A Bayesian Classifier for X-Ray Pulsars Recognition

Recognition for X-ray pulsars is important for the problem of spacecraft’s attitude determination by X-ray Pulsar Navigation (XPNAV). By using the nonhomogeneous Poisson model of the received photons and the minimum recognition error criterion, a classifier based on the Bayesian theorem is proposed. For X-ray pulsars recognition with unknown Doppler frequency and initial phase, the features of every X-ray pulsar are extracted and the unknown parameters are estimated using the Maximum Likelihood (ML) method. Besides that, a method to recognize unknown X-ray pulsars or X-ray disturbances is proposed. Simulation results certificate the validity of the proposed Bayesian classifier

LAMP: a micro-satellite based soft X-ray polarimeter for astrophysics

The Lightweight Asymmetry and Magnetism Probe (LAMP) is a micro-satellite mission concept dedicated for astronomical X-ray polarimetry and is currently under early phase study. It consists of segmented paraboloidal multilayer mirrors with a collecting area of about 1300 cm^2 to reflect and focus 250 eV X-rays, which will be detected by position sensitive detectors at the focal plane. The primary targets of LAMP include the thermal emission from the surface of pulsars and synchrotron emission produced by relativistic jets in blazars. With the expected sensitivity, it will allow us to detect polarization or place a tight upper limit for about 10 pulsars and 20 blazars. In addition to measuring magnetic structures in these objects, LAMP will also enable us to discover bare quark stars if they exist, whose thermal emission is expected to be zero polarized, while the thermal emission from neutron stars is believed to be highly polarized due to plasma polarization and the quantum electrodynamics (QED) effect. Here we present an overview of the mission concept, its science objectives and simulated observational results

Hidden blood loss between PCCP and PFNA in elderly femoral intertrochanteric fracture

To compare perioperative hidden blood loss in the treatment of femoral intertrochanteric fractures with percutaneous compression plate (PCCP) and proximal femoral nail anti-rotation (PFNA) in elderly patients, and analyse its influencing factors in order to provide the necessary data support for clinical perioperative treatment, and choice of appropriate internal fixation method. Retrospective analyses was carried out on data obtained from 158 patients with intertrochanteric fracture treated with PCCP or PFNA from January 2010 to May 2017. Data were obtained from variables such as age, gender, height, weight, operative bleeding and postoperative drainage, operation time, etc. Upon blood routine examination before and after surgery (RBC, Hb and Hct), total and hidden blood losses were calculated using Gross equations. A comparative analysis was carried out on the differences in hidden blood loss, postoperative complications and prognosis between PCCP and PFNA.Visible blood loss was higher in PCCP than in PFNA, but total and hidden blood losses were significantly lower in PFNA(

A Fast Detection Algorithm for the X-Ray Pulsar Signal

The detection of the X-ray pulsar signal is important for the autonomous navigation system using X-ray pulsars. In the condition of short observation time and limited number of photons for detection, the noise does not obey the Gaussian distribution. This fact has been little considered extant. In this paper, the model of the X-ray pulsar signal is rebuilt as the nonhomogeneous Poisson distribution and, in the condition of a fixed false alarm rate, a fast detection algorithm based on maximizing the detection probability is proposed. Simulation results show the effectiveness of the proposed detection algorithm

An identification technique for the co-frequency mixed communication signals based on cumulants

Abstract Identification of the co-frequency interference is a common problem in wireless digital communication systems. The high-order statistics (HOS) feature based on cumulants is a widely adopted solution. However, prior knowledge of the timings and the symbol period is required to extract the cumulants, which is quite difficult in a blind environment. In order to solve this problem, this paper proposed a more general calculation for the cumulants based on the over-sampled data with consideration of the inter-symbol interference (ISI). The generalized theoretical value of the cumulants is deduced in this paper. Besides, the HOS feature based on the generalized cumulants for identification is found to be robust with different roll-off factor and sampling number per symbol. Computer simulations are performed to prove the validity of the proposed method

Network Simulators for Satellite-Terrestrial Integrated Networks: A Survey

Satellite-terrestrial integrated networks have been proposed as a promising solution to provide global seamless coverage in next-generation communication networks. Network simulation is a fundamental and economically efficient step to enable the integration of satellite and terrestrial networks, compared with the high cost of field trials and real-world system deployment. Simulation challenges arise with the fast growth of LEO mega-constellations, including frequent re-connection and handover, long satellite transmission delays, high dynamics of satellite network topologies, and the integration of heterogeneous infrastructures. More requirements emerge for satellite-terrestrial integrated simulations, including fidelity, scalability, extensibility, agility, and real-time. However, there is a lack of state-of-the-art reviews of relevant simulators. To the best of our knowledge, this study is the most comprehensive and latest survey that covers network simulators for satellite-terrestrial integrated networks, with all or partial simulation functionalities for satellite orbit simulation, physical layer modeling, and network protocols and algorithms. Compared with existing surveys, this survey contributes to three aspects: (1) an up-to-date collection and a comprehensive taxonomy of simulation tools in the past decade, (2) a summary of the main requirements and challenges, and (3) an inspiring summary of new research opportunities and publicly available simulation tools for follow-up research

A Fine-Tuned Positioning Algorithm for Space-Borne GNSS Timing Receivers

To maximize the usage of limited transmission power and wireless spectrum, more communication satellites are adopting precise space–ground beam-forming, which poses a rigorous positioning and timing requirement of the satellite. To fulfill this requirement, a space-borne global navigation satellite system (GNSS) timing receiver with a disciplined high-performance clock is preferable. The space-borne GNSS timing receiver moves with the satellite, in contrast to its stationary counterpart on ground, making it tricky in its positioning algorithm design. Despite abundant existing positioning algorithms, there is a lack of dedicated work that systematically describes the delicate aspects of a space-borne GNSS timing receiver. Based on the experimental work of the LING QIAO (NORAD ID:40136) communication satellite’s GNSS receiver, we propose a fine-tuned positioning algorithm for space-borne GNSS timing receivers. Specifically, the proposed algorithm includes: (1) a filtering architecture that separates the estimation of satellite position and velocity from other unknowns, which allows for a first estimation of satellite position and velocity incorporating any variation of orbit dynamics; (2) a two-threshold robust cubature Kalman filter to counteract the adverse influence of measurement outliers on positioning quality; (3) Reynolds averaging inspired clock and frequency error estimation. Hardware emulation test results show that the proposed algorithm has a performance with a 3D positioning RMS error of 1.2 m, 3D velocity RMS error of 0.02 m/s and a pulse per second (PPS) RMS error of 11.8ns. Simulations with MATLAB show that it can effectively detect and dispose outliers, and further on outperforms other algorithms in comparison