Passive keyless entry system

A vehicle-based communication system for a vehicle includes a vehicle-based electronic control unit disposed within an interior structure of the vehicle for passively controlling entry to the vehicle. At least a portion of the vehicle-based electronic control unit and at least a portion of the interior structure are unshielded at low electromagnetic frequencies. A housing encloses the vehicle-based electronic control unit. A transmitter is disposed within the electronic control unit for generating a wake-up signal. A single antenna is integrated within the electronic control unit for transmitting the wake-up signal to a respective portable communication device exterior of the vehicle. The wake-up signal challenges the respective portable communication device for determining a presence of the portable communication device for allowing access to the vehicle.