Self-interference Research Articles

A Full-Duplex MIMO System Based on CP-Free OFDM in Sensor Network

Recently, results have shown that full-duplex (FD) system based on orthogonal frequency division multiplexing (OFDM) is potential for wireless sensor networks. However, extending FD to further improve spectral efficiency by removing cyclic prefix (CP) with optimal canceling self-interference (SI) remains a challenge. In this paper, we analytically study the conventional FD OFDM system and proposed a CP-free system on this basis. The key point of the proposed scheme is the symbols transmitted in a unit of two identical symbols without CP. To eliminate the intersymbol interference, the disturbed part are replaced by the repeated signal at the receiver, which has the same effect as CP. Finally, an SI cancellation is down to restore the transmitted symbols. As a key of analysis, a multiple-input multiple-output (MIMO) FD simulation model is carried to show that our proposed scheme is effectiveness in terms of the bit error ratio (BER).

A Two-Stage Wideband RF Cancellation of Coupled Transmit Signal for Bi-Static Simultaneous Transmit and Receive System

Wireless technology is growing at a fast rate to accommodate the expanding user demands. Currently, the radio frequency (RF) spectrum is overcrowded. Hence, it is more susceptible to signal fratricide and interference. To enhance spectrum access, in-band full duplex systems are implemented to achieve simultaneous transmission and reception (STAR) and double the spectral efficiency. However, STAR systems require suppression of the high power transmit signals that can leak into the receiver chain. This type of self-interference (SI) can significantly reduce the receiver.s dynamic range and often leads to its desensitization. Therefore, successful STAR implementation requires considerable isolation between the transmitter and receiver to reduce the SI signal. To do so, RF self-interference cancellation (RFSIC) stages are considered. In this paper, we present a two-stage SIC system that includes transmit and receive antennas isolation and RFSIC filter stages. Notably, the isolation between the transmit and receive antennas is based on a novel symmetric suppression technique. The RFSIC filter is based on a hybrid finite impulse response (FIR) filter and resonator architecture. Adding a resonator to the FIR filter provides improved matching to approximate and suppress the direct SI coupling. Our design achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 52 dB isolation on average across a 500 MHz bandwidth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">viz.</i> 1-1.5 GHz) in simulation. Simulation results show a minimum cancellation of 41 dB and a maximum cancellation of 65 dB. A prototype was fabricated and tested, showing an average of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 44 dB cancellation which is in good agreement with our simulation.

Joint Dynamic Passive Beamforming and Resource Allocation for IRS-Aided Full-Duplex WPCN

This paper studies intelligent reflecting surface (IRS)-aided full-duplex (FD) wireless-powered communication network (WPCN), where a hybrid access point (HAP) broadcasts energy signals to multiple devices for their energy harvesting in the downlink (DL) and meanwhile receives information signals in the uplink (UL) with the help of IRS. Particularly, we propose three types of IRS beamforming configurations to strike a balance between the system performance and signaling overhead as well as implementation complexity. We first propose the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fully dynamic IRS beamforming</i> , where the IRS phase-shift vectors vary with each time slot for both DL wireless energy transfer (WET) and UL wireless information transmission (WIT). To further reduce signaling overhead and implementation complexity, we then study two special cases, namely, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">partially dynamic IRS beamforming</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">static IRS beamforming</i> . For the former case, two different phase-shift vectors can be exploited for the DL WET and the UL WIT, respectively, whereas for the latter case, the same phase-shift vector needs to be applied for both DL and UL transmissions. We aim to maximize the system throughput by jointly optimizing the time allocation, HAP transmit power, and IRS phase shifts for the above three cases. Two efficient algorithms based on alternating optimization and penalty-based algorithms are respectively proposed for both perfect self-interference cancellation (SIC) case and imperfect SIC case by applying successive convex approximation and difference-of-convex optimization techniques. Simulation results demonstrate the benefits of IRS for enhancing the performance of FD-WPCN, especially with fully dynamic IRS beamforming, and also show that the IRS-aided FD-WPCN is able to achieve significantly performance gain compared to its counterpart with half-duplex when the self-interference (SI) is properly suppressed.

