# On Self-Interference Cancellation and Non-Idealities Suppression in Full-Duplex Radio Transceivers
###### Abstract  
One of the major impediments in the design and operation of a full-duplex radio transceiver is the presence of self-interference (SI), that is, the transceiver's transmitted signal, 60-100 dB stronger than the desired signal of interest. To reduce the SI signal below the receiver's sensitivity before coupling it to the receiver, radio frequency (RF)/analog domain cancellation is carried out. Even after SI cancellation to the required level in the analog domain, the residual SI signal still exits and lowers the transceiver's performance. For residual SI cancellation, a digital domain cancellation is carried out. RF impairments are the major obstacle in the residual SI cancellation path in the digital domain. Linearization of RF impairments such as IQ mixer imbalance in the transmitter and receiver chain, non-linear PA with memory, and non-linear LNA are also carried out. Performance evaluation of the proposed techniques is carried out based on SINR, the power of different SI signal components, PSD, output to input relationship, SNR vs. BER, spectrum analyzer, constellation diagram, and link budget analysis. The proposed techniques provide attractive RF/analog SI cancellation of up to 80-90 dB, digital residual SI cancellation of up to 35 to 40 dB, total SI cancellation of up to 110 to 130 dB, and an SINR improvement of up to 50 dB. RF/analog cancellation; channel state information at receiver (CSIR); digital SI cancellation; full-duplex (FD); self-interference (SI); residual self-interference; transceiver RF impairments/ non-idealities +
Footnote †: journal: _Mathematics_  
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sense multiple access control (MAC) networks, and fairness in a network. The FD communication system lowers the transmission delay. It is suitable for implementing feasible cognitive radio to detect and avoid delay, and limit a primary transmission and security of wireless data transfer [1; 2; 3]. The FD communication system has some advantages over frequency division duplexing (FDD) and time division duplexing (TDD). These include increased spectral efficiency by almost double, sharing single frequency between uplink and downlink, sensing the network traffic during its transmission, improved throughput, and lowering transmission delay. Despite these advantages, the practical realization and implementation of FD radio transceivers still have many challenges. Complications arise when co-located transmit and receive antennae (either single antenna or closely spaced two separate antennae) operate on the same carrier frequency at the same time, such as in FD radio transceivers [1; 4; 5; 6; 7; 8; 9; 10]. A most substantial and prime obstacle to the practical realization and implementation of FD radio transceivers is SI and inter-node interference. SI signal is almost 60-100 dB stronger than the desired received signal. SI signal overshadows the signal being received and highly degrades the receiver sensitivity and link throughput [1]. SI phenomenon is one of the biggest challenges in FD communication systems, stemming from imperfect electromagnetic isolation between transmitter (Tx) and receiver (Rx). Hence, in order for the FD communication system to achieve maximum efficiency and throughput, efficient SI cancellation mechanisms and appropriate antenna isolation is required. These are necessary to reduce the SI signal down to a sufficiently low level, i.e., ideally to the level below the receiver's noise floor and sensitivity level. FD transceivers capable of overcoming self-interference (SI) have the potential to improve the spectral efficiency, capacity of wireless networks and flexibility of spectrum use. FD can maximize the end-to-end transmission and hence result in extended coverage and enhanced communication system link quality.