Spread spectrum receiver using a pseudo-random noise code for ranging applications in a way that reduces errors when a multipath signal is present
First Claim
1. A method of decoding an incoming signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
- locally generating a PRN signal corresponding to the PRN code of the incoming signal,mixing the locally generated PRN signal with the incoming signal,developing, from a result of mixing the locally generated PRN signal with the incoming signal, an error signal having a magnitude as a function of a relative phase difference between the incoming signal PRN code and the locally generated PRN signal that (a) is zero for a zero relative phase difference and for a majority of a range of the relative phase difference between plus and minus one chip, and (b) increases as the relative phase difference changes from zero to another value within a central portion of said range, andwhen the error signal has a non-zero magnitude within said central portion of said range, adjusting said relative phase difference by adjusting the phase of the locally generated PRN signal a manner to drive the error signal to zero, thereby to drive the relative phase difference between the incoming signal PRN code and the locally generated PRN signal to zero.
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Abstract
A receiver of a radio frequency signal having a pseudo-random noise (PRN) code, and techniques of processing such a signal that are especially adapted for ranging applications. A signal corresponding to the PRN code is locally generated and used for decoding the received signal in a manner to reduce ranging errors that can result when multipath (delayed) versions of the radio frequency signal are also present. A significant application of the receiver and signal processing techniques of the present invention is in a Global Positioning System (GPS), wherein a number of such signals from several satellites are simultaneously received and processed in order to obtain information of the position, movement, or the like, of the receiver. A delay locked loop (DLL) correlator, provided in each of the receiver'"'"'s multiple processing channels, locks onto a line of sight signal from one of the satellites with the effect of any multipath signal(s) being significantly reduced.
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Citations
24 Claims
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1. A method of decoding an incoming signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
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locally generating a PRN signal corresponding to the PRN code of the incoming signal, mixing the locally generated PRN signal with the incoming signal, developing, from a result of mixing the locally generated PRN signal with the incoming signal, an error signal having a magnitude as a function of a relative phase difference between the incoming signal PRN code and the locally generated PRN signal that (a) is zero for a zero relative phase difference and for a majority of a range of the relative phase difference between plus and minus one chip, and (b) increases as the relative phase difference changes from zero to another value within a central portion of said range, and when the error signal has a non-zero magnitude within said central portion of said range, adjusting said relative phase difference by adjusting the phase of the locally generated PRN signal a manner to drive the error signal to zero, thereby to drive the relative phase difference between the incoming signal PRN code and the locally generated PRN signal to zero. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In a receiver of a radio frequency signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, a method of locking onto the PRN code of a primary signal received in a line of sight from a transmitter when a multipath version of that signal is also received with a time delay of a fraction of one chip, comprising:
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generating a PRN signal corresponding to the PRN code of the received signal by generating an operating set of recurring non-zero gating signals representing edges of the PRN code and which initially (i) are less than one chip in duration, and (ii) have a single positive or negative polarity that designates whether a PRN code edge is respectively positive or negative going, and then subsequently (a) are less than one chip in duration, (b) have equal positive and negative areas, and (c) have a positive or negative polarity at a center thereof corresponding to whether a PRN code edge is positive or negative going, mixing the generated PRN signal with the received signal which includes both the primary signal and the delayed multipath version thereof, adjusting a relative phase of the generated PRN signal in response to an error signal, and initially generating the error signal from comparing the phase of the generated PRN signal with the phase of a composite of the primary and multipath signals, and then subsequently generating the error signal from comparing the phase of the generated PRN signal with the phase of the primary signal without the multipath signal.
