RF Self-interference Cancellation Research Articles

A New Tuning Algorithm Based on Variable Step Approaching for RF Self-Interference Cancellation

A New Tuning Algorithm Based on Variable Step Approaching for RF Self-Interference Cancellation

Full-Duplex Receiver With Wideband, High-Power RF Self-Interference Cancellation Based on Capacitor Stacking in Switched-Capacitor Delay Lines

Full-Duplex Receiver With Wideband, High-Power RF Self-Interference Cancellation Based on Capacitor Stacking in Switched-Capacitor Delay Lines

Integrated photonic RF self-interference cancellation on a silicon platform for full-duplex communication

In-band full-duplex (IBFD) technology can double the spectrum utilization efficiency for wireless communications, and increase the data transmission rate of B5G and 6G networks and satellite communications. RF self-interference is the major challenge for the application of IBFD technology, which must be resolved. Compared with the conventional electronic method, the photonic self-interference cancellation (PSIC) technique has the advantages of wide bandwidth, high amplitude and time delay tuning precision, and immunity to electromagnetic interference. Integrating the PSIC system on chip can effectively reduce the size, weight, and power consumption and meet the application requirement, especially for mobile terminals and small satellite payloads. In this paper, the silicon integrated PSIC chip is presented first and demonstrated for IBFD communication. The integrated PSIC chip comprises function units including phase modulation, time delay and amplitude tuning, sideband filtering, and photodetection, which complete the matching conditions for RF self-interference cancellation. Over the wide frequency range of C, X, Ku, and K bands, from 5 GHz to 25 GHz, a cancellation depth of more than 20 dB is achieved with the narrowest bandwidth of 140 MHz. A maximum bandwidth of 630 MHz is obtained at a center frequency of 10 GHz. The full-duplex communication experiment at Ku-band by using the PSIC chip is carried out. Cancellation depths of 24.9 dB and 26.6 dB are measured for a bandwidth of 100 MHz at central frequencies of 12.4 GHz and 14.2 GHz, respectively, and the signal of interest (SOI) with 16-quadrature amplitude modulation is recovered successfully. The factors affecting the cancellation depth and maximum interference to the SOI ratio are investigated in detail. The performances of the integrated PSIC system including link gain, noise figure, receiving sensitivity, and spurious free dynamic range are characterized.

Photonics-Assisted Simultaneous RF Channelization and Self-Interference Cancellation

Both RF channelization and self-interference cancellation are urgently required for modern in-band full-duplex systems. A photonics-assisted RF receiver for simultaneous wideband channelization and self-interference cancellation is proposed and demonstrated. The key is the implementation of dual optical frequency combs (OFCs) followed by microwave photonic image-reject mixers (IRMs) using a dual-output Hartley structure. The received RF signal and the reference signal are modulated to a pair of signal OFCs with orthogonal polarization states, respectively. The microwave photonic IRM is applied on each polarization state, respectively. For each local OFC comb line, two components will be sliced and downconverted from each copy of the optically-carried received RF signal. Meanwhile, another two components will be sliced and downconverted from the optically-carried reference signal. After combining the outputs of the IRMs, the components from the image signal and the self-interference signal will be eliminated simultaneously. Two channels of the signal of interest will be obtained for each local OFC comb line. Experimental results show that an RF signal with an instantaneous bandwidth of 6 GHz (from 7 to 13 GHz) is channelized into 6 channels, each of which has a 1-GHz bandwidth. The isolation of larger than 28 dB between the channels is realized, and the simultaneous self-interference cancellation and image-rejection are achieved.

Lossless Decoupling Networks for RF Self-Interference Cancellation in MIMO Full-Duplex Transceivers

Lossless Decoupling Networks for RF Self-Interference Cancellation in MIMO Full-Duplex Transceivers

Standalone RF Self-Interference Cancellation System for In-Vivo Simultaneous Transmit and Receive (STAR) MRI.