RF Self-Interference Cancellation and Frequency Downconversion With Immunity to Power Fading Based on Optoelectronic Oscillation

We report a photonic approach to achieve simultaneous radio frequency (RF) self-interference cancellation (SIC) and frequency downconversion with immunity to power fading based on an optoelectronic oscillator (OEO) for an in-band full-duplex (IBFD) radio-over-fiber (ROF) system. A dual-drive Mach–Zehnder modulator (DDMZM) in a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to cancel the RF self-interference (SI) signal and generate optical carrier-suppressed double sidebands (CS-DSBs) of the signal of interest (SOI). Meanwhile, another DDMZM in the PDM-MZM is used to construct an OEO loop to generate optical CS-DSBs of the local oscillation (LO) signal. After detection at a photodetector (PD), a frequency downconverted signal is recovered with the RF self-interference cancellation (SIC). The proposed scheme can directly cancel the RF SI signal in the optical domain, meaning that it can overcome the limitation of SIC in the electrical domain. With the phase compensation introduced by a polarization controller, the desired signal is unaffected by the power fading over fiber transmission, which is significant for IBFD ROF systems. In addition, instead of an external microwave source, an OEO loop is used to generate an LO signal with a high spectral purity, which is very promising for integrated microwave photonics systems.

Hybrid-Layers Neural Network Architectures for Modeling the Self-Interference in Full-Duplex Systems

Full-duplex (FD) systems have been introduced to provide high data rates for beyond fifth-generation wireless networks through simultaneous transmission of information over the same frequency resources. However, the operation of FD systems is practically limited by self-interference (SI), and efficient SI cancelers are sought to make the FD systems realizable. Typically, polynomial-based cancelers are employed to mitigate the SI; nevertheless, they suffer from high complexity. This article proposes two novel hybrid-layers neural network (NN) architectures to cancel the SI with low complexity. The first architecture is referred to as hybrid-convolutional recurrent NN (HCRNN), whereas the second is termed as hybrid-convolutional recurrent dense NN (HCRDNN).In the HCRNN, a convolutional layer is employed to extract the input data features using a reduced network scale. Moreover, a recurrent layer is then applied to assist in learning the temporal behavior of the input signal from the localized feature map of the convolutional layer. In the HCRDNN, an additional dense layer is exploited to add another degree of freedom for adapting the NN settings in order to achieve the best compromise between the cancellation performance and computational complexity. The complexity analysis of the proposed NN architectures is provided, and the optimum settings for their training are selected. The simulation results demonstrate that the proposed HCRNN and HCRDNN-based cancelers attain the same cancellation of the polynomial and the state-of-the-art NN-based cancelers with an astounding computational complexity reduction. Furthermore, the proposed cancelers show high design flexibility for hardware implementation, depending on the system demands.

Design and Analysis of Wideband In-Band-Full- Duplex FR2-IAB Networks

This paper develops a 3GPP-inspired design for the in-band-full-duplex (IBFD) integrated access and backhaul (IAB) networks in the frequency range 2 (FR2) band, which can enhance the spectral efficiency (SE) and coverage while reducing the latency. However, the self-interference (SI), which is usually more than 100 dB higher than the signal-of-interest, becomes the major bottleneck in developing these IBFD networks. We design and analyze a subarray-based hybrid beamforming IBFD-IAB system with the RF beamformers obtained via RF codebooks given by a modified Linde-Buzo-Gray (LBG) algorithm. The SI is canceled in three stages, where the first stage of antenna isolation is assumed to be successfully deployed. The second stage consists of the optical domain (OD)-based RF cancellation, where cancelers are connected with the RF chain pairs. The third stage is comprised of the digital cancellation via successive interference cancellation followed by minimum mean-squared error baseband receiver. Multiuser interference in the access link is canceled by zero-forcing at the IAB-node transmitter. Simulations show that under 400 MHz bandwidth, our proposed OD-based RF cancellation can achieve around 25 dB of cancellation with 100 taps. Moreover, the higher the hardware impairment and channel estimation error, the worse digital cancellation ability we can obtain.

