Full-Duplex Communications: Antenna Story

Mitigating self-interference (SI) is vital for advancing simultaneous transmit and receive (STAR) systems. The noise and linearity of the canceller impose limitations on SI power handling. This article proposes a novel dual-path SI cancelling scheme for high-power SI handling. The proposed approach breaks self-interference cancellation (SIC) tradeoffs between operating frequency, SI power handling, and canceller noise/distortion by using a frequency-translated (FT) SI canceller and an auxiliary FT noise-cancelling (NC) path that cancels the noise/distortion from the primary canceller. This approach can work well for both full-duplex (FD) and frequency-division duplex (FDD) schemes. The 65-nm CMOS implementation achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 45-dB SIC for 12-dBm receiver (RX) SI peak power (9-dBm avg.) with only 4-dB noise figure (NF) degradation and 207-mW power consumption at 600 MHz. The SIC approach enables a blocker-1 dB with respect to SI 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> 16 dBm (8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> higher than prior work) while operating from 0.5 to 1.3 GHz. Therefore, this implementation can support watt-level SI power handling with transmitter (TX)–RX isolation <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> 15 dB. This is demonstrated through measurements that show 30-dBm TX power handling with 22-dB initial isolation from the circulator.

In-band full-duplex (IBFD) systems require promising resource allocation (RA) strategies to fully exploit the available time-frequency resources. Furthermore, the acquisition of channel state information and signal reception in IBFD systems are significantly impacted by insufficient self-interference cancellation (SIC), impeding the applications of IBFD in practical wireless systems. Multicarrier-division duplex (MDD), which benefits low-budget SI mitigation in digital domain and flexible subcarrier assignment, is expected to be a promising transitional technique from half-duplex (HD) to IBFD. To demonstrate the advantages of MDD over HD, this paper first compares the upper-bound performance of MDD and HD by applying unfair greedy RA. Then, considering the millimeter-wave (mmWave) with hybrid beamforming, we propose the RA optimization with the quality-of-service constraints on both downlink (DL) and uplink (UL) mobile-stations (MSs). To solve this non-convex RA problem, we divide it into a suboptimal subcarrier allocation problem solved by the proposed improved fair greedy (IFG) algorithm, and a convex power allocation problem. Furthermore, we design two general hybrid precoder based on matrix factorization and direct approach, and a combiner having high SIC capability. Our results show that the proposed RA algorithm can achieve the performance near the upper-bound achieved by the unfair greedy algorithm, while guaranteeing the proportional fairness among all DL/UL MSs. The performance of the two precoding schemes is depended on the number of radio frequency chains supported. Finally, the proposed SIC algorithm is able to provide sufficient SI mitigation, which can be implemented without impacting the RA operation.

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.

In next generation Wireless Local Area Network (WLAN), increasing spectral efficiency is indispensable in order to provide enhanced throughput. Spectral efficiency can be increased though Simultaneous Transmit and Receive (STR) technology. In this paper, an efficient WLAN transmission scheme using STR technology is proposed. Since STR technology allows simultaneous reception while receiving, at most network throughput can be doubled. However, in order to utilize STR technology, at least two non- interfering parties are required. Railroad communication environment of busy railroad station is able to provide good STR environment with plenty number of non-interfering communication parties. Therefore, the proposed scheme is able to provide very efficient railroad communication scheme.

In-band full duplex (IBFD) is regarded as one of the most significant technologies for addressing the issue of spectrum scarcity in 5G and beyond systems. In the realization of practical IBFD systems, self-interference, i.e., the interference that the transmitter causes to the collocated receiver, poses a major challenge to antenna designers; it is a prerequisite for applying other self-interference cancellation (SIC) techniques in the analog and digital domains. In this paper, a comprehensive survey on SIC techniques in the antenna/propagation (AP) domain is provided and the pros and cons of each technique are studied. Opportunities and challenges of employing IBFD antennas in future wireless communications networks are discussed.

Aiming at the application of full-duplex (FD) method in phased array for different kinds of waveforms for different functions, based on the modeling of coupling path characteristics for different spatial links using adaptive system identification method, five representative waveforms, including linear frequency modulation (LFM), pseudorandom frequency shift keying (FSK), continuous phase frequency shift keying (CPFSK), dense repeated jamming (DRJ), and wide-band noise (WBN), are designed and applied in full-duplex mode to validate their self-interference cancellation (SIC) performance in practical experiments. From the experiments' results, where the best SIC is about 38dB for LFM, while the worst SIC is just 5∼7dB for DRJ and WBN, we can draw the conclusion that different kinds of waveforms used for different functions can bring on obviously inconsistent SIC, even in the same frequency bandwidth of 300MHz. Thus it can be seen that waveform characteristics used in multifunction phased array play an important role for self-interference cancellation of simultaneous transmit and receive (STAR).

