Multi-channel TDOA system

A method for accurately measuring the Time Difference Of Arrival (TDOA) of messages transmitted at different channels in a multiple-channel wireless network comprising:

• synchronously transmitting the messages in multiple channels using a transmit clock signal of a wireless unit, the transmitting of the messages occurring at intervals consisting of at least one of one or more periods of the transmit clock signal so that transmission of two of the messages is separated by a time interval of one or more periods of the transmit clock signal, wherein the wireless unit does not transmit during the time interval;
• receiving the messages transmitted by the wireless unit by a plurality of location receivers within the wireless network on at least two different channels;
• determining a time of arrival data for the received messages by the plurality of location receivers;
• receiving time of arrival data by at least one master unit;
• and
• determining a location of the wireless unit based on the Time Difference Of Arrival (TDOA) of the transmitted messages.

A wireless unit that synchronously transmits messages in multiple channels of a multiple channel wireless data communication system including wireless units that communicate with one or more location receivers, wherein the wireless communication system is configured to locate the wireless unit, the wireless unit comprising:

• a communication controller that generates data to be transmitted;
• and
• a transmitter coupled to the communication controller to modulate the data and transmit the messages in a programmed channel, the transmitter starting transmission of the messages at intervals consisting of at least one of one or multiple periods of a transmit clock signal,
• wherein the wireless unit further comprises a counter coupled to the communication controller to count cycles of the transmit clock signal, and
• wherein the communication controller clears and enables the counter to start counting when transmission of a first signal starts, the communication controller samples and reads a counter value when transmission of a second signal on a different channel starts, and the counter continuing counting clock cycles.

A wireless unit that synchronously transmits messages in multiple channels of a multiple channel wireless data communication system including wireless units that communicate with one or more location receivers, the wireless communication system configured to locate the wireless unit, the wireless unit comprising:

• a communication controller that generates data to be transmitted;
• a transmitter coupled to the communication controller to modulate the data and transmit the messages in a programmed channel, the transmitter starting transmission of the messages at intervals consisting of at least one of one or multiple periods of a transmit clock signal;
• and
• a timing circuit coupled to the transmitter to provide synchronization of the transmit signals, the timing circuit comprising:
• a clock divider coupled to the transmit clock signal for generating a window clock signal, wherein the window clock signal and the transmit clock signal are synchronized, and
• a flip-flop device coupled to the communication controller, the flip flop device receiving start and stop transmission signals and outputting the synchronized start transmission signal on an edge of the window clock.

A wireless network comprising:

• a wireless unit that synchronously transmits messages in multiple channels using a transmit clock signal, the wireless unit starting transmission of the messages at intervals comprising of at least one of one or multiple periods of the transmit clock signal, wherein the wireless unit comprises a communication controller that generates data to be transmitted and a counter coupled to the communication controller to count cycles of the transmit clock signal, wherein the communication controller clears and enables the counter to start counting when transmission of a first message begins and samples and reads a counter value when transmission of a second message on a different channel begins, and the counter continuously counts clock cycles;
• a plurality of location receivers for receiving the messages in one of at least two different channels, said messages transmitted by the wireless unit within the wireless network and determining a time of arrival for the received messages;
• and
• at least one master unit for receiving the time of arrival from each of the location receivers, whereby a location of the wireless unit is determined based on a Time Difference Of Arrival (TDOA) of the transmitted messages at the location receivers.

A method for synchronously transmitting messages at different channels in a multiple-channel wireless data communication system configured to determine the location of a wireless unit, comprising:

• transmitting a first message by the wireless unit to a first location receiver that determines a first time of arrival data for the first message that is used by a master unit, wherein transmitting the first message includes:
• clearing and enabling a counter that counts cycles of a transmit clock signal to start counting when transmission of the first message begins;
• and
• transmitting a second message on a different channel by the wireless unit to a second location receiver that determines a second time of arrival data for the second message that is used by the master unit to determine a location of the wireless unit based on a Time Difference Of Arrival (TDOA) of the transmitted first and second messages, wherein transmitting the second message includes:
• sampling and reading a counter value when transmission of the second message on the different channel begins while the counter continues to count clock cycles,
• wherein the first and second messages are synchronized using the transmit clock signal and the first and second messages are transmitted at intervals comprising of at least one of one or multiple periods of the transmit clock signal.