Radio Frequency Self-interference Research Articles

Full-duplex multi-band 5G/6G coexistence mobile fronthaul network based on RoF with RF self-interference cancellation

A bidirectional multi-band mobile fronthaul network based on the radio over fiber technology is proposed, which allows three different radio frequency (RF) bands at 3.5 GHz, 26 GHz, and 60 GHz full-duplex transmission, and 2.1 GHz RF band transmission as supplementary uplink, aiming for fifth-generation (5G)/sixth-generation (6G) mobile communication coexistence. The proposed scheme uses a dual-drive Mach-Zehnder modulator and dual-polarization binary phase-shift keying modulator to alleviate the interference between multiple RF bands. The transmission performance of the proposed system is evaluated by the simulation. The error vector magnitude of the system conforms to the 3GPP specification when the received optical powers of downlink and uplink are above −2.2 and −4.6 dBm, respectively. The Y-polarized optical carrier in the downlink is reused as the carrier of the uplink signals. Besides, a dual-parallel Mach-Zehnder modulator is used to realize RF self-interference cancellation at 60 GHz RF band in the uplink of the in-band full-duplex transmission. The cancellation depth of 27.08 dB is achieved by the proof-of-concept simulation.

Frequency-Domain RF Self-Interference Cancellation for In-Band Full-Duplex Communications

Wireless backhaul has recently gained a significant amount of interest as a cost-effective solution in comparison with conventional backhaul technologies with dedicated microwave links or fiber optics. Self-interference cancellation (SIC) is an enabling technology that allows wireless backhaul to operate in the more spectrum-efficient in-band full-duplex (IBFD) operation mode instead of the out-of-band mode. Compared to Wi-Fi IBFD transceivers, wireless in-band backhaul systems face some unique challenges, such as significantly higher transmission power and much larger propagation delay spread for the self-interference signal, especially in the low-frequency bands under 1 GHz, which often prevent accurate SIC performance. The SIC is often implemented with an interference-cancelling filter, where the filter weights are essentially the channel estimates of the self-interference signals. In this paper, a frequency-domain Radio Frequency (RF) SIC (RF-SIC) framework with a novel filter weight optimization algorithm is proposed to tackle the challenges of wireless in-band backhaul. The proposed RF-SIC does not require a dedicated training phase which needs to stop the transmission of the backhaul signal. Moreover, it has the capability of tracking the self-interference channel variation since the filter weights are updated in a block-by-block fashion.

Photonic-Assisted Reconfigurable LO Harmonic Downconverter With RF Self-Interference Cancellation and Image-Rejection

A photonic-assisted reconfigurable LO harmonic downconverter with simultaneous image-rejection and RF self-interference cancellation (SIC) for in-band full-duplex communication is proposed and experimentally investigated based on a dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). The received signal from the antenna, which includes the radio frequency (RF) signal, image signal (IM) and self-interference (SI) signal, is input into one sub-MZM of the X-DPMZM. The self-reference (SR) signal is input into the other. The Y-DPMZM is used to load the LO signal and is properly biased to obtain the high-order sideband of the LO signal, which was then set as the LO signal of the reconfigurable harmonic frequency downconverter. By matching the power and delay of the SR signal and changing the main bias of the X-DPMZM, the SI signal can be eliminated directly in optical domain. With power splitting after the output of the DP-DPMZM, the quadrature IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Then, photonics image-rejection down-conversion based on phase cancellation is realized after a low-frequency electrical 90° hybrid coupler (HC) combines the quadrature IF signals. Both theoretical and experimental investigations are performed. The results show that the SIC has a cancellation depth more than 32 dB for the 10-MHz bandwidth and greater than 19 dB for the 500-MHz bandwidth, the image-rejection has an image-rejection ratio larger than 31 dB for 10-MHz bandwidth and larger than 22 dB for the 100-MHz bandwidth, both in 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> - and 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> -order harmonic down-conversion mode. Experiments are also carried out on the reconfigurable LO harmonic downconverter with simultaneous SIC and image-rejection. A 16-quadrature amplitude modulation (16-QAM) -modulated RF signal is successfully down-converted to a 1-GHz intermediate frequency (IF) signal with self-interference and image frequency cancelled. It is verified that the RF signal can be well recovered from SI and IM signals by the proposed system.

