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A novel photonic-assisted multifunctional radar system was proposed and experimentally investigated. This system can simultaneously achieve frequency-doubled linear frequency modulation (LFM) signal generation, de-chirp reception, self-interference cancellation, and frequency measurement in an integrated transmit-receive radar. First, a high-frequency and broadband LO signal was obtained with photonic frequency doubling, which improved the center frequency and bandwidth of the radar detection system. Then, photonic-assisted interference cancellation was used to reduce the impact of interference signals in radar de-chirp reception. Finally, the microwave frequency measurement was achieved by establishing a mapping relationship between the envelope response time of the intermediate frequency (IF) electrical filter and the microwave frequency to be tested. Both theoretical and experimental investigations were performed. The results showed that an LFM signal with a frequency range of 12–18 GHz was obtained with photonic frequency doubling. Photonic-assisted self-interference cancellation reduced the impact of interference signals in radar de-chirp reception by more than 12.1 dB for an LFM signal bandwidth of 6 GHz. In the frequency measurement module, the difference between the frequency to be tested, generated by the external signal source, and that calculated in the experiment is the measurement error, and a measurement resolution better than 14 MHz was achieved in the range of 12.14 GHz–18.14 GHz. The proposed system is suitable for miniaturized multifunctional radar signal processing systems with continuous operation of transmitting and receiving antennas in unmanned aerial vehicles (UAVs), automotive radar, relatively close spatial locations, and so on. In addition, it can simplify the system structure and reduce space occupation. [ABSTRACT FROM AUTHOR]

Recently, reconfigurable intelligent surfaces (RISs) have attracted increasing attentions in the design of full-duplex (FD) systems due to their novel capability of propagation environment reconfiguration. However, in conventional RIS-assisted FD systems, the beamforming for self-interference cancellation (SIC) and sum rate maximization (SRM) are highly coupled during RIS optimization, which significantly degrades the system performance. To tackle this issue, we exploit a novel bilayer intelligent omni-surface (BIOS) structure in FD systems. Compared with the conventional RIS designs, the BIOS provides independent beams on both sides, thus enabling more flexible achievement of SRM and SIC. For the BIOS-assisted FD system, we first formulate an optimization problem to achieve SRM and efficient SIC simultaneously. Then, we exploit the relationship between the SRM and mean square error (MSE), and propose a weighted MSE minimization with SIC algorithm to solve the problem. Specifically, we jointly design the beamforming at the base station and the BIOS with manifold optimization while guaranteeing an SIC constraint. Furthermore, we theoretically derive a lower band for the BIOS size required for efficient SIC in FD systems. Simulation results indicate that the BIOS outperforms the conventional RIS designs in FD systems, and verify the accuracy of the derived lower bound for the BIOS size. [ABSTRACT FROM AUTHOR]

This paper presents the design results for a self-interference canceller (SIC) based on a symmetric delay-line radio frequency finite impulse response (RF-FIR) filter with a ladder structure. The proposed SIC effectively removes self-interference signals in the receiver caused by the low isolation of the circulator applied to the monostatic radar front end and the impedance mismatch of the antenna. Consequently, it enhances the isolation between the transmitter and receiver. The proposed filter consists of six taps with adjustable sizes and phases. The phase-delay values for each filter tap are implemented at a reference frequency of 3.1 GHz. The measurement results demonstrate that the proposed SIC achieves over 25 dB suppression of self-interference signals in the frequency range of 3.05 to 3.22 GHz. When applied to a monostatic radar transceiver with an RF circulator, it exhibits isolation strength of over 50 dB in the frequency range of 3.04 to 3.22 GHz. [ABSTRACT FROM AUTHOR]

With the increasing demand for data exchange between nearby devices in proximity-based services, enhancing the security of wireless mutual broadcast (WMB) networks is crucial. However, WMB networks are inherently vulnerable to eavesdropping due to the open broadcast nature of their communication. This paper investigates the improvement of secrecy performance in random-access-based WMB (RA-WMB) networks by integrating physical layer security (PLS) techniques with hybrid duplex (HBD) operations under a stochastic geometry framework. The HBD method balances half-duplex (HD) receiving and full-duplex (FD) transceiving, utilizing self-interference cancellation (SIC) to enhance PLS performance. Key operational parameters, including transmission probability (TxPr), friendly jammer density, and conditions for FD operation, are designed to maximize secrecy performance. The analytical and numerical results demonstrate significant improvements in PLS performance, with SIC playing a critical role, particularly in scenarios with dense legitimate nodes, and with TxPr adjusted to balance HD receiving and FD transceiving based on SIC imperfections. The proposed design principles provide a comprehensive framework for enhancing the security of WMB networks, addressing the complex interplay of interference and SIC in various network configurations. [ABSTRACT FROM AUTHOR]

Collision detection is a fundamental problem in the field of human-machine interaction. Inaccurate robotic models caused by unknown loads significantly impact the sensitivity of collision detection and can even result in algorithm failures. This study proposes a collision detection method, inspired by the concept of "interference cancellation" in communication, to overcome the limitations of existing methods in eliminating the influence of unknown loads. The method is based on the self-interference cancellation extended state observer (SICESO). The method establishes a relationship between the output of a feedback control system and the state of robotic motion through dynamics. Computational efficiency is enhanced by employing a reduced-order extended state observer (ESO) to construct an external force observer. The internal disturbance influence caused by dynamic model errors is removed by appropriately setting the observation positions of ESOs based on the delay response characteristics between the physical system and the control commands. The proposed method achieves accurate estimation of external forces independent of the load. Experimental results demonstrate that the proposed method effectively eliminates the influence of unknown loads, achieves collision detection within 0.001s, and accurately estimates external forces with an accuracy of 10−2 Nm. The proposed method has significantly improved sensitivity and robustness. [ABSTRACT FROM AUTHOR]