Demonstrated is a standalone RF self-interference canceller for simultaneous transmit and receive (STAR) magnetic resonance imaging (MRI) at 1.5T. Standalone STAR cancels the leakage signal directly coupled between transmit and receive RF coils. A cancellation signal, introduced by tapping the input of a transmit coil with a power divider, is manipulated with voltage-controlled attenuators and phase shifters to match the leakage signal in amplitude, 180° out of phase, to exhibit high isolation between the transmitter and receiver. The cancellation signal is initially generated by a voltage-controlled oscillator (VCO); therefore, it does not require any external RF or synchronization signals from the MRI console for calibration. The system employs a field programmable gate array (FPGA) with an on-board analog to digital converter (ADC) to calibrate the cancellation signal by tapping the receive signal, which contains the leakage signal. Once calibrated, the VCO is disabled and the transmit signal path switches to the MRI console for STAR MR imaging. To compensate for the changes of parameters in RF sequences after the automatic calibration and to further improve isolation, a wireless user board that uses an ESP32 microcontroller was built to communicate with the FPGA for final fine-tuning of the output state. The standalone STAR system achieved 74.2 dB of isolation with a 94 second calibration time. With such high isolation, in-vivo MR images were obtained with approximately 40 mW of RF peak power.

Photonics-Assisted Analog Wideband Self-Interference Cancellation for In-Band Full-Duplex MIMO Systems With Adaptive Digital Amplitude and Delay Pre-Matching

A photonics-assisted analog wideband RF self-interference (SI) cancellation and frequency downconversion approach for in-band full-duplex (IBFD) multiple-input multiple-output (MIMO) systems with adaptive digital amplitude and delay pre-matching is proposed based on a dual-parallel Mach–Zehnder modulator (DP-MZM). In each MIMO receiving antenna, the received signal, including different SI signals from different transmitting antennas and the signal of interest, is applied to one arm of the upper dual-drive Mach–Zehnder modulator (DD-MZM) of the DP-MZM, the reference signal is applied to the other arm of the upper DD-MZM, and the local oscillator signal is applied to one arm of the lower DD-MZM. The SI signals are canceled in the optical domain in the upper DD-MZM and the frequency downconversion is achieved after photodetection. To cancel the SI signals, the analog reference signal is constructed in the digital domain, while the amplitude and delay of the constructed reference are adjusted digitally by upsampling with high accuracy. Experiments are performed when two different SI signals are employed. The genetic algorithm or least squares algorithm is combined with segmented search respectively for the SI signal reconstruction and amplitude and delay pre-matching. A cancellation depth of around 20 dB is achieved for the 1-Gbaud 16 quadrature-amplitude modulation orthogonal frequency-division multiplexing signal.

Photonics-assisted wideband RF self-interference cancellation with digital domain amplitude and delay pre-matching

A photonics-based digital and analog self-interference cancellation approach for in-band full-duplex communication systems and frequency-modulated continuous-wave radar systems is reported. One dual-drive Mach-Zehnder modulator is used to implement the analog self-interference cancellation by pre-adjusting the delay and amplitude of the reference signal applied to the dual-drive Mach-Zehnder modulator in the digital domain. The amplitude is determined via the received signal power, while the delay is searched by the cross-correlation and bisection methods. Furthermore, recursive least square or normalized least mean square algorithms are used to suppress the residual self-interference in the digital domain. Quadrature phase-shift keying modulated signals and linearly frequency-modulated signals are used to experimentally verify the proposed method. The analog cancellation depth is around 20 dB, and the total cancellation depth is more than 36 dB for the 2-Gbaud quadrature phase-shift keying modulated signals. For the linearly frequency-modulated signals, the analog and total cancellation depths are around 19 dB and 34 dB, respectively.

Open-access full-duplex wireless in the ORBIT and COSMOS testbeds

In order to support experimentation with full-duplex (FD) wireless, we integrated two generations of FD radios in the open-access ORBIT and COSMOS testbeds. In the indoor ORBIT testbed, we integrated a customized 1st generation (Gen-1) narrowband FD radio. In the city-scale PAWR COSMOS testbed, we integrated four 2nd generation (Gen-2) wideband FD radios, as well as static and mobile Gen-1 FD radios.Each integrated FD radio consists of an antenna, a customized RF self-interference (SI) canceller box, a USRP software-defined radio (SDR), and a remotely accessible compute node. The Gen-1/Gen-2 RF SI canceller box includes an RF canceller printed circuit board (PCB) which emulates a customized integrated circuit (IC) RF canceller implementation. The amplitude- and phase-based Gen-1 narrowband RF canceller achieves 45dB RF SIC across 5MHz bandwidth. The Gen-2 wideband canceller is based on the technique of frequency-domain equalization (FDE) and achieves 50dB RF SI cancellation (SIC) across 20MHz bandwidth. In this paper, we present the design of the two generations of FD radios, and their integration in various forms in the ORBIT and COSMOS testbeds. We then present example experiments that can be remotely run and modified by experimenters. Finally, we discuss future improvements and potential FD wireless experiments that can be supported by these open-access FD radios integrated in the COSMOS testbed.

