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We propose and experimentally demonstrate an ultraefficient broadband photonic channelizer. By polarization-division multiplexing the received signal and using dual-output Hartley image-reject receiving topology, $4N$ channels can be generated with only ($N +1$)-line signal optical frequency comb (OFC) and $N$ -line local oscillator (LO) OFC, and the frequency interval of the OFC is reduced to half of the typical value. With the use of the integrated dual-polarization coherent detection receiver (DP-CDR), the required quadrature optical hybrid (QOH) and the balanced photodetectors (BPDs) are reduced to half. The system size is reduced and stability is improved. Besides, assisted with a digital signal processor (DSP) algorithm, the IQ imbalance can be compensated, and approximately, ideal image rejection can be realized. A proof-of-concept experiment is carried out. A 2–14-GHz wideband signal is successfully divided into 12 channels with 1-GHz bandwidth by applying four-line signal OFC and three-line LO OFC. The image rejection ratio (IRR), channel isolation (CI), and spurious-free dynamic range (SFDR) are also measured and discussed. [ABSTRACT FROM AUTHOR]

A radio frequency memory (RFM) based on microwave photonic mixing and digital RFM is proposed and demonstrated. By introducing the microwave photonic mixing, the operational frequency range is largely extended. Besides, the mixing spurs are effectively suppressed, which is important to guarantee the system efficiency and avoid generating significant feature for the jamming recognition. Meanwhile, by applying the digital RFM, flexible modulation and reconstruction are achieved. A proof-of-concept experiment is carried out. The wide working frequency range from C- to Ka- bands is achieved. The mixing spurs over the 0–40 GHz frequency range are experimentally suppressed. Radar imaging is successfully deceived. A radar waveform with a bandwidth of 500 MHz in the K band is successfully received and reconstructed. Two false targets are added. To the best of our knowledge, it is the first time that a photonics-assisted RFM is reported to have the functions of storage, flexible modulation, and reconstruction with wideband RF signals at a high frequency. The proposed scheme shows the great potential to be applied in electronic warfare, electronic environment simulation and testing, and so on. [ABSTRACT FROM AUTHOR]

Error vector magnitude (EVM) or alternately offset EVM (OEVM) is one of the most important performance to verify for RF circuits, such as ZigBee transmitters in order to ensure that the quality of the generated modulated signal complies with the requirements of the wireless communication standard. The conventional solution to measure this performance relies on the use of an automatic test equipment (ATE) equipped with expensive RF channels. This article presents a low-cost solution that permits to realize EVM measurement using only a standard digital ATE. The approach is based on 1-bit undersampled acquisition of the RF modulated signal by a digital tester channel associated with a specifically tailored processing algorithm. This algorithm involves many different steps that are detailed in this article, including phase and amplitude fluctuation extraction, RF signal reconstruction, symbol clock recovery, symbol bits detection, and synthesis of reference data for EVM calculation. The proposed digital test solution is first evaluated through lab hardware experiments and then validated with EVM measurements on an industrial ATE. [ABSTRACT FROM AUTHOR]

Energy efficiency (EE) and spectrum efficiency (SE) are two key performance metrics in the sixth generation (6G) wireless communication networks due to the ultra-massive connectivity requirements in future Internet of Things scenarios such as smart cities and factories. Reconfigurable intelligent surface (RIS)-based symbiotic radio (SR) is a promising technology to simultaneously achieve high EE and SE. In this article, a comprehensive review of the RIS-based SR system is presented including the system architectures, operating principles, technical advantages, application scenarios and state-of-the-art transceiver design. Moreover, a star-QAM-aid-ed joint spatial modulation scheme is proposed to realize RIS-based SR and simulation results are provided to illustrate the performance of the proposed scheme. Finally, the critical design challenges for the implementation of RIS-based SR and some promising future research directions are discussed. [ABSTRACT FROM AUTHOR]