Combined in-band full duplex-multiple input multiple output (IBFD–MIMO) technology can significantly improve spectrum efficiency and data throughput, and has broad application prospects in communications, radar, the Internet of Things (IoT), and other fields. Targeting the self-interference (SI) issue in microwave photonic-based IBFD–MIMO communication systems, a microwave photonic self-interference cancellation (SIC) method applied to the narrowband 2 × 2 IBFD–MIMO communication system was proposed, simulated, and analyzed. An interleaver was used to construct a polarization multiplexing dual optical frequency comb with a frequency shifting effect, generating a dual-channel reference interference signal. The programmable spectrum processor was employed for filtering, attenuation, and phase-shifting operations, ensuring amplitude and phase matching to eliminate the two self-interference (SI) signals. The simulation results show that the single-frequency SIC depth exceeds 45.8 dB, and the narrowband SIC depth under 30 MHz bandwidth exceeds 32.7 dB. After SIC, the desired signal, employing a 4QAM modulation format, can be demodulated with an error vector magnitude (EVM) as low as 4.7%. Additionally, further channel expansion and system performance optimization are prospected. [ABSTRACT FROM AUTHOR]

Simultaneous transmit and receive wireless communications have been highlighted for their potential to double the spectral efficiency. However, it is necessary to mitigate self-interference (SI). Considering both the SI channel and remote transmission (RT) channel need to be estimated before equalizing the received signal, we propose two adaptive algorithms for linear and nonlinear self-interference cancellation (SIC), based on a multi-layered joint channel estimator structure. The proposed algorithms estimate the RT channel while performing SIC, and the multi-layered structure ensures improved performance across various interference-to-signal ratios. The M-estimate function enhances the robustness of the algorithm, allowing it to converge even when affected by impulsive noise. For nonlinear SIC, this paper introduces an adaptive algorithm based on generalized Hammerstein polynomial basis functions. The simulation results indicate that this approach achieves a better convergence speed and normalized mean squared difference compared to existing SIC methods, leading to a lower system bit error rate. [ABSTRACT FROM AUTHOR]

This paper introduces a novel spatial domain-based self-interference cancellation (SIC) method named constrained minimum mean square error (C-MMSE) for massive multiple-input multiple-output (mMIMO) full-duplex (FD) communication systems. The main idea involves treating the self-interference (SI) signal emitted from an FD node as a distinct spatial stream arriving at the receiver part of that same FD node. This SI signal needs to be spatially postcoded alongside other relevant signals coming from different transmitters, ensuring it falls into the null space of the MIMO channel, which includes the FD node transmitter part as an input. To establish this approach, we first adapt the expressions of spatial combiners for conventional zero forcing (ZF) and minimum mean square error combining (MMSE) criteria. We demonstrate that MMSE alone is insufficient for efficient SI signal cancellation unless an additional constraint is added to enable proper SIC. Consequently, we design the innovative C-MMSE combiner and derive its expression. In addition to our proposal, the originality of our work stems from employing a spherical wave model (SWM) to model the SI channel. The choice is justified by the proximity of the transmit and receive antenna panels in the FD node. We examine and compare the SIC performance of the modified ZF combiner, the modified MMSE combiner, and the newly introduced C-MMSE combiner by evaluating the spectral efficiency (SE). Additionally, we highlight the robustness of the SWM-based SI channel modeling in comparison to conventional planar wave modeling (PWM), emphasizing the relevance of its usage.

A novel photonic-assisted multifunctional radar system was proposed and experimentally investigated. This system can simultaneously achieve frequency-doubled linear frequency modulation (LFM) signal generation, de-chirp reception, self-interference cancellation, and frequency measurement in an integrated transmit-receive radar. First, a high-frequency and broadband LO signal was obtained with photonic frequency doubling, which improved the center frequency and bandwidth of the radar detection system. Then, photonic-assisted interference cancellation was used to reduce the impact of interference signals in radar de-chirp reception. Finally, the microwave frequency measurement was achieved by establishing a mapping relationship between the envelope response time of the intermediate frequency (IF) electrical filter and the microwave frequency to be tested. Both theoretical and experimental investigations were performed. The results showed that an LFM signal with a frequency range of 12–18 GHz was obtained with photonic frequency doubling. Photonic-assisted self-interference cancellation reduced the impact of interference signals in radar de-chirp reception by more than 12.1 dB for an LFM signal bandwidth of 6 GHz. In the frequency measurement module, the difference between the frequency to be tested, generated by the external signal source, and that calculated in the experiment is the measurement error, and a measurement resolution better than 14 MHz was achieved in the range of 12.14 GHz–18.14 GHz. The proposed system is suitable for miniaturized multifunctional radar signal processing systems with continuous operation of transmitting and receiving antennas in unmanned aerial vehicles (UAVs), automotive radar, relatively close spatial locations, and so on. In addition, it can simplify the system structure and reduce space occupation.

Recently, reconfigurable intelligent surfaces (RISs) have attracted increasing attentions in the design of full-duplex (FD) systems due to their novel capability of propagation environment reconfiguration. However, in conventional RIS-assisted FD systems, the beamforming for self-interference cancellation (SIC) and sum rate maximization (SRM) are highly coupled during RIS optimization, which significantly degrades the system performance. To tackle this issue, we exploit a novel bilayer intelligent omni-surface (BIOS) structure in FD systems. Compared with the conventional RIS designs, the BIOS provides independent beams on both sides, thus enabling more flexible achievement of SRM and SIC. For the BIOS-assisted FD system, we first formulate an optimization problem to achieve SRM and efficient SIC simultaneously. Then, we exploit the relationship between the SRM and mean square error (MSE), and propose a weighted MSE minimization with SIC algorithm to solve the problem. Specifically, we jointly design the beamforming at the base station and the BIOS with manifold optimization while guaranteeing an SIC constraint. Furthermore, we theoretically derive a lower band for the BIOS size required for efficient SIC in FD systems. Simulation results indicate that the BIOS outperforms the conventional RIS designs in FD systems, and verify the accuracy of the derived lower bound for the BIOS size.

