Multiband Signals Research Articles

Large-tunable microwave photonics frequency multiplier overcoming the fixed filter bandwidth limitation on improved feed-forward modulation technology

Improved feed-forward modulation (IFFM) technology is a two-stage modulation photonics design that achieves coherent frequency up-conversion based on incoherent optical carriers. For the scheme, at least two optical fixed filters are required; the first is used to extract desired optical sidebands for the second-stage modulation’s driving signal generation, and the second filter is to suppress unwanted optical harmonics for high-quality heterodyne detection. This is for a fixed-frequency signal generation. To accommodate tunable frequency signal generation, at least two tunable optical filers are needed. In this paper, a wide frequency tunable method for an IFFM-based frequency multiplier with only a fixed bandwidth optical filter is proposed. A proof-of-concept experiment successfully demonstrates the tuning mechanism of the scheme. The scheme exploits the two pairs of coherent optical sidebands generated from two incoherent light sources to realize coherent addition of the two beat signals from each pair to attain a high-power frequency-multiplied signal for enhanced transmission power budget. From the simulation, a frequency multiplication factor of 16 and a 160-GHz signal with a stable frequency and a power level enhanced by 19 dB are achieved by employing two incoherent lasers. By adjusting the output frequency of the local oscillator, we show that multi-band signals generation, including microwave, millimeter- and terahertz-wave, can be realized, and the performance of the generated signals is also investigated.

Multiband Signal Receiver by Using an Optical Bandpass Filter Integrated with a Photodetector on a Chip

Photonic integration brings the promise of significant cost, power and space savings and propels the real applications of microwave photonic technology. In this paper, a multiband radio frequency (RF) signal simultaneous receiver using an optical bandpass filter (OBPF) integrated with a photodetector (PD) on a chip is proposed, which was experimentally demonstrated. The OBPF was composed of ring-assisted Mach-Zehnder interferometer with a periodical bandpass response featuring a box-like spectral shape. The OBPF was connected to a PD and then integrated onto a single silicon photonic chip. Phase-modulated multiband RF signals transmitted from different locations were inputted into the OBPF, by which one RF sideband was filtered out and the phase modulation to intensity modulation conversion was realized. The single sideband with carrier signals were then simultaneously detected by the PD. A proof-of-concept experiment with the silicon photonic integrated chip was implemented to simultaneously receive four channels of 8 GHz, 12 GHz, 14 GHz and 18 GHz in the X- and Ku-bands. The performance of the integrated microwave photonic multiband receiver-including the receiving sensitivity, the spurious free dynamic range, the gain and the noise figure across the whole operation frequency band-was characterized in detail.

Rapid reconstruction of sparse multiband signals based on MMV-SWACGP algorithm

In this paper, an MMV-SWACGP algorithm is proposed, in order to solve the problem of pseudo-inverse computation in the iterative process of OMPMMV algorithm for multi-band signal reconstruction by compressed sensing. This algorithm reduces the complexity and computation of OMPMMV reconstruction algorithm. It is of great significance to the fast reconstruction of sparse multiband signals. Theoretical analysis and simulation results show that the proposed algorithm has faster computation speed and better noise stability.

Multi-Band Triangular Frequency Modulation Signal Generation Based on Gain-Switched Laser

Multi-Band Triangular Frequency Modulation Signal Generation Based on Gain-Switched Laser

Nonuniform MIMO Sampling and Reconstruction of Multiband Signals in the Fractional Fourier Domain

This paper explores nonuniform multiple-input multiple-output (MIMO) sampling and reconstruction of signals with multiple bands in the fractional Fourier domain. We investigate discrete-time fractional Fourier transforms of nonuniformly sampled output signals of MIMO channel and study the resulting fractional spectral aliasing. In order to tackle the problem that the spectral aliasing differs with respect to multiple-output signals, we define combined aliasing boundaries and perform spectrum analysis within the fractional frequency sub-intervals separated by these elaborated boundaries. Moreover, we derive the conditions for combined reconstructing the fractional spectra of the input/output signals of MIMO channel and devise relevant reconstruction methods. Simulation results verify the effectiveness of our proposed methods.

