Self-interference Cancellation Circuit Research Articles

Dual-polarization MZM-based photonic nonlinear analog self-interference cancellation for in-band full-duplex radios

In this paper, we propose a dual-polarization Mach-Zehnder modulator-based photonic nonlinear analog self-interference cancellation (SIC) technique for in-band full duplex (IBFD) systems. By using the proposed technique, an arbitrary 4th order nonlinear transfer function can be generated, meaning the performance limitation caused by the nonlinearity of the analog SIC circuit can be overcome by imitating the nonlinear transfer function of the analog SIC circuit before cancellation. This paper also presents a performance analysis through simulations and the results of a proof-of-concept demonstration. In the experiment, the proposed nonlinear SIC technique could achieve 29 dB cancellation over 500 MHz bandwidth centered at 1.25 GHz frequency along various degree of distortion caused by nonlinearity. In addition, the performance enhancements achieved by the proposed technique are evaluated in terms of error vector magnitudes (EVMs) and constellations of the signal-of-interest (SOI) in the simulation which is based on the experimental SIC results. More than 3 dB of SOI power gain could be obtained in evaluated EVM performances.

Maximizing Secondary Users’ Sum-Throughput in an In-Band Full-Duplex Cognitive Wireless Powered Backscatter Communication Network

This article studies the secondary users’ sum-throughput in an in-band full-duplex (I-FD) cognitive wireless powered backscatter communication network. The secondary network consists of a hybrid access point (H-AP) and a finite number of geographically distributed secondary backscatter sensors (SBSs), each capable of using either the conventional or backscatter communication. The secondary network shares the primary network’s spectrum using an underlay spectrum sharing model. In this model, the H-AP and SBSs operate in I-FD mode to achieve improved spectral and time efficiency. Moreover, when an SBS has little available energy, it switches to the low-energy consumption backscatter method instead of the conventional transmission method. The goal is to maximize the sum-throughput of the SBSs. It is shown that such a problem is a convex optimization problem. Closed-form expressions for the optimal allocated time and energy to SBSs are derived and solved via a low complexity and efficient algorithm called joint optimal time and energy allocation (JOTEA). Numerical results illustrate that the JOTEA algorithm achieves a higher sum-throughput than the benchmark equal time allocation method. Furthermore, if the self-interference cancellation circuit considerably cancels self-interference in the H-AP, the I-FD mode achieves a higher sum-throughput performance than that of the half-duplex mode. Moreover, using backscatter communication results in a further increase in the sum-throughput.

A 3.1-5.2GHz, Energy-Efficient Single Antenna, Cancellation-Free, Bitwise Time-Division Duplex Transceiver for High Channel Count Optogenetic Neural Interface.

We report an energy-efficient, cancellation-free, bit-wise time-division duplex (B-TDD) transceiver (TRX) for real-time closed-loop control of high channel count neural interfaces. The proposed B-TDD architecture consists of a duty-cycled ultra-wide band (UWB) transmitter (3.1-5 GHz) and a switching U-NII band (5.2 GHz) receiver. An energy-efficient duplex is realized in a single antenna without power-hungry self-interference cancellation circuits which are prevalently used in the conventional full-duplex, single antenna transceivers. To suppress the interference between up- and down-links and enhance the isolation between the two, we devised a fast-switching scheme in a low noise amplifier and used 5× oversampling with a built-in winner-take-all voting in the receiver. The B-TDD transceiver was fabricated in 65 nm CMOS RF process, achieving low energy consumption of 0.32 nJ/b at 10 Mbps in the receiver and 9.7 pJ/b at 200 Mbps in the transmitter, respectively. For validation, the B-TDD TRX has been integrated with a μLED optoelectrode and a custom analog frontend integrated circuit in a prototype wireless bidirectional neural interface system. Successful in-vivo operation for simultaneously recording broadband neural signals and optical stimulation was demonstrated in a transgenic rodent.

A Compact, Bistatic Antenna System with Very High Interport Isolation for 2.4 GHz In-Band Full Duplex Applications

This paper presents a compact, dual polarized bistatic (two closely spaced transmit and receive radiators) patch antenna with excellent interport isolation performance. The presented antenna system employs differential receive mode operation for the cancellation of self-interference (SI) to achieve very high interport isolation for 2.4 GHz in-band full duplex (IBFD) applications. The presented antenna is based on two closely spaced radiators and a simple 3 dB/180° coupler for differentially excited receive mode operation. The 3 dB/180° coupler performs as a passive self-interference cancellation (SIC) circuit for the presented antenna. The small form-factor structure is realized through via interconnections between the receiving patch and SIC circuit. The prototype of the presented antenna characterizes better than 105 dB peak interport isolation. Moreover, the recorded interport isolation is more than 90 dB and 95 dB within 60 MHz and 40 MHz bandwidths, respectively. The measured gain and cross-polarization levels reflect superior radiation performance for the validation model of the proposed antenna. The presented antenna offers DC interport isolation too, which is required for active antenna applications. The novelty of this work is a compact (small form-factor) antenna structure with very high peak interport isolation along with wider SIC bandwidth as compared to previously reported antennas for full duplex applications.

