In-band Full-duplex Research Articles

Beamforming Design for In-Band Full-Duplex Multi-Cell Multi-User MIMO Networks With Global and Local CSI

This paper investigates beamforming techniques for in-band full-duplex multi-cell multi-user (IBFD-MCMU) wireless networks considering hardware impairments (HWIs), channel uncertainty, and limited channel state information (CSI). For the global CSI scenario, we first enhance zero-forcing (ZF), maximum ratio transmission and combining (MRTC), and minimum mean-squared error (MMSE) beamforming to be compatible with multi-antenna users and IBFD base stations. Then, we investigate beamforming schemes for the local CSI assumption where only intra-cell channel knowledge is fully available at the base stations, and inter-cell channels are known statistically due to the limited training resources. With these limitations, two MMSE-based methods are proposed, which regard unknown CSI as random instances (i.e., eMMSE-RI) and noise (i.e., eMMSE-N). We explore the self-interference cancellation (SIC) capability of beamformers and evaluate the performance of these methods in 3GPP scenarios. Numerical results reveal that the enhanced MMSE beamforming can achieve the desired IBFD with low analog SIC depth, inspiring a low-cost IBFD transceiver design. The practical imperfections (e.g., transceiver HWIs, channel uncertainty, limited CSI) decrease the achievable sum rate but do not reduce the IBFD gain. With CSI limitations, eMMSE-RI outperforms eMMSE-N for microcells, where the probability of the presence of LOS is high, whereas eMMSE-N performs better when cell size is enlarged.

Broadband co-polarized antenna using monolithic slotted dielectric patch for full-duplex system

This paper suggests a broadband co-polarized antenna utilizing monolithic slotted dielectric patch (DP) for the applications of in-band full-duplex (IBFD). Three slot pairs with different sizes in the center of the monolithic DP are constructed and reduce the effective dielectric constant at this region. As a result, the E-field distributions of the two employed modes (TM10 and TE12 modes) inside the DP are moved to the unetched part (apart from the center of the DP). In this way, a broadband co-polarized antenna using the TM10 and TE12 modes is constructed while the isolation between the two ports for transmitting (TX) and receiving (RX) can be enhanced significantly in a broadband. The measured results of the antenna prototype are quite consistent with the simulated results. The experimental results illustrate that within the operating bandwidth of about 18% (|S11|< −10 dB), an isolation measured greater than 28 dB is attained, with a maximum value of 49.8 dB. Overall, the proposed co-polarized antenna owns advantages of simple structure, broad bandwidth, high efficiency, and low profile.

Gain and Frequency-Selectivity Enhancement of Dual- Polarized Filtering IBFD Antenna Using PRS

A dual-polarized filtering Fabry–Perot antenna (FPA) with high selectivity and high isolation is proposed for in-band full-duplex (IBFD) applications. The proposed antenna utilizes a square patch as the feeding element, which is fed by a double differential-fed scheme for dual-polarized radiation with high isolation. The patch is loaded with a symmetrical cross-slot and four shorting pins for a broad passband filtering feature. To enhance broadside gain across a wide frequency range, the patch is incorporated with a partially reflecting surface (PRS), which is composed of two complementary cross-slot and patch arrays. Moreover, the frequency selectivity of PRS is exploited to improve the filtering characteristic. The double differential feeds are realized based on out-of-phase power dividers, which are combined with simple low-pass filters to further improve the out-of-band suppression. The final design was fabricated and measured. The measurement results show excellent results with a 10-dB return loss bandwidth of 21.5% (4.91–6.09 GHz), isolation of greater than 40 dB, peak gain of 13.7 dBi, out-of-band suppression level of better than 27 dB, and a cross-polarization level of less than –27 dB.

Photonic-Enabled Image Rejection Mixer with Simultaneous Wideband Self-Interference Cancellation for In-Band Full-Duplex System

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-Band Full-Duplex Communications in ATSC 3.0 Single Frequency Network