Image-Rejected Multi-Band Frequency Down-Conversion Based on Photonic Sampling

An image-rejected multi-band frequency down-conversion scheme is proposed and experimentally demonstrated based on photonic sampling. The multi-band radio-frequency (RF) signals to be processed are copied into two replicas in quadrature, which are then sampled by an ultra-short optical pulse train via a polarization-multiplexed modulator. After polarization demultiplexing and detection using a pair of low-speed photodetectors, the multi-band RF signals are simultaneously down-converted to the intermediate frequency (IF) band. The image components can be suppressed by quadrature coupling the two generated IF signals via an electrical 90° hybrid coupler (HC). In the experiment, multi-band RF signals in the frequency range of 6 GHz to 39 GHz are down-converted to the IF band below 4 GHz using a local oscillator (LO) signal at 8 GHz to generate the ultra-short optical pulse train. Image rejection is achieved in the digital domain using digital signal processing to compensate for the amplitude and phase mismatch between the two IF signals and to implement quadrature coupling. In addition, through using an electrical phase shifter, an electrical attenuator, and an electrical 90° HC to achieve quadrature coupling of the two IF signals, image-rejected multi-band frequency down-conversion is also verified in the analog domain.

Multi-Static Multi-Band Synthetic Aperture Radar (SAR) Constellation Based on Integrated Photonic Circuits

Multi-static SARs from LEO orbits allow the single-pass high-resolution imaging and detection of moving targets. A coherent MIMO approach requires the generation of multi-band, thus orthogonal, signals, the fusion of which increases the system resolution. Up to now the synchronization capability of SAR signals of different satellites is critical. Here, we propose the use of photonics to generate, receive and distribute the radar signals in a coherent multi-static SAR constellation. Photonics overcomes issues in the implementation of MIMO SAR, allowing for the flexible generation of multi-band signals and centralized generation in a primary satellite with coherent distribution to all the secondary satellites of the SAR signals over FSO links. The numerical analysis shows the proposed system has a NESZ < −29.6 dB, satisfying the SAR system requirements. An experimental proof of concept based on COTS, for both signal up- and down-conversion, is implemented to demonstrate the system functionality, showing performance similar to the simulations. The implementation of the proposed systems with integrated technologies could reduce the system SWaP and increase robustness to vibrations. A design based on the consolidated SOI platform with the transfer printing-based hybrid integration of InP semiconductor optical amplifiers is proposed. The amplifiers compensate for the losses of the passive SOI waveguides, decreasing the overall conversion loss. The polarization multiplexing of the modulated and unmodulated combs to be sent from (to) the primary to (from) the secondary satellite over the FSO links avoids complex space-consuming optical filters requiring several control signals.

Photonic-Assisted Generation of Flexible and Switchable Multi-Band Linearly Frequency Modulated Microwave Waveforms

A novel photonic scheme based on parallel dual-drive Mach-Zehnder modulator (DDMZM) to generate flexible and switchable multi-band linearly frequency modulated (LFM) microwave waveforms is proposed. In the scheme, a radio frequency (RF) local oscillator is applied to one arm of DDMZM1 and DDMZM2 with a relative phase of 90°, respectively; while a single-chirp signal to the other arms of the two DDMZMs with a tunable relative phase shift. The generated two independently lightwaves are detected by a balanced photodetector (BPD) and the switchable multi-band LFM signals are generated flexibly. By appropriately adjusting the phase difference <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> , dual-band complementary LFM signals and multi-band LFM signals can be easily switched. Based on simulations, the dual-band complementary LFM waveforms centered at 10 GHz and 30 GHz are generated with a doubled bandwidth (3.2 GHz) as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ =</i> 0, the multi-band LFM microwave waveforms with center frequency-bandwidth of 10 GHz-1.6 GHz, 20 GHz-6.4 GHz and 30 GHz-1.6 GHz, covering X, K and Ka bands, are simultaneously obtained with flatness of 1.9 dB as <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">θ</i> = π/2 or 3π/2. Their autocorrelation results manifest high peak-to-sidelobe ratio (PSR) about 14 dB, and good pulse compression capabilities. The presented scheme features its compact structure, easiness in switching control, as well as larger bandwidth, and has potential applications in multifunctional radars.

