Spread spectrum localizers

• US 6,400,754 B2
• Filed: 12/07/2000
• Issued: 06/04/2002
• Est. Priority Date: 07/22/1994
• 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:
  US09/733,006
• Publication Number:
  US 20010053174A1
• Time in Patent Office: 544 Days
• Field of Search: 375/140, 375/354, 327/142, 327/160, 327/291, 331/173, 713/400, 713/502
• US Class Current: 375/140
• CPC Class Codes: G01S 1/026 of associated receivers
• CPC Class Codes: G01S 1/045 Receivers
• 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 5/0063 of measured values, i.e. measurement on base station and position calculation on mobile
• 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: G01S 5/145 Using a supplementary range measurement, e.g. based on pseudo-range measurements
• 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 measuring propagation times of pseudorandom sequences of electromagnetic impulses. The propagation time is determined from a correlator 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. Using pattern recognition the arrival time 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. A stage in the low-frequency clock uses low-noise circuitry during transmissions and receptions, and standard circuitry at other times.

Claims

1. A timebase of a spread spectrum transceiver providing a first communication triggering signal having a beginning communication time, comprising:

a low-frequency clock signal source providing a low-frequency clock signal having a sequence of low-frequency clock pulses;

a low-noise phase-lock loop for generating a high-frequency clock signal from said low-frequency clock signal;

a stage-one low-noise counter maintaining a first count of clock impulses of said high-frequency clock signal;

a stage-one event register for storing a high-frequency portion of said beginning communication time;

a stage-one low-noise comparator for providing said first communication triggering signal when said first high-frequency portion of said beginning communication time is equal to said first count;

a stage-one low-noise switching means for activating said stage-one low-noise counter, and stage-one low-noise reception comparator when a stage-one enable signal is received;

and

a stage-two low-noise counter for maintaining a second count of said low-frequency clock pulses when active;

a stage-two standard-circuitry counter for maintaining a third count of said low-frequency clock pulses when active;

a stage-two event register for storing an intermediate-frequency portion of said beginning communication time;

a stage-two low-noise comparator for sending said stage-one enable signal to said stage-one low-noise switching means when said intermediate-frequency portion of said beginning communication time corresponds to said second count;

a stage-two switching means for activating said stage-two low-noise counter and said stage-two low-noise comparator, and inactivating said stage-two standard-circuitry counter, after a stage-two enable signal is received;

and

a stage-three standard-circuitry counter for maintaining a fourth count of terminal counts from said stage-two low-noise counter and said stage-two standard-circuitry counter;

a stage-three event register for storing a reception low-frequency portion of said beginning communication time; and

a stage-three standard-circuitry comparator for sending said stage-two enable signal to said stage-two reception switching means when said low-frequency portion of said beginning communication time corresponds to said fourth count.

2. The timebase of claim 1 wherein said stage-one triggering signal activates a pseudorandom code sequence generator.

3. The timebase of claim 1 wherein said stage-two switching means activates said stage-two low-noise counter and said stage-two low-noise reception comparator and inactivates said stage-two standard-circuitry counter, following a terminal count from said stage-two standard-circuitry counter.

4. The timebase of claim 1 further including a delay register, and a low-noise programmable delay for delaying said stage-one communication triggering signal according to a delay value stored in said delay register.

5. The timebase of claim 1 wherein said stage-one low-noise reception switching means deactivates said stage-one low-noise counter and said stage-one low-noise reception comparator after a communication stop signal is detected, and wherein said stage-two low-noise reception switching means inactivates said stage-two low-noise counter and said stage-two low-noise reception comparator, and activates said stage-two standard-circuitry counter, after said communication stop signal is detected.

6. The timebase of claim 5 wherein said stage-two low-noise switching means inactivates said stage-two low-noise counter and said stage-two low-noise comparator, and activates said stage-two standard-circuitry counter, following a terminal count from said stage-two low-noise counter.

7. The timebase of claim 1 wherein said stage-two and stage-three event registers include standard-logic circuitry.

8. The timebase of claim 1 wherein said first communication triggering signal is a high-frequency clock signal.

9. The timebase of claim 1 further comprising a transmitter code sequence generator and a transmitter antenna driver, both being activated by said stage-one enable signal, said transmitter code sequence generator generating a code sequence which said transmitter antenna driver passes across an antenna to provide a transmission.

10. The timebase of claim 9 wherein said first communication triggering signal is a system clock signal directed to said transmitter code sequence generator.

11. The timebase of claim 1 further comprising a time integrating correlator and a receiver code sequence generator, said receiver code sequence generator being activated by said stage-one enable signal and generating an integration sequence resembling a received signal, said time integrating correlator producing a set of delayed versions of said integration sequence and integrating products of said delayed versions of said integration sequence and said received signal to determine an arrival time of said received signal.

12. The timebase of claim 11 wherein said first communication triggering signal is a system clock signal directed to said time integrating correlator and said receiver code sequence generator.