Wideband Self-Adaptive RF Cancellation Circuit for Full-Duplex Radio: Operating Principle and Measurements (original) (raw)
Related papers
Active Self-Interference Cancellation Mechanism for Full-Duplex Wireless Transceivers
Proceedings of the 9th International Conference on Cognitive Radio Oriented Wireless Networks, 2014
This paper investigates active cancellation techniques for a Full-Duplex transceiver. An auxiliary transmit chain is employed to create the cancellation signal, which is then injected at the receiver RF front-end by using a microstrip coupler. Two methods are proposed to calculate the self-interference cancellation signal. While the first method assumes the transmit chain to be strictly linear, the second one additionally incorporates nonlinear effects, occurring especially in the RF power amplifier. The linear method reports experimentally around 48 dB of selfinterference suppression under linear system behavior. Experimental results show also 50 dB of suppression by using the nonlinear method and under nonlinear system behavior, whereas the linear one reports 47 dB of suppression under the same conditions.
Solving Self-Interference Issues in a Full-Duplex Radio Transceiver
Proceedings, 2019
Most wireless devices transmit and receive at different spectrum frequency bands. This approach is no longer optimal due to increasing electromagnetic exhaustion. Besides, interference among all present and future working services should be negligible. A full-duplex scheme using the same band for simultaneous uplink and downlink is a huge step towards solving this issue. However, sharing the same frequency band involves a large interference of transmitted signal over received signal. To fix this problem, we propose the usage of a hybrid multistage cancellation system, consisting of an analog cancellation setup at RF frequencies and a baseband digital cancellation stage.
Active RF Cancellation with Closed-Loop Adaptation for Improved Isolation in Full-Duplex Radios
2018 IEEE Globecom Workshops (GC Wkshps), 2018
A key challenge in realizing simultaneous radio transmission and reception is suppressing the so-called selfinterference (SI) caused by coupling of the own transmitter (TX) signal to the receiver (RX). Moreover, the inherent nonlinearities of the TX and RX front-end components can seriously limit the achievable SI cancellation. In this paper, we present an active radio frequency (RF) cancellation architecture for SI suppression in radio transceivers operating under nonlinear TX power amplifier (PA) and the RX low noise amplifier (LNA). The proposed technique is based on pre-distorting the TX signal to reduce the unwanted PA-induced emissions, and then creating an opposite-phase baseband replica of the linear SI in the transceiver digital front-end through adaptive filtering of the known transmit data. The equivalent RF cancellation signal is finally generated in an auxiliary TX chain and combined with the received signal at the RX LNA input. A closed-loop parameter learning technique, based on the decorrelation principle, is also developed to efficiently estimate both the PA pre-distorter and the digital cancellation filter coefficients in a flexible manner. Experimental results show that the proposed scheme can achieve up to 50 dB SI suppression at the RX LNA input, even at high TX output power and with wide transmission bandwidth, thereby enabling improved TX-RX isolation while reducing the linearity requirements of RF components in in-band full duplex (IBFD) radios.
Widely Linear Digital Self-Interference Cancellation in Direct-Conversion Full-Duplex Transceiver
IEEE Journal on Selected Areas in Communications, 2014
This article addresses the modeling and cancellation of self-interference in full-duplex direct-conversion radio transceivers, operating under practical imperfect radio frequency (RF) components. Firstly, detailed self-interference signal modeling is carried out, taking into account the most important RF imperfections, namely transmitter power amplifier nonlinear distortion as well as transmitter and receiver IQ mixer amplitude and phase imbalances. The analysis shows that after realistic antenna isolation and RF cancellation, the dominant self-interference waveform at receiver digital baseband can be modeled through a widely-linear transformation of the original transmit data, opposed to classical purely linear models. Such widely-linear self-interference waveform is physically stemming from the transmitter and receiver IQ imaging, and cannot be efficiently suppressed by classical linear digital cancellation. Motivated by this, novel widely-linear digital self-interference cancellation processing is then proposed and formulated, combined with efficient parameter estimation methods. Extensive simulation results demonstrate that the proposed widely-linear cancellation processing clearly outperforms the existing linear solutions, hence enabling the use of practical low-cost RF frontends utilizing IQ mixing in full-duplex transceivers.
