# LSOS: An FG Position Method Based on Group Phase Ranging Ambiguity Estimation of BeiDou Pseudolite
## 1 Introduction
\tag{2}\]  
From the above equation, it can be found that the distance difference between channels becomes a function related only to the true distance and the integer ambiguity of the signal. The formula contains M \(-\) 1 single-difference integer ambiguity and 3D user coordinate vector. M + 2 unknowns are actually larger than the number of observed equations. If we want to get the current position, we must complete the whole-cycle estimation process [6; 7]. This process mainly includes initial position setting, search space selection, and ambiguity search strategy. However, there is relatively little research on the issue of fast carrier phase ambiguity estimation of pseudolite in indoor space. Here, we refer to the scientific research results published by domestic and foreign experts and scholars in the past decade. The Wuhan University team of Dr. [PERSON] has carried out some deep research on the problem of rapid ambiguity fixation in indoor space. Dr. [PERSON]'s team developed a double-difference ambiguity fixation model and verified its performance by setting up a test environment in the laboratory. Furthermore, [PERSON] proposed a new indoor pseudolite positioning method using the combination of a robust unscented Kalman filter (RUKF) and partial AR (PAR) to improve the reliability of the position [8; 9]. [PERSON] and [PERSON] propose a projected cancellation (PC) technique. This method can effectively improve the influence of nonlinear error by pseudo-range single difference according to the relationship between the base station and the user's virtual site. This method effectively improves the convergence speed of the traditional algorithm [10]. Dr. [PERSON]'s team proposes a technique for constructing an autonomous coordinate system without prior reference points. Through the fuzzy estimation of a three-step position estimation process, this method achieves the high precision positioning of the transmitter station in centimeter-level [11]. Using the existing four GNSS antenna platforms, Dr. [PERSON] proposed a baseline-constrained ambiguity function method. This method can effectively improve the unreliable or inaccurate estimation solution of RTK localization, and further directly assist the estimation of altitude direction [12; 13; 14; 15]. Professor [PERSON] of the Japanese Waseda University has been working on indoor pseudolite for many years and has extensive experience in rapid RTK positioning. In order to realize centimeter-level high-precision positioning in indoor environments, [PERSON] proposed a doppler RTK attitude estimation method based on the relative motion of two antennas. The position and attitude of the user terminal can be calculated by means of doppler shifts and phase measurement between the receiver antennas and transmitters [16; 17; 18]. Dr. [PERSON]'s team of Zhejiang University of Science and Technology proposed a carrier ambiguity resolution method based on the combination of pseudolite and UWB [19]. By using the high-precision ranging characteristic of UWB, the initial ambiguity of pseudolite is fixed. At present, research concerning integer ambiguity estimation is mainly based on the GNSS spatial signal. It is still less in the field of indoor location. Both Wuhan University and Seoul University have proposed a method to solve integer ambiguity quickly by using indoor RTK, which has achieved good positioning results in the experimental environment. Japanese Waseda University have developed a doppler-assisted fast ambiguity fixation method that provides cm-level positioning accuracy in indoor scenes. But according to the test data in the paper, the test is mainly carried out in slow motion, and the data is relatively stable. After the carrier phase cycle slips appear, the proposed method can't complete the fast ambiguity estimation. Not conducive to the protection of positioning continuity.