Spread spectrum localizers

• US 6,795,491 B2
• Filed: 12/11/2000
• Issued: 09/21/2004
• Est. Priority Date: 07/22/1999
• Status: Expired due to Term

• Current Assignee: Zebra Technologies Corporation
• Original Assignee: Aether Wire & Location, Inc.
• Inventors: Fleming, Robert Alan, Kushner, Cherie Elaine
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/734,118
• Publication Number:
  US 20010033607A1
• Time in Patent Office: 1,380 Days
• Field of Search: 342/118-146, 342/458, 702/97, 375/224, 375/213, 375/219
• US Class Current: 375/213
• CPC Class Codes: G01S 11/02 using radio waves G01S19/00 takes precedence
• CPC Class Codes: G01S 13/876 Combination of several spaced transponders or reflectors of known location for determining the position of a receiver G01S13/874 takes precedence
• CPC Class Codes: G01S 5/0072 Transmission between mobile stations, e.g. anti-collision systems
• CPC Class Codes: G01S 5/009 Transmission of differential positioning data to mobile
• CPC Class Codes: G01S 5/14 Determining absolute distances from a plurality of spaced points of known location
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/709 Correlator structure

Abstract

A network of localizers determines relative locations in three-dimensional space to within 1 cm by cooperatively measuring propagation times of pseudorandom sequences of electromagnetic impulses. Ranging transmissions may include encoded digital information to increase accuracy. The propagation time is determined from a correlator circuit which provides an analog pseudo-autocorrelation function sampled at discrete time bins. The correlator has a number of integrators, each integrator providing a signal proportional to the time integral of the product of the expected pulse sequence delayed by one of the discrete time bins, and the non-delayed received antenna signal. With the impulses organized as doublets the sampled correlator output can vary considerably in shape depending on where the autocorrelation function peak falls in relation to the nearest bin. Using pattern recognition the time of arrival of the received signal can be determined to within a time much smaller than the separation between bins. Because operation of standard CMOS circuitry generates noise over a large frequency range, only low-noise circuitry operates during transmission and reception. To provide the time accuracy necessary for distancing, a high-frequency clock operates during inter-localizer communications. The high-frequency clock uses a phase-lock loop circuit to increase the clock rate and a programmable delay to provide still finer time graduations. A stage in the low-frequency clock uses low-noise circuitry during transmissions and receptions, and standard circuitry at other times.

Claims

1. A method for determining a distance between a first transceiver and a second transceiver, comprising the steps of:

(a) determining an approximate separation distance between said first and second transceivers;

(b) choosing a first transmission time for transmitting a first distancing communication from said first transceiver to said second transceiver;

(c) choosing a first delay time for said second transceiver to wait from a first central time of a first reception window before transmitting a second distancing communication back to said first transceiver, said first central time of said first reception window being equal to said first transmission time plus said approximate separation distance divided by the speed of light;

(d) transmitting said first distancing communication from said first transceiver to said second transceiver at said first transmission time;

(e) receiving said first distancing communication at said second transceiver during said first reception window;

(f) transmitting said second distancing communication from said second transceiver to said first transceiver after said first delay time;

(g) determining a first arrival time of said first distancing communication at said second transceiver subsequent to step (f);

(h) receiving said second distancing communication at said first transceiver during a second reception window, a second central time of said second reception window being equal to said second transmission time plus said approximate separation distance divided by the speed of light;

(i) determining a second arrival time of said second distancing communication at said first transceiver; and

(j) calculating a first updated separation distance between said first and second transceivers based on said first and second arrival times.

2. The method of claim 1 wherein said first transmission time is offset by a first privacy transmission time offset unknown to said second transceiver to provide location privacy for said first transceiver.

3. The method of claim 1 wherein said delay time is offset by a second privacy transmission time offset unknown to said first transceiver to provide location privacy for said second transceiver.

4. The method of claim 1 further comprising the step of transmitting a set of correction bits representing said first arrival time to said first transceiver, wherein said calculating of step (j) occurs at said second transceiver.

5. The method of claim 1 further comprising the steps of:

(k) choosing a third transmission time for transmitting a third distancing communication from said first transceiver to said second transceiver;

(l) choosing a second delay time for said second transceiver to wait from a third central time of a third reception window before transmitting a fourth distancing communication back to said first transceiver, said third central time of said third reception window being equal to said third transmission time plus said first updated separation distance divided by the speed of light;

(m) transmitting said third distancing communication from said first transceiver to said second transceiver at said third transmission time;

(n) receiving said third distancing communication at said second transceiver during said third reception window;

(o) transmitting said fourth distancing communication from said second transceiver to said first transceiver after said second delay time;

(p) determining a third arrival time of said third distancing communication at said second transceiver subsequent to step (f);

(q) receiving said fourth distancing communication at said first transceiver during a fourth reception window, a fourth central time of said fourth reception window being equal to said fourth transmission time plus said first updated separation distance divided by the speed of light;

(r) determining a fourth arrival time of said fourth distancing communication at said first transceiver; and

(s) calculating a second updated separation distance between said first and second transceivers based on said third and fourth arrival times;

whereby a third separation between said third arrival time and said third central time is less than a first separation between said first arrival time and said first central time, and a fourth separation between said fourth arrival time and said fourth central time is less than a second separation between a second arrival time and a second central time.

