In-band Full-duplex Research Articles

Comparative analysis of antenna isolation characteristic with & 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&S) technology. In realisation of IBFD and JC&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).

Spectral-Efficiency of Cell-Free Massive MIMO With Multicarrier-Division Duplex

A multicarrier-division duplex (MDD)-based cell-free (CF) scheme, namely MDD-CF, is proposed, which enables downlink (DL) data and uplink (UL) data or pilots to be concurrently transmitted on mutually orthogonal subcarriers in distributed CF massive MIMO (mMIMO) systems. To demonstrate the advantages of MDD-CF, we firstly study the spectral-efficiency (SE) performance in terms of one coherence interval (CT) associated with access point (AP)-selection, power- and subcarrier-allocation. Since the formulated SE optimization is a mixed-integer non-convex problem that is NP-hard to solve, we leverage the inherent association between involved variables to transform it into a continuous-integer convex-concave problem. Then, a quadratic transform (QT)-assisted iterative algorithm is proposed to achieve SE maximization. Next, we extend our study to the case of one radio frame consisting of several CT intervals. In this regard, a novel two-phase CT interval (TPCT) scheme is designed to not only improve the SE in radio frame but also provide consistent data transmissions over fast time-varying channels. Correspondingly, to facilitate the optimization, we propose a two-step iterative algorithm by building the connections between two phases in TPCT through an iteration factor. Simulation results show that, MDD-CF can significantly outperform in-band full duplex (IBFD)-CF due to the efficient interference management. Furthermore, compared with time-division duplex (TDD)-CF, MDD-CF is more robust to high-mobility scenarios and achieves better SE performance.

Two-Way Waveguide Diplexer and Its Application to Diplexing In-Band Full-Duplex Antenna

A design of a diplexing in-band full-duplex (IBFD) slot antenna based on the quadruple-mode resonator (QMR) is presented for the first time. First, a two-way waveguide diplexer integration using QMR is designed. Four waveguide modes, namely, TE011, TE101, TM210, and TM120, are primarily used. These four modes are modal orthogonal to each other in a single QMR. Each of the quadruple modes can be independently manipulated with low mutual interference with other modes. Taking advantage of this characteristic, a two-way waveguide diplexer integration can be implemented with four independent frequency channels. In each diplexer, the downlink channel is dominated by fundamental mode TE011/TE101, while the uplink channel is dominated by high-order mode TM210/TM120. By cascading QMRs, higher order frequency responses are achieved with expected 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> ) and 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">$Q_{{\text {e}}}$ </tex-math></inline-formula> ). Based on the proposed two-way diplexer concept, a diplexing IBFD antenna with a turnstile junction is designed by replacing the inputs with a cross-coupled radiating slot. It integrates the filtering, diplexing, orthomode transducing, and radiating functions into a single element. Four channels can work independently to transmit/receive two orthogonal signals. The two-way waveguide diplexer and diplexing IBFD waveguide antenna with a second-order response were implemented and tested for the proof-of-concept.

Multicarrier-Division Duplex for Solving the Channel Aging Problem in Massive MIMO Systems

The separation of training and data transmission as well as the frequent uplink/downlink (UL/DL) switching make time-division duplex (TDD)-based massive multiple-input multiple-output (mMIMO) systems less competent in fast time-varying scenarios due to the resultant severe channel aging. To this end, a multicarrier-division duplex (MDD) mMIMO scheme associated with two types of well-designed frame structures are introduced for combating channel aging when communicating over fast time-varying channels. For comparison, the corresponding TDD frame structures related to the 3 rd Generation Partnership Project (3GPP) standards and their variant forms are presented. The MDD-specific general Wiener predictor and decision-directed Wiener predictor are introduced to predict the channel state information, respectively, in the time domain based on UL pilots and in the frequency domain based on the detected UL data, considering the impact of residual self-interference (SI). Moreover, by applying the zero-forcing precoding and maximum ratio combining, the closed-form approximations for the lower bounded rate achieved by TDD and MDD frame structures over time-varying channels are derived. Our main conclusion from this study is that the MDD, endowed with the capability of full-duplex but less demand on SI cancellation than in-band full-duplex (IBFD), outperforms both the conventional TDD and IBFD in combating channel aging.

