Method for Optimizing an Acquisition of a Spread-Spectrum Signal from a Satellite by a Mobile Receiver

• US 20110206090A1
• Filed: 09/25/2009
• Published: 08/25/2011
• Est. Priority Date: 09/26/2008
• Status: Active Grant

• Current Assignee: Centre National D'Etudes Spatiales, Thales SA
• Original Assignee: Centre National D'Etudes Spatiales, Thales SA
• Inventors: Ries, Lionel, Monnerat, Michel, Artaud, Géraldine, Kubrak, Damien
• Granted Patent: US 8,472,504 B2
• Time in Patent Office: Days
• US Class Current: 375/142
• CPC Class Codes: G01S 19/26 involving a sensor measurement for aiding acquisition or tracking
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

A method for optimizing the acquisition phase of a spread-spectrum signal by a mobile receiver includes searching for the path having the maximum energy for different frequency assumptions and among all the positive trend paths of said frequencies between two initial and final instants marking the beginning and the end of a coherent signal integration.

Claims

1. A method for optimizing an acquisition of a spread-spectrum signal originating from a satellite by a mobile receiver, said method comprising:

receiving a signal transmitted by at least one transmitter, the signal being modulated by a pseudo-random code;

generating a local replica of the pseudo-random code of the signal transmitted;

transmitting a plurality of assumptions relating to the frequency f_i of the signal received at an initial instant t₀ and to the trend of this frequency over time up to a final instant t_n corresponding to an integration time, each assumption concerning the trend of the frequency of the signal between the initial instant and the final instant being called trend path;

calculating the correlation functions s(f_i, t_k, τ

) of all the pairs of frequency-time assumptions (f_i, t_k);

choosing a first initial frequency assumption f₁ corresponding to the initial instant t₀;

acquiring at least one information item concerning the movement of the receiver, and deducing therefrom, for the initial frequency assumption f₁, the trend assumptions for the frequency of the signal over time;

determining the respective total energy, corresponding to the maximum of the correlation function, also called correlation peak, of all the possible trend paths of the frequency of the signal between the instants t₀ and t_n, the total energy of each possible trend path being obtained by coherently aggregating correlation results between the initial t₀ and final t_n instants, the frequency taking in succession all the frequency values located on the chosen trend path;

selecting the trend path whose total energy is the strongest;

choosing in succession all the other possible initial frequency assumptions and, for each initial frequency assumption, in selecting the trend path of the frequency of the signal whose total energy is the strongest; and

deciding that, out of all the paths selected on each frequency assumption, the path which has the strongest energy is the most likely path and corresponds to the real path followed by the receiver.

2. The method as claimed in claim 1, wherein the total energy of each possible trend path of the frequency of the signal is obtained by coherently aggregating the correlation results between the initial instant t₀ and final instant t_n, the frequency successively taking all the frequency values located on the chosen path.

3. The method as claimed in claim 1, wherein, for each initial frequency assumption, the possible trend paths of the frequency of the signal are determined by taking into account information delivered by at least one inertial sensor located in the receiver.

4. The method as claimed in claim 3, wherein the information delivered by the inertial sensor is taken into account in an error envelope established on the basis of the characteristics of the sensor.

5. The method as claimed in claim 4, wherein, when the variation of the information delivered by the sensor, between two measurement instants, is below a predetermined variation threshold, it is decided that the receiver has not moved between the two measurement instants and a frequency that is stable during integration is then assumed.

6. The method as claimed in claim 2, wherein, for each initial frequency assumption, the possible trend paths of the frequency of the signal are determined by taking into account information delivered by at least one inertial sensor located in the receiver.