Full-duplex Wireless Research Articles

A Two-Stage Analog Self-Interference Cancelation Structure for High Transmit Power In-Band Full-Duplex Radios

High transmit power in-band full-duplex (IBFD) systems are promising due to their tremendous advantages in both civilian and military applications. However, mitigating self-interference (SI) in such a high transmit power condition is significantly challenging. A two-stage analog filtering structure is proposed in this letter to tackle this problem successfully. The first stage is based on a vector modulator and a balun to cancel the direct leakage SI component. The second stage is constructed from an analog least mean square (ALMS) loop to adaptively cancel the residual SI. The performance of the second stage with nonlinear transmit signals is investigated analytically. Simulation results show that a total 75 dB of SI cancellation can be achieved by the proposed structure, ensuring the residual SI falls into the linear range of the analog-to-digital converter.

On the Impacts of I/Q Imbalance in Analog Least Mean Square Adaptive Filter for Self-Interference Cancellation in Full-Duplex Radios

Frequency-dependent in-phase/quadrature-phase imbalance (IQI) is a critical hardware impairment, which affects the performance of the self-interference (SI) cancellation structure in full-duplex systems. A novel frequency-dependent IQI model is proposed in this paper, providing a theoretical tool to evaluate the impacts of this impairment in the analog domain. The model is then applied to investigate the performance of the analog least mean square (ALMS) loop under both frequency-selective and frequency-independent IQI. The degradation in the SI cancellation performance of the ALMS loop is revealed and its upper bound is derived. Numerical results show that the ALMS loop is resilient to both types of IQI with the maximum level of only 3.5 dB performance degradation even when the image rejection ratio is just 15 dB.

Optical Multi-Tap RF Canceller for In-Band Full-Duplex Wireless Communication Systems

In-band full-duplex (IBFD) technology has become important for future wireless communications, due to its ability of increasing the radio-frequency (RF) spectrum efficiency. However, the benefits can only be realized if the self-interference (SI) is sufficiently suppressed. RF cancellation is important for IBFD systems due to its ability of SI mitigation. But it becomes more difficult for RF cancellation while the frequency and bandwidth increase. In real scenarios, the response of the multi-path SI channel is not frequency-flat, which also limits the cancellation performance. To solve these problems, we present a photonic-enabled multi-tap RF canceller in this paper. The proposed RF canceller has the ability of cancelling multi-path SI. The tap coefficients are precisely adjusted by optical spectrum processing. A prototype system with 8 taps is demonstrated in this paper. The measured results show 25 dB average cancellation depth over 1 GHz cancellation bandwidth under over-the-air conditions. To verify the signal of interest (SOI) recovery capability of the novel RF canceller, an IBFD wireless communication experiment based on 16-quadrature amplitude modulation (16-QAM) was demonstrated, the SOI was successfully recovered.

Full-duplex wireless deep ultraviolet light communication.

With recent advancements in deep ultraviolet (DUV) light-emitting diodes (LEDs) and solar-blind photodetectors, wireless DUV light communication is emerging as a novel technique, which can extend transmission ranges and avoid solar interference. Herein, a full-duplex, real-time wireless light communication system using 275 nm DUV LEDs is proposed. We adopted high-power DUV LEDs and designed a high-speed transmitter, a high-sensitivity receiver, and a main processing unit for the system. Furthermore, the DUV communication system, using a Reed-Solomon (RS) encoder and an on-off keying (OOK) modem with frequency control, achieves a 10 Mbit/s bidirectional data transmission rate within 5 m in free space, while a full-duplex video communication link is formed. The encapsulated DUV communication system described in this Letter provides a feasible scheme for confidential and anti-electromagnetic interference communication in Internet of Things (IoT) applications.

