Photonics-Based Adaptive RF Self-Interference Cancellation and Frequency Downconversion

A photonics-based approach for simultaneous adaptive radio-frequency (RF) self-interference cancellation and frequency downconversion is proposed and demonstrated. By introducing photonic polarization-multiplexing, the reference signal and the self-interference signal are separated in the optical domain. Thus, the phase shift, the precise amplitude and the time delay adjustments can be achieved with the reference signal by using optical methods which are program controllable. An intelligent algorithm particle swarm optimization (PSO) algorithm is applied to optimize these parameters for adaptive operation. Meanwhile, the local oscillator (LO) signal is introduced to the two orthogonal polarization states to perform frequency downconversion. Therefore, simultaneous adaptive self-interference cancellation and downconversion are realized. A theoretical model is established for analyses. A proof-of-concept experiment is taken. The simultaneous adaptive self-interference cancellation and downconversion are achieved. The X-band RF signals are downconverted, and the self-interference cancellation depth of 31 dB over a 500-MHz bandwidth and 28 dB over a 1-GHz bandwidth are obtained. The RF signals in the Ku-band are downconverted, with the self-interference cancellation of 28 dB over a 500-MHz bandwidth and 26 dB over a 1-GHz bandwidth. A 16-QAM signal with a 10-Msym/s symbol rate is recovered from the self-interference signals with 500-MHz and 1-GHz bandwidths.