A photonics-assisted simultaneous frequency and angle of arrival (AOA) measurement system based on parameter mapping method is proposed and demonstrated by simulation and experiment. Using optical sideband sweeping and envelope detection, the frequencies of the signals under test (SUT) are mapped to the time domain of the output amplitude of the electrical pulses, and the AOA-dependent phase differences are mapped to the amplitudes of the output electrical pulses. The experiment achieved multiple-frequency signal measurements, and the absolute measurement error was between 1.8 MHz and 5.4 MHz in the range from 9.4 GHz to 13 GHz. The frequency range can be adjusted by modifying the bandwidth of the frequency-swept signal or the DC bias voltage. Furthermore, the unambiguous AOA measurement from - 90 degrees to 90 degrees is successfully realized simultaneously, and the error of the AOA measurement ranging from - 66.44 degrees to 66.44 degrees is confined to within +/- 1.4 degrees. Due to its robustness and flexibility, this dual-function measurement system can find various applications in future electronic warfare systems.

A photonic approach to the cancellation of self-interference in the optical domain with fiber dispersion immunity and harmonic frequency down-conversion function is proposed based on an integrated, dual-parallel, dual-drive Mach–Zehnder modulator (DP-DMZM). A dual-drive Mach–Zehnder modulator (DMZM) is used as an optical interference canceller, which cancels the self-interference from the impaired signal before fiber transmission to avoid the effect of fiber transmission on the cancellation performance. Another DMZM is used to provide carrier-suppressed, local-oscillation (LO)-modulated, high-order double optical sidebands for harmonic frequency down-conversion to release the strict demand for high-frequency LO sources. By regulating the DC bias of the main modulator, the signal of interest (SOI) can be down-converted to the intermediated frequency (IF) band after photoelectric conversion with improved frequency-conversion efficiency, immunity to the fiber-dispersion-induced power-fading (DIPF) effect, and effective signal recovery. Theoretical analyses and simulation results show that the desired SOI in the X and K bands with a bandwidth of 500 MHz and different modulation formats can be down-converted to the IF frequency. The self-interference noise with the 2 GHz bandwidth is canceled, and successful signal recovery is achieved after a 10 km fiber transmission. The recovery performance of down-converted signals and the self-interference cancellation depth under different interference-to-signal ratios (ISRs) is also investigated. In addition, the compensation performance of DIPF is verified, and a 6 dB improvement in frequency conversion gain is obtained compared with previous work. The proposed scheme is compact, cost-effective, and thus superior in wideband self-interference cancellation, long-range signal transmission, and effective recovery of weak desired signals.

A multiple microwave frequency measurement approach based on frequency-to-time mapping (FTTM) is reported. The FTTM is constructed by optical sideband sweeping and electric-domain intermediate frequency envelope monitoring. Two optimized operations are implemented. First, the use of balanced photodetection cancels out the beat components generated by the signals under test (SUT) themselves, so as to exclude frequency misjudgment. Second, a reference signal is introduced to map the SUT frequency to a relative time difference instead of an absolute time value, avoiding the measuring bias caused by time synchronization. As a result, the proposed scheme with improved robustness could be attractive for future practical applications. An experiment is performed. Microwave frequency measurement from 16 to 26 GHz is demonstrated, with an average error of 7.53 MHz.

In this paper, a photonic-enabled image rejection mixer (IRM) that features an ultrawideband self-interference cancellation (SIC) function and a compact configuration is proposed. The parameter tuning of SIC is realized in an optical domain, which avoids the use of electrically tuned devices with limited bandwidth and precision, so that high-precision parameter matching can be realized in the optical domain to realize deep and ultrawideband SIC. The key point of image rejection (IR) is to construct a pair of orthogonal local oscillation (LO) signals through DC-bias-induced phase shift. This not only avoids a high-frequency electrical 90-degree hybrid coupler (HC) applied in the traditional Hartley structure, but also compensates the phase deviation in the electrical intermediate frequency (IF) 90-degree HC flexibly, ensuring wideband and deep IR operation. The simulation results show that the proposed IRM can achieve ultrawideband SIC and IR with the simultaneous high-efficiency recovery of useful signals. They also verify that the scheme has good resistance to strong interference, and can cope with the phase imbalance of the IF 90-degree electrical HC, ensuring the good performance of the system, which has a wide application prospect in various in-band full-duplex (IBFD) systems.

