Self-Interference Cancellation for Full-Duplex Transceivers

In in-band full-duplex (FD) systems, the self-interference (SI) power can be more than 100 dB higher than the power of the received data signal. In order to enable FD transmissions, several SI cancellation stages are required in an FD transceiver. By combining the cancellation at the radio frequency (RF) with a specially designed antenna and cancellation circuitry, and SI cancellation at the digital baseband, the required level of SI cancellation can be achieved. In this thesis, an FD transceiver architecture is modelled with simulation tools that allow one to use realistic antenna and analog transceiver models and at the same time enable algorithm studies. The analog SI cancellation at the RF is controlled by the baseband digital processing unit, and the tuning of the RF canceller is performed with an automatic gain control enhanced iterative algorithm. When a power amplifier is the only non-linear component at the SI channel, the digital baseband SI cancellation is based on the Hammerstein model in order to take the power amplifier non-linearity into account. When realistic values for the phase noise and imbalance between the in-phase and quadrature branches of the transceiver (IQ imbalance) are taken into account, the SI after all the cancellation stages can decrease the signal-to-interference-and-noise-ratio. In order to further enhance the SI cancellation, the Hammerstein based SI canceller is extended to cancel also the effect of the receiver IQ imbalance. With the extended baseband canceller, the cancellation performance is mainly limited by the phase noise. When the non-linear operation of a low noise amplifier at the receiver is also considered, the SI channel is modelled with the Hammerstein-Wiener model. In this case, the best SI cancellation performance at the digital baseband processing is achieved with a neural network type SI canceller.