Digital global positioning system receiver
AssigneeMotorola, Inc.
InventorsRobert V. Janc, Steven C. Jasper
Life of this patent
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Abstract
A digital receiver for GPS C/A-code signals is described. The GPS receiver of the present invention provides reception and tracking a plurality of satellites simultaneously, using four separate receiver channels. The GPS receiver of the present invention includes an analog front-end for selecting and frequency translating the received GPS signal. The GPS receiver further includes a highspeed digital signal processor for recovering the despread data of the GPS signal. The baseband signal is further processed by a general purpose digital signal processor for signal search, tracking, and data recovery operations, and a microprocessor provides overall receiver control, and interface with the operator of the GPS receiver.
Claims38
An improved substantially digital receiver apparatus for the reception of one or more direct-sequence-coded spread spectrum signals, which exhibit substantially equal carrier frequencies, except for Doppler shifting, said apparatus comprising:
- (a) first means for coupling a wideband radio frequency (RF) signal containing said spread spectrum signals to said receiving apparatus;
- (b) second means, including preselector and down-converting means, coupled to said first means, for selecting a composite signal containing said spread spectrum signals from said wide-band RF signal and for frequency-translating said composite signal to an intermediate frequency;
- (c) digitizing means, coupled to said second means, for converting said translated composite signal to a digital composite signal, at a predetermined sampling rate, wherein the predetermined sampling rate is determined according to the relationship:
- m f.sub.s =4f.sub.i wherein f.sub.i is said intermediate frequency and f.sub.s is the predetermined sampling rate;
- (d) first processing means, coupled to said digitizing means, for separating and despreading each of said spread spectrum signals from said digital composite signal, and for deriving a prompt and auxiliary late-early signal corresponding to each spread-spectrum signal;
- and
- (e) second processing means, coupled to said first processing means, providing for each desired signal, code delay search and tracking and carrier search and tracking processing for each of said doppler shifted signals, and data recovery processing.
An improved method for digitally receiving one or more direct-sequence-coded spread spectrum signals, which exhibit substantially equal carrier frequencies, except for Doppler shifting, said method comprising the steps of:
- (a) coupling a wideband radio frequency (RF) signal containing at least said direct-sequence-coded spread spectrum signals to said receiving apparatus;
- (b) selecting a composite signal containing said spread spectrum signals from said wide-band RF signal;
- (c) converting said selected composite signal to a digital composite signal, at a predetermined sampling rate determined according to the relationship:
- f.sub.s =4f.sub.i ;
- wherein f.sub.i is an intermediate frequency;
- (d) separating and despreading each of said direct-sequence-coded spread spectrum signals from said digital composite signal, including generating a prompt pseudorandom code signal and a late/early signal corresponding to each direct-sequence-coded spread spectrum signal;
- and
- (e) code delay searching and tracking and carrier searching and tracking the doppler-shifted signal corresponding to each desired spread spectrum signal, and recovering a data signal.
An improved method for digitally receiving one or more direct-sequence-coded spread spectrum signals, which exhibit substantially equal carrier frequencies, except for Doppler shifting, said method comprising the steps of:
- (a) coupling a wideband radio frequency (RF) signal containing at least said direct-sequence-coded spread spectrum signals to said receiving apparatus;
- (b) selecting a composite signal containing said spread spectrum signals from said wide-band RF signal;
- (c) converting said selected composite signal to a digital composite signal, at a predetermined sampling rate;
- (d) separating and despreading each of said direct-sequence-coded spread spectrum signals from said digital composite signal, including generating a prompt pseudorandom code signal and a late/early signal corresponding to each direct-sequence-coded spread spectrum signal;
- (e) estimating a code-delay for the desired direct-sequence-coded spread spectrum signal, and generating a pseudorandom code signal corresponding to said delay;
- (f) measuring the spectral power of the prompt signal for the current code delay generated by said separating and despreading step;
- (g) comparing the power values measured in said measuring step to a predetermined threshold value, wherein a power value exceeding said threshold value indicates the proper code delay and doppler shifted carrier frequency;
- and
- (h) incrementing the code delay and repeating steps (e) through (h) until a proper code delay and doppler shifted carrier frequency is found and recovering a data signal therefrom.
