Achieving High Power Efficiency with Variable Envelope Signals

Future 6G wireless communication systems will require high spectral and energy efficiencies for both economic and environmental reasons. Current amplifiers can have very low amplification efficiency, especially when used with variable-envelope broadband signals like the OFDM-based schemes and single-carrier schemes with compact spectrum (both widely employed in broadband wireless land and satellite communications). In fact, the maximum amplification efficiency for quasi-linear amplifiers (like class-A amplifiers) is 50%. This value drops to 5-10% when high-PAPR signals are employed. By using strongly nonlinear, switched amplifiers (like class D or F amplifiers), we can increase the maximum theoretical amplification to 100%, but the strong nonlinear distortion levels preclude its use with variable-envelope signals.

In this presentation, we make an overview on block transmission techniques for broadband wireless communications, as well as current power amplification schemes, with their advantages and limitations when employed with variable-envelope signals. We also present an innovative and highly disruptive amplification scheme named quantized digital amplification (QDA), which can overcome those limitations. It is shown that the QDA allows a quasi-linear amplification of variable-envelope signals like OFDM ones, while maintaining very high energy efficiency, being able to fulfill the spectral masks and EVM (Error Vector Magnitude) requirements of the most demanding wireless systems, including OFDM-based MIMO systems employing large QAM constellations. The power efficiency gains of the QDA allow significant improvements in bit rates and coverage for wireless systems in general.