Self-interference Cancellation Scheme Research Articles

Reconfigurable Intelligent Surfaces Between the Reality and Imagination

One interesting idea that could improve wireless communication systems is reconfigurable intelligent surfaces or RIS. To control the spread of wireless signals, RIS uses a plethora of tiny, inexpensive, and customizable reflecting devices. Signal strength, energy consumption, spectrum efficiency, and adaptability to changes in the wireless environment can all be improved by altering the phase shift of the reflecting elements. This is how RIS works. 5G and beyond, the IoT, and smart cities are just a few of the many potential uses for RIS. More study is required before this technology can reach its full potential since it is still in its infancy. Still, RIS is going to be big in the next generation of wireless networks. A great deal of excitement has enveloped the whole 6G development industry. There has been no shortage of grandiose and frequently unfounded assertions that, in reality, the creation of a full-duplex 5G technology that can introduce new services is just around the corner, even though self-interference cancellation schemes for full-duplex communications and the difficulties of building full-duplex base stations have long been known.

Self‐interference cancellation using dmrs‐based power estimation for in‐band full‐duplex transmission

AbstractThis letter presents an improved Self‐Interference Cancellation (SIC) receiver with Demodulation Reference Signal (DMRS)‐based power estimation for In‐band Full‐duplex (IBFD) transmission. The performance of the SIC scheme is highly dependent on the power of transmit signal. The DMRS‐based power estimation can obtain accurate power. Numerical results show that SIC with DMRS‐based power estimation improves the performance of an IBFD system.

Microwave photonic dispersion immune self-interference cancellation scheme for a radio over fiber based in-band full duplex communication link

A microwave photonic scheme for multi-functional radio over fiber based in-band full duplex communication links to realize deep self-interference cancellation, long range transmission, and efficient signal recovery is proposed. In the proposed scheme, double sideband modulation helps avoid applying electrical couplers or optical filters and is beneficial to improve the frequency conversion efficiency. By virtue of the intermediate frequency signal amplitude regulation mechanism induced by fiber dispersion, the conditions of dispersion induced power fading compensation, amplitude matching, and phase reversion between self-interference and reference signals can be satisfied through joint DC bias tuning. The high precision delay matching in the optical domain is advantageous to the deep self-interference cancellation performance in a wide frequency range compared to its electrical counterparts. Furthermore, the deterioration of signal quality and self-interference cancellation performance caused by fiber dispersion is avoided. Experimental analyses show that a single tone signal in a wide frequency range of 2–20 GHz can be cancelled over 60 dB. A broadband signal with bandwidth of 50 MHz in the C-band, X-band, and K-band can be cancelled over 35 dB. Furthermore, the recovery performance of the signal of interest with different modulation formats and different signal to interference ratios is investigated, showing high quality signal transmission and efficient signal recovery. The capability of dispersion induced power fading compensation is also verified, and the spurious-free dynamic range is measured to be 88.47dB⋅Hz2/3.

Digital self-interference cancellation for full-duplex systems based on deep learning

Full-duplex (FD) systems can double the spectrum efficiency by allowing users to transmit and receive signals at the same time and in the same frequency band. However, in FD systems the receiver suffers severe self-interference (SI) caused by the transmitter and eliminating the SI is challenging. In this paper, we propose a novel digital self-interference cancellation (SIC) scheme based on deep learning, which combines the power of sliding window, gated recurrent unit (GRU) network and attention mechanism (AM). The proposed scheme can accurately reconstruct the SI through two steps. It first processes the sample signals utilizing the sliding window and then extracts the dependence in preprocessed signals by applying the GRU with AM. We adopt the orthogonal frequency division multiplexing (OFDM) signal as the baseband transmitted signal to verify the proposed scheme. Extensive experiments demonstrate that the SIC capability of the developed scheme is at least 14.46 dB higher than the existing polynomial and neural network (NN) schemes. Furtherly, the effectiveness of the scheme is verified in different interference-to-noise ratio (INR), multipath channel, training sample and OFDM symbol situations.