An improved substantially digital receiver apparatus for the reception of one or more global positioning system (GPS) coarse acquisition/clear access (C/A) coded spread spectrum signals, which exhibit substantially equal carrier frequencies (except for Doppler shifting);
- said apparatus comprising:
- (a) first means for coupling a wideband radio frequency (RF) signal containing said GPS C/A coded spread spectrum signals to said receiving apparatus;
- (b) second means, including preselector and down-converting means, coupled to said first means, for selecting a composite signal containing said GPS C/A coded spread spectrum signals from said wide-band RF signal and for frequency-translating said composite signal to an intermediate frequency;
- (c) digitizing means, coupled to said second means, for converting said translated composite signal to a digital composite signal, at a predetermined sampling rate, wherein the predetermined sampling rate is determined according to the relationship:
- f.sub.s =4f.sub.i wherein f.sub.i is said intermediate frequency and f.sub.s is the predetermined sampling rate;
- (d) first processing means, coupled to said digitizing means, for separating and despreading each of said GPS C/A coded spread spectrum signals from said digitial composite signal, and for deriving prompt and auxiliary late-early signal corresponding to each spread-spectrum signal;
- and
- (e) second processing means, coupled to said first processing means, providing for each desired signal, carrier search and tracking and code delay search and tracking processing in response to said prompt and auxiliary late-early signals, and data recovery processing.
A method for the reception of one or more global positioning system (GPS) coarse acquisition/clear access (C/A) coded spread spectrum signals, which exhibit substantially equal carrier frequencies (except for Doppler shifting);
- said method comprising the steps of:
- (a) coupling a wideband radio frequency (RF) signal containing said GPS C/A coded spread spectrum signals to said receiving apparatus;
- (b) selecting a composite signal containing said GPS C/A coded spread spectrum signals from said wide-band RF signal and for frequency-translating said composite signal to an intermediate frequency;
- (c) converting said translated composite signal to a digital composite signal, at a predetermined sampling rate, wherein the predetermined sampling rate is determined according to the relationship:
- f.sub.s 4f.sub.i wherein f.sub.i is said intermediate frequency and f.sub.s is the predetermined sampling rate;
- (d) separating and despreading each of said GPS spread spectrum signals from said digitial composite signal, including generating a prompt C/A code signal and a late/early C/A code signal and deriving a prompt and auxiliary late-early signal corresponding to each GPS spread-spectrum signal;
- and
- (e) code delay searching and tracking and carrier searching and tracking the doppler-shifter signal corresponding to each desired GPS spread spectrum signal, and recovering a data signal.
A method for the reception of one or more global positioning system (GPS) coarse acquisition/clear access (C/A) coded spread spectrum signals, which exhibit substantially equal carrier frequencies, except for Doppler shifting, said method comprising the steps of:
- (a) coupling a wideband radio frequency (RF) signal containing at least said GPS C/A coded spread spectrum signals to said receiving apparatus;
- (b) selecting a composite signal containing said GPS C/A coded spread spectrum signals from said wide-band RF signal and frequency translating said composite signal to an intermediate frequency;
- (c) converting said selected composite signal to a digital composite signal, at a predetermined sampling rate determined according to the relationship:
- f.sub.s =4f.sub.i ;
- wherein f.sub.i is said intermediate frequency;
- (d) separating and despreading each of said GPS spread spectrum signals from said digital composite signal, including generating a prompt C/A code signal and an late/early C/A signal and deriving a prompt and auxiliary late/early signal corresponding to each GPS spread spectrum signal;
- (e) estimating a code-delay for the desired GPS spread spectrum signal, and generating a C/A code signal corresponding to said delay;
- (f) measuring the spectral power of the prompt signal for the current code delay generated by said separating and despreading step;
- (g) comparing the power values measured in said measuring step to a predetermined threshold value, wherein a power value exceeding said threshold value indicates the proper code delay and doppler shifted carrier frequency;
- and
- (h) incrementing the code delay and repeating steps (e) through (h) until a proper code delay and doppler shifted carrier frequency is found and recovering a data signal therefrom.
Dependencies are inferred from the claim text.