Full-duplex Transceiver Research Articles

Full duplex based collision detection to enhance the V2X sidelink autonomous mode

The Third Generation Partnership Project (3GPP) recently introduced the fifth-generation (5G) new radio (NR) sidelink to enable vehicle-to-everything (V2X) communications supporting advanced safety services. Nevertheless, improvements over the previous generation still pose challenges to meet the reliability and latency requirements of V2X communications, particularly in the allocation of distributed resources, i.e., Mode 2. In Mode 2, vehicles autonomously select radio resources for their message transmissions and can maintain the selected resources for a given reservation period to efficiently handle periodic data traffic. However, potential collisions during this period may remain undetected due to half-duplex communications and unacknowledged broadcast transmissions, resulting in persistent message losses and posing a threat to road safety. This paper aims to improve the 5G NR-V2X sidelink for systems beyond 5G-Advanced by exploiting full-duplex transceivers. We propose a novel medium access control (MAC) scheme where vehicles can detect collisions while transmitting, dynamically adapt the collision detection threshold according to the measured channel load, and react to detected collisions through appropriate resource reselection and retransmission procedures. Extensive simulations conducted under various settings show that this MAC scheme brings substantial performance gains in terms of reliability and latency, compared to the current legacy Mode 2 procedure and a benchmark full-duplex scheme from the literature.

A 2.4-GHz Full-Duplex Transceiver With Broadband, Linearity-Enhanced, and Long-Delay Spread Self-Interference Cancellation

A 2.4-GHz Full-Duplex Transceiver With Broadband, Linearity-Enhanced, and Long-Delay Spread Self-Interference Cancellation

Two closely spaced microstrip patches with high isolation for full-duplex/MIMO applications.

This paper shows an effective method to significantly enhance the isolation of a closely spaced two-port patch antenna, which can be deployed for full-duplex transceivers as well as multiple-input-multiple-output (MIMO) systems. Two rectangular microstrip patches are arranged in the E-plane configuration. To achieve high isolation, a grounded stub is positioned between the radiating patches. For validation of the proposed concept, an antenna prototype is fabricated for measurements. The measured data demonstrates that the port-to-port mutual coupling can be suppressed to -50 dB, which is useful in self-interference cancellation for full-duplex communication systems. Compared with the coupled design, the isolation is significantly enhanced by 43 dB with an inter-element spacing of 0.034λc, where λc is a free-space wavelength at the center operating frequency. Regarding MIMO metrics, the antenna also shows good MIMO diversity performance based on an envelope correlation coefficient and a diversity gain.

Efficient Real-Time Whitening for Blind Eigenvalue-Based Detection in mmWave Full Duplex Cognitive Radio

Although combining Full Duplex (FD) and Cognitive Radio (CR) technologies can provide several benefits, the presence of the residual self-interference (RSI) at the FD transceiver may influence the spectrum sensing capabilities. In particular, focusing on the blind eigenvalue-based detectors (EVDs), this paper shows that operating at mmWave widebands, the RSI is a colored noise strongly affecting the detection performance even when it is characterized by low power. Consequently, we propose here a whitened detector whose novelty consists in the real-time computation of the whitening matrix, differently from previous works which employ an offline computation. The proposed whitening matrix computation uses a sample covariance matrix (SCM) regularization tailored for the FD scenario, instead of the conventional SCM estimator. Particularly, we prove that the proposed whitened detector is robust against RSI power uncertainty, attaining a constant false alarm rate under typical FD operating conditions. Finally, we show that our method provides computational load reduction and faster convergence to the theoretical false alarm probability characteristic of the white noise case. Numerical simulations validate the theoretical analysis confirming the better performance of the proposed whitening approach, particularly when applied to the sphericity test, in comparison to the offline-based approach.

Lossless Decoupling Networks for RF Self-Interference Cancellation in MIMO Full-Duplex Transceivers

Lossless Decoupling Networks for RF Self-Interference Cancellation in MIMO Full-Duplex Transceivers

RIS-Assisted Self-Interference Mitigation for In-Band Full-Duplex Transceivers

The wireless in-band full-duplex (IBFD) technology can in theory double the system capacity over the conventional frequency division duplex (FDD) or time-division duplex (TDD) alternatives. But the strong self-interference of the IBFD can cause excessive quantization noise at the output of the analog-to-digital converters (ADCs), which hampers its real implementation. Fortunately, the reconfigurable intelligent surface (RIS) can reconfigure the wireless channels by dynamically adjusting the reflection coefficients, which makes it a promising solution to self-interference mitigation (SIM) for the IBFD system. This paper considers a RIS-assisted IBFD (RAIBFD) system where a full-duplex base station (BS), assisted by a co-located RIS, receives and transmits signals on the same frequency band simultaneously. We propose to jointly design the DL precoding matrix and the RIS coefficients to mitigate the strong self-interference before the ADCs of finite bit resolutions. To gauge the performance of the proposed RAIBFD system, we also consider an idealistic RIS-assisted IBFD (I-RAIBFD) system with ADCs of infinite bit resolutions and RIS-assisted FDD (RAFDD) system, and take them as performance benchmarks. The effectiveness of the proposed RAIBFD system is verified by simulation studies, even if the phases of the RIS have only finite resolutions.

