Method of deriving phase of pseudo-random code signal in global positioning system receiver

• US 5,081,462 A
• Filed: 05/16/1991
• Issued: 01/14/1992
• Est. Priority Date: 05/16/1990
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Ikeda, Ken, Tachita, Ryobun
• Primary Examiner(s): Blum, Theodore M.
• Application Number:
  US07/701,273
• Time in Patent Office: 243 Days
• Field of Search: 342/352, 342/353, 342/356, 375/1
• US Class Current: 342/352
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A method, for use in a receiver for the NAVSTAR global positioning system (GPS), of deriving successive values of phase of a received pseudo-random code signal following a momentary interruption of satellite signal reception, with the effects of signal noise eliminated by averaging processing, by first setting a replica pseudo-random code signal to an initial phase value which provides high correlation with the received code signal, and thereafter periodically executing phase derivation operations to obtain the phase of the received code signal, by obtaining the phase difference between the received and replica code signals, obtaining the average value of all of such phase differences obtained up to that point since the initial phase derivation operation, and adding that average value to the sum of a phase value obtained in the first phase derivation operation and a total estimated amount of change of phase of the received code since that first operation. The estimated phase change is obtained based on a corresponding amount of frequency change that has occurred in the carrier of the received signal.

Claims

1. A method of measuring the phase of a received pseudo-random code signal, for use in a global positioning system receiver apparatus adapted for receiving a radio signal including a received carrier which is modulated by a pseudo-random code signal, the receiver apparatus including means for obtaining a value of frequency of said received carrier, means for demodulating the received carrier to obtain a received pseudo-random code signal, means for generating a replica pseudo-random code signal having a code sequence that is identical to a code sequence of said received pseudo-random code signal, and means for indicating when a predetermined condition of phase correlation occurs between said received pseudo-random code signal and replica pseudo-random code signal, the method comprising, when a momentary interruption of reception of said radio signal occurs, a step of successively varying the phase of said replica pseudo-random code signal until said correlation condition is indicated, and setting the phase of said replica pseudo-random code signal at the phase value for which the correlation condition occurs, then repetitively executing at periodic intervals a phase derivation operation to obtain a current value of phase of said received pseudo-random code signal, the phase derivation operation including steps of:

deriving a cumulative total amount of change of

phase (Δ

τ

(n)) of said received pseudo-random code signal that has occurred since said correlation condition was indicated, based on an amount of change of frequency of said received carrier, and

setting the phase of said replica pseudo-random code signal to a value that is the sum of said initial phase value (t₁) and said total amount of phase change (Δ

τ

(n));

measuring an amount of phase difference (D_n) between said received pseudo-random code signal and replica pseudo-random code signal;

calculating an average value of a cumulative total of successively derived ones of said amount of phase difference, respectively obtained since said initial value of phase was measured; and

calculating the sum of said average value, said initial value of phase (t₁) and said total amount of phase change (Δ

τ

(n)), to obtain said current value of phase (t_n) of said received pseudo-random code signal.

2. The method according to claim 2, and in which said step of deriving a cumulative value of phase change of the received pseudo-random code includes deriving an amount of change (d(n)) of said pseudo-random code phase that has occurred since an immediately preceding repetition of said phase derivation operation, based on an amount of change of frequency of said received carrier, and storing said amount of phase change (d(n)) in a memory, the method further comprising a step of judging when a predetermined number of repetitions of said phase derivation operation has been executed, and when that predetermined number is reached, using successive ones of said stored amount of phase change in conjunction with a value of phase of said received pseudo-random code signal that is derived when said predetermined number of repetition is reached, to derive respective recalculated values (t'"'"'_n) for each of the values of received pseudo-random code signal phase (t_n) previously derived up to said predetermined number,

3. A method of measuring the phase of a received pseudo-random code signal, for use in a global positioning system receiver apparatus adapted for receiving a radio signal including a received carrier which is modulated by a pseudo-random code signal, the receiver apparatus including means for obtaining a value of frequency of said received carrier, means for demodulating the received carrier to obtain a received pseudo-random code signal, means for generating a replica pseudo-random code signal having a code sequence that is identical to a code sequence of said received pseudo-random code signal, and means for indicating when a predetermined condition of phase correlation occurs between said received pseudo-random code signal and replica pseudo-random code signal, the method comprising, when a momentary interruption of reception of said radio signal occurs, a step of successively varying the phase of said replica pseudo-random code signal until said correlation condition is indicated, and setting the phase of said replica pseudo-random code signal at the phase value for which the correlation condition occurs, then repetitively executing at periodic intervals a phase derivation operation to obtain a current value of phase of said received pseudo-random code signal, the phase derivation operation including steps of:

deriving a cumulative total amount of change of phase (Δ

τ

(n) of said received pseudo-random code signal that has occurred since said correlation condition was indicated, based on an amount of change of frequency of said received carrier, and

setting the phase of said replica pseudo-random code signal to a value that is the sum of said initial phase value (t₁) and said total amount of phase change (Δ