Photonics-based radio frequency self-interference cancellation for radio-over-fiber systems

A photonics-based radio frequency (RF) self-interference cancellation approach for radio-over-fiber (RoF) systems is proposed and demonstrated. An intermediate frequency (IF) signal and a local oscillator (LO) signal are separately modulated to a pair of optical carriers with orthogonal polarization states in the central station. The generated optically carried RF signal is then transmitted to remote base stations over fibers. After performing photodetection at the two outputs of the polarization beam splitter (PBS), a pair of upconverted RF signals with inverse phases are generated. One is used as the transmitted signal, while the other is used as the reference signal for the self-interference cancellation. In this way, the phase inversion between them is realized in the optical domain. In addition, the adjustments with the time delay and the amplitude of the reference signal are both achieved in the optical domain, guaranteeing the self-interference cancellation in a wide bandwidth. Meanwhile, the independent optical system for self-interference cancellation is avoided, simplifying the complex hardware requirements with the base stations. The cancellation depths of 33, 30, and 22 dB over 0.5-, 1-, and 3-GHz bandwidths are experimentally achieved, respectively. The ranging and imaging functions of a frequency modulated continuous wave (FMCW) radar system using the established self-interference cancellation structure are experimentally verified.

A Two-Stage Wideband RF Cancellation of Coupled Transmit Signal for Bi-Static Simultaneous Transmit and Receive System

Wireless technology is growing at a fast rate to accommodate the expanding user demands. Currently, the radio frequency (RF) spectrum is overcrowded. Hence, it is more susceptible to signal fratricide and interference. To enhance spectrum access, in-band full duplex systems are implemented to achieve simultaneous transmission and reception (STAR) and double the spectral efficiency. However, STAR systems require suppression of the high power transmit signals that can leak into the receiver chain. This type of self-interference (SI) can significantly reduce the receiver.s dynamic range and often leads to its desensitization. Therefore, successful STAR implementation requires considerable isolation between the transmitter and receiver to reduce the SI signal. To do so, RF self-interference cancellation (RFSIC) stages are considered. In this paper, we present a two-stage SIC system that includes transmit and receive antennas isolation and RFSIC filter stages. Notably, the isolation between the transmit and receive antennas is based on a novel symmetric suppression technique. The RFSIC filter is based on a hybrid finite impulse response (FIR) filter and resonator architecture. Adding a resonator to the FIR filter provides improved matching to approximate and suppress the direct SI coupling. Our design 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> 52 dB isolation on average across a 500 MHz bandwidth ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">viz.</i> 1-1.5 GHz) in simulation. Simulation results show a minimum cancellation of 41 dB and a maximum cancellation of 65 dB. A prototype was fabricated and tested, showing an average of <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> 44 dB cancellation which is in good agreement with our simulation.

RF Self-Interference Cancellation and Frequency Downconversion With Immunity to Power Fading Based on Optoelectronic Oscillation

We report a photonic approach to achieve simultaneous radio frequency (RF) self-interference cancellation (SIC) and frequency downconversion with immunity to power fading based on an optoelectronic oscillator (OEO) for an in-band full-duplex (IBFD) radio-over-fiber (ROF) system. A dual-drive Mach–Zehnder modulator (DDMZM) in a polarization-division multiplexing Mach–Zehnder modulator (PDM-MZM) is used to cancel the RF self-interference (SI) signal and generate optical carrier-suppressed double sidebands (CS-DSBs) of the signal of interest (SOI). Meanwhile, another DDMZM in the PDM-MZM is used to construct an OEO loop to generate optical CS-DSBs of the local oscillation (LO) signal. After detection at a photodetector (PD), a frequency downconverted signal is recovered with the RF self-interference cancellation (SIC). The proposed scheme can directly cancel the RF SI signal in the optical domain, meaning that it can overcome the limitation of SIC in the electrical domain. With the phase compensation introduced by a polarization controller, the desired signal is unaffected by the power fading over fiber transmission, which is significant for IBFD ROF systems. In addition, instead of an external microwave source, an OEO loop is used to generate an LO signal with a high spectral purity, which is very promising for integrated microwave photonics systems.

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.

Photonics-Based Adaptive RF Self-Interference Cancellation and Frequency Downconversion

A photonics-based approach for simultaneous adaptive radio-frequency (RF) self-interference cancellation and frequency downconversion is proposed and demonstrated. By introducing photonic polarization-multiplexing, the reference signal and the self-interference signal are separated in the optical domain. Thus, the phase shift, the precise amplitude and the time delay adjustments can be achieved with the reference signal by using optical methods which are program controllable. An intelligent algorithm particle swarm optimization (PSO) algorithm is applied to optimize these parameters for adaptive operation. Meanwhile, the local oscillator (LO) signal is introduced to the two orthogonal polarization states to perform frequency downconversion. Therefore, simultaneous adaptive self-interference cancellation and downconversion are realized. A theoretical model is established for analyses. A proof-of-concept experiment is taken. The simultaneous adaptive self-interference cancellation and downconversion are achieved. The X-band RF signals are downconverted, and the self-interference cancellation depth of 31 dB over a 500-MHz bandwidth and 28 dB over a 1-GHz bandwidth are obtained. The RF signals in the Ku-band are downconverted, with the self-interference cancellation of 28 dB over a 500-MHz bandwidth and 26 dB over a 1-GHz bandwidth. A 16-QAM signal with a 10-Msym/s symbol rate is recovered from the self-interference signals with 500-MHz and 1-GHz bandwidths.

