Object location system and method

A method of determining a position of an object in a monitored region, said method comprising:

• transmitting an RF tag signal from an object to be located,
• transmitting a reference signal from a known location,
• providing a common clock signal to respective timers of plural monitoring stations, said timers having an index frequency being a frequency multiple of said common clock signal to provide incremental count values indicative of times of arrival of said tag signal and said reference signal,
• measuring, at the monitoring stations, times of arrival of the reference signal and the tag signal,
• determining relative offsets among timers of the monitoring stations using times of arrival of said reference signal measured in said measuring step,
• adjusting measured times of arrival according to relative offsets among timers of the monitoring stations, and
• determining the position of the object according to the relative offsets and measured times of arrival of the tag signal at the respective monitoring stations.

A method of determining a position of an object in a monitored region, said method comprising:

• transmitting an RF tag signal from the object to be located,
• transmitting a reference signal from a fixed location,
• receiving the RF tag signal and the reference signal at fixed monitoring stations,
• providing a common clock signal to plural monitoring stations,
• at said fixed monitoring stations, generating incremental count values using a counter having a cycle that is relatively phase-locked with, and index at a frequency relatively higher than a frequency of said common clock source to measure, times of arrival of the reference signal and the tag signal, and
• determining the position of the object according to times of arrival of the tag signal at the respective monitoring stations.

A system to determine a location of an object that emits a UWB signal, said system comprising:

• a clock source that generates periodic clock pulses at a fixed-frequency,
• at least two monitoring stations positioned at known locations each including an incremental time counter having an index frequency higher than said fixed frequency to measure arrival times of UWB signals in discrete increments of time and a phase-locking circuit to lock cycles of said counter with clock source,
• a reference transmitter also positioned at a known location to transmit a reference signal that effects latching of incremental time values indicative of times of arrival of the reference signal at the monitoring stations, and
• a processor that utilizes the incremental time values to determine relative offsets between respective timers of the monitoring station based on known locations thereof and to determine the location of the object based on said relative offsets and times of arrival of the UWB signal at the monitoring stations.

A method of locating an object comprising the steps of:

• positioning multiple monitoring stations at known locations,
• transmitting a UWB tag signal from the object,
• generating a periodic clock signal of a relatively low fixed-frequency,
• at the monitoring stations, receiving the periodic clock signal and phase-locking respective incremental timers of the monitoring stations relative to each other using said periodic clock signal, said timers operating at a relatively higher frequency than said periodic clock signal to provide discrete count values indicative of times of arrival of received signals,
• transmitting a reference signal from a known location to effect latching of respective count values at the monitoring stations indicative of times of arrival of the reference signal,
• determining relative offsets in the incremental timers of the monitoring stations based on the known locations and count values associated with receipt of the reference signal at respective monitoring stations, and
• locating the object based on the relative offsets and times of arrival of the UWB tag signal at the respective monitoring stations.

A method of locating an object comprising:

• positioning multiple monitoring stations at known locations,
• transmitting a UWB tag signal from the object,
• generating a fixed-frequency clock signal,
• receiving and utilizing the fixed-frequency clock signal at the monitoring stations to relatively phase-lock cycling of respective counters of the monitoring stations relative to each other utilizing the fixed-frequency clock signal to frequency-lock cycling of the respective counters, said counters being indexed at a frequency multiple of said fixed frequency clock signal to generate and latch count values indicative of times of arrival of received signals,
• transmitting a reference signal from a known location to effect latching of count values indicative of times of arrival of the reference signal at the monitoring stations,
• determining relative offsets in the counters of the monitoring stations based on the known locations and count values associated with receipt of the reference signal at respective monitoring stations, and
• locating the object based on the relative offsets and times of arrival of the UWB tag signal at the monitoring stations.

A system to locate an object that transmits a tag signal, said system comprising:

• a primary clock to generate periodic clock pulses of a relatively low fixed frequency,
• at least two monitoring stations positioned at known locations, each of said monitoring stations including a secondary clock of relatively high frequency to produce count values indicative of times of arrival and a phase-locking circuit to lock cycle in intervals of the secondary clock with occurrences of said periodic clock pulses of the primary clock whereby to maintain a constant phase offset between cycles of respective secondary clocks of the monitoring stations,
• a reference transmitter also positioned at a known location to transmit a reference signal that effects latching of clock count values indicative of times of arrival of the reference signal at the monitoring stations, and
• a processor that obtains digital representations of the count values from the monitoring stations to determine offsets between the secondary clocks of the monitoring stations based on the known locations and to locate the object based on the offsets and times of arrival of the tag signal at the monitoring stations.