Wireless in-band backhaul, a.k.a. in-band distribution links (IDL), is a spectrum-efficient and cost-effective enabling technology to the realization of Advanced Television Systems Committee (ATSC) 3.0 in the single frequency network (SFN) mode, where all the transmitter towers are synchronized to transmit the same broadcast signal in the same frequency band. Inter-tower communications network (ITCN) transforms the broadcast towers into a mesh network, thereby introducing datacasting capability to the traditional broadcast network. Both the ITCN and IDL can be operated in the most spectrum-efficient in-band full-duplex (IBFD) mode. In these situations, the ITCN/IDL receivers at the SFN towers receive the signal of interest (SOI) not only severely corrupted by the self-interference signal from its co-located transmitter, but also the co-channel interference signals from neighbouring transmitters. Moreover, the ITCN/IDL signals may be combined with the broadcast signal in the Layer Division Multiplexing (LDM) format to achieve better overall spectral efficiency. Therefore, the LDM inter-layer interference must also be mitigated. In this paper, the interferences for the ITCN/IDL signal in the SFN environment are analyzed, and a novel iterative successive signal cancellation scheme is proposed to effectively mitigate the interferences in the ITCN/IDL signal detection process in ATSC 3.0 SFNs.

Implementation of Wireless Backhaul and Inter-Tower Communications With MIMO in ATSC 3.0

Wireless backhaul, i.e., in-band distribution links (IDL) and inter-tower communications networks (ITCN) were previously proposed as key enabling technologies for the next-generation digital broadcasting systems, e.g., the Advanced Television Systems Committee (ATSC) 3.0 system. Both ITCN/IDL can be operated in the spectrum-efficient in-band full-duplex (IBFD) mode and the same frequency band is shared between the broadcast service signal and the ITCN/IDL signals. It is desirable to integrate multi-input multi-output (MIMO) into ITCN/IDL transmission to increase the throughput and reduce the portion of spectrum occupation by ITCN/IDL. However, due to the backward compatibility constraint, conventional symmetrical MIMO techniques cannot be applied directly to the existing broadcast infrastructure without affecting legacy receivers. In this paper, the practical implementation of a non-symmetrical MIMO for ITCN/IDL while maintaining backward compatibility is considered. In addition to the existing broadcasting antenna, the non-symmetrical MIMO comprises an additional low-power RF feeder cable and one or more highly directional antennas to achieve low-cost MIMO implementation for high throughput data distribution and inter-tower communications. When the broadcast service signal and the MIMO signal are multiplexed in Time Division Multiplexing (TDM) format, the signal structure is ATSC 3.0 standard compliant. When the broadcast service signal and the MIMO signal are multiplexed in Layer Division Multiplexing (LDM) format, modification of the ATSC 3.0 standard, i.e., introducing a new pilot encoding scheme, is required. Moreover, MIMO self-interference cancellation (SIC) is investigated for IBFD operation.

Performance analysis of full-duplex densely distributed MIMO with wireless backhaul

In this paper, the spectral efficiency of a full-duplex (FD) densely distributed multi-input multi-output (MIMO) system with wireless backhaul is considered. In-band full-duplex (IBFD) backhauling, in which the backhaul and access transmissions take place on the same spectrum, is exploited for wireless backhauling to enable an efficient spectrum reuse. However, the severe cross-tier interference and cross-link interference reduce the gains of IBFD backhauling. To evaluate the achievable spectral efficiency with imperfect channel state information (CSI), we propose a two-phase channel estimation scheme to estimate the CSI for two wireless links, and the scheme estimates an effective interference CSI between access points (APs) based on beamforming training to perform interference cancelation at APs. Given the estimated CSI, the closed-form expressions of the uplink and downlink achievable rates with maximum ratio transmission beamforming and maximum ratio combining receivers, respectively, are derived with Gamma approximation. Numerical results verify the accuracy of the derived closed-form expressions and the effectiveness of the two-phase channel estimation scheme for interference cancelation. Moreover, compared with half-duplex densely distributed MIMO systems, FD systems with interference cancelation have a better performance.

In band full duplex (IBFD) technology for next generation wireless networks: A survey in cellular networks

Next-Generation (NextG) wireless communication networks with their widespread applications require high data rates, seamless connectivity and high quality of service (QoS). To cope up with an unprecedented rise of data hungry applications, users demand more spectral resources imposing a limitation on available wireless spectrum. One of the potential solutions to address the spectrum scarce issue is to incorporate in band full duplex (IBFD) or full duplex (FD) paradigm in next generation networks including 5G new radio (NR). Recently, FD has gained the research interest in cellular networks for its potential to double the wireless link capacity and enhancing spectral efficiency (SE). In half duplex (HD) cellular networks, base stations (BSs) can either perform uplink (UL) or downlink (DL) transmission at a particular time instant leading to reduced throughput levels. Due to the advancement in the self interference reduction (SIR) techniques, full duplex base stations (FD-BSs) can be employed to allow simultaneous UL and DL transmissions at the same time-frequency resources as compared to its HD counterpart. It ideally achieves twice the throughput without any additional complexity at user-equipment(UE). This paper covers a detailed survey on FD cellular networks. A series of SIR approaches, UE-UE mitigation techniques are summarized. Various existing MAC protocols and antenna architectures for FD cellular networks are outlined. An overview of security aspects for FD in cellular networks is also presented. Lastly, various open issues and possible research directions are brought up for FD cellular networks.

