In-band Full-duplex Communication Research Articles

Deep learning based detection of signal of interest of uplink NOMA multi-users in NOMA In-band Full-duplex Radio communication

The research focuses on investigating the symbol error rate (SER) performance of the Non Orthogonal Multiple Access (NOMA) In-band Full-duplex Radio communication system, which is considered a promising technology for 5G/6G. This system facilitates simultaneous transmission and reception of data over the same resource block for multiple users via power domain multiplexing. However, the system faces a significant challenge in the form of self-interference signal (SI). The SI signal transmitted from the NOMA In-band full-duplex radio transmitting antenna is also received by its own receiving antenna. It limits perfect successive interference cancellation (SIC) for channel estimation and signal detection of the signal of interest (SoI) from uplink NOMA multi-users at the receiver of NOMA In-band Full-duplex radio. Furthermore the SER performance is significantly degraded due to various SI and SoI channel imperfections. To address this, a three-phase-based efficient approach has been proposed for simultaneous non-linear SI cancellation and detection of the SoI from uplink NOMA two users under aforementioned SI and SoI channel imperfections. The approach uses the Least Square-SIC Estimator, Minimum Mean Square Error-SIC Estimator, and deep learning (DL) methods. The reported 4 dB SNR gain compared to least square-SIC/minimum mean square error SIC and DNN-based methods demonstrate the robustness of the proposed DL-aided approach against various SI and SoI channel imperfections for NOMA In-band Full-duplex Radio communication.

Characterizing in-band full-duplex in broadcast communications: From field trials to a loopback channel model

In-band full duplex (IBFD) communications are a potential solution to spectrum scarcity. IBFD communications offer greater spectral efficiency than traditional half-duplex communications by transmitting and receiving on the same frequency channel. However, IBFD operation requires overcoming the challenge of eliminating the self-interference coupled from the transmit antenna to the receive subsystem. Knowledge of the characteristics of the loopback propagation channel makes it easier to cancel out the self-interference. Nevertheless, complex field trials are required to adequately characterize loopback channels, which is still lacking in the recent literature. This paper proposes a measurement campaign in a real and ongoing broadcast transmission center to characterize the main characteristics of loopback channels. The work proposes a set of loopback channels based on field trials and an empirical analysis of the most relevant parameters of the channel model, such as the Doppler spectrum, the delay spread, and the K-factor.

Joint Equalization and Self-Interference Cancellation for Underwater Acoustic In-Band Full-Duplex Communication

Joint Equalization and Self-Interference Cancellation for Underwater Acoustic In-Band Full-Duplex Communication

Iterative Successive Nonlinear Self-Interference Cancellation for In-Band Full-Duplex Communications

Iterative Successive Nonlinear Self-Interference Cancellation for In-Band Full-Duplex Communications

Switched Radio Architecture With Non-Linear Frequency-Domain Estimation for In-Band Full-Duplex Communication

Switched Radio Architecture With Non-Linear Frequency-Domain Estimation for In-Band Full-Duplex Communication

Reference signal aided self-interference cancellation for in band full duplex underwater wireless optical communication

A novel self-interference cancellation method for in-band full-duplex (IBFD) underwater wireless optical communication (UWOC) system is proposed and experimentally verified. This method reduces the self-interference to its intrinsic noise level using a reference optical signal whose amplitude is opposite to the self-interference signal, together with a deep neural network to compensate for the nonlinear distortion enhanced by increased DC. The bit error rates (BERs) before and after self-interference cancellation at different data rates are tested and compared with the existed polarization-based cancellation scheme. Results presented in this paper show that more than 10 dB self-interference cancellation ratio can be achieved by the proposed scheme at 100 MHz signal rate, and outperforms the polarization-based scheme. With the assistance of the proposed method, a data rate of 100Mbps was achieved simultaneously at the uplink and downlink within IBFD based UWOC.

