Digital Suppression of Power Amplifier Spurious Emissions at Receiver Band in FDD Transceivers

As the duplexing distances in emerging wireless systems are getting more and more narrow, achieving sufficient isolation between transmit and receive chains using radio frequency (RF) filtering alone becomes increasingly complex. Particularly challenging problem in this context is the spectral regrowth of nonlinear power amplifiers (PAs) in the transmit chain, and other transmitter out-of-band (OOB) emissions, which can heavily desensitize the receiver chain. In this letter, we first carry out detailed modeling of transmitter OOB emissions due to practical wideband PAs with memory effects. Stemming from this modeling, and using the known digital transmit data inside the transceiver as reference, we then propose an efficient nonlinear digital cancellation technique to suppress the transmitter OOB emissions in the receiver path. The proposed technique is verified and analyzed using extensive computer simulations, rendering excellent suppression properties, hence enabling sufficient TX-RX isolation in frequency division duplexing (FDD) transceivers without any extra analog/RF filtering or PA linearization.