GPS+BDS pseudorange single point positioning computation problem

I would like to ask a question to all the experts in the community. My MATLAB version is 24.2.0.2712019 (R2024b).This compressed package contains an observation file, a navigation file, a ground truth file,and a meteorological file. These files can be used to perform a GPS+BDS single-frequency pseudorange single point positioning (SPP) calculation.

I have attempted to complete this task using MATLAB. However, due to my limited background in GNSS navigation and my relatively weak programming skills, the receiver coordinates obtained from my solution appear to be incorrect. The estimated latitude and longitude show some discrepancy compared with the reference truth values, while the height error is significantly larger.

I would appreciate any help in reviewing the processing workflow, positioning model, and MATLAB implementation to identify potential issues and improve the positioning accuracy.