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We propose a novel grant-based pilot access scheme to tackle the pilot collision in crowded massive multiple-input multiple-output (MIMO) systems. The proposed scheme divides the cell into several annuluses. Then, weaker user equipments (UEs) in each annulus, judged by a decision rule in a strongest-user collision resolution (SUCRe) scheme, send their reselected or allocated idle pilots to a base station (BS). We call this scheme enhanced SUCRe combined idle pilots access (E-SUCR-IPA). We analyze the number of successful UEs and the successful access probability of one UE with respect to its distance to the BS for the E-SUCR-IPA scheme. Numerical results show that the E-SUCR-IPA scheme significantly increases the number of successful UEs while ensuring fairness among UEs compared to baselines.

Organic piezoelectric nanogenerators (PENGs) with light weight, good flexibility, and simple processing are promising in mechanical energy conversion. Here, a high-output polymer PENG composed of a poly(vinylidene fluoride-trifluorethylene)/SnSe nanosheet (NS) nanocomposite film has been fabricated and tested. After a treatment with mixed solvents of N,N-dimethylformamide and 1,1,2,2-tetrachloroethane (TCE), the optimal nanocomposite PENG exhibits high piezoelectric properties with a piezoelectric coefficient (d33) of 25.06 pC·N-1, a prominent open-circuit voltage (Voc) of 15.36 V·cm-2, and a short-circuit current (Isc) of 1.02 μA·cm-2. Moreover, the PENG can generate an output power density of up to 10.72 μW·cm-2 under a vertical force of 50 N. The attractive piezoelectric performance results from the doping of SnSe NSs with a high piezoelectric coefficient and also the increased β-phase ascribed to the introduction of nucleating agent NSs and the TCE solvent. The PENGs reveal great application potentials in consumer electronics.

Benefiting from high flexibility and lightweight characteristics, flexible piezoelectric nanogenerators (PENGs) have the potential to become a ubiquitously available and sustainable alternative sou...

A new random access scheme is proposed to solve the intra‐cell pilot collision for M2M communication in crowded asynchronous massive multiple‐input multiple‐output systems. The proposed scheme utilizes the proposed estimation method of signal parameters to estimate the effective timing offsets, and then active user equipments obtain their timing errors from the effective timing offsets for uplink message transmission. The mean squared error of the estimated effective timing offsets of user equipments and the uplink throughput are analysed. Simulation results show that, compared to the exiting random access scheme for the crowded asynchronous massive multiple‐input multiple‐output systems, the proposed scheme can improve the uplink throughput and estimate the effective timing offsets accurately at the same time.

Piezo-phototronic effect has been extensively investigated for the third generation semiconductor nanowires. Here, we present a demonstration that piezo-phototronic effect can even be applied to tune polarization-sensitive photodetectors based on cation-mixed organic–inorganic perovskite nanowires. A big anisotropic photoluminescence (PL) with linearly polarized light-excitation was found due to a strong spontaneous piezoelectric polarization besides the anisotropic crystal structure and morphology. The piezo-phototronic effect was utilized to tune the PL intensity, and an improved anisotropic PL ratio from 9.36 to 10.21 for linearly polarized light-excitation was obtained thanks to the modulation by piezo-potential. And a circularly polarization-sensitive PL characterized with circular dichroism ratio was also discovered, which was found to be modulated from 0.085 to 0.555 (with a 5.5-fold improvement) within the range of applied strain. The circular dichroism was resulted from the joint effects of the modulated Rashba spin–orbit coupling and the asymmetric carriers separation and recombination for right- and left-handed helicity due to the presence of effective piezo-potential. These findings not only reveal the promising optoelectronic applications of piezo-phototronic effect in perovskite-based polarization-sensitive photodetectors, but also illuminate fundamental understandings of their polarization properties of perovskite nanowires.

