On self-interference cancellation in wireless full duplex

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Electrical and Electronics Engineering, Turkey

Approval Date: 2016




Full duplex is a newly promising duplexing method. Unlike traditional time division or frequency division duplexing, in full duplex the transmit and receive signals of a transceiver are active at the same time and in the same frequency band. This can double the spectral efficiency. However, since the transmit signal is typically much more powerful than the receive signal at the receive antenna, it acts as a strong interferer to the received signal and this interference must be mitigated first, in order to fully leverage full duplex. Until recently, because of the interference problem, the use of full duplex in data communications was generally avoided. Recently, however, as a result of demand for higher spectral efficiency e specially f or f uture g eneration c ellular a nd wireless communications, research advances are made in the mitigation of this interference which paved the way for achieving practical full duplex. In this thesis the following work has been done, 1) a survey of full duplex with its brief history and recent advances is presented, 2) critical presentation and analysis of selected methods of self-interference cancellation in analog and digital domains are made, 3) a selected adaptive filtering method is expanded, 4) selected methods’ and expansion’s performance are evaluated with simulations, 5) experiments are carried out using software defined radios. It was shown with experiments and simulations that, local oscillator phase noise constitutes a bottleneck for full duplex operation. In simulations, without phase noise, cancellation of self-interference up to the thermal noise floor is accomplished. However, in the presence of phase noise in experiments, also verified by simulations, the cancellation in digital domain hits a limit which prevents complete cancellation of self-interference after a certain power. This limitation impels the use of other means of self interference cancellation than digital, if one wishes to cancel out all self interference even at high powers.