MEMS IMU/ODO-Aided GNSS Long Coherent Integration PLL for Urban Vehicle Precise Positioning

Global Navigation Satellite System (GNSS) carrier phase measurement is highly vulnerable to signal attenuation, multipath and blockage in urban environments, which significantly degrades the availability of precise GNSS positioning. Long coherent integration (LCI) serves as an effective approach to suppress thermal noise and mitigate multipath interferences within phase-locked loops (PLLs); however, its performance is constrained by the dynamic stress resulting from satellite-receiver motions. This study proposes a GNSS/INS/ODO deeply coupled (GIO-DC) system with LCI phase-locked loops. An Odometer (ODO) distance increment measurement model is integrated with a MEMS IMU to estimate and compensate for the PLLs’ dynamic stress with enhanced accuracy and reliability, thereby enabling extended coherent integration time. In addition, a four-quadrant phase discriminator is adopted to expand the PLL pull-in range and reduce the likelihood of cycle slips. Field tests on a wheeled vehicle in typical urban complex environments were conducted to evaluate the performance of the GIO-DC system from multiple perspectives. The results confirmed the superiority of the proposed approaches. A coherent integration time of 800 milliseconds was achieved, realizing continuous carrier phase measurement and robust centimeter-level positioning. The proposed deeply integrated system, built on the low-cost MEMS IMU and ODO, delivers performance on par with that of a system based on a navigation-grade IMU.