RF Self-Interference Cancellation for Radio-Over-Fiber Link Based on Dual Phase Modulation in Sagnac Loop

The in-band full-duplex (IBFD) systems can send and receive data simultaneously in the same frequency band. Although the electromagnetic interference among RF channels can be released using radio over fiber (RoF) links, the receiving antenna is susceptible to the signal leakage from adjacent transmitting antennas. Due to the electronic bottlenecks, traditional RF self-interference cancellation (SIC) systems have some problems, such as low operating frequency, narrow transmission bandwidth, and electromagnetic interference, which seriously reduces the communication performance. In this paper, a photonic RF SIC system based on dual-phase modulation in a Sagnac loop is proposed to further increase the resistance to electromagnetic interference of the IBFD systems. Based on the principle of polarization multiplexing, the damaged received signal and local interference signal are modulated on two beams of a light wave with orthogonal polarization states. The received interference signal can be canceled by polarization adjustment. In the experiment, a single- frequency interference cancelation depth of 45 dB is achieved in the proposed photonic SIC system over the operating frequency range of 5-20 GHz. Also, a demonstration of cancellation for modulated interference with a center frequency of 10 GHz and bandwidths of 20, 30, and 50 MHz is carried out.

Wideband Full-Duplex Phased Array With Joint Transmit and Receive Beamforming: Optimization and Rate Gains

Full-duplex (FD) wireless and phased arrays are both promising techniques that can significantly improve data rates in future wireless networks. However, integrating FD with transmit (Tx) and receive (Rx) phased arrays is extremely challenging, due to the large number of self-interference (SI) channels. Previous work relies on either RF canceller hardware or on analog/digital Tx beamforming (TxBF) to achieve SI cancellation (SIC). However, Rx beamforming (RxBF) and the data rate gain introduced by FD nodes employing beamforming have not been considered yet. We study FD phased arrays with joint TxBF and RxBF with the objective of achieving improved FD data rates. The key idea is to carefully select the TxBF and RxBF weights to achieve wideband RF SIC in the spatial domain with minimal TxBF and RxBF gain losses. Essentially, TxBF and RxBF are repurposed, thereby not requiring specialized RF canceller circuitry. We formulate the corresponding optimization problem and develop an iterative algorithm to obtain an approximate solution with provable performance guarantees. Using SI channel measurements and datasets, we extensively evaluate the performance of the proposed approach in different use cases under various network settings. The results show that an FD phased array with 9/36/72 elements can cancel the total SI power to below the noise floor with sum TxBF and RxBF gain losses of 10.6/7.2/6.9dB, even at Tx power level of 30dBm. Moreover, the corresponding FD rate gains are at least 1.33/1.66/1.68 ×.

A Survey and Quantitative Evaluation of Integrated Circuit-Based Antenna Interfaces and Self-Interference Cancellers for Full-Duplex

Full-duplex (FD) wireless - simultaneous transmission and reception on the same frequency - is a promising technique that can significantly improve spectrum efficiency and reduce communication latency in future wireless networks. To enable FD operation, the powerful self-interference (SI) signal leaking from the transmitter (TX) into the receiver (RX) needs to be suppressed and canceled to an extreme degree at the antenna interface as well as in the RF/analog and digital domains. Various approaches to achieve TX-RX isolation at the antenna interface and SI cancellation (SIC) in the RF/analog and digital domains have been demonstrated, with a focus on using bench-top off-the-shelf components. Recent advances in integrated circuit (IC) implementations of various types of shared antenna interfaces and cancellers in the RF and/or analog baseband (BB) domains have further pushed the frontier of realizing FD wireless in small-form-factor/hand-held devices. Moreover, it is still important to fundamentally study the SIC performance that can be achieved by different types of cancellers. In this paper, we present a first-of-its-kind comprehensive overview on the implementation and comparison of various state-of-the-art integrated shared antenna interfaces and SI cancellers in both the RF and analog BB domains. We define two figures of merit (FOM) for the IC-based shared antenna interfaces and SI cancellers, which capture various design considerations and performance tradeoffs including the achievable isolation/SIC, bandwidth, noise figure degradation, TX/SI power handling, and power consumption. In particular, we focus on two types of integrated shared antenna interfaces including electrical-balance duplexers and circulators. We also discuss two types of SI cancellers based on the time-domain and frequency-domain approaches, which respectively employ parallel delay lines and bandpass filters to emulate the SI channel. Based on realistic measurements, we perform extensive numerical evaluations to illustrate and compare the achievable RF SIC performance in different scenarios, as well as discuss various design tradeoffs. Finally, we provide an overview of the IC-based implementations and performance evaluations of both types of cancellers based on our recent work.