A Lazy Learning-Based Self-Interference Cancellation Approach for In-Band Full-Duplex Wireless Communication Systems

We propose a new lazy learning-based cancellation approach to improve spectral efficiency for current wireless communication systems, suppress self-interference (SI) sent from base stations, and enable in-band full-duplex (IBFD) transmissions in cellular networks. Our proposed approach consists of two phases based on traditional IBFD systems: an offline phase for database generation and an online phase for data transmission. In the offline phase, the output before a 0/1 decision is premeasured without the desired signal input and recorded in a database with self-defined feature vectors (FVs). In the online phase, a suitable result is sought from the generated database with the help of a learning method and FV for the same system architecture with the desired signal input. The result is then assigned an SI cancellation value. Regular and eager learning-based cancellation approaches are employed to evaluate the proposed method and simulate the transmission output. Computer simulation results indicated that the proposed cancellation methods could achieve about 134 dB SI suppression and achieve nearly the same transmission levels as methods with no SI effect, enabling the IBFD operations in wireless communication systems better than the regular and eager learning-based techniques.

Dual polarized patch antenna array with improved isolation and gain for full-duplex wireless communications

Dual polarized patch antenna array with improved isolation and gain for full-duplex wireless communications

A New Online Nonlinear Self-Interference Cancelation Method With Random Fourier Features

In this letter, we present a new online nonlinear digital self-interference cancelation method for full duplex radios. In this method, random Fourier features transformation is performed before utilizing the least mean squares algorithm, which is applied to the residual of linear digital cancelation. The proposed solution’s performance is evaluated against prominent nonlinear cancelation schemes on the same full duplex radio set-up, consisting only of a monostatic antenna and a WARP v3 board. Our experimental results show that the proposed solution provides the highest self-interference cancelation while reducing the complexity of the batch solutions by up to two orders of magnitude.

An RTS–CTS based medium access control protocol for full-duplex wireless local area networks

In-band full-duplex (IB-FD) wireless is a promising next generation communication technology which can double the spectral efficiency with respect to the conventional in-band half-duplex (IB-HD) radio. Hidden stations degrade the performances of any practical wireless networks, but unlike IB-HD networks, hidden station scenarios are different in IB-FD wireless networks. In this paper, we have presented a novel energy-efficient medium access control protocol exploiting the network allocation vector, whereby mitigating the hidden station problem in an IB-FD wireless network. Moreover, an analytical model has been devised to unveil the impact of the distance between a primary–secondary transceiver pair in order to select a secondary receiver to initiate a successful relay like IB-FD link, thereby diminishing the inter-station interference problem. In addition, we have shown that the number of IB-FD transmission link increases if the secondary transmitter uses adaptive transmission power. We have evaluated the performance of the proposed protocol through detailed simulations using a modified version of NS-3 in which the wireless module has been re-designed to accommodate the concept of IB-FD radio. Results show that our proposed protocol achieves at least 61% and 41% throughput gain and consumes 58% and 60% lower energy than IEEE 802.11 DCF RTS–CTS and FD-MAC protocols, respectively. Our proposed protocol outperforms the baseline protocols with respect to throughput, energy consumption, average re-transmission rate, average packet drop rate, etc. The proposed scheme can be very useful to IB-FD wireless networks which contain bandwidth-hungry applications.

Design and analysis of IEEE 802.11 based Full Duplex WLAN MAC protocol

Full-Duplex (FD) communication is a promising technique that can be used in 5G to potentially double the system throughput compared to conventional Half Duplex (HD) transmission. Recent experiments have demonstrated near-perfect self-interference suppression techniques in the PHY layer to aid the possibility of FD communication. This paper presents a Synchronized Mode Full-Duplex (SM-FD) wireless LAN MAC protocol with appropriate modification of the IEEE 802.11 standard. The proposed SM-FD MAC protocol maintains synchronization between nodes and Access Point (AP) to increase efficiency. SM-FD MAC protocol supports WLAN having both FD and HD capable nodes by establishing both symmetrical links (Node1 ↔ AP) and asymmetrical links (Node1 → AP → Node2). To this end, we have utilized the packet-alignment-based capture effect in an efficient way. The proposed SM-FD MAC protocol has been analyzed using a Markov chain model. The analytical results for RTS and data collision probability, saturated throughput, delay, and energy spent per packet transmission have been derived and validated against simulation.

