In the attitude measurement using GPS carrier phase, in order to achieve high accuracy, it is necessary to ensure that there is no carrier phase cycle slip in the observation data. Therefore, the correct detection and repair of cycle slip is a key problem in GPS data processing. Current cycle slip detection The methods mainly include polynomial fitting method, pseudorange phase combination method and ionospheric residual method. These methods can detect and repair non-poor integer ambiguity, but these methods have their own limitations: polynomial fitting method can generally only detect The cycle slip is greater than 5 weeks, which cannot meet the requirements for high-precision attitude measurement systems. The detection capability of the pseudo-range phase combination method depends on the accuracy of the pseudo-range observation. Generally, the receiver needs to be able to output the P code pseudo-range. The single frequency receiver is not suitable; the ionospheric residual method is one of the best cycle slip detection methods at present, but it requires the carrier phase observation of the two frequencies of LUL2 and cannot be applied to the single frequency receiver.
In the GPS attitude system, in order to eliminate additional observation errors, such as ionospheric error, tropospheric error, ephemeris error receiver clock error, etc., the carrier phase double difference information is generally used as an observation. In this paper, GPS attitude using a single frequency receiver The problem of cycle slip detection and repair in the double-difference carrier phase observation in the system was studied. First, a method for cycle slip detection and repair based on extrapolation was applied in static situations, and an active, The detection and repair method of cycle slip based on redundant double-difference measurement can be used in static situations, and the experimental results and analysis are given for the two methods.
1 Cycle slip detection and repair method based on extrapolation method In a static situation, the receiver is stationary, only the movement of the satellite. Since the satellite is far away from the receiver on the earth, the movement of the satellite around the earth can be considered to be uniform. The change of carrier phase observation value with time is smooth and regular, and cycle slip will destroy this regularity. According to this characteristic, using the previous observations to extrapolate the estimated value of the phase observation at the current time, and according to whether the difference between the actual observation value and the corresponding extrapolation value is greater than a threshold value, it can be determined whether the current observation value contains a cycle slip. For double-difference observations, since the satellite ephemeris error and atmospheric propagation delay error have been greatly weakened, it is easier to obtain better results using this method. The difference carrier phase observations are, -i, a2, and 1, tk-2 The double-difference carrier phase observations at two moments have no cycle slip, then the carrier phase estimation value at tk can be obtained by extrapolation from the double-difference carrier phase observations at tk-1 and tk-2. If the double difference is at tk If there is no cycle slip in the observation, the ALk value is very small, but as long as one of the two satellites forming the double difference produces a cycle slip, resulting in the cycle slip in the double difference observation, the ALk value will be greater than a wavelength X (about 0.19m ) If a cycle slip occurs, the amount of cycle slip can be obtained by the following formula, where the symbol indicates the integer closest to X.
Two GG24 receivers conducted static experiments, and the main star was selected as PRN19, which is a double-differential measurement week without cycle slips. Therefore, this method can detect all cycle slips in the static state. Because people walk around the antenna, the satellite PRN3 Both PRN27 and PRN27 produced week 5 hops, 3 is the AL calculated from the double-difference measurement of the two satellites and the host star. Table 1 lists the results of detecting and repairing the cycle slip. * In the table indicates that the program detected And the week slip value after repair.
Table 1 Whole week ambiguity cycle slip detection and repair results based on extrapolation method Satellite No. 2 Cycle slip detection and repair method based on redundant double-difference measurement Cycle slip detection and repair method based on extrapolation method is very effective at static time Well, under dynamic conditions, due to the random nature of the carrier movement, the effect is not good. This paper proposes a method of cycle slip detection and repair based on redundant double difference observation based on GPS carrier phase. This method can be applied to dynamic conditions, provided that at least 4 satellites in adjacent epochs are locked and the ambiguity of the whole cycle At fixed time t, there are n satellites in use, the baseline vector is b (t), the ambiguity of the whole cycle is N, the double-difference carrier phase observation equation is entered as the carrier wavelength; H is the direction cosine array under the geographic system; V Observe the noise for the carrier phase double difference.
When the ambiguity N of the whole cycle is correctly solved, if no cycle slip occurs, N remains unchanged. The least square method can be used to obtain the baseline vector of each epoch and the baseline length during the observation process. If N1, N2, N3 Three double-difference full-week ambiguities without cycle slip are used, and when a cycle slip occurs, this method can clearly detect the occurrence of cycle slip = by looking for 4 satellites without cycle slip, and then find the double satellites of the remaining satellites The method of difference ambiguity can obtain the same cycle slip detection results as in Table 2 (threshold X is 0. 02m in the experiment). The results show that the redundant double difference measurement method can detect and correctly repair all occurrences of the week in the experiment jump.
Baseline length error when a cycle slip occurs. Due to the fact that the cycle slip situation is complicated in practice, it is difficult to find a method that is suitable for the detection and repair of cycle slip in all cases. This paper proposes two types of cycle slip for single-frequency GPS receivers. The detection and repair methods can deal with the cycle slip problem under certain circumstances, but each has its own shortcomings. The cycle slip detection and repair method based on extrapolation can only be applied to static conditions, and can detect and repair static All cycle slips; the cycle slip detection and repair method based on redundant double-difference measurement can be applied to dynamic and static conditions after the entire week ambiguity has been fixed correctly, but requires more than 4 adjacent epochs Satellite no cycle slip comprehensively uses the two methods proposed in this article in the GPS attitude system developed by the author, and achieves good results.
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