Neural Network Aided Digital Self-Interference Cancellation for Full-Duplex Communication Over Time-Varying Channels

In-band full duplex communication requires precise self-interference cancellation (SIC) to successfully decode the received desired signal. The existing neural network (NN) based SIC scheme uses offline trained NN to estimate the non-linear component of received self-interference (SI) over a static SI channel without additional NN training. For the time-varying SI channel, the NN-aided SIC method needs to retrain the NN during in-band full duplex communication to adapt time-varying channels. However, NN training is not fast enough to be done during full duplex communication. Thus, the SIC performance degrades. In this paper, we propose a digital SIC scheme using channel robust NN which takes estimates of linear SI channel coefficients as an input. It was found that the NN could learn the static part of the non-linear behavior of the SI channel well. Our solution can adapt the time-varying SI channel with only the channel coefficient estimation of linear components and a pre-trained NN. The proposed scheme can successfully reduce the SI to the noise floor for both time-invariant and time-varying SI channels.

Waveform Design and Performance Analysis for Full-Duplex Integrated Sensing and Communication

Integrated sensing and communication (ISAC) is a promising technology to fully utilize the precious spectrum and hardware in wireless systems, which has attracted significant attentions recently. This paper studies ISAC for the important and challenging monostatic setup, where one single ISAC node wishes to simultaneously sense a radar target while communicating with a communication receiver. Different from most existing schemes that rely on either radar-centric half-duplex (HD) pulsed transmission with information embedding that suffers from extremely low communication rate, or communication-centric waveform that suffers from degraded sensing performance, we propose a novel full-duplex (FD) ISAC scheme that utilizes the waiting time of conventional pulsed radars to transmit communication signals. Compared to radar-centric pulsed waveform with information embedding, the proposed design can drastically increase the communication rate, and also mitigate the sensing eclipsing and near-target blind range issues, as long as the self-interference (SI) is effectively suppressed. On the other hand, compared to communication-centric ISAC waveform, the proposed design has better auto-correlation property as it preserves the classic radar waveform for sensing. Performance analysis is developed by taking into account the residual SI, in terms of the probability of detection and ambiguity function for sensing, as well as the spectrum efficiency for communication. Numerical results are provided to show the significant performance gain of our proposed design over benchmark schemes.

Universal Performance Bounds for Joint Self-Interference Cancellation and Data Detection in Full-Duplex Communications

This paper studies the joint digital self-interference (SI) cancellation and data detection in an orthogonal-frequency-division-multiplexing (OFDM) full-duplex (FD) system, considering the effect of phase noise introduced by the oscillators at both the local transmitter and receiver. In particular, an universal iterative two-stage joint SI cancellation and data detection framework is considered and its performance bound independent of any specific estimation and detection methods is derived. First, the channel and phase noise estimation mean square error (MSE) lower bounds in each iteration are derived by analyzing the Fisher information of the received signal. Then, by substituting the derived MSE lower bound into the SINR expression, which is related to the channel and phase noise estimation MSE, the SINR upper bound in each iteration is computed. Finally, by exploiting the SINR upper bound and the transition information of the detection errors between two adjacent iterations, the universal bit error rate (BER) lower bound for data detection is derived.

Finite-Order Filter Designs of Source and Multiple Full-Duplex Relays for Cooperative Communications in Presence of Frequency- Selective Fading and Inter-Relay Interference

This paper considers the finite-order filter design problem for the source and multiple full-duplex (FD) relays in a cooperative communication system under frequency-selective fading channels. The goal is to optimize the source and relay filters such that the end-to-end signal-to-interference-plus-noise ratio (SINR) of minimum mean-squared error decision-feedback equalizer (MMSE-DFE) can be maximized. The resultant design problem is very difficult since we need to deal with self interference (SI), inter-relay interference (IRI), and inter-symbol interference (ISI) at the same time. Novel designs are then proposed to overcome the difficulty in this work. Transforming the signals into the frequency domain and using some optimization techniques, we first theoretically derive the power spectrum of the source filter and the spectrums of the relay filters. Then, the finite-order design is developed to approach the derived spectrums. Based on the weighted least-square (WLS) criterion, the Steiglitz-McBride method is exploited to obtain the filter coefficients in finite lengths. Numerical results demonstrated that complete removal of SI may not be a good strategy; preserving a certain amount of SI at each relay instead provides better SINR performance.

