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Introduction to GPS The Global Positioning System - Part 6

Ambiguity-Resolution Techniques Chương trước đã cho thấy rằng độ chính xác cm cấp định vị có thể đạt được với các quan sát tàu sân bay giai đoạn trong chế độ định vị tương đối. Một điều kiện tiên quyết này, tuy nhiên, việc xác định thành công của các tham số không rõ ràng ban đầu số nguyên (trên thực tế, sự khác biệt không rõ ràng các thông số tăng gấp đôi số nguyên). Quá trình này thường được gọi là độ phân giải không rõ ràng. Giải quyết các thông số không rõ ràng một cách chính xác. | 6 Ambiguity-Resolution Techniques The previous chapter showed that centimeter-level positioning accuracy could be achieved with the carrier-phase observables in the relative positioning mode. A prerequisite to this however is the successful determination of the initial integer ambiguity parameters in fact the integer double-difference ambiguity parameters . This process is commonly known as ambiguity resolution. Resolving the ambiguity parameters correctly is equivalent to having very precise ranges to the satellites which leads to high-accuracy positioning 1 . The ambiguity parameters are initially determined as part of the leastsquares or Kalman filtering solution 2 3 . Unfortunately however neither method can directly determine the integer numbers of the ambiguity parameters. What can be obtained are the real-valued numbers along with their uncertainty parameters so-called covariance matrix only. These real-valued numbers are in fact difficult to separate from the baseline solution 4 . As such since we know in advance that the ambiguity parameters are integer numbers it becomes clear that further analysis is required. Traditionally high-precision GPS relative positioning with carrierphase observables was carried out using long observational time spans typically a few hours . This allows for the receiver-satellite geometry to 85 86 Introduction to GPS change considerably which helps in separating the ambiguity parameters from the baseline solution. As such even though the least-squares solution would contain real-valued numbers for the ambiguity parameters they were very close to integer values. Consequently the correct integer values were simply obtained by rounding off the real-valued numbers to the nearest integers 4 . Another least-squares adjustment was then to be carried out considering the integer-valued ambiguity parameters as known values while the baseline components are unknowns. It is clear that although this method is capable of determining the .