6. The method of claim 5 wherein said third central time is a prearranged time from said first central time, and said fourth transmission time is said prearranged time from said second transmission time.

7. The method of claim 6 wherein said third transmission time is said prearranged time from said first transmission time, and said fourth central time is a prearranged time from said second central time.

8. A method for determining a separation distance and a ratio of clock rates of a first and a second localizer, said first localizer having a first clock and said second localizer having a second clock, comprising the steps of:

determining an approximate separation distance between said first and second transceivers;

choosing a first transmission time for transmitting a first distancing communication from said first transceiver to said second transceiver;

choosing a first delay time for said second transceiver to wait from a first reception window before transmitting a second distancing communication back to said first transceiver;

transmitting said first distancing communication from said first transceiver to said second transceiver at said first transmission time according to said first clock;

receiving said first distancing communication at said second transceiver during said first reception window;

transmitting said second distancing communication from said second transceiver to said first transceiver after said first delay time according to said second clock;

determining a first arrival time of said first distancing communication at said second transceiver according to said second clock;

receiving said second distancing communication at said first transceiver during a second reception window;

determining a second arrival time of said second distancing communication at said first transceiver according to said first clock;

choosing a third transmission time for transmitting a third distancing communication from said second transceiver to said first transceiver;

choosing a second delay time for said first transceiver to wait from a third reception window before transmitting a fourth distancing communication back to said second transceiver;

transmitting said third distancing communication from said second transceiver to said first transceiver at said third transmission time according to said second clock;

receiving said third distancing communication at said first transceiver during said third reception window;

transmitting said fourth distancing communication from said first transceiver to said second transceiver after said second delay time according to said first clock;

determining a third arrival time of said third distancing communication at said first transceiver according to said first clock;

receiving said fourth distancing communication at said second transceiver during a fourth reception window;

determining a fourth arrival time of said fourth distancing communication at said second transceiver according to said second clock;

calculating said separation distance and said ratio of clock rates from said first, second, third and fourth transmission times and said first, second, third and fourth arrival times.

9. The method of claim 8 wherein said determining said first arrival time step occurs subsequent to said transmitting said second distancing communication step, and said determining said third arrival time step occurs subsequent to said transmitting said fourth distancing communication step.

10. A method for synchronization of communications of a first localizer and a second localizer, comprising the steps of:

said second localizer transmitting a series of beacon signals at beacon transmission times separated by a prearranged time interval;

said first localizer repeatedly attempting to receive one of said beacon signals during a reception window at a time equal to a previous time a failed attempt was made to receive one of said beacon signals plus said prearranged time interval plus a width of said reception window, until an initial success time when one of said beacon signals is successfully received;

said first localizer making an initial estimate of a distance of separation between said first and second localizers equal to half the speed of light multiplied by said width of said reception window;

said first localizer setting said current estimate of said distance equal to said initial estimate;

said first localizer setting said current success time equal to said initial success time;

said first localizer repeatedly transmitting a contact transmission at said current success time;

said first localizer repeatedly attempting to receive an acknowledgement communication from said second localizer at an acknowledgement reception time equal to said current success time plus an acknowledgement delay time minus said current estimate of said distance divided by the speed of light, until an acknowledgement acheived time when said first localizer receives said acknowledgement communication from said second localizer indicating that said distance is approximately equal to said current estimate of said distance;

said first localizer incrementing said current estimate of said distance by the speed of light multiplied by said width of said reception window following each of said repeatedly attempting to receive said acknowledgement communication steps;

said first localizer repeatedly incrementing said current success time by said prearranged time interval minus a prearranged turnaround delay time minus twice said current estimate of said distance divided by the speed of light following each of said repeatedly attempting to receive said acknowledgement communication steps;

said second localizer receiving one of said contact transmissions during a reception window said turnaround time prior to one of said beacon transmission times;

said second localizer determining an arrival time of said one of said contact transmissions; and

said second localizer transmitting said acknowledgement communication said acknowledgement delay time after said one of said beacon transmission times.

