Spread spectrum receiver with multi-path correction

• US 6,917,644 B2
• Filed: 12/11/2000
• Issued: 07/12/2005
• Est. Priority Date: 04/25/1996
• Status: Expired due to Fees

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Kohli, Sanjai, Cahn, Charles R., Chansarkar, Mangesh
• Primary Examiner(s): Ha, Dac V.
• Application Number:
  US09/735,249
• Publication Number:
  US 20010002203A1
• Time in Patent Office: 1,674 Days
• Field of Search: 375/142, 375/145, 375/149, 375/150, 375/267, 375/317, 375/326, 375/327, 375/343, 375/359, 375/366, 375/367, 370/320, 370/324, 370/335, 370/342, 370/441, 370515-519
• US Class Current: 375/142
• CPC Class Codes: G01C 21/26 specially adapted for navigation in a road network
• CPC Class Codes: G01C 22/00 Measuring distance traversed on the ground by vehicles, persons, animals or other moving solid bodies, e.g. using odometers, using pedometers
• CPC Class Codes: G01S 19/11 wherein the cooperating elements are pseudolites or satellite radio beacon positioning system signal repeaters
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 2001/70706 using a code tracking loop, e.g. a delay locked loop
• CPC Class Codes: H04B 2201/70715 with application-specific features
• CPC Class Codes: H04B 7/216 Code division or spread-spectrum multiple access [CDMA, SSMA]

Abstract

A spread spectrum receiver uses a comparison of the magnitude of the code correlation amplitudes at equal power at a one chip spacing to the magnitude at a central position there between to determine if multipath interference is present. The lead or lag error from constructive or destructive multipath interference may also be determined. Inaccuracies due to such interference may then be corrected or minimized by, for example, determining the residual code phase error and/or the prompt or accurate code phase delay.

Claims

1. A method for processing a spread spectrum signal, comprising:

receiving a code modulated spread spectrum signal;

generating a code modulated signal replica of the received signal;

correlating the received signal with a code phase delayed replica to generate an early correlation product;

correlating the received signal with a second code phase delayed replica to generate a prompt correlation product;

correlating the received signal with a third code phase delayed replica to generate a late correlation product;

detecting a relative magnitude of and a sign of a multipath error in the received signal based on at least one relationship between an amplitude of the early correlation product, an amplitude of the prompt correlation product and an amplitude of the late correlation product;

wherein determining the sign of the multipath error comprises comparing a ratio of the amplitude of the prompt correlation product to an equal amplitude of the early and late correlation products, wherein the early and late correlation products are offset symmetrically from the prompt correlation product;

determining that a lag error exists when the amplitude of the prompt correlation product is less than twice the equal amplitude;

determining that a lead error exists when the amplitude of the prompt correlation product is more than twice the equal amplitude; and

determining that no multipath error exists if the amplitude of the prompt correlation product is equal to twice the equal amplitude.

2. A method for processing a spread spectrum signal, comprising:

receiving a code modulated spread spectrum signal;

generating a code modulated signal replica of the received signal;

correlating the received signal with a first code phase delayed replica to generate an early correlation product;

correlating the received signal with a second code phase delayed replica to generate a prompt correlation product;

correlating the received signal with a third code phase delayed replica to generate a late correlation product;

detecting a relative magnitude of and a sign of a multipath error in the received signal based on at least one relationship between an amplitude of the early correlation product, an amplitude of the prompt correlation product and an amplitude of the late correlation product;

wherein determining the sign of the multipath error comprises comparing a ratio of the amplitude of the prompt correlation product to an equal amplitude of the early and late correlation products, wherein the early and late correlation products are offset symmetrically from the prompt correlation product; and

if the relative magnitude of the multipath error is determined to be below a predetermined value, determining a correction to a pseudorange calculation, wherein the correction is proportional to a sum of the amplitudes of the early correlation product and the late correlation product divided by the prompt correlation product.

3. A method for processing a spread spectrum signal, comprising:

receiving a code modulated spread spectrum signal;

generating a code modulated signal replica of the received signal;

correlating the received signal with a first code phase delayed replica to generate an early correlation product;

correlating the received signal with a second code phase delayed replica to generate a prompt correlation product;

correlating the received signal with a third code phase delayed replica to generate a late correlation product;

detecting a relative magnitude of and a sign of a multipath error in the received signal based on at least one relationship between an amplitude of the early correlation product, an amplitude of the prompt correlation product and an amplitude of the late correlation product; and

using the multipath error to generate a control signal to control a phase relationship between respective early and late correlation products and further to control a relationship of the prompt correlation product with respect to the early correlation product and the late correlation product.

4. An apparatus for receiving a signal, the apparatus comprising:

a receiver configured to receive a signal comprising a PN code;

a code generator coupled to the receiver, the code generator configured to generate a PN code replica of the received signal;

an error detector coupled to the receiver and to the code generator, wherein the error detector detects code phase error in the received signal based on detecting at least one of;

power of a first correlation product of an early code phase delayed version of the code replica and the received signal, a second correlation product of a prompt code phase delayed version of the code replica and the received signal, and a third correlation product of a late code phase delayed version of the code replica and the received signal;

phase of respective first, second and third correlation products; and

quadrature of respective first, second and third correlation products, the apparatus further comprising;

a code phase error detector coupled to the at least one detector and configured to determine a sign of the code phase error and a relative magnitude of the code phase error, wherein determining a sign of the code phase error comprises the code base error detector comparing a ratio of the amplitude of the second correlation product to an equal amplitude of the first and third correlation products, wherein the first and third correlation products are offset symmetrically from the second correlation product; and

wherein the code phase error detector is further configured to;

determine that a lag error exists when the amplitude of the second correlation product is less than twice the equal amplitude;

determine that a lead error exists when the amplitude of the second correlation product is more than twice the equal amplitude; and

determine that no code phase error exists if the amplitude of the second correlation product is equal to twice the equal amplitude.

