Emergency locating system and method using spread-spectrum transceiver

1. A method for locating a person in distress comprising:

activating an emergency transceiver to generate a direct-sequence spread-spectrum distress transmission by a person in distress;

receiving the direct-sequence spread-spectrum distress transmission at a locator transceiver;

transmitting a ranging command from the locator transceiver to the emergency transceiver;

receiving the ranging command at the emergency transceiver; and

transmitting a direct-sequence spread-spectrum ranging message from the emergency transceiver to the locator transceiver in response to the ranging command;

receiving the direct-sequence spread-spectrum ranging message at the locator transceiver;

determining a range between the emergency transceiver and the locator transceiver based on delay between the transmitting a ranging command and the receiving the direct-sequence ranging message; and

displaying the range to a rescue user.

2. The method of claim 1 , wherein the activating comprises entering an authorization code into the emergency transceiver by the person in distress.

3. The method of claim 1 , wherein the transmitting a ranging command comprises transmitting the ranging command upon entry of an authorization code by a rescue user.

4. The method of claim 1 , further comprising displaying an indication to the person in distress in response to reception of the ranging command at the emergency transceiver.

5. The method of claim 1 , wherein the direct-sequence spread-spectrum distress transmissions comprises a layered spreading code.

6. The method of claim 1 , wherein the direct-sequence spread-spectrum distress transmission and the ranging command uses a common spread-spectrum waveform encoding.

7. The method of claim 1 , wherein the determining a range comprises:

measuring a time of arrival of the spread-spectrum ranging message at the emergency transceiver;

determining a time difference between the time of arrival and a time of transmission of the ranging command;

converting the time difference to a range while taking into account a predefined time delay between the receiving the ranging command and the transmitting a direct-sequence spread-spectrum ranging message implemented in the emergency transceiver.

8. The method of claim 1 , further comprising:

determining a plurality of ranges between the emergency transceiver and a plurality of locator transceivers; and

using the plurality of ranges to determine a location of the emergency transceiver.

9. The method of claim 8 , wherein the determining a plurality of ranges comprises:

transmitting a ranging command from each of the plurality of locator transceivers to the emergency transceiver;

receiving the ranging commands at the emergency transceiver; and

transmitting a direct-sequence spread-spectrum ranging message from the emergency transceiver to each of the plurality of locator transceivers in response to each ranging command;

determining a range between the emergency transceiver and each of the plurality of locator transceivers based on round trip propagation delay; and

combining to the range between the emergency transceiver and each of the plurality of locator transceivers to determine a location of the emergency transceiver.

10. The method of claim 1 , further comprising:

transmitting a plurality of ranging commands from the locator transceiver to the emergency transceiver from a plurality of different locator transceiver locations;

receiving the plurality of ranging commands at the emergency transceiver;

transmitting a plurality of direct-sequence spread-spectrum ranging messages from the emergency transceiver to the locator transceiver in response to the ranging commands;

determining a plurality of range between the emergency transceiver and the locator transceiver corresponding to each of the plurality of ranging commands;

calculating a location of the emergency transceiver based on the plurality of ranges and the plurality of different locations.

11. An emergency locating system for communications of a distress signal from a mobile unit, the system comprising:

an emergency transceiver configured to transmit of spread-spectrum encoded messages when actuated by a user and configured to receive of spread-spectrum encoded commands; and

a locator transceiver configured to transmit of spread-spectrum encoded commands and reception of spread-spectrum encoded message to perform two-way ranging with the emergency transceiver; and

a location calculation unit operatively coupled to the locator transceiver and configured to determine a distance between the emergency transceiver and the locator transceiver based on the two-way ranging wherein the locator transceiver comprises: a locator transmitter configured to transmit the direct-sequence spread-spectrum commands;

a locator receiver configured to receive the spread-spectrum encoded messages from the emergency transceiver, wherein the locator transmitter transmits a ranging command in response to a received distress message; and

wherein the location calculation unit calculates range based on a time delay between the transmission of a ranging command and the reception of a ranging message.

12. The system of claim 11 , wherein the emergency transceiver comprises:

an emergency transmitter configured to transmit the direct-sequence spread-spectrum encoded messages;

an emergency receiver configured to receive the direct-sequence spread-spectrum encoded ranging commands and operatively coupled to the emergency transmitter to initiate transmission of ranging messages in response to ranging commands; and

an actuator operatively coupled to the emergency transmitter to initiate transmission of distress messages when the actuator is operated.

13. The system of claim 12 , wherein the emergency transmitter transmits a distress message in response to a predefined authorization code entered through the actuator.

14. The system of claim 11 , wherein the locator transmitter transmits a ranging command in response to a predefined authorization code entered into the locator transceiver.

15. The system of claim 11 , wherein the locator transceiver comprises a display operatively coupled to the location calculation unit to display the distance between the emergency transceiver and the locator transceiver.

16. The system of claim 11 , wherein the spread-spectrum encoded messages and the spread-spectrum encoded commands are each encoded using a layered spreading code.

17. The system of claim 11 , wherein the spread-spectrum encoded messages and the spread-spectrum encoded commands are each encoded using the same waveform.

18. The system of claim 11 , further comprising:

a plurality of locator transceivers each capable of transmission of spread-spectrum encoded commands and reception of spread-spectrum encoded message to perform two-way ranging with the emergency transceiver; and

wherein the location calculation unit is in communication with each of the plurality of locator transceivers and capable of combining two-way ranging information from each of the locator transceivers to determine a location of the emergency transceiver.

19. The system of claim 11 , wherein the emergency transceiver does not include a global positioning system receiver.