11. The method of claim 10 further including the steps of:

said first localizer successfully receiving a second beacon signal during a reception time window centered about said initial success time plus said prearranged time interval;

determining a time difference according to a first clock in said first localizer between said initial success time and a time of reception of said second beacon signal;

calculating a ratio of clock rates of said first clock to a second clock in said second localizer from a ratio of said prearranged time interval to said time difference.

12. An iterative method for determining a separation distance between a first transceiver and a second transceiver, comprising the steps of:

said first transceiver transmitting a first distancing communication at a first transmission time;

said second transceiver receiving said first distancing communication during a first reception window centered about said first transmission time plus a current estimate of said separation distance divided by the speed of light;

said second transceiver transmitting a second distancing communication after a first turnaround delay time from said first reception window;

said second transceiver determining a first arrival time of said first distancing communication subsequent to the previous step;

said first transceiver receiving said second distancing communication during a second reception window centered about said second transmission time plus said current estimate of said separation distance divided by the speed of light;

said first transceiver determining a second arrival time of said second distancing communication; and

said first transceiver transmitting a third distancing communication at a third transmission time equal to said first transmission time plus a first prearranged waiting time;

said second transceiver receiving said third distancing communication during a third reception window centered approximately about said third transmission time plus said current estimate of said separation distance divided by the speed of light;

said second transceiver transmitting a fourth distancing communication at a second turnaround delay time from said third reception window, said fourth distancing communication having a first polarity if said first communication arrived in a first half of said first reception window, said fourth distancing communication having a second polarity if said first communication arrived in a second half of said first reception window;

said second transceiver determining a third arrival time of said third distancing communication subsequent to the previous step;

said first transceiver receiving said fourth distancing communication during a fourth reception window centered about said fourth transmission time plus said current estimate of said separation distance divided by the speed of light;

said first transceiver determining a fourth arrival time of said fourth distancing communication; and

said first transceiver transmitting a fifth distancing communication at a fifth transmission time, said fifth transmission time being equal to said third transmission time plus a second prearranged waiting time minus an iteration increment if said fourth transmission had said first polarity, and said fifth transmission time being equal to said third transmission time plus said second prearranged waiting time minus said iteration increment if said fourth transmission had said second polarity;

said second transceiver receiving said fifth distancing communication during a fifth reception window centered approximately about said fifth transmission time plus said current estimate of said separation distance divided by the speed of light;

said second transceiver transmitting a sixth distancing communication at a third turnaround delay time from said sixth reception window, said sixth distancing communication having a first polarity if said third communication arrived in a first half of said third reception window, said sixth distancing communication having a second polarity if said third communication arrived in a second half of said third reception window;

said first transceiver receiving said sixth distancing communication during a sixth reception window, said sixth reception window being centered about said sixth transmission time plus said current estimate of said separation distance divided by the speed of light plus said iteration increment if said fourth distancing communication arrived in a second half of said fourth reception window, and said sixth reception window being centered about said sixth transmission time plus said current estimate of said separation distance divided by the speed of light minus said iteration increment if said fourth distancing communication arrived in a first half of said fourth reception window;

said first transceiver determining a sixth arrival time of said sixth distancing communication; and

said first transceiver updating said current estimate of said separation distance based on said fifth transmission time, said sixth arrival time, and said third turnaround time.

13. The iterative method of claim 12 further including the steps of:

said first transceiver dividing said iteration increment by two;

said first transceiver transmitting a seventh distancing communication at a seventh transmission time, said seventh transmission time being equal to said fifth transmission time plus a third prearranged waiting time minus an iteration increment if said sixth transmission had said first polarity, and said seventh transmission time being equal to said fifth transmission time plus said third prearranged waiting time minus said iteration increment if said sixth transmission had said second polarity;

said second transceiver receiving said seventh distancing communication during a seventh reception window centered approximately about said seventh transmission time plus said current estimate of said separation distance divided by the speed of light;

said second transceiver transmitting an eighth distancing communication at a fourth turnaround delay time from said seventh reception window, said eighth distancing communication having a first polarity if said fifth communication arrived in a first half of said fifth reception window, said eighth distancing communication having a second polarity if said fifth communication arrived in a second half of said fifth reception window;

said first transceiver, receiving said eighth distancing communication during an eighth reception window, said eighth reception window being centered about said eighth transmission time plus said current estimate of said separation distance divided by the speed of light plus said iteration increment if said sixth distancing communication arrived in a second half of said sixth reception window, and said eighth reception window being centered about said eighth transmission time plus said current estimate of said separation distance divided by the speed of light minus said iteration increment if said sixth distancing communication arrived in a first half of said sixth reception window;

said first transceiver determining an eighth arrival time of said eighth distancing communication; and

said first transceiver updating said current estimate of said separation distance based on said seventh transmission time, said eighth arrival time, and said fifth turnaround time.