Iterative phase noise suppression for full-duplex communication systems

Oscillator phase noise is one of the bottlenecks that limits the self-interference (SI) cancellation capability of full-duplex systems. In this paper, we propose a method for the suppression of common phase error (CPE) and intercarrier interference (ICI) induced by the phase noise in full-duplex orthogonal frequency division multiplexing (OFDM) systems. First, we regard the effect of CPE as a portion of the SI channel and perform estimation, reconstruction and elimination in the time domain. Then, the ICI signal is estimated and suppressed in the frequency domain. Additionally, by analysing the performance of proposed algorithm, we further develop an iterative mechanism to reduce the parameter estimation error and improve SI cancellation capability. Simulation results show that the proposed method has a significant SI cancellation capability improvement over the traditional SI cancellation schemes.

A Digital Self-Interference Cancellation Scheme for In-Band Full-Duplex-Applied 5G System and Its Software-Defined Radio Implementation

The development of mobile communication technology toward 6G is difficult because the required spectrum resources have already been allocated to existing systems. Therefore, new communication systems must have high spectral efficiency to effectively utilize the available resources. This article proposes a digital self-interference (SI) canceller that can be applied to full-duplex cellular systems based on the current 5G signal format (5G-FDC) to introduce in-band full-duplex systems beyond 5G. Specifically, we reorganize the 5G demodulation reference signal (DMRS) and define a novel DMRS configuration, in which the DMRSs for uplink and downlink communications do not interfere with each other. The proposed DMRS configuration effectively improves the accuracy of the SI channel estimation. Moreover, we propose a channel extrapolation scheme that suppresses the channel estimation degradation, which deteriorates the block error rate performance. Additionally, we propose a noise estimation method to improve the low-density parity check decoding performance of the desired signal in 5G-FDC systems. The effectiveness of the proposed method is demonstrated through computer simulations and experimentally by using our developed and implemented software-defined radio-based 5G-FDC prototype. Digital SI cancellation performances of 50 dB and 30.6 dB are observed in the simulation and experimental evaluations, respectively.

Full-Duplex UAC Receiver With Two-Sensor Transducer

In this brief we present a design of a full-duplex (FD) underwater acoustic communication (UAC) receiver with a two-sensor transducer. The transducer consists of two piezo-ceramic cylinders cast together in polyurethane resin; one acts as a hydrophone and the other a projector. As the distance between the projector and hydrophone is extremely short, a high level of self-interference (SI) from the projector is received at the hydrophone. This SI must be eliminated to enable far-end data demodulation. In this brief, we adopt a digital SI cancellation scheme based on adaptive filtering. We investigate the SI cancellation and far-end data demodulation performance with the two-sensor transducer in tank and lake experiments. The Rake receiver is used for the far-end data demodulation. As demonstrated by the experimental results, the far-end SNR loss in the FD experiment is less than 3 dB compared to the half-duplex experiment when there is only far-end transmission.

Pseudo-doppler aided cancellation of self-interference in full-duplex communications

In this work, a novel scheme is proposed to enhance the self-interference (SI) cancellation in full-duplex communications. Beyond conventional SI cancellation schemes that rely on the SI suppression, our proposed scheme exploits periodic antenna switching to generate the pseudo-Doppler effect, thus completely removing the SI at the fundamental frequency. In this way, the desired signal is readily obtained through a low-pass filter. For the purpose of performance evaluation, the SI cancellation capability is defined as the difference between the output signal-to-interference-plus-noise ratio (SINR) and the input SINR. Theoretical formulations and numerical results validate that our pseudo-Doppler aided scheme has higher SI cancellation capability than the conventional SI suppression schemes. Moreover, the impact of the SI suppression achieved by conventional schemes and the influence of antenna switching timing difference on the practical implementation of the proposed scheme are investigated, to further substantiate the validity of our pseudo-Doppler aided SI cancellation.