A novel scheme with simultaneous measurement of Angle-of Arrival (AOA) and Doppler-frequency-shift (DFS) of microwave signal without direction ambiguity is proposed and demonstrated. At remote antenna unit (RAU), two received high-frequency microwave signals and a reference signal are modulated by a dual-polarization dual-drive Mach-Zehnder modulator (DPol-DDMZM). After transmission over a segment of fiber link, two signals in low-frequency bands are generated at central station (CS) through a frequency down-conversion. The DFS (including values and direction) and the non-ambiguous AOA in the range of 180° can be simultaneously calculated by monitoring the power and frequency of the two low-frequency electrical signals. The proposed structure not only improves the concealment and security of the CS but also can be extended to have multiple antenna elements in remote locations to realize multi-target detection.

A photonic-assisted scheme capable of self-interference cancellation (SIC) and image rejection mixing (IRM) is demonstrated to solve the intractable problem of in-band interference for in-band full duplex (IBFD) systems with high frequency and large bandwidth. In the proposed scheme, a single optical path configuration is constructed based on an integrated modulator applied as the main device. The SIC operation is implemented in the optical domain making it immune to the influence caused by fiber dispersion. Owing to the intermediate frequency (IF) signal amplitude regulation mechanism under the combined action of fiber dispersion induced phase and double sideband (DSB) modulation, the scheme can realize IRM without increasing the system complexity. Experimental results show that the 50 MHz 16-quadrature amplitude modulation (16-QAM) signal of interest (SOI) centered at different frequencies are down-converted to 2.5 GHz. The depth of SIC and image-rejection (IR) is over 35 dB and 25 dB after transmitted through a span of 10.1 km optical fiber. The received 16-QAM down-converted signal can be recovered with an error vector magnitude (EVM) which satisfies the requirement of 3GPP-specified EVM limit. The signal recovery performance, SIC depth and image rejection ratio (IRR) under different signal to interference ratio (SIR) is also investigated. In addition, a comparison of relevant literature with this scheme from the perspective of technical discussion is also presented. The proposed scheme can realize effective functional integration with compact structure, simple parameter tuning mechanism, improved stability and high costeffectiveness to solve the in-band interference problem which is of great value to be applied in IBFD centralized radio access networks (CRAN) towards future 5G communication.

A microwave photonic scheme for multi-functional radio over fiber based in-band full duplex communication links to realize deep self-interference cancellation, long range transmission, and efficient signal recovery is proposed. In the proposed scheme, double sideband modulation helps avoid applying electrical couplers or optical filters and is beneficial to improve the frequency conversion efficiency. By virtue of the intermediate frequency signal amplitude regulation mechanism induced by fiber dispersion, the conditions of dispersion induced power fading compensation, amplitude matching, and phase reversion between self-interference and reference signals can be satisfied through joint DC bias tuning. The high precision delay matching in the optical domain is advantageous to the deep self-interference cancellation performance in a wide frequency range compared to its electrical counterparts. Furthermore, the deterioration of signal quality and self-interference cancellation performance caused by fiber dispersion is avoided. Experimental analyses show that a single tone signal in a wide frequency range of 2–20 GHz can be cancelled over 60 dB. A broadband signal with bandwidth of 50 MHz in the C-band, X-band, and K-band can be cancelled over 35 dB. Furthermore, the recovery performance of the signal of interest with different modulation formats and different signal to interference ratios is investigated, showing high quality signal transmission and efficient signal recovery. The capability of dispersion induced power fading compensation is also verified, and the spurious-free dynamic range is measured to be ${88.47}\;{\rm{dB\cdot H}}{{\rm{z}}^{2/3}}$.

