An apparatus and method for improved locationing system performance in non-line of sight conditions of a mobile device within an environment includes providing a model of the environment that maps transmitters within and objects that obstruct signals from the transmitters, including mapped areas where the signal from a nearby transmitter is obstructed. A location of a device moving within the environment is tracked using the signals. When it is determined that the device is moving into a mapped area having an obstructed signal from a nearby transmitter, a locationing system parameter is modified for that obstructed signal so that the mobile communication device can be located using at least the modified signal parameter.