Photonics-Assisted Ultrawideband RF Self-Interference Cancellation With Signal of Interest Recovery and Fiber Transmission

Self-interference and chromatic dispersion are two main limiting factors that influence the recovery of the signal of interest (SOI) in in-band full-duplex (IBFD) radio-over-fiber (RoF) links. An ultrawideband photonic-assisted approach to radio-frequency (RF) self-interference cancellation (SIC) with high-speed SOI recovery and fiber transmission capability is proposed. The key to achieve the above optimum performances in a compact system is the combined use of fiber dispersion induced RF time delay and optical carrier phase-shifted double sideband (CPS-DSB) modulation. A high precision and tunable time delay matching between the reference signal and the SI signal can be achieved by dispersion induced RF time delay. Meanwhile, the equal amplitude, phase reversal, and dispersion-induced SOI power fading compensation conditions are satisfied simultaneously by manipulating the optical carrier phase of the CPS-DSB signal. For 25 km fiber transmission, 30 dB cancellation depth over 2.7 GHz bandwidth, 160 Mbit/s 16-quadrature amplitude modulation (16-QAM) SOI recovery, and good immunity to fiber dispersion are experimentally demonstrated. In addition, the proposed scheme facilitates multipath SIC by implementing an array of tunable lasers (TLs) with a shared electro-optic modulator at the reference branch.

Simultaneous RF Self-Interference Cancellation, Local Oscillator Generation, Frequency up- and down-Conversion in an Integrated In-Band Full-Duplex 5G RF Transceiver Front-End

Wideband radio-frequency (RF) self-interference cancellation (SIC), local oscillator (LO) generation, frequency up-, and down-conversion are all crucial for an in-band full-duplex (IBFD) 5G RF transceiver front-end. In this paper, a microwave photonic approach enabled by only one optical dual-polarization IQ modulator (DP-IQMZM) is proposed to simultaneously realize wideband RF SIC, LO generation, frequency up- and down-conversion. Note that, the LO signal with high spectral purity and low phase noise is produced by a dual-loop optoelectronic oscillator (OEO) using a self-polarization stabilization structure, and the generated LO signal is applied for frequency up- and down-conversion. Besides, the optical single-sideband signal is produced at the output of this 5G RF transceiver for uplink transmission from the remote antenna unit (RAU) to the baseband unit (BBU), so the power fading induced by fiber dispersion could be completely suppressed. A proof-of-concept experiment is performed, and the LO signal with the central frequency of 10&#x00A0;GHz, the phase noise performance of &#x2212;108.97&#x00A0;dBc&#x002F;Hz at a frequency offset of 10&#x00A0;kHz is achieved. A 5 &#x00D7; 20&#x00A0;MHz Long Term Evolution (LTE) 16&#x002F;64-ary quadrature amplitude modulation-orthogonal frequency division multiplexing (16&#x002F;64QAM-OFDM) signal with the central frequency of 12.6&#x00A0;GHz is down-converted to 2.6&#x00A0;GHz. Meanwhile, the cancellation ratio of 30.22&#x00A0;dB and 26.26&#x00A0;dB could be achieved when the bandwidth of the self-interference signal is 150&#x00A0;MHz and 300&#x00A0;MHz, respectively. Moreover, a 3 &#x00D7; 20&#x00A0;MHz LTE 64QAM-OFDM signal with a central frequency of 2.6&#x00A0;GHz is up-converted to 12.6&#x00A0;GHz, and the electrical signal-to-noise ratio of the generated RF signal can achieve 31.34&#x00A0;dB. The measured error vector magnitude performance shows that the generated down- and up-converted signal both meet the 3^rd Generation Partnership Project (3GPP) requirements for 5G systems.

Photonic-assisted radio frequency self-interference cancellation and frequency down-conversion based on polarization multiplexing modulation.

