Aiming at the problem of signal demodulation performance degradation caused by time delay and Doppler shift in ionospheric time-frequency dual-selected channels, a highly robust multiple frequency shift chirp modulation (RO-M-FSCM) method based on linear frequency modulation was proposed. Through address code design, identical time-frequency resources were mapped into multiple parallel transmission channels exhibiting fractional orthogonality. Real-time correction of the information-branch demodulation window alignment with the main path was achieved by the synchronization branch. An equivalent offset was introduced to reveal the coupling effect of delay and Doppler shift on the signal's spectral peak in the fractional domain. Consequently, the asymptotic closed-form expression for the symbol error rate of RO-M-FSCM signals was derived, and the length of robust code was optimized. The received SNR for non-coherent demodulation of RO-M-FSCM signals was enhanced based on a robust-domain multipath energy aggregation method. Simulation results demonstrated that under typical ionospheric broadband channel environment, the RO-M-FSCM scheme achieved co-optimization of transmission reliability and transmission rate. This approach provides an effective solution for ultra-long-distance communication in complex time-frequency dual-selected channels.

Depression, a severe psychiatric disorder with potential implications for suicide, has garnered increasing attention from researchers and the general public alike. Due to the accessibility of speech data, researchers have proposed many automatic depression recognition methods based on speech. Extracting effective features and designing an efficient recognition framework pose challenges in speech-based depression recognition. This study proposed a hierarchical multi-task learning framework based on interactive multi-head attention feature fusion (HMTL-IMHAFF), aiming to enhance the depression recognition accuracy by effectively leveraging the emotional and gender-related information embedded in speech. Firstly, we proposed a feature fusion approach based on interactive multi-head attention (IMHAFF) to comprehensively investigate the interplay among emotion valence, gender, and depression in order to obtain enhanced feature representation for depression recognition. Secondly, we developed a hierarchical multi-task learning framework with two levels. The first level consisted of sub-models related to emotion valence and gender to obtain the primary recognition results. The second level served as the final decision-making stage, which included a connection layer followed by a softmax layer that received input from the outputs of the first level. In addition, HMTL-IMHAFF used Long short-term memory (LSTM) model to capture the temporal relationship of speech feature sequences. Finally, the proposed method was comprehensively tested on the AVEC2014 dataset, and good results were achieved. Compared with the current related methods, the proposed method also stood out, obtaining an accuracy of 83.02%, which was 15% higher than the baseline method.

The dietary intake of branched-chain amino acids (BCAAs) has been reported to be associated with both elevated blood pressure (BP) and hypertension risk, while published findings were inconsistent, and the causality has never been well disclosed. We performed this prospective study aiming to find out the relationship between dietary BCAAs intake and hypertension risk in the Chinese population. A total of 8491 participants (40,285 person-years) were selected. The levels of dietary BCAAs intake were estimated using the 24-h Food Frequency Questionnaire. Associations of both BP values and hypertension risk with per standard deviation increase of BCAAs were estimated using linear and COX regression analysis, respectively. The hazard ratios and 95% confidence interval were given. Restricted cubic spline analysis (RCS) was used to estimate the nonlinearity. Both systolic and diastolic BP values at the end points of follow-up were positively associated with dietary BCAAs intake. Positive associations between BCAAs intake and hypertension risk were shown in both men and women. By performing a RCS analysis, the nonlinear relationship between BCAAs intake and hypertension was shown. As the intake levels of Ile, Leu, and Val, respectively, exceeded 2.49 g/day, 4.91 g/day, and 2.88 g/day in men (2.16 g/day, 3.84 g/day, and 2.56 g/day in women), the hypertension risk increased. Our findings could provide some concrete evidence in the primary prevention of hypertension based on dietary interventions.

The first three-dimensional potential energy surface (PES) for the ground-state of F-Li 2 polymer by CCSD(T) method were present. Two Jacobi coordinates, R and θ and the frozen molecular equilibrium geometries were used. We mixed basis sets aug-cc-pCVQZ for the Li atom and aug-cc-pCVDZ for the F atom, with an additional (3s3p2d) set of midbond functions. The total of about 365 points were generated for the PES. Our ab initio calculations were consistent with the experimental data very well.

In recent years, LoRa has been extensively researched in the satellite Internet of Things (IoT). However, the multiple access technology of LoRa is still one of the bottlenecks of satellite IoT. To improve the multiple access performance of LoRa satellite IoT, based on the orthogonality of LoRa symbols in the fractional domain, this paper proposes a low complexity Orthogonal LoRa Multiple Access (OLMA) algorithm for multiple LoRa users occupying the same frequency bandwidth. The algorithm introduces the address code to divide the fractional bandwidth into multiple parts, and the OLMA users with different address codes occupy different parts to transmit the information code, thus avoiding mutual interference caused by collisions in the same frequency bandwidth. The multiple access capability of OLMA can be flexibly configured only by simply adjusting the length of the address code according to the actual application requirements of data transmission. Theoretical analysis and simulation results show that the OLMA algorithm can greatly improve the multiple access capability and the total transmission bit rate of LoRa IoT without changing the existing LoRa modulation parameters and process.

