Detection of multipath and transmit level adaptation thereto for ultrasonic locationing

1. A system for detection of multipath and transmit level adaptation thereto in ultrasonic locationing of a mobile device within an environment, the system comprising:

a plurality of fixed ultrasonic emitters within the environment, the fixed ultrasonic emitters operable to transmit ultrasonic bursts at predetermined times to a communication device located within the environment;

a communication device operable to measure at least a direct signal of each ultrasonic burst and detect multipath of each ultrasonic burst by comparing an amplitude of the direct signal with other signals related to the ultrasonic burst; and

a controller coupled to the emitters, wherein if multipath is detected the controller is operable to adapt a transmit power level of the ultrasonic burst until an amplitude of the direct signal is above a threshold in detecting whereby multipath is no longer detected, and wherein if multipath is not detected the controller is operable to locate the communication device using the direct signal of each of a plurality of ultrasonic bursts.

2. The system of claim 1 , wherein communication device is operable to measure at least a direct signal of each ultrasonic burst and detect multipath of each ultrasonic burst again after a predetermined length of time to create repeated measurements, and wherein if multipath is not detected the predetermined length of time between the repeated measurements is reduced for subsequent measuring.

3. The system of claim 1 , wherein at least one of the other signal includes reflected signals of the ultrasonic burst, and wherein the communication device is operable to compare an amplitude of the direct signal with a composite amplitude of the reflected signals, and multipath of the ultrasonic burst is detected by the controller when a ratio of the amplitude of the direct signal with the composite amplitude of the reflected signals is less than a first multipath threshold.

4. The system of claim 1 , wherein at least one of the other signal includes an estimated direct signal to the communication device in a line-of-sight condition, and wherein the communication device is operable to compare an amplitude of the direct signal with an estimated amplitude of the estimated direct signal to the communication device in a line-of-sight condition, and multipath of the ultrasonic burst is detected by the controller when a ratio of the amplitude of the direct signal with the estimated amplitude of the estimated direct signal to the communication device in a line-of-sight condition is less than a second multipath threshold.

5. The system of claim 1 , wherein the controller is further operable to reduce the transmit power level of the ultrasonic burst to a minimum power level where all devices maintain a line-of-sight condition.

6. The system of claim 1 , wherein the fixed ultrasonic emitters can be affixed to a ceiling of the environment and oriented towards a floor of the environment to provide a limited region for communication devices to receive the ultrasonic burst.

7. The system of claim 1 , where the fixed ultrasonic emitters utilize ultrasonic bursts having a frequency between 19 kHz and 22.05 kHz and the communication device utilizes existing, unmodified audio circuitry to measure the signals from the ultrasonic burst.

8. The method of claim 7 , wherein measuring includes repeated measuring over subsequent windows of time having a predetermined length of time, and wherein if multipath is not detected in detecting reducing the length of time of the subsequent windows.

9. The method of claim 7 , wherein at least one of the other signal in measuring includes reflected signals of the ultrasonic burst, and wherein detecting includes comparing an amplitude of the direct signal with a composite amplitude of the reflected signals, and multipath of the ultrasonic burst is detected when a ratio of the amplitude of the direct signal with the composite amplitude of the reflected signals is less than a first multipath threshold.

10. The method of claim 7 , wherein at least one of the other signal in measuring includes an estimated direct signal to the communication device in a line-of-sight condition, and wherein detecting includes comparing an amplitude of the direct signal with an estimated amplitude of the estimated direct signal to the communication device in a line-of-sight condition, and multipath of the ultrasonic burst is detected when a ratio of the amplitude of the direct signal with the estimated amplitude of the estimated direct signal to the communication device in a line-of-sight condition is less than a second multipath threshold.

11. The method of claim 7 , further comprising reducing the transmit power level of the ultrasonic burst to a minimum power level where all devices maintain a line-of-sight condition.

12. The method of claim 7 , wherein the step of providing a plurality of fixed ultrasonic emitters includes affixing the fixed ultrasonic emitters to a ceiling of the environment and oriented towards a floor of the environment to provide a limited region for communication devices to receive the ultrasonic burst.

13. The method of claim 7 , where transmitting utilizes ultrasonic bursts having a frequency between 19 kHz and 22.05 kHz and the communication device utilizes existing, unmodified audio circuitry to measure the signals from the ultrasonic burst.

14. The method of claim 7 , wherein locationing utilizes time-of-flight information of the direct signal of the ultrasonic burst.

15. The system of claim 1 , wherein the controller utilizes time-of-flight information of the direct signal of the ultrasonic burst to location the communication device.

16. A method for detection of multipath and transmit level adaptation thereto in ultrasonic locationing of a mobile device within an environment, the method comprising the steps of:

providing a plurality of fixed ultrasonic emitters within the environment;

transmitting ultrasonic bursts by the fixed ultrasonic emitters at predetermined times to a communication device located within the environment;

measuring at least a direct signal of each ultrasonic burst; and

detecting multipath of each ultrasonic burst by comparing an amplitude of the direct signal with at least one other signal related to the ultrasonic burst;

wherein if multipath is detected adapting a transmit power level of the ultrasonic burst in the transmitting step until an amplitude of the direct signal in measuring is above a detection threshold in detecting whereby multipath is no longer detected, and

wherein if multipath is not detected locationing of the communication device uses the direct signal of each of a plurality of ultrasonic bursts.