5. An apparatus for receiving a signal, the apparatus comprising:

a receiver configured to receive a signal comprising a PN code;

a code generator coupled to the receiver, the code generator configured to generate a PN code replica of the received signal;

an error detector coupled to the receiver and to the code generator, wherein the error detector detects code phase error in the received signal based on detecting at least one of;

power of a first correlation product of an early code phase delayed version of the code replica and the received signal, a second correlation product of a prompt code phase delayed version of the code replica and the received signal, and a third correlation product of a late code phase delayed version of the code replica and the received signal;

phase of respective first, second and third correlation products; and

quadrature of respective first, second and third correlation products, the apparatus further comprising;

a code phase error detector coupled to the at least one detector and configured to determine a sign of the code phase error and a relative magnitude of the code phase error, wherein the code phase error detector is further configured to determine a correction to a pseudorange calculation when the relative magnitude is determined to be below a predetermined value, wherein the correction is proportional to a sum of the amplitudes of the first correlation product and the third correlation product divided by the second correlation product.

6. An apparatus for receiving a signal, the apparatus comprising:

a receiver configured to receive a signal comprising a PN code;

a code generator coupled to the receiver, the code generator configured to generate a PN code replica of the received signal;

an error detector coupled to the receiver and to the code generator, wherein the error detector detects code phase error in the received signal based on at least one relationship between a first correlation product of an early code phase delayed version of the code replica and the received signal, a second correlation product of a prompt code phase delayed version of the code replica and the received signal, and a third correlation product of a late code phase delayed version of the code replica and the received signal; and

an adjustable delay element coupled to the code generator and further coupled to the code phase error detector to receive a code phase error signal, wherein the at adjustable delay element is configured to use the code phase error signal to adjust a phase of the PN code replica such that phases of respective first, second and third correlation products are adjusted.

7. An apparatus for receiving a signal, the apparatus comprising:

a receiver configured to receive a signal comprising a PN code;

a code generator coupled to the receiver, the code generator configured to generate a PN code replica of the received signal;

an error detector coupled to the receiver and to the code generator, wherein the error detector detects code phase error in the received signal based on at least one relationship between a first correlation product of an early code phase delayed version of the code replica and the received signal, a second correlation product of a prompt code phase delayed version of the code replica and the received signal, and a third correlation product of a late code phase delayed version of the code replica and the received signal; and

at least one delay element coupled to at least one correlator and further coupled to the code phase error detector, wherein the at least one delay element is configured to use the code phase error signal to generate a control signal to control a phase relationship between respective first and third correlation products and further to control a relationship of the second correlation product with respect to the first correlation product and the third correlation product.

8. An apparatus for processing global positioning system (GPS) satellite signals, the apparatus comprising:

receiver means for receiving a GPS signal;

code generator means for generating a PN code replica of the received GPS signal;

multipath error detector means for detecting a multipath error in the received GPS signal based on detecting at least one of;

power of a first correlation product of an early code phase delayed version of the code replica and the received signal, a second correlation product of a prompt code phase delayed version of the code replica and the received signal, and a third correlation product of a late code phase delayed version of the code replica and the received signal;

phase of respective first, second and third correlation products; and

quadrature of respective first, second and third correlation products, wherein the multipath error detector means is further configured to;

determine that a lag error exists when the amplitude of the second correlation product is less than twice the equal amplitude;

determine that a lead error exists when the amplitude of the second correlation product is more than twice the equal amplitude; and

determine that no multipath error exists if the amplitude of the second correlation product is equal to twice the equal amplitude.

9. An apparatus for processing global positioning system (GPS) satellite signals, the apparatus comprising:

receiver means for receiving a GPS signal;

code generator means for generating a PN code replica of the received GPS signal;

multipath error detector means for detecting a multipath error in the received GPS signal based on at least one relationship between a first correlation product of the received GPS signal with a first PN code phase delayed replica, a second correlation product of the received GPS signal with a second PN code phase delayed replica, and a third correlation product of the received GPS signal with a third PN code phase delayed replica; and

an adjustable delay means coupled to the code generator means and further coupled to the multipath error detector means to receive a multipath error signal, wherein the at adjustable delay element is configured to use the multipath error signal to adjust a phase of the PN code replica such that phases of respective first, second and third correlation products are adjusted.

10. An apparatus for processing global positioning system (GPS) satellite signals, the apparatus comprising:

receiver means for receiving a GPS signal;

code generator means for generating a PN code replica of the received GPS signal;

multipath error detector means for detecting a multipath error in the received GPS signal based on at least one relationship between a first correlation product of the received GPS signal with a first PN code phase delayed replica, a second correlation product of the received GPS signal with a second PN code phase delayed replica, and a third correlation product of the received GPS signal with a third PN code phase delayed replica; and

at least one delay means coupled to at least one correlator and further coupled to the multipath error detector means, wherein the at least one delay means is configured to use the multipath error signal to generate a control signal to control a phase relationship between respective first and third correlation products and further to control a relationship of the second correlation product with respect to the first correlation product and the third correlation product.