Joint Active and Passive Beamforming Design for RIS-Aided IBFD IoT Communications: QoS and Power Efficiency Considerations

In a reconfigurable intelligent surface (RIS) aided communication network, a RIS equipped with multiple passive reflecting elements assists in extending the coverage of wireless networks by overcoming the effects of non-line-of-sight propagation. Accordingly, to present the case for utilizing RIS panels in future consumer internet of things (IoT) networks, in this paper, we focus on a RIS-aided IoT network operating in in-band full-duplex (IBFD) mode. Since all the IoT node pairs communicate simultaneously through individual IBFD links at the same time-frequency resources, the nodes suffer from strong self-interference (SI) and inter-node interference. Consequently, in this paper, we investigate a joint active and passive beamforming design at each IoT node and the RIS, respectively, by minimizing the total transmission power of the network, subject to a minimum rate constraint for each IoT node and a constraint that guarantees a unit modulus phase shift at the RIS. As the original joint active and passive beamforming design problem is non-convex and intractable, we decompose the problem into two sub-problems. For a given passive beamformer design, we solve the original problem to obtain the optimal beamforming vectors at each IoT node. Next, for the obtained active beamformer, we propose two algorithms based on i) gradient descent (GD) search and ii) Riemannian conjugate gradient (RCG) to obtain the optimal passive beamformer at the RIS. Through extensive numerical analysis, we verify the effectiveness of the proposed algorithms and also show the effects of using RIS and transmitting in IBFD mode on the average rate and power of the considered consumer IoT network. We investigate the impact of several system parameters such as RIS elements, node pairs, level of hardware impairments at the transmitter and receiver, etc. We also highlight the trade-off between performance improvement and complexity due to elements used at RIS.

Highly Integrated In-Band Full-Duplex TRx Antennas for mmWave V2X Communications

A compact mmWave co-circularly polarized (CP) Tx and Rx (TRx) antenna array for in-band full-duplex (IBFDX) V2X communications is proposed. The proposed TRx antenna is based on highly integrated coplanar TRx antenna elements with high Tx-to-Rx isolation maintained in n257 5G NR band. The TRx antenna elements are coplanar patches with the same CP and concentrically integrated to form individual 2 × 2 array on the same substrate. The proposed mmWave IBFDX antenna is designed at 28 GHz with a multilayered printed circuit board (PCB) having sequetially rotated feed networks. Also, the designed antenna is fabricated with the size of 1.867 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.867 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.087 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> including both CP feed network and ground plane. The measured 2 × 2 Tx impedance bandwith and peak gain at 28 GHz are 27.14% and 8.43 dBic, respectively. Also, the measured 2 × 2 Rx impedance bandwith and peak gain at 28 GHz are 28.57% and 6.17 dBic, respectively. Further, IBFDX operation of the proposed antenna is verified by n257 5G NR 256-QAM test signals with the maximum 400 MHz bandwidth.

Theoretical Investigation and Optimization of Power Amplifier Nonlinearity for In-Band Full-Duplex Radios

Although in-band full-duplex (IBFD) communication can theoretically double the spectral efficiency compared with conventional wireless communication technologies, it cannot be realized without reducing a high-power self-interference (SI) signal. Since the SI signal is affected by nonlinear distortion of radio-frequency (RF) circuits of its own terminal, cancellation systems capable of removing the nonlinear distorted SI have been actively developed. Detailed theoretical analysis based on the authors’ past literature shows that for IBFD using a nonlinear self-interference canceller, the symbol error rate is improved when the power amplifier has certain distortion characteristics rather than being ideally linearized. However, it is not yet known what amplifier characteristics are best for the IBFD system. In this study, we theoretically analyze the self-interference signal to clarify the optimum amplifier characteristics for the IBFD system. An optimization problem to obtain an optimum transfer function from theoretical analysis is formulated as an Rayleigh quotient with constraints, and we introduce a numerical technique to solve the optimization problem. By numerical experiments, we show that the SI cancellation performance, signal-to-interference-distortion-plus-noise ratio (SIDNR), and amplifier’s power efficiency are improved by the optimization.