Implementation of In-Band Full-Duplex Using Software Defined Radio with Adaptive Filter-Based Self-Interference Cancellation

For next generation wireless communication systems, high throughput, low latency, and large user accommodation are popular and important required characteristics. To achieve these requirements for next generation wireless communication systems, an in-band full-duplex (IBFD) communication system is one of the possible candidate technologies. However, to realize IBFD systems, there is an essential problem that there exists a large self-interference (SI) due to the simultaneous signal transmission and reception in the IBFD systems. Therefore, to implement the IBFD system, it is necessary to realize a series of effective SI cancellation processes. In this study, we implemented a prototype of SI cancellation processes with our designed antenna, analog circuit, and digital cancellation function using an adaptive filter. For system implementation, we introduce software-defined radio (SDR) devices in this study. By using SDR devices, which can be customized by users, the evaluations of complicated wireless access systems like IBFD can be realized easily. Besides the validation stage of system practicality, the system development can be more effective by using SDR devices. Therefore, we utilize SDR devices to implement the proposed IBFD system and conduct experiments to evaluate its performance. The results show that the SI cancellation effect can reach nearly 100 dB with 10−3 order bit error rate (BER) after signal demodulation. From the experiment results, it can be seen obviously that the implemented prototype can effectively cancel the large amount of SI and obtain satisfied digital demodulation results, which validates the effectiveness of the developed system.

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

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

Sagnac Loop Based Broadband Self-Interference Cancellation and Down-Conversion for Distributed Antenna Systems

Focusing on distributed antenna systems, we propose a photonics-assisted self-interference cancellation and down-conversion method based on a Sagnac loop structure. Two inversely cascaded modulators form a Sagnac loop through polarization multiplexing. To support in-band full duplex (IBFD) communication, a double parallel Mach–Zehnder modulator (DPMZM) operated in a clockwise direction is used as a self-interference canceller (SIC) to achieve the phase conversion in the optical domain. Another MZM modulator working in the counterclockwise direction is used to modulate the local oscillation (LO) signal for frequency down-conversion. The adjustment of bias voltage is analyzed to optimize the conversion efficiency of the system. The power fading effect generated by fiber dispersion is compensated by a polarization-sensitive phase modulator (PS-PM). The experimental results show that the average cancellation depth is 56.4 dB at a single frequency in the operating frequency range of 6–22 GHz, and 29.1 dB and 23.7 dB for 20 MHz and 100 MHz bandwidth signals, respectively. In addition, the error vector map is improved from 16.50% to 6.26% after dispersion compensation. The self-interference cancellation, down-conversion and dispersion compensation are integrated in a microwave photonics link. Two cascaded modulators are equivalent to a parallel structure by the Sagnac loop, simultaneously ensuring high LO isolation and conversion efficiency. The proposed method provides an alternative for IBFD-based distributed antenna communication applications.

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

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

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.

Signal Isolation Characterization of ITCN In-Band Full-Duplex Communications

Future digital terrestrial television (DTT) systems are introducing revolutionary changes to their architectures and operation modes. One of the best examples is ATSC 3.0, which is pushing to incorporate the Internet Protocol (IP) into the protocol stack. This way, implementing new applications (e.g., target advertisement, connected cars, 4k/8k video content) is closer than ever. Indeed, recent works have suggested designing and implementing an Inter-Tower Communications Network (ITCN) and wireless In-band Distribution Link (IDL) inside the ATSC 3.0 forums. ITCN will interconnect all broadcast towers to form a communication network for control, monitoring, data communication, and localized datacast and broadcast services. Nevertheless, this application has a significant challenge: the self-interference (SI) or loopback signal that is generated and added to the received signal. To reduce the impact of the SI, the transmission centers combine different signal isolation and cancellation techniques. This paper focuses on characterizing the signal power isolation between the transmitted and the received signals under different conditions. In particular, this paper shows the signal isolation values measured during various field trials in real broadcast transmission centers. The results show that the total signal isolation varies depending on the transmission/reception configuration between 70-90 dB. Moreover, due to the measurements, we have demonstrated that the antenna distance is a more relevant parameter for signal isolation than the center frequency. Finally, the possible antenna pattern discrimination has been calculated and discussed.

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.

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.