With the increasing demand for data exchange between nearby devices in proximity-based services, enhancing the security of wireless mutual broadcast (WMB) networks is crucial. However, WMB networks are inherently vulnerable to eavesdropping due to the open broadcast nature of their communication. This paper investigates the improvement of secrecy performance in random-access-based WMB (RA-WMB) networks by integrating physical layer security (PLS) techniques with hybrid duplex (HBD) operations under a stochastic geometry framework. The HBD method balances half-duplex (HD) receiving and full-duplex (FD) transceiving, utilizing self-interference cancellation (SIC) to enhance PLS performance. Key operational parameters, including transmission probability (TxPr), friendly jammer density, and conditions for FD operation, are designed to maximize secrecy performance. The analytical and numerical results demonstrate significant improvements in PLS performance, with SIC playing a critical role, particularly in scenarios with dense legitimate nodes, and with TxPr adjusted to balance HD receiving and FD transceiving based on SIC imperfections. The proposed design principles provide a comprehensive framework for enhancing the security of WMB networks, addressing the complex interplay of interference and SIC in various network configurations.

A new method for capacity and spectral efficiency increases is a full-duplex communication, where sending and receiving are done simultaneously. Hence, severe interference leaked from the transmitter to the receiver, which can disrupt the system's operation completely. For interference reduction, the transceiver tries to estimate the interfering symbols to remove their effects. A typical method is to use the Hammerstein model. In this method, nonlinear power amplifier (PA) and multipath channel are modeled with a successive nonlinear system and a finite impulse response filter. Then, the model parameters are adjusted, and interference symbols are estimated from the transmitted symbols. In the Hammerstein method, the interference symbols are estimated directly from the transmitted symbols. But practically, the transmitted symbols first pass through the pulse-shaping filter and become a signal. Then, this signal passes through the nonlinear PA and communication channel. Finally, the received signal is filtered by the matched filter (MF) at the receiver and converted to the symbols again. In this procedure, the amplifier and the communication channel affect the transmitted signal directly and distort transmitted symbols indirectly. Therefore, in the practical situation, when we consider the transmitter's pulse-shaping filter and the receiver's MF, the estimated symbols with the Hammerstein method are erroneous. To solve this problem, a new MF at the receiver is proposed and adjusted according to the interfering signal. We have shown that this method is far better than the Hammerstein method. [ABSTRACT FROM AUTHOR]

This paper proposes a Self-interference (SI) cancellation system model of Underwater acoustic (UWA) communication for in-band full-duplex (IBFD) technology. The SI channel is separated from the Far channel by exploiting a concurrently orthogonal pilot channel estimation technique using two orthogonal frequency-division multiplexing (OFDM) blocks to establish orthogonality between them based on a unitary matrix. Compared to the half-duplex channel estimator, the mean squared error (MSE) and the bit error rate (BER) provided strong evidence for the efficiency of the proposed SI cancellation. Since full-duplex systems are more efficient than half-duplex ones, the proposed approach might be seen as a viable option for them. The proposed method proved effective when used with a fixed full-duplex (FD) position and FD shifting of up to 4°. Different channel lengths and distances are adopted to evaluate the proposed method. Initial findings indicate that MSE for the SI channel minimum mean-square error (MMSE) estimator at 20 dB is 0.118 · 10−3, for fixed FD. In addition, this paper presents a geometry channel model for the Far channel in the IBFD underwater communication system that describes the propagation delay of the multipath reflection. The simulation results for the multipath propagation delay spread are similar to the traditional results, with the delay spread of the suggested model reaching (79 ms), which is close to the Bellhop simulator result (78 ms).

In-band full-duplex (IBFD) communications is a promising technique to achieve spectral-efficient communication in the underwater environment. To achieve IBFD underwater communications, suppression of self-interference (SI) is a prerequisite. In this paper, SI suppression using physical separation and digital SI cancellation is investigated under different transmitter-receiver geometries. An iterative IBFD receiver combining joint channel estimation, SI cancellation, and multichannel decision feedback equalizer is developed. Due to the potential deterioration of the channel estimation accuracy, a digital SI cancellation control mechanism is used to regulate the suppression process. The feasibility of coherent IBFD underwater acoustic communications was tested in a lake environment. The two SI suppression methods, the SI cancellation control mechanism, and the receiver performance were evaluated using the experimental measurements. A bit error rate (BER) in the order of $10^{-2}$ was achieved at the range of 80 m for IBFD communications.

This study proposes a heterogeneous in-band full-duplex system for the simultaneous transmission of the existing wireless smart ubiquitous network (Wi-SUN) using IEEE 802.15.4g-compliant frequency-shift keying for smart utility network (SUN-FSK) and reception of the next-generation Wi-SUN using IEEE 802.15.4-2020-compliant orthogonal frequency-division multiplexing for SUN (SUN-OFDM). In particular, we propose a digital self-interference (SI) cancellation scheme based on high-precision SI channel estimation using the moving average method, which can be used when the SI signal is a SUN-FSK signal and the desired signal is a SUN-OFDM signal. Furthermore, we propose a highly efficient SUN-OFDM demodulation technique that considers the effect of residual SI. We evaluate the proposed methods through computer simulations. The proposed methods can achieve 67 dB of SI cancellation in the digital domain when the SI signal power and desired signal power ratio in the digital domain is 50 dB. The results of this study enable more efficient coexistence of the existing and next-generation Wi-SUNs, which is expected to improve the throughput and responsiveness of next-generation Wi-SUN systems employing SUN-OFDM.

In this paper, a photonic-enabled image rejection mixer (IRM) that features an ultrawideband self-interference cancellation (SIC) function and a compact configuration is proposed. The parameter tuning of SIC is realized in an optical domain, which avoids the use of electrically tuned devices with limited bandwidth and precision, so that high-precision parameter matching can be realized in the optical domain to realize deep and ultrawideband SIC. The key point of image rejection (IR) is to construct a pair of orthogonal local oscillation (LO) signals through DC-bias-induced phase shift. This not only avoids a high-frequency electrical 90-degree hybrid coupler (HC) applied in the traditional Hartley structure, but also compensates the phase deviation in the electrical intermediate frequency (IF) 90-degree HC flexibly, ensuring wideband and deep IR operation. The simulation results show that the proposed IRM can achieve ultrawideband SIC and IR with the simultaneous high-efficiency recovery of useful signals. They also verify that the scheme has good resistance to strong interference, and can cope with the phase imbalance of the IF 90-degree electrical HC, ensuring the good performance of the system, which has a wide application prospect in various in-band full-duplex (IBFD) systems. [ABSTRACT FROM AUTHOR]

This paper employs a self-interference cancellation (IBFD-UWA) system for shallow-water acoustic channels by depending on the model of communication channel for SI cancellation, which is based on geometry to accommodate any possible changes in the underwater environment. UWA channels have propagation characteristics based on the configurations of straight and multi-direction mirrors between a transmitter and a receiver. This propagation at the node itself and between the two nodes to transfer information between the nodes operating in the IBFD mode, orthogonal frequency division multiplex (OFDM) modulation with quadrature phase-shift keying (QPSK) mapping. By using numerical simulations, it can be shown that the developed model is able to accurately describe the underwater acoustic environment. The results indicate that local multipath propagation delays can exceed 1.4s with transmission losses of up to 80dB, and the SIC requires about 4 seconds to reduce SI signals to background noise levels successfully.

