Tuning algorithm for multi-tap signal cancellation circuit

A method for performing a self-interference signal cancellation in a full-duplex wireless communication system with a cancellation circuit having a plurality of parallel signal paths, each of the signal paths including a delay element and a variable attenuator, the method comprising:

• supplying a first sample of a transmit signal at a first frequency by a transmitter to the cancellation circuit;
• setting a first attenuation level to one or more of the variable attenuators;
• obtaining a first output signal of the cancellation circuit;
• setting a second attenuation level to the one or more of the variable attenuators;
• obtaining a second output signal of the cancellation circuit;
• generating a matrix based on the first and second output signals;
• receiving a signal at a receiver;
• and
• varying an attenuation level of each of the variable attenuators so that a product of the matrix and the attenuation levels of the variable attenuators is substantially equal to the received signal;
• wherein generating a matrix comprises iteratively performing the following steps:
• supplying a second sample of the transmit signal at a second frequency by the transmitter to the cancellation circuit;
• setting the first attenuation level to the one or more of the variable attenuators;
• obtaining a third output signal of the cancellation circuit;
• setting the second attenuation level to the one or more of the variable attenuators;
• obtaining a fourth output signal of the cancellation circuit;
• and
• expanding the matrix based on the third and fourth output signals.

A circuit comprising:

• a transmitter that transmits a transmit signal;
• a plurality of signal paths, each signal path including a delay element and a variable attenuator;
• wherein each signal path receives a portion of the transmit signal;
• a control unit that sets one or more signal paths to a first attenuation level and a second attenuation level;
• a combiner that generates an output signal by combining outputs of the plurality of signal paths;
• a circulator having a first port coupled to an antenna, a second port coupled to a transmit line of the circuit, and a third port coupled to a receive line of the circuit;
• and
• a receiver that receives a signal,
• wherein the circuit computes a matrix based on first and second output signals associated with the respective first and second attenuation levels, and
• wherein the control unit concurrently varies an attenuation level of each signal path so that a product of the matrix and the attenuation level of each signal path is substantially equal to the received signal;
• wherein the third port of the circulator is disconnected from the receiver while the circuit is computing the matrix;
• wherein the third port of the circulator is connected to the receiver while the control unit concurrently varies the attenuation level of each signal path to minimize the sum of the product and the received signal.