Position fixing system
View Patent ↗In a first aspect the present invention provides a method of producing an ultra wide band signal in which a carrier signal is modulated by a spreading waveform which is a periodic deterministic wideband signal and 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.
1. A method of producing an ultra-wideband signal comprising:
modulating a carrier signal by a spreading waveform which is a periodic deterministic wideband signal to generate a carrier frequency;
changing the carrier frequency by a predetermined amount at a predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is a corresponding frequency hopping rate;
wherein there is a harmonic relationship between the carrier frequency configured to be transmitted, the predetermined amount of frequency change configured to be transmitted, and a period of the spreading waveform configured to be transmitted, so that a deterministic ultra-wideband signal having the harmonic relationship is configured to be transmitted.
2. A method according to claim 1 , wherein the spreading waveform is a Pseudo Random Binary Sequence signal having a determined chipping rate, wherein a code length of the spreading waveform divided by the determined chipping rate is the period of the spreading waveform.
3. A method according to claim 1 , wherein 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 a first chirp and a second chirp.
4. A method according to claim 1 , further comprising frequency hopping in a pseudo-random manner.
5. A method according to claim 1 , further comprising selecting the carrier frequency of each part of the ultra-wideband signal according to a pseudo-random algorithm.
6. A method according to claim 1 , further comprising selecting a set of carrier frequencies to avoid the use of one or more frequencies or bands of frequencies within a selected bandwidth.
7. A method according to claim 1 , further comprising applying power control to each individual frequency hop in order to control a signal-to-noise ratio of each hop or to reduce interference to third parties.
8. A method according to claim 1 , further comprising weighing information received according to a function of a frequency on which the information is received.
9. A method according to claim 1 , further comprising replacing information received on a frequency with information derived from information received on any of the frequencies prior to determining positional or time information.
10. A method according to claim 9 , wherein the replaced information is an estimation of the information that would have been received if an environment experienced by the information passed from the transmitter and receiver was more favourable.
11. An apparatus for producing an ultra-wideband signal comprising:
a modulator configured to modulate a carrier signal by a spreading waveform which is a periodic deterministic wideband signal generating a carrier frequency; and
a frequency changing device configured to change the carrier frequency by a predetermined amount at a predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is a corresponding frequency hopping rate, wherein there is a harmonic relationship between the carrier frequency configured to be transmitted, the predetermined amount of frequency change configured to be transmitted, and a period of the spreading waveform configured to be transmitted, so that a deterministic ultra-wideband signal having the harmonic relationship is configured to be transmitted.
12. Apparatus according to claim 11 , wherein the spreading waveform is a Pseudo Random Binary Sequence signal having a determined chipping rate, wherein a code length of the spreading waveform divided by the determined chipping rate is the period of the spreading waveform.
13. Apparatus according to claim 11 , wherein 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 a first chirp and a second chirp.
14. Apparatus according to claim 11 wherein the frequency hopping device is configured to frequency hop in a pseudo-random manner.
15. Apparatus according to claim 14 , wherein the frequency hopping device changes the carrier frequency to avoid the use of one or more frequencies or bands of frequencies within a selected bandwidth.
16. A transmitter including apparatus according to claim 11 .
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 for receiving a signal comprising:
a demodulator configured to demodulate a deterministic ultra-wideband signal having a harmonic relationship between a transmitted carrier signal, a predetermined amount of transmitted frequency change, and a period of a transmitted spreading waveform, wherein the transmitted carrier signal is modulated by the transmitted spreading waveform which is a periodic deterministic wideband signal; and
a synchronizer configured to synchronize a local oscillator to match a frequency of the carrier which changes by a predetermined amount at predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is the hopping rate; and
a frequency changing device configured to change a carrier frequency of the local oscillator to predetermined values.
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 for receiving a signal comprising:
a demodulator configured to demodulate a deterministic ultra-wideband signal having a harmonic relationship between a transmitted carrier signal, a predetermined amount of transmitted frequency change, and a period of a transmitted spreading waveform, wherein the transmitted carrier signal is modulated by the transmitted spreading waveform which is a periodic deterministic wideband signal; and
a synchronizer configured to synchronize a local oscillator to match a frequency of the carrier which changes by a predetermined amount at predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is the hopping rate; and
a frequency changing device configured to change a carrier frequency of the local oscillator to predetermined values.
21. Apparatus for receiving a signal comprising:
a demodulator configured to demodulate a deterministic ultra-wideband signal having a harmonic relationship between a transmitted carrier signal, a predetermined amount of transmitted frequency change, and a period of a transmitted spreading waveform, wherein the transmitted carrier signal is modulated by the transmitted spreading waveform which is a periodic deterministic wideband signal; and
a synchronizer configured to synchronize a local oscillator to match a frequency of the carrier which changes by a predetermined amount at a predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is the hopping rate; and
a frequency changing device configured to change a carrier frequency of the local oscillator to predetermined values.
22. Apparatus according to claim 21 , wherein the spreading waveform is a Pseudo Random Binary Sequence signal having a determined chipping rate, wherein a code length of the spreading waveform divided by the determined chipping rate is the period of the spreading waveform.
23. Apparatus according to claim 21 , wherein 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 a first chirp and a second chirp.
24. An apparatus for producing deterministic ultra-wideband signal comprising:
modulating means for modulating a carrier signal by a spreading waveform which is a periodic deterministic wideband signal generating a carrier frequency; and
means for changing the carrier frequency by a predetermined amount at a predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is a corresponding frequency hopping rate, wherein there is a harmonic relationship between the carrier frequency configured to be transmitted, the predetermined amount of frequency change configured to be transmitted, and a period of the spreading waveform configured to be transmitted, so that the deterministic ultra-wideband signal having the harmonic relationship is configured to be transmitted.
25. Apparatus for receiving a signal comprising:
a means for demodulating a deterministic ultra-wideband signal having a harmonic relationship between a transmitted carrier signal, a predetermined amount of transmitted frequency change, and a period of a transmitted spreading waveform, wherein the transmitted carrier signal is modulated by the transmitted spreading waveform which is a periodic deterministic wideband signal; and
a means for synchronising a local oscillator to match a frequency of the carrier which changes by a predetermined amount at a predetermined interval to generate a predetermined amount of frequency change, wherein a reciprocal of the predetermined interval is the hopping rate; and
means for changing a carrier frequency of the local oscillator to predetermined values.