Digital Control of RF Self-Interference Canceller in Full-Duplex Radio
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Itseishäiriön Kumoajan Digitaalinen Ohjaus
In traditional wireless communication systems, transmission and reception are divided in either time or frequency domain. In-band full-duplex means that the transmission and reception take place on the same frequency simultaneously, theoretically doubling the spectral efficiency. The most significant challenge in wireless full-duplex communication is the self-interference, which causes the systems own transmission signal to be coupled into the receiver. An analog canceller is designed to remove this self-interference from the reception signal. The cancellation takes place entirely in the RF domain. Any variation in the surroundings of the antenna also affect the self-interference. A control system is required to track these changes and adjust the canceller accordingly. This thesis presents a digital control system for the canceller. The control system is implemented using a field-programmable gate array (FPGA). The canceller and the control system were developed at Tampere University of Technology (TUT) in collaboration with Intel Labs. The project was concluded in January 2016, when the finished setup was delivered to Intel Labs. Using the digital control system, the canceller is capable of canceling up to 68 dB, 66 dB and 63 dB of the self-interference from the reception signal with 20 MHz, 40 MHz and 80 MHz signal bandwidths respectively. Roughly 20 dB of the cancellation originates from the intrinsic attenuation between the transmitter and the receiver. The control system is also capable of reacting and adapting to any changes in the self-interference quickly in order to maintain sufficient cancellation in a dynamic environment.