Satellite transmission capturing method for GPS receiver

• US 5,203,030 A
• Filed: 01/31/1991
• Issued: 04/13/1993
• Est. Priority Date: 02/13/1990
• Status: Expired due to Term

• Current Assignee: Pioneer Electronic Corporation (Pioneer Corporation)
• Original Assignee: Pioneer Electronic Corporation (Pioneer Corporation)
• Inventors: Kawasaki, Kenichiro
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): FAILE, ANDREW I
• Application Number:
  US07/648,800
• Time in Patent Office: 803 Days
• Field of Search: 455/147, 455/148, 455/164.2, 455/167.1, 455/180.3, 455/182.2, 455/192.2, 455/192.3, 455/260, 455/265, 455/304, 455/164.1, 375/1, 375/97, 375/102, 331/4, 331/1 A, 331/10, 331/25, 331/22
• US Class Current: 455/164.2
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: H03D 1/2254 and a phase locked loop
• CPC Class Codes: H03D 2200/0031 PLL circuits with quadrature locking, e.g. a Costas loop
• CPC Class Codes: H03L 7/12 using a scanning signal
• CPC Class Codes: H04L 2027/0034 using hypothesis testing
• CPC Class Codes: H04L 2027/0051 Harmonic tracking
• CPC Class Codes: H04L 27/2273 associated with quadrature demodulation, e.g. Costas loop

Abstract

A satellite transmission capturing method for the GPS receiver whereby PLL operation is stopped until the demodulation intensity of a demodulator reaches a predetermined level. The frequency of the reproduced carrier of the demodulator is consecutively changed in increments of a frequency range wider than the PLL capture range in search for satellite transmissions. This allows the demodulation intensity to reach the predetermined level in fewer frequency changing steps than ever before. Thus the time required to capture the desired satellite transmission is reduced. Where the integral time constant of a low pass filter in the demodulator is set to a value smaller than that in effect during PLL operation until the demodulation intensity of the demodulator reaches the predetermined level, a wide band demodulation intensity curve is used in search for satellite transmissions until that level is exceeded. This further widens the frequency range in which to search satellite transmissions, and the time required to capture the desired satellite transmission is further shortened accordingly.

Claims

1. A satellite transmission capturing method for GPS receivers wherein a reference carrier is reproduced by a demodulator comprising a first multiplier for inverse diffusing said satellite transmission, a second multiplier for in-phase channel signal demodulation, a third multiplier for orthogonal channel signal demodulation, a first low-pass filter corresponding to said second multiplier, a second low-pass filter corresponding to said third multiplier, a fourth multiplier for detecting the phase difference of said satellite transmission and said reference carrier, a phase-locked loop (PLL) filter, a voltage controlled oscillator for generating said reference carrier, a demodulation intensity calculating circuit, a control circuit and a switch for switching to said PLL loop when said reference carrier is synchronized with said satellite transmission, said method comprising the steps of:

inverse diffusing said satellite transmission and applying the resulting received satellite transmission to said second and third multipliers;

generating the reference carrier;

demodulating said received satellite transmission by multiplying said received satellite transmission by an in-phase component of said reference carrier with said second multiplier and multiplying said received satellite transmission by an orthogonal component of the reference carrier with said third multiplier to obtain a demodulated in-phase channel signal I(t) and a demodulated orthogonal channel signal Q(t);

incrementing a frequency of said reference carrier within a predetermined Doppler-shift frequency range beginning at a starting frequency in frequency increments greater than a capture frequency range required for PLL operation to lock onto a captured transmission;

calculating a demodulation intensity based upon said in-phase channel signal I(t) and said orthogonal channel signal Q(t) corresponding to a particular frequency obtained following each frequency increment, said frequency increments being determined by a bandwidth corresponding to a predetermined threshold level of said demodulation intensity;

comparing said demodulation intensity obtained at each frequency increment to said threshold level;

reducing said frequency increments to correspond to said capture frequency range when said demodulation intensity of said particular frequency reaches said threshold level;

determining whether said particular frequency is located substantially at the peak of demodulation intensity corresponding to a received frequency of said received satellite transmission; and

initiating said PLL operation when said particular frequency is located substantially at the peak of demodulation intensity corresponding to said received frequency of said received satellite transmission to phase synchronize said reference carrier with said received frequency.

2. The satellite transmission capturing method according to claim 1, wherein said particular frequency is determined to be located substantially at the peak of demodulation when said particular frequency lies between the frequency range defined by frequencies resulting from the subtraction and addition of a frequency increment corresponding to said PLL capture range with said particular frequency.

3. A satellite transmission capturing method for GPS receivers according to claim 3, whereby the integral time constant of said first and second low pass filters in said demodulator is switched to a value lower than that in effect during PLL operation until the demodulation intensity of said demodulator reaches said threshold level.