Delay-Sum Group Delay Controller With Low-Loss and Low-Phase Variation

This article presents a group delay controller (GDC) circuit based on the delay-sum method. The proposed circuit can potentially be employed in a self-interference cancellation circuit in full-duplex radio systems. The proposed GDC splits the input signal into two signals with different magnitudes and then combines them in-phase at the output port. Variable group delay can be achieved by changing the power ratio of the two signals. The power dividing ratio (PDR) is changed by employing a variable power divider/combiner (VPD/VPC). The resonant reflective loads substitute for a single varactor diode such that the limited PDR of the VPD/VPC does not degrade the group delay variation range of the GDC. The resonant load can provide infinite PDR by covering open to short susceptance. In addition, asymmetrically connecting the VPD and VPC provides a flatter group delay response. As a result, the delay-sum method enables the proposed GDC to provide low and constant insertion loss while providing low insertion phase variation. The proposed delay sum GDC is demonstrated at 2.5 GHz. The measured insertion loss is only 2.18± 0.28 dB with a continuously controlled relative group delay of 430 ps. Furthermore, the insertion phase variation is only 7.3° at 2.5 GHz, and input/output matchings are maintained for all delay settings.

A compact, dual-polarized patch antenna with improved Tx–Rx isolation for 2.4 GHz single frequency full-duplex applications

AbstractA compact dual-polarized monostatic antenna (single radiator for transmit and receive modes) is presented with differential receive mode operation to achieve excellent interport isolation for 2.4 GHz single frequency full-duplex or in-band full-duplex applications. The presented antenna comprises three ports radiating element (patch) and a simple 3 dB/180o ring hybrid coupler has been utilized for differentially excited receive mode operation. The 3 dB/180o ring hybrid coupler acts as a self-interference cancellation (SIC) circuit for effective suppression of RF leakage from the transmit port to provide very high interport decoupling between transmit and receive ports. A compact antenna structure has been realized by using two-layered printed circuit board through vias interconnections of both receive ports of the antenna with inputs of SIC circuit. The validation model of proposed antenna offers more than 95 dB peak interport isolation. Moreover, the experimentally measured interport isolation is better than 70 dB throughout the antenna's 10 dB return-loss impedance bandwidth (BW) of 50 MHz (2.38–2.43 GHz). Furthermore, the recorded isolation is more than 80 dB in 20 MHz BW. The implemented antenna has good radiation characteristics including nice gain and low cross-polarization levels as endorsed by measurements. Same antenna structure with microstrip-T feeds can provide DC isolated ports with same interport RF isolation performance for active antenna applications. Such antenna with DC interport isolation will avoid the requirements of additional series capacitors on transmit and receive ports of antenna.

Implementation of time-window based analog self-interference cancellation for full-duplex radios

Multi-tap delay line circuits are widely used to model the analog self-interference multipath channel in full-duplex wireless communication systems. However, the complexity of these circuits is a considerable problem. To overcome this issue, this paper investigates a simple dual-channel analog self-interference cancellation circuit. Instead of modeling the multi-tap for multipath reflections, the key sight is that the light-of-sight self-interference is estimated by designing a dual-channel with the fixed delay and tunable attenuator circuit. Feasibility of only canceling the light-of-sight self-interference is explored first. Then, according to the distance of transceiver antennas, delays of the dual-channel are calculated which acts as a time-window to let the light-of-sight self-interference pass. Additionally, due to the error caused by the non-light-of-sight self-interference, attenuators of the dual-channel are designed be tuned adaptively based on the minimum residual mean square error. Finally, the experimental results show that the proposed method can provide up to 50 dB cancellation over different transmission signal bandwidths.

Characteristic-Mode-Based Design of Planar In-Band Full-Duplex Antennas

In-band full-duplex radios demand simultaneous transmit and receive (STAR) antennas with high isolation, compact and ultra-low profiles, and simple feed networks. Current state-of-the-art designs rarely meet all of these requirements at the same time. In this paper, we present a characteristic-mode-based design approach to achieve high isolation using compact fully-planar STAR antennas with a simple feed structure. The proposed method utilizes two characteristic modes of a conducting object as transmit and receive chains to achieve high isolation without a complicated self-interference cancellation circuit. The design example in this work is fully-planar, and it has a physical height of 1.6 mm. The measured -10 dB overlapped $|S_{11}| ~{\mathrm {and}}~ |S_{22}|$ fractional bandwidth of this STAR antenna is 2.5% and the measured isolation between the transmit and receive ports is greater than 30 dB over the entire frequency band of operation.

