Transmit signal cancelation apparatus and methods

Apparatus and methods disclosed herein implement an RF receive-band filter at a receive chain input of a wireless base station with a co-located transmitter and receiver. The RF receive-band filter includes an adaptive filter component to perform filtering operations on samples of a digital baseband or intermediate frequency signal x(n) from a transmit chain associated with the wireless base station. An adaptive filter transfer function is determined in real time such that samples of the baseband transmit signal x(n) are transformed into a cancellation baseband signal z(n). The digital cancelation baseband signal z(n) is then digital-to-analog converted and the resulting analog baseband signal z(t) is up-converted to obtain a subtractive RF cancelation signal c(t). C(t) is summed with a desirable received signal RF component r(t) and an undesirable transmitter leakage RF signal component l(t) appearing at the input to the base station receiver. C(t) cancels l(t), leaving r(t) to be processed by the receiver section of the base station.