# On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers
## 4 Conclusions  
FD has gained a great deal of attention with regard to next-generation wireless radio communication systems such as 5G. Recently, the attention of researchers in FD wireless radio communication systems has led to the study of SI cancellation techniques for co-located Tx and Rx pairs. For efficient and reliable FD systems, SI needs to be mitigated to a sufficiently low level, i.e., below the Rx sensitivity and noise floor both on the analog and the digital side. Even after applying RF/analog cancellation techniques, there is still residual SI signal. Digital SI cancellation techniques are applied to mitigate the residual SI signal. In this article, two SI cancellation techniques, a digital SI cancellation technique, and \begin{table}
\begin{tabular}{|c|c|c|c|c|} \hline \multicolumn{4}{|c|}{**Techniques**} & \multicolumn{2}{c|}{**Results**} \\ \hline
**Analog/RF SIC** & **Digital SIC** & **Linearization Techniques (LT)** & **Analog/RF SIC** & **Digital SIC** & **Papers** \\ \hline Assumed 15 dB & Orthogonalization of the & & & \\ circulator isolation & design matrix using QR & - & As low as 50 dB & [80] \\ with variable RF & decomposition & & & \\ cancellation & & & & \\ \hline Hybrid multi-stage & & Base-band digital & & \\ cancellation system, & cancellation & & & \\ cancellation setup at & i. LMS (Least Mean & - & Up to 80 dB of power interference & \\ RF frequencies & Square) & - & cancellation can be achieved with a & \\ following the so-called & ii. APA (Affine Projection & & full-duplex OFDM scheme & \\ Stanford architecture & Algorithm) methods & & & \\ \hline Nonlinear signal & & Iteratively estimation & & \\ reconstruction and & & of coefficients (IQ & & \\ cancellation with & & Imbalance, PA and & & \\ post-distortion, & - & LNA) using & Approximately 50 dB & [46] \\ least-squares method & & [PERSON]’s method \& discrete Fourier & \\ for channel estimation & & transform & & \\ \hline Antenna cancellation, & & - & & \\ self-reflector and & Develop custom Arduino & & & \\ develop custom & code for updating the & & 58 dB & 26 dB & \\ Arduino code for & weights in in-house chip & & & \\ updating the weights & using SPI & & & \\ \cline{2-2}  & & & Total of 84 dB & \\ \hline Assumed 30 dB and 40 & Extended Kalman Filter & & - & 40–45 dB & **Our previous work**[69] \\ dB antenna isolation & (EKF) & & & & \\ \hline i & & IQ mixer LT & & & \\  & & (BAFF \& BA) & & \\ i & CSI using LS and & & ii & PA LT (Doherty & \\  & MMSE & & + pre-distortion & ii & 75–85 dB & \\ ii & GALL Filter & & \& Feedforward) & iii & 75–85 dB & 40–45 dB & **PROPOSED** \\ iii & Kautz Filter & & iii & LNA LT (Negative \& Feedfor- & \\  & & & ward) & & \\ \hline  & & & i & 100–120 dB & \\  & i & CSI + KALMAN Filter + LT & ii & 115–130 dB & \\ Proposed model results. & ii & GALL Filter + KALMAN Filter + & iii & 115–130 dB & \\ (Assumed antenna isolation of 30 & & LT & & \\ dB \& 40 dB) & iii & Kautz Filter + KALMAN Filter + & & 45 dBm \\  & & LT & * If EKF (our own previous work) & \\  & & & is used for digital SIC, SIC of & \\  & & & & 115–130 dB. & \\ \hline \end{tabular}
\end{table} 
Table 4: _Cont._different techniques for reducing the nonlinearity are presented. System performance was evaluated based on SINR, the power of different components of SI signal, and link budget analysis. Through the CSI active cancellation technique employed in the LS estimator, the SI signal cancellation up to 70 dB was achieved. SINR obtained, in this case, is almost equal to the ideal, i.e., the one calculated at the Rx input. The Kautz and GALL filters are adaptive filters used to cancel the SI signal at the Rx side, and they achieve 70-75 dB and 80-85 dB SI cancellation, respectively. The Kalman filter is applied to mitigate the residual SI signal on the digital side, and the SI cancellation of about 30 to 35 dB is achieved. SINR obtained at the Rx side after applying the Kalman filter is almost equal to the ideal, i.e., the one calculated at the Rx output, i.e., before digital signal processing.