Mixed-Signal Based Enhanced Widely Linear Cancellation of Modulated Spur Interference in LTE-CA Transceivers

The implementation of carrier aggregation (CA) in cellular handsets leads to the generation of several unwanted spurs in the radio frequency (RF) transceiver chip. In frequency division duplex (FDD) mode this may lead to the down-conversion of the transmit (TX) leakage signal in one of the receivers creating a so-called modulated spur interference. Such interference can severely degrade the receive (RX) performance when the handset is operating in a cell edge scenario. A recently proposed mixed signal cancellation technique suggests to sense the TX leakage signal using an auxiliary receiver. When IQ-imbalance is present in the auxiliary path, the obtained reference signal, which serves as input for the digital modulated spur cancellation, is contaminated by its sectral image component. This limits the cancellation performance of a classical widely linear architecture targeting the cancellation of the main and image modulated spur. In this paper, we propose an enhanced widely linear cancellation architecture, which significantly improves the cancellation performance by digitally suppressing the image component in the reference signal. The performance of the cancellation architecture is verified by means of system simulations.