Positioning systems
We describe a device that is able to compute its range and time offset relative to another similar device, and thereby also a three-dimensional position, speed and time relative to other similar devices provided that at least four are present and within range. It does so by transmitting at least two signals at different frequencies and by receiving similar signals transmitted by the other devices. The signals are constructed so that they are independent of the radio band used and so that they lead to cancellation of common-mode effects in the transmitter and receiver circuits. No fixed infrastructure of transmitters, receivers or local measurement units is required and the devices do not need to be synchronized. The system scales to very large networks of devices in which they work collectively each solving a part of the problem that describes the relative positions of all interconnected devices.
1. A method of determining a relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of a first device with respect to a second device, the method comprising:
sending a first reference signal from said first device to said second device at a first time, wherein said first reference signal has a frequency and phase determined by a first reference clock of said first device;
receiving at said first device a second reference signal sent from said second device at a second time, wherein said second reference signal has a frequency and phase determined by a second reference clock of said second device;
determining a phase of said second reference signal with respect to said first reference clock and determining a frequency of said second reference signal;
receiving from said second device measurement data, said measurement data comprising data from a determination of a phase of said first reference signal with respect to said second reference clock and from a determination of a frequency of said second reference signal at said second device;
determining at least one of said relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of said first device with respect to said second device by determining a substantially self-consistent solution to at least one equation of a set of equations of the form:
d ( t i )= f d (Φ m ( t i ),θ( t i ))
v ( t i )= f v (Δ f m ( t i ),ζ)
where
f d and f v are respective range and velocity determining functions;
t i labels said reference times;
d(t i ) labels said relative range at said reference times;
v(t i ) labels said relative velocity at said reference times;
Φ m (t i ) labels said determined phase at said reference times;
θ(t i ) labels a phase offset between said first and second reference clocks at said reference times;
Δf m (t i ) labels a frequency difference between a said determined frequency and a frequency of a said reference clock at the device at which said frequency is determined, at said reference times; and
ζ labels a frequency offset between said first and second reference clocks at said reference times; and
wherein said first and second reference clocks are unsynchronised with one another, and wherein said determining of said substantially constant solution comprises compensating for a said phase and frequency offset between said first and second reference clocks such that a frequency offset and changing phase one of said unsynchronised reference clocks is characterised with respect to the other of said reference clocks by said parameters θ(t i ) and ζ.
2. A method, using the method of claim 1 , of determining a position of a device in two or three dimensions by determining one or both of relative range and relative velocity of two or more pairs of devices in an interconnected cluster of three or more devices, the method using the method of claim 1 and then using said determined information to calculate said position of said device.
3. A method, using the method of claim 2 , of using one device to identify one or both of relative range and velocities of a plurality of devices in a cluster of devices, the method using the method of claim 2 then capturing corresponding range data from a plurality of other devices of said cluster.
4. A method, using the method of claim 1 , of determining relative position of devices in cluster of devices, the method comprising:
selecting a first reference said device to define a fiducial point of a co-ordinate system;
identifying positions of a plurality of second devices with reference to said first device using the method of claim 1 ;
sharing data for said positions with said second devices; and
using one or more of said second devices to identify positions of a plurality of third devices in said coordinate system each with reference to one of said one or more second devices using the method of claim 1 .
5. A method as claimed in claim 4 wherein said sharing comprises sharing a reference time or time offset data with said second devices to effectively determine a time standard within said cluster of devices.
6. A method as claimed in claim 4 wherein determining of a said position using the method of claim 1 comprises representing a position of said device in said co-ordinate system in said equations for which said substantially self-consistent solution is determined.
7. A method as claimed in claim 1 comprising determining both a relative range and a relative velocity of said devices and using one of said relative range and relative velocity, in combination with the other of said relative range and relative velocity and a time interval between two or more of said times, to constrain one of said relative range and relative velocity.
