总被引：1，自引：0，他引：1  

Jensen  M.A. Rice  M.D. Anderson  A.L. 《IEEE transactions on aerospace and electronic systems》2007,43(1):262-272

The placement of multiple antennas on an air vehicle is one possible practice for overcoming signal obstruction created by vehicle maneuvering during air-to-ground transmission. Unfortunately, for vehicle attitudes where more than one of these antennas has a clear path to the receiving station, this practice also leads to self-interference nulls, resulting in dramatic degradation in the average signal integrity. This paper discusses application of unitary space-time codes such as the Alamouti transmit diversity scheme and unitary differential space-time codes to overcome the self-interference effect observed in such systems. The mathematical foundations of these techniques within the context of this application as well as computational performance gains associated with their implementation are provided. Issues such as the cost of channel estimation for trained techniques as well as the throughput performance of nondifferential and differential schemes for realistic air-vehicle motion are analyzed  相似文献   

    

Martin A. Lee 《Space Science Reviews》2007,130(1-4):221-229

Gradual solar energetic particle (SEP) events are evidently accelerated by coronal/interplanetary shocks driven by coronal mass ejections. This talk addresses the different factors which determine the composition of the accelerated ions. The first factor is the set of available seed populations including the solar wind core and suprathermal tail, remnant impulsive events from preceding solar flares, and remnant gradual events. The second factor is the fractionation of the seed ions by the injection process, that is, what fraction of the ions are extracted by the shock to participate in diffusive shock acceleration. Injection is a controversial topic since it depends on the detailed electromagnetic structure of the shock transition and the transport of ions in these structured fields, both of which are not well understood or determined theoretically. The third factor is fractionation during the acceleration process, due to the dependence of ion transport in the turbulent electromagnetic fields adjacent to the shock on the mass/charge ratio. Of crucial importance in the last two factors is the magnetic obliquity of the shock. The form of the proton-excited hydromagnetic wave spectrum is also important. Finally, more subtle effects on ion composition arise from the superposition of ion contributions over the time history of the shock along the observer’s magnetic flux tube, and the sequence of flux tubes sampled by the observer.  相似文献   

    

M. A. Barucci  M. Fulchignoni  A. Rossi 《Space Science Reviews》2007,128(1-4):67-78

In preparation for the flyby of the Rosetta spacecraft, the state of the knowledge of 21 Lutetia and 2867 Steins obtained by ground based observations is reported. Preliminary determination of shape and/or size, rotational properties and taxonomic types are presented for both asteroids. The dusty environment of the targets has been studied in order to help in defining safe fly-by trajectories without the risk of damaging collisions. The expected science return from the asteroid fly-by is also discussed.  相似文献   

    

Maraschi  L.  Treves  A. 《Space Science Reviews》1983,36(2):161-171

Space Science Reviews - The possibility of producing γ-rays in a close binary system is examined. First the case of systems containing a young pulsar is discussed. It is shown that high energy...  相似文献   

    

Geller  Marvin A. 《Space Science Reviews》1983,34(4):359-375

Space Science Reviews - It is demonstrated by means of model calculations that while the general configuration of middle atmosphere dynamics (i.e., winter westerlies and summer easterlies) is...  相似文献   

    

Rijsdijk  F.B. van der Spek  G.A. 《IEEE transactions on aerospace and electronic systems》1978,(2):226-236

For a planar-array antenna with a monopulse feed horn, this study describes a simple algorithm for the determination of the direction of target echoes. Antenna pattern measurements of the array indicate that the direction sines of a received wavefront can be independently obtained with one simple relation between a normalized difference channel output and a direction sine. This paper determines the accuracy of the algorithm.  相似文献   

    

Farina  A. Pardini  S. 《IEEE transactions on aerospace and electronic systems》1978,(5):769-779

A track-while scan (TWS) algorithm is developed for targets in a clutter environment. The problem has been studied using only the position measurements [1, 5-8], but the simulation results have not been satisfactory. Modern processing techniques (FFT processor) ) in air traffic control and surveillance radar receivers provide both position and radial velocity. The radial velocity measurement may be conveniently used in the target-track correlation process, which will reduce the association ambiguity in the clutter environment. t. In the clear environment the algorithm using the position and radial velocity measurements has been treated in [3, 4]. A TWS algorithm, using both position and radial velocity measurements for targets in a clutter environment, is presented here. The algorithm obtained is nonlinear and adaptive. In order to evaluate the improvement due to radial velocity measurement a simulation has been performed on a digital computer. The algorithm was run with and without radial velocity measurements to compare its performances. An improvement was noted especially when the target path included an accelerated portion.  相似文献   

    

Martin A. Pomerantz  Shakti P. Duggal 《Space Science Reviews》1971,12(1):75-130

This paper reviews the present state of knowledge concerning the diurnal and semidiurnal variations in the galactic cosmic ray intensity. The analytical procedures that are required for extracting from the original data the desired information concerning the characteristics of the anisotropies outside the magnetosphere are described. These include corrections for atmospheric fluctuations, the determination of the amplitudes and phases of the daily variations, and their interpretation in terms of the free space anisotropies that give rise to them. The experimental results concerning the 24-h wave, including its long-term variations with periods of one and two solar cycles, and the characteristics of the total diurnal anisotropy are then discussed. The semidiurnal anisotropy is considered next. Transient anisotropies which manifest themselves as day-to-day variations, recurrence tendencies, cosmic ray storms, and diurnal variation trains, and which can introduce appreciable changes in the spectral parameters, are also of interest. The evolution of theoretical models developed to account for the diurnal and semidiurnal anisotropies, and fluctuations thereof, are then discussed in the light of the experimental results. Finally, the general features that are now well established, and the nature of the remaining problems, are summarized.  相似文献   

    

Rue  A.K. 《IEEE transactions on aerospace and electronic systems》1970,(5):697-706

Corrections of pointing data provided by gimbal readout transducers can be used to compensate for the errors that arise because of gimbal misalignments and inaccuracies in transducer readout. This paper reviews the sources of pointing error in precision gimbaled pointing systems and describes the techniques for determining them. In particular, a method of calibration that is suitable for systems in which constraints on gimbal travel preclude the use of conventional calibration procedures is presented, and the pointing readout accuracy that can be achieved by this method is evaluated.  相似文献   

  总被引：1，自引：0，他引：1  

Maybeck  P.S. Jensen  R.L. Harnly  D.A. 《IEEE transactions on aerospace and electronic systems》1981,(2):173-180

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