We report a photonic-assisted radio frequency self-interference cancellation (RF-SIC) and frequency down-conversion scheme based on a dual-polarization Mach-Zehnder modulator (DP-MZM) by using a polarization manipulation method. In the proposed scheme, the self-interference signal is directly canceled in the optical domain by simply controlling the polarization states between the output of the DP-MZM and the polarizer. Frequency down-conversion is achieved by optoelectronic frequency mixing. In the proof-of-concept experiment, the interference cancellation of the single-frequency signal and wideband signal was conducted. The proposed RF-SIC and frequency down-conversion system has flexible tunability, simple structure, and low cost, which can find potential applications in radio-over-fiber systems.

Photonic-based analog and digital RF self-interference cancellation with high spectral efficiency.

A photonic-assisted analog and digital radio frequency (RF) self-interference cancellation (SIC) approach with high spectral efficiency is reported for base stations in in-band full-duplex radio-over-fiber systems on the basis of our previous research. One dual-polarization quadrature phase-shift keying (DP-QPSK) modulator is used as the canceller for one base station. The two dual-parallel Mach-Zehnder modulators of the DP-QPSK modulator are both biased as carrier-suppressed single-sideband modulators and driven by the received signal and reference signal, respectively, to achieve high spectral efficiency while implementing the SIC in the optical domain. The baseband optical signal after SIC is further transmitted to the central station, where the electrical signal is recovered, sampled, and processed to further suppress the residual self-interference in the digital domain by using the recursive least-square (RLS) algorithm. An experiment is then performed. The proposed system is demonstrated by employing two independent channels. The analog cancellation depths of the 200, 500, and 800 Mbaud QPSK-modulated self-interferences are around 24, 20, and 20 dB, respectively; the total cancellation depths are around 29, 28, and 25 dB, respectively, when the analog cancellation and the RLS algorithm digital cancellation are applied. Meanwhile, the fiber distribution has no significant influence on SIC performance.

Photo-assisted self-interference cancellation for in-band full-duplex radio-over-fiber system.

An optical approach to cancel the radio frequency self-interference for an in-band full-duplex radio-over-fiber system is proposed and experimentally demonstrated based on two Mach-Zehnder modulators and a balanced photodetector (BPD). The cancellation depth is larger than 50 dB and 24 dB for the single frequency and for a wideband signal, respectively. The application of the BPD eliminates the common mode noise and reduces no system flexibility because signal transmission is in one optical fiber by polarization multiplexing technology, instead of two fibers in the traditional self-interference cancellation system with a BPD. In addition, with no electrical delay and attenuation applied, the operational frequency band and cancellation depth are not confined by electronic devices.

RF self-interference cancellation by using photonic technology [Invited

Radio frequency (RF) self-interference is a key issue for the application of in-band full-duplex communication in beyond fifth generation and sixth generation communications. Compared with electronic technology, photonic technology has the advantages of wide bandwidth and high tuning precision, exhibiting great potential to realize high interference cancellation depth over broad band. In this paper, a comprehensive overview of photonic enabled RF self-interference cancellation (SIC) is presented. The operation principle of photonic RF SIC is introduced, and the advances in implementing photonic RF SIC according to the realization mechanism of phase reversal are summarized. For further realistic applications, the multipath RF SIC and the integrated photonic RF SIC are also surveyed. Finally, the challenges and opportunities of photonic RF SIC technology are discussed.

Residual self‐interference suppression guided resource allocation for full‐duplex orthogonal frequency division multiple access system

In a wideband full-duplex system, the residual self-interference (SI) channel exhibits significant frequency selective fading characteristics after radio frequency SI cancellation. Resource allocation using the difference between the signal channel and the residual SI channel is a new method of suppressing residual SI and increasing system capacity. In this work, the residual SI channel and the user uplink channel are modelled as multi-path frequency selective fading channels that satisfy the Rayleigh distribution. To improve system capacity, the authors propose to allocate the spectrum resource avoiding occupation of subcarriers with high residual SI, while guaranteeing a fair subcarrier assignment (SA) and power allocation (PA). A sum rate of uplink maximisation is formulated, and an algorithmic solution is developed to effectively conduct SA and PA. Numerical results demonstrate the effectiveness of the scheme in increasing system capacity and suppressing residual SI.

Photonic-Assisted RF Self-Interference Cancellation With Improved Spectrum Efficiency and Fiber Transmission Capability

An approach to photonic-assisted carrier-suppressed single-sideband radio-frequency (RF) self-interference cancellation with improved spectrum efficiency and fiber transmission capability is proposed for in-band full-duplex radio-over-fiber systems. The key to achieve RF self-interference cancellation is to generate two single-sideband signals with one having a received signal with the RF self-interference signal and the other having only the RF self-interference signal, which is implemented by using a dual-polarization binary phase-shift keying (DP-BPSK) modulator. By controlling the arrival time and power of the electrical signals applied to the DP-BPSK modulator, the RF self-interference can be fully cancelled, and only a carrier-suppressed single-sideband signal with modulation is obtained. In addition to self-interference cancellation, the received signal can be directly converted to an optical baseband signal, so that the spectrum efficiency is increased. An experiment is performed. The results show that a cancellation depth of around 40 dB for a single-frequency self-interference and around 22 dB for a 100-Mbaud QPSK modulated wideband self-interference is achieved.

