Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1999-07-28
2001-05-29
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C375S150000
Reexamination Certificate
active
06239743
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to receivers for processing information containing signals and, in particular, to positioning system receivers such as global positioning system (“GPS”) receivers which may be adapted to receive and process split spectrum positioning system signals and/or standard (non-split) spectrum GPS navigation signals.
BACKGROUND OF THE INVENTION
GPS is a navigation and position service offering worldwide, 24 hour coverage. GPS includes satellites to broadcast GPS satellite signals, stations to monitor and control the satellites, and receivers. GPS receivers demodulate the satellite signals to calculate a range for each satellite from which signals are being received (“in view”), and from that range compute the location of the receiver.
GPS satellites broadcast two codes. Each of these codes, as part of the standard GPS signal structure, contain and are modulated with information from which the location of the receiver can be derived. The two codes are: (1) Precision or Protected code (“P code”); and (2) Coarse Acquisition code (“C/A code”). Although P code can be encrypted by an additional code to prevent unauthorized use, C/A code is freely available.
Each GPS satellite broadcasts on two frequency bands (“carrier bands”), one centered on 1575.42 megahertz, the “L1” frequency band, and the other centered on 1227.6 megahertz, the “L2” frequency band. Each frequency band includes the P code, but only the L1 band includes the C/A code. Each GPS satellite is assigned a unique C/A code and a unique P code. The unique codes enable a GPS receiver to distinguish the GPS signals being received from each other.
To enhance system performance, the standard GPS signal structure can be augmented with split spectrum modulation. The power distribution of a split spectrum modulated signal is substantially different from that of a standard spectrum signal. That is, the power distribution of the standard GPS signal largely surrounds the L1 carrier center frequency, whereas the power distribution of a split spectrum signal is concentrated away from and on opposite sides of the center frequency. This separation of power distribution concentrations may be used advantageously to improve jamming performance, and is described in connection with at least one of the embodiments of the invention described below. Split spectrum modulation can be added to transmissions from satellites or ground-based sources (“pseudolites”) in the same frequency band used by the standard GPS signal structure.
BRIEF SUMMARY OF THE INVENTION
The invention provides a method and apparatus for receiving and processing information containing signals, particularly navigation signals such as GPS signals as to which the receiver is adapted to perform signal tracking, code and carrier phase measurements, and data demodulation. In one embodiment, the invention provides a method of or apparatus for tracking a positioning signal from a positioning signal source where the positioning signal energy contains positioning information and is split within its frequency band so as to be concentrated about at least first and second frequencies within the frequency band. The method includes the step of correlating a first signal derived from energy concentrated about the first frequency with a first tracking signal to generate a first correlation signal. The method also includes the step of correlating a second signal derived from energy concentrated about the second frequency with a second tracking signal to generate a second correlation signal. The first tracking signal and the second tracking signal are adjusted respectively according to the first and second correlation signals so as to optimize energy representative of the positioning information for further processing by the receiver.
Other objects, advantages, and features of the invention will become apparent to those skilled in the relevant art upon consideration of the following description of the invention.
REFERENCES:
patent: 5228055 (1993-07-01), Uchida et al.
patent: 5781152 (1998-07-01), Renard et al.
patent: 6058135 (2000-05-01), Spilker, Jr.
McDonald, Keith D., “The GPS Modernization Dilemma and Some Topics For Resolution”, ION Newsletter, vol. 8, No. 2, Summer 1998.
Cooper & Dunham LLP
Dowden Donald S.
Issing Gregory C.
Pelton William E.
Trimble Navigation Limited
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