A True Full-Duplex IO (TFD-IO) With Background SI Cancellation for High-Density Interfaces

In this work, we have proposed and experimentally demonstrated a true full-duplex input–output (TFD-IO) for high-speed high-density interfaces. The proposed TFD-IO can be used as an independent module that converts a unidirectional IO/interconnect to a fully bidirectional IO/interconnect, to ideally double the throughput of the high-speed interface. The TFD-IO uses a correlation-based technique to cancel the self-interference (SI) and echoes adaptively in the background. The signals transmitted from the near-end and the far-end can use independent baud-rates and signaling schemes in a TFD-IO. A proof-of-concept design of the TFD-IO module has been fabricated in a 65-nm CMOS technology, and demonstrated with bidirectional throughputs of up to 12.8 Gb/s.

Frequency-Domain Successive Cancellation of Nonlinear Self-Interference With Reduced Complexity for Full-Duplex Radios

Nonlinear self-interference (SI) cancellation is crucial for eliminating the impact of the transmitter-side nonlinearity on the comprehensive SI cancellation performance in full-duplex radios. However, in the propagation environment with rich reflection paths of signals, the number of the delayed taps required for time-domain nonlinear SI cancellation booms exponentially with the increase of the multi-path number, leading to unacceptable complexity. In this paper, a novel frequency-domain nonlinear SI canceller based on successive interference cancellation (SIC) technique is proposed for orthogonal frequency division multiplexing (OFDM) modulated full-duplex systems subjected to both transmitter nonlinearity and receiver nonlinearity. The proposed frequency-domain nonlinear SIC (FD-NSIC) cancels nonlinear components one by one via separately estimating the channel frequency response suffered by each order nonlinear component, which significantly relaxes the computational cost. Besides, to avoid the influence of the strong correlation between nonlinear components, orthogonalization is operated before SIC to white basis functions, which accelerates the convergence speed of the proposed FD-NSIC. Simulations are explicitly performed, showing that compared with the conventional frequency-domain nonlinear canceller based on recursive least squares (RLS) channel estimation, the proposed FD-NSIC is capable of canceling the SI to the noise floor with only 52% computational cost under 50 dB interference-to-noise ratio.

Dynamic User Clustering and Optimal Power Allocation in UAV-Assisted Full-Duplex Hybrid NOMA System

This paper investigates unmanned aerial vehicles (UAVs)-assisted full-duplex (FD) non-orthogonal multiple access (NOMA) system based cellular network, aiming to improve overall sum-rate throughput of the system through dynamic user clustering, optimal UAV placement and power allocation. Since each UAV operates in FD mode, self-interference (SI), co-channel interference (CCI), inter-UAV interference (IUI) and intra-node interference (INI) dominate the system&#x2019;s performance. Consequently, we propose an unconventional two-stage dynamic user clustering for user nodes (UNs) to reduce the cross-interference in multi-UAV aided FD-NOMA system. Particularly, all UNs are initially clustered into <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> clusters using k-means clustering in the first stage where each cluster is served by an UAV. Furthermore, each cluster is further divided into sub-clusters and each sub-clusters are operated in FD-NOMA scheme. Finally, to control interferences, a sum-rate throughput maximization problem is formulated for each UAV to jointly optimize uplink and downlink power allocation and UAV placement. The joint optimization problem is non-convex and difficult to solve directly, for which we decoupled the original problem by addressing UAV placement and power allocation separately. We first fix the UAV position and then solve the problem iteratively using successive convex approximation (SCA) method. By utilizing brute-force search algorithm, an optimal UAV placement is later performed which corresponds to maximum possible sum-rate throughput. Simulation results demonstrate that the proposed solution for the considered FD-NOMA system outperforms the conventional schemes.

