Envelope tracking
Envelope tracking means that, a envelope detector to adjust the bias of a linear PA, in order to prevent the PA from working in the shallow class A which is inefficient.........The key is always keeping the linearity param (IMR, ACPR...etc.) satisfied within your spec.
An alike way is named "Envelope Elimination & Restoration" (EER or Kahn method), the difference is the PA in EER is a nonlinear PA(switching PA)...driven by a phase-only signal and modulated by a envelope driver......
If the envelope and phase signal is already apart in baseband, another name of "polar method" is more usual. In recent years, many papers on GSM PA --> EDGE PA adopted this method.