We demonstrate a wideband scanning 4-arm spiral antenna array with high transmit/receive isolation for Simultaneous Transmit and Receive (STAR). STAR increases a channel's spectral efficiency by transmitting and receiving across the full bandwidth of a channel. To our knowledge, this is the first STAR array to demonstrate scanning across GHz bandwidths. Each 4-arm spiral element is divided into two arms for transmit and two more for receive. To suppress grating lobes, the element spacing is kept at less than λ/2. A 3×3 array prototype was fabricated and measurements agree well with simulations.

Code-domain signal processing techniques implemented at radio frequencies (RFs) enable simultaneous transmit and receive (STAR) applications. With direct sequence spread spectrum (DSSS) techniques and RF correlators, transmit (TX) self-interference (SI) is separated from the receive (RX) signal at the antenna interface for STAR. The processing gain inherent in the code-domain approach increases the TX SI rejection in the RF domain to relax filtering and linearity requirements of the RX. A code-domain RX demonstrates 52 dB of TX SI rejection with TX code-notch and RX code-pass filters operating at the same center frequency. The RX is tunable from 0.25 to 1.25 GHz and has a gain of 39 dB at 1 GHz while consuming 90 mW of which 40 mW are consumed in the front-end filters. The RX is implemented in a 45-nm CMOS SOI process and full-duplex operation is verified through an over-the-air demonstration.

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

In-band full-duplex (IBFD) transmission represents an attractive option for increasing the throughput of wireless communication systems. A key challenge for IBFD transmission is reducing self-interference. Fortunately, the power associated with residual self-interference can be effectively canceled for feasible IBFD transmission with combinations of various advanced passive, analog, and digital self-interference cancellation schemes. In this survey paper, we first review the basic concepts of IBFD transmission with shared and separated antennas and advanced self-interference cancellation schemes. Furthermore, we also discuss the effects of IBFD transmission on system performance in various networks such as bidirectional, relay, and cellular topology networks. This survey covers a wide array of technologies that have been proposed in the literature as feasible for IBFD transmission and evaluates the performance of the IBFD systems compared to conventional half-duplex transmission in connection with theoretical aspects such as the achievable sum rate, network capacity, system reliability, and so on. We also discuss the research challenges and opportunities associated with the design and analysis of IBFD systems in a variety of network topologies. This work also explores the development of MAC protocols for an IBFD system in both infrastructure-based and ad hoc networks. Finally, we conclude our survey by reviewing the advantages of IBFD transmission when applied for different purposes, such as spectrum sensing, network secrecy, and wireless power transfer.

In-Band Full-Duplex (IBFD) Underwater Acoustic (UWA) communication technology can transmit and receive communication signals in the same frequency band at the same time. Theoretically, its frequency utilization efficiency can reach twice of the traditional half-duplex (HD) UWA communication systems. Therefore, it holds great research significance and application value for UWA communication where available spectrum resources are seriously limited. The main challenge in the implementation of IBFD-UWA communication system is to counteract the local self- interference (SI) signal. Generally, SI cancellation (SIC) can be divided into three main aspects, namely, SI suppression in space, SIC in analog domain and digital domain. Digitally Assisted Analog SIC (DAA-SIC) is concerned as it can deal with complexSI propagation channel. However, in the implementation process of the DAA-SIC scheme, its performance will be affected by hardware conditions, such as the effective number of bits of analog to digital converter (ADC) of auxiliary acquisition link, non-linear distortion of power amplifier (PA) and so on. To deal with the influence of hardware parameters on the performance of DAA-SIC scheme, this paper proposes a new analog SIC scheme. The core of this scheme is to reconstruct the output signal of PA and reduce the non-linear distortion of power amplifier and the influence of effective number of bits of auxiliary link through Memory Polynomial (MP) model and Digital Pre- Distortion (DPD) process. The performance of the existing scheme and the new DAA-SIC scheme is verified by numerical simulation. The simulation results show the effectiveness of the proposed scheme.

