# On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers
### Related Work  
Numerous SI cancellation methods have been proposed to lessen the transceiver's SI effects on the receiver's performance. These SI cancellation methods can be categorized as passive and active cancellation techniques. It has been reported in [8; 15; 16; 17; 18] that SI signal can be significantly alleviated to the desired level by using the passive SI cancellation technique, also known as antenna cancellation technique. The active SI cancellation technique includes SI cancellation in propagation or analog domain, also known as RF cancellation, as presented in [2; 3; 19; 20; 21; 22; 23], to lessen the SI signal significantly. The residual SI signal cancellation at the receiver chain has been demonstrated in [24; 25], as a digital SI cancellation technique. SI, i.e., the transmitter's transmitted signal is at a higher level (dB) than our desired signal of interest. Digital SI cancellation techniques are useless if the receiver gets saturated due to the SI signal. Hence, for SI cancellation to the desired level, passive and analog cancellation techniques are used as pre-cancellation techniques. Effective analog pre-cancellation is an essential prerequisite for the implementation of digital cancellation. However, neither of these techniques alone is enough to mitigate the SI to the desired level fully. Typically, the FD communication system deploys both active and passive cancellation techniques sequentially to significantly reduce the SI signal, i.e., below the receiver's thermal noise floor or sensitivity level. The implementation of the antenna cancellation technique and analog/RF cancellation does not effectively cancel the SI signal because of imperfect channel estimation between Tx and Rx antennae. Similarly, antenna cancellation and digital cancellation do not effectively mitigate the SI signal because of the limited dynamic range of analog to digital convertor (ADC) in the receiver chain. However, by implementing an antenna cancellation technique combined with noise cancellation and digital interference cancellation, the mitigation of the SI signal up to 60 dB can be achieved, permitting a node to transmit and receive simultaneously [1]. Upon implementing both active cancellation techniques, i.e., analog/RF cancellation and digital cancellation simultaneously, 60 dB SI signal mitigation has been stated in [26; 27] and 70-73 dB in [6; 7]. Antenna separation and both active cancellation techniques (analog and digital) are effective because a reasonable amount of SI signal can be cancelled before it is coupled to the receiver; otherwise, the receiver goes to saturation and this degrades the performance. A maximum of 100 dB SI cancellation has been reported in the literature up until now, when both passive (antenna) cancellation and active (analog and digital) SI cancellation techniques are used at once [28]. Perfect suppression of SI is impossible in practice; even after applying antenna and analog cancellation techniques, residual SI still exists. The statistical properties of SI are different from those of thermal noise, but they always act in a similar way to noise, and are also treated as noise [29]. Digital cancellation techniques are applied at the transceiver's baseband side and are used to suppress residual SI, i.e., low power multi-path components of SI [6; 7; 24; 25]. It is also applied to compensate for non-linear components of the transmitter and receiver front end [30]. Performance of the FD communication system's transceiver is highly degraded due to non-idealities in different transceivers' architecture stages, i.e., Tx and Rx front-end components (low cost, low-quality components) and due to the circuitry used for active and passive cancellation [31; 32].