Differential Fed Antenna With High Self-Interference Cancellation for In-Band Full-Duplex Communication System

This paper presents a novel design of high self-interference cancellation (SIC) technique for microstrip antennas. The proposed antenna consists of two closely-spaced orthogonal antennas with differential feeding as SIC circuit so as to achieve high interport isolation between the transmitter and receiver. In order to achieve high RF leakage cancellation, a novel differential feeding network (DFN) is also proposed in this paper, which provides amplitude and out-of-phase imbalances within 0.12 ± 0.03dB and -180 ± 1°, respectively, for the bandwidth of 500 MHz at a center frequency of 2.50 GHz. General analytical design equations are derived for achieving high SIC over the wide bandwidth. For experimental validation, prototypes are designed and fabricated at the center frequency of 2.50 GHz using an FR-4 substrate with dielectric constant of 4.4 and loss tangent of 0.02. A good agreement is observed among the theoretical analysis, and the simulation and measurement results. The first fabricated prototype provides more than 64 dB SIC for the bandwidth of 110 MHz, while the second prototype achieved more than 60 dB SIC for 160 MHz bandwidth. In addition, the SIC of the antenna using the proposed DFN is high over the wideband frequency bandwidth as compared to conventional 180° ring hybrid feeding network. Due to ease of implementation and excellent performances, the proposed antennas have potential application for wideband in-band full duplex systems.

Wideband RF Self-Interference Cancellation Circuit for Phased Array Simultaneous Transmit and Receive Systems

With the growing demand for spectrum utilization, the concept of full duplex transceivers has become attractive. These simultaneous transmit and receive systems (STAR) are attractive as they double bandwidth utilization. To realize STAR, we must suppress self-interference (SI) between transmit and receive antennas. Doing this across a wide bandwidth presents an even greater challenge. Further, for antenna arrays, SI can be higher due to mutual coupling among neighboring elements. In this paper, we achieve 100 dB isolation for practical STAR, across a large 500 MHz bandwidth. Specifically, four stages of the self-interference cancellation are proposed. In addition to high isolation cross-polarized array elements, we employ multi-tap filters at the transceiver RF front-end for interference cancellation. These filters emulate direct SI coupling using frequency-domain optimization techniques. Measured results show an average of 25 dB filter cancellation is possible across 500 MHz.

Compact dual‐polarised microstrip patch antenna with high interport isolation for 2.5 GHz in‐band full‐duplex wireless applications

In-band full duplex (IBFD) wireless operation can be accomplished by mitigating the self-interference (SI) at the receiver that is caused by coupling of radio-frequency power from its own transmitter. Maximum amount of SI cancellation (SIC) should be achieved at antenna stage to enable full-duplex wireless communication operation at same frequency. This study presents the design and implementation of a compact two-port dual-polarised microstrip patch antenna which uses three-port microstrip patch antenna with 3 dB ring hybrid coupler as SIC circuit to achieve high interport isolation. The implemented antenna provides 57dB interport isolation between transmit and receive ports at centre frequency of 2.5GHz with linear orthogonal polarisation and interport isolation is better than 40dB for 50MHz bandwidth. The fabricated compact microstrip patch antenna has 3.1 and 3.7 dBi gains for Tx and Rx modes, respectively. The proposed antenna has comparatively wider 10dB input bandwidth (50MHz) along with high interport isolation.

Integrated full duplex radios

Full duplex wireless has drawn significant interest in the recent past due to the potential for doubling network capacity in the physical layer and offering numerous other benefits at higher layers. However, the implementation of integrated full duplex radios is fraught with several fundamental challenges. Achieving the levels of self-interference cancellation required over the wide bandwidths mandated by emerging wireless standards is challenging in an integrated circuit implementation. The dynamic range limitations of integrated electronics restrict the transmitter power levels and receiver noise floor levels that can be supported in integrated full duplex radios. Advances in compact antenna interfaces for full duplex are also required. Finally, networks employing full duplex nodes will require a complete rethinking of the medium access control layer as well as cross-layer interaction and co-design. This article describes recent research results that address these challenges. Several generations of full duplex transceiver ICs are described that feature novel RF self-interference cancellation circuits, antenna cancellation techniques, and a non-magnetic CMOS circulator. Resource allocation algorithms and rate gain/improvement characterizations are also discussed for full duplex configurations involving IC-based nodes.

