Time-sharing Mode Research Articles

A new oversampling-based full-duplex radar jamming method with a single antenna

With the fast development of jamming technology, strong coherent jamming based on digital radio frequency memory (DRFM) technology poses serious threats to radar detection capabilities due to their flexibility and deception characteristics. However, the extremely high isolation between transmitter and receiver is difficult to implement in practice, and jammers typically operate in a transmit/receive time-sharing mode. Consequently, the duty cycle of jamming signal received by radar is less than 100% in the time domain, enabling the radar systems to detect targets amidst jamming. To generate a full duty cycle jamming signal, a new oversampling-based full-duplex DRFM jamming generation method is proposed in the transmit/receive time-sharing mode. This method requires that the intercepting width of jammer must be less than the reciprocal of value which is the product of forwarding times incremented by one and the radar signal bandwidth. Therefore, the jammer first intercepts extremely short segments from the radar signal using oversampling, with lengths measured in nanoseconds. Then, the jammer rapidly re-modulates and re-transmits the intercepted signal segments within the corresponding interception period. The jamming signal is filtered by the radar receiver. Then, the spectrum of the signal only contains the complete fundamental component, and the pulse width of the signal matches that of the transmitted signal, achieving a duty cycle of 100% and realizing the full-duplex jamming effect. In addition, the frequency modulation technique is utilized to generate dense false targets corresponding to the transmitted signal, thereby improving jamming efficiency. This paper elucidates the generation mechanism and ramifications of the jamming signal through rigorous signal analysis, delineating the relationship between intercepting length and full-duplex radar jamming generation across various DRFM jamming styles. Finally, the efficacy of full-duplex jamming is substantiated through theoretical analysis and simulation.

Joint downlink user association and interference avoidance with a load balancing approach in backhaul-constrained HetNets.

In heterogeneous networks (HetNets), different lower-power base stations are added in a typically unplanned manner to the well-planned macro-only network, bringing new challenges to the network functions. Small cells experience limited backhaul capacity since cost-effective backhaul is not easily accessible to them. This study focuses on the issue of user association in backhaul-constrained HetNets. It shows that it is necessary to associate users with cells using a load balancing approach in order to fully leverage the addition of small cells. The cell association needs to be done jointly with an interference management technique that protects offloaded users and those prone to harmful interference. After modeling the system and describing the interference model, the problem of cell and subband allocation is formulated. We first examine the problem in a time-sharing mode and present a centralized heuristic solution to the cell and subband allocation problem. This is accomplished by solving the convex problem using the gradual removal method. The importance of providing distributed algorithms for HetNets leads to the development of a new algorithm through the application of the dual decomposition method to a reformulated problem and the use of an admission control mechanism. In the achieved algorithm, all computations are performed locally, with each user and base station relying only on local information. This algorithm obtains near-optimal answers, as confirmed by the simulation results. Compared with conventional cell allocation methods, our distributed algorithm prevents intensive interference for all users and achieves better load balance between network tiers, resulting in improved network utility.

Detection and analysis of Wi-Fi signals for address direction finding

Statement of problem. The active use of wireless technologies requires the development of radio equipment that monitors devices and data transmission networks and, in particular, wireless local area networks of the 802.11 standard (Wi-Fi). The need to identify unauthorized access points and subscriber devices of these networks, including their bearing and localization, is an urgent task of radio monitoring services. Correlation-interferometric direction finders based on a two-channel radio receiving equipment cyclically connected to various pairs of elements of a multi-element antenna system are an effective tool for bearing radio signals. For the direction finding of packet radio signals, direction finders accumulate time samples from different antenna pairs over long time intervals; joint processing of these data allows determining the direction of arrival of radio signals. However, in the frequency range of transmission of signals of the IEEE 802.11 standard, many sources carry out parallel transmission of information in the time-sharing mode, therefore, the direct accumulation of samples entails mixing and combining data generated by different sources. This causes gross bearing errors and requires the development of new ways of joint identification and bearing of packet radio signals. The purpose of the work is to propose a method for determining the identification features of access points and subscriber devices of Wi-Fi networks, which allows combining fragments of data samples when bearing radio sources. Results. The presented method of address bearing, focused on signals of the 802.11 standard, allows detecting OFDM signals, identifying access points and subscriber devices of the local network and forming an estimate of the direction to these sources of radio emissions. Practical importance. The use of address bearing of Wi-Fi network devices increases the functionality of existing analyzers. The presented method of address bearing is implemented based on the mobile direction finder ARTICLE-M [1], which is used in search and localization systems of unauthorized sources of radio emissions.

