# LSOS: An FG Position Method Based on Group Phase Ranging Ambiguity Estimation of BeiDou Pseudolite
## 1 Introduction
In previous tests, the team's Dr. [PERSON] proposed a location method based on Doppler's difference [20; 21], but it is difficult to apply in large-scale space due to the constraint of initial location points. It is also difficult to popularize the pseudo-satellite positioning technology due to the heavy workload in the large-scale space. In the same way, the fingerprint localization [22] method proposed by Dr. [PERSON] faces a huge workload when applied in large-scale space, which is not conducive to the popularization of pseudo-satellite positioning technology. Although several typical schemes have been applied to the study of the carrier phase ambiguity estimation in indoor environment, there are still some problems in the comprehensive analysis. The main problems are as follows:  
1. The ambiguity estimation in the difference mode is based on the short baseline and is affected by the multipath signals of indoor reflectors. In general, the effectiveness of the difference information is limited to the local finite view-through space. It is not suitable for complex space application with indoor grid. 2. In indoor spaces, the direct propagation distance of pseudo-satellite signal is limited. Affected by the range error of receiver from 3 to 10 m, the user can not realize the initial position estimation by the least square algorithm with the pseudo-range information obtained directly. 3. The carrier phase space ambiguity search process of RTK is based on the continuous epoch without cycle slip, which usually needs to consider the setting of the search space. Assuming that there are L integers in the whole-cycle search space for each set of observations, \((m-1)^{L}\) times are required for the whole-cycle search space. The large amount of computation and the long estimation time make it difficult for the user to fix the ambiguity quickly when the indoor continuous grid space is switched. 4. Due to the complexity of indoor physical space environments, shielding of moving bodies and strong reflection effect of adjacent reflectors will lead to frequent cycle slip phenomenon of the user receiver. The ambiguity of the integer needs to be re-estimated for each cycle slip, which is not conducive to the fast deblurring of measurement. Thus, it can be seen that it is difficult to provide good ranging accuracy for indoor location estimation based on the current carrier phase ambiguity estimation method. Therefore, the question concerning how to solve the high-precision ranging problem is the key to realize the absolute positioning in LSOS. In response to this problem, the main work of this article is as follows: In the second chapter, as the key of BeiDou pseudo-satellite phase feature extraction and group phase feature ranging application, the basic theory of BeiDou pseudo-satellite network platform is introduced. In the third chapter, according to the multi-frequency characteristics of BeiDou pseudolite, the phase quantization period theory and the phase whole cycle estimation process are described in detail. In the fourth chapter, the performance of the proposed method is analyzed in detail from two aspects of measurement and simulation. Finally, on the basis of the existing results, we summarize the technical advantages of the current method and provide some follow-up research directions.