Systems and methods for non-linear digital self-interference cancellation

1. A system for non-linear digital self-interference cancellation comprising:

a pre-processor communicatively coupled to a digital transmit signal of a communication system that generates a first pre-processed digital transmit signal from the digital transmit signal;

a non-linear transformer, comprising a first transform path and a second transform path, that transforms the first pre-processed digital transmit signal into a non-linear self-interference signal according to a transform configuration; wherein the first transform path has a model component of an order specified by a first positive integer and the second transform path has a model component of an order specified by a second positive integer; wherein the first transform path includes an upsampler that upsamples the first pre-processed digital transmit signal by a factor of the first positive integer to create an upsampled signal, a model component that generates a first non-linear self-interference signal component of an order specified by the first positive integer from the upsampled signal, a low-pass filter that removes undesired high frequency components from the first non-linear self-interference signal component, and a downsampler that downsamples the first non-linear self-interference signal component by a factor of the first positive integer;

a transform adaptor that sets the transform configuration of the non-linear transformer; and

a post-processor that combines the non-linear self-interference signal with a digital receive signal of the communication system.

2. The system of claim 1 , wherein the first pre-processed digital transmit signal is unmodified from the digital transmit signal.

3. The system of claim 1 , wherein the first positive integer is greater than one.

4. The system of claim 3 , wherein the second transform path includes an upsampler that upsamples the second pre-processed digital transmit signal by a factor of the second positive integer to create an upsampled signal, a model component that generates a second non-linear self-interference signal component of an order specified by the second positive integer from the upsampled signal, a low-pass filter that removes undesired high frequency components from the second non-linear self-interference signal component, and a downsampler that downsamples the second non-linear self-interference signal component by a factor of the second positive integer.

5. The system of claim 4 , wherein the non-linear transformer creates the non-linear self-interference signal from a weighted sum of the first and second non-linear self-interference signal components.

6. The system of claim 1 , further comprising a linear transformer that transforms a second preprocessed digital transmit signal into a linear self-interference signal according to a transform configuration.

7. The system of claim 6 , wherein the pre-processor splits the digital transmit signal into non-linear components and linear components, wherein the first pre-processed digital transmit signal is composed of the non-linear components and the second pre-processed digital transmit signal is composed of the linear components.

8. The system of claim 1 , wherein the non-linear transformer uses a generalized memory polynomial model.

9. The system of claim 8 , wherein the transform configuration comprises generalized memory polynomial coefficients and the generalized memory polynomial coefficients are adapted by the transform adaptor according to a gradient-descent optimization algorithm.

10. The system of claim 1 , further comprising a digital pre-distortion circuit that performs digital pre-distortion on the digital transmit signal and passes a pre-distorted digital transmit signal to a transmitter of the full-duplex wireless communication system, and an analog signal sampler that provides RF transmit signal samples to the system, wherein the RF transmit signal samples are used to adjust the digital pre-distortion circuit.

11. A method for non-linear digital self-interference cancellation comprising:

receiving a digital transmit signal of a communication system;

transforming the digital transmit signal into a non-linear self-interference signal according to a transform configuration; wherein transforming the digital transmit signal comprises generating a first non-linear self-interference signal component and a second non-linear self-interference signal component, and combining the first and second non-linear self-interference signal components to create the non-linear self-interference signal; and

combining the non-linear self-interference signal with a digital receive signal of the communication system;

wherein generating the first non-linear self-interference signal component comprises upsampling the digital transmit signal by a factor of a first integer, processing the digital transmit signal with a model component of an order specified by the first integer, filtering the digital transmit signal, and downsampling the digital transmit signal by a factor of the first integer; wherein generating the second non-linear self-interference signal component comprises upsampling the digital transmit signal by a factor of a second integer, processing the digital transmit signal with a model component of an order specified by the second integer, filtering the digital transmit signal, and downsampling the digital transmit signal by a factor of the second integer; wherein the first integer and the second integer are not equal.

12. The method of claim 11 , further comprising adapting the transform configuration dynamically based on the non-linear self-interference signal and the digital receive signal.

13. The method of claim 12 , wherein adapting the transform configuration comprises adapting the transform configuration according to a gradient descent algorithm.

14. The method of claim 11 , further comprising pre-processing the digital transmit signal into a linear digital transmit signal and a non-linear digital transmit signal, further comprising transforming the linear digital transmit signal into a linear self-interference signal, wherein transforming the digital transmit signal into a non-linear self-interference signal comprises transforming the non-linear digital transmit signal into a non-linear self-interference signal.

15. The method of claim 11 , further comprising digitally pre-distorting the digital transmit signal using a digital pre-distortion circuit.

16. The method of claim 15 , wherein the digital pre-distortion circuit is adapted according to samples of an RF transmit signal of the full-duplex wireless communication system.

17. The method of claim 11 , wherein generating the first non-linear self-interference signal component comprises upsampling the digital transmit signal by a factor of a first positive integer, processing the digital transmit signal with a model component of an order specified by the first positive integer, filtering the digital transmit signal, and downsampling the digital transmit signal by a factor of a second positive integer; wherein generating the second non-linear self-interference signal component comprises upsampling the digital transmit signal by a factor of a third positive integer, processing the digital transmit signal with a model component of an order specified by the third positive integer, filtering the digital transmit signal, and downsampling the digital transmit signal by a factor of a fourth positive integer; wherein at most two of the first, second, third, and fourth positive integers are equal.