Signal Detection in GSM-Based In-Band Full-Duplex Communication Using DNN

An in-band full-duplex (IBFD) multiple-input multiple-output (MIMO) radio's self-interference (SI) cancellation strength usually determine its performance gains over conventional half-duplex ones. Accordingly, this letter explores an alternative to traditional optimization driven design (ODD) techniques available in literature for beamformer design in IBFD radios. In particular, we consider a generalized spatial modulation (GSM) based bi-directional IBFD system, that provides the flexibility of choosing active antennas among a set of antennas for the spatial symbol. We propose a run-time data-driven prediction approach to solve the multiple multivariate regression problem of detection of the transmitted signal in this GSM based IBFD system in the presence of residual SI arising from non-ideal SI cancellation. We compare the performance of the proposed detector with respect to conventional detectors under several communication parameters that are of practical interest. The proposed DNN-based detector learns the deviations from a standard model without SI and achieves performance that is superior to zero forcing and minimum mean squared error detectors and very close to maximum likelihood detector at faster computation time.

Design and Performance Analysis of an In-Band Full-Duplex MAC Protocol for Ad Hoc Networks

This paper proposes a MAC protocol for ad hoc networks using In-band Full-duplex (IBFD) wireless communications, which are named as AdHoc-FDMAC. To utilize IBFD communications in ad hoc networks, this protocol modifies a number of control frames in the IEEE 802.11 Distributed Coordination Function (DCF) MAC standard. Here, the detailed time sequences for all types of IBFD communications are shown for the data transmission and routing. In this paper, the probability and throughput equations for IBFD communications in different situations have been derived. The performance of the proposed AdHoc-FDMAC has been analysed in terms of probability, throughput, and routing time. The Maximum throughput of AdHoc-FDMAC has been found to be 48.34 Mbps, and it is compared with a recently published ad hoc MAC as well as with the conventional HD MAC. The AdHoc-FDMAC outperforms the recently published ad hoc MAC and conventional HD MAC by 16.80% and 66.50% throughput gain, respectively. AdHoc-FDMAC incorporates the existing Ad hoc On-demand Distance Vector (AODV) routing protocol, but this AODV routing is utilized here using IBFD communications. This paper also compares the routing time of the IBFD-based AODV with the conventional AODV. The result shows that the IBFD-based AODV requires 33.33% less routing time than that of the conventional AODV for 3-hop distance between the transmitter and receiver. This paper suggests that the AdHoc-FDMAC protocol provides much more throughput in ad hoc networks by utilizing IBFD communications.

Lake Experimentation of in-Band Full-Duplex Underwater Acoustic Communications With a Receiving Array

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-2}$ </tex-math></inline-formula> was achieved at the range of 80 m for IBFD communications.

Photonic-Assisted Reconfigurable LO Harmonic Downconverter With RF Self-Interference Cancellation and Image-Rejection

A photonic-assisted reconfigurable LO harmonic downconverter with simultaneous image-rejection and RF self-interference cancellation (SIC) for in-band full-duplex communication is proposed and experimentally investigated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The received signal from the antenna, which includes the radio frequency (RF) signal, image signal (IM) and self-interference (SI) signal, is input into one sub-MZM of the X-DPMZM. The self-reference (SR) signal is input into the other. The Y-DPMZM is used to load the LO signal and is properly biased to obtain the high-order sideband of the LO signal, which was then set as the LO signal of the reconfigurable harmonic frequency downconverter. By matching the power and delay of the SR signal and changing the main bias of the X-DPMZM, the SI signal can be eliminated directly in optical domain. With power splitting after the output of the DP-DPMZM, the quadrature IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Then, photonics image-rejection down-conversion based on phase cancellation is realized after a low-frequency electrical 90° hybrid coupler (HC) combines the quadrature IF signals. Both theoretical and experimental investigations are performed. The results show that the SIC has a cancellation depth more than 32 dB for the 10-MHz bandwidth and greater than 19 dB for the 500-MHz bandwidth, the image-rejection has an image-rejection ratio larger than 31 dB for 10-MHz bandwidth and larger than 22 dB for the 100-MHz bandwidth, both in 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> - and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order harmonic down-conversion mode. Experiments are also carried out on the reconfigurable LO harmonic downconverter with simultaneous SIC and image-rejection. A 16-quadrature amplitude modulation (16-QAM) -modulated RF signal is successfully down-converted to a 1-GHz intermediate frequency (IF) signal with self-interference and image frequency cancelled. It is verified that the RF signal can be well recovered from SI and IM signals by the proposed system.