Photonic-Assisted RF Self-Interference Cancellation Based on Optical Spectrum Processing

In band full-duplex (IBFD) wireless systems increase the RF spectrum efficiency and have become one of the key technologies in the future wireless communication systems. But it is only possible if the radio-frequency (RF) self-interference (SI) generated by the transmitter is sufficiently mitigated. SI cancellation becomes more difficult while the bandwidth and frequency increases. Herein, a novel approach to photonic-assisted RF SI cancellation based on optical processing is proposed for IBFD wireless systems. In this scheme, reference signal and the received signal are converted to optical signals by two Mach-Zehnder modulators. The phase and amplitude between reference and received signal are matched by optical spectrum processing, and the delay time is aligned by finely tuning the tunable optical delay line (TODL). The broadband interference signal within the received signal is removed in the optical domain. Experimental results show more than 30 dB cancellation depth in 10 GHz bandwidth. Besides, IBFD transmission performance based on 16-QAM for different symbol rates and different signal-to–interference ratios (SIR) are also demonstrated, as well as 92.6 dB•Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> spurious-free dynamic range (SFDR) is obtained.

Digital-Assisted Photonic Analog Wideband Multipath Self-Interference Cancellation

A digital-assisted photonic analog wideband radio-frequency multipath self-interference cancellation (SIC) and frequency downconversion method based on a dual-drive Mach–Zehnder modulator and the recursive least square (RLS) algorithm is proposed and demonstrated for in-band full-duplex systems. Besides the reference for the direct-path self-interference (SI) signal, the RLS algorithm is used to construct another reference for the residual SI signal from the direct path and the SI signals from the reflection paths. The proposed method can solve the performance limitation in the previously reported SIC methods of constructing the multipath SI signal using a single reference which is caused by the limited dynamic range of the digital-to-analog converter when the direct-path SI signal is much stronger than the sub-weak reflection-path SI signals. An experiment is performed. When the carrier frequency of the multipath SI signal is 10 GHz and the direct-path SI signal is much stronger than the sub-weak multipath SI signal, cancellation depths of about 26.7 and 26.1 dB are realized with SI baud rates of 0.5 and 1 Gbaud. When the direct-path SI signal and sub-weak multipath SI signal own closer power, the corresponding cancellation depths are 24.7 and 20.8 dB, respectively.

Characterization of mmWave X‐duplex multi‐relay system in 5G mobile network

SummaryIn this paper, we propose a millimeter wave (mmWave) X‐duplex (XD) amplify‐and‐forward (AF) multirelay system for 5G and beyond. Each XD AF relay is equipped with a shared antenna for both transmission and reception radio frequency (RF) chains. Also, the performance of mmWave XD AF multirelay system is analyzed, and a relay selection method in this scenario is suggested, where the best relay and the best operation mode are selected based on maximum end‐to‐end signal‐to‐interference‐plus‐noise ratio (SINR). XD relays can switch adaptively between half‐duplex (HD) and full‐duplex (FD) operation modes. As a practical channel model, Rician fading, path loss with line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) propagation, and blockage effects are considered for mmWave channel model in both source–relay and relay–destination links. We derive closed‐form expressions for end‐to‐end SINR and its distribution, outage probability, energy efficiency (EE), rate, and average symbol error rate (SER) based on the relay selection method. Monte Carlo simulations are performed to validate our analytical derivations, and also, the simulation results depict that XD relays outperform both HD and FD operation modes in terms of outage probability, EE, SER, and rate. Furthermore, the effects of self‐interference (SI) cancellation, blockage, and number of XD AF relays over the performance and also the comparison of XD relay selection to different existing relay selection policies are presented. In addition, it is shown that the XD relay selection method in our proposed system eliminates the performance floor of the FD caused by the residual SI that it is considered as a significant advantage of our proposed system.

