Position fixing system

• US 20030058924A1
• Filed: 09/05/2002
• Published: 03/27/2003
• Est. Priority Date: 09/05/2001
• Status: Active Grant

• Current Assignee: Thales Research & Technology UK Limited (Thales SA)
• Original Assignee: Thales Research & Technology UK Limited (Thales SA)
• Inventors: Diederich, Pierre, Darby, Barry James, Frazer, Ewan Lindsay
• Granted Patent: US 7,215,698 B2
• Time in Patent Office: Days
• US Class Current: 375/135
• CPC Class Codes: G01S 1/022 Means for monitoring or calibrating
• CPC Class Codes: G01S 5/0081 Transmission between base stations
• CPC Class Codes: G01S 5/06 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/12 takes precedence
• CPC Class Codes: G01S 5/10 Position of receiver fixed by co-ordinating a plurality of position lines defined by path-difference measurements , e.g. omega or decca systemsG01S5/12 takes precedence ; beacons and receivers cooperating therewith G01S1/306, G01S1/308
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04B 1/71632 Signal aspects H04B1/7172 and H04B1/7176 take precedence
• CPC Class Codes: H04B 1/719 Interference-related aspects
• CPC Class Codes: H04B 2001/7152 with means for suppressing interference
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

In a first aspect the present invention provides a method of producing an ultra wide band signal in which (I) a carrier signal is modulated by a spreading waveform which is a periodic deterministic wideband signal and (II) the frequency of the carrier signal is changed by a predetermined amount at predetermined intervals (the reciprocal of this interval being the hopping rate), wherein there is a harmonic relationship between the carrier frequency, the predetermined amount of frequency change, and the period of the spreading waveform. In this way, an ultra wide band signal is created using both direct sequence and frequency hopping techniques and the signal so created may be detected using a coherent detector at a receiver. This provides a wide bandwidth signal, or even an ‘ultra wide bandwidth’ (UWB) signal which mitigates the problems of multi-path signals (through coherent combining across a wide bandwidth) and also interference.

Claims

1. A method of producing an ultra-wideband signal in which (I) a carrier signal is modulated by a spreading waveform which is a periodic deterministic wideband signal and (II) the frequency of the carrier signal is changed by a predetermined amount at predetermined intervals (the reciprocal of this interval being the hopping rate), wherein there is a harmonic relationship between the carrier frequency, the predetermined amount of frequency change, and the period of the spreading waveform.

2. A method according to claim 1 in which the spreading waveform is a PRBS signal having a determined chipping rate, the code length divided by the chipping rate is the period of the spreading waveform.

3. A method according to claim 1 in which the spreading waveform is a chirp signal having a predetermined modulation rate and duration wherein the period of the spreading waveform is the interval between chirps.

4. A method according to any of the above claims wherein the frequency hopping is carried out in a pseudo-random manner.

5. A method according to any of the above claims wherein the carrier frequency of each part of the signal may be selected according to a pseudo-random algorithm.

6. A method according to any of the above claims wherein the selection of the set of carrier frequencies is carried out so as to avoid the use of one or more frequencies or bands of frequencies within the selected bandwidth.

7. A method according to any of the above claims wherein power control is applied to each individual frequency hop in order to control the signal-to-noise ratio of each hop or to reduce interference to third parties.

8. A method according to any of the above claims wherein the information received is weighted or scaled according to a function of the frequency on which it is received.

9. A method according to any of the above claims in which the information received on a frequency is replaced with information derived from the information received on any of the frequencies prior to determining positional or time information.

10. A method according to claim 9 in which the replaced information is an estimation of the information that would have been received if the environment experienced by the information passed from the transmitter and receiver was more favourable.

11. An apparatus for producing an ultra-wideband signal including (I) modulating means for modulating a carrier signal by a spreading waveform which is a periodic deterministic wideband signal and (II) means for changing the frequency of the carrier signal by a predetermined amount at predetermined intervals (the reciprocal of which is the hopping rate), wherein there is a harmonic relationship between the carrier frequency, the predetermined amount of frequency change, and the period of the spreading waveform.

12. Apparatus according to claim 11 in which the spreading waveform is a PRBS signal having a determined chipping rate, the code length divided by the chipping rate is the period of the spreading waveform.

13. Apparatus according to claim 11 in which the spreading waveform is a chirp signal having a predetermined modulation rate and duration wherein the period of the spreading waveform is the interval between chirps.

14. Apparatus according to claim 11, 12 or 13 including means for carrying out the frequency hopping in a pseudo-random manner.

15. Apparatus according to claim 14 wherein the means for changing the frequency of the carrier signal is operable to be carried out so as to avoid the use of one or more frequencies or bands of frequencies within the selected bandwidth.

16. A transmitter including apparatus according to any of claims 11-15.

17. A positioning system including a plurality of reference stations, each reference station including a transmitter according to claim 16.

18. A positioning system according to claim 17 wherein the reference stations are part of a cellular telephone network.

19. A positioning system according to claim 17 or 18 including a mobile terminal which includes apparatus according to claim 21.

20. A positioning system including a mobile terminal which includes a transmitter according to claim 16, the positioning system also including a plurality of reference stations which each include apparatus according to 21.

21. Apparatus for receiving a signal including (I) means for demodulating a carrier signal modulated by a spreading waveform which is a periodic deterministic wideband signal and (II) means for synchronising a local oscillator to match the frequency of the carrier which changes by predetermined amounts at predetermined intervals (the reciprocal of which is the hopping rate), and means for changing the carrier frequency to predetermined values.

22. Apparatus according to claim 21 in which the spreading waveform is a PRBS signal having a determined chipping rate, the code length divided by the chipping rate is the period of the spreading waveform.

23. Apparatus according to claim 21 in which the spreading waveform is a chirp signal having a predetermined modulation rate and duration wherein the period of the spreading waveform is the interval between chirps.

24. A method of producing an ultra-wideband signal substantially as any of the embodiments herein described with reference to the accompanying drawings.

25. An apparatus for producing an ultra-wideband signal substantially as any of the embodiments herein described with reference to the accompanying drawings.

26. A positioning system substantially as any of the embodiments herein described with reference to the accompanying drawings.

27. Apparatus for receiving a signal substantially as any of the embodiments herein described with reference to the accompanying drawings.