Fast Single-Snapshot DOA Estimation of Coherent Sources for Distributed mmWave Radar System

This brief considers the Direction of Arrival (DOA) estimation for Distributed mmWave Radar System (DmmWRS) in the presence of coherent sources and a single snapshot. To this end, the large virtual aperture is firstly derived assuming that DmmWRS works in time-sharing mode. Then, a Fast Local Iterative Search Algorithm (FLISA) resorting to Iterative Adaptive Approach (IAA) and prior DOA information obtained by a single radar, is developed to accurately estimate DOA within a small azimuth region of interest. Finally, numerical simulations and actual measurements show the superiority of the proposed approach than some counterparts providing better angle measurement performance, more importantly, FLISA has lower computational complexity and faster convergence than IAA.

Research on electric vehicle charging scheduling algorithms based on a 'fractional knapsack'

The large-scale disorderly charging of electric vehicles creates challenges for the security of power systems, especially power distribution systems. To avoid peak power consumption during the day and improve the utilisation rate of the power grid at night, a charging scheduling algorithm for electric vehicles based on a 'fractional knapsack' is proposed. Considering the constraints of the user's charging demand and charging system capacity, a charging model based on a fractional knapsack is established to optimise the peak-valley load difference and reduce load fluctuation and charging cost, which is the objective function. To verify the effectiveness of the proposed algorithm, the Monte Carlo method is used to simulate the charging demand of electric vehicles, and the disorderly charging and orderly charging scheduling are simulated and compared under a time-sharing tariff mode. The results show that the proposed scheduling algorithm improves the peak-valley difference of the power grid, reduces fluctuation in the power grid load, and improves the utilisation rate of the power grid.

Method to Reduce Imaging Errors in Dynamic Target Observation of the Geostationary Interferometric Microwave Sounder

The Geostationary Interferometric Microwave Sounder (GIMS) is a synthetic aperture microwave sounder working in time-sharing sampling mode with a rotating circular antenna array, thus having a relatively long imaging period. Since target motion in the imaging period will pose a problem to imaging effect, observing dynamic target such as fast changing weather of tropical cyclones will introduce imaging error to the retrieved image of GIMS. A method that combines Kalman filter and interpolation to reduce imaging error are presented, which utilizes a time sequence of visibilities collected by time-sharing sampling method. Simulations of GIMS's observation process in viewing a series of near real case brightness temperature maps modeled by the National Center for Environmental Prediction Final Operational Global Analysis data/Weather Research and Forecasting Model/Radiative Transfer for Television Infrared Observation Satellite Operational Vertical Sounder method, together with postprocessing of dynamic observation error-correction processing and image retrieval are conducted for the method. Results show that the method can reduce imaging error even if there are random noises in visibilities.

Production line capacity planning concerning uncertain demands for a class of manufacturing systems with multiple products

In this paper, we study a class of manufacturing systems which consist of multiple plants and each of the plants has capability of producing multiple distinct products. The production lines of a certain plant may switch between producing different kinds of products in a time-sharing mode. We optimize the capacity configuration of such a system0s production lines with the objective to maximize the overall profit in the capacity planning horizon. Uncertain demand is incorporated in the model to achieve a robust configuration solution. The optimization problem is formulated as a nonlinear polynomial stochastic programming problem, which is difficult to be efficiently solved due to demand uncertainties and large search space. We show the NP-hardness of the problem first, and then apply ordinal optimization (OO) method to search for good enough designs with high probability. At lower level, an mixed integer programming (MIP) solving tool is employed to evaluate the performance of a design under given demand profile.

