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Spread spectrum receiver using a pseudo-random noise code for ranging applications in a way that reduces errors when a multipath signal is present
| Details |
Inventors: Zhodzicshsky, Mark; Veitsel, Victor; Sila-Novatisky, Stanislov; Ashjaee, Javad; Garin, Lionel;
Assignee: Magellan Corporation (Santa Clara, CA)
Primary Examiner: Bocure; Tesfaldet
Assistant Examiner:
Attorney, Agent or Firm: Harriman, II, Esq.; J. D. Coudert Brothers LLP
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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DETAILED DESCRIPTION This and additional objects of the present invention are realized, briefly and generally, by providing a DLL correlator having a zero loop gain over a majority of a range of relative phase difference between the locally generated PRN code and that encoded in the radio frequency signal being received from a satellite or other source, while, at the same time, providing a finite magnitude of loop gain in an operating phase difference region positioned about a zero phase difference.
That is, the DLL operates to minimize the error signal for a received signal having a relative phase within a narrow operating phase window and is thus unaffected by multipath versions of that signal which are outside of the window in a region where the loop gain is zero.
The present invention exhibits a code loop error which goes practically to zero for far multipath delay, virtually eliminating the influence of the far multipath on the pseudorange measurement accuracy.
This improvement is not obtained at the expense of the performances on near multipath, however, in which case the performance is similar to that of the narrow correlator.
In one form of the invention, the radio frequency signal is initially acquired by operating the DLL as a narrow correlator, where there is some gain over the entire range of relative phase differences.
After the signal has been acquired by locking the DLL onto a combination of the line-of-sight and multipath signals, the DLL is switched to provide a loop gain in only the small central region of the combination of the line-of-sight and multipath signals, thereby discriminating against the multipath signals.
According to one specific aspect of the present invention, this DLL response is obtained by providing more than one early-late correlator in parallel, with the early-late delays being different.
The results of the correlations are arithmetically combined.
The size of the central relative phase operating range of the loop response is set by the specific early-late delay values chosen for the correlators
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