A novel grant-free random access scheme is proposed to support massive connectivity with low access delay and overhead for machine-to-machine communication in massive multiple-input–multiple-output systems. This scheme allows all active user equipments (UEs) to transmit their pilots and uplink messages via the same time–frequency resource and performs the joint active UEs detection and uplink message decoding without channel estimation in one shot by utilizing the proposed ensemble independent component analysis (EICA) decoding algorithm. We call the proposed scheme the EICA-based pilot random access (EICA-PA). We analyze the successful access probability, probability of missed detection, and uplink throughput of the EICA-PA scheme. Numerical results show that the EICA-PA scheme significantly improves the successful access probability and uplink throughput, decreases missed detection probability and provides low-frame error rate at the same time.

Relative spectral responsivity is a basic parameter for detecting and evaluating the in-band response non-consistency of the channel polarization remote sensor (CPRS) in laboratory calibration. In ...

With the rapid development of new energy, the problem of power oscillation caused by large-scale wind farm access system has become increasingly prominent, such as the subsynchronous resonance between doubly-fed induction generator (DFIG) and fixed series compensation, which threatening the security and stability of the system seriously. Since there may not be a single type of wind turbine in the same wind farm, this paper aims to clarify whether there is interaction between different types of wind turbines in the wind farm, thus focuses on the subsynchronous oscillation (SSO) of a system that including DFIG based wind farm, direct-drive permanent magnet synchronous generator (PMSG) based wind farm and fixed series compensation. A linearization model of hybrid-based wind farm is established to analyze the influence of wind farm proportion, control parameters on the operation stability of the system. Based on the dynamic impedance model of hybrid-based wind farm, the mechanism of SSO is further revealed. A time-domain simulation model is built in EMTDC / PSCAD to verify the correctness and effectiveness of the theoretical analysis.

Aiming at the subsynchronous oscillation problem of direct drive wind farm in low operating conditions, the eigenvalue analysis method and impedance analysis method are used to analyze two kinds of subsynchronous oscillation problems caused by different current loop parameters of direct drive wind turbine group dominated by current inner loop control. The results show that: for the first kind of subsynchronous oscillation, the dominant influencing factors are the power grid strength and the current inner loop control parameters; with the decrease of the power grid strength, the current inner loop control parameters decrease, weakening the system damping, and the oscillation frequency gradually decreases; for the second kind of subsynchronous oscillation, the dominant influencing factors are the current inner loop control parameters, with the decrease of the power grid strength The damping of the system is weakened and the oscillation frequency increases slightly. In EMTDC/PSCAD, the time domain simulation model of direct drive wind turbine group connected to AC power grid is built, which verifies the correctness and effectiveness of the theoretical analysis.

A novel rate splitting space division multiple access (SDMA) scheme based on grouped code index modulation (GrCIM) is proposed for the sixth generation (6G) downlink transmission. The proposed RSMA-GrCIM scheme transmits information to multiple user equipments (UEs) through the space division multiple access (SDMA) technique, and exploits code index modulation for rate splitting. Since the CIM scheme conveys information bits via the index of the selected Walsh code and binary phase shift keying (BPSK) signal, our RSMA scheme transmits the private messages of each user through the indices, and the common messages via the BPSK signal. Moreover, the Walsh code set is grouped into several orthogonal subsets to eliminate the interference from other users. A maximum likelihood (ML) detector is used to recovery the source bits, and a mathematical analysis is provided for the upper bound bit error ratio (BER) of each user. Comparisons are also made between our proposed scheme and the traditional SDMA scheme in spectrum utilization, number of available UEs, etc. Numerical results are given to verify the effectiveness of the proposed SDMA-GrCIM scheme.

While fifth-generation (5G) communications are being rolled out around the world, sixth-generation (6G) communications have attracted much attention from both the industry and the academia. Compared with 5G, 6G will have a wider frequency band, higher transmission rate, spectrum efficiency, greater connection capacity, shorter delay, wider coverage and stronger anti-interference capability, so as to meet the various network requirements for industries. In this paper, we present a survey of potential essential technologies in 6G. In particular, we will introduce index modulation, artificial intelligence, intelligent surfaces, and terahertz communications technologies in detail, while giving a brief introduction to other potential technologies, including visible light communications, blockchain-enabled wireless network, advanced duplex, holographic radio and network in box.