Frequency-Domain Successive Cancellation of Nonlinear Self-Interference With Reduced Complexity for Full-Duplex Radios

Nonlinear self-interference (SI) cancellation is crucial for eliminating the impact of the transmitter-side nonlinearity on the comprehensive SI cancellation performance in full-duplex radios. However, in the propagation environment with rich reflection paths of signals, the number of the delayed taps required for time-domain nonlinear SI cancellation booms exponentially with the increase of the multi-path number, leading to unacceptable complexity. In this paper, a novel frequency-domain nonlinear SI canceller based on successive interference cancellation (SIC) technique is proposed for orthogonal frequency division multiplexing (OFDM) modulated full-duplex systems subjected to both transmitter nonlinearity and receiver nonlinearity. The proposed frequency-domain nonlinear SIC (FD-NSIC) cancels nonlinear components one by one via separately estimating the channel frequency response suffered by each order nonlinear component, which significantly relaxes the computational cost. Besides, to avoid the influence of the strong correlation between nonlinear components, orthogonalization is operated before SIC to white basis functions, which accelerates the convergence speed of the proposed FD-NSIC. Simulations are explicitly performed, showing that compared with the conventional frequency-domain nonlinear canceller based on recursive least squares (RLS) channel estimation, the proposed FD-NSIC is capable of canceling the SI to the noise floor with only 52% computational cost under 50 dB interference-to-noise ratio.

Photonic-Assisted RF Self-Interference Cancellation Based on Optical Spectrum Processing

In band full-duplex (IBFD) wireless systems increase the RF spectrum efficiency and have become one of the key technologies in the future wireless communication systems. But it is only possible if the radio-frequency (RF) self-interference (SI) generated by the transmitter is sufficiently mitigated. SI cancellation becomes more difficult while the bandwidth and frequency increases. Herein, a novel approach to photonic-assisted RF SI cancellation based on optical processing is proposed for IBFD wireless systems. In this scheme, reference signal and the received signal are converted to optical signals by two Mach-Zehnder modulators. The phase and amplitude between reference and received signal are matched by optical spectrum processing, and the delay time is aligned by finely tuning the tunable optical delay line (TODL). The broadband interference signal within the received signal is removed in the optical domain. Experimental results show more than 30 dB cancellation depth in 10 GHz bandwidth. Besides, IBFD transmission performance based on 16-QAM for different symbol rates and different signal-to–interference ratios (SIR) are also demonstrated, as well as 92.6 dB•Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> spurious-free dynamic range (SFDR) is obtained.

Throughput Analysis for Wireless Full-Duplex Multi-Hop Networks with RTS/CTS-Based MAC

Medium access control (MAC) protocol operations for in-band full duplex multi-hop networks play an important role in efficient data relaying and throughput enhancement. Knowledge of the relationship between essential operations in MAC protocol for full duplex MAC (FD MAC) networks and network performance is important and useful in terms of the protocol and network design. FD MAC protocols often require exchanging control frames, e.g., request to send/clear to send (RTS/CTS). However, the conventional model cannot analyze the performance of wireless multi-hop networks with RTS/CTS-based FD MAC. Thus, this paper proposes a throughput analysis model for wireless multi-hop networks with RTS/CTS-based FD MAC. The proposed model includes novel “airtime expressions”, which allows us to handle RTS/CTS operations under FD MAC. The proposed model provides the end-to-end throughput of multi-hop networks with RTS/CTS-based FD MAC for any number of hops and any payload size. The validity of the analytical expressions is confirmed through comparisons with simulation results.