A photonics-based frequency mixer for up converting an IF signal into an RF signal with very large suppression in the carrier and the sideband is presented. The mixer is filter free and has a simple structure. It enables off-the-shelf bias controllers to be incorporated into the system. This solves the problem of the carrier and sideband suppression reduces with time that is present in all reported photonics-based single sideband mixers. Experiments are conducted to verify the proposed mixer structure. Results show the single sideband mixer generates an up converted RF signal with more than 40 dB suppression in the carrier and sideband over a wide frequency range. This is a 10-dB improvement compared to the reported structures. A conversion efficiency of around -6 dB is attained, which is over 10 dB higher than the reported structures. Frequency up conversion of an IF signal with a band of frequency and a long-term stable performance are also demonstrated. [ABSTRACT FROM AUTHOR]

We numerically perform the classification of IQ-modulated radiofrequency signals using reservoir computing based on narrowband optoelectronic oscillators (OEOs) driven by a continuous-wave semiconductor laser. In general, the OEOs used for reservoir computing are wideband and are processing analog signals in the baseband. However, their hardware architecture is inherently inadequate to directly process radiotelecom or radar signals, which are modulated carriers. On the other hand, the high- Q OEOs that have been developed for ultra-low phase noise microwave generation have the adequate hardware architecture to process such multi-GHz modulated signals, but they have never been investigated as possible reservoir computing platforms. In this article, we show that these high-Q OEOs are indeed suitable for reservoir computing with modulated carriers. Our dataset (DeepSig RadioML) is composed with 11 analog and digital formats of IQ-modulated radio signals (BPSK, QAM64, WBFM, etc.), and the task of the high-Q OEO reservoir computer is to recognize and classify them. Our numerical simulations show that with a simpler architecture, a smaller training set, fewer nodes and fewer layers than their neural network counterparts, high-Q OEO-based reservoir computers perform this classification task with an accuracy better than the state-of-the-art, for a wide range of parameters. We also investigate in detail the effects of reducing the size of the training sets on the classification performance. [ABSTRACT FROM AUTHOR]

Photonics-assisted frequency conversion based on cascaded modulators is an effective way to satisfy the requirements of distributed antenna array applications. A filter-free photonic image-rejection down-converter with immunity to dispersion-induced power fading is proposed and demonstrated. The radio frequency (RF) signal from the distributed antenna unit is injected into a dual-drive Mach–Zehnder modulator (DDMZM) through an electrical 90° hybrid coupler (HC), and a single-sideband (SSB) signal is realized. It is then transmitted to the center office by an optical fiber link. At the center office, the modulated RF signal is injected into a dual-polarization dual-parallel MZM (DP-DPMZM) after a polarization controller (PC). Afterwards, an LO signal remodulates it through the Y-DPMZM, and carrier-suppressed SSB modulation is fulfilled via another electrical 90° HC. After the power splitting, quadrature I and Q IF signals can be obtained by a photonics-based continuously adjustable phase shifter. Through a combination of the I/Q IF signals with a low-frequency electrical 90° HC, a photonics image-rejection down-converter based on phase cancellation is realized. Moreover, no optical filter is required; thus, the image-rejection down-converter can work with a large bandwidth. The proposed filter-free photonic image-rejection down-converter is theoretically analyzed and experimentally verified. [ABSTRACT FROM AUTHOR]

A bandwidth-efficient and low-cost spectral-null-filling scheme simultaneously delivering a 56-Gbps 4-level pulse amplitude modulation (PAM-4) digital signal and a 10 × 400-MHz analog radio frequency (RF) signal on a single wavelength is demonstrated for high-capacity wired and wireless optical access networks. The data rate of the PAM-4 signal is consistent with the next-generation passive optical network (PON), and the PAM-4 signal inherently provides a spectral null at 28 GHz, which can be filled with the RF signal exactly at the 5G-specified millimeter wave (mmW) band. Since pulse shaping is not essential in this hybrid transmission system, a low-cost 2-bit digital-to-analog converter (DAC) is adopted for the PAM-4 signal generation. Volterra nonlinear equalizer is adopted to effectively eliminate the analog-to-digital crosstalk without reserving a frequency gap in between. The digital-analog hybrid signal is simultaneously transmitted over a 25-km standard single-mode fiber in telecom C-band and the impact of chromatic dispersion on the number of supported mmW bands is analyzed. In addition, three types of hybrid transmitters are experimentally demonstrated, among which the first-time proposed IQ-modulator-based hybrid transmitter shows the best performance. [ABSTRACT FROM AUTHOR]