Simultaneous transmit and receive wireless communications have been highlighted for their potential to double the spectral efficiency. However, it is necessary to mitigate self-interference (SI). Considering both the SI channel and remote transmission (RT) channel need to be estimated before equalizing the received signal, we propose two adaptive algorithms for linear and nonlinear self-interference cancellation (SIC), based on a multi-layered joint channel estimator structure. The proposed algorithms estimate the RT channel while performing SIC, and the multi-layered structure ensures improved performance across various interference-to-signal ratios. The M-estimate function enhances the robustness of the algorithm, allowing it to converge even when affected by impulsive noise. For nonlinear SIC, this paper introduces an adaptive algorithm based on generalized Hammerstein polynomial basis functions. The simulation results indicate that this approach achieves a better convergence speed and normalized mean squared difference compared to existing SIC methods, leading to a lower system bit error rate.

Combined in-band full duplex-multiple input multiple output (IBFD–MIMO) technology can significantly improve spectrum efficiency and data throughput, and has broad application prospects in communications, radar, the Internet of Things (IoT), and other fields. Targeting the self-interference (SI) issue in microwave photonic-based IBFD–MIMO communication systems, a microwave photonic self-interference cancellation (SIC) method applied to the narrowband 2 × 2 IBFD–MIMO communication system was proposed, simulated, and analyzed. An interleaver was used to construct a polarization multiplexing dual optical frequency comb with a frequency shifting effect, generating a dual-channel reference interference signal. The programmable spectrum processor was employed for filtering, attenuation, and phase-shifting operations, ensuring amplitude and phase matching to eliminate the two self-interference (SI) signals. The simulation results show that the single-frequency SIC depth exceeds 45.8 dB, and the narrowband SIC depth under 30 MHz bandwidth exceeds 32.7 dB. After SIC, the desired signal, employing a 4QAM modulation format, can be demodulated with an error vector magnitude (EVM) as low as 4.7%. Additionally, further channel expansion and system performance optimization are prospected.

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity and harmonic frequency down-conversion function is proposed based on an integrated, dual-parallel, dual-drive Mach–Zehnder modulator (DP-DMZM). A dual-drive Mach–Zehnder modulator (DMZM) is used as an optical interference canceller, which cancels the self-interference from the impaired signal before fiber transmission to avoid the effect of fiber transmission on the cancellation performance. Another DMZM is used to provide carrier-suppressed, local-oscillation (LO)-modulated, high-order double optical sidebands for harmonic frequency down-conversion to release the strict demand for high-frequency LO sources. By regulating the DC bias of the main modulator, the signal of interest (SOI) can be down-converted to the intermediated frequency (IF) band after photoelectric conversion with improved frequency-conversion efficiency, immunity to the fiber-dispersion-induced power-fading (DIPF) effect, and effective signal recovery. Theoretical analyses and simulation results show that the desired SOI in the X and K bands with a bandwidth of 500 MHz and different modulation formats can be down-converted to the IF frequency. The self-interference noise with the 2 GHz bandwidth is canceled, and successful signal recovery is achieved after a 10 km fiber transmission. The recovery performance of down-converted signals and the self-interference cancellation depth under different interference-to-signal ratios (ISRs) is also investigated. In addition, the compensation performance of DIPF is verified, and a 6 dB improvement in frequency conversion gain is obtained compared with previous work. The proposed scheme is compact, cost-effective, and thus superior in wideband self-interference cancellation, long-range signal transmission, and effective recovery of weak desired signals. [ABSTRACT FROM AUTHOR]

Cetaceans show high cognitive abilities and strong social bonds. Their primary sensory modality to communicate and sense the environment is acoustics. Research on their echolocation and social vocalizations typically uses visual and tactile systems adapted from research on primates or birds. Such research would benefit from a purely acoustic communication system to better match their natural capabilities. We argue that a full duplex system, in which signals can flow in both directions simultaneously is essential for communication research. We designed and implemented a full duplex system to acoustically interact with cetaceans in the wild, featuring digital echo-suppression. We pilot tested the system in Arctic Norway and achieved an echo suppression of 18 dB. We discuss the limiting factors and how to improve the echo suppression further. The system enabled vocal interaction with the underwater acoustic scene by allowing experimenters to listen while producing sounds. We describe our motivations, then present our pilot deployment and give examples of initial explorative attempts to vocally interact with wild orcas and humpback whales. [ABSTRACT FROM AUTHOR]

In this paper, we propose a wideband Full Duplex (FD) Multiple-Input Multiple-Output (MIMO) communication system comprising of an FD MIMO node simultaneously communicating with two multi-antenna UpLink (UL) and DownLink (DL) nodes utilizing the same time and frequency resources. To suppress the strong Self-Interference (SI) signal due to simultaneous transmission and reception in FD MIMO systems, we propose a joint design of Analog and Digital (A/D) cancellation as well as transmit and receive beamforming capitalizing on baseband Orthogonal Frequency-Division Multiplexing (OFDM) signal modeling. Considering practical transmitter impairments, we present a multi-tap wideband analog canceller architecture whose number of taps does not scale with the number of transceiver antennas and multipath SI components. We also propose a novel adaptive digital cancellation based on truncated singular value decomposition that reduces the residual SI signal estimation parameters. To maximize the FD sum rate, a joint optimization framework is presented for A/D cancellation and digital beamforming. Finally, our extensive waveform simulation results demonstrate that the proposed wideband FD MIMO design exhibits higher SI cancellation capability with reduced complexity compared to existing cancellation techniques, resulting in improved achievable rate performance. [ABSTRACT FROM AUTHOR]