An approach for photonic generation of multilevel frequency-hopping (FH) microwave signal based on a Sagnac loop is proposed and investigated. In the Sagnac loop, several Mach-Zehnder Interferometers (MZI), driven by the coding signals, are connected in series to act as a tunable photonic filter. By carefully adjusting the coding signals, the photonic filter can select the specific frequency component from the input optical frequency comb (OFC), so as to generate multilevel FH microwave signal. Theoretical analysis and simulation works are per-formed to demonstrate a 7-level FH microwave signal generator, and the discussion about the impact of non-ideal factors is given. The approach features high FH speed, wideband and amenable to photonic integration. In addition, the Sagnac loop ensures the equal optical path for clockwise and counterclockwise lights, which can enhance signal performance due to the better phase stability.

Self-interference (SI) influenced the recovery of the signal of interest (SOI) in In Band Full Duplex (IBFD) radio-over-fiber (ROF) links. The multipath effect and nonlinear distortion aggravate the difficulty of the SI signal elimination. A fiber-transmission-assisted digital self-interference cancellation (DSIC) scheme is proposed to solve the problem at a low time complexity. The key to removing the impact of harmful factors is combined with the advantages of photonics architecture and digital filter algorithm. A fiber-transmission-assisted scheme achieves the transmission of reference signals with all the linear and nonlinear features which transform the nonlinear problem into a linear question for DSIC subsequently. In DSIC, a fast transversal recursive least-squares (FTRLS) algorithm realizes a fast-channel estimating process when the SOI is involved. For 10 km fiber transmission, exceeding 38 dB and 34 dB cancellation depth over 50 MHz bandwidth in the X band and Ku band are experimentally demonstrated, and 25 Mbaud 16-quadrature amplitude modulation (16-QAM) SOI is successfully recovered after SIC. In addition, FTRLS merely consumed 7N + 14 multiplication times at each iteration (filter order N) in the channel estimating process, which saves multiplications amount above 86% than RLS, DNN, Volterra-RLS algorithm, when N is equal to 80.

A novel scheme that can simultaneously measure the Doppler frequency shift (DFS) and angle of arrival (AOA) of microwave signals based on a single photonic system is proposed. At the signal receiving unit (SRU), two echo signals and the reference signal are modulated by a Sagnac loop structure and sent to the central station (CS) for processing. At the CS, two low-frequency electrical signals are generated after polarization control and photoelectric conversion. The DFS without direction ambiguity and wide AOA measurement can be real-time acquired by monitoring the frequency and power of the two low-frequency electrical signals. In the simulation, an unambiguous DFS measurement with errors of ±3 × 10−3 Hz and a −90° to 90° AOA measurement range with errors of less than ±0.5° are successfully realized simultaneously. It is compact and cost-effective, as well as has enhanced system stability and improved robustness for modern electronic warfare systems.

The Sagnac effect is an important factor that leads to nonreciprocity in long-haul fiber-optic time and a frequency transfer system. For high-precision time transfer, correction must be performed to eliminate the time difference based on the trajectory of the path. However, the routing information may be not detailed enough to guarantee sufficient precision for Sagnac correction. Thus, nodes along the path must be surveyed with a certain sparsity. We provide a practical method for estimating the average distance of these nodes. Six simulated paths are generated to validate the method for different uncertainties.

A novel photonic-assisted system for realizing the simultaneous measurement of Doppler frequency shift (DFS) and angle of arrival (AOA) is proposed. It is a simplified structure that is based on a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DDMZM). The DFS direction can be accurately determined by comparing the phase relationship between the upper and lower low-frequency signal waveforms. An amplitude comparison function (ACF), which constructs a one-to-one mapping between the power ratio and the phase difference of echo microwave signals, can reduce the AOA measurement errors. The simulation results show that the simulated ACFs agree well with the theoretical ACFs, and the measurement errors of AOA are less than ±2.8° in a range of 0° to 78°. Moreover, the DFS can be realized by analyzing the spectrum of the low-frequency electrical signal with a measurement error of less than ±0.05 Hz. The system structure is compact and cost-effective, which provides an alternative solution for modern radar and electronic warfare receivers.