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.

Photonic-assisted radio frequency self-interference cancellation and frequency down-conversion based on polarization multiplexing modulation.

We report a photonic-assisted radio frequency self-interference cancellation (RF-SIC) and frequency down-conversion scheme based on a dual-polarization Mach-Zehnder modulator (DP-MZM) by using a polarization manipulation method. In the proposed scheme, the self-interference signal is directly canceled in the optical domain by simply controlling the polarization states between the output of the DP-MZM and the polarizer. Frequency down-conversion is achieved by optoelectronic frequency mixing. In the proof-of-concept experiment, the interference cancellation of the single-frequency signal and wideband signal was conducted. The proposed RF-SIC and frequency down-conversion system has flexible tunability, simple structure, and low cost, which can find potential applications in radio-over-fiber systems.

ALMS Loop Analyses With Higher-Order Statistics and Strategies for Joint Analog and Digital Self-Interference Cancellation

Joint analog and digital self-interference cancellation (SIC) is essential for enabling in-band full duplex (IBFD) communications. Analog least mean square (ALMS) loop is a promising low-complexity high-performance analog SIC technique with multi-tap adaptive filtering capability, but its properties on the tap coefficient variation have not been fully understood. In this paper, analysis based on higher-order statistics of the transmitted signal is performed to solve the problem of evaluating the variance of the ALMS loop’s weighting coefficient error, which reveals two additional types of irreducible residual self-interference (SI) produced by an ALMS loop if it runs freely. The residual SI channel impulse response in digital baseband is also analysed and its unique properties are investigated. By introducing a simple track and hold control to the ALMS loop’s tap coefficients, a joint analog and digital SIC scheme is proposed to stop the tap coefficient variation and achieve very low residual SI close to the IBFD receiver’s noise floor. In a coordinated application scenario, the noise figure of the digital SIC algorithm is proved to be only 1.76 dB at most. Simulation results are provided to verify the theoretical analyses.

Low-Complex Digital Cancellation of Transmitter Harmonics in LTE-A/5G Transceivers

Nowadays, mobile communication radio frequency transceivers for LTE-A/5G usually operate in frequency-division duplex mode and support carrier aggregation. The resulting complexity requires compromises in the analog front-end. One consequence is a limited stop-band attenuation of the duplex filters that separate the transmit and the receive paths. The resulting transmit leakage signal combined with other non-idealities, like power amplifier (PA) harmonics, can create self-interference problems that desensitize the receivers. In this work, we propose an optimized digital self-interference cancellation scheme to mitigate the unacceptable performance degradation caused by PA induced harmonics. We derive an appropriate interference model and quantify the interference power levels for a specific PA. Based on these results, our low-complex cancellation approach solely targets the dominating components. Our algorithm relies on the auto-covariance matrix for the second and third power of LTE signals, which we derive for the first time in an analytic form. This statistical information can be combined with the transform-domain concept to noticeably improve the performance of a least-mean squares based cancellation algorithm. The capabilities of the approach are demonstrated by means of simulations and are validated on measurement data.

Efficient scheme for attenuators and phase shifters adjustment in analogue self‐interference cancellation for full‐duplex systems

With self-interference cancellation (SIC), a wireless full-duplex terminal is allowed to transmit and receive signal simultaneously in the same frequency band. In this study, the authors first briefly described the impact on the conventional analogue SIC method from the interested signal. To solve this problem, they propose a new practical analogue SIC scheme for full-duplex systems, which is then mathematically analysed in terms of SIC capacity. Simulation results show that the analogue SIC performance obtained by the proposed method outperform the existing analogue SIC method.