τ

(n));

measuring an amount of phase difference (D_n) between said received pseudo-random code signal and replica pseudo-random code signal;

calculating an average value of a cumulative total of successively derived ones of said amount of phase difference, respectively obtained since said initial value of phase was measured; and

calculating the sum of said average value, said initial value of phase (t₁) and said total amount of phase change (Δ

τ

(n)), to obtain said current value of phase (t_n) of said received pseudo-random code signal;

the method further comprising a step of judging when a predetermined number of repetitions of said phase derivation operation has been executed, and when that predetermined number is reached, setting a finally obtained value of phase (t_n) of said received pseudo-random code signal as an initial phase value for a loop filter of a negative feedback type of code tracking loop, and thereafter executing phase tracking of said received pseudo-random code signal by said code tracking loop to thereby obtain successive values of phase of said received pseudo-random code signal.

5. The method according to claim 3, wherein each of said recalculated phase values is obtained by adding a stored value of phase change amount (d(n)) to the difference between a value of received pseudo-random code signal phase (t₅₀₀) obtained in a final one of said repetitions of the phase derivation operation and a value of cumulative phase change (Δ

τ

(500)) obtained in said final phase derivation operation.

4. A method of measuring the phase of a received pseudo-random code signal, for use in a global positioning system receiver apparatus adapted for receiving a radio signal including a received carrier which is modulated by a pseudo-random code signal, the receiver apparatus including means for obtaining a value of frequency of said received carrier, means for demodulating the received carrier to obtain a received pseudo-random code signal, means for generating a replica pseudo-random code signal having a code sequence that is identical to a code sequence of said received pseudo-random code signal, and means for indicating when a predetermined condition of phase correlation occurs between said received pseudo-random code signal and replica pseudo-random code signal, the method comprising, when a momentary interruption of reception of said radio signal occurs, a step of successively varying the phase of said replica pseudo-random code signal until said correlation condition is indicated, and setting the phase of said replica pseudo-random code signal at the phase value for which the correlation condition occurs, then repetitively executing at periodic intervals a phase derivation operation to obtain a current value of phase of said received pseudo-random code signal, the phase derivation operation including steps of:

deriving an amount of change of phase (d(n)) of the received pseudo-random code signal that has occurred since execution of an immediately preceding phase derivation operation, based on an amount of change of frequency of said received carrier, and storing that amount of phase change in a memory, computing a total amount of cumulative change of phase of said received pseudo-random code signal that has occurred since said correlation condition was indicated, based on a change in frequency of said received carrier, and setting the phase of said replica pseudo-random code signal to a value that is the sum of said initial phase value (t₁) and said total amount of phase change (Δ

τ

(n));

measuring an amount of phase difference (D_n) between said received pseudo-random code signal and replica pseudo-random code signal;

calculating an average value of a cumulative total of successively derived ones of said amount of phase difference, respectively obtained since said initial value of phase was measured; and

calculating the sum of said average value, said initial value of phase (t₁) and said total amount of phase change (Δ

τ

(n)), to obtain said current value of phase (t_n) of said received pseudo-random code signal;

the method further comprising a step of judging when a predetermined number of repetitions of said phase derivation operation has been executed, and when that predetermined number is reached, using said stored values of amount of phase change (d(n)) in conjunction with a value or received pseudo-random code signal phase that is derived when said predetermined number of repetitions is reached, to derive recalculated values (t'"'"'_n) for each of the values of received pseudo-random code signal phase (t_n) previously derived up to said predetermined number, then a step of setting a phase value derived when said predetermined number was reached, as an initial phase value of a negative feedback type of code tracking loop, and thereafter executing phase tracking of said received pseudo-random code signal by said code tracking loop to thereby obtain successive values of phase of said received pseudo-random code signal.