The globally accurate potential energy surface (PES) for the ground-state of Li 2 F and Na 2 F clusters by the coupled-cluster singles and doubles excitation approach with perturbative treatment of triple excitations[CCSD(T)] were present. The total of about 2080 points were generated for the three-dimensional surfaces. Both the Li 2 F and Na 2 F molecule was confirmed to be bent at equilibrium.The Li-F-Li angle of 90° the depth of potential well is -6.267eV at R =2 a 0 and the barrier to linearity of Li-Li-F angle of 0° the height of the barrierl is 285.76eV at R =2.6 a 0. The Na-F-Na angle of 90° the depth of potential well is -5.3061eV at R =3 a 0 and the barrier to linearity of Na-Na-F angle of 0° the height of the barrierl is 721eV at R =2.6 a 0.

We present a new three-dimensional global potential energy surface (PES) for the ground state of Na2F system. A total of about 1460 points were generated for the PES. All of the points have been carried out by using the coupled-cluster single-, double-, and perturbative triple-excitations [CCSD(T)]. Two Jacobi coordinates, R and θ , and the frozen molecular equilibrium geometries were used. We mixed the basis sets of aug-cc-pCVQZ for the sodium atom and the basis sets of aug-cc-pCVDZ for the fluorine atom with an additional (3s3p2d) set of midbond functions; the energies obtained were extrapolated to the complete basis set limit. The whole calculation adopted supramolecular approximation approach. We divided the potential energy surface into three regions, the peak region, the well region, and the long range region, and calculate the single point energy, respectively. Our ab initio calculations will be useful for future studies of the collision-induced absorption for the Na2-F dimer, and it can be used for modeling the dynamical behavior in Na2F system too.

The globally accurate potential energy surface for the ground state of Li2F and Na2F systems was presented using the coupled-cluster singles and doubles excitation approach with perturbation treatment of triple excitations. Mixed basis sets were applied, aug-cc-pCVQZ for the lithium and sodium atoms and aug-cc-pCVDZ for the fluoride atom, with midbond functions (3s3p2d). In total, about 2080 points were generated for three-dimensional surfaces. Both the Li2F and Na2F molecules were confirmed to be bent at equilibrium. For Li-F-Li with an angle of 90 degrees, the depth of the potential well is 3.87 eV at R = 2a(0,) and the height of the barrier required to linearity with 0 degrees angle equals 285.76 eV at R = 5.6a(0). For Na-F-Na with an angle of 90 degrees, the depth of the potential well is 5.289 eV at R = 3a(0), and the height of the barrier required to linearity with 0 degrees angle equals 721 eV at R = 2.6a(0). Our ab initio calculations of potential surface and potential energy surface were compared with the experimental results.

LoRa has been widely used in the Internet of Things (IoT) recently for its advantages of long distance and low power consumption. However, the security problem restricts its practical application scenarios. The existing Advanced Encryption Standard (AES) technology has high computational complexity and high energy consumption for LoRa terminals with limited hardware resources. Therefore, this letter proposes a novel physical layer encryption algorithm based on LoRa modulation characteristics, which is suitable for low-cost LoRa terminals. The algorithm combines the secret key extraction approach based on Received Signal Strength Indicator (RSSI) with the secret sharing scheme based on Chinese Remainder Theorem (CRT). Simulation results show that the proposed algorithm can protect the LoRa transmission bits from eavesdroppers. While, compared with the conventional LoRa without security, the proposed algorithm has no bit error rate (BER) performance loss with different SNR and will not cause more serious spectrum leakage under different synchronization offsets.

基于工科院校研究生教学、研究生培养及研究生就业的特点,将研究生培养的各环节及具体过程与现代企业项目管理及其结构化流程有机融合,立足提高研究生科研创新、思想品德、身心健康和沟通表达等各方面的综合素质能力,探索构建可管可控可量化的研究生杰出人才精细化培养模式.该模式不仅可为研究生培养过程提供质量保证,而且可为研究生就业后从事科学研究工作奠定良好的现代企业项目管理及结构化流程基础.