Outage Probability and Throughput Analyses in Full-Duplex Relaying Systems With Energy Transfer

In this article, we consider a dual-hop full-duplex (FD), amplify-and-forward, orthogonal frequency division multiplexing (OFDM) relaying network, where the relay operates based on a time-switching architecture to harvest energy from radio frequency signals. We use a polarization-enabled digital self-interference cancellation (PDC) scheme to cancel the self-interference signal at the relay in order to achieve FD communications. The paper provides a comprehensive analysis of the system performances in terms of outage probability and throughput over multipath Rayleigh fading channels. Furthermore, the optimal time split between the duration of energy harvesting and signal transmission to maximize the system throughput is numerically calculated. We also derive the asymptotic lines to simplify the expressions of outage probability and throughput at high transmit signal-to-noise ratios (SNR). Our analysis and simulation results show that the proposed FD relaying system by utilizing a proper time split fraction can boost the system throughput significantly over an appreciable range of transmitting SNR values, compared to half-duplex (HD) relaying systems.

Performance Analysis of Multi-Cell Full-Duplex Cellular Networks

We analyze the performance of a cellular network, where Poisson point process distributed half-duplex (HD) downlink (DL) and uplink (UL) users are served by multiple full-duplex (FD) base stations (BSs). To address the surge in interference in the network due to the simultaneous operation in time and frequency of the FD BSs, we (a) adopt a self-interference cancellation scheme at each BS, and (b) apply linear interference alignment in each cell to cancel the intra-cell interference. Further, to better capture the distribution of the FD BSs, we model the BSs as a Matérn hard-core point process, in which a minimum distance is imposed between points. The performance of both UL and DL users is analyzed by deriving general expressions and closed-form approximations for the outage probability and throughput. Next, simulations are carried out for both macro and micro cell environments under both FD and HD operations with respect to various network parameters. Our results reveal several fundamental characteristics and the necessary conditions required for the successful deployment of such networks.

Self-Interference Cancellation and Channel Estimation in Multicarrier-Division Duplex Systems With Hybrid Beamforming

Design of full-duplex (FD) wireless systems faces many challenges, including self-interference cancellation (SIC), capability to provide high capacity, high flexibility for operation, best usage of resources, etc. In this paper, we propose and investigate a multicarrier-division duplex (MDD) based hybrid beamforming system operated in FD mode, which is endowed with the advantages of both time-division duplex and frequency-division duplex. It also shares some merits of FD and allows to be free of self-interference (SI) in digital domain, but faces the same challenge of SI as the FD in analog domain. Hence in this paper, we first propose an adaptive beamforming assisted SI cancellation scheme with taking into account the practical requirement of analog-to-digital conversion (ADC). It can be shown that the proposed approach is capable of jointly coping with the desired signals' transmission and SI suppression. Then, channel estimation (CEst) in MDD/MU-MIMO system is proposed by exploiting the reciprocity between the uplink and downlink subcarrier channels that is provided by MDD. Correspondingly, the orthogonality-achieving pilot symbols are designed, and the least-square (LS) CEst as well as linear minimum mean-square error (LMMSE) CEst are derived. Finally, the performance of MDD/MU-MIMO systems employing the proposed SIC method is investigated, with respect to the SI cancellation capability, sum-rate potential, CEst performance, and the effect of CEst on the achievable performance. Our studies show that MDD/MU-MIMO provides an effective option for design of future wireless transceivers.

Optimized self-interference cancellation based on optical dual-parallel MZM for co-frequency and co-time full duplex wireless communication under nonlinear distortion and emulated multipath effect.

