Crest factor reduction and digital pre-distortion for wireless RF power amplifier optimization

Higher-order modulation schemes such as orthogonal frequency division multiplexing (OFDM) employed by some current and virtually all next-generation wireless systems demand the highest possible transmitter linearity and power-added efficiency (PAE). This requirement extends from RF power transistors to the power amplifiers (PAs) in which they are employed. As a result, PA designers must find ways to effectively balance the need to achieve the highest PAE with ensuring the resulting RF output signal does not interfere with neighboring signals through spectral re-growth. Techniques including digital pre-distortion and crest factor reduction have been developed to achieve maximum efficiency and dynamic range while minimizing spectral re-growth through high adjacent-channel leakage power (ACLR). This paper describes both techniques, illustrates how the benefits achievable with each one can be effectively determined during the early stages of design, and shows the level of potential improvement using a multi-carrier 3GPP WCDMA HSDPA signal as an example.