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10. In a receiver of a radio frequency signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, a method of locking onto the PRN code of a primary signal received in a line of sight from a transmitter when a multipath version of that signal is also received with a time delay of a fraction of one chip, comprising:
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generating a PRN signal corresponding to the PRN code of the received signal by initially generating a first replica advanced in phase N/2K of said chip with respect to a reference and a second replica delayed in phase N/2K of said chip with respect to said reference, and then subsequently adding a third replica advanced in phase 1/2K of said chip with respect to said reference and a fourth replica delayed in phase 1/2K of said chip with respect to said reference, wherein N and K are integers with N being smaller than K, mixing the generated PRN signal with the received signal which includes both the primary signal and the delayed multipath version thereof, adjusting a relative phase of the generated PRN signal in response to an error signal, and initially generating the error signal from comparing the phase of the generated PRN signal with the phase of a composite of the primary and multipath signals, and then subsequently generating the error signal from comparing the phase of the generated PRN signal with the phase of the primary signal without the multipath signal. - View Dependent Claims (11)
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12. A method of decoding an incoming signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
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locally generating recurring non-zero operating gating signals representing PRN code edges and which individually (a) are less than one chip in duration, (b) have equal positive and negative areas, and (c) have a positive or negative polarity at a center thereof that designates whether a PRN code edge represented by an individual gating signal is positive or negative going, mixing the incoming signal with each of the locally generated gating signals, thereby generating first and second mixed signals, correlating and accumulating said first and second mixed signals, thereby obtaining a correlation signal, and using the correlation signal to adjust the phase of the locally generated gating signals with respect to the PRN code of the incoming signal in order to maximize the correlation, thereby to lock the phase of the locally generated gating signals to the phase of the PRN code in the incoming signal. - View Dependent Claims (13, 14)
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15. A method of decoding an incoming signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
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locally generating replicas of the incoming signal PRN code including a first replica advanced in phase 1/2K of said chip with respect to a reference, a second replica delayed in phase 1/2K of said chip with respect to said reference, a third replica advanced in phase N/2K of said chip with respect to said reference, and a forth replica delayed in phase N/2K of said chip with respect to said reference, wherein N and K are integers with N being smaller than K, mixing the incoming signal with the locally generated PRN code replicas, combining and accumulating the mixed incoming and PRN code replicas, thereby obtaining a correlation signal, and using the correlation signal to adjust the phase of the locally generated PRN code replicas with respect to the PRN code of the incoming signal in order to maximize the correlation, thereby to lock the phase of the locally generated PRN code replicas to the phase of the PRN code in the incoming signal. - View Dependent Claims (16)
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17. A method of decoding an incoming signal containing a carrier having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
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locally generating replicas of the incoming signal PRN code including a first replica advanced in phase 1/2K of said chip with respect to a reference, a second replica delayed in phase 1/2K of said chip with respect to said reference, a third replica advanced in phase N/2K of said chip with respect to said reference, and a forth replica delayed in phase N/2K of said chip with respect to said reference, wherein N and K are integers with N being smaller than K, mixing the incoming signal with the locally generated PRN code replicas, wherein mixing the incoming signal with the first, second, third and fourth locally generated PRN code replicas results in corresponding first, second, third and fourth mixed signals, combining and accumulating the mixed incoming and PRN code replicas, thereby obtaining a correlation signal, wherein combining and accumulating said mixed signals includes giving the first and fourth mixed signals the same polarity that is different from a common polarity of the second and third mixed signals, and using the correlation signal to adjust the phase of the locally generated PRN code replicas with respect to the PRN code of the incoming signal in order to maximize the correlation, thereby to lock the phase of the locally generated PRN code replicas to the phase of the PRN code in the incoming signal. - View Dependent Claims (18, 19)
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20. A receiver of a composite radio frequency signal including a plurality of signals that individually include a carrier signal having encoded thereon a pseudo-random noise (PRN) binary code, comprising:
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means receiving the composite radio frequency signal for transforming the composite signal into an intermediate frequency signal, whereby the intermediate frequency signal includes a plurality of signals that individually include an intermediate frequency carrier signal having the PRN code encoded thereon, a plurality of channel circuits receiving the intermediate frequency signal, individual ones of said plurality of channel circuits including means for decoding one of the plurality of intermediate frequency signals that comprises; means responsive to an error signal for locally generating a PRN signal corresponding to the PRN code of the intermediate frequency signal with a relative phase controlled by a magnitude of the error signal, means for mixing the locally generated PRN signal with the intermediate frequency signal, means using the mixed signal for generating an error signal having a magnitude as a function of a relative phase difference between the PRN code of one of the intermediate frequency signals and the locally generated PRN signal that (a) is zero for a zero relative phase difference and for a majority of a range of the relative phase difference between plus and minus one chip, and (b) increases as the relative phase difference changes from zero to another value within a central portion of said range. - View Dependent Claims (21, 22, 23, 24)
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Specification