TCAR (three carrier ambiguity resolution)

Three Carrier Ambiguity Resolution (TCAR) is a technique used in Global Navigation Satellite Systems (GNSS) to resolve the integer ambiguities associated with carrier-phase measurements from three satellite carriers. It is employed to enhance the accuracy and reliability of positioning in GNSS applications.

Here are the key aspects and features of Three Carrier Ambiguity Resolution (TCAR):

1. Integer Ambiguities: In GNSS positioning, carrier-phase measurements are used to calculate the precise distance between a receiver and multiple satellites. However, these carrier-phase measurements contain an unknown integer number of cycles, referred to as the integer ambiguities. Resolving these ambiguities is crucial for achieving centimeter-level accuracy in positioning.
2. Three Carrier Approach: TCAR utilizes carrier-phase measurements from three satellite carriers to resolve the integer ambiguities. By employing three carriers, the ambiguity resolution process becomes more reliable and robust compared to using fewer carriers. It improves the success rate of ambiguity resolution and enhances the precision of GNSS positioning.
3. Carrier-Phase Observations: GNSS receivers measure the phase of the carrier wave transmitted by the satellites. These carrier-phase observations are highly precise and provide accurate information about the distance between the receiver and the satellites. However, the integer number of cycles in the carrier-phase measurements needs to be determined for accurate positioning.
4. Geometry and Baseline Length: The geometry of the satellite constellation and the baseline length, which represents the distance between the GNSS receivers, play a crucial role in TCAR. The relative positions of the satellites and the baseline length influence the quality of the carrier-phase measurements and affect the success rate of ambiguity resolution.
5. Least Squares Estimation: TCAR employs least squares estimation techniques to estimate the integer ambiguities from the carrier-phase measurements. The least squares method determines the most likely values of the integer ambiguities that best fit the carrier-phase observations, considering the known baseline length and the geometry of the satellites.
6. Integer Ambiguity Search Space: The ambiguity search space refers to the set of possible values for the integer ambiguities. The TCAR process involves searching the integer ambiguity search space and finding the integer values that yield the most accurate positioning solution. This search can be performed through exhaustive search algorithms or more efficient methods such as the Successive Interference Cancellation (SIC) technique.
7. Benefits and Applications: TCAR improves the accuracy and reliability of GNSS positioning, especially in Real-Time Kinematic (RTK) applications where centimeter-level precision is required. It is utilized in surveying, precision agriculture, geodetic positioning, autonomous vehicle navigation, and other applications that demand highly accurate and reliable positioning information.

TCAR is a vital technique in GNSS positioning to resolve the integer ambiguities associated with carrier-phase measurements. By employing carrier-phase observations from three satellite carriers, TCAR enhances the accuracy and reliability of positioning solutions, enabling precise and reliable positioning in a variety of GNSS applications.