Ergodic Rate and Outage Performance of Full-Duplex NOMA Relaying with Channel Estimation Errors and Low-Resolution ADCs

In this paper, we analyze the performance of a full-duplex (FD) cooperative non-orthogonal multiple access (C-NOMA) relaying system with an amplify-and-forward (AF) protocol in the presence of loopback interference in FD transceivers. Particularly, by considering channel estimation errors and quantization noise in low-resolution analog-to-digital converters (ADCs), the accurate approximation expression for the ergodic rate and closed-form solution for the outage probability are derived, respectively. The validity of the theoretical results is verified by Monte Carlo simulations, which show that both channel estimation errors and quantization noise have deleterious effects on ergodic rate and outage performance for moderate and high signal-to-noise ratios (SNR). In the second phase of the C-NOMA system, both the outage performance and ergodic sum rate decrease at high SNRs due to the effects of loop interference. When the ADC dynamic range reaches a certain level, the system performance is more affected by loopback interference and channel estimation errors compared to the quantization noise of the ADCs.

Joint Analog and Digital Self-Interference Cancellation for Full Duplex Transceiver With Frequency-Dependent I/Q Imbalance

An effective and practical joint analog and digital self-interference cancellation (SIC) scheme without additional signalling overhead for an I/Q imbalanced full duplex transceiver is proposed in this paper. This scheme combines an I/Q imbalanced analog least mean square (ALMS) loop at the transceiver radio frequency frontend and a two-stage digital signal processing (DSP) at the digital baseband to achieve excellent SIC performance with low complexity. The steady state weighting coefficients of the I/Q imbalanced ALMS loop with periodical transmitted signal and the loop’s convergence behaviour are firstly analysed. The residual SI is then modelled as the output of a time-varying widely linear system. With a track/hold control mechanism applied to the ALMS loop, the system model for digital SIC is further presented, followed by the DSP algorithms suitable for real-time implementation. The noise enhancement in each stage digital cancellation is also analysed and formulated. Finally, simulation results are provided to verify the theoretical analyses and demonstrate the overall SIC performance.

Performance Analysis of Zero-Padded Sequences for Joint Communications and Sensing

Self-interference (SI) is a known but critical issue at the receiver side of a monostatic radar in joint communications and sensing (JCAS) systems, and this is particularly true for high spectral-efficient waveforms. Full-duplex transceivers are usually assumed in the literature, but it is arguable if they can be taken for granted in many devices. We propose a different approach, by eliminating the SI using zero-padded (ZP) orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-division multiple access (SC-FDMA), instead of the more widespread cyclic-prefix (CP)-OFDM. ZP-sequences do not need full-duplex for the monostatic radar operation, as there is no SI between the transmit and receive antennas during the guard interval (GI), which can be used for radar detection. We derive the required radar receiver processing for ZP-sequences and CP-OFDM in time and frequency domains, respectively, to show that when the SI in JCAS is high, ZP-sequences can be beneficial, depending on the target range. Furthermore, we prove analytically that the low peak-to-average power ratio (PAPR) of ZP-SC-FDMA, when compared to ZP-OFDM, is beneficial in time-domain radar processing. This is demonstrated also by means of numerical simulation with ROC curves, for all the candidate waveforms in both coherent and incoherent receiver processing.

Widely-Linear Digital Self-Interference Cancellation in Full-Duplex USRP Transceiver.

Full-duplex (FD) communication systems allow for increased spectral efficiency but require effective self-interference cancellation (SIC) techniques to enable the proper reception of the signal of interest. The underlying idea of digital SIC is to estimate the self-interference (SI) channel based on the received signal and the known transmitted waveform. This is a challenging task since the SI channel involves, especially for mass-market FD transceivers, many nonlinear distortions produced by the impairments of the analog components from the receiving and transmitting chains. Hence, this paper first analyzes the power of the SI components under practical conditions and focuses on the most significant one, which is proven to be produced by the I/Q mixer imbalance. Then, a widely-linear digital SIC approach is adopted, which simultaneously deals with the direct SI and its image component caused by the I/Q imbalance. Finally, the performances achieved by linear and widely-linear SIC approaches are evaluated and compared using an experimental FD platform relying on software-defined radio technology and GNU Radio. Moreover, the considered experimental framework allows us to set different image rejection ratios for the transmission path I/Q mixer and to study its influence on the SIC capability of the discussed approaches.

