Round-trip phase ranging in the presence of deep fade

A first apparatus comprising:

• at least one transceiver;
• at least one memory;
• and
• at least one processor, communicatively coupled to the at least one transceiver and the at least one memory, configured to:
• transmit, via the at least one transceiver, a plurality of first signals with each having a respective frequency of a plurality of frequencies spanning a frequency band of interest;
• receive, via the at least one transceiver, first phase measurement information at the first apparatus from a second apparatus, the first phase measurement information corresponding to a phase measurement of each of the plurality of first signals;
• receive, via the at least one transceiver from the second apparatus, a plurality of second signals with each having a respective frequency of the plurality of frequencies;
• measure phase of each of the plurality of second signals to obtain second phase measurement information;
• determine a plurality of product channels, corresponding to the plurality of frequencies, by multiplying the first phase measurement information by the second phase measurement information for each of the plurality of frequencies;
• determine at least one deep-fade frequency, of the plurality of frequencies, that corresponds to deep fading;
• determine a plurality of sub-bands within the frequency band of interest based on the at least one deep-fade frequency;
• determine a plurality of root channels each corresponding to a respective one of the plurality of sub-bands;
• and
• determine a range estimate based on the plurality of root channels, the range estimate being an estimate of a distance between the first apparatus and the second apparatus.

A first apparatus comprising:

• means for transmitting a plurality of first signals with each having a respective frequency of a plurality of frequencies spanning a frequency band of interest;
• means for receiving first phase measurement information from a second apparatus, the first phase measurement information corresponding to a phase measurement of each of the plurality of first signals;
• means for receiving, from the second apparatus, a plurality of second signals with each having a respective frequency of the plurality of frequencies;
• means for measuring phase of each of the plurality of second signals to obtain second phase measurement information;
• means for determining a plurality of product channels, corresponding to the plurality of frequencies, by multiplying the first phase measurement information by the second phase measurement information for each of the plurality of frequencies;
• means for determining at least one deep-fade frequency, of the plurality of frequencies, that corresponds to deep fading;
• means for determining a plurality of sub-bands within the frequency band of interest based on the at least one deep-fade frequency;
• means for determining a plurality of root channels each corresponding to a respective one of the plurality of sub-bands;
• and
• means for determining a range estimate based on the plurality of root channels, the range estimate being an estimate of a distance between the first apparatus and the second apparatus.