Likelihood-based acoustic positioning

A positioning system comprising a plurality of acoustic transmitter units, a mobile device, and a processing system, wherein the processing system is configured:

• to receive a first position estimate for the mobile device;
• to receive data representative of an acoustic signal received by the mobile device from one of the plurality of acoustic transmitter units that are configured to transmit respective acoustic signals at intervals;
• for each of the plurality of acoustic transmitter units, to determine spatial likelihood data representative of a likelihood of the received acoustic signal having been transmitted by the respective acoustic transmitter unit by comparing i) a time-of-flight range value, determined from a time of arrival of the received acoustic signal at the mobile device and scheduling data representative of a time of transmission of an acoustic signal by the respective acoustic transmitter unit, with ii) a geometric distance value, representative of a distance between the respective acoustic transmitter unit and the first position estimate;
• to process the spatial likelihood data to identify a strict subset of one or more of the plurality of acoustic transmitter units;
• and
• to process information relating to positions of the acoustic transmitter units in the strict subset and/or relating to the acoustic signals transmitted by the acoustic transmitter units in the strict subset to determine a second position estimate for the mobile device;
• wherein the processing system is configured to:
• identify the strict subset such that each acoustic transmitter unit in the strict subset has a higher likelihood of having transmitted the acoustic signal received by the mobile device than at least one acoustic transmitter unit, of the plurality of acoustic transmitter units, that is not in the strict subset;
• or
• determine the second position estimate, after identifying the strict subset of one or more acoustic transmitter units, without using information relating to a position of any of the acoustic transmitter units that is not in the strict subset and without using information relating to the acoustic signals transmitted by any of the acoustic transmitter units that is not in the strict subset;
• or
• determine the spatial likelihood data for each acoustic transmitter unit by comparing the respective time-of-flight range value with a respective statistical distribution, representative of likelihood against range, that has an expected value equal to the geometric distance value for the respective acoustic transmitter unit.

A non-transitory computer-readable storage medium storing computer software comprising instructions that, when executed by a processing system, cause the processing system:

• to receive a first position estimate for a mobile device;
• to receive data representative of an acoustic signal received by the mobile device from one of a plurality of acoustic transmitter units that are configured to transmit respective acoustic signals at intervals;
• for each of the plurality of acoustic transmitter units, to determine spatial likelihood data representative of a likelihood of the received acoustic signal having been transmitted by the respective acoustic transmitter unit by comparing i) a time-of-flight range value, determined from a time of arrival of the received acoustic signal at the mobile device and scheduling data representative of a time of transmission of an acoustic signal by the respective acoustic transmitter unit, with ii) a geometric distance value, representative of a distance between the respective acoustic transmitter unit and the first position estimate;
• to process the spatial likelihood data to identify a strict subset of one or more of the plurality of acoustic transmitter units;
• and
• to process information relating to positions of the acoustic transmitter units in the strict subset and/or relating to the acoustic signals transmitted by the acoustic transmitter units in the strict subset to determine a second position estimate for the mobile device;
• wherein the instructions executed by the processing system cause the processing system to:
• identify the strict subset such that each acoustic transmitter unit in the strict subset has a higher likelihood of having transmitted the acoustic signal received by the mobile device than at least one acoustic transmitter unit, of the plurality of acoustic transmitter units, that is not in the strict subset;
• or
• determine the second position estimate, after identifying the strict subset of one or more acoustic transmitter units, without using information relating to a position of any of the acoustic transmitter units that is not in the strict subset and without using information relating to the acoustic signals transmitted by any of the acoustic transmitter units that is not in the strict subset;
• or
• determine the spatial likelihood data for each acoustic transmitter unit by comparing the respective time-of-flight range value with a respective statistical distribution, representative of likelihood against range, that has an expected value equal to the geometric distance value for the respective acoustic transmitter unit.