Inherent Self-Interference Cancellation for In-Band Full-Duplex Single-Antenna Systems
IEEE Transactions on Microwave Theory and Techniques, 2018
We propose a new analog self-interference cancellation (SIC) technique for in-band full-duplex transmission (IBFD) in single-antenna systems. We use an RF circulator to separate transmitted (Tx) and received (Rx) signals. Instead of estimating the self-interference (SI) signals and subtracting them from the Rx signals, we use the inherent secondary SI signals at the circulator, reflected by the antenna, to cancel the primary SI signals leaked from the Tx port to the Rx port. We modified the frequency response of the secondary SI signals using a reconfigurable impedance mismatched terminal (IMT) circuit, which consists of two varactor diodes at the antenna port. We can also adjust the frequency band and bandwidth by controlling the varactor diodes bias voltages. The IMT adjustability makes it robust to antenna input impedance variations and fabrication errors. We analyze and fabricate a prototype of the proposed technique at 2.45 GHz. We achieved more than 40 dB cancellation over 65 MHz of bandwidth. Our technique is independent of the RF circulator and antenna type and it can be applied to any frequency band. It is also very relevant to small mobile devices because it provides a simple, low-power and low-cost adjustable analog SIC technique.
Proceedings of the 9th International Conference on Cognitive Radio Oriented Wireless Networks, 2014
In this paper we provide an overview regarding the feasibility of in-band full-duplex transceivers under imperfect RF components. We utilize results and findings from the recent research on full-duplex communications, while introducing also transmitter-induced thermal noise into the analysis. This means that the model of the RF impairments used in this paper is the most comprehensive thus far. By assuming realistic parameter values for the different transceiver components, it is shown that IQ imaging and transmitter-induced nonlinearities are the most significant sources of distortion in in-band full-duplex transceivers, in addition to linear self-interference. Motivated by this, we propose a novel augmented nonlinear digital selfinterference canceller that is able to model and hence suppress all the essential transmitter imperfections jointly. This is also verified and demonstrated by extensive waveform simulations.
Modeling and efficient cancellation of nonlinear self-interference in MIMO full-duplex transceivers
2014 IEEE Globecom Workshops (GC Wkshps), 2014
This paper addresses the modeling and digital cancellation of self-interference in in-band full-duplex (FD) transceivers with multiple transmit and receive antennas. The self-interference modeling and the proposed nonlinear spatiotemporal digital canceller structure takes into account, by design, the effects of I/Q modulator imbalances and power amplifier (PA) nonlinearities with memory, in addition to the multipath selfinterference propagation channels and the analog RF cancellation stage. The proposed solution is the first cancellation technique in the literature which can handle such a self-interference scenario. It is shown by comprehensive simulations with realistic RF component parameters and with two different PA models to clearly outperform the current state-of-the-art digital selfinterference cancellers, and to clearly extend the usable transmit power range.
Self-Interference Cancellation in MIMO Full-Duplex Transceivers
2018
The transceiver nonlinearities have recently been shown to limit the performance of in-band FD (Full-Duplex) devices. In this article, detailed modeling and mitigation algorithms of more critical of these nonlinearities, in order to obtain better SI (Self-Interference) cancellation performance are presented. In the transmitter side, we applied DPD (Digital Predistortion) to both, transmit and cancellation chains in order to obtain output signals free from nonlinearities of RF components, and crosstalk, which allow better RF cancellation. In the receiver side, the nonlinearities of RF components are modeled and the residual SI that will experiment these nonlinearities is removed by digital cancellation. Our proposed method, ''DPD cancellation'', provides one of the simple signal models that takes into account more of RF impairments, such as PA (Power Amplifier) nonlinearity, LNA (Low Noise Amplifier), DAC (Digital to Analog Converter) nonlinearities, IQ imbalance at b...
Advanced self-interference cancellation and multiantenna techniques for full-duplex radios
2013 Asilomar Conference on Signals, Systems and Computers, 2013
In an in-band full-duplex system, radios transmit and receive simultaneously in the same frequency band at the same time, providing a radical improvement in spectral efficiency over a half-duplex system. However, in order to design such a system, it is necessary to mitigate the self-interference due to simultaneous transmission and reception, which seriously limits the maximum transmit power of the full-duplex device. Especially, large differences in power levels in the receiver frontend sets stringent requirements for the linearity of the transceiver electronics. We present an advanced architecture for a compact full-duplex multiantenna transceiver combining antenna design with analog and digital cancellation, including both linear and nonlinear signal processing.
Analog Least Mean Square Adaptive Filtering for Self-Interference Cancellation in Full Duplex Radios
IEEE Wireless Communications, 2021
In-band full-duplex (IBFD) radio represents one of the key technologies for future wireless communication and radar applications. A major challenge of this technology is to mitigate the strong self-interference (SI), so that the residual SI level falls below the receivers noise floor. Radio frequency (RF) selfinterference cancellation (SIC) is essential for preventing an IBFD receiver from becoming saturated by the SI. We commence with an in-depth review of the promising analog least mean square (ALMS) adaptive filtering architecture, conceived for RF SIC in the IBFD radio RF frontend. The cancellation circuits employing this architecture can be implemented purely by analog components without any involvement of more power-thirsty digital signal processing (DSP). The behaviours, performance and implementation of the ALMS loop are presented. Finally, their applications in various IBFD radios are discussed and future research directions are provided.