As the number of communication devices rapidly grows, limited radio resources hardly accommodate the every-increasing tele-traffic. As a remedy, spatial modulation (SM) is capable of modulating additional information onto the index of transmit or receive antennas, which results in substantial improvement of spectrum efficiency. Moreover, radio frequency (RF) signal based simultaneous wireless information and power transfer (SWIPT) has attracted tremendous research interest, in order to relieve the energy-thirst of massively deployed low-power communication devices. In this paper, a receive spatial modulation (RSM) aided SWIPT system with finite alphabets is studied, in which three different transmission schemes are proposed, namely the general scheme, the superimposed scheme and the distinct scheme. Furthermore, the performance of these transmission schemes in the RSM aided SWIPT system is theoretically analysed. The energy harvested by the receiver is then maximised by jointly optimising the transmit power of the information signal and the covariance matrix of the energy signal as well as the power splitting ratio, while satisfying the quality of service of the wireless information transfer. At last, simulation results validate our theoretical analysis, while they also demonstrate that the distinct scheme has the best SWIPT performance among these three transmission schemes. [ABSTRACT FROM AUTHOR]

Ambient backscatter communication (AmBC) over orthogonal-frequency-division-multiplexing (OFDM) signals has recently been proposed as an appealing technique for low power Internet-of-Things (IoT) applications. The special spectrum structure of OFDM signals provides a range of flexibility in terms of bit-error-rate (BER) performance, data rate, and power consumption. In this paper, we study subcarrier-wise backscatter communication over ambient OFDM signals. This new AmBC is to exploit the special spectrum structure of OFDM to transmit data over its squeezed orthogonal subcarriers. We propose a basis transmission scheme, and its two modifications to support a higher data rate with superior BER performance compared to existing methods. The basis scheme can transmit one bit per subcarrier using on-off keying (OOK) modulation in the frequency domain. In the first modification, interleaved subcarrier block transmission model is employed to improve the BER performance of the system in frequency-selective channels. It results in a trade-off between the size of the blocks, and data rate. Thus, in the second modification, interleaved index modulation (IM) is employed to mitigate the data rate decrementation of the former modification. It also stabilizes, and controls the power of the signal to result in interference reduction for a legacy receiver. Analytical, and numerical evaluations provide a proof to see the performance of the proposed method in terms of BER, data rate, and interference. [ABSTRACT FROM AUTHOR]

A photonic method to generate hybrid binary digitally modulated radio frequency (RF) signals (i.e. ASK, PSK, and FSK) by using a polarization-division-multiplexed Mach-Zehnder modulator (PDM-MZM) is proposed. The PDM-MZM is driven by two RF signals with different carrier frequencies and two multiplied digital signals. By properly controlling the offsets and the amplitudes of the digital signals, ASK, PSK, and FSK signals can be generated and switched fastly. RF signals at 4/6 GHz and 10/15 GHz with switchable modulation formats are experimentally generated. Moreover, the performances of the generated signals are evaluated in a wireless transmission system and corresponding bit error rate (BER) curves of the signals are presented. [ABSTRACT FROM AUTHOR]

A code-domain transceiver front end that incorporates a transmit modulator and a receive (RX) RF signal correlator is presented. An integrate-and-dump $N$ -path filter improves rejection by 8 dB. We propose an RF chopper switch with 12.1-/23.1-dBm P1dB/IIP3 for both RF correlation and filtering that rejects TX self-interference by 49.5 dB. Walsh and Barker codes are generated with fine and coarse tuning for synchronization. The RX power consumption is 18 mW, including dynamic power (1-V supply) and four analog amplifiers (1.5 V) at the operating frequency of 1 GHz and the code rate of 200 megachip-per-second (Mc/s). The TX modulator operates to RF power levels up to 34.3 dBm and consumes less than 40 mW for 300 Mc/s. Over the air testing demonstrates synchronization with Barker codes. [ABSTRACT FROM AUTHOR]

