Pulse or digital communications – Spread spectrum – Direct sequence
Reexamination Certificate
1998-02-11
2001-09-11
Chin, Stephen (Department: 2734)
Pulse or digital communications
Spread spectrum
Direct sequence
C375S343000
Reexamination Certificate
active
06289041
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of global positioning systems, and more particularly to receiving and tracking satellite signals in an integrated fast acquisition, high sensitivity receiver.
BACKGROUND OF THE INVENTION
Most conventional Global Positioning System (GPS) receivers utilize serial correlators in order to acquire, track, and demodulate signals transmitted from Navstar satellites. Each transmitted GPS signal is a direct sequence spread spectrum signal. The signal available for commercial use is that associated with Standard Positioning Service (SPS) and utilizes a direct sequence biphase spreading signal with a 1.023 Mchip per second spread rate placed upon a carrier at 1575.42 MHz. The Pseudo-random Noise (PN) sequence length is 1023 chips, corresponding to 1 msec time period. Each satellite transmits a different PN code (Gold code) which allows the signals to be simultaneously transmitted from several satellites and to be simultaneously received by a receiver, with little interference from one another. In addition, data superimposed on each signal is 50 baud binary phase shift keyed (BPSK) data with bit boundaries aligned with the beginning of a PN frame; 20 PN frames occur over 1 data bit period (20 msec).
A primary goal of a GPS receiver is to determine the time-of-arrival of the PN codes. This is accomplished by comparing (for each received signal) a locally generated PN reference against the received signal and “sliding” the local reference in time until it is time-aligned with the received signal. The two signals are compared with one another by a multiplication and integration process known as a correlation process. When the two signals are time aligned a large output results. Typical serial correlators used in standard GPS receivers compare the local and received signals one time offset at a given time. If such a comparison is done every half-chip interval, there are 2046 comparisons (or tests) required to completely search over one PN epoch. Such a search must be done for several of the satellites in view. In addition, errors in received signal frequency often require additional searches to be made for various hypotheses of signal frequency. The time to perform this search may be very lengthy, especially under low input signal-to-noise ratio situations. Conventional GPS receivers utilize a multiplicity of such correlators operating in parallel to speed up the acquisition process. Nevertheless, the search and acquisition process is very time consuming, especially in low received signal-to-noise situations.
It is therefore desirable to provide a hardware architecture that improves the acquisition speed and sensitivity of current conventional GPS receivers. Such an architecture would allow the receiver to operate at a very low input signal-to-noise ratio. It is further desirable to integrate a method for tracking such signals, following the acquisition procedure, in which a commonality of hardware is used for both the acquisition and tracking of received GPS signals.
SUMMARY OF THE INVENTION
The present invention discloses a method and apparatus for acquiring and tracking global positioning system signals with a fast acquisition speed and high sensitivity. In a method of the present invention, a first pseudo-random noise matching filter operation is performed on a current sample of global positioning system signals to provide a current matched filter result. The current matched filter result is then accumulated with a prior matched filter result from a prior sample of global positioning system signals to produce an accumulated matched filter result.
In one embodiment of the present invention, a matched filter and detection circuit are combined with a pre-detection loop integrator and a post-detection loop integrator. The loop integrators allow the acquisition and tracking of multiple frames of data comprising the received global positioning system signal. This results in a combination of rapid acquisition performance and high sensitivity. Efficient means for implementing the matched filter are disclosed.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.
REFERENCES:
patent: 4112372 (1978-09-01), Holmes et al.
patent: 4426712 (1984-01-01), Gorski-Popiel
patent: 4660164 (1987-04-01), Leibowitz
patent: 4841544 (1989-06-01), Nuytkens
patent: 4998111 (1991-03-01), Ma et al.
patent: 5199050 (1993-03-01), Linsky
patent: 5233626 (1993-08-01), Ames
patent: 5237587 (1993-08-01), Schoolcraft
patent: 5373531 (1994-12-01), Kawasaki
patent: 5414728 (1995-05-01), Zehavi
patent: 5548583 (1996-08-01), Bustamante
patent: 5557641 (1996-09-01), Weinberg
patent: 5572216 (1996-11-01), Weinberg et al.
patent: 5576715 (1996-11-01), Litton et al.
patent: 5579014 (1996-11-01), Brooksby et al.
patent: 5579338 (1996-11-01), Kojima
patent: 5589833 (1996-12-01), Randall et al.
patent: 5600328 (1997-02-01), Tachita et al.
patent: 5640416 (1997-06-01), Chalmers
patent: 5663983 (1997-09-01), Lin
patent: 5736961 (1998-04-01), Fenton et al.
patent: 5799010 (1998-08-01), Lomp et al.
patent: 5809064 (1998-09-01), Fenton et al.
patent: 5822363 (1998-10-01), LeRoy
patent: 5955986 (1999-09-01), Sullivan
patent: 5991308 (1999-11-01), Fuhrmann et al.
patent: 41 14 058 A1 (1992-11-01), None
patent: 0 488 739 A1 (1992-06-01), None
patent: 0 526 040 A2 (1993-02-01), None
patent: 0 718 998 A2 (1996-06-01), None
patent: 0 773 635 A2 (1997-05-01), None
patent: 2 016 760 A (1979-09-01), None
patent: 2 297 229 A (1996-07-01), None
patent: WO 97/14057 (1997-04-01), None
patent: WO 97/40398 (1997-10-01), None
patent: WO 98/02830 (1998-01-01), None
Written Opinion for PCT International Appln No. PCT/US98/07471, mailed May 15, 2000 (4 pgs).
Eric Holm & Edwin Westerfield, “A GPS Fast Acquisition Receiver,” IEEE National Telesystem Conference, Nov. 14-16, 1983, pp. 214-218, XP-002100664.
PCT International Search Report for Int'l Appln No. PCT/US98/07471 mailed Aug. 31, 1999.
PCT International Search Report for Int'l Appln No. PCT/US98/11375 mailed Sep. 30, 1998.
J.J. Spilker, Jr. “Signal Structure and Theoretical Performance; Chapter 3: GPS Signal Structure and Theoretical Performance”,American Institute of Aeronautics and Astronautics, Inc. 1994, pp. 57-83.
Blakely & Sokoloff, Taylor & Zafman
Chin Stephen
Jiang Lenny
SnapTrack, Inc.
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