Adaptive Learning Rate Tuning Algorithm for RF Self-Interference Cancellation

Future wireless systems that take advantage of in-band full-duplex (IBFD) technology require that the consequential self-interference (SI) be sufficiently mitigated for successful operation. Many IBFD designs utilize a multitap RF cancellation stage that necessitates the optimal configuration of multiple weights to accurately replicate real-world multipath SI channels. The nonconvex error surfaces generated by these channels present different features that can be challenging to navigate for canceller tuning algorithms. This article introduces a novel adaptive learning rate approach that utilizes a target error and a gradient estimation that is progressively forgotten over time to accelerate convergence speed and maximize cancellation performance. The tuning characteristics of a prototype system using this algorithm to set the weights of a two-tap canceller were measured over a 20-MHz bandwidth centered at 2.5 GHz and produced an average of more than 35 dB of cancellation for various SI channels with tuning times that are significantly less than previous approaches. The performance of this unique method was also studied against other tuning techniques, and results indicate that it could supplant traditional adaptive learning approaches for future IBFD systems.

Optical Multipath RF Self-Interference Cancellation Based on Phase Modulation for Full-Duplex Communication

Optical multipath RF self-interference cancellation (SIC) based on phase modulation for full-duplex communication is proposed and demonstrated experimentally. Phase modulation is utilized to convert the RF signal into optical domain, in which the time delay tuning, amplitude tuning and phase inversion for multipath RF SIC are completed. The comprehensive theoretical model of the optical multipath RF SIC system is established, and the factors affecting SIC performance including the time delay, amplitude and phase deviations are analyzed. The experimental results verify the feasibility of the proposed scheme for full-duplex communication with the cancellation depth of 26 dB and 28 dB over 100 MHz at central frequency of 6 GHz and 10 GHz, respectively. A figure of merit of the maximum interference to signal of interest ratio is defined to characterize the SOI recovery capability of optical RF SIC system.

A Photonic-Based Wideband RF Self-Interference Cancellation Approach With Fiber Dispersion Immunity

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity is proposed. A dual-drive Mach–Zehnder modulator (DD-MZM) in a dual-polarization binary phase-shift keying (DP-BPSK) modulator is used as an optical interference canceller, which cancels the self-interference from the received signal and generates two optical sidebands of the signal of interest (SOI) in the received signal. Another DD-MZM in the DP-BPSK modulator is used to provide a pure optical carrier. By combing the optical signals from the two DD-MZMs and beating them at a photodetector, the SOI can be recovered. In addition, if the SOI needs to be transmitted in optical fiber, the power fading effect caused by fiber dispersion can be overcome by simply introducing a proper phase shift to the pure optical carrier. An experiment is performed. RF self-interference cancellation (SIC) with a bandwidth up to 2 GHz is experimentally demonstrated and a cancellation depth of more than 20 dB is achieved even if the bandwidth of the self-interference is about 2 GHz. The SIC with 25-km fiber transmission and the RF power of the SOI after 25-km fiber transmission are also demonstrated, which proves that the SIC has very good immunity to fiber dispersion and the SOI can be transmitted without power fading.

