System and method for navigation using two-way ultrasonic positioning

A method of operating a positioning system having a plurality of objects each configured to transmit and receive ultrasonic signals, comprising

• transmitting an initiating ultrasonic signal from a first one of the plurality of objects, the initiating ultrasonic signal being accompanied by a radio frequency signal triggering a second one of the plurality of objects to receive the initiating ultrasonic signal;
• transmitting a responding ultrasonic signal from the second one of the plurality of object;
• receiving the responding ultrasonic signal at the first one of the plurality of objects;
• and
• determining a distance between the first one and the second one of the plurality of objects based on a time period starting at the transmission of said initiating ultrasonic signal and ending at the reception of said responding ultrasonic signal.

An ultrasonic positioning system, comprising:

• a plurality of objects each configured to transmit and receive ultrasonic signals, a number of the plurality of objects being greater than 2;
• a first ultrasonic array positioned on a first one of the plurality of objects and configured to transmit initiating ultrasonic signals, each initiating ultrasonic signal including a code that identifies another one of the plurality of objects for responding to the initiating ultrasonic signal;
• a second ultrasonic array positioned on a second one of the plurality of objects and configured to respond to an initiating ultrasonic signal coded to identify the second one of the plurality of objects by transmitting a responding ultrasonic signal after a predetermined time delay from receiving an initiating ultrasonic signal;
• and
• wherein the first ultrasonic array is configured to receive the responding ultrasonic signal, and is coupled to a timer that records a time of transmitting the initiating ultrasonic signal and a time of receiving the responding ultrasonic signal;
• and
• wherein the first ultrasonic array is also coupled to a processor that determines a distance between the first one and the second one of the plurality of objects based on the recorded times, and the predetermined time delay.

An ultrasonic positioning system, comprising:

• a plurality of objects each configured to transmit and receive ultrasonic signals;
• a first ultrasonic array positioned on a first one of the plurality of objects and configured to transmit initiating ultrasonic signals;
• a radio transmitter positioned on the first one of the plurality of objects and configured to transmit a radio frequency signal with each initiating ultrasonic signal to trigger another one of the plurality of objects to respond to the initiating ultrasonic signal;
• a radio receiver positioned on a second one of the plurality of objects and configured to receive radio frequency signals;
• and
• a second ultrasonic array positioned on the second one of the plurality of objects and configured to receive initiating ultrasonic signals and to transmit a responding ultrasonic signal in response to receiving an initiating ultrasonic signal that follows a radio frequency signal triggering the second one of the plurality of objects to respond to the initiating ultrasonic signal;
• and
• wherein the first ultrasonic array is configured to receive the responding ultrasonic signal, and is coupled to a timer that records a time period between the transmission of the initiating ultrasonic signal and the reception of the responding ultrasonic signal.

A method for calibrating a positioning system having a plurality of beacons, comprising

• placing the beacons in or around a service volume according to a set of predetermined constraints;
• determining a set of inter-beacon distances using inter-beacon 2-way ultrasonic measurements;
• setting the origin of a coordinate frame at a first beacon;
• setting one axis of the coordinate frame along the direction from the first beacon and a second beacon;
• determining initial coordinates of the second beacon based on the distance between the first beacon and the second beacon;
• determining initial coordinates of a third beacon based on the distances between the first beacon and the second beacon, between the second beacon and the third beacon, and between the third beacon and the first beacon, and based on the predetermined constraints.

A mobile platform capable of positioning itself with respect to a plurality of beacons in fixed locations, comprising:

• an ultrasonic array including a first set of ultrasonic transceivers or transducer pairs, the first set of ultrasonic transceivers or transducer pairs configured to transmit simultaneously a first set of initiating ultrasonic signals in different directions to poll a beacon;
• a timer coupled to the ultrasonic array and configured to record a time of transmitting the first set of initiating ultrasonic signals by the first set of ultrasonic transceivers or transducer pairs and a time of receiving a responding ultrasonic signal from the beacon by one of the first set of ultrasonic transceivers or transducer pairs;
• and
• a processor coupled to the timer and configured to determine a distance between the mobile platform and the beacon based on the time of transmitting the first set of initiating ultrasonic signals and the time of receiving the responding ultrasonic signal.