On the effect of S-parameter stability of antenna and coupler on electrical balance duplexing

Electrical Balance Duplexers (EBDs) provide transmit-receive isolation to implement a form of self-interference cancellation to facilitate simultaneous transmission and reception from a single antenna in systems like In-Band Full-duplex (IBFD) transceivers. EBD works by coupling transmitter, receiver, antenna, and balancing impedance using a hybrid coupler. In recent pieces of literature, antenna impedance variations are considered the main factor limiting the EBD isolation bandwidth, while the EBD balancing impedance needs to be equal as much as possible to the antenna impedance to achieve high isolation. But hybrid couplers are also not ideal elements, and their S-parameters are not stable in the frequency domain. In this work, five broadband RF devices (two antennas, two couplers, and a 50-Ohm RF-load) are used to form four EBD set-ups. One of the antennas, designed by the authors, has more impedance stability in the frequency domain than the other one, which is a commercial antenna. Also, one of the couplers, designed by the authors, has more S-parameter stability in Ultra-Wideband (UWB) frequency domain than the other one, which is a commercial UWB coupler. The implemented EBDs show that when both antenna and coupler have strong S-parameter stabilities in the frequency domain, wider isolation bandwidth (UWB 1.5–3.5 GHz range) and higher EBD isolation are obtained.

Surface Plasmon Polaritons in Time-Modulated Metallic Materials for Non-Reciprocal Controllable Leaky-Wave Antennas

In this work, we propose using time-modulation in metallic materials, which can be realized through either optical pumps or electric signals, as a coupling mechanism between radiation and surface plasmon polaritons (SPP) without using any optical component. By applying temporal changes in the permittivity of metallic materials, scattered waves yield different frequencies from incident waves, potentially satisfying the continuous wave vector condition and enabling SPP from radiation. The coupling is observed in finite-difference time-domain simulations, where the dispersive metallic materials are modeled using auxiliary differential equations. Under the same modulation, coupling from radiation to SPP and from SPP to radiation differ strongly, showing clear evidence of the non-reciprocity. In addition, the coupling is also actively controllable via strength and frequency modulation. We also demonstrate the coupling at multiple angles, which is difficult to achieve with common methods such as Kretschmann or Otto configurations. The direct and non-reciprocal coupling between radiation and SPP can be beneficial for the application of telecommunication to form transmitting-only and receiving-only leaky-wave antennas in full-duplex transceivers.

SICNet—Low Complexity Sample Adaptive Neural Network-Based Self-Interference Cancellation in LTE-A/5G Mobile Transceivers

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.

Hybrid Beamforming for Millimeter Wave Full-Duplex Under Limited Receive Dynamic Range

Full-duplex millimeter wave (mmWave) communication has shown increasing promise for self-interference cancellation via hybrid precoding and combining. This paper proposes a novel mmWave multiple-input multiple-output (MIMO) design for configuring the analog and digital beamformers of a full-duplex transceiver. This work is the first to holistically consider the key practical constraints of analog beamforming codebooks, a minimal number of radio frequency (RF) chains, limited channel knowledge, beam alignment, and a limited receive dynamic range. To prevent self-interference from saturating receive components, such as LNAs and ADCs, a design framework is developed that limits the degree of self-interference on a per-antenna and per-RF chain basis. We present a means for constructing analog beamforming candidates from beam alignment measurements to afford our design greater flexibility in its aim to reduce self-interference. Numerical results evaluate the design in a variety of settings and validate the need to prevent receiver-side saturation. These results and corresponding insights serve as useful design references and benchmarks for practical full-duplex mmWave transceivers.

Improvement in bit error rate of in-band full-duplex transceiver using clipping and clip-noise compensation techniques

Improvement in bit error rate of in-band full-duplex transceiver using clipping and clip-noise compensation techniques

Non-Linear Self-Interference Cancelation for Full-Duplex Transceivers Based on Hammerstein-Wiener Model

The main challenge in a full-duplex transceiver design is created by the self-interference caused by the coupling of the transmitted signal to the transceiver’s own receiver. The effect of the non-linear operation of both the power amplifier at the transmitter and the low noise amplifier at the receiver are considered in the self-interference cancelation. The performance of three self-interference cancelers are studied: linear cancelation, auto-regressive moving-average (ARMA) based cancelation and a neural network (NN) based canceler. The NN based cancelation outperforms both the linear and ARMA based canceler but requires considerably more operations than the other two.