Wideband RF Self-Interference Cancellation for FMCW Phased-Array Radar

In this article, a segmented self-interference cancellation (SSIC) method is proposed for frequency-modulated continuous-wave phased-array radar for canceling wideband multipath self-interference (SI) signals. A radio frequency canceller based on the SSIC method that uses the time-frequency segmentation equivalence of the linear frequency-modulated (LFM) signal is designed that can convert wideband SI cancellation (SIC) into several narrowband SICs. Numerical and simulation results show that the proposed method can achieve better cancellation performance with lower hardware complexity than the conventional multi-tap SI cancellation (MTSIC) method. Furthermore, the superior performance of the SSIC method is verified by experiments with a 250 MHz LFM signal.

Analysis and Design of a Full-Duplex Two-Element MIMO Circulator-Receiver With High TX Power Handling Exploiting MIMO RF and Shared-Delay Baseband Self-Interference Cancellation

In this article, we present how full-duplex (FD) operation can be integrated with multi-input multi-output (MIMO) operation using RF and baseband (BB) self-interference cancellation (SIC). MIMO operation increases the SIC requirements by a factor of $N^{2}$ , resulting in severe area, power consumption, and noise penalty. We present the detailed analysis, design, and implementation of RF/BB cancellers that address this challenge, as well as a bootstrapping technique to enhance the power handling of integrated circulator-receivers (circ.-RX). A 65-nm CMOS scalable two-element MIMO FD circ.-RX array with integrated $N$ -path-filter-based nonmagnetic circulators is described that: 1) exploits bootstrapping in the circulator $N$ -path filters to enhance Transmitter (TX) power handling by 8 dB and 2) features area- and power-efficient passive RF and active BB wideband MIMO cancellation with shared-delay elements to address the O( $N^{2}$ ) cancellation challenge. The prototype exhibits: 1) up to 35-/45-dB average SIC across 40-/20-MHz BW; 2) more than 42-/53-dB average crosstalk (CT)-SIC across 40-/20-MHz BW with <2.1-dB degradation in RX NF; and 3) overall TX power handling of +14 dBm enabled by clock bootstrapping.

2.4 GHz dual polarised monostatic antenna with simple two‐tap RF self‐interference cancellation (RF‐SIC) circuitry

This Letter presents a dual polarised monostatic patch antenna with a simple two-tap RF/analogue domain-based self-interference cancellation (SIC) (RF-SIC) circuitry to achieve high interport isolation in a comparatively wider bandwidth for a 2.4 GHz in-band full duplex wireless transceiver. A brief mathematical description for the deployed two-tap RF-SIC is also presented to provide insight into self-interference (SI) suppression in a comparatively wider bandwidth. The implemented antenna with a two-tap RF-SIC circuitry achieves around 80 dB T-x-R-x isolation for a 20 MHz bandwidth in addition to more than 90 dB peak isolation for measurements performed in a lab environment where SI may result from the nearby placed objects. The deployed two-tap RF-SIC circuit can be tuned to effectively cancel out SI caused by reflections of the radio signal from the surroundings. Moreover, an 80 dB isolation bandwidth can be tuned within a 10 dB return loss bandwidth of the implemented dual polarised antenna.

Self-interference cancellation in full-duplex wireless devices: A survey

Full-duplex wireless nodes can transmit and receive at the same time and in the same frequency band, thus effectively doubling the data rate. In these systems, the transmit signal interferes with the receive signal, a phenomena termed as self-interference. Self-interference is a major impediment to realising a full-duplex wireless node. In the recent years, there has been significant research on self-interference mitigation. In this paper, we survey important techniques for self-interference cancellation from the past few years. In particular, we focus on the various RF and baseband self-interference cancellation techniques for realising an ideal full-duplex node.

A Hilbert Transform Equalizer Enabling 80 MHz RF Self-Interference Cancellation for Full-Duplex Receivers

A passive, time-domain equalizer is presented that achieves a broadband self-interference cancellation (SIC) over 80 MHz of RF bandwidth for simultaneous full-duplex radios. A baseband Hilbert transform technique reduces the number of equalizer taps needed for SIC, and with frequency translations, results in an equivalent RF-domain equalization. A proof-of-concept prototype in 0.13- $\mu \text{m}$ CMOS process attains a measured 23 dB of SIC over an 80 MHz signal bandwidth at 900 MHz, and consumes 13 mW of clocking power independent of SIC equalizer settings. Its impact on the receiver noise figure is 1.4 dB. The equalizer and the receiver together consume 64.4 mW from a 1.2 V supply in an active area of 0.72 mm2.