Advanced RF Self-Interference Canceller for Full-Duplex Radio : Prototype Implementation and Measurement

Abstract

Current wireless communication systems use frequency-domain duplexing (FDD) or time-domain duplexing (TDD) to separate transmission and reception in frequency or time domain. With these duplexing methods the interference from own transmission called self-interference (SI) can be avoided with filtering in FDD or time separtion in TDD. In so-called in-band full-duplex (IBFD), transmission and reception are done simultaneously in the same freqeuncy. The issue is now that the SI cannot be avoided with a simple filter. If the SI could be suppressed to the receiver noise floor, then the IBFD operation would be possible. To solve this issue, an analog RF canceller is designed to cancel the SI. Cancelling all SI with RF-cancellation is not currently possible so the SI is first suppressed with a circulator isolation and then in the post-processing with a digital canceller. With combination of these three mehtods, it is shown that the SI can be supressed below receiver noise floor. The IBFD can in theory double the spectral efficiency. Any changes in the surroudings of the RF-canceller and the antenna changes the SI-channel.The RF-canceller is controlled with digital control system that is implemented on a field-programmable gate array (FPGA). This allows the RF-canceller to suppress the SI even if there are moving objects in the surroundings. Performance of designed and built RF-canceller is then verified with multiple measurements, testing the operation in different enviroments with different waveforms, bandwidths and transmission powers. This thesis shows that it is possible to have in-band full-duplex operation and using analog RF canceller is an essential ingredient in such systems. The canceller can provide, in mostscenarios over 40 dB cancellation with bandwidths up to 80 MHz. It is also shown that the canceller can support transmission powers up to 30 dBm. The RF-canceller was successfully utilized in the context of orthogonal frequency-division multiplexing (OFDM) radar. This joint operation of communication and radar is part of RF convergence. The IBFD has also military applications as it allows simultaneous jamming and reception.