摘要:

ABSTRACTA summary of ongoing research analyzing the VLF noise environment and various structures of nonlinear Omega receivers is presented. First, the noise amplitude is seen to have a probability density function that can be modeled as Gaussian for small amplitudes and as decreasing proportionally to (amplitude)−2.2for large amplitudes. This model of probability density function suggests a maximum likelihood nonlinearity that is linear for small amplitudes and of the form f(x) ˜ 1/x for large amplitudes.Analysis of the behavior of two approximations of this nonlinearity (hole punch and clipper) is presented. Issues addressed include performance relative to a linear receiver as a function of structure, threshold for either nonlinearity, bandwidth prior to nonlinearity, and signal level. The study included both synthesized signals added to actual noise and off‐the‐air signals. Improvements of 7–14 dB relative to a linear receiver were observed. Finally, it is observed that the presence of a strong local Omega station within the receiver passband results in virtually no improvement for a weaker station, relative to a linear

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01551.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTA program of measurements is reported which has confirmed that carrier‐wave interference is the key factor controlling Loran‐C signal‐to‐noise ratio in Northwest Europe. The tests, at eight sites in Ireland and the U.K., identified 68 interfering signals, 17 of which exceeded the worst‐case atmospheric noise. Many interferers were synchronous with Loran‐C spectral lines. Especially prominent among the most serious interferers were Decca Navigator signals. The paper discusses the need for efficient filtering techniques and, where notch filters are used, the development of strategies to balance the conflicting claims of high‐powered, wide‐area interferers with those of the many low‐power

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01552.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe filtering of observed pseudoranges with concurrent measures of phase or integrated Doppler can benefit significantly both absolute and differential positioning. The argument proceeds rather simply. If the position recovery uncertainty is predicted to be equal to the position dilution of precision (PDOP) times the range uncertainty, then reducing the range error will in turn reduce the recovered position uncertainty. With typical PDOP values of, say, 4 m/m, then for every meter improvement of the pseudorange, the recovered position uncertainty will also be reduced by 4 m. It has been argued that very significant improvements can be made when incorporating millimeter‐level phases into pseudorange filtering algorithms. Here the filtering algorithm is examined, with emphasis on the ionospheric contribution. It will be argued that some degradation in the filter performance must be tolerated in order to accommodate this error source when using single‐frequency receivers. During periods of peak solar activity or in geographic areas where unpredictable ionospheric activity is common, it will be seen that the optimal filter is one that averages the pseudorange and phase range measures, which then causes an improvement in the filtered pseudoranges of one‐half the raw pseudorange noise. This improvement is significant. However, it is not as spectacular in its reduction as others have claimed who considered a cancellation of ionospheric contribution to the 10−6level for relative or differential posi

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01553.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe standard method of using GPS to compare the times of distant clocks is called the common view technique, by which two or more ground stations simultaneously observe a single GPS space vehicle (SV). In the most widely used form of common view, the positions of the SVs must be known because the signal transit times must be calculated. However, common view is one form of multilateration, by which solutions can be obtained for the positions of both stations and satellites, as well as clock offsets. We show in this paper how to adapt the principles from the classical geodetic literature on multilateration to time transfer. We discuss the need to optimize the geographic distribution of common view stations and the times of observation. A proposal for field tests is also presented, based on numerical simulations.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01554.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTThe Microwave Landing System (MLS) avionics convert the received signals of range, azimuth angle, and elevation angle to yield aircraft position in Cartesian coordinates relative to a point on the centerline of the selected runway. This enables area navigation, including multileg, curved, and computed centerline approaches. The MLS ground equipment transmitters may be sited in various arrangements relative to the runway; an iterative algorithm is required in the avionics to compute the correct approach path. The size and speed of the algorithm, and its computational burden, affect the MLS avionics storage and timing requirements. The principal candidate algorithms are Gauss‐Seidel (GS) and Newton‐Raphson (NR) types. The usual GS types may diverge within the minimum MLS coverage, while the NR types have problems with singularities and multiple solutions, need more storage, and impose a greater computational burden. This paper presents a GS algorithm which, by an ideal rotation of the coordinate system, enables fast convergence everywhere in the maximum MLS cover

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01555.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

ABSTRACTGPS will offer extremely high navigation performance and has a very promising future for most civil navigation needs. However, certain users consider that it may have insufficient integrity and limited availability. Sensitivity to these inadequacies varies according to size of constellation, type of user, navigation phase in which GPS is used, level of service expected, and complementary equipment operated. However, for a given constellation, GPS availability can be inferred from two fundamental factors: probability of constellation being in a given state (number of working satellites), and service availability when the constellation is in that state.This paper looks at the first of these factors by examining the consistency of the data currently being published by the civilian community on GPS system failures and availability. The paper also contains a plausible set of parameters based on a Markov chain model. These can be used to determine plausible state probabilities for a 24 satellite constellation.The analysis and results described in this paper are used in a previous paper (GPS Availability, Part I) published in the Summer 1990 issue of this journal.

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01556.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0028-1522    

DOI:10.1002/j.2161-4296.1990.tb01557.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY