Communications: directive radio wave systems and devices (e.g. – Directive – Beacon or receiver
Reexamination Certificate
1999-12-03
2001-05-29
Tarcza, Thomas H. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Beacon or receiver
C342S417000, C342S441000
Reexamination Certificate
active
06239746
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process and a device for cooperative radio direction finding in transmission mode for waveforms comprising a signal modulated by linear modulation or which can be approximated as such, this signal being composed of frames comprising learning sequences known to the receiver and of useful information sequences.
The invention can be applied in particular to digital cellular mobile radio communications networks, such as GSM, etc. Within such a context, a base station can perform direction finding on each mobile by using the bursts naturally emitted in the course of the communication, so as subsequently to transmit directionally towards each mobile, by knowing the arrival directions through direction finding. Such a procedure, based on the direction finding of each of the mobiles of the network, thus makes it possible to limit the risks of jamming of the other cells and affords the possibility of introducing the SDMA (Spatial Division Multiple Access) mode, where several users can use the same frequency at the same time.
DISCUSSION OF THE BACKGROUND
At present, several types of high-resolution or super-resolution methods make it possible to perform direction finding in the presence of several sources. Among these methods, it is common to use those known under the names MUSIC, ESPRIT, Minimum Norm or “Maximum likelihood” for high-resolution direction finding, and that known by the name CAPON for super-resolution direction finding.
By way of indication, a description of these methods can be found in the following articles.
The MUSIC method has been published in the article entitled “Multiple Emitter Location and Signal Parameter Estimation” from the journal IEEE Trans. Ant. Prop., Vol. AP-34, No. 3, pp 276-280, March 1986, author M. R. D. SCHMIDT.
The ESPRIT method is known from the article entitled “Estimation of Signal Parameters via Rotational Invariance Techniques” from the journal IEEE Transaction ASSP, Vol. ASSP-37, No. 7, pp 984-995, July 1989, authors MM. R. ROY, T. KAILATH.
The Minimum Norm or Modified FB2B (MFBCP) method is known from the article entitled “Estimating the Angles of Arrival of Multiple plane waves” from the journal IEEE Trans. Aerosp. Elect-syst., Vol. AES-19, No. 1, pp 134-138, January 1983, authors MM. R. KUMARESAN, D. W. TUFTS.
The maximum likelihood method is known from the article entitled “Maximum Likelihood Localizated of Multiple Sources by Alternating Projection” from the journal IEEE Trans. ASSP, Vol. ASSP-36, No. 10, pp 1553-1560, October 1988, authors MM. I. ZISKIND, M. WAX.
The CAPON, MV, MLM method is known from the article entitled “High Resolution Frequency—Wave number Spectrum Analysis” from the journal IEEE, Vol. No. 8, pp 1408-1418, August 1969, author M. J. CAPON.
Nevertheless, these methods are limited by the number of sensors of the network used. Experimentally, with N sensors, it is possible to separate N/2 paths arriving at the network. Now, when several sources are present, each of these sources can be associated with several propagation paths:
reflections of the ionospheric layers for the HF frequency range,
reflections of obstacles (buildings, hills, etc.) in urban or mountainous type environments for the other frequency ranges,
and the number of paths associated with all the sources can become too large for the direction finding method to be able to separate them all.
SUMMARY OF THE INVENTION
The aim of the invention is to isolate each of the sources reaching the network, so that the direction finding need process only the paths associated with a single source.
For this purpose, the subject of the invention is a process of cooperative radio direction finding in transmission mode in a radio direction finding receiver for radio communication system comprising several emission sources, the receiver being of the type comprising a network of sensors coupled to a radio direction finder characterized in that it comprises:
a first step consisting in digitizing the signal received by each sensor,
a second step consisting in performing a capture of synchronization on the signals emanating from the first step;
and a third step consisting, on the basis of the learning sequences inserted into the waveforms emitted by each source, in isolating the contribution of each source in the sensor signals so as to perform the direction finding on a single source only.
Its subject is also a device for implementing the aforesaid process.
The process described in the invention makes it possible to improve the direction finding performance in the presence of several sources in a transmission context. It also has the advantage of making it possible to locate the mobiles, so as to transmit directionally towards each mobile by knowing the arrival direction of the mobiles subjected to direction finding. It makes it possible to reduce the emission power at constant range, or to increase the emission range at constant power and hence to reduce the jamming of the other cells.
As another advantage, the process according to the invention makes it possible to ascertain the source to which the paths subjected to direction finding correspond, this not being possible with conventional direction finding where one of the difficulties is to allocate a source to each path detected since the arrival directions associated with one and the same source may be totally different.
When propagation takes place along a dominant path, the method of direction finding implemented after the step of isolating each source can be conventional, by channel formation or by interferometry as described for example in the article entitled “Les techniques d'interférométrie utilisées dans les radiogoniomètres à Thomson-CSF” [Interferometry Techniques used in Thomson-CSF radio direction finders] published in the Thomson-CSF Technical Journal, Vol. 19, No. 2, pp 249-287, June 1987.
REFERENCES:
patent: 5752168 (1998-05-01), Monot et al.
patent: 5812090 (1998-09-01), Chevalier et al.
patent: 5870430 (1999-02-01), Pipon et al.
Separation of cochannel signals in TDMA mobile radio, Keerthi, A.V.; Shynk, J.J., Signal Processing, IEEE Transactions on , vol. 46 Issue: 10 , pp.:2684-2697, Oct. 1998.
Aste Thierry
Chevalier Pascal
Monot Jean-Jacques
Pipon Francois
"Thomson-CSF"
Mull Fred H
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tarcza Thomas H.
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