Self-Interference Cancellation Antenna Using Auxiliary Port Reflection for Full-Duplex Application

An aperture-coupled microstrip patch antenna pair with wideband self-interference cancellation (SIC) performance is proposed. It consists of two orthogonal linearly polarized antennas and an auxiliary port loaded with a proper reflective terminal. Besides the direct coupling between two antennas, an indirect coupling path is introduced and controlled by the auxiliary port reflection. The coupling between these two paths will superpose and cause cancellation at the receiving antenna output, while a high isolation between the antennas can be achieved accordingly. For the validation of the proposed SIC, one prototype was designed and fabricated. Good agreement can be observed between the simulated and measured results. A high isolation of 35.9-46.5 dB over the entire working band of (2.40-2.62 GHz) is observed, while the radiation patterns are almost the same for the antenna pairs with and without SIC circuit. Due to the merits of good performances and easy implementation, the proposed SIC technique has potential application for full-duplex transceiver to suppress the self-interference.

A Full-Duplex Single-Chip Transceiver With Self-Interference Cancellation in 0.13 <inline-formula> <tex-math notation="LaTeX">$\mu$ </tex-math> </inline-formula>m SiGe BiCMOS for Electron Paramagnetic Resonance Spectroscopy

This paper presents a miniaturized EPR spectrometer based on a single-chip transceiver. Utilizing a novel on-chip self-interference cancellation circuit, the electromagnetic coupling from the transmitter (TX) to the receiver (RX) is minimized, allowing simultaneous achievement of large TX output power and low RX noise figure (NF). In the measurement, the RX achieves a NF of 3.1 dB/6.3 dB at 10 MHz/50 kHz baseband frequencies, when the TX and cancellation circuits are turned off. The measured flicker noise corner is 60 kHz, more than $10\times $ lower than the prior work. Moreover, for the first time, the operation of the RX and cancellation circuit is demonstrated when a co-integrated TX is operating at the same time and frequency, while producing >20 dBm output power. When the TX and cancellation circuits are turned on, at −10 dBm interference power, the measured NF is 6.8 dB/11.1 dB at 10 MHz/50 kHz baseband frequencies. This is lower by 5.6 dB/9.6 dB at 10 MHz/50 kHz baseband frequencies, compared to the NF with the cancellation circuit off at the same interference power. The transceiver chip is implemented in IBM $0.13~\mu \text {m}$ BiCMOS process and consumes a power of 2 W. Utilizing this transceiver, an electron paramagnetic resonance (EPR) spectrometer is built and tested. It is observed, through measurement, that the interference cancellation circuit increases the signal-to-noise ratio (SNR) of the EPR signal by 7 dB at −10 dBm interference power. Compared to prior work, the reported EPR spectrometer improves the sensitivity of the system by 25 dB.

Integrated Wideband Self-Interference Cancellation in the RF Domain for FDD and Full-Duplex Wireless

A fully integrated technique for wideband cancellation of transmitter (TX) self-interference (SI) in the RF domain is proposed for multiband frequency-division duplexing (FDD) and full-duplex (FD) wireless applications. Integrated wideband SI cancellation (SIC) in the RF domain is accomplished through: 1) a bank of tunable, reconfigurable second-order high-Q RF bandpass filters in the canceller that emulate the antenna interface’s isolation (essentially frequency-domain equalization in the RF domain) and 2) a linear $N$ -path $G_m$ - $C$ filter implementation with embedded variable attenuation and phase shifting. A 0.8–1.4 GHz receiver (RX) with the proposed wideband SIC circuits is implemented in a 65 nm CMOS process. In measurement, $>20\;\text{MHz}\;20\;\text{dB}$ cancellation bandwidth (BW) is achieved across frequency-selective antenna interfaces: 1) a custom-designed LTE-like 0.780/0.895 GHz duplexer with TX/RX isolation peak magnitude of 30 dB, peak group delay of 11 ns, and 7 dB magnitude variation across the TX band for FDD and 2) a 1.4 GHz antenna pair for FD wireless with TX/RX isolation peak magnitude of 32 dB, peak group delay of 9 ns, and 3 dB magnitude variation over 1.36–1.38 GHz. For FDD, SIC enhances the effective out-of-band (OOB) IIP3 and IIP2 to $+\text{25}\text{-}27\;\text{dBm}$ and $+90\;\text{dBm}$ , respectively (enhancements of 8–10 and 29 dB, respectively). For FD, SIC eliminates RX gain compression for as high as $-8\;\text{dBm}$ of peak in-band (IB) SI, and enhances effective IB IIP3 and IIP2 by 22 and 58 dB.