This paper proposes a deep learning based intelligent method for detecting and identifying radio signals considering two applications: first, cognitive radar for identifying micro unmanned aerial systems and second, an automated modulation classification scheme for cognitive radio, which can be used for aeronautical communication systems. Our proposed intelligent method is designed of a spectral correlation function based feature extractor and a low-complexity deep belief network classifier with low FPGA logic utilization. [ABSTRACT FROM AUTHOR]

Three-order inter-modulation distortions (IMD3) is a tough problem which appears in analog photonics links (APL). In multi-carrier systems, out-band signals will also lead to nonlinear distortion which is referred as cross-modulation distortion (XMD). The two kinds of distortion will jointly limit dynamic range. In this paper, we propose to adopt an artificial neural network (ANN) as the processing approach which could mitigate IMD3 and XMD simultaneously. The IMD3 and XMD are suppressed by 29.76 dB and 22.18 dB respectively in the experiment. Compared with traditional approaches, the proposed method shows better performance and generalization ability. [ABSTRACT FROM AUTHOR]

Radio frequency (RF) signals can be relied upon for conventional wireless information transfer (WIT) and for challenging wireless power transfer (WPT), which triggers the significant research interest in the topic of simultaneous wireless information and power transfer (SWIPT). By further exploiting the advanced non-orthogonal-multiple-access (NOMA) technique, we are capable of improving the spectrum efficiency of the resource-limited SWIPT system. In our SWIPT system, a hybrid access point (H-AP) superimposes the modulated symbols destined to multiple WIT users by exploiting the power-domain NOMA, while WPT users are capable of harvesting the energy carried by the superposition symbols. In order to maximize the amount of energy transferred to the WPT users, we propose a joint design of the energy interleaver and the constellation rotation-based modulator in the symbol-block level by constructively superimposing the symbols destined to the WIT users in the power domain. Furthermore, a transmit power allocation scheme is proposed to guarantee the symbol-error-ratio (SER) of all the WIT users. By considering the sensitivity of practical energy harvesters, simulation results demonstrate that our scheme is capable of substantially increasing the WPT performance without any remarkable degradation of the WIT performance. [ABSTRACT FROM AUTHOR]

A microwave photonic link with flexible suppression of the even-order and third-order distortions is proposed by using a single integrated polarization-multiplexing dual parallel Mach-Zehnder modulator (PM-DPMZM). A 180° electric hybrid is applied to introduce a phase shift of 180° between the even and odder modulation sidebands of the radio frequency (RF) signal. One DC bias voltage of the PM-DPMZM is adjusted to implement not only the optimal suppression of the even-order or third-order distortions but also a simultaneous suppression of these two distortions. The experimental system is carried out. In the best suppression points for the second or third intermodulation distortions (IMD2 or IMD3), the spurious-free dynamic range (SFDR) of IMD2 and IMD3 is improved by 17.1 and 17.7 dB, comparing with the conventional MZM based MPL. In the case of the simultaneous suppression, the SFDR values of IMD2 and IMD3 are enhanced by 10.6 and 6.4 dB. The proposed link has great flexibility, simple structure, and convenient operation, and it can be applied in both the single-octave and multi-octave communication systems. [ABSTRACT FROM AUTHOR]

In order to satisfy the power demands of IoT devices and thus extend their lifespan, radio frequency (RF) signal aided wireless power transfer (WPT) is exploited for remote charging. Carefully coordinating both the WPT and wireless information transfer (WIT) yields an emerging research trend in simultaneous wireless information and power transfer (SWIPT). However, SWIPT systems designed by assuming Gaussian distributed input signals may suffer from a substantial performance degradation in practice, when the finite alphabetical input is considered. In this article, we will provide a design guide of coding controlled SWIPT and study the modulation design in both single-user and multi-user SWIPT systems. We hope this guide may push SWIPT a step closer from theory to practice. [ABSTRACT FROM AUTHOR]