Imaging Analysis and First Results of the Geostationary Interferometric Microwave Sounder Demonstrator

The Geostationary Interferometric Microwave Sounder (GIMS) is a new concept of atmospheric microwave sounder for China's future geostationary Earth orbit meteorological satellite (FY-4). It is a microwave interferometric radiometer (MIR) using aperture synthesis and working in rotating time-sharing mode with a circular antenna array. A GIMS proof-of-concept demonstrator operating in the temperature sounding bands of 50-56 GHz has been successfully developed. The instrument uses a circular array with 28 elements (including one in the center of the array). It is capable of imaging a scene with an angular resolution of about 0.08. and a radiometric resolution of less than 1 K with 5-m integration time within a 5. field of view (FOV). Some theoretical aspects of the imaging characteristics of GIMS are discussed, such as the alias-free FOV, angular resolution, radiometric resolution, and imaging algorithm. Some early tests and preliminary imaging experiments of the GIMS demonstrator are also presented.

A multichannel current stimulator chip for spatiotemporal pattern stimulation of neural tissues.

We developed a prototype very-large-scale integration chip of a multichannel current stimulator for stimulating neural tissues by utilizing 0.25 μm high-voltage complementary metal-oxide-semiconductor technology. Our designed chip has 20 output channels that are driven by five current buffers arranged in parallel; each buffer controls four output channels in time-sharing mode. The amplitude of a stimulation pulse can be controlled within a range of approximately ±100 μA/phase in each output channel. The stimulus parameters, e.g., amplitude and duration, are controlled separately for each channel by digital codes stored in built-in registers. Combinations of anode and cathode electrodes to pass the current can be changed online. We integrated our stimulator chip with a multielectrode array and studied the neuronal responses to multichannel current stimulations with various temporal patterns in mouse brain slices.

Photoemission Spectroscopy and Photoemission Electron Microscopy Beamline at the Siam Photon Laboratory

A beamline to utilize radiation from the first undulator at the Siam Photon Laboratory was designed and constructed. The beamline employs a varied line-spacing plane grating monochromator with three interchangeable gratings, which provides energy between 40-160 and 220-1040 eV. There are two optical branches downstream of the monochromator allowing two different measurement techniques, i.e. photoemission spectroscopy and photoemission electron microscopy, to be utilized in a time-sharing mode. In this report, the detailed descriptions of the beamline as well as the performance of the beamline and the commissioning results will be presented. Problems found during the undulator commissioning will also be discussed.

Monitoring of the coagulation process of soymilk by an integrated electrical sensing and control system

Coagulation of soymilk is the most important process in tofu making. The aim of this study is to develop a method which can monitor the coagulation process of soymilk by electrical impedance spectroscopy (EIS) and to control the temperature of soymilk accurately by ohmic heating. Monitoring and heating were operated with the same electrodes in a time-sharing mode. The soymilk coagulation process was investigated by electrical impedance spectroscopy and rheological analysis of tofu breaking stress, breaking strain and Young’s modulus were performed. The impedance amplitude of soymilk decreased at frequencies of 42–200 Hz and increased over 200 Hz with the progress of coagulation. The soymilk coagulation process was considered as two first-order reactions. During the tofu coagulation process, the electrical conductivity at 10 kHz showed a positive linear correlation with the rheological properties. Therefore, impedance measurement can provide a simple, safe and rapid approach for predicting the tofu physical quality. The developed method is capable of controlling the soymilk coagulation process and estimating the tofu textural properties.

Coagulation process of soymilk characterized by electrical impedance spectroscopy

Soymilk coagulation process is the most important step in tofu making. An experimental setup was developed to control the coagulation temperature and heating rate by ohmic heating and to perform impedance measurement in time-sharing mode. Soymilk coagulation process was characterized by electrical impedance spectroscopy. Frequency 10 kHz was chosen to analyze the coagulation process. Normalized conductivity was useful in determination of the endpoint of soymilk coagulation process. The coagulation process was considered as two successive first-order reactions. The rate constant in the first stage was 10 times higher than that in the second stage, both rate constants increased with coagulation temperature. The activation energy in the second stage was three times greater than that in the first stage. The successive reaction process was elucidated by using soymilk coagulation mechanism. The use of impedance measurement to analyze the coagulation process provides a basis for the control of soymilk coagulation process.