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.

Wideband Co-Linearly Polarized Magneto-Electric Dipole Antenna for In-Band Full-Duplex Applications

A wideband co-linearly-polarized magnetoelectric (ME) dipole antenna is proposed for the in-band full-duplex (IBFD) application, having identical radiation properties in the operating frequency band. Good isolation between the transmitting and receiving ports is obtained over a wide frequency range by modifying the shared central part of the ME dipole without a complex feeding structure. The central part is a defected rectangular tube suspended above the ground. To validate the proposed antenna, a prototype is fabricated and measured. The measured port isolation is higher than 22 dB over the operating frequency band from 1.90 to 2.91 GHz (42.0%). The proposed antenna has a simple structure and good wideband radiation performance, with high potential for IBFD applications.

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.

Throughput Enhancement of Dynamic Full-Duplex Cellular System by Distributing Base Station Reception Function

In-band full-duplex (IBFD) is a promising technology for improving spectral efficiency beyond 5G and 6G. The dynamic duplex cellular (DDC) system has been proposed as a method for the phased introduction of IBFD into cellular systems while maintaining backward compatibility. Although previous studies have shown that DDC systems can improve the average user throughput, twice the spectral efficiency compared to half-duplex (HD), ideally expected for IBFD, has not been achieved. The main component that disturbs throughput enhancement is the residual component of self-interference (SI) at the base station (BS), which SI cancellers cannot entirely suppress. In this study, we propose a DDC system with a dedicated transmitter (DT) and multiple distributed receivers called remote receivers (RRs) for the BS to reduce the effective SI and enhance uplink reception quality. We implement user equipment scheduling and power control for the DDC system in the topology with DT and multiple RRs and improvement by IBFD. evaluate its performance using computer simulations in a single-cell environment. The proposed DDC system with receiver-distributed topology achieves up to 96% improvement in average user throughput of uplink and downlink from the HD system with the same topology, which is close to the ideal performance.

MM-Wave High Isolated Dual Polarized Dielectric Resonator Antenna for In-Band Full-Duplex Systems

A novel high-isolation dual-polarized in-band full-duplex (IBFD) dielectric resonator antenna (DRA) for satellite communications using a decoupling structure is proposed. Good isolation between transmit and receive ports is achieved by placing two identical linearly polarized resonators orthogonal to each other. Each resonator consists of a main rectangular dielectric resonator of the dielectric constant of 10 and is loaded by a thin dielectric slab of lower permittivity of 5 to broaden the matching bandwidth further. The isolation is further improved by loading an absorber and etching several slots in the ground plane. Finally, the proposed DRA is fabricated and measured to validate the concepts. Measurement results show high isolation of more than 50 dB over the desired operating bandwidth from 23.04 GHz to 24.08 GHz (ka-band) with a peak gain of about 8.93 dBi and 8.09 dBi for Port 1 and Port 2, respectively. In addition, the proposed IBFD DRA provides 11.87 GHz and 4.84 GHz isolation bandwidths over 25 dB and 30 dB, respectively, making it a potential candidate for mm-wave terrestrial applications.

Design of Self-Decoupling Dielectric Resonator Antenna With Shared Radiator

The method of mode cancellation to design a two-port dielectric resonator antenna (DRA) for an in-band full-duplex (IBFD) application is investigated in this communication. The whole antenna structure is straightforward, only composed of a single DRA element, a pair of feeding lines, and a pair of metallic probes. Attributing to the features of different modes used in this design, mutual coupling between the exciting port and the passive port can be suppressed to an extremely low level without using an extra decoupling structure. A prototype is fabricated and measured for verification. The measured results demonstrate that the proposed antenna has broad bandwidth and high isolation level can be achieved throughout the whole working band.