A mobile platform capable of positioning itself with respect to a plurality of beacons, comprising

• an ultrasonic array configured to transmit a sequence of initiating ultrasonic signals to poll a beacon, the sequence of initiating ultrasonic signals including a first initiating ultrasonic signal transmitted in a first direction and a second initiating ultrasonic signal transmitted in a second direction different from the first direction, wherein the ultrasonic array is further configured to receive from the beacon a first responding ultrasonic signal corresponding to the first initiating ultrasonic signal and a second responding ultrasonic signal corresponding to the second initiating ultrasonic signal;
• a timer coupled to the ultrasonic array and configured to record a time of transmitting the first initiating ultrasonic signal, a time of receiving the first responding ultrasonic signal, a time of transmitting the second ultrasonic signal, and a time of receiving the second responding ultrasonic signal;
• and
• a processor coupled to the timer and configured to determine a distance between the mobile platform and the beacon based on a shorter one of a first time period and a second time period, wherein the first time period is between the time of transmitting the first initiating ultrasonic signal and the time of receiving the first responding ultrasonic signal, and the second time period is between the time of transmitting the second initiating ultrasonic signal and the time of receiving the second responding ultrasonic signal.

A beacon for positioning a mobile platform, comprising:

• an ultrasonic array including multiple ultrasonic transceivers or transducer pairs facing different directions, each ultrasonic transceiver or transducer pair configured to transmit and receive ultrasonic signals;
• a matched filter coupled to each ultrasonic transceiver or transducer pair, and the matched filter configured to detect a reception of an ultrasonic signal by the ultrasonic transceiver or transducer pair and to produce a figure of merit when a reception is detected;
• and
• a processor coupled to the ultrasonic array and configured to select an ultrasonic transceiver or transducer pair to respond to the ultrasonic signal based on the figure of merit produced by the matched filter coupled to each ultrasonic transceiver or transducer pair receiving the ultrasonic signal.

A method of operating a positioning system having a plurality of objects each configured to transmit and receive ultrasonic signals, comprising

• from a first one of the plurality of objects, transmitting simultaneously a set of initiating ultrasonic signals for receipt by a second one of the plurality of objects, the set of initiating ultrasonic signals including ultrasonic signals transmitted in different directions;
• transmitting a responding ultrasonic signal from the second one of the plurality objects after a predetermined time delay from receiving one initiating ultrasonic signal by the second one of the plurality of objects, the one initiating ultrasonic signal being the first among the set of initiating ultrasonic signals to arrive at the second one of the plurality of objects;
• receiving the responding ultrasonic signal at the first one of the plurality of objects;
• and
• determining a distance between the first one and the second one of the plurality of objects based on a time of transmitting the set of initiating ultrasonic signal, a time of receiving the responding ultrasonic signal, and the predetermined time delay.

A method of operating a positioning system having a plurality of objects each configured to transmit and receive ultrasonic signals, comprising

• transmitting a first initiating ultrasonic signal in a first direction from a first one of the plurality of objects;
• in response to receiving the first initiating ultrasonic signal by a second one of the plurality of objects, transmitting a first responding ultrasonic signal from the second one of the plurality of objects;
• receiving the first responding ultrasonic signal at the first one of the plurality of objects;
• computing a first time period starting at a time of transmitting the first initiating ultrasonic signal and ending at a time of receiving the first responding ultrasonic signal;
• subsequent to transmitting the first initiating ultrasonic signal, transmitting a second initiating ultrasonic signal in a second direction from the first one of the plurality of objects, the second direction being different from the first direction;
• in response to receiving the second initiating ultrasonic signal by the second one of the plurality of objects, transmitting a second responding ultrasonic signal from the second one of the plurality of objects;
• receiving the second responding ultrasonic signal at the first one of the plurality of objects;
• computing a second time period starting at a time of transmitting the second initiating ultrasonic signal and ending at a time of receiving the second responding ultrasonic signal;
• and
• determining a distance between the first one and the second one of the plurality of objects based on a shorter one of the first time period and the second time period.