GNSS Software Simulation System for Realistic High-Multipath Environments

Kurzfassung

Compared to the various effects which degrade GNSS performance in general, nowadays multipath propagation accounts for the most dominant error in satellite navigation. Other error sources like satellite clock deviation and atmospheric effects for example can be compensated to a certain degree by the use of high-stability timing equipment (as for example the hydrogen maser in GIOVE-B represents), SBAS corrections, multi-frequency Galileo ranging and pilot signals, and the future availability of civil signals with a higher bandwidth than the currently available C/A code signal. Especially in high-multipath environments like urban and suburban areas, the performance of GNSS receivers is severely affected by multipath propagation. Extensive measurement campaigns were undertaken in 2005 by the German Aerospace Center (DLR) for different scenarios such as the vehicular urban, sub-urban, and rural environments, and the pedestrian use case to record and model effects caused by multipath signal reception. These measurement campaigns lead to the availability of sophisticated channel models consisting of combined stochastic and deterministic parts that allow for the investigation of multipath effects on GNSS receiver performance. These realistic channel models provide series of channel impulse responses (CIR) as outputs where the plethora of distinct echoes in urban scenarios is represented by Dirac impulses at quasi time-continuous instants. However, the application of such time-continuous CIRs to an accurate GNSS signal propagation simulation proves to be a demanding task due to the high sampling rates which are necessary to cover the channel's complexity. Before the time continuous CIRs can be applied in a simulation they have to be adjusted to fit to the time discrete sampling instants. This process is done using low-pass interpolation with a sinc function. The presented work introduces a modular C++ framework that is able of reproducing the harsh conditions of urban environments in a very precise manner. This new efficient and flexible software tool implements the whole GNSS simulation chain consisting of “signal generation – channel model – receiver” in time-domain as a sample-true simulation. The software’s main features are given after a description of the DLR GNSS urban channel model. Additionally the interpolation process of transforming the time-continuous channel impulse responses to FIR coefficients is outlined. Eventually, a demonstration of simulation runs using the urban channel model, a BOC(1,1), and a CBOC signal is given.