SATELLITE TELECOMMUNICATION SYSTEM COMPRISING A MECHANISM FOR SEPARATING MESSAGES TRANSMITTED BY A PLURALITY OF TRANSMITTERS

• US 20120120870A1
• Filed: 05/19/2011
• Published: 05/17/2012
• Est. Priority Date: 05/21/2010
• Status: Active Grant

• Current Assignee: Thales SA
• Original Assignee: Thales SA
• Inventors: Bardout, Yves
• Granted Patent: US 8,824,363 B2
• Time in Patent Office: Days
• US Class Current: 370/326
• CPC Class Codes: H04B 7/1851 Systems using a satellite or space-based relay H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576

Abstract

A satellite telecommunications system comprises at least one satellite receiving signals originating from a plurality of transmitters present in a surveillance zone called a task, the transmission of the signals by the transmitters being discontinuous and organized into time slots. The satellite includes an array of reception antennas, a set of digital reception filters being associated with each antenna. The satellite also includes means for separating the signals originating from various transmitters and colliding in one and the same slot, said separation being carried out by adapting the coefficients of the digital reception filters, said coefficients being deduced from predictions of the position of the transmitters.

Claims

1. A satellite telecommunications system, comprising:

at least one satellite receiving signals originating from a plurality of transmitters present in a surveillance zone called a task, the transmission of the signals by the transmitters being discontinuous and organized into time slots, the satellite comprising

an array of reception antennas;

a set of digital reception filters being associated with each antenna,

means for separating the signals originating from various transmitters and colliding in one and the same slot, said means for separating adapting the coefficients of the digital reception filters, said coefficients being deduced from predictions of the positions of the transmitters, wherein

the positions of the transmitters at a given instant are predicted by using the content of a historical database comprising a historical log of the positions of the transmitters, the model used for the prediction taking into account the position of each of the transmitters at a given instant as well as their visibility by the antenna array onboard the satellite.

2. The system according to claim 1, wherein the transmitters transmit messages comprising information indicating at least their positions, the information being stored in one or more historical databases.

3. The system according to claim 2, wherein one of the one or more historical databases is located in the satellite.

4. The system according to claim 2, wherein one of the one ore more historical databases is located in a ground station.

5. The system according to claim 1, wherein, for a given velocity and a direction of a transmitter, a position P_est(t) of the transmitter at the instant t is estimated at the instant t by using the following expression:

P_est(t)=P(t₀)+{right arrow over (d)}(t−

t₀)v

in which;

P(t₀) represents the known position acquired during the last observation of the transmitter by the satellite at the instant t₀;

{right arrow over (d)}(t−

t₀) represents the direction of the transmitter during the time interval t−

t₀; and

v represents the velocity of the transmitter.

6. The system according to claim 1, wherein the prediction error ε

is estimated by using an expression;

ε

=Δ

d(t−

t₀)v+(t−

t₀)Δ

v

in which;

Δ

d represents the angular accuracy of direction; and

Δ

v the accuracy of velocity.

7. The system according to claim 5, wherein the predicted position of each of the transmitters is adjusted by using trajectory adjustment techniques by projecting the estimated position P_est(t) of each transmitter onto a route R, said route being represented by a curve.

8. The system according to claim 1, wherein the predicted positions of the transmitters are stored in a database onboard the satellite.

9. The system according to claim 1, wherein elevation and azimuth parameters representative of the incident signals received at the level of the various antennas of the antenna array of the satellite are deduced from the relative positions of the transmitters with respect to the satellite.

10. The system according to claim 1, wherein the satellite scans with the aid of a reception beam the spot associated with the satellite, a narrow lobe of the antenna diagram being determined so as to be directed by priority toward the bin or bins of the spot having a low collision density, the choice of these bins being deduced from the results of the analysis of the historical databases.

11. The system according to claim 1, wherein the weights of the filters are determined so as to adjust M zeros of the antenna diagram in accordance with the directions of M selected interferer signals, said interferer signals being selected on the basis of an estimation of the nuisance level in terms of interference compared with a predetermined threshold value, said nuisance level being deduced from the power received and from the Doppler shift which are estimated for a given interferer signal.

12. The system according to claim 1, wherein the weights of the filters are adjusted on the incident signals originating from selected transmitters whose spatial separation is greater than the directivity increment of the antenna system.

13. The system according to claim 1, wherein the weights of the filters are determined on each slot so as to extract some of the messages predicted in this slot, in accordance with a dynamically defined order of priority, the priorities being calculated on the historical database so as to attain the fixed objectives of system performance.

14. The system according to claim 1, wherein the weights of the filters are determined so as to extract a subset of the predicted transmitters in accordance with the period of each, the set of the transmitters also being distributed over all the transmission slots in the tracking period, until detection.