Heterogeneous In-Band Full-Duplex System for Simultaneous SUN-FSK Transmission and SUN-OFDM Reception

Heterogeneous In-Band Full-Duplex System for Simultaneous SUN-FSK Transmission and SUN-OFDM Reception

Filter-Less Photonic RF Image-Reject Mixing With Simultaneous Self-Interference Cancellation and Fiber Transmission

A filter-free photonic method to simultaneously realize radio frequency (RF) image-reject mixing, self-interference cancellation (SIC), and fiber transmission for in-band full-duplex (IBFD) radio-over-fiber (RoF) link is reported. The key to achieving multi-functions is the joint manipulation of fiber dispersion-induced intermediate frequency (IF) amplitude and time delay changes, which is implemented by sideband phase-shifted optical carrier suppression (SPS-OCS) modulation and frequency tuning of the optical carrier. Owing to the control of IF amplitude and delay variation introduced by fiber dispersion, simultaneous deep image rejection and SIC over wide bandwidth can be realized after fiber transmission. Since no optical filter is required, the proposed system can work at a lower frequency, featuring a large frequency tuning range. For 25 km single-mode fiber (SMF) transmission, simultaneous 20 dB SIC within 1 GHz bandwidth and 29 dB image rejection ratio (IRR) at 6.6 GHz RF frequency in the C band, 21 dB SIC and 19 dB IRR within 1 GHz bandwidth in the X band, 24 dB SIC within 1 GHz bandwidth and 20 dB IRR at 16 GHz RF frequency in the Ku band are experimentally demonstrated. Furthermore, weak SOI with various modulation formats are well recovered after the cancellation of strong interference and fiber transmission.

A QoS-Adaptive Interference Alignment Technique for In-Band Full-Duplex Multi-Antenna Cellular Networks

In this paper, we propose a novel interference alignment (IA) technique for an in-band full-duplex (IBFD) multiple-input multiple-output (MIMO) cellular network where a base station (BS) and user equipment (UE) are equipped with multiple antennas, and the local channel state information (CSI) is available at all nodes. Considering a practical IBFD MIMO cellular network, it is assumed that only the BS operates with full-duplex (FD) communication while UE operate in half-duplex (HD) mode. These IBFD networks introduce a new type of interference called cross-link interference (CLI), in which uplink UE affects downlink UE. The proposed IA technique consists of two symmetric IA schemes according to the number of antennas in the uplink and downlink UE, and both schemes effectively mitigate CLI in the IBFD MIMO network. It is worth noting that both IA schemes are adaptively applicable according to the network's quality-of-service (QoS) requirements, such as uplink and downlink traffic demands. Furthermore, we theoretically characterize and prove the achievable sum-degrees-of-freedom (DoF) of the proposed IA technique. Simulation results show that the proposed IA technique significantly improves the sum rate performance compared to conventional HD communications (multi-user MIMO) while achieving the same achievable DoF as the interference-free IBFD MIMO network.

Exploring the Past, Present, and Future of In-Band Full-Duplex Wireless Systems [Book/Software Reviews

Kenneth Kolodziej is a technical staff member in the RF Technology Group at the Massachusetts Institute of Technology (MIT) Lincoln Laboratory, where he is a principal investigator on wideband electronics and in-band full-duplex (IBFD), commonly known as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">simultaneous transmit and receive</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">STAR</i> ) systems. He has conducted research on RF, microwave, and photonic circuits, including antenna, radar, and communications systems. He received his B.E. and M.E. degrees in electrical engineering from the Stevens Institute of Technology in Hoboken, NJ. He has published numerous journal articles and conference papers and holds several patents in the field of antennas and RF systems. He is also an IEEE Member and is very actively serving the IEEE Society.

Electric-Field Null Bending of a Single Dual-Port Patch Antenna for Colinear Polarization Decoupling Using Characteristic Modes Analysis

A novel design concept for bending the electric-field nulls of a single dual-port microstrip patch antenna (MPA) for colinear polarization decoupling is proposed in this communication. Initially, the electric-field distributions of the traditional MPA are theoretically studied by using characteristic mode analysis (CMA). The results demonstrate that the of electric-field nulls could be bent by combining its two modes. Hence, when the antenna is excited at the left port, electric-field nulls could be formed around the right port. In contrast, electric-field nulls are formed on the left port for the MPA under excitation of the right port. Next, a set of shorting pins is loaded below the radiating patch. Hence, the MPA reallocates the resonant frequencies of these dual modes closely to each other and combines them for low mutual coupling. After that, the slot is cut on the radiator, aiming to improve the impedance matching over the operating band. With these arrangements, the mutual coupling of the MPA between dual ports is successfully decreased with good impedance matching. In final, the proposed MPA is fabricated and measured. Good agreement between the simulated and measured results is obtained, and it proves that the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{11}\vert &lt; -10$ </tex-math></inline-formula> dB of the antenna is operated in a range from 5.3 to 5.54 GHz. Besides, the antenna maintains the low-profile, single-layer, and single-element properties. Most importantly, it has generated a broadside radiation pattern with the same polarization, and its isolation is satisfactorily enhanced to above 17 dB, which is much higher than the 3.5 dB of the traditional counterpart. Hence, it can be used for in-band full-duplex (IBFD) systems.