8. A method of determining a relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of a first device with respect to a second device, the method comprising:
receiving a first reference signal at said first device, from said second device, at a first time, wherein said first reference signal has a frequency and phase defined by a second reference clock of said second device;
determining a phase of said first reference signal with respect to a first reference clock of said first device, and determining a frequency of said first reference signal;
repeating said receiving and determining for second and third said reference signals received at second and third respective times;
determining at least one of said relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of said first device with respect to said second device by determining a substantially self-consistent solution to a set of equations of the form:
d ( t i )= f d (Φ m ( t i ),θ( t i ))
v ( t i )= f v (Δ f m ( t i ),ζ)
where
f d and f v are respective range and velocity determining functions;
t i labels said reference times;
d(t i ) labels said relative range at said reference times;
v(t i ) labels said relative velocity at said reference times;
Φ m (t i ) labels said determined phase at said reference times;
θ(t i ) labels a phase offset between said first and second reference clocks at said reference times;
Δf m (t i ) labels a frequency difference between said determined frequency of said first reference signal and a frequency of said first reference clock at said reference times;
ζ labels a frequency offset between said first and second reference clocks at said reference times; and
wherein said first and second reference clocks are unsynchronised with one another, and wherein said determining of said substantially constant solution comprises compensating for a said phase and frequency offset between said first and second reference clocks such that a frequency offset and changing phase of one said unsynchronised reference clocks is characterised with respect to the other of said reference clocks by said parameters θ(t i ) and ζ.
9. A method, using the method of claim 8 , of sending a reference clock signal over a wired link, the method using the method of claim 8 to determine a relative distance or time offset between said first and second devices, said first and second devices being connected by said wired link.
10. A method as claimed in claim 1 wherein said functions f d and f v have the form:
d ( t i )=α(Φ m ( t i )−θ( t i ))
v ( t i )=β(Δ f m ( t i )−ζ)
where α and β are constants.
11. A method as claimed in claim 1 wherein said characterisation is at a reference point in time of one of said first and second times such that said determined substantially consistent solution is effectively at said reference point in time.
12. A method as claimed in claim 11 wherein said reference point in time is a most recent one of said respective times.
13. A method as claimed in claim 1 wherein a said reference signal comprises a pair of tones modulated onto a carrier.
14. A non-transitory carrier carrying processor control code to, when running, determine the substantially self-consistent solution of claim 1 .
15. A device comprising a system for determining a relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of a first device with respect to a second device, the system comprising:
a transmitter to send a first reference signal from said first device to said second device at a first time, wherein said first reference signal has a frequency and phase determined by a first reference clock of said first device;
a receiver to receive at said first device a second reference signal sent from said second device at a second time, wherein said second reference signal has a frequency and phase determined by a second reference clock of said second device;
a system to determine a phase of said second reference signal with respect to said first reference clock and determining a frequency of said second reference signal;
a receiver to receive from said second device measurement data, said measurement data comprising data from a determination of a phase of said first reference signal with respect to said second reference clock and from a determination of a frequency of said second reference signal at said second device; and
a system to determine at least one of said relative range, relative velocity of motion, clock frequency offset, clock phase offset or time reference of said first device with respect to said second device by determining a substantially self-consistent solution to at least one equation of a set of equations of the form:
d ( t i )= f d (Φ m ( t i ),θ( t i ))
v ( t i )= f v (Δ f m ( t i ),ζ)
where
f d and f v are respective range and velocity determining functions;
t i labels said reference times,
d(t i ) labels said relative range at said reference times;
v(t i ) labels said relative velocity at said reference times;
Φ m (t i ) labels said determined phase at said reference times;
θ(t i ) labels a phase offset between said first and second reference clocks at said reference times;
Δf m (t i ) labels a frequency difference between a said determined frequency and a frequency of a said reference clock at the device at which said frequency is determined, at said reference times; and
ζ labels a frequency offset between said first and second reference clocks at said reference times;
wherein said first and second reference clocks are unsynchronised with one another, and wherein said determining of said substantially constant solution comprises compensating for a said phase and frequency offset between said first and second reference clocks such that a frequency offset and changing phase one of said unsynchronised reference clocks is characterised with respect to the other of said reference clocks by said parameters θ(t i ) and ζ.