Design of 3-D Integrated SIW Multiband Bandpass Filter With Split-Type Extended Doublet Topology

A new class of 3-D integrated multiband bandpass filters (BPFs) based on substrate integrated waveguide (SIW) technology is presented in this work, for the first time. Split-type dual-extended doublet (SDED) coupling topologies are developed to propose these BPFs with a desired multiband response by the LEGO-style assembly of planar SIW resonant-mode blocks. These design schemes offer attractive and promising advantages with regard to compact size, low cost, flexible and expandable topology, as well as integration of high-density integrated circuits. For demonstration, dual- and triple-band BPFs are designed, fabricated, and measured. The measurement results are in good agreement with the simulation ones. Results indicate that the proposals can provide not only nice selective multiband signal transmission in such flexibly extensible topologies with new spatial schemes but also increase space utilization and reduce footprint.

Multiband RoF System with Good Transmission Performance Based on Additional SCS

A wavelength division multiplexing radio-over-fiber (WDM-RoF) system that can support multiband radio signals based on an additional subcentral station (SCS) is proposed and demonstrated in this paper. The dispersion characteristics of the multiband radio signals over fiber transmission are explored, and we exploit an improved transmission structure consisting of the central station (CS), the SCS, and base stations (BSs) to optimize the antidispersion performance of the proposed RoF system. At the SCS, a dual-drive Mach-Zehnder modulator (MZM) is employed to realize a cost-effective multiband radio signal generation of WDM signals with great spectral flatness, and an optical cross-connect unit is utilized to achieve a flexible distribution of different band radio signals for remote BSs. Based on the additional SCS, we establish a verification WDM-RoF system, which can support reliable transmission of multiband radio signals including 13 GHz, 26 GHz, 39 GHz, and 52 GHz. The WDM signals with each data rate at 2.5 Gbps are successfully transmitted over a 40 km standard single-mode fiber.

Multi-band microwave signals generation based on a photonic sampling with a flexible ultra-short pulse source.

We propose and experimentally demonstrate a photonic sampling-enabled multi-band microwave signals generation scheme. The intermediate-frequency input signal is up-converted to high frequency output signals in multiple frequency bands, after being optically sampled by an ultra-short optical pulse train and subsequently being detected by a photodetector (PD). The ultra-short pulse source, realized by using an electro-optic modulation-based time lens with the chirp compensation, can be flexibly adjusted to enhance the performance of multi-band frequency up-conversion. In the experiment, after optimizing the optical ultra-short pulse source with a repetition frequency of 8 GHz, ten phase-coded up-converted microwave signals with a 13-bit Barker code were successfully generated within a frequency range from 7 GHz to 41 GHz. The power fluctuation among the generated microwave signals in multi-band is measured to be 5.9 dB. The experiment results indicate that, our proposed scheme can realize the multi-band up-conversion with a high fidelity.

Compressive Wideband Spectrum Sensing and Signal Recovery With Unknown Multipath Channels

We study the problem of joint wideband spectrum sensing and recovery of multi-band signals in a multi-antenna-based sub-Nyquist sampling framework. Specifically, the multi-band signal is composed of a number of uncorrelated narrowband signals spreading over a wide frequency band. Unlike existing works which assume the source signals impinge on the receiver via a line-of-sight (LOS) path, we consider a more practical unknown MIMO channel which results from multipath propagation. A new sub-Nyquist sampling architecture is proposed, where each antenna output passes through two channels, namely, a direct path and a delayed path with a controlled amount of time delay. The signal at each channel is then sampled by a synchronized low-rate analog-to-digital converter (ADC). We utilize the collected data samples to build a set of cross-correlation matrices with different time lags and develop a CANDECOMP/PARAFAC (CP) decomposition-based method to recover the carrier frequencies, power spectra as well as the source signals themselves. Recovery conditions of the proposed method are analyzed, and Cramér-Rao bound (CRB) results for our estimation problem are derived. Simulation results are presented to illustrate the effectiveness of the proposed method.