Configurable Independent Component Analysis Preprocessing Accelerator

An independent component analysis (ICA) has been used in many applications, including self-interference cancellation (SIC) for in-band full-duplex (IBFD) wireless systems and anomaly detection in industrial Internet of Things (IoT). This article presents a high-throughput and highly efficient configurable preprocessing accelerator for the ICA algorithm. The proposed ICA accelerator has three major blocks that perform data centering, covariance matrix for computation, and eigenvalue decomposition (EVD). Specifically, the proposed accelerator is based on a high-performance matrix multiplication array (MMA). The proposed MMA architecture uses time-multiplexed processing, so that the efficiency of hardware utilization is greatly enhanced. Furthermore, the processing flow utilizes parallel processing, such that the centering, the calculation of the covariance matrix, and the EVD are conducted simultaneously and are individually pipelined to maximize throughput. This article presents the architecture, circuit design, and performance estimates based on post-layout extraction of the proposed preprocessing ICA accelerator. The proposed design achieves a throughput of 40.7 kMatrices/s at a complexity of 73.3 kGE.

Interference cancellation and frequency down-conversion receiver based on Sagnac loop

Compared with traditional duplex technology, in-band full-duplex (IBFD) technology can improve spectrum utilization, network capacity and system throughput. However, strong co-frequency signals from adjacent transmission antennas may cause the received signals to be flooded, significantly degrading the communication performance. In addition, frequency down-conversion is an essential function of the receiver, and the subsequent image interference will also block the receiver. A self-interference cancellation (SIC) and image rejection down-conversion receiver based on the Sagnac loop is presented to solve these two problems. The self-interfering signals are eliminated using polarization control and delay matching in the optical domain. Image rejection is achieved by adjusting the DC bias of the modulator. Therefore, all operations required for the above two functions are implemented using optical methods. The theoretical and experimental validation is carried out. The results show that a self-interference cancellation depth of over 43 dB and an image interference rejection ratio of 45 dB is achieved for single-tone signal after frequency down-conversion. For 16 quadrature amplitude modulation (16QAM) signals with a bandwidth range from 20 MHz to 50 MHz, the self-interference cancellation depth exceeds 26 dB, and the image interference rejection ratio exceeds 30 dB.

UE Grouping Algorithms to Maximize Frequency Sharing in Hybrid IBFD Networks

Demonstrated Spectral Efficiency (SE) gain by In Band Full Duplex (IBFD) makes it an attractive radio technology. Owing to inherent complexities in IBFD, Hybrid IBFD Cellular Network (HICN) is opted in practice because it limits IBFD capability only to Base Station and continues with legacy Half Duplex (HD) User Equipments (UEs). Since sharing frequencies within UE groups maximizes sum-SE in a HICN, we formulate a grouped UEs maximization problem for achieving maximum frequency sharing. Unlike heuristic search methods developed in literature, in this paper, we build a mathematical framework for UE grouping. Three grouping algorithms are analytically derived in closed-forms with varying performance and time complexity trade-offs. The optimal algorithm provides benchmarking on these performance measures. Using structural advantages of a HICN, we derive reduced search-optimal algorithm that reduces time complexity while guaranteeing optimal grouping, whereas near-optimal algorithm achieves close-to-optimal grouping with substantially reduced time complexity for real-time cellular systems. We further introduce the concept of ineligible UEs, which uniformly reduces time complexity of all three algorithms without impacting their grouping performance. Extensive simulations reveal that the proposed near-optimal algorithm achieved a median sum-SE of 93.5% of theoretically doubling maximum over legacy HD systems, thus emerging as a prospective solution.