Two pass detection technique for non-echo pulsed ranging

A system for non-echo pulsed ranging, the system comprising:

• a plurality of emitters at fixed locations within an environment, the emitters operable to transmit signal pulses of a predefined frequency;
• and
• a mobile device operable to:
• receive at least one of the signal pulses from the plurality of emitters,
• convert the at least one of the signal pulses into a digital waveform,
• store the digital waveform into a buffer having a predetermined length of time, and
• perform a first analysis to analyze the digital waveform to detect a detected signal pulse at the predefined frequency;
• wherein if the detected signal pulse is detected, the mobile device is further operable to perform a second analysis to re-analyze the digital waveform to attempt to detect another signal pulse at the predefined frequency, a presence of the another signal pulse indicating an existence of a reflected signal pulse, and
• wherein if the another signal pulse is detected, the mobile device is further operable to select a selected signal pulse that was received first in time for use in ranging of the mobile device, the selected signal pulse being one of the detected signal pulse or the another signal pulse.