  Transceivers operating in frequency division duplex experience a transmitter
leakage (TxL) signal into the receiver due to the limited duplexer stop-band
isolation. This TxL signal in combination with the second-order nonlinearity of
the receive mixer may lead to a baseband (BB) second-order intermodulation
distortion (IMD2) with twice the transmit signal bandwidth. In direct
conversion receivers, this nonlinear IMD2 interference may cause a severe
signal-to-interference-plus-noise ratio degradation of the wanted receive
signal. This contribution presents a nonlinear Wiener model recursive
least-squares (RLS) type adaptive filter for the cancellation of the IMD2
interference in the digital BB. The included channel-select-, and DC-notch
filter at the output of the proposed adaptive filter ensure that the provided
IMD2 replica includes the receiver front-end filtering. A second, robust
version of the nonlinear RLS algorithm is derived which provides numerical
stability for highly correlated input signals which arise in e.g. LTE-A
intra-band multi-cluster transmission scenarios. The performance of the
proposed algorithms is evaluated by numerical simulations and by measurement
data.