As the impairments of hardware circuits, such as the nonlinearities of power amplifiers (PAs), limit the self-interference suppression performance in full-duplex systems, nonlinear self-interference cancellation (SIC) has attracted much research attention. According to some existing studies, nonlinear SIC in full-duplex systems can be implemented with either nonlinear modeling or radio frequency (RF) signal feedback. However, to the best of our knowledge, there is no theoretical analysis and comparison of the cancellation performance with the two methods. In this paper, the performance of the digital nonlinear SIC with RF signal feedback and nonlinear modeling is analyzed and compared for the first time. The theoretical SIC capabilities of the two methods are derived, and the closed-form solutions are obtained. The factors affecting the performance of the two methods are discussed with the theoretical analysis. Then, by simulations, the theoretical results are verified and the performances of the nonlinear SIC with the two methods are compared in different environments. [ABSTRACT FROM AUTHOR]

This paper describes a 26-GHz fully integrated In-band Full-duplex Circulator (IBFD) Receiver (RX), which employs passive and active Self-interference Cancellation (SIC) techniques in the mm-wave domain. Coverage of wireless networks at mm-wave frequencies can be enhanced by deploying a large number of base stations economically based on Integrated Access and Backhaul (IAB) relays and repeaters. However, to retain the channel capacity, IAB needs to be implemented using full-duplex schemes that suffer from a strong Transmitter (TX) to RX SI. This SI leakage can significantly impact the receiver sensitivity and increase the baseband/ADC dynamic range requirements. Canceling SI at mm-wave applications is particularly challenging given the high frequency of operation, wide bandwidth, and antenna (ANT) impedance sensitivity to the surroundings. Proposed mm-wave RX with a shared ANT interface based on a circulator with active SI cancelers provide ~53 dB SIC over 400 MHz and ~40 dB SIC over 400 MHz in mm-wave domain to meet the link budget requirements. Proposed architecture achieves SIC by (i) introducing a shared ANT interface based on a hybrid-coupler and a non-reciprocal delay line that provides wideband SIC and additionally creates a SI replica (ii) subsequent active cancellation using SI replica processed with variable gain amplifiers and phase shifters. This system also accommodates SI channel variations due to surroundings. Proposed 26-GHz circulator RX has >100x better SIC at high TX power (>10dBm) levels in comparison to the state-of-the-art and it consumes ~111 mW power. The system is implemented in 45nm SOI CMOS and has an active area of $4.54\, mm^{2}$ . Stand-alone RX NF is ~5.8 dB and TX to ANT insertion loss (IL) is ~3.1 dB. Over-the-air measurements with modulated TX (128 QAM 2.1 Gb/s) and RX (128 QAM 4.2 Gb/s) signals show an EVM of 3.3%.

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’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.

This work introduces a novel full-duplex hybrid beamforming (FD-HBF) technique for the millimeter-wave (mmWave) multi-user massive multiple-input multiple-output (MU-mMIMO) systems, where a full-duplex (FD) base station (BS) simultaneously serves half-duplex (HD) downlink and uplink user equipments over the same frequency band. Our main goal is jointly enhancing the downlink/uplink sum-rate capacity via the successful cancellation of the strong self-interference (SI) power. Furthermore, FD-HBF remarkably reduces the hardware cost/complexity in the mMIMO systems by interconnecting the radio frequency (RF) and baseband (BB) stages via a low number of RF chains. First, the RF-stage is constructed via the slow time-varying angular information, where two schemes are proposed for both maximizing the intended signal power and canceling the SI power. Particularly, orthogonal RF beamformer (OBF) scheme only aims canceling the far-field component of SI, while non-orthogonal RF beamformer (NOBF) scheme applies perturbations to the orthogonal beams for also suppressing the near-field component of SI channel. Considering the high computational complexity during the search for optimal perturbations, we apply swarm intelligence to find the optimal perturbations. Second, the BB-stage is designed based on only the reduced-size effective intended channel matrices, where the BB precoder/combiner solutions are obtained via regularized zero-forcing (RZF) and minimum mean square error (MMSE). Hence, the proposed FD-HBF technique does not require the instantaneous SI channel knowledge. It is shown that FD-HBF with NOBF+MMSE achieves 78.1 dB SI cancellation (SIC) on its own. Additionally, FD-HBF with the practical antenna isolation can accomplish more than 130 dB SIC and reduce the SI power below the noise floor. The numerical results present that FD-HBF greatly improves the sum-rate capacity by approximately doubling it compared to its HD counterpart.

In-band full-duplex (IBFD) systems can double the spectral efficiency by enabling simultaneous transmission and reception within the same band. Key to realizing full-duplex radios is the cancellation of the self-interference (SI) that couples from the transmitting antenna into the receiving path. This is done by introducing a self-interference cancellations (SIC) circuit to significantly reduce the coupled transmit signal and avoid receiver’s desensitization. Additionally, SI suppression becomes more challenging across broader bandwidths. This paper presents a novel, wideband, and low profile SIC circuit based on a hybrid Finite Impulse Response (FIR) and resonator filter topology. The latter is optimized to provide an average of 22dB cancellation across 800MHz in the L-band. Conventional, SIC circuits require a filter bank with at least two FIR filters to achieve such a wide bandwidth. Conversely, our FIR resonator design is low profile with a circuit size nearly half of that of a filter bank. Simulations show a minimum cancellation of 15dB and a maximum cancellation of 45dB. A prototype was fabricated and tested, showing an average of $\sim ~20$ dB cancellation which is in good agreement with our simulation. Further, measured results show a minimum cancellation of 15dB and maximum cancellation of 27dB.