Co-frequency and co-time full duplex (CCFD) technique has the potential to further improve the capacity of the fifth-generation (5G) system. However, in a CCFD-based transceiver, the self-interference-cancellation (SIC) module is essential because the transmitted signal is also captured by the receiving antenna. In this paper, an optimized SIC technique is proposed based on a dual-parallel Mach-Zehnder modulator (DP-MZM). In addition to the multipath effect between the transmitting and receiving antennas, the nonlinear distortion induced by the used optical and electrical components is considered and analyzed for the first time. In this scheme, one of the children MZMs is biased at 90°. The bias points of the other child MZM and the parent MZM are swept for SIC optimization. Compared to the traditional SIC scheme using DP-MZM, the power of the received signal is increased by 6 dB and the robustness to the bias point drift is improved. In our experiment, over 35 dB cancellation ratio is achieved for 200 MHz filtered orthogonal frequency division multiplexing (F-OFDM) interference signal with carrier frequency from 2.5 GHz to 6 GHz. To mitigate the influence of multipath effect and nonlinear distortion, the recursive least squared (RLS) linear equalizer and the RLS Volterra equalizer are designed and compared. Finally, 42 dB cancellation ratio is achieved for 200 MHz F-OFDM signal with carrier frequency of 4.5 GHz in the presence of nonlinear distortion and emulated multipath effect.

Self-Interference Cancellation Scheme for Secure AF Satellite Communication Based on FH-MWFRFT

This letter focuses on the self-interference cancellation problem for a secure two-way amplify-and-forward (AF) satellite communication system with eavesdropper at both the transmitter and the receiver. Several multi-antenna earth stations (ESs) aim to exchange messages through a multi-antenna satellite in two hops. We apply the frequency hopping multiple-term weighted fractional fourier transform (FH-MWFRFT) with different transform orders at the earth stations in the first hop to eliminate the self-interference existing in the two-way communication and enhance the security. The second hop of the communication is secured by null space beamforming, which steer the signal to the null space of the eavesdroppers’ channel. We demonstrate the improvement in secrecy capacity brought by the self-interference cancellation scheme via various simulation results and discussions. The simulations are carried out under the conditions of perfect channel state information (CSI) and imperfect CSI to verify the robustness of the proposed scheme.

Perfect Self-Interference Cancellation Based on Mode-Switching for Differential Channel-Unaware Two-Way Relay Networks

We consider channel-unaware two-way relay networks in which two single-antenna nodes exchange information through multiple single-antenna half-duplex amplify-and-forward relays. For these networks, we develop a novel self-interference (SI) cancellation scheme that does not invoke channel information neither at the relays nor at the nodes. Unlike its previous counterparts, the scheme proposed herein enables perfect SI cancellation even when the relays have a single antenna each. This was not possible previously without employing an even number of antennas at each relay. In the first phase of the proposed scheme, the network is operated in a one-way relaying mode, whereas in the second phase it is operated in a two-way relaying mode. In the latter mode, the vectors received by the nodes at the end of the first phase are used to completely eliminate SI, without estimating the channel as in existing methodologies. To analyze the effectiveness of the proposed scheme, we derive upper bounds on the pairwise error probability for the Alamouti and $SP(2)$ codes. Using these bounds, we investigate the dependence of the system performance on the data rate. In addition, we show that for all data rates, the proposed scheme outperforms previously proposed ones. Theoretical results are confirmed by simulations.

Self-Interference Cancellation With Frequency Offset and Nonlinear Distortion Suppression for Cooperative Jamming Communications

Cooperative jamming is envisioned as a key technique to enhance the wireless secrecy. With the help of a cooperative node, confidential communications are ensured by emitting a jamming signal to combat against eavesdropping. Concurrently, this jamming signal also propagates into the legitimate node through the multipath wireless channel, then becomes the self-interference (SI). In this letter, a nonlinear SI cancellation scheme is proposed by jointly taking into account the frequency offset, the power amplifier nonlinearity, and the multipath effect. These practical imperfections induced SI is first formulated based on a memory polynomial model. After a Taylor series expansion to the SI, the time-invariant coefficients from the SI are derived and subsequently estimated to yield a SI cancelling signal. Simulation results show that the proposed scheme has a significant SI cancellation improvement over the current method, and extends the transmit power range to provide a better security performance.