Constructing a Large Scale Wireless Sensors Network and Resources Scheduling among Multiple Personal Area Networks

Constructing a Large Scale Wireless Sensors NetworkA real challenge of wireless sensors network applications is how to expand it to a larger scale. We proposed the idea of “One Zone Multi-PAN (Personal Area Network)” to build a Large-Scale Wireless Sensors Network (LS-WSN). Its key points include: the elementary component of LS-WSN is PAN; different PANs work on different channels; different PANs use customized policies and execute different tasks; every PAN covers and surveillances the same area, but senses different circumstance information. Based on the idea, we proposed a two-level distributed LS-WSN model. The first level is the PAN-level, which works in a distributed mode. On this level, the up to 16 PANs bridged by a specially designed gateway coexist like a multi-layer sandwich. This gateway is a common children node of different PANs; therefore it can join in different PANs in a time-sharing mode. The second level is the inner-PAN-level, whose work mode is determined by the specific manufacturer. The size of this model can be expanded up to 16 times of the size of a single PAN. Furthermore, QoS of LS-WSN can be guaranteed, data fusion and data management can be simplified and improved. Using Zigbee stack, we set up a prototype system of LS-WSN, whose performances are validated by our experiments. Resources Scheduling among PANsFor executing resource reconfiguration in LS-WSN, we proposed an application framework of resources scheduling (RSAF). Its key principles include: radio channels, superframe time-slots, and energy resources are named as “Common Resources;” “the whole network is more important than a single PAN” in LS-WSN; keep the key PANs alive; the lifespan of a LS-WSN is determined by that of key PANs. RSAF can be comprehended as a collaboration mechanism at PAN level. It includes three components: superframe time-slots scheduling, radio channel scheduling, and energy scheduling. Their algorithms are different. Especially, a typical working cycle of energy scheduling contains four steps. First, the coordinators of different PANs gather different PANs' state information in a piggyback mode. Then the gateway periodically evaluates different PANs' states and makes the decisions of resources scheduling. After that, the specified coordinators send the control messages to certain nodes. Finally, the specified nodes will join and reinforce the key PAN in danger due to certain reasons (e.g., out of energy). Our experimental results validate the feasibility of RSAF in our prototype system.

Gapped pulses for frequency-swept MRI

A recently introduced method called SWIFT (SWeep Imaging with Fourier Transform) is a fundamentally different approach to MRI which is particularly well suited to imaging objects with extremely fast spin–spin relaxation rates. The method exploits a frequency-swept excitation pulse and virtually simultaneous signal acquisition in a time-shared mode. Correlation of the spin system response with the excitation pulse function is used to extract the signals of interest. With SWIFT, image quality is highly dependent on producing uniform and broadband spin excitation. These requirements are satisfied by using frequency-modulated pulses belonging to the hyperbolic secant family (HS n pulses). This article describes the experimental steps needed to properly implement HS n pulses in SWIFT. In addition, properties of HS n pulses in the rapid passage, linear region are investigated, followed by an analysis of the pulses after inserting the “gaps” needed for time-shared excitation and acquisition. Finally, compact expressions are presented to estimate the amplitude and flip angle of the HS n pulses, as well as the relative energy deposited by the SWIFT sequence.

Design of the first undulator beamline for the Siam Photon Laboratory

The first VUV/soft X-ray undulator beamline (BL3) is being constructed at the Siam Photon Laboratory. This beamline employs a varied line-spacing plane grating monochromator which operates in two constant-included-angle configurations to cover two photon energy ranges of 40–160 eV and 220–1040 eV. The two branchlines, designed for photoemission electron microscopy and photoemission measurements, will be operated in a time-sharing mode.