The accuracy of low probability of intercept (LPI) radar waveform recognition is an important and challenging problem in electronic warfare. Aiming at the problem of the difficulty in feature extraction and the low recognition rates of the LPI radar signal under a low signal-to-noise ratio, and inspired by the symmetry theory, we propose a new approach for the LPI radar signal recognition method based on a dual-channel convolutional neural network (CNN) and feature fusion. Our new approach contains three main modules: the preprocessing module that converts the LPI radar waveforms into two-dimensional time-frequency images using the Choi–Williams distribution (CWD) transformation and performs image binarization, the feature extraction module that extracts different features obtained from the images, and the recognition module that utilizes a multi-layer perceptron (MLP) network to fuse these features and distinguish the type of LPI radar signals. In the feature extraction module, a two-channel CNN model is proposed that extracts Histogram of Oriented Gradients (HOG) features and deep features from time-frequency images, respectively. Finally, the recognition module recognizes the radar signals using a Softmax classifier based on the fused features from two channels. The experimental results from 12 types of LPI radar signals prove the superiority and robustness of the proposed model. Its overall recognition rate reaches 97% when the signal-to-noise ratio is −6 dB.

Generalised spatial modulation (GSM) activates more than one transmit antenna to send information each time and can achieve higher transmission rates than conventional spatial modulation (SM). Because the GSM information matrix cannot have a unitary matrix structure, the usual differential scheme cannot be used directly in GSM systems. A new scheme based on generalized spatial modulation is proposed(NGSM), in which each transmit frame consists of a reference block and normal blocks. Every normal block is differentially coded based on reference. Reference blocks are allocated more power than normal blocks. The performance of the NGSM system is analysed, and an analytical expression for a tight bound of the average bit error probability (ABEP) is derived. A sub-optimal low-complexity detection algorithm, message passing (MP), is presented to reduce the computational complexity of detection. Simulation and theoretical results demonstrate that the proposed NGSM scheme has only 0.5 dB of ABEP performance loss as compared to coherent GSM when the frame length is 400. The MP algorithm achieves near-maximum likelihood detection accuracy, while reducing complexity by 70%.

Graphene and its analogous 2D nanomaterials demonstrate high potential as reinforcements in bulk metallic materials with high performance, but homogenous dispersion within metal matrices remains considerable challenging. Here we report the successful fabrication of Ni superalloys from graphene oxide (GO)-decorated spherical Ni superalloy powder. The GO-reinforced Ni superalloys show an exceptional combination of yield strength and tensile ductility. The high yield strength arises from collective effects of specific microstructures, including good interfacial bonding between GO and the matrix, uniformly-distributed precipitates, and GO-induced twin boundaries. The good ductility is attributed to a sustainable work hardening ability of GO-reinforced Ni superalloys by the addition of GO, enhanced by and dislocation-precipitate interaction and stacking fault hardening mechanisms. This work reveals a novel strategy to obtain GO reinforced metallic materials with high strength and high ductility.

A novel A-D-A (acceptor-donor-acceptor) type non-fullerene small molecule, A201, consisting of an asymmetric thieno[1,2-b]indaceno[5,6-b′]thienothiophene (TITT) unit as middle D part and 2-(3-oxo-2,3-dihydroinden-1-ylidene) malononitrile (IC) groups as end-capped A parts was designed and synthesized. The asymmetric TITT building block showed a higher dipole moment of 0.85 Debye (1 Debye = 3.33564 × 10−30 cm) compared with the symmetric analogues of indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) of 0.098 and 0.13 Debye, respectively. The solution-processed bulk heterojunction solar cells using a benzotriazole (BTA)-based polymer of J71 as donor and A201 as acceptor, showed a power conversion efficiency (PCE) of 9.36% with an open-circuit voltage (Voc) of 0.88 V, a short-circuit current (Jsc) of 13.15 mA cm−2, and a fill factor (FF) of 0.67, under the illumination of AM 1.5G at 100 mW cm−2. The high PCE of this material combination could be attributed to its broad absorption spectrum and the high hole mobility (μh) and electron mobility (μe) of 9.56 × 10−4 and 5.17 × 10−4 cm2 V−1 s−1, respectively. These results indicate that the asymmetric electron-donating segments are promising to construct A-D-A type small molecular acceptors, which could largely enhance the diversity of building blocks to design photovoltaic materials.