LoRa has been widely used in the Internet of Things (IoT). However, since LoRa only supports single symbol transmission in its bandwidth, the bit rate of LoRa is limited. This restricts the future development of LoRa, such as Smart Home, Internet of Vehicles, Satellite IoT, etc. Toward this end, based on the energy convergence characteristic of LoRa symbol in the fractional domain, we propose a multiplexed LoRa (MuLoRa) which transmits multiple LoRa symbols simultaneously in the same bandwidth. By adding address bits, the collision between multiple LoRa symbols of MuLoRa is avoided. Considering the hardware consumption of MuLoRa modulation in the time domain, a fractional domain MuLoRa modulation method based on fractional Fourier transform (FRFT) is designed. Simulation results show that MuLoRa can significantly improve the transmission bit rate than conventional LoRa under the same bandwidth. And MuLoRa can be configured more flexibly to meet the performance requirements of rate, power, collision avoidance and BER in different application scenarios in the future high data rate IoT era.

In recent years, with the rapid development of location-based social networks (LBSN) in the Internet, point of interest (POI) recommendation has become a hot spot. Most existing researches make use of contextual information to model users' interest preferences. However, the existing methods for extracting various auxiliary information still need to be improved, such as how to treat the users' social relations equally. In order to obtain users' actual preferences more accurately, in POI recommendation, we propose a deep learning framework KEAN (Knowledge Embedded and Attention Based Network) based on knowledge graph and attention model. The framework includes knowledge-graph embedding method, preference extraction network based on attention mechanism and recommendation network. Our study used knowledge-graph embedding method to get the embedding of each user and POI. In addition, an LSTM network based on attention mechanism was proposed, which uses LSTM network to learn the user's preferences according to the user's check-in sequence. Besides, the attention mechanism was used to extract friends' preferences and merge them with the user's preferences to generate end-user preferences. Finally, our model use fully-connected neural networks to realize recommendations. The effectiveness of the model was proved by the experimental results based on real LBSN datasets.

Admittance analysis has been widely used to investigate the underlying mechanism of organic semiconductors. In this article, charges stored in organic devices with Alq(3) and PMMA under light is investigated using capacitance/conductance-voltage (C/G-V) as well as its frequency characteristics. For the control device without PMMA, the capacitance has two peaks. Under dark condition, the first peak is depletion capacitance determined by built-in field and the second peak is diffusion capacitance used to inject carriers. Under illumination, however, the first peak is related to storage of space charges and the second peak is derived from both injected and light-induced carriers. By inserting 2 nm, 4 nm and 10 nm PMMA, the first capacitance peak under illumination ceased to behave as a peak gradually. As the thickness increased, after the first capacitance reached its maximum, it decreased slowly to thin PMMA but not up to 10 nm PMMA. Combined with C/G-V and its frequency characteristics, it evidently originated from the reversed field induced by interfacial accumulated charges. All the results emphasize the importance of the approach based on C/G-V and its frequency characteristics, paving a new way for the investigation of the storage of charges and the selection of blocked layer.

In this paper, capacitance/conductance-voltage characteristics (C/G-V) under illumination was achieved to investigate the dynamic mechanism of stored charges in OLEDs with a structure of ITO/ PEDOT:PSS/PMMA/Alq3/Al. For all devices, at least two peaks presented in the optical capacitance-voltage curve. Compared to curves of devices under dark, the first peak increased remarkably with a deviation to Vbi, which can be explained in the form of stored charges combined with the optical conductance characteristics. It was also found that a great decrease in capacitance is followed by the collapse of the first peak with PMMA thickness increased. It can account for the presence of interfacial charges, which is proved further by the conductance curves. To the device with 10 nm PMMA, a third peak took place in optical capacitance and it was due to the storage of electrons by PMMA. Also, the first capacitance peak enhanced approximate linearly as the illumination power increased, which can verify the contribution of the stored charges. Additionally, it shows the potential for the stored charges in optical detections.

The OFDM technology is widely used in wireless communication systems, but it is highly sensitive to narrowband interference (NBI). The existing NBI suppression algorithms are mainly for single NBI or multiple NBIs with an assumption that the frequency distance of the multiple NBIs is large enough. However, in reality, there are more and more multiple interacting NBIs with small frequency distance, such as NB-IoT. Unfortunately, due to the interaction of multiple NBIs, the performance of existing NBI suppression algorithms is degraded. Aiming at this problem, we propose a multiple interacting NBIs suppression algorithm jointed time-frequency domain for OFDM systems. First, in order to achieve a high-precision and low-complexity frequency estimate for a single NBI, an interference frequency estimation method based on chirp-z transform (CZT-IFE) is studied. Then, for multiple interacting NBIs, based on the analysis of NBI frequency distance and spectral aliasing, a highly robust interference frequency estimation method combining IIR notch filter and CZT-IFE (NF-CZT-IFE) is given. It eliminates the interaction of multiple NBIs and obtains the accurate frequency estimates of the NBIs. Finally, based on NF-CZT-IFE, the multiple interacting NBIs are suppressed by using IIR notch filters. Simulation results demonstrate that the proposed multiple interacting NBIs suppression algorithm has better interference suppression performance on the NBIs with different frequency distances and different interference numbers. The proposed algorithm improves the robustness of OFDM systems in complex NBI environments.

