Mitigating the Electromagnetic Coupling Between the Tx and Rx Channels in Software-Defined Radio Through a Digital-Domain Cancellation Algorithm

Full-duplex communication receives a particular interest for a better use of the spectrum. Software-defined radio (SDR) is a key enabler for intelligent full-duplex operation as it provides a few reconfigurable transmitter (Tx) and receiver (Rx) channels. As demonstrated in this article, electromagnetic coupling between the Tx and Rx channels in commercial SDR devices cannot be overlooked as it can affect the quality of the received signal. To overcome this issue, this article presents a cancellation algorithm in digital domain. This method exploits the typical architecture of SDR devices and uses the known Tx signal for cancellation without any extra hardware. Details of the algorithm are discussed, including the generation of cancellation signals, amplitude control, orthogonal identification, and phase alignment. GNU-radio platform is used to implement the cancellation algorithm in a commercial SDR device (USRP B210). Experimental results reveal that the averaged cancellation level achieves 42 dB for single-tone signal, 35 dB for single sideband signal, and 20 dB for quadrature phase shift keying signal (with a date rate of 2 Mb/s) in the frequency range of 100-6000 MHz. This work provides a cost-efficient solution for solving the coupling issues between the Tx and Rx channels in SDR, which is critical for full-duplex communication systems.