An efficient Ru3(CO)12-catalyzed dehydrogenative Si N coupling reaction of indoles, pyrrole, and carbazole with hydrosilanes is reported. The reaction does not need any external additive. This catalytic reaction has a wide substrate range, excellent functional group tolerance, and high to excellent reaction efficiency. Gram-scale synthesis demonstrates the practicability of this synthetic method.

In order to satisfy the requirements of pre-launch laboratory calibration with high accuracy for polarization remote sensor, an innovative high precision polarimetric calibration instrument with adjustable degree of linear polarization (DoLP) in a wide dynamic range called adjustable polarization light source (APOLS) has been developed. APOLS consists of a collimated light source (CLS) and a polarization state adjuster (PSA). The PSA contains four parallel K9 glass plates, which can be orientated from 0° to 65° accurately controlled by electromechanical driving mechanism whose rotation accuracy is better than ±5″. Regarding the DoLP of APOLS, its adjustment range is from 0 to 0.72 within the spectral range from 460 to 2000 nm. The theoretical model of APOLS was established to describe the DoLP produced by multiple refraction of transmitted light. Meanwhile, the major systematic factors contributing to the DoLP uncertainty such as refractive index and absorption of K9 glass, incident angle, instability and parallelism of light source were analyzed. By using the spectro-polarimetric analyzer (SPOLA), the uncertainty evaluation experiments of APOLS were carried out. The results showed that when the DoLP value was in the range of 0.26 to 0.72, the uncertainty was less than 0.5%, and when the DoLP value was in the range of 0.003 to 0.26, the uncertainty was in the range of 8.5993% to 0.5534%. Moreover, the uncertainty was in the range of 0.0027% to 0.0032% when the uncertainty of the CLS was not considered. The consistency evaluation between APOLS and SPOLA ranged from -0.36 to 0.6 indicates the experimental results are satisfying. It can be concluded that the APOLS significantly improved the dynamic range and accuracy of the polarimetric calibration instrument.

Polymer piezoelectric nanogenerators (PENGs) have attracted extensive interest in mechanical energy conversion and wearable electronics for the advantages they have to offer owing some of their characteristics, e.g., the fact that they are light weight, possess a desirable flexibility, and benefit from a high adaptability and simple large-scale manufacturing processes. In this paper, a high-performance organic flexible PENG based on a poly(vinylidene fluoride-trifluorethylene) [P(VDF-TrFE)] film doped with a SnS nanosheet (NS) micropillar array has been prepared and characterized. The piezoelectric coefficient of the P(VDF-TrFE)/SnS NSs (0.3 wt. %) nanocomposite has been greatly enhanced compared with that of the pristine P(VDF-TrFE) film, from 13 to 21 pC N−1. It also demonstrates outstanding open-circuit voltage (Voc) and short-circuit current (Isc) outputs of 17.28 V cm−2 and 0.94 μA cm−2 under the pressure of 0.5 MPa, which represents a 6-fold and 4-fold improvement, respectively, compared with what a neat P(VDF-TrFE) film was able to deliver. The device was capable of producing a high output power density of 10.69 μW cm−2 under an applied pressure of 0.5 MPa. The dramatic enhancement obtained using nanocomposite micropillar array films results from a more developed β-phase content in the organic film, the higher piezoelectric properties of SnS NSs, and the better alignment of dipoles induced by the micropillar array structure. These remarkably enhanced PENG performances seem to hold much promise for the development of wearable electronics exploiting ambient mechanical energy, thanks to its ability to produce different signals depending on the nature of the source of stimuli.