The aperture-level simultaneous transmit and receive (ALSTAR) system uses full digital architecture with an observation channel to achieve remarkably effective isotropic isolation (EII). However, the number of observation channels must be the same as the number of transmit channels, which increases the system's complexity. To balance the system cost and performance of the ALSTAR, this paper proposes a joint design of sparse arrays and beamforming, which are achieved by a genetic algorithm and an alternating optimization algorithm, respectively. In the sparse design, we introduce beamforming technology to guarantee the EII while decreasing the corresponding elements of observation channel that contribute slightly to the EII. The simulation results are presented for a 32-element array that achieves 185.87 dB of the EII with 1000 W of transmit power. In the cases of sparsity rates at 0.875 and 0.75 (≥0.6), i.e., the number of observation channels decreases by 12.5% (2/16) and 25% (4/16), the reductions in EII do not exceed 1 dB and 3 dB, respectively. However, the EII decreases rapidly with a sparsity rate less than 0.25. Results demonstrate that our proposed joint design of sparse arrays and beamforming can reduce the system cost with little performance loss of EII. [ABSTRACT FROM AUTHOR]

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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.

In this paper, a photonic-enabled image rejection mixer (IRM) that features an ultrawideband self-interference cancellation (SIC) function and a compact configuration is proposed. The parameter tuning of SIC is realized in an optical domain, which avoids the use of electrically tuned devices with limited bandwidth and precision, so that high-precision parameter matching can be realized in the optical domain to realize deep and ultrawideband SIC. The key point of image rejection (IR) is to construct a pair of orthogonal local oscillation (LO) signals through DC-bias-induced phase shift. This not only avoids a high-frequency electrical 90-degree hybrid coupler (HC) applied in the traditional Hartley structure, but also compensates the phase deviation in the electrical intermediate frequency (IF) 90-degree HC flexibly, ensuring wideband and deep IR operation. The simulation results show that the proposed IRM can achieve ultrawideband SIC and IR with the simultaneous high-efficiency recovery of useful signals. They also verify that the scheme has good resistance to strong interference, and can cope with the phase imbalance of the IF 90-degree electrical HC, ensuring the good performance of the system, which has a wide application prospect in various in-band full-duplex (IBFD) systems.

In this paper, we combine two new techniques: non-orthogonal multiple access (NOMA) and full-duplex (FD) in a downlink of wireless cooperative relay communication system with two end users. The NOMA approach is applied to both the source and the relay. Whereas, the FD is only applied to the relay. The system performance is investigated in the case of vehicle-to-vehicle (V2V) communication. The self-interference (SI) due to FD protocol is taken into consideration, and then the outage probability (OP) and ergodic capacity (EC) of the considered FD-NOMA-V2V system are derived over the double Rayleigh fading channels. Furthermore, an impact of distance between the vehicles and a path loss exponent on the system performance is discussed. The numerical results show that the system performance strongly decreases in comparison with that over the Rayleigh fading channel, and the SI lets the performance of the considered system decrease significantly. Due to the FD mode and NOMA scheme, the system performance in terms of OP and EC reaches the floor at the high signal-to-noise ratio (SNR) region. Based on the distance between the vehicles, the path loss exponent and the residual self-interference (RSI), the power allocation coefficients is decided in the sense of similar performance of both users in the cooperative FD-NOMA-V2V system. Additionally, we can choose locations of the relay to achieve the best performance of the considered system. Finally, the perfect match between the theoretical and simulation results validates our proposed method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In-band full-duplex (IBFD) technology has the potential to not only double the communication throughput but also enable additional capabilities. The fusion of radar and communication subsystems is an excellent example of how IBFD facilitates integration of radar functionality into a communication system. Developing and analysis of a joint IBFD radar-communication (RadCom) system is at the core of this article. This system derives the range-Doppler image from the state of an adaptive filter, which already exists in a typical IBFD transceiver. Our approach is waveform-independent and reuses the radio frequency (RF) front-end while it requires little additional digital logic. The proposed system is prototyped to assess the modem-radar coexistence in a real-world IBFD communication link budget. Employing the prototyped system, we quantify the additional required logic resources and investigate whether such a RadCom approach dictates a tradeoff between the two intended functionalities. The experimental results show that the proposed solution enables a communication system to detect targets within 20 m while maintaining an IBFD link with another communication node. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper reports a bi-port, wideband, parasitic-fed, single/shared patch antenna with enhanced interport isolation for 2.4 GHz in-band full duplex (IBFD) applications. The employed parasitic feeding provides comparatively the wider impedance bandwidth and better gain for the presented antenna. The improved self-interference cancellation (SIC) levels across the required bandwidth are obtained through differentially-driven receive (Rx) mode operation. The differential Rx operation performs effective cancellation of in-band self-interference (SI) through signal inversion mechanism to achieve the additional isolation on the top of the intrinsic isolation of polarization diversity. The validation model for the presented antenna features ≥88 dB peak isolation between the dual-polarized Tx and Rx ports. In addition, the measured Tx–Rx isolation for prototype is >70 dB across the 10 dB return loss bandwidth of 100 MHz (2.42–2.52 GHz). The measured gain for each mode is better than 7.0 dBi. The novelty of this work is that compared to previously reported designs, the presented antenna offers wider impedance bandwidth and improved SIC levels in addition to superior gain performance. To the best of our knowledge, this is the first single/shared patch antenna which provides better than 70 dB interport isolation across the 10 dB return loss bandwidth of 100 MHz along with 7.0 dBi gain for Tx/Rx modes. [ABSTRACT FROM AUTHOR]

This paper studies a solution for efficient industrial Internet of things (IIoT) communications through an in-band full-duplex (IBFD) enabled private 5G network in frequency range 2 (FR2) band ( $\geq 24.250$ GHz), where ultra-reliable low-latency communications (URLLC) and enhanced mobile broadband (eMBB) devices can be simultaneously served. Large-scale antenna array and RF beamforming are applied, and a self-interference cancellation (SIC) scheme is proposed under such architecture. Particularly, the proposed RF cancellation scheme addressed two key issues of extending current technologies to wideband operations in FR2 band: limited operational bandwidth and the requirement for a large number of cancellers. Then, a frequency domain-based digital canceller is proposed to process with the residual self-interference (RSI) with short processing latency. A game theoretic user allocation algorithm is proposed to minimise co-channel interference (CCI) in a heterogeneous environment. Given a typical IIoT scenario, the performance of such IBFD private 5G network is evaluated in terms of bit error rate (BER) and spectral efficiency (SE) through simulations and analysed based on numerical results and theoretical calculations. It is demonstrated that the latency of uplink eMBB devices can be reduced by 54% through IBFD radios, and the latency of downlink URLLC devices can be reduced to 0.5 ms with the help of flexible numerology, mini-slot, and self-contained sub-frames introduced in 5G NR. IBFD radios can enhance the SE by 92% compared to HD radios with our SIC and user allocation policy. The high SE in conjunction with abundant resources in FR2 band provides multi-Gbps peak data rates, high reliability, and massive connectivity.