Secrecy Performance of Full-Duplex Jamming and Reception Under I/Q Imbalance

Investigating the physical layer security performance of full-duplex (FD) radio transceivers has been the subject of numerous research studies. However, self-interference cancellation that enables full exploitation of FD communications is a crucial aspect that deserves special attention. Hence, in this paper, we analyze the effect of a FD transceiver's in-phase and quadrature imbalance (IQI) on simultaneously jamming the receiver of an eavesdropper and detecting a signal of interest by deriving an expression for the secrecy outage probability (SOP) metric. Through further analysis for some special and limiting cases, performance insights are drawn by showing that the SOP is dependent on the image rejection capability of the FD transceiver and is approximately equal to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\frac{3}{\text{IRR}}(\ln {(\text{IRR})} - 1.83)$</tex-math></inline-formula> , where the IRR is the image-rejection ratio. The accuracy of the derived SOP expression is verified through Monte-Carlo simulations.

A full‐duplex transceiver for 20‐Gbps high‐speed simultaneous bidirectional signaling across global on‐chip interconnections

AbstractThis paper presents a high‐speed simultaneous bidirectional transceiver (SBT) for on‐chip wireline communications. A MOS hybrid transistor is utilized to split the received data from the superimposed signal at both ends of the on‐chip interconnection with the assistance of two drivers, namely main and auxiliary. Moreover, a high‐pass filter (HPF) is used as a differentiator to generate the echo cancelation signal. Consequently, the echo‐cancelation for simultaneous bidirectional signaling (SBS) is realized by the combination of the hybrid device and the differentiator. The proposed SBT has been designed and evaluated using 28‐nm CMOS technology over a narrow 5‐mm on‐chip interconnection, which possesses 11.9‐dB loss at the Nyquist frequency (half a bit rate). The energy‐efficiency of the proposed full‐duplex transceiver (FDT) for 20‐Gbps simultaneous bidirectional data transmission is 0.147 PJ/b/mm. The performance results show that the proposed SBT has better overall performance compared to the previous architectures reported in the literature to date. The layout of the presented SBT occupies a low area of 1574 μm2.

A chip-less and battery-less subharmonic tag for wireless sensing with parametrically enhanced sensitivity and dynamic range

Massive deployments of wireless sensor nodes (WSNs) that continuously detect physical, biological or chemical parameters are needed to truly benefit from the unprecedented possibilities opened by the Internet-of-Things (IoT). Just recently, new sensors with higher sensitivities have been demonstrated by leveraging advanced on-chip designs and microfabrication processes. Yet, WSNs using such sensors require energy to transmit the sensed information. Consequently, they either contain batteries that need to be periodically replaced or energy harvesting circuits whose low efficiencies prevent a frequent and continuous sensing and impact the maximum range of communication. Here, we report a new chip-less and battery-less tag-based WSN that fundamentally breaks any previous paradigm. This WSN, formed by off-the-shelf lumped components on a printed substrate, can sense and transmit information without any need of supplied or harvested DC power, while enabling full-duplex transceiver designs for interrogating nodes rendering them immune to their own self-interference. Also, even though the reported WSN does not require any advanced and expensive manufacturing, its unique parametric dynamical behavior enables extraordinary sensitivities and dynamic ranges that can even surpass those achieved by on-chip sensors. The operation and performance of the first implementation of this new WSN are reported. This device operates in the Ultra-High-Frequency range and is capable to passively and continuously detect temperature changes remotely from an interrogating node.

A 0.75 V Sub-mW CMOS LNA employing transmitted signal suppression technique in a full-duplex wireless brain-machine interface transceiver

This paper presents a sub-milliwatt (sub-mW) low-voltage CMOS low-noise amplifier (LNA) that can be utilized in a full-duplex transceiver without using duplexer. The topology of the proposed LNA includes a wideband RLC network to suppress and isolate the receiver from a high-power ultra-wideband transmitted signal. This feature is comparable to other reported LNAs, which are only applicable to a narrowband signal instead of a wideband signal. In addition, the combination of a source-degenerated cascode LNA with an inverter-based LNA in the proposed topology achieves an ultra-low-voltage low-power operation with a 0.75 V bias voltage. Analytical results and the circuit implementation in a 180 nm CMOS technology verify that the proposed LNA presents an noise figure (NF) of less than 3.45 dB over a 200 MHz bandwidth at a carrier frequency of 2.4 GHz. Simulation results also demonstrate a 14 dB gain (S21), less than −11 dB input return loss (S11) and 50 dB transmitted signal attenuation rather than the desired signal. The power consumption is only 980 μW at a 0.75 V supply. The input-referred third-order intercept point (IIP3) is about −8 dBm, and the chip occupies an area of 0.37 mm2.