Fault Feature Extraction of Rolling Element Bearing under Complex Transmission Path Based on Multiband Signals Cross-Correlation Spectrum

Fault Feature Extraction of Rolling Element Bearing under Complex Transmission Path Based on Multiband Signals Cross-Correlation Spectrum

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.

Toward integrating bidirectional multiband data and power transmission using double clad optical fibers for the next generation disaster resilient managing communication systems

AbstractDuring the cyclones and floods, all through the nation, the telecommunication network services were the most hit, leaving numerous individuals stripped from the ability to contact their precious ones. This paper is to demonstrate potential communications during such power blackouts. The double clad fiber is used for optically powering, transmitting and receiving the data to and from the remote antenna units by the Bidirectional method. The RoF multiband signals such as baseband, millimeter wave, and microwave, are transmitted and received bidirectionally by the single mode core, and power in outer clad to the Remote Antenna Unit. By the proposed RoF link transmission of 1 Gbps over a 100‐Km DCF with an optical power of about12.0 W is achieved.

Nonreciprocal transmission of multi-band optical signals in thermal atomic systems

Multi-band signal propagation and processing play an important role in quantum communications and quantum computing. In recent years, optical nonreciprocal devices such as an optical isolator and circulator are proposed via various configurations of atoms, metamaterials, nonlinear waveguides, etc. In this work, we investigate all-optical controlled nonreciprocity of multi-band optical signals in thermal atomic systems. Via introducing multiple strong coupling fields, nonreciprocal propagation of the probe field can happen at some separated frequency bands, which results from combination of the electromagnetically induced transparency (EIT) effect and atomic thermal motion. In the proposed configuration, the frequency shift resulting from atomic thermal motion takes converse effect on the probe field in the two opposite directions. In this way, the probe field can propagate almost transparently within some frequency bands of EIT windows in the opposite direction of the coupling fields. However, it is well blocked within the considered frequency region in the same direction of the coupling fields because of destruction of the EIT. Such selectable optical nonreciprocity and isolation for discrete signals may be greatly useful in controlling signal transmission and realizing selective optical isolation functions.

Approaching Sub-Nyquist Boundary: Optimized Compressed Spectrum Sensing Based on Multicoset Sampler for Multiband Signal

Compressed spectrum sensing naturally pursues the use of fewer sampling resources to achieve spectrum support reconstruction and signal recovery. The theoretical lower boundary of averaging sampling rate to recover the multiband signal has been proved to be twice the Landau rate. However, it is still unreachable in practice. Based on the multicoset sampling architecture, this paper analyzes the influencing factors on perfect spectrum reconstruction from three aspects: data model, sampling pattern and greedy reconstruction algorithms, for which practical and feasible optimization schemes are proposed. To reduce redundant reconstruction for the multiple measurement vectors (MMV) signal model, a block MMV model is proposed to improve the accuracy in the spectrum support set reconstruction process. A sampling pattern selection algorithm is proposed to ensure a higher success rate of the spectrum support reconstruction to optimize the sensing matrix. We also deduced the representation of the signal and noise energy in the reconstructed spectrum based on the mathematical model of compressed sensing. We thus proposed a non-orthogonal double-threshold matching pursuit algorithm to avoid a high false-alarm rate due to the manually set converging conditions for matching pursuit algorithms. Numerical experiments on real-world wideband signals are carried out to demonstrate the feasibility and advantages of the proposed approaches. With integrated optimization, the required sampling density to ensure perfect reconstruction is approaching the sub-Nyquist sampling boundary.