In-band full-duplex (IBFD) is an attractive solution for increasing the throughput of Power Line Communication (PLC) systems. In IBFD, each network node is allowed to transmit and receive simultaneously in the same frequency band. This paper discusses the importance of defining figures of merit to analyze IBFD performance, which is often forgotten by the literature that addresses IBFD from a pure system level and signal processing perspective. This is because in IBFD hardware-related aspects are of great importance. The focus is then given to the first self-interference (SI) cancellation stage, namely the analog coupling and self-interference cancellation stage (ASICS). Two architectures are considered. A detailed analysis is offered by taking into account circuit-level aspects. A broadband multiple conductor PLC scenario is assumed to enable multiple-input multiple-output (MIMO) IBFD communication. The first considered architecture performs SI subtraction exploiting operational amplifiers. The second proposed architecture exploits the characteristics of a three ports magnetic circuit together with a signal generator to remove the SI. Design, analysis, and hardware realization of these circuits have been done to compare and show the practical feasibility of the ASICS for PLC, well known to be challenged by its line impedance matching problems and severe frequency selective channel characteristics. This paper is the first documented contribution of the IBFD ASICS for $2\times 2$ MIMO broadband PLC physically realized and tested in the field.

In this paper, we propose a closely spaced two-port microstrip patch antenna system with significant isolation enhancement (> 90 dB), which can be deployed for MIMO as well as full-duplex transceiver systems. We deploy a resonant combination of rectangular defected ground structure (DGS) and a near-field decoupling structure (NFDS) in the vicinity of a closely spaced (inter-element spacing $= {0.01\lambda _{0}}$ ) two-port microstrip patch antenna system at 5.85 GHz. This drastically reduces the port-to-port mutual coupling (< −90 dB), which can help in self-interference cancellation for full-duplex point of view without any additional circuitry, while still preserving desired impedance matching performance (< −15 dB). The broadside gain of individual antennas in the two port MIMO system is 7.11 dBi, with 97% efficiency and co-to-cross-polar level < 25 dB. The proposed concept is validated by full-wave simulation in CST Microwave Studio, as well as experimental results on fabricated prototype. Moreover, MIMO performance metrics such as total active reflection coefficient (TARC), envelop correlation coefficient (ECC) and channel capacity loss (CCL) are analysed using simulation and measurement.

This paper presents a $0.2\sim 3.8$ -GHz in-band (IB) full-duplex (FD) mixer-first receiver based on a vector self-interference (SI) canceller. To ensure the wideband orthogonality of the reconstructed SI signal while minimizing the noise figure (NF) degradation in FD mode, a low insertion loss two-stage polyphase filter (PPF) with a lacking resistance and capacitance (LRC) structure is used in the SI canceller. A 6-bits passive capacitor digital to analog converter (C-DAC) attenuator not only realizes the high-precision amplitude adjustment of the reconstructed SI signal but also avoids the linearity limitation of the back-end modules of the canceller and reduces the noise contribution of the front-end modules at the canceller output. A four-phase mixer-first receiver with enhanced out-of-band (OOB) interference suppression is designed to provide sufficient linearity to reduce the SI-induced nonlinear distortion. As a proof of concept, a prototype FD receiver is fabricated in CMOS 65 nm technology and measured in chip-on-board (COB) package. Measurement results show that it can operate in the frequency range of $0.2\sim 3.8$ -GHz with more than 25 dB SIC amount for 10 MHz bandwidth (BW) 64-QAM modulated signals in fixed (30 dB) channel attenuation test setup. The receiver achieves OOB input-referred third-order intercept point (OOB-IIP3) of +24 dBm and OOB input-referred second-order intercept point (OOB-IIP2) of +82 dBm at 1-GHz local oscillator (LO) frequency. In FD mode, the NF degradation is $\leqslant 1.5$ dB. The effective IB-IIP3 and effective IB-IIP2 are enhanced by 15 dB and 28 dB, respectively. The power consumption of entire FD receiver including the SI canceller is less than 44 mW. The active chip area is 0.55 mm2.

In this paper, we investigate the usage of a nonlinear energy harvester at a full-duplex (FD) relay, which can harvest the energy from radio frequency (RF) signals transmitted from the source. We mathematically derive the exact closed-form expressions of outage probability (OP), throughput, and average symbol error rate (ASER) of the nonlinear energy harvester-wireless information and power transfer-FD relaying (N-WIPT-FDR) system over Rayleigh fading channels. Unlike linear energy harvester, nonlinear energy harvester results in more computational complexity. Furthermore, it makes the outage floor happen faster even when self-interference cancellation (SIC) techniques are effectively applied due to the saturation power threshold of the nonlinear energy harvester. The combination of nonlinear energy harvester characteristic and residual self-interference (RSI) has significant impacts on the OP, throughput, and ASER of the considered N-WIPT-FDR system. On the other hand, there is an optimal energy harvesting (EH) time duration, which minimizes the OP. This optimal value depends on the transmission power of the source and the saturation power threshold of the nonlinear energy harvester. Monte-Carlo simulations are conducted to validate the derived mathematical expressions.

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.

