Method for Doppler-replica harmonic avoidance

• US 5,987,059 A
• Filed: 06/26/1997
• Issued: 11/16/1999
• Est. Priority Date: 07/12/1996
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Harrison, Daniel David, Tiemann, Jerome Johnson
• Primary Examiner(s): Pham, Chi H.
• Assistant Examiner(s): Tran, Khai
• Application Number:
  US08/883,420
• Time in Patent Office: 873 Days
• Field of Search: 375/208, 375/206, 375/200, 375/210, 375/343, 342/352, 342/357, 342/375
• US Class Current: 375/150
• 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 19/34 Power consumption
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 5/0027 of actual mobile position, i.e. position determined on mobile
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/0054 of actual mobile position, i.e. position calculation on base station
• CPC Class Codes: G06F 17/15 Correlation function computation including computation of convolution operations arithmetic circuits for sum of products per se, e.g. multiply-accumulators G06F7/5443; digital filters, e.g. FIR, IIR, adaptive filters H03H17/00
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/708 Parallel implementation
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 2201/70709 with discontinuous detection
• CPC Class Codes: H04W 52/0283 with sequential power up or power down of successive circuit blocks, e.g. switching on the local oscillator before RF or mixer stages
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A direct sequence spread spectrum receiver receives an input signal on a signal carrier frequency. The receiver generates a local oscillator signal which is offset from the carrier frequency. The input signal and the local oscillator signal are mixed producing an IF signal which is converted to a digital sample and stored in memory. A corresponding replica signal is generated and correlated with the digital sample. The offset of the local oscillator frequency from the carrier frequency is sufficiently large to cause the harmonics of the replica signal to fall above the highest frequency of the IF signal. Such a receiver is useful in global positioning satellite (GPS) signal processing where a replica generator must be used to acquire the incoming satellite transmissions.

Claims

1. In a Global Positioning Satellite receiver, the method of avoiding false correlation with Doppler replica harmonics, comprising:

receiving an input signal having a signal carrier frequency;

generating a local oscillator signal having frequency which is offset from said carrier frequency;

mixing said input signal with said local oscillator signal to produce an intermediate frequency signal;

converting said intermediate frequency signal to a multiple-sample digital representation;

generating a multiple-sample digital representation of a replica signal; and

correlating said multiple-sample digital representation of said intermediate frequency signal with said multiple-sample digital representation of said replica signal to produce a correlation result;

said local oscillator frequency offset being sufficient such that harmonics of said digital representation of said replica signal fall above the highest frequency of said intermediate frequency signal;

wherein

the correlating step comprises employing a parallel correlator to produce said correlation result.

2. The method of claim 1, including the step of:

storing said multiple-sample digital representation of said intermediate frequency signal in an input signal memory prior to said correlating step.

3. The method of claim 1, including the step of:

storing said multiple-sample digital representation of said replica signal in a replica memory prior to said correlating step.

4. The method of claim 1, wherein:

said digital representation of a replica signal is in one-bit sign format.

5. The method of claim 1, wherein:

said digital representation of a replica signal is in two-bit sign-magnitude format.