A communication system comprises a base station (104) positioned in the vehicle (102) and a mobile communication unit (122). The base station (104) is configured to determine a first location and a second location of the mobile communication unit (122) relative to the vehicle (102), and to determine a baseline pattern of movement of the mobile communication unit (122) based at least in part on the first location and the second location. The base station (104) is also configured to determine whether a user-initiated interaction with the vehicle (102) occurs in connection with the baseline pattern of movement, and if no user-initiated interaction with the vehicle (102) occurs in connection with the baseline pattern of movement, to classify the baseline pattern of movement as an incidental pattern of movement and apply a zone adjustment to the authorization zone (138) so as to exclude to the incidental pattern of movement.