UAV Relay-Assisted Emergency Communications in IoT Networks: Resource Allocation and Trajectory Optimization

Unmanned aerial vehicle (UAV) communication has emerged as a prominent technology for emergency communications (e.g., natural disaster) in the Internet of Things (IoT) networks to enhance the ability of disaster prediction, damage assessment, and rescue operations promptly. A UAV can be deployed as a flying base station (BS) to collect data from time-constrained IoT devices and then transfer it to a ground gateway (GW). In general, the latency constraint at IoT devices and UAV&#x2019;s limited storage capacity highly hinder practical applications of UAV-assisted IoT networks. In this paper, full-duplex (FD) radio is adopted at the UAV to overcome these challenges. In addition, half-duplex (HD) scheme for UAV-based relaying is also considered to provide a comparative study between two modes (viz., FD and HD). Herein, a device is considered to be successfully served if its data is collected by the UAV and conveyed to GW timely during flight time. In this context, we aim to maximize the number of served IoT devices by jointly optimizing bandwidth, power allocation, and the UAV trajectory while satisfying each device&#x2019;s requirement and the UAV&#x2019;s limited storage capacity. The formulated optimization problem is troublesome to solve due to its non-convexity and combinatorial nature. Towards appealing applications, we first relax binary variables into continuous ones and transform the original problem into a more computationally tractable form. By leveraging inner approximation framework, we derive newly approximated functions for non-convex parts and then develop a simple yet efficient iterative algorithm for its solutions. Next, we attempt to maximize the total throughput subject to the number of served IoT devices. Finally, numerical results show that the proposed algorithms significantly outperform benchmark approaches in terms of the number of served IoT devices and system throughput.

A Bidirectional RoF System for the Multi-Band Signal with Mitigation of the Nonlinear Effects

A bidirectional full duplex radio over fiber (RoF) system is proposed for multi-band signal generation and transmission. A multi-band signal is generated at the central station (CS), which includes 10 GHz baseband, 40, and 70 GHz millimeter-wave (mm-wave) by optical frequency multiplication technique of radio frequency (RF) local oscillator (LO) with frequency of 15 GHz. The simultaneous transmission of the 16-QAM OFDM-based multi-band downlink signal and 4-QAM uplink signal over a single fiber is demonstrated. The carrier for uplink transmission is extracted from the unmodulated downlink signal with tunable FBG which is modulated by OFDM-based 4-QAM uplink data obtained from the user end via an antenna. The frequency reuse from the downlink signal makes the base station (BS) free from the laser source. At the user end, the multi-band signals for multi-serve application are obtained by heterodyne beating of multiple bands. An increase in launch power induces fiber dispersion and non-linearities like self-phase modulation (SPM) and cross phase modulation (XPM), which depends on the nonlinear refractive index of the fiber. Different industrial standard fibers with common specifications and modulation format along with co-shared components are deployed, and system performance is analyzed. The stimulated Brillouin scattering (SBS) can be mitigated by optimizing the launch power within the SBS threshold. The nonlinear effects are minimized at the system level without the requirement of additional digital signal processor (DSP) . The theoretical and simulation analysis shows that the designed bidirectional RoF link exhibits an improved system performance for bidirectional transmission with negligible power penalty.

Antenna/Propagation Domain Self-Interference Cancellation (SIC) for In-Band Full-Duplex Wireless Communication Systems

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.

Impact of CSI on Single channel In-band Full-duplex Radio implemented with 60 nm Vertical TFET-based CMOS structure

Impact of CSI on Single channel In-band Full-duplex Radio implemented with 60 nm Vertical TFET-based CMOS structure

Total Secrecy From Anti-Eavesdropping Channel Estimation

Anti-eavesdropping channel estimation (ANECE) is useful for a network of cooperative full-duplex radio devices/users. Using ANECE, a secret key can be generated by each pair of users, and additional secret information can be transmitted between a pair of users. This paper analyzes the capacity of the secret key based on ANECE, and compares it with the conventional method for channel training. The paper also analyzes the secrecy capacity of information transmission using an one-way scheme, and compares it with a two-way scheme. It is shown that the total amount of secrecy generated from ANECE can be substantially larger than that based on the conventional method especially when an eavesdropper may have an unlimited number of antennas. The paper also formulates a total secure degree of freedom (TSDoF) of the ANECE based scheme, and compares it with a prior scheme of secret information transmission from a multi-antenna node to another against a multi-antenna eavesdropper where channel state information is unknown everywhere initially. The comparison shows that there is a substantial gain of TSDoF by exploiting full-duplex radios and reciprocal channels via ANECE. Most of the key insights are highlighted in twelve proven properties.