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

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

High isolation circularly polarized in-band full-duplex anisotropic dielectric resonator antenna

A novel high-isolation, monostatic, circularly polarized (CP) simultaneous transmit and receive (STAR) anisotropic dielectric resonator antenna (DRA) is presented. The Proposed antenna is composed of two identical but orthogonally positioned annular sectoral anisotropic dielectric resonators. Each circularly polarized (CP) resonator consists of alternating stacked dielectric layers of relative permittivities of 2 and 15 and is excited by a coaxial probe from the two opposite ends to have left and right-hand CP. Proper element spacing and a square absorber are placed between the resonators to maximize Tx/Rx isolation. Such a structure provides an in-band full-duplex (IBFD) CP-DRA system. Measurement results exhibit high Tx/Rx isolation better than 50 dB over the desired operating bandwidth (5.87–5.97 GHz) with a peak gain of 5.49 and 5.08 dBic for Ports 1 and 2, respectively.

Real-time adaptive optical self-interference cancellation for in-band full-duplex transmission using SARSA(λ) reinforcement learning.

Self-interference (SI) due to signal leakage from a local transmitter is an issue in an in-band full-duplex (IBFD) transmission system, which would cause severe distortions to a receiving signal of interest (SOI). By superimposing a local reference signal with the same amplitude and opposite phase, the SI signal can be fully canceled. However, as the manipulation of the reference signal is usually operated manually, it is difficult to ensure a high speed and high accurate cancellation. To overcome this problem, a real-time adaptive optical SI cancellation (RTA-OSIC) scheme using a SARSA(λ) reinforcement learning (RL) algorithm is proposed and experimentally demonstrated. The proposed RTA-OSIC scheme can automatically adjust the amplitude and phase of a reference signal by adjusting a variable optical attenuator (VOA) and a variable optical delay line (VODL) achieved through an adaptive feedback signal, which is generated by evaluating the quality of the received SOI. To verify the feasibility of the proposed scheme, a 5 GHz 16QAM OFDM IBFD transmission experiment is demonstrated. By using the proposed RTA-OSIC scheme, for an SOI at three different bandwidths of 200, 400, and 800 MHz, the signal can be adaptively and correctly recovered within 8 time periods (TPs), which is the required time of a single adaptive control step. The cancellation depth for the SOI with a bandwidth of 800 MHz is 20.18 dB. The short- and long-term stability of the proposed RTA-OSIC scheme is also evaluated. The experimental results indicate that the proposed approach could be a promising solution for real-time adaptive SI cancellation in future IBFD transmission systems.

A ±45°-Polarized Antenna System With Four Isolated Channels for In-Band Full-Duplex (IBFD)

An in-band full-duplex (IBFD) antenna system having four ports with good self-interference cancellation (SIC) is presented in this article. Two of the four ports provide +45°-polarized radiation and the other two generate − 45°-polarized radiation. Every port of the proposed antenna is well isolated from the other three ports, enabling simultaneous transmitting (TX) and receiving (RX) with both two polarizations. To achieve this goal, three different types of couplings need to be addressed simultaneously. In this work, a novel isolation feed network is proposed, which is the first of its kind that can achieve three targets at the same time, i.e., feeding the antenna differentially, forming the original horizontal and vertical polarizations into ± 45° polarizations, and canceling out the reflected and coupled signals between the TX and RX ports. Then, a double-antenna IBFD system with four isolated channels is attained by combining the proposed feed network, defected ground structure (DGS), cross-shaped walls, and metal baffles, which effectively mitigated all the three types of couplings at the same time. The double-antenna system has high isolations of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$ </tex-math></inline-formula> 39 dB between any two of the four ports from 3.3 to 3.9 GHz. The four radiation patterns obtained by exciting the four ports are very similar to each other and are stable with frequency, which makes it an excellent candidate for 5G sub-6 GHz IBFD applications.

Evaluating Analog Self-Interference Cancellation for In-Band Full-Duplex Wireless Communication

In-band full-duplex (IBFD) technology allows simultaneous transmission and reception in the same frequency band to boost spectral efficiency. However, selfinterference, introduced by transmitter-to-receiver leakage, poses the biggest obstacle to the realization of IBFD. Altogether IBFD radio performance and effective network throughput are directly correlated with the amount of energy suppressed by self-interference cancellation (SIC). In this work a model of an IBFD transceiver, featuring an adaptive, analog-domain, tapped-branch self-interference canceller, was developed to evaluate the inimical effects attributable to the various noise and nonlinear distortions of the simulated transceiver components. Results of the simulation show that noise incursions and nonlinearity in the transmission channel produced a negligible effect on the overall cancellation performance. However, the effectiveness of the cancellation hardware is highly dependent on the level of intrinsic nonlinearity within the canceller’s own components. Consideration of these non-ideal characteristics should be an essential part of analog SIC design to prevent any intrinsic limitations on the cancellation performance.