A filter-free photonic method to simultaneously realize radio frequency (RF) image-reject mixing, self-interference cancellation (SIC), and fiber transmission for in-band full-duplex (IBFD) radio-over-fiber (RoF) link is reported. The key to achieving multi-functions is the joint manipulation of fiber dispersion-induced intermediate frequency (IF) amplitude and time delay changes, which is implemented by sideband phase-shifted optical carrier suppression (SPS-OCS) modulation and frequency tuning of the optical carrier. Owing to the control of IF amplitude and delay variation introduced by fiber dispersion, simultaneous deep image rejection and SIC over wide bandwidth can be realized after fiber transmission. Since no optical filter is required, the proposed system can work at a lower frequency, featuring a large frequency tuning range. For 25 km single-mode fiber (SMF) transmission, simultaneous 20 dB SIC within 1 GHz bandwidth and 29 dB image rejection ratio (IRR) at 6.6 GHz RF frequency in the C band, 21 dB SIC and 19 dB IRR within 1 GHz bandwidth in the X band, 24 dB SIC within 1 GHz bandwidth and 20 dB IRR at 16 GHz RF frequency in the Ku band are experimentally demonstrated. Furthermore, weak SOI with various modulation formats are well recovered after the cancellation of strong interference and fiber transmission.

In this paper, a novel and efficient photonic-assisted remote frequency measurement (RFM) system with a significantly simplified structure and flexible operation range is proposed. In this system, the remote antenna unit (RAU) and the the central station (CS) are separated to ensure the concealment and safety of the signal processing unit. At the RAU, the unknown radio frequency (RF) signal is modulated by a dual-polarization dual-drive Mach–Zehnder modulator (DPol-DMZM). In the CS, changing the dispersion coefficient or length of the dispersion medium, the microwave frequency measurement range of the RFM system can be easily tuned without system reconstruction, and different RAUs located at different places can be controlled to work at the same measurement range. The simulation results show that a frequency measurement over the high frequency range (> 18 GHz) can be achieved with a measurement error better than ± 0.2 GHz. Noteworthy, the impact of the non-ideal factors such as bias drift, intensity noise, phase noise, the equivalent deviation of the polarization beam splitter (PBS), and the dispersion value of the single mode fiber (SMF) are also discussed. It has been proved that they have little influence on the system performance over the high frequency range.

A photonic-assisted approach for instantaneous frequency measurement (IFM) based on a 1×4 Mach–Zehnder interferometer (MZI) structure is proposed and experimentally demonstrated. In this IFM method, a Mach–Zehnder modulator (MZM) in conjunction with an optical filter play the role of CS-SSB signal generator, mapping the unknown microwave into a tunable optical sideband. Due to the property of the subsequent 1×4 MZI structure, two amplitude comparison function (ACF) that convert the frequency information into optical power ratio can be established. A detailed theoretical analysis illustrates the realization of frequency measurement with a range of full free spectral range (FSR) and optimized estimation error by using these two ACFs. Simulation has been carried out to verify the mechanism, and the discussion about the merits of CS-SSB modulation and the applicable scenarios is also given. A proof-of-concept experiment is performed, in which the microwave frequency measurement from 7.5 to 20 GHz is demonstrated with an estimation error of less than 100 MHz.

A compact and cost-effective photonic approach for generating switchable multi-format linearly chirped signals is proposed and experimentally demonstrated. The core component is a dual-drive Mach–Zehnder modulator driven by a coding sequence and a linearly chirped waveform. By properly setting the amplitudes of the coding sequence, a linearly chirped signal with different formats, including the frequency shift keying (FSK), phase shift keying (PSK), dual-band PSK, and FSK/PSK modulation formats, can be generated. Experiments are conducted to verify the feasibility of the proposed scheme. Linearly chirped signals with the above four formats are successfully generated. The scheme features multiple formats and high tunability based on a compact structure, which has potential applications in modern multifunctional systems.