The high levels of antibiotic residues in pharmaceutical wastewater treatment plants (PWWTPs) make these plants the hotspots for the proliferation of antibiotic resistance genes (ARGs). This study investigated the fate and removal of 11 ARG subtypes for sulfonamide, tetracycline, β-lactam, and macrolide resistance in each processing stage of two full-scale PWWTPs in northern China. The levels of typical ARG subtypes in the final effluents ranged from (2.56 ± 0.13) × 10(1) to (2.36 ± 0.11) × 10(7) copies/ml. The absolute abundance of ARGs in effluents accounted for only 0.03-78.1 % of influents of the two PWWTPs, while the majority of the ARGs were transported to the dewatered sludge with concentrations from (2.65 ± 0.43) × 10(5) to (4.27 ± 0.03) × 10(10) copies/g dry weight (dw). The total loads of ARGs discharged through dewatered sludge plus effluent was 1.01-14.09-fold higher than that in the raw influents, suggesting the proliferation of ARGs occurred in the wastewater treatment. The proliferation of ARGs mainly occurs in biological treatment process, such as aeration tank, anoxic tank, sequencing batch reactor (SBR), and bio-contact oxidation, facilitates the proliferation of various ARGs, implying significant replication of certain ARG subtypes may be attributable to microbial growth. Chemical oxidation seems promising to remove ARGs, with removal efficiency ranged from 29.3 to 85.7 %, while the partial correlation analysis showed significant correlations between antibiotic concentration and ARG removal. Thus, the high antibiotic residues within the PWWTPs may have an influence on the proliferation, fate, and removal of the associated ARG subtypes.

Performance analysis is presented for the joint estimation of symbol timing, frequency offset, and phase offset with continuous-phase modulation. In this study, undesirable influences on parameters to be estimated, which arise from the inaccuracy of the already estimated parameters, are computed mathematically. Based on performance analysis, a conditional Cramer-Rao bound (CRB) is put forward, and a hypothesise is made that phase offset variance with frequency error present should match with the conditional CRB for any digital phase modulation. Moreover, the hypothesis is manifested by analysing the log-likelihood function in a more general mathematical manner. To alleviate the influences, a data-aided acquisition and phase-locked loop tracking algorithm is proposed. The results of Monte Carlo simulations are presented, showing good agreement with theoretical analysis. Simulation results also show that the proposed algorithm can improve performance in terms of phase error variance at the expense of a high signal-to-noise ratio threshold.

Optical sensor on orbit is usually calibrated by on-board calibrator or some astronomical objects such as moon, sun or other stars in the visible and near infrared band, primary standard and standard transfer train are the most important sources of uncertainty during the process of calibration . Currently many satellite’s calibrators are needed to be installed on orbit. Calibrator can be used to calibrate satellite sensor periodicity, it is helpful to improve the quality of science data products derived from sensor observations, but it’s difficult to evaluate itself change of calibrator, calibration accuracy on orbit is difficult to less than 3%.A new self-calibration spectral radiometer of correlated photons is developed based on spontaneous parametric down-conversion (SPDC) effect, including radiometric observation and self-calibration mode, radiometric observation can be used to measure radiance of optical sensor and transfer to other satellite sensor using cross calibration method. Self calibration mode can calibrate response change of optics and electronic on orbit and modify calibration coefficient of optical sensor periodicity, compared with other calibration method on orbit, correlated photons is absolute and not dependent on primary standard and standard transfer train, only by measuring the ratio of the number of coincidence events to the number of trigger detection, trigger channel optical transmittance, the quantum efficiency of trigger detector is not need to be konwn.Principle of the new spectral radiometer is introduced, optics system of eight channel radiometer is designed, electronic and signal processing is analysed. ICMOS low light sensor is used to observe of space and spectral distribution of correlated photons, some measurement results are introduced in detail, its uncertainty is assessed, combine uncertainty is less than 0.35%. It is hopeful that the self-calibration spectral radiometer will be used in the fields of on-orbit calibration, cross calibration of other satellite sensor, field observation instrument calibration and climate change observation in future, etc.

Out-of-band response (out-of-band light leaks) is a significant uncertainty factor in multi-spectral remote sensing instruments radiometric calibration. In this paper, a method using a spectrum-tunable reference light source (STIS) which possess new functions of continuous and discrete spectral coverage to measure, correct and validate the 443 nm band of a multi-spectral camera has been mentioned. Adjusting STIS output two discrete radiance spectrum with its spectral width of about 50 nm in the out-of-band spectral region to directly measure out-of-band radiance responsivity. Correcting out-of-band response via spectral radiance measured by reference spectral radiometer and out-of-band radiance responsivity with the help of out-of-band response correction model. Validating out-of-band response correction accuracy via contrasting the relative departure between band-weighted radiance measurement of 443 nm band with out-of-band response correction and reference spectral radiometer measurement, under the conditions of measuring the test continuous spectrum produced by STIS. The result shows that the relative departure between the band-weighted radiance and the reference is decreased from 8.8 to 3.1% before and after the out-of-band response correction. The results demonstrate that STIS is suitable for measuring, correcting and validating the out-of-band response of multi-spectral remote instruments.

