Method and system for determining position on a moving platform, such as a ship, using signals from GPS satellites

A system for determining range data from a composite of code modulated, overlapping spread spectrum signals received on a moving platform from a plurality of GPS satellites, comprising:

• registers containing estimates of phase and delay of selected signals inherent therein;
• phase and delay error detection means responsive to the received composite and the estimates for determining phase and delay of the selected signals;
• feedback means responsive to the phase and delay error detection means for updating the estimates to derive phase and delay observations;
• and
• averaging means responsive to the observations for deriving instantaneous platform range data.

A method of deriving dual-band observations from a composite of code modulate, overlapping spread spectrum signals transmitted by a plurality of GPS satellites in L1 and L2 frequency bands and modulated by satellite specific C/A codes in the L1 band, comprising:

• applying replicas of the C/A codes to the composite to detect separately the satellite specific signals modulated thereby;
• deriving therefrom a first series of observations related to those satellite specific signals;
• and
• applying the first series of observations to the composite, to derive observations related to signals received in the L2 band independently of externally derived knowledge of the information content of the modulating codes applied to the L2 band signals.

A system for deriving dual-band observations from a composite of code modulated, overlapping spread spectrum signals, transmitted by a plurality of GPS satellites in L1 and L2 frequency bands and modulated by satellite specific C/A codes in the L1 band, comprising:

• code correlating means for applying replicas of the C/A codes to the composite to detect separately the satellite specific signals modulated thereby;
• means for deriving therefrom a first series of observations related to those satellite specific signals;
• and
• aiding means responsive to the first series of observations, for deriving a second series of observations from the composite related to signals received in the L2 band independently of externally derived knowledge of the information content of the modulating codes applied to the L2 band signals.

A method of determining ionospheric information, comprising:

• collecting a first composite signal simultaneously including code modulated, overlapping spread spectrum signals received from a plurality of GPS satellites;
• separating the first composite signal into portions representing different frequency bands each including modulation products of a particular code from each satellite;
• multiplying one such portion by another to form a second composite signal including a plurality of demodulated components, each related to the modulation products from a satellite;
• deriving an estimate related to the Doppler shift of the signals from a selected satellite;
• combining the estimate with the second composite to select therefrom the demodulated component having a phase responsive to the difference between the ionospheric phase shifts of the signal from the selected satellite in both bands, independently of prior knowledge of the information content of the particular code from that satellite;
• and
• determining ionospheric information in response to the selected component.

A system for determining ionospheric information, comprising:

• omni-directional antenna means for collecting a first composite signal simultaneously including code modulated, overlapping spread spectrum signals from a plurality of GPS satellites;
• frequency-selective means for separating the first composite signal into portions representing different frequency bands each including modulation products of a particular code from each satellite;
• cross-correlation means for correlating one portion with another to form a second composite signal simultaneously including a plurality of demodulated components, each related to the modulation products from a satellite;
• estimating means for generating an estimate related to the Doppler shift of the signals from a selected satellite;
• codeless selection means responsive to the estimate for selecting the demodulated component from the second composite having a phase responsive to the difference between the ionospheric phase shift of the signal from the selected satellite in both bands, independently of prior knowledge of the information content of the related code;
• phase detector means for determining the phase of the selected component;
• and
• processing means for determining ionospheric information in response to the phase determination.

A method of deriving range information from a modulated, suppressed carrier signal being received from a GPS satellite, comprising:

• generating a range estimate in the form of a number having a first portion and a second portion;
• generating a model of the received signal in response to said range estimate, said model having a carrier component which is generated in response to the first portion of said number, and a modulation component which is generated in response to the second portion of said number;
• correlating the model with the received signal to detect carrier phase and modulation delay differences between the model and the signal;
• changing the first portion of said number in response to detected carrier phase differences to maintain carrier phase lock between the model and the received signal;
• changing the second portion of said number in response to variations of a selected magnitude in the first portion of said number and in response to detected modulation delay differences between the model and the received signal to maintain modulation delay lock between the model and the received signals;
• and
• deriving range information from the range estimate.

A system for deriving range information from a modulated suppressed carrier signal being received from a GPS satellite, comprising:

• means for generating a range estimate in the form of a number having a first portion and a second portion;
• means for generating a model of the received signal in response to said range estimate, said model having a carrier component which is generated in response to the first portion of said number, and a modulation component which is generated in response to the second portion of said number;
• means for correlating the model with the received signal to detect carrier phase and modulation delay differences between the model and the signal;
• means for changing the first portion of said number in response to detected carrier phase differences to maintain carrier phase lock between the model and the received signal;
• means for changing the second portion of said number in response to variations of a selected magnitude in the first portion of said number and in response to detected modulation delay differences between the model and the received signal to maintain modulation delay lock between the model and the received signal;
• and
• means for deriving range information from the range estimate.