Spectrum Analysis for Multiband Signals With Nonuniform Sub-Nyquist Sampling in the Fractional Fourier Domain

This paper explores fractional spectrum analysis for periodically and nonuniformly sampled signals with finite disjoint bands in the fractional Fourier domain. Considering that spectrum aliasing occurs in sub-Nyquist sampling in the fractional Fourier domain, we study the conditions for reconstructing the fractional spectrum and devise relevant reconstruction methods. To obtain these goals, we investigate discrete-time fractional Fourier transform of the sampled signal that enables disjoint fractional frequency sub-intervals separated by aliasing boundaries. In order to implement perfect fractional spectrum reconstruction with reduced computations, we minimize the average sampling rate required by nonuniform sampling by means of properly choosing a sampling period. The theoretical lower bound on the optimized average sampling rate is much smaller than the lowest sampling rate required by uniform sampling under the same condition. Moreover, we derive the upper and lower bounds on the mean square error of fractional spectrum reconstruction with incorrect fractional spectrum modeling that assumes the signal as bandlimited to a large fractional frequency interval. Based on the derivations, we then obtain the optimal reconstruction parameters for spectrum reconstruction. Simulation results verify the effectiveness of our proposed methods.

A 12-b 16-GS/s RF-Sampling Capacitive DAC for Multi-Band Soft Radio Base-Station Applications With On-Chip Transmission-Line Matching Network in 16-nm FinFET

A 16-GS/s single 1.2-V supply direct RF-sampling capacitive D/A converter for soft radio base-station applications is implemented in a 16-nm FinFET technology. Due to co-integration with a wideband on-chip matching network, the D/A converter (DAC) is capable of signal synthesis between 600 MHz and 8 GHz, with a measured peak RF output power of &#x002B;5.6 dBm. The linearity required by cellular base-station applications is achieved by employing several analog-domain linearization techniques, yielding a two-tone intermodulation distortion of better than &#x2212;70 dBc up to the first Nyquist frequency. When transmitting a true multiband signal covering an instantaneous bandwidth of 1 GHz, an adjacent channel leakage ratio (ACLR) of better than &#x2212;69 dBc is achieved. Digital segment mismatch correction is shown to improve the linearity of a segmented DAC in deep digital backoff operation. A full-rate digital pre-distortion (DPD) method with efficient model identification is experimentally demonstrated. Using DPD, the design achieves an spurious free dynamic range (SFDR) of better than 72 dBc over the entire 0.6&#x2013;6-GHz frequency range.

Follow-up Photometry in Another Band Helps to Reduce Kepler’s False-positive Rates

Abstract The Kepler mission’s single-band photometry suffers from astrophysical false positives, most commonly of background eclipsing binaries (BEBs) and companion transiting planets (CTPs). Multicolor photometry can reveal the color-dependent depth feature of false positives and thus exclude them. In this work, we aim to estimate the fraction of false positives that cannot be classified by Kepler alone but can be identified from their color-dependent depth feature if a reference band (z, K s , and Transiting Exoplanet Survey Satellite (TESS)) is adopted in follow-up observation. We construct physics-based blend models to simulate multiband signals of false positives. Nearly 65%–95% of the BEBs and more than 80% of the CTPs that host a Jupiter-sized planet will show detectable depth variations if the reference band can achieve a Kepler-like precision. The K s band is most effective in eliminating BEBs exhibiting features of any depth, while the z and TESS bands are better for identifying giant candidates, and their identification rates are more sensitive to photometric precision. Given the radius distribution of planets transiting the secondary star in binary systems, we derive a formalism to calculate the overall identification rate for CTPs. By comparing the likelihood distribution of the double-band depth ratio for BEB and planet models, we calculate the false-positive probability (FPP) for typical Kepler candidates. Additionally, we show that the FPP calculation helps distinguish the planet candidate’s host star in an unresolved binary system. The framework of the analysis in this paper can be easily adapted to predict the multicolor photometric yield for other transit surveys, especially TESS.