Method of sounding a channel

Details Method of sounding a channel Method of sounding a channel

1996-02-16

1997-03-04

Sotomayor, John B.

Communications: directive radio wave systems and devices (e.g.,

With particular circuit

Digital processing

342 22, 342 26, G01S 7292, G01S 7295

Patent

active

056084080

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method of sounding a channel such as a radio channel, or an acoustic channel, in a general manner.
2. Description of the Prior Art
A method of this kind has applications in the ionosphere sounding techniques, for example. Being made up of ionized layers, the ionosphere behaves as a medium of which the dielectric constant varies according to the ionization and the square of the frequency of the received wave leading accordingly to reflection of this received wave.
The person skilled in the art will nevertheless understand that the invention is equally applicable to the sounding of transmission channels on wires, to the detection of targets in radar or sonar applications, or to the radiography of organs in medical applications or of structures in industrial applications.
All the applications mentioned above are based on the emission by an emitter of a signal that is reflected or transmitted in the channel and received as a noise signal added to a sounding signal characterizing the medium in which the emitted signal was propagated, for example indicative of the presence of targets, ionized layers, . . . etc. The sounding signal received as a result of reflection or transmission has characteristics correlated to the characteristics of the emitted signal but with a highly attenuated and therefore very low amplitude. The very low amplitude of the sounding signal received as the result of reflection or transmission is not a problem in itself since it is sufficient to amplify the received signal before analyzing it.
However, this attenuation of the sounding signal received as the result of reflection or transmission is always accompanied by background noise of internal or external origin, such as atmospheric noise. This means that errors can arise on analyzing the received signal through confusing a high amplitude noise peak with the sounding signal (false alarm) and conversely through confusing a low amplitude received sounding signal with noise.
All prior art solutions partially solve this problem by calculating the correlation between the emitted signal and the received signal or by filtering the received signal, for example. They all require very high power signal emitters, for example a power in the order of several hundred kilowatts, for a sounding range of 1000 km, and are therefore very costly to implement.


OBJECT OF THE INVENTION

This invention provides a method that remedies the above drawback, as far as the particularly high power of the emitters is concerned. For a predetermined range, an emitter for implementing the invention has a power approximately 10.sup.3 to 10.sup.6 times less than that of the prior art emitters.


SUMMARY OF THE INVENTION

Accordingly, a method of sounding a channel by emitting signals and processing noise and sounding signals received from the channel in response to the emitted signals, comprising the following cyclic steps:
emitting a short pulse into the channel separated from a preceding short pulse by a predetermined time interval,
receiving and acquiring an impulse response during a time interval equal to the predetermined time interval and succeeding the step of emitting the short pulse, and
sampling the impulse response to produce a series of M initial samples which are defined by time ranks and which are stored in an initial sample matrix,
is characterized in that it further comprises the steps of:
change-of-space transforming M sample columns each made up of N initial samples that have equal respective time ranks in N latest impulse responses that has been successively acquired and sampled to produce a transformed sample matrix,
associating with the transformed sample matrix a binary matrix containing binary elements that are respectively associated with the transformed samples in the transformed sample matrix and that each take one of two binary states depending on the result of comparing a modulus of the transformed associated sample to a threshold,
spatial filtering of the

REFERENCES:
patent: 3629813 (1971-12-01), Drenkelfort
patent: 4351038 (1982-09-01), Alais
patent: 4430653 (1984-02-01), Coon et al.
patent: 4937580 (1990-06-01), Wills
patent: 5122805 (1992-06-01), Peterman et al.
patent: 5357253 (1994-10-01), Van Etten et al.
patent: 5486833 (1996-01-01), Barrett

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