GNSS NLOS Signal Modeling and Quantification Method in Railway Urban Canyon Environment

Global Navigation Satellite System (GNSS) performance varies in different environments, accuracy as the fundamental KPI depends on various factors, such as satellite orbit error, signal propagation delay in ionosphere and troposphere, and most importantly the effects on the ground as multipath. In railway train operation scenarios, the trains are travelling on the track passing through various environment scenarios, in several environment scenarios such as urban canyon, the GNSS signal can be easily blocked and reflected by the tall buildings and skyscrapers, which heavily reduces satellite visibility and satellite geometry. The multipath effect especially the non-line-of-sight (NLOS) signals will bring significant errors in user location solution. This paper proposes a GNSS NLOS signal propagation modeling method to evaluate the GNSS signal propagation path in the railway urban canyon environment near Shenyang North Railway Station. A 3D environment model is established, and a ray tracing technique is applied to model the signal propagation path, using the model and signal path, the results are used to evaluate and quantify the errors included in the NLOS signal. A field test is carried out as a performance comparison to the proposed method, the results showed that the simulation errors are consistent with the results in real environment field test, but the positioning results of field test is better than simulation results due to the receiver filtering algorithm inside the GNSS receivers.