Normal conducting linear accelerators are widely used in many free-electron laser (FEL) machines all over the world. They normally consist of multiple RF stations either with standing wave cavities (e.g., RF Gun) or with traveling wave accelerating structures working at different frequencies. Low-level radio frequency (LLRF) systems are used to measure the RF fields in cavities or structures and correct the fluctuations in RF fields with pulse-to-pulse feedback controllers. To facilitate the operations of multiple RF stations, the LLRF system should also provide algorithms and procedures to automate the setup, calibration, and optimization of the RF systems. In this paper, several typical algorithms and procedures will be described, such as calibrating the digital-to-analog converters offset to reduce the RF leakage from vector modulator, calibrating the RF signal group delay, and flattening the intrapulse phase distribution with an adaptive feed forward. The algorithms and procedures have been implemented as an LLRF high-level applications (HLAs) software for SwissFEL, which is an FEL machine under commissioning at Paul Scherrer Institut, Switzerland. The architecture of the LLRF HLA software will be introduced, and the test results at SwissFEL will also be described. [ABSTRACT FROM PUBLISHER]

In this paper, a simple and cost-effective packaging scheme for improving the modulation bandwidth of directly modulated laser is presented and demonstrated. Combined with the equivalent circuit, the effect of disequilibrium on signal injection efficiency is comprehensively and systematically studied. The simulation and measurement results have a good agreement, which show that the high frequency performance of module can be effectively improved with the proposed packaging scheme. Finally, employing the proposed packaging scheme, we achieve the 3-dB bandwidth of up to 32 GHz regarding the directly modulated semiconductor laser module with the butterfly package. [ABSTRACT FROM PUBLISHER]

An ultra-flat and broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated by directly modulating a dual-driven Mach–Zehnder Modulator (MZM) with only one RF signal. The proposed scheme can generate two forms of OFCs by simply adjusting the bias voltages of the MZM and the power of the RF signal. One form is a 20-line OFC with a frequency spacing equals the frequency of the RF signal, the other form is a 16-line OFC with a frequency spacing of two times the frequency of the RF signal. The generated OFCs have low power variation and broad bandwidth. The proposed scheme is verified by an experiment. A 20-line OFC with a frequency spacing of 10 GHz and flatness of 0.7 dB, and a 16-line OFC with a frequency spacing of 20 GHz and flatness of 0.3 dB are experimentally demonstrated. [ABSTRACT FROM PUBLISHER]

Switched mode RF power amplifiers (PAs) under bitstream modulations, such as bandpass or envelope delta–sigma modulations (EDSMs), have received increasing attentions over the past years. Such amplifiers offer high power efficiencies under power back-off conditions with pulse train voltage waveforms yet maintain their linearity in amplification through digital coding and modulations. This paper presented an $X$ -band switched mode PA based on the pulsed load modulation (PLM) technique with multilevel EDSM to realize broadband efficient amplification of nonconstant-envelope signals. The complete theory of power efficiency for PLM under three-level EDSM is presented. The X$ -band PA is implemented with 0.25- \mu \text{m} discrete GaN transistors from Triquint. Both two-level and three-level EDSM techniques were tested and compared in regard to their quantization noise levels and power efficiencies. Under the three-level EDSM, the PA delivered 34.6-dBm output power for a WCDMA uplink signal with 100-MHz bandwidth and 5.3-dB peak-to-average power ratio at the carrier frequency of 9.2 GHz. The measured drain efficiency and the power-added efficiency with the modulation were 34.6% and 26.5%, respectively. The adjacent channel leakage power ratio at the output was measured to be 32.2/32.3 dBc at the 100-MHz offsets without using digital predistortion. [ABSTRACT FROM AUTHOR]

