Ray-Tracing Correction for GNSS Velocity Estimation Using Doppler Frequency: A Feasibility Analysis

Accurate positioning from the global navigation satellite system (GNSS) is critical for various civil applications, such as location-based services (LBSs) and intelligent transportation systems (ITSs). GNSS Doppler frequency can provide reliable velocity estimation to improve the positioning performance. Unfortunately, the quality of Doppler frequency measurements can be significantly degraded in urban canyons. This is due to the non-line-of-sight (NLOS) receptions altering the incoming signal direction and its dynamic characteristics. Thus, correcting the NLOS error on Doppler frequency is essential for the velocity as well as position estimation in urban canyons. The 3-D mapping-aided (3DMA) GNSS is a promising technique for NLOS error correction. Its effectiveness on pseudorange measurements has been well proven. However, its feasibility on Doppler frequency correction has not been investigated yet. Therefore, this article first verifies the feasibility of ray tracing in modeling Doppler frequency. Then, an urban Doppler frequency assessment is conducted. Finally, the effectiveness of ray tracing in correcting velocity estimation accuracy is evaluated. The assessment and evaluation assessment are conducted via experiments in both open-sky and urban areas. The results demonstrate that ray tracing has an excellent capability in modeling the NLOS Doppler frequency, which reduces the corresponding measurement error by 62.8% in average and the root-mean-square (RMS) of velocity estimation error by 51.92%.