A kind of novel calibration source with dual output modes, namely, narrow-band and broadband, was designed. The optical system of the source is refractive, in spectrometer-like optical configurations using a prism as the dispersion device. The Digital Micromirror Device (DMD) is used as the spatial light modulator, which locates at the focal plane of the dispersion unit. The dispersive wavelengths are located at the active area of DMD, every column of the DMD corresponds to a different wavelength and the rows of each DMD column correspond to the intensity of that wavelength. With the modulation of the DMD, it can produce narrow-band/monochromatic output like a monochromator by switching the corresponding columns on, and broadband output by switching several different columns on. The source’s operating band spans 450~2250nm, consisting of two independent parts which span 450~1000nm and 1000~2250nm, respectively. The narrow-band bandwidths spans 5~28nm for VIS-NIR and 20~40nm for SWIR subsystems. Several broadband target spectra, including sea water, plants and sun, were simulated by this source through spectral simulation algorithm. The source’s radiometric metrics are suitable to be traced to the absolute cryogenic radiometer (ACR), the most accurate optical power standard at present, which is helpful to improve the calibration accuracy for remote sensors at the beginning. The capability of simulating target spectra will reduce the calibration uncertainties caused by the spectral mismatch between calibration sources and targets viewed by the remote sensors. Based on the considerations above, the source is very appropriate and applicable for remote sensor’s calibration.

A coherent detection receiver for multiple symbol trellis-coded continuous phase frequency shift keying (MSTC-CPFSK) system in burst-mode transmission is proposed. The receiver exploits a joint data-aided (DA) acquisition and phase-locked loop (PLL) tracking algorithm (DA-PLL) for coherent demodulation. Firstly, an all-zero sequence is utilized as a pilot for DA acquisition and then, a second-order PLL structure is introduced for tracking processing; subsequently, we calculate the equivalent Cramer-Rao bound (ECRB) for the PLL structure of the MSTC-CPFSK system; finally, some simulations are performed to verify our structure design and performance analysis.

This paper studies the parameter-tuned stochastic resonance (PSR) effect in Binary PAM Signal Processing under coherent and non-coherent received by the measure of Bit Error Rate (BER). Based on probability density function of general Gaussian noise, we derive an analytical expression of the BER under coherent and non-coherent received through different types of noise. The theoretical and numerical results demonstrate that the noise-enhanced transmission BER occur for non-coherent received in various noise scenarios. The BER of the signal from a nonlinear system over that of a linear system. For coherent received, whatever background noise is not favorable for the signal processing. The performance of a linear system is best.

In this paper, we present a simple Stokes parameter measurement method for a rotating quarter-wave plate polarimeter. This method is used to construct a model to describe the principle of how the magnitudes of errors influence the deviation of the output light Stokes parameter, on the basis of accuracy analysis of the retardance error of the quarter-wave plate, the misalignment of the analyzing polarizer, and the phase shift of the measured signals, which will help us to determine the magnitudes of these errors and then to acquire the correct results of Stokes parameters. The method is validated by the experiments on left-handed circularly polarized and linear horizontal polarization beams. With the improved method, the maximum measurement deviations of Stokes parameters for these two different polarized states are reduced from 2.72% to 2.68%, and from 3.83% to 1.06% respectively. Our results demonstrate that the proposed method can be used as a promising approach to Stokes parameter measurement for a rotating quarter-wave plate polarimeter.

A data-aided technique for carrier frequency offset estimation with continuous phase modulation (CPM) in burst-mode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio (SNR) required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods: it eliminates the need for fast Fourier transform (FFT) and modulation removal, and exhibits faster convergence rate without accuracy degradation.