1. A navigation unit for use by a user, comprising: at least one sensor; a processing unit coupled to the sensor, wherein the processing unit generates navigation-related output derived at least in part on information output by the sensor; and a wireless interface coupled to the processing unit, wherein when the navigation-related output is transmitted from the navigation unit to a portable device being used by the user over a wireless communication link, the wireless interface transmits the navigation-related output to the portable device over the wireless communication link; wherein the portable device comprises at least one of a time difference of arrival interface, a time of arrival interface, or a global position receiver, wherein at least one of time difference of arrival information, time of arrival information, or global position system information is transmitted to the navigation unit over the wireless communication link; wherein the navigation unit receives the at least one of time difference of arrival information, time of arrival information, or global position system information for use by the navigation unit in generating the navigation-related output; and wherein the navigation unit is configured to be carried by the user.