RTK + 4G Combination Positioning Method Under Sheltered Environment for High-Accuracy of MMS

The accuracy of the existing positioning methods is not sufficiently ideal in mobile mapping system (MMS) when GPS signals are sheltered by such as tall buildings, mountain peaks. To solve this problem, this paper presents a new positioning method through RTK (Real-time kinematic) + 4G (4th generation mobile communication technology) combination. This method is divided into two positioning modes: GNSS positioning mode and 4G positioning mode. Under normal conditions, the system operates in the GNSS positioning mode with the GNSS satellite signals and performs differential correction to obtain the precise position coordinates. When the system is under the sheltered environment, or the number of satellite signals receivable are less than 4, it switches to the 4G positioning mode. This means that the proposed positioning mode obtains the raw position coordinates by receiving the radio signals from the 4G base station and iteratively compute the coordinates using the UKF (Unscented Kalman Filter). Finally, a system, consisting of both software and hardware, was developed and constructed, and accuracy verification experiments are conducted under a variety of the sheltered environments. With the experimental results, it can be demonstrated that the developed system runs in a good working condition and the error of positioning is less than 0.1m when GNSS signal are sheltered.