Photonic Radio Frequency Self-Interference Cancellation and Harmonic Down-Conversion for In-Band Full-Duplex Radio-Over-Fiber System

We report a photonic radio frequency (RF) self-interference cancellation (SIC) and harmonic down-conversion (HDC) scheme based on a dual-parallel dual-drive Mach-Zehnder modulator (DDMZM). The proposed scheme can eliminate the chromatic-dispersion induced power fading (CDIP) effect and thus is very suitable for in-band full-duplex (IBFD) radio-over-fiber (ROF) system. The self-interference RF signal is directly cancelled in optical domain, which overcomes the electronics bottleneck limitation of electrical SIC. Moreover, the HDC allows us to use a cost-effective low frequency local oscillation (LO) source to down-convert a high-frequency RF signal into an intermediate frequency (IF) band. In addition, the harmonic odd-order single-sideband (SSB) down-conversion is naturally free from the CDIP effect. The proposed photonic SIC+HDC system is theoretically analyzed and experimentally verified.

Analysis of Desired Receive Signal Impact in Wireless Co-time Co-frequency Full Duplex

With self-interference cancellation (SIC), a wireless full duplex terminal is allowed to transmit and receive signal simultaneously in the same frequency band. This paper focuses on the analysis of desired receive signal impact on the radio frequency (RF) SIC performance. The full-duplex system model is rst given, and the principle of radio frequency self-interference cancellation is introduced. Then, from the perspective of the convex function, the in uence of the desired signal on the RF SIC is analyzed when the total power of the signal after RF SIC is taken as the objective function. It is found that when there is no desired signal, the objective function is a convex function, and the residual self-interference power can converge to the minimum value by the gradient descent method. If the desired signal exists and the channel is constant, the objective function is also a convex function, and the residual self-interference power can also converge to the minimum value. However, in the presence of the desired signal and the channel uctuates, the target is not a convex function, and the residual self-interference power cannot be converged to the minimum value by the gradient descent method.

On Cancellation Capability of Full-Duplex RF Self-Interference Cancellation Schemes

In this work, we study the self-interference cancellation (SIC) capability of two basic radio frequency (RF) SIC schemes: auxiliary antenna cancellation and multireconstruction-path (MRP) cancellation (including particular two-reconstruction-path balun cancellation), and derive their cancellation capability in detail. Theoretical results show that auxiliary antenna cancellation capability and balun cancellation capability are related to the ratio of bandwidth to carrier frequency, the latter is further related to an angle ratio; that is, the ratio of the angle between the self-interference vector and the first fixed delay vector to the angle between the two fixed delay vectors, and common MRP cancellation capability is essentially related to the channel response of self-interference and the canceller frequency response. Numerical results confirm a perhaps obvious intuition: MRP cancellation outplays auxiliary antenna cancellation to cancel self-interference, especially when multiple self-interference paths exist, and MRP cancellation with more reconstruction paths achieves higher cancellation capability.

Simultaneous Transmission and Reception Transponder for Nano-satellite

The feasibility of simultaneous transmission and reception (STAR) in the same frequency for space transponder in nano-satellite is discussed. The demand of the self-interference cancellation for the transponder is analysed by space-ground link budget, and a STAR superheterodyne architecturebased transponder is also presented. Based on the conventional space TT&C frequency scheme, a feasible frequency scheme and digital signal processing process for the STAR transponder are expatiated. A FFT based carrier acquisition method is modified to adapt to such STAR transponder.The implementation of the STAR transponder is simulated. The simulation results show that with properly deployingthe passive and active self-interference cancellation modules, the self-interference can be cancelled to meet with the demand of demodulation which also implies that the STAR transponder presented in this paper is feasible.The simulation results also show that the radio frequency self-interference cancellation(RFSIC) does matter in such STAR transponder by realizing 29dB self-interference cancellation, and a total self-interference cancellation of about 68dB can be realized by the combination of passive suppression and RFSIC. The numerical results show that the digital self-interference cancellation is not necessary for the transponder when the transmission power of ground-satellite uplink is high enough, and the phase noise power is increased by the digital self-interference module.