Signal simulations in urban environments

In this paper we use a realistic channel model (ITU-R 681-7) to realistically simulate multipath and fading conditions in an urban environment. From these simulations we have found three major conclusions: The receiver performance is very dependent on the used signal in space. It turns out that for this difficult environment the narrow band signals such as GPS C/A and BOC (1,1) can be robustly tracked by the receivers while the wideband signals such as GPS L2, L5, GALILEO E5b, and E5 are causing the loss of tracking. This behavior can be explained by the fact, that the wideband signals are designed suppress multipath components of the signal. If the LOS is then shadowed too little signal power is left to track these signals. Furthermore it can be seen that BOC (1,1) clearly outperforms the GPS C/A signal. A comparison of different receivers has been carried out: A classical narrow correlation DLL, a DLL using a double delta correlator, a multipath estimating DLL and a particle filter based receiver have been compared. In this difficult environment the particle filter receiver showed the best performance followed by the MEDLL and the classical DLLs. Last but not least a critical situation for a DLL receiver has been envisaged: The "short line of sight hit" (SLOSH) - a situation where the receiver is faced wit a LOS with a short duration after a shadowing period can mislead the DLLs integrators and cause a loss of lock.