Spatial Structure of Solar Coronal Magnetic Loops Revealed by Transient Microwave Brightenings

We present the measurement of magnetic field gradient in magnetic loops in the solar corona, based on the multi-wavelength Very Large Array observations of two transient microwave brightenings (TMBs) in the solar active region 7135. The events were observed at 2 cm (spatial resolution ∼ 2=) and 3.6 cm (spatial resolution ∼ 3=) with a temporal resolution of 3.3 s in a time-sharing mode. Soft X-ray data (spatial resolution ∼ 2.5=) were available from the Soft X-ray Telescope on board the Yohkoh satellite. The three-dimensional structure of simple magnetic loops, where the transient brightenings occurred, were traced out by these observations. The 2-cm and 3.6-cm sources were very compact, located near the footpoint of the magnetic loops seen in the X-ray images. For the two events reported in this paper, the projected angular separation between the centroids of 2 and 3.6-cm sources is about 2.3= and 3.1=, respectively. We interpret that the 2 and 3.6-cm sources come from thermal gyro-resonance emission. The 2-cm emission is at the 3rd harmonic originating from the gyro-resonance layer where the magnetic field is 1800 G. The 3.6-cm emission is at the 2nd harmonic, originating from the gyro-resonance layer with a magnetic field of 1500 G. The estimated magnetic field gradient near the footpoint of the magnetic loop is about 0.09 G km=1 and 0.12 G km=1 for the two events. These values are smaller than those observed in the photosphere and chromosphere by at least a factor of 2.

A four-level storage 4-Gb DRAM

A 4-Gb DRAM with multilevel-storage memory cells has been developed. This large memory capacity is achieved by storing data at four levels, each corresponding to two-bit-data storage in a single memory cell. The four-level storage reduces the effective cell size by 50%. A sense amplifier using charge coupling and charge sharing was developed for the four-level sensing and restoring. The sense amplifier uses a hierarchical bit-line scheme and operates in a time-sharing mode, thus reducing the sense amplifier area. A 4-Gb DRAM fabricated using 0.15-/spl mu/m CMOS technology measures 986 mm/sup 2/. The memory cell is 0.23 /spl mu/m/sup 2/. Its capacitance of 60 fF is achieved by using a high-dielectric-constant material BST.

European Synchrotron Radiation Facility

European Synchrotron Radiation Facility (ESRF) is the first representant of a new (the third) generation of synchrotron radiation sources delivering high brilliance radiation in the hard X-rays. The first generation sources were initially built as part of high-energy physics programs and used as synchrotron radiation sources in a parasitic mode. Some are still used this way, some are operated for both programs in a time-sharing mode while others have been totally converted into dedicated synchrotron radiation sources. The second generation sources are those which were exclusively designed as dedicated synchrotron radiation sources. They have emittances in the range of 100 nm rad. The main radiation sources are bending magnets, a few insertion devices may have been added. The third generation sources finally have a lower emittance (< 20 nm rad) and many long straight sections for a maximum of insertion devices. In the following we give a short review of the hisory of the ESRF:

The collision channel without feedback

A model is proposed for the situation where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> users share a common communication resource but, because of unknown time offsets among their clocks, cannot transmit their data packets in a time-sharing mode and, because of the lack of a feedback link, can never determine these time offsets and also can never be sure of the outcomes of their individual packet transmissions. Each user is required to make his packet transmissions at times determined by a protocol signal that is independent of the data to be sent. The capacity and zero-error capacity regions of this channel are determined for both the unsynchronized and slot-synchronized cases; these four regions are shown to coincide. It is further shown that a dense set of rate points on the outer boundary of this region can be achieved in the slot-synchronized case. Specific constructions of protocol sequences for achieving these points are given, and the technique of "decimation decoding" is introduced for identifying the sender of each successfully transmitted packet. Maximum-erasure burst-correcting codes over an alphabet of arbitrary size are constructed and shown to suffice for reconstructing the packets lost in "collisions" when these protocol sequences are used.

Application of a digital computer to data acquisition and shield temperature control of a high-temperature, adiabatic calorimeter

The use of a digital computer, operating under real-time, time-sharing mode, for the operation of a high-temperature (300–1300 K), adiabatic calorimeter is described. The specimen temperature and power to the specimen heater are logged continuously, from which the heat capacity is calculated for specified temperature intervals (e.g., 20 K). The determinate error in the calculated heat capacity is about ±0.6%. The temperature control of the adiabatic shields is quite comparable with that obtained previously with analog controllers. The temperature difference between the specimen and a shield can be maintained to about ±0.1 K. The heat capacity of a pure titanium specimen has been measured from 320 to 1020 K using the computer and also using the analog control. No discernible difference in results can be seen. The heat capacity data scatter about ±1% from a smooth curve fitted through the 325 data points.