Variable direction‐based self‐interference full‐duplex channel model for underwater acoustic communication systems

SummaryIn‐band full‐duplex (IBFD) underwater acoustic (UWA) communication can approximately double the capacity of UWA communication networks, which is particularly attractive in UWA systems due to the severely band‐limited nature of the channels encountered. In this paper, a geometry‐based channel model for self‐interference (SI) cancelation in an IBFD modem was proposed. Due to the movement of things, the variable full‐duplex (FD) modem direction with deviation reaches 5° is designed to meet the potential change in the underwater environment. In addition, the settings of direct and multipath reflections between a transmitter (T) and a receiver (R) are considered to present the propagation characteristics of the UWA channels. The numerical simulation results match the conventional transmission loss and propagation delay results, showing that the proposed model can characterize the UWA environment. According to preliminary findings, the propagation delay of local multipath can reach up to 1.4 s before it attains the noise floor level, with transmission loss reaching 80 dB at different angles.

SICNet—Low Complexity Sample Adaptive Neural Network-Based Self-Interference Cancellation in LTE-A/5G Mobile Transceivers

The limited transmitter-to-receiver stop-band isolation of the duplexers in long term evolution (LTE) and 5G/NR frequency division duplex transceivers induces leakage signals from the transmitter(s) (Tx) into the receiver(s) (Rx). These leakage signals are the root cause of a multitude of self-interference (SI) problems in the receiver path(s) diminishing a receiver&#x2019;s sensitivity. Traditionally, these effects are counteracted by the use of various different SI cancellation (SIC) architectures which typically solely target one specific problem. In this paper, we propose two novel neural networks based architectures that can handle a variety of different SI effects without the need for a different architecture for each effect. We additionally show the suitability of the proposed architecture on SI effects occurring in in-band full duplex transceivers. Further, we introduce two novel low-cost training algorithms to enable online adaptation (as opposed to offline training currently proposed in literature). The combination of these two concepts is shown to not only beat existing algorithms in their cancellation performance, but also to provide sufficiently low computational complexity allowing on-chip implementations.

Per-Antenna Self-Interference Cancellation Beamforming Design for Digital Phased Array

Almost all current beamforming-based designs of self-interference cancellation (SIC) for digital phased array systems neglect the practical issue of the limited dynamic range of analog-to-digital converters (ADCs) and, thus, lack restriction for self-interference (SI) that is incident at each receiving antenna. Other than beamforming, these methods usually require additional SIC techniques to provide a part of isolation, which brings higher system complexity. In this letter, a SIC method is proposed to overcome these issues. By developing a transmit SIC beamformer design that minimizes the power of SI on a per-antenna basis, we can obtain more isolation before the ADCs in each receiving channel and better prevent them all from being saturated. Then, the residual SI can be further suppressed by adaptive receive beamformers to achieve high total isolation performance. The proposed method reduces the need for other SIC techniques than beamforming technology in phased array systems and, thus, facilitates lower system complexity. Numerical results demonstrate the effectiveness of the proposed method.

RF self-interference canceller prototype for 100-W full-duplex operation at 225–400 MHz

Military applications require more and different characteristics from in-band full-duplex radio technology than what the research prototypes developed for civil/commercial applications can offer. While the challenge of cancelling the strong transmit–receive coupling, i.e., self-interference (SI), in a full-duplex radio has been largely resolved at higher ultra high frequency (UHF) bands for low-power transmission, tactical communication and electronic warfare applications require major research efforts toward supporting lower military-relevant frequencies and significantly higher transmission power levels. In this paper, we present a prototype of a radio-frequency SI cancellation circuit for the lower UHF band at 225–400 MHz and transmit power of up to 100–200 W. The experimental results demonstrate that the canceller can suppress SI by 40–50 dB depending on the operation frequency within the band. It is targeted for the military application of simultaneous full-duplex jamming and interception of communications, where we can estimate that a 5-W signal-of-interest could be intercepted from 10 km away when simultaneously jamming with 100 W power.