Background : Hippocampal atrophy is a characteristic of Alzheimer’s disease (AD). However, alterations in structural connectivity (number of connecting fibers) between the hippocampus and whole brain regions due to hippocampal atrophy remain largely unknown in AD and its prodromal stage, amnestic mild cognitive impairment (aMCI). Methods : We collected high-resolution structural MRI (sMRI) and diffusion tensor imaging (DTI) data from 36 AD patients, 30 aMCI patients, and 41 normal control (NC) subjects. First, the volume and structural connectivity of the bilateral hippocampi were compared among the three groups. Second, correlations between volume and structural connectivity in the ipsilateral hippocampus were further analyzed. Finally, classification ability by hippocampal volume, its structural connectivity, and their combination were evaluated. Results : Although the volume and structural connectivity of the bilateral hippocampi were decreased in patients with AD and aMCI, only hippocampal volume correlated with neuropsychological test scores. However, positive correlations between hippocampal volume and ipsilateral structural connectivity were displayed in patients with AD and aMCI. Furthermore, classification accuracy (ACC) was higher in AD vs. aMCI and aMCI vs. NC by the combination of hippocampal volume and structural connectivity than by a single parameter. The highest values of the area under the receiver operating characteristic (ROC) curve (AUC) in every two groups were all obtained by combining hippocampal volume and structural connectivity. Conclusions : Our results showed that the combination of hippocampal volume and structural connectivity (number of connecting fibers) is a new perspective for the discrimination of AD and aMCI.

目的 研究腹式呼吸放松训练对移居高原人群的动脉血氧饱和度及睡眠质量的综合改善作用.方法 选取232名移居高原者(>180 d)进行短期的连续4 d的腹式呼吸放松训练;另选605名移居高原者(>180 d)进行为期4周的长期的腹式放松训练.在固定时间段进行动脉血氧饱和度、心率的监测和睡眠相关调查问卷评估.结果 短期的腹式呼吸放松训练能够明显改善移居高原者的动脉血氧饱和度(t=2.05,P=0.04);长期腹式腹式呼吸放松训练能够明显改善动脉血氧饱和度、入睡时间、总睡眠时间(t=6.05,14.88,10.98,P<0.01).结论 腹式呼吸放松训练能够明显提升移居高原者的动脉血氧饱和度,长期练习能够明显改善由于机体缺氧导致的睡眠障碍等慢性高原疾病症状.

在高原地区从事军事作业的解放军官兵根据驻地情况以及执行任务的多样化往往有其自身特点,与平原地区相比,高原军事作业人员常面临驻守地区低压低氧、寒冷干燥、昼夜温差大、辐射强等气候特点,随之而来对生理和心理应激的强度、频率以及持续时间常常远超普通人.睡眠是人体重要的生命活动形式,其中海拔高度、急进高海拔地区、年龄、进驻高原时间、性别和兵种(执行任务种类)等均是导致睡眠障碍的影响因素[1].本文立足于高原基层军事作业人员的生活与任务特点,综述近年来睡眠障碍对相关人群带来的不良影响以及相关卫生保障措施的研究成果,以期为相关军事训练计划的制定与高原驻守官兵的生活管理提供参考.

Objective: To investigate the effects of transcranial direct current stimulation (tDCS) on the disturbance of brain network dysfunction after sleep deprivation (SD). Methods: The experimental design of self-control was used in the study. All 16 subjects received 2 times of 24 h SD with an interval of 3 weeks. After the first normal sleep, 24 h SD and transcranial electrical stimulation (true or false stimulation) intervention (the current magnitude of true and false stimulation was 1 mA, and the action time was 20 min and 2 s, respectively. The intervention experiment lasted for 20 min. ) and the resting magnetic resonance imaging data were collected after the second transcranial electrical stimulation (sham or true stimulation). The resting fMRI data were collected as baseline before SD, the bilateral posterior cingulate cortex in the default mode network was selected as the seed point, and the functional connectivity between the seed points and the whole brain was calculated. Results: Compared with the rest wakefulness, the functional connectivity among bilateral posterior cingulate cortex, bilateral thalamus and hippocampus was increased (P＜0. 01), but connected with the right precuneus, bilateral insula was decreased after 24 h SD (P＜0. 01). Compared with the sham tDCS group, the functional connectivity between left posterior cingulate cortex seed point and right precuneus of tDCS group was increased (P＜0. 01); but decreased with the bilateral thalamus, insula and right cerebral cortex (P＜0. 01). There was a decrease in the functional connectivity among the right posterior cingulate cortex and the bilateral thalamus, right insula, and cerebral cortex(P＜0. 01). Conclusion: 24-hours sleep deprivation can cause functional connection disorder of bilateral posterior cingulate gyrus, and transcranial electrical stimulation can improve the functional connection disorder after sleep deprivation to some extent.