Device for a mobile terminal for determining position by filtering integrity data from an augmentation device

1. A position determination device for a mobile terminal, said device comprising means for acquiring pseudorandom codes and navigation data contained in received signals and associated augmentation data representative of an instantaneous approximate position of said terminal and an associated radius of protection and contained in received messages, position calculation means adapted, in the presence of a radius of protection corresponding to a quality level lower than a chosen quality level or in the momentary absence of a radius of protection, associated with an approximate position at a time T, to determine an estimated radius of protection as a function of a weighting law applied to a chosen number of earlier radii of protection and then to determine an estimated position of said terminal at said time T as a function of at least said estimated radius of protection and said pseudorandom codes, navigation data and approximate position acquired at said time T.

2. The device claimed in claim 1 further comprising a memory adapted to store said earlier radii of protection and wherein said position calculation means are adapted to compare each quality level corresponding to an acquired radius of protection to said chosen quality level defined by the quality level of the immediately preceding radius of protection stored in said memory.

3. The device claimed in claim 2 wherein said position calculation means are adapted to store in said memory either an acquired radius of protection if the corresponding quality level is greater than or equal to said chosen quality level so that it constitutes an earlier radius of protection or an estimated radius of protection if said quality level of the associated acquired radius of protection is lower than said chosen quality level so that it constitutes an earlier radius of protection.

4. The device claimed in claim 2 wherein each estimated radius of protection is stored in said memory in corresponding relationship to the corresponding acquired radius of protection.

5. The device claimed in claim 1 wherein said position calculation means are adapted to modify on command the number of earlier radii of protection used to determine an estimated radius of protection.

6. The device claimed in claim 1 wherein said position calculation means comprise filtering means adapted to apply said weighting law to said earlier radii of protection.

7. The device claimed in claim 6 wherein said filtering means constitute a linear filter adapted to apply a linear weighting law.

8. The device claimed in claim 6 wherein said filtering means constitute a Kalman filter.

9. The device claimed in claim 1 wherein said navigation data comes from a satellite navigation system.

10. The device claimed in claim 9 wherein said augmentation data comes from an augmentation system coupled to said satellite navigation system.

11. A mobile terminal comprising a position determination device as claimed in claim 10 .

12. The terminal claimed in claim 11 constituting a communication terminal.

13. The terminal claimed in claim 12 adapted to communicate within a cellular communications network in which each cell is managed by a base transceiver station and said approximate position is representative of the cell in which it is located.