RF self-interference canceller prototype for 100-W full-duplex operation at 225–400 MHz

Military applications require more and different characteristics from in-band full-duplex radio technology than what the research prototypes developed for civil/commercial applications can offer. While the challenge of cancelling the strong transmit–receive coupling, i.e., self-interference (SI), in a full-duplex radio has been largely resolved at higher ultra high frequency (UHF) bands for low-power transmission, tactical communication and electronic warfare applications require major research efforts toward supporting lower military-relevant frequencies and significantly higher transmission power levels. In this paper, we present a prototype of a radio-frequency SI cancellation circuit for the lower UHF band at 225–400 MHz and transmit power of up to 100–200 W. The experimental results demonstrate that the canceller can suppress SI by 40–50 dB depending on the operation frequency within the band. It is targeted for the military application of simultaneous full-duplex jamming and interception of communications, where we can estimate that a 5-W signal-of-interest could be intercepted from 10 km away when simultaneously jamming with 100 W power.

Practical Hybrid Beamforming for Millimeter Wave Massive MIMO Full Duplex With Limited Dynamic Range

Full Duplex (FD) radio has emerged as a promising solution to increase the data rates by up to a factor of two via simultaneous transmission and reception in the same frequency band. This paper studies a novel hybrid beamforming (HYBF) design to maximize the weighted sum-rate (WSR) in a single-cell millimeter wave (mmWave) massive multiple-input-multiple-output (mMIMO) FD system. Motivated by practical considerations, we assume that the multi-antenna users and hybrid FD base station (BS) suffer from the limited dynamic range (LDR) noise due to non-ideal hardware and an impairment aware HYBF approach is adopted by integrating the traditional LDR noise model in the mmWave band. In contrast to the conventional HYBF schemes, our design also considers the joint sum-power and the practical per-antenna power constraints. A novel interference, self-interference (SI) and LDR noise aware optimal power allocation scheme for the uplink (UL) users and FD BS is also presented to satisfy the joint constraints. The maximum achievable gain of a multi-user (MU) mmWave FD system over a fully digital half duplex (HD) system with different LDR noise levels and numbers of the radio-frequency (RF) chains is investigated. Simulation results show that our design outperforms the HD system with only a few RF chains at any LDR noise level. The advantage of having amplitude control at the analog stage is also examined, and additional gain for the mmWave FD system becomes evident when the number of RF chains at the hybrid FD BS is small.

Wideband, Low Profile Coupling Suppression Circuit for Simultaneous Transmit and Receive System Based on Hybrid Finite Impulse Response and Resonator Topology

In-band full-duplex (IBFD) systems can double the spectral efficiency by enabling simultaneous transmission and reception within the same band. Key to realizing full-duplex radios is the cancellation of the self-interference (SI) that couples from the transmitting antenna into the receiving path. This is done by introducing a self-interference cancellations (SIC) circuit to significantly reduce the coupled transmit signal and avoid receiver’s desensitization. Additionally, SI suppression becomes more challenging across broader bandwidths. This paper presents a novel, wideband, and low profile SIC circuit based on a hybrid Finite Impulse Response (FIR) and resonator filter topology. The latter is optimized to provide an average of 22dB cancellation across 800MHz in the L-band. Conventional, SIC circuits require a filter bank with at least two FIR filters to achieve such a wide bandwidth. Conversely, our FIR resonator design is low profile with a circuit size nearly half of that of a filter bank. Simulations show a minimum cancellation of 15dB and a maximum cancellation of 45dB. A prototype was fabricated and tested, showing an average of ~ 20dB cancellation which is in good agreement with our simulation. Further, measured results show a minimum cancellation of 15dB and maximum cancellation of 27dB.