Complete radio navigation receiver, particularly of the GPS...

Details Complete radio navigation receiver, particularly of the GPS... Complete radio navigation receiver, particularly of the GPS...

1998-10-02

2001-01-16

Tsang, Fan (Department: 2746)

Telecommunications

Receiver or analog modulated signal frequency converter

C342S357490, C342S357490, C342S357490, C455S456500, C455S457000, C455S067150, C455S067700, C375S130000, C375S347000

Reexamination Certificate

active

06175725

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to radio navigation on the basis of the propagation time of an electromagnetic wave with a time marker between a transmitter and a receiver.
In recent navigation systems, the time marker of the carrier wave is of the repetitive pseudo-noise type; in practice, a random noise code is used. On reception, the propagation time of the wave is demonstrated both by a time off-set in the pseudo-random code and by a phase off-set in the carrier wave. In the context of relative movement on the transmitter/receiver line (line of sight), there is added a carrier frequency off-set due to the Doppler effect.
There are various sources of error: Some of them in connection with passage through the troposphere or ionosphere or variation in conductivity of ground surfaces—will affect the speed of propagation of waves in general; other error sources take account of the fact that the path followed by the radioelectrical wave as far as the receiver is not rectilinear, whilst others arise from the fact that the receiver experiences a combination of different paths originating from various reflections, which are generally due to surfaces adjacent to the reception antenna. These are termed multiple path errors: the direct path (the shortest) is overlaid with other, unwanted paths.
Within radio navigation systems, the most frequently employed systems at present, “GPS” and “GLONASS”, their transmissions originate from satellites.
Currently, the main problem is how to combat the effects of multiple paths, as instanced by the article “Conquering multipath: The GPS accuracy battle”, by Lawrence R WEILL, in the revue GPS World, April 1997, pages 59-66.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to combat the abovementioned effects of multiple paths.
The invention relates to a device for reception of radioelectrical signals or waves which bear a time marker based on repetitive pseudo noise, of the pseudo-random code type, with particular regard to radio navigation.
A device of this type comprises a high frequency reception system whose output (or “wanted signal”) is distributed via several channels or modules, each of which is allocated to searching for coincidence (time phase) with a respective selected radioelectrical signal, distinguished by its code and/or its carrier frequency. To this there are added the means for analysis of time phase data provided by these coincidence search modules (more simply referred as coincidence modules).
Each coincidence module comprises firstly the means for formation of a chronometric memory, which is suitable for reception and/or storage of a code phase estimate and a frequency/phase carrier status estimate, and from deducing from such information by means of a local clock: a local carrier image and at least on e local repeat of the code for the relevant radioelectrical signal. It also comprises closed-loop control systems whose purpose is to produce co incidence between the code local repeat and the received code. These closed loop control systems comprise a code control loop operating by correlation between the wanted signal and the local code repeat and a carrier control loop which operates by means of a frequency/phase off-set signal between the carrier wave present in the wanted signal and the above-mentioned carrier wave image.
A coincidence module of this type can provide information with regard to the correct operation of its control loops. It is possible to take account of this partly for purposes of incoming radioelectrical signals which produce satisfactory results and secondly for purposes of analysis of time phase data.
According to one aspect of the invention, the receiving device further comprises media which are capable of bringing about Fourier transformation receiving a signal representative of the carrier frequency & phase off-set. On the basis of the Fourier transform, decision-making aids may at least partially invalidate the time phase data, particularly where the Fourier transformation indicates the presence of energy outside the vicinity of a central line, where such line corresponds to coincidence. Further on, we shall specify various characteristics, in greater detail, of the mode of operation of this frequency monitoring system.
In a preferred application of the coincidence module, media which constitute a chronometric memory comprise a carrier oscillator for purposes of defining the local carrier image, a code oscillator and a generator of at least one local repeat of the code. The code and carrier control loops, for their part comprise a discrete correlation channel comprising demodulation according to the above-mentioned carrier image and supplying a coincidence signal between the time position of the code in the wanted signal and its estimate, and at least one differential correlation channel comprising demodulation according to the above-mentioned carrier image and supplying an off-set signal between the code time position in the wanted signal and its estimate. The coincidence signal provides an off-set variable for a phase-lock carrier loop which provides pilot control of the local image generator for the carrier wave; and the code off-set signal provides the off-set variable for a delay-locking code loop, whose output is combined with that of the phase-locking carrier loop for purposes of pilot control of the code repeat generator.
A further aspect of the invention, which is very valuable in itself, is in “temporal”analysis. According to this analysis, we establish a further indication of the presence of multiple paths by recourse to the off-set signal originating from at least one differential correlation channel. For purposes of implementation of temporal analysis, present preference accrues to a system whereby each coincidence module comprises at least one second differential correlation channel whose spacing differs from that of the first. In such a context we resort to media to exploit the off-set signal originating from this second correlation channel, on its own and/or by its comparison (difference) in relation to the first off-set signal, as an indication of the presence of multiple paths.
Further on, we shall stipulate various, more detailed characteristics of the mode of operation of this temporal monitoring or analysis.
Other characteristics and advantages of the invention will transpire upon examination of the following detailed description, and the appended drawings.


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Brown, A Baseline RAIM Scheme and a Note on the Equivalence of Three RAIM Methods, Iowa State University, pp. 127-137.
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