Adaptive Nonlinear RF Cancellation for Improved Isolation in Simultaneous Transmit–Receive Systems

Abstract

This paper proposes an active radio frequency (RF) cancellation solution to suppress the transmitter (TX) passband leakage signal in radio transceivers supporting simultaneous transmission and reception. The proposed technique is based on creating an opposite-phase baseband equivalent replica of the TX leakage signal in the transceiver digital front-end through adaptive nonlinear filtering of the known transmit data, to facilitate highly accurate cancellation under a nonlinear power amplifier (PA). The active RF cancellation is then accomplished by employing an auxiliary transmitter chain, to generate the actual RF cancellation signal, and combining it with the received signal at the receiver (RX) low noise amplifier (LNA) input. A closed-loop parameter learning approach, based on the decorrelation learning rule, is also developed to efficiently estimate the coefficients of the nonlinear cancellation filter in the presence of a nonlinear PA with memory, finite passive isolation, and a nonlinear LNA. The performance of the proposed cancellation technique is evaluated through comprehensive RF measurements adopting commercial LTE-Advanced transceiver hardware components. The results show that the proposed technique can provide an additional suppression of up to 54 dB for the TX passband leakage signal at the LNA input, even at very high transmit power levels and with wide transmission bandwidths. Such novel cancellation solution can therefore substantially improve the TX-RX isolation, hence reducing the requirements on passive isolation and RF component linearity, as well as increasing the efficiency and flexibility of the RF spectrum use in the emerging 5G radio networks.

Impact of Self and Co-Channel Interference on An DNF Full-Duplex One-Way Relay System

“…transmits and receives simultaneously, there will be self-interference (SI) swamping the signal received from the source node. However, the experimental results in [2]- [6], [13]- [15] have demonstrated that SI signal can be efficiently suppressed. Hence, the residual self-interference (RSI) should be included in the description of the received signal at the relay, which is given as…”

“…Moreover, a hybrid SIC system, which comprises adaptive radio frequency (RF) cancellation and digital cancellation schemes, was proposed in [5]. Next, an active RF cancellation algorithm that exploits adaptive nonlinear filtering to attain effective SI cancellation when a nonlinear power amplifier (PA) is used, was presented in [6].…”

Optimal Transmission Using a Self-Sustained Relay in a Full-Duplex MIMO System

“…Using β = 1 implies that the residual interference increases linearly with the relay transmit power P r and the chosen value of α corresponds to a 40dB interference cancellation. This can be achieved through a common passive device, like a circulator, which is able to provide 20-40 dB isolation between the transmit and receive chains [28] [46]. We see that for low source transmit powers, the active cancellation FD is unable to harvest sufficient power for cancellation and transmission, and therefore achieves zero rate for P s ≤ 20 dBm.…”

On Cancellation Capability of Full-Duplex RF Self-Interference Cancellation Schemes

“…e reconstruction may also be done equivalently in the digital domain, where the digital baseband signal is ltered and then converted to the RF signal by an auxiliary transmit chain. Kiayani et al [11] report that their MRP scheme of this form cancels up to 54 dB for 20 MHz bandwidth. ese two kinds of RF-SIC schemes, as shown in experimental results of previous studies, have reduced self-interference signi cantly; however, their theoretical cancellation capability has not been presented yet.…”

“…erefore, there is a fundamental issue, i.e., selfinterference cancellation, in full-duplex wireless communication. Recent studies have shown that a strong selfinterference should be cancelled first in the RF domain to ensure the useful signal to pass through RF front end [3][4][5][6][7][8][9][10][11][12][13][14]. e commonly used RF-SIC schemes may be divided into two kinds.…”