the improvement in efficiency will outweigh the inconvenience. Note that as stated earlier higher data rates require better control of transmit and receive linearity in or- der to avoid unacceptable EVM on the transmitted signal and/or demodulation errors in the receiver. Linearisation techniques have to work harder as operational bandwidth increases (see match- ing comments above), as channel bandwidth increases (from 3, 5, 10 to 20 MHz), as data rates increase and as distance from the cell site increases. After taking these factors into account the consensus is that Options 1 through 5 should all be realisable for market introduction by 2012/2014. Options 2 or 3 are the favoured options from two/three of the major RFPA vendors as this leverages existing R and D investment. The generally accepted principle is that component-count reduction, one of the objectives of options 2 through 6, is only commercially worthwhile if performance is at least as good as individually band optimised solutions (option 1). To be financially and commercially viable from an operator perspective, options 2 through 6 would have to have a similar or better RF performance than option 1 and would have to deliver additional differentiation on the basis of cost and/or component count reduction, real-estate occupancy and powe