A system and method for using a portable device to communicate with a vehicle to authorize one or more vehicle operations. The portable device may authorize the vehicle to unlock/lock doors, start the vehicle engine, or mobilize the vehicle, or a combination thereof. The vehicle may include a vehicle transmitter system with one or more transmitters disposed at various locations on the vehicle, and the portable device may be configured to monitor a communication strength between the portable device and the one or more transmitters of the transmitter system. Based on the monitored signal strength, the portable device may determine location information about itself.