Frequency-Domain RF Self-Interference Cancellation for In-Band Full-Duplex Communications

Wireless backhaul has recently gained a significant amount of interest as a cost-effective solution in comparison with conventional backhaul technologies with dedicated microwave links or fiber optics. Self-interference cancellation (SIC) is an enabling technology that allows wireless backhaul to operate in the more spectrum-efficient in-band full-duplex (IBFD) operation mode instead of the out-of-band mode. Compared to Wi-Fi IBFD transceivers, wireless in-band backhaul systems face some unique challenges, such as significantly higher transmission power and much larger propagation delay spread for the self-interference signal, especially in the low-frequency bands under 1 GHz, which often prevent accurate SIC performance. The SIC is often implemented with an interference-cancelling filter, where the filter weights are essentially the channel estimates of the self-interference signals. In this paper, a frequency-domain Radio Frequency (RF) SIC (RF-SIC) framework with a novel filter weight optimization algorithm is proposed to tackle the challenges of wireless in-band backhaul. The proposed RF-SIC does not require a dedicated training phase which needs to stop the transmission of the backhaul signal. Moreover, it has the capability of tracking the self-interference channel variation since the filter weights are updated in a block-by-block fashion.

In-Band Full-Duplex Filtering Antenna Arrays Using High-Order Mode Cavity Resonators

In this article, a series of narrowband and wideband in-band full-duplex (IBFD) filtering antenna arrays (FAAs) using cavity-based high-order modes are investigated. It is found that the pairs of degenerate high-order modes in a single cavity resonator, TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{1n0}$ </tex-math></inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{n10}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n$ </tex-math></inline-formula> is even), are suitable for the IBFD FAA designs due to their advantages: 1) in-phase and same amplitude for each magnetic loop, which helps to enhance the gain, and 2) the modal orthogonality, which guarantees the isolation and cross-polarization level between two channels. The higher order response can be achieved by cascading more high-order mode resonators with the required external quality factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{e}$ </tex-math></inline-formula> ) and coupling coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> ). For proof of concept, two types of full-duplex waveguide arrays are implemented and tested. First, a second-order IBFD FAA with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times $ </tex-math></inline-formula> 5 elements, using a pair of degenerate modes TM610 and TM160, is designed with 1% overlapped 10-dB bandwidth and 18.4-dBi realized gain within the passband. The method to improve realized gain and isolation level without increasing any circuit volume is also presented. Second, a fifth-order IBFD FAA using TM410 and TM140 modes is implemented with an overlapped 10-dB bandwidth of 15.6% and a realized gain of 12.5 dBi. The measured isolation between the two channels is better than 40.4 dB. An excellent agreement between simulated and measured results verifies that the proposed design methodology is feasible for designing high-order mode IBFD FAA.

Comparative analysis of antenna isolation characteristic with &amp; without self‐interference reduction techniques towards in‐band full‐duplex operation

AbstractThe advancement of communication and radar systems has triggered the demand for in‐band full‐duplex (IBFD) operation. IBFD is regarded as one of the most outstanding technologies in terms of its ability to improve spectral efficiency and data rate. IBFD operation has the potential not only to enable communication or radar systems separately, but to help realising radar sensing and communication at the same time, known as Joint Communication and Sensing (JC&amp;S) technology. In realisation of IBFD and JC&amp;S systems, self‐interference (SI) is the key challenge for antenna designers. In this article, a comprehensive survey on SI reduction techniques in the antenna domain is provided and the advantages and disadvantages of each technique are studied. SI reduction techniques have been proposed separately but an elaborated review of relevant techniques with a comparative study has not been presented yet. For the first time, a systematic comparative study of different SI reduction techniques is graphically presented to cover a comparison based on isolation, gain, and impedance bandwidth in terms of before and after SI reduction techniques. Moreover, this study also explores how antenna isolation characteristics vary with respect to the thickness and the permittivity of the substrate without any SI reduction technique.

Self-interference cancellation in underwater acoustic communications systems using orthogonal pilots in IBFD

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).