In this paper, we investigate a two-hop communication system in which the source utilizes radio frequency (RF) energy harvesting for the transmission of information. An intermediate relay works in a half-duplex (HD) mode in the energy harvesting (EH) phase to provide energy to the source. In the information transmission phase, the relay works in a full-duplex (FD) mode to receive information signals from the source and simultaneously transmit information signals to the destination in the same frequency band. The paper provides the analysis of outage probability and throughput of a FD relaying system and two HD relaying systems. The first HD system ( $HD_{1}$ ) has the same EH duration as the FD system while the second HD one ( $HD_{2}$ ) has the same transmitting power from the source as the FD one. The results show that the throughput with respect to the time split between the EH phase and the information transmission one is a concave function and the optimal time split can be calculated numerically. Besides, the polarization dissimilarity factor of the antennas used has an influence on the system throughput, which is maximized when polarization states are orthogonal. The FD system can double the system throughput while having the outage probability as low as that of the $HD_{1}$ system, at a cost of adopting the extra polarization-enabled digital cancellation (PDC) scheme. Meanwhile, the FD system can nearly double the system throughput while having the outage probability superior to that of the $HD_{2}$ system. Simulations are run to confirm the above analyses.

The fifth-generation wireless system framework provides the option to evaluate the performance of in-band full-duplex (IBFD) operation through flexible duplexing. The resulting self-interference, however, must be mitigated within a fraction of a symbol duration for successful communication. This paper introduces the use of neural network machine learning to accelerate the tuning of multi-tap adaptive RF cancellers. Additionally, the optimal network configurations, input data structures and training dataset densities that optimize the performance of this technique are presented. The tuning results of a prototype system using a two-tap canceller were measured over 20 and 100 MHz bandwidths centered at 2.5 GHz, and demonstrated averages of 40 dB cancellation and 6 tuning iterations. These results are compared to a survey of previously-reported adaptive cancellers, and illustrate that this novel application of machine learning to RF canceller tuning provides the fastest convergence speed to date, which can enable IBFD operation in dynamic interference environments.

In this paper, we analyze the performance of an in-band full-duplex (IBFD) decode-and-forward (DF) two-way relay (TWR) system whose two terminal nodes exchange information via a relay node over the same frequency and time slot. Unlike the previous works on full-duplex two-way relay systems, we investigate the system performance under the impacts of both hardware impairments and imperfect self-interference cancellation (SIC) at all full-duplex nodes. Specifically, we derive the exact expression of outage probability based on the signal to interference plus noise and distortion ratio (SINDR), thereby determine the throughput and the symbol error probability (SEP) of the considered system. The numerical results show a strong impact of transceiver impairments on the system performance, making it saturate at even a low level of residual self-interference. In order to tackle with the impact of hardware impairments, we derive an optimal power allocation factor for the relay node to minimize the outage performance. Finally, the numerical results are validated by Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Self-interference and chromatic dispersion are two main limiting factors that influence the recovery of the signal of interest (SOI) in in-band full-duplex (IBFD) radio-over-fiber (RoF) links. An ultrawideband photonic-assisted approach to radio-frequency (RF) self-interference cancellation (SIC) with high-speed SOI recovery and fiber transmission capability is proposed. The key to achieve the above optimum performances in a compact system is the combined use of fiber dispersion induced RF time delay and optical carrier phase-shifted double sideband (CPS-DSB) modulation. A high precision and tunable time delay matching between the reference signal and the SI signal can be achieved by dispersion induced RF time delay. Meanwhile, the equal amplitude, phase reversal, and dispersion-induced SOI power fading compensation conditions are satisfied simultaneously by manipulating the optical carrier phase of the CPS-DSB signal. For 25 km fiber transmission, 30 dB cancellation depth over 2.7 GHz bandwidth, 160 Mbit/s 16-quadrature amplitude modulation (16-QAM) SOI recovery, and good immunity to fiber dispersion are experimentally demonstrated. In addition, the proposed scheme facilitates multipath SIC by implementing an array of tunable lasers (TLs) with a shared electro-optic modulator at the reference branch. [ABSTRACT FROM AUTHOR]

A photonics-assisted frequency conversion and self-interference cancellation approach is proposed and experimentally demonstrated for in-band full-duplex (IBFD) communication. Carrier suppressed single sidebands (CS-SSB) of the intermediate frequency (IF) signal and the local oscillator (LO) signal are simultaneously obtained through the X-DPMZM in a dual-polarization dual-parallel Mach-Zehnder (DP-DPMZM) modulator. A transmit signal with high purity is produced, and a shared LO optical sideband is also provided for the subsequent downconversion. The carrier suppressed double sideband (CS-DSB) modulation for the signal of interest (SOI) is achieved via the Y-DPMZM. The self-interference signal is suppressed by adjusting the bias voltage of its main MZM. An optical bandpass filter (OBPF) is combined to realize frequency downconversion. The experimental results show that the spurious-free dynamic range (SFDR3) is 102.6 dB/Hz2/3 for frequency upconversion, a cancellation depth of more than 50 dB for single-frequency self-interference cancellation (SIC), and more than 22 dB for wideband SIC. The proposed link has superiority in multifunctionality, including in-band transmission, reception, and self-interference cancellation, with a shared LO. [ABSTRACT FROM AUTHOR]

Full-duplex unmanned aerial vehicle (UAV) communication systems are characterized by mobility, so the self-interference (SI) channel characteristics change over time constantly. In full-duplex UAV communication systems, the difficulty is to eliminate SI in time-varying channels. In this paper, we propose a pilot-aid digital self-interference cancellation (SIC) method. First, the pilot is inserted into the data sequence uniformly, and the time-varying SI is modeled as a linear non-causal function. Then, the time-varying SI channel is estimated by the discrete prolate spheroidal basis expansion model (BEM). The error of block edge channel estimation is reduced by cross-block interpolation. The result of channel estimation is convolved with the transmitted data to obtain the reconstructed SI, which is subtracted from the received signal to achieve SIC. The simulation results show that the SIC performance of the proposed method outperforms the dichotomous coordinate descent recursive least square (DCD-RLS) and normalized least mean square (NLMS) algorithms. When the interference to noise ratio (INR) is 25 dB, the performance index normalized least mean square (NMSE) is reduced by 5.5 dB and 4 dB compared with DCD-RLS and NLMS algorithms, which can eliminate SI to the noise floor, and the advantage becomes more obvious as the INR increases.