DSP-based suppression of spurious emissions at RX band in carrier aggregation FDD transceivers

Abstract

In frequency division duplex transceivers employing non-contiguous carrier aggregation (CA) transmission, achieving sufficient isolation between transmit and receive chains using radio frequency filtering alone is increasingly difficult. Particularly challenging problem in this context is spurious intermodulation (IM) components due to nonlinear power amplifier (PA), which may easily overlap the receiver band. With realistic duplex filters, the residual spurious IM at RX band can be several dBs stronger than the thermal noise floor, leading to own receiver desensitization. In this paper, we carry out detailed signal modeling of spurious emissions due to wideband PAs at the third-order IM band. Stemming from this modeling, and using the known transmit data, we present an efficient nonlinear digital identification and cancellation technique to suppress the unwanted IM components at RX band. The proposed technique is verified with computer simulations, showing excellent calibration properties, hence relaxing filtering and duplexing distance requirements in spectrally-agile CA transceivers.