针对窄带干扰(NBI)的频谱泄漏导致正交频分复用(OFDM)系统误比特率性能下降的问题,提出一种适于OFDM系统的高精度的减小频谱泄漏的频域窄带干扰抑制算法.首先,利用傅里叶变换(FFT)推导出NBI频率的分数因子与NBI频谱泄漏的定量关系,得出当分数因子小于0.005时NBI频谱泄漏小于总能量0.01％的结论;其次,在时域将接收信号与频率搬移矩阵相乘实现干扰对齐,在频域将对齐的干扰信号置零完成干扰抑制,且证明了残留的频谱泄漏仅与分数因子估计误差有关而与分数因子无关;最后,基于FFT粗定位的NBI频谱范围,利用Chirp-Z变换对该范围的频谱进行细化,得到估计误差小于0.005且分布均匀的高精度的分数因子估计值.仿真结果表明,所提算法对OFDM系统误比特率性能的改进与陷波干扰抑制算法接近,且实时性更好;在分数因子为0.5、误比特率为10-4时,所提算法、陷波干扰抑制算法及查表干扰抑制算法所需的信噪比分别为4.5、4.5及6 dB.

To reduce the secrecy loss due to the correlation between main and wiretap channels, this paper introduces a cooperative jamming relay to degrade the reception at the eavesdropper. We consider slow-fading multiple-input-single-output wiretap channels with a passive single-antenna eavesdropper, where full information for the channels to the legitimate receiver and statistical information for the channels to the eavesdropper is available. By deploying the cooperative jamming relay reasonably, the correlation between the channels from the introduced relay to the legitimate receiver and the eavesdropper can be much below than that between the main and wiretap channels. Thus, the relay can interfere with the eavesdropper more effectively than the traditional scheme of artificial noise-aided beamforming at the transmitter. The simulation results demonstrate that the secrecy outage probability under the transmit power and target secrecy rate constraints is reduced substantially.

With the increasing demand for the command and dispatch service of private network communication system, broadband trunking communication (B-TrunC) system and its standards are improving steadily. In order to improve the performance of group service of B-TrunC system, we propose a system model with same-frequency multicell coordination for group users and a multicast beamforming algorithm based on the system model. The proposed system model combines multicell coordination and same-frequency scheduling. The multicast beamforming optimization problem is a non-deterministic polynomial hard (NP-hard) problem. The mathematical model of the proposed algorithm is obtained according to direction of departure (DOD) of group users and max-min fairness (MMF) principle; the optimal approximate solution of transmitting multicast beamforming weight vector, which maximizes the least received SNR of group users, is obtained on the basis of semidefinite relaxation (SDR). Theoretical analysis and simulation results show that the proposed multicast beamforming algorithm based on same-frequency multicell coordination can significantly improve the SNR of cell-edge users and increase the group user channel capacity. As the group user angle interval decreases or the base station antenna number increases, the performance of the proposed algorithm is further improved.

The OFDM technology has been widely used in 4G, 5G, and other wireless communication systems for its anti-frequency selective fading and high spectral efficiency. However, OFDM systems are very sensitive to narrowband interference (NBI). There are many existing NBI suppression algorithms for OFDM systems. Unfortunately, in these existing algorithms, the NBI is typically modeled as a sinusoidal signal. With the widespread use of LoRa, which is one of the most imposing IoT technologies, the sinusoidal interference model is unreasonable since LoRa adopts non-stationary chirp signals. Toward this end, we study LoRa interference suppression for OFDM Systems (IEEE 802.11ah). First, we derive the analytical expression of LoRa signal in the fractional Fourier transform (FRFT) domain. Then, we present the principle and procedure of the proposed FRFT-domain interference suppression algorithm for OFDM systems interfered by LoRa. Simulation results show that the proposed FRFT-domain algorithm can significantly improve the BER performance of OFDM systems interfered by LoRa at different signal to interference ratios, compared with the frequency-domain algorithm.

An artificial-noise (AN)-aided beamformer for reducing secrecy loss due to the correlation between the main and wiretap channels is designed in this letter. We consider slow-fading multiple-input-single-output wiretap channels with a passive single-antenna eavesdropper, where the source has accurate main channel information and statistical wiretap channel information. By exploiting the channel correlation, the power of the AN in the null space of the main channel can be placed more reasonably instead of using a simple uniform distribution. Then, an efficient algorithm for power allocation between the information-bearing signal and the AN is developed. The simulation results show that the secrecy rate under the transmit power and secrecy outage constraint is improved.