Simultaneous transmit and receive (STAR) architectures must continually improve receiver isolation techniques to support more demanding frequency agile and instantaneous RF bandwidth requirements. To ensure adequate lifetime and STAR performance, leakage signals above receive saturation levels must be suppressed to protect sensitive front end components. A commonly used technique to suppress leakage signals, known as selfinterference cancellation (SIC), can provide a sufficient level of analog isolation for full duplex operation. The adaptive self-interference canceller developed in this paper utilizes a novel transversal filter approach that passively replicates the strongly distorted transmitted signal, coupled at the receiver, for true time delay cancellation. Conventional transversal filter implementations introduce significant divider, combiner, and attenuator losses between each tap, severely limiting the synthesizable order of the multiple-path leakage channel, which effectively degrades the cancellation performance. To avoid these fixed losses, the novel transversal filter prototype incorporates a lineup of tunable coupler pairs transversely through delay lines as a theoretically lossless alternative to set amplitude and phase weighting coefficients at each tap. Minimizing transversal filter loss lessens the required coupling factor and improves insertion and power efficiency loss penalties at receive and transmit paths respectively. The loss improvements of the SIC architecture define the maximum interference power that can be cancelled. Therefore, to maximize the dynamic range of a STAR system, the SIC architecture should utilize a matching filter that balances loss, noise, and distortion. We propose a technique that provides a completely passive method to cancel strongly coupled signals up to 25 dBc below the transmitted power. The work outlines an avenue to substitute loss driven amplitude and phase weighting components with tunable reflective discontinuities, see equation (1) for a 2-tap filter expression, which can be extended to N-taps by cascading N-1 tunable coupler pairs. Analysis of the novel lossless transversal filter architecture has shown a cancellation performance of 30 dB across a125 MHz bandwidth centered at 2.4 GHz.

An efficient method for simultaneous nonlinear self-interference (SI) cancellation and signal-of-interest (SOI) recovery is proposed and experimentally verified in a mmWave over fiber testbed, based on a specially designed dual-input deep neural network (DI-DNN). The mmWave band has been adopted in the U.S. to provide 5G wireless access services due to its wide-bandwidth, light-of-sight propagation, and inherent compatibility with small cell architecture. To further meet the uprising bandwidth-demanding services, the in-band full-duplex (IBFD) scheme is introduced to magnify the mmWave channel capacity for the 5G and beyond wireless communications. Fortunately, the mmWave band is more realistic to implement IBFD compared with the conventional sub-6GHz band, as it operates as a highly directional beam and shorter transmission distance resulting in a higher SOI to SI ratio. In our proposed solution, a DI-DNN is, for the first time, proposed and implemented to simultaneously realize the SI cancellation and the SOI recovery. Moreover, we firstly mitigate the nonlinearity arising from the transmitters of both the SI and SOI, as well as the nonlinear crosstalk from the SI to the SOI after detection by a nonlinear receiver. The demonstration of the DI-DNN joint with the experimental implementation in a mmWave over fiber system, promise spectral efficient, high-capacity signal transport in the 5G and beyond wireless communications.

Self-interference (SI) channel characteristics are crucial for SI cancellation (SIC) techniques of in-band full-duplex (IBFD) wireless communications. This paper develops two geometry-based statistical channel models-geometry-based concentric ellipses model (GBCEM) and geometry-based concentric circles model (GBCCM)-for full-duplex systems in micro- and macrocell environments, respectively, to analyze the characteristics of reflected-path SI (RSI) compared with the desired signal (DS). The probability density functions of incident angle and path length are derived to identify the fading characteristics of RSI and DS. The simulations based on GBCEM and GBCCM intuitively present the signal characteristics by the signal envelope in the time domain, the statistics of signal envelope, the autocorrelation properties, and the power spectral density. We find that the fading characteristics of RSI and DS can be modeled as Rayleigh when reflectors sit far away from the receiver. We also find that RSI is still likely to be Rayleigh fading, even if DS is not when reflectors scatter in a specific region restricted by the range of incident angle. Our works on the characteristics of RSI and DS are generally helpful to explore a more efficient SIC mechanism for IBFD systems, and the developed models are useful for both simulation and analysis purposes.

As we are witnessing the surge of ongoing wireless communication systems, simultaneous transmit and receive (STAR) schemes are proving to be advantageous due to the doubling of spectral efficiency. However, for the successful realization of STAR, we need to overcome a major bottleneck in suppressing the self-interference from the transmitter onto the colocated receiver. Currently, mitigating this interference requires complex hardware and advanced algorithms when employing an array for applications such as multiple input, multiple output (MIMO), and beamforming. This interference can arise from both near-field and far-field coupling in a MIMO beamforming system. Consequently, this paper presents a unique STAR approach that provides an average isolation of 40 dB between Tx and Rx ports across all elements of the MIMO beamforming system. The proposed approach can be extended to large antenna arrays.