Photonic generation of high-power pulsed microwave signals is demonstrated using charge-compensated modified unitraveling-carrier photodiodes. The impulse response without RF modulation achieved unsaturated peak voltage of 33.5 V and full-width at half-maximum of 50 ps. The peak power levels for gated modulation at 1 and 10 GHz were 41.5 dBm (14.2 W) and 40 dBm (10 W), respectively. [ABSTRACT FROM PUBLISHER]

Orthogonal frequency-division multiplexing (OFDM) is susceptible to multiple access interference and synchronization errors due to sidelobes, which hinder the integration of various applications and multiple access in OFDM-based optical transmission. In this letter, an adaptively modulated optical filter bank multicarrier with offset quadrature amplitude modulation-based sidelobe suppression is proposed in a wired/wireless converged optical network. We experimentally verified both the improvements in signal performance and spectral efficiency compared with OFDM in a multisender-supported optical network after a 50-km transmission. [ABSTRACT FROM PUBLISHER]

A new method of spatial linear modulation is presented for the RF signal modulation. The constant envelope and phase modulated signals are transmitted to an antenna array and then combined in space; the linear modulation is realized at the same time. The concentric antenna pairs are applied to eliminate the mismatch of phase delay among the modulated signals from different antenna pairs. The measurement results of an RF signal around 2.45 GHz modulated by a 3.84 Mbps QPSK signal are presented. The proposed spatial modulator is able to simplify RF transmitter design and achieve highly efficient power transmission. [ABSTRACT FROM AUTHOR]

We have proposed two methods of enhancing efficiency of an envelope tracking power amplifier (ET PA) from an interlock operation. The first is the utilization of sinking current. The sinking current is a critical efficiency reduction factor since it is a wasted power. To reduce the sinking current, the gate bias of the power amplifier (PA) is increased so that the sinking current is delivered to the PA and is utilized for amplification. The other one is the RF input shaping method. The input signal of ET PAs is a modulated RF signal, and the signal does not guarantee fully saturated operation of the PA at all power levels due to g m nonlinearity of a device. To obtain the maximum efficiency for all of the envelope voltage, we have found the optimum RF input conditions and applied it to the input of the PA. To verify the methods, the proposed ET PA is implemented using a Cree CGH40045 GaN HEMT. For a long-term evolution 5-MHz signal with 6.5-dB peak-to-average power ratio, the PA delivers power-added efficiency of 58.76% with 40.14-dBm output power at 889 MHz. [ABSTRACT FROM AUTHOR]

An ultra-low-power RF envelope-detection radio has been designed for low-power short-range wireless applications. It introduces an interference rejection technique that improves the in-band selectivity by 24.5 dB. The transmitter adopts the power-efficient direct-modulation architecture, and the receiver maintains the simplicity and low power consumption of envelope detection receivers. In the 915 MHz ISM band at 10 kbps the transmitter output level reaches -3 dBm with 33.9% global efficiency, while the receiver achieves -83 dBm sensitivity with 121 \muW power consumption. The Tx and Rx implemented in 90 nm CMOS technology occupy 0.71 and 1.27 mm^2, respectively. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a novel and simple predistortion circuit using reflective antiparallel diodes for linearization of electro-absorption modulators (EAMs) in multiband orthogonal frequency-division multiplexing (MB-OFDM) ultra-wideband (UWB) radio-over-fiber systems for UWB signals from 3.1 to 4.8 GHz. In this novel predistortion circuit, neither amplifiers, nor phase shifters are used, while only two antiparallel connected diodes are used, and the predistortion signal is adjusted by tuning the diodes' dc-bias current. The simple architecture makes the circuit cost effective and suitable for UWB system applications. By adding the predistortion circuit before the EAM, more than 7-dB suppression in third-order intermodulation distortion and 11-dB improvement in spurious-free dynamic range are achieved over the frequency range of 3.1–4.8 GHz, i.e., bandgroup 1 of MB-OFDM UWB. Correspondingly, 1-dB improvement in error vector magnitude is obtained experimentally when the designed predistortion circuit is used. [ABSTRACT FROM PUBLISHER]