Automatic mode change in ultrasonic locationing

1. A method for automatically changing modes for ultrasonic locationing of a mobile device within an environment, the method comprising:

transmitting ultrasonic pulses to be used for locationing of mobile communication devices within the environment in accordance with a transmit schedule by a plurality of fixed ultrasonic devices within the environment;

determining when a fixed access point within the environment begins serving a newly registered mobile communication device;

instructing only those ultrasonic devices proximal to the serving access point to deactivate their transmit mode and switch to a receive mode to listen for an ultrasonic acoustic tone from the newly registered mobile communication device;

directing the newly registered mobile communication device to emit the ultrasonic acoustic tone;

establishing an initial location of the newly registered mobile communication device using measurements of the ultrasonic acoustic tone at each proximal ultrasonic device;

adapting the transmit schedule to accommodate the newly registered mobile communication device at the initial location; and

returning the proximal ultrasonic devices to transmit mode using the adapted transmit schedule.

2. The method of claim 1 , wherein the establishing step includes measuring a signal strength of the ultrasonic acoustic tone at each proximal ultrasonic device, indicative of a distance between the newly registered mobile communication device and each proximal ultrasonic device, and used to establish the initial location.

3. The method of claim 1 , wherein the acoustic tone lasts approximately 200 milliseconds.

4. The method of claim 1 , wherein the transmit schedule includes an individually-assigned time-slice for each mobile communication device to perform locationing using the ultrasonic pulses transmitted during that time-slice.

5. The method of claim 1 , wherein the proximal ultrasonic devices include at least three ultrasonic devices proximal to the serving access point.

6. The method of claim 1 , wherein the determining step also includes determining that the newly registered mobile communication device is operable to be enrolled for ultrasonic locationing.

7. The method of claim 1 , where in the transmitting step the emitters are affixed to a ceiling of the environment and oriented towards a floor of the environment to provide a limited region for the mobile communication devices to receive the ultrasonic pulses.

8. The method of claim 1 , where in the transmitting and directing steps the ultrasonic pulses and acoustic tone utilized each have a frequency between 19 kHz and 22.05 kHz and the mobile device utilizes existing, unmodified audio circuitry for receiving the pulses and emitting the acoustic tone.

9. The method of claim 1 , wherein the ultrasonic pulses in the transmitting step provide time-of-flight information used for locationing of the mobile communication device.

10. A system for automatically changing modes for ultrasonic locationing of a mobile device within an environment, the system comprising:

a plurality of fixed ultrasonic devices within the environment, the ultrasonic devices each including an ultrasonic emitter and microphone, the ultrasonic emitters operable, in a transmit mode, to transmit ultrasonic pulses to be used for locationing of mobile communication devices within the environment in accordance with a transmit schedule;

a plurality of fixed access points within the environment and operable on a communication network;

at least one mobile communication device operable to register with one of the access points; and

a backend controller coupled to the access points and the ultrasonic devices, the backend controller operable to:

determine when an access point begins serving a newly registered mobile communication device,

instructing only those ultrasonic devices proximal to the serving access point to switch to a receive mode that activates their associated microphones and deactivates their associated emitters,

directing, via the serving access points, the newly registered mobile communication device to emit an ultrasonic acoustic tone,

establishing an initial location of the newly registered mobile communication device using measurements of the ultrasonic acoustic tone at each proximal ultrasonic device,

adapting the transmit schedule to accommodate the newly registered mobile communication device at the initial location, and

returning the proximal ultrasonic devices to transmit mode using the adapted transmit schedule.

11. The system of claim 10 , wherein the microphones provide measurements of a signal strength of the ultrasonic acoustic tone at each proximal ultrasonic device, indicative of a distance between the newly registered mobile communication device and each proximal ultrasonic device, and used to establish the initial location.

12. The system of claim 10 , wherein the acoustic tone lasts approximately 200 milliseconds.

13. The system of claim 10 , wherein the transmit schedule includes an individually-assigned time-slice for each mobile communication device to perform locationing using the ultrasonic pulses transmitted during that time-slice.

14. The system of claim 10 , wherein the proximal ultrasonic devices include at least three ultrasonic devices proximal to the serving access point.

15. The system of claim 10 , wherein the newly registered mobile communication device is operable to be enrolled for ultrasonic locationing.

16. The system of claim 10 , where the emitters of the fixed ultrasonic devices are affixed to a ceiling of the environment and oriented towards a floor of the environment to provide a limited region for the mobile communication devices to receive the ultrasonic pulses.

17. The system of claim 10 , wherein the ultrasonic pulses and acoustic tone utilized each have a frequency between 19 kHz and 22.05 kHz and the mobile device utilizes existing, unmodified audio circuitry for receiving the pulses and emitting the acoustic tone.

18. The system of claim 10 , wherein the ultrasonic pulses provide time-of-flight information used for locationing of the mobile communication device.