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Global Positioning System: Difference between revisions
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Receivers that have the correct decryption key can relatively easily decode the P(Y)-code transmitted on both L1 and L2 to measure the error. Receivers that do not possess the key can still use a process called ''codeless'' to compare the encrypted information on L1 and L2 to gain much of the same error information. However, this technique is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies. When these become operational, non-encrypted users will be able to make the same comparison and directly measure some errors. | Receivers that have the correct decryption key can relatively easily decode the P(Y)-code transmitted on both L1 and L2 to measure the error. Receivers that do not possess the key can still use a process called ''codeless'' to compare the encrypted information on L1 and L2 to gain much of the same error information. However, this technique is currently limited to specialized surveying equipment. In the future, additional civilian codes are expected to be transmitted on the L2 and L5 frequencies. When these become operational, non-encrypted users will be able to make the same comparison and directly measure some errors. | ||
A second form of precise monitoring is called '''Carrier-Phase Enhancement''' (CPGPS). The error, which this corrects, arises because the pulse transition of the | A second form of precise monitoring is called '''Carrier-Phase Enhancement''' (CPGPS). The error, which this corrects, arises because the pulse transition of the PRN is not instantaneous, and thus the [[cross-correlation|correlation]] (satellite-receiver sequence matching) operation is imperfect. The CPGPS approach utilizes the L1 carrier wave, which has a [[Periodicity|period]] 1000 times smaller than that of the C/A bit period, to act as an additional [[clock signal]] and resolve the uncertainty. The phase difference error in the normal GPS amounts to between 2 and 3 meters (6 to 10 ft) of ambiguity. CPGPS working to within 1% of perfect transition reduces this error to 3 centimeters (1 inch) of ambiguity. By eliminating this source of error, CPGPS coupled with [[Differential GPS|DGPS]] normally realizes between 20 and 30 centimeters (8 to 12 inches) of absolute accuracy. | ||
'''Relative Kinematic Positioning''' (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to an accuracy of less than 10 [[centimeters]] (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time ([[Real Time Kinematic|real-time kinematic positioning]], RTK). | '''Relative Kinematic Positioning''' (RKP) is another approach for a precise GPS-based positioning system. In this approach, determination of range signal can be resolved to an accuracy of less than 10 [[centimeters]] (4 in). This is done by resolving the number of cycles in which the signal is transmitted and received by the receiver. This can be accomplished by using a combination of differential GPS (DGPS) correction data, transmitting GPS signal phase information and ambiguity resolution techniques via statistical tests—possibly with processing in real-time ([[Real Time Kinematic|real-time kinematic positioning]], RTK). | ||
