Dynamic channel selection for RF telemetry with implantable device

1. A telemetry system for enabling radio-frequency (RF) communications between an implantable medical device and an external device over a wireless medium, comprising:

an antenna, an RF transmitter, an RF receiver, and a controller incorporated into each of the implantable and external devices,

wherein the RF transmitter and receiver of each device are tunable and may be switched among a plurality of different communications channels which differ in frequency;

wherein the controller is interfaced to the RF transmitter and receiver in each device to enable establishment of a communications session and data transfer over a selected channel;

wherein the external device and implantable device controllers are programmed to establish a communications session over one of a plurality of designated control channels;

after establishment of a communications session, the external device controller is programmed to search among a plurality of designated data channels to select an unused data channel and transmit an identification of the selected channel to the implantable device;

wherein the external device and implantable device controllers are programmed to switch to the selected data channel for subsequent data transfer during the communications session;

wherein the external device and implantable device controllers are programmed to revert to the designated control channel that is farthest away in frequency from the selected data channel upon a degradation in the quality of the selected data channel sufficient to constitute a failure in the selected data channel.

2. The system of claim 1 wherein the external device controller is programmed to monitor the quality of a communications channel by determining if the channel throughput over a certain time falls below a certain level.

3. The system of claim 1 wherein the external device controller is programmed to monitor the quality of a communications channel by determining if a specified number of data frames are unacknowledged.

4. The system of claim 1 wherein the external device controller is programmed to monitor the quality of a communications channel by determining if the frame error rate exceeds a threshold value.

5. The system of claim 1 wherein the implantable device and external device controllers are programmed to cycle among designated control channels after a specified period time if the devices are unable to establish communications over the designated control channel farthest away in frequency from the selected data channel that failed.

6. The system of claim 1 wherein the external device and implantable device controllers are programmed to attempt to re-establish communications over another designated data channel after reverting to one of the designated control channels upon a failure in the selected data channel.

7. The system of claim 6 wherein the external device controller is programmed to search for an available data channel by checking the data channels for activity.

8. The system of claim 7 wherein the external device controller is programmed to tune its receiver to a particular data channel, listen for a valid preamble known to be transmitted by all devices during the transmission of data frames, and regard the data channel as unused if no such preambles are detected over a specified time period.

9. The system of claim 7 wherein the external device controller is programmed to tune its receiver to a particular data channel, measure the signal strength of the channel over a specified period of time, and regard the channel as unused if the peak signal strength over specified period of time is less than a specified value.

10. The system of claim 7 wherein the external device controller is programmed to:

tune its receiver to a particular data channel;

listen for a valid preamble known to be transmitted by all devices during the transmission of data frames;

measure the signal strength of the channel over a specified period of time; and,

regard the data channel as unused if no such preambles are detected over a specified time period and if the peak signal strength over specified period of time is less than a specified value.

11. A method by which an implantable medical device and an external device may communicate over a wireless medium, comprising:

providing a plurality of different communications channels which differ in frequency;

programming the external device and implantable device to establish a communications session over one of a plurality of designated control channels;

programming the external device controller to search among a plurality of designated data channels to select an unused data channel and transmit an identification of the selected channel to the implantable device after establishment of a communications session over a designated control channel;

programming the external device and implantable device to switch to the selected data channel for subsequent data transfer during the communications session; and,

programming the external device and implantable device to revert to the designated control channel that is farthest away in frequency from the selected data channel upon a degradation in the Quality of the selected data channel sufficient to constitute a failure in the selected data channel.

12. The method of claim 11 further comprising programming the external device to monitor the quality of a communications channel by determining if the channel throughput over a certain time falls below a certain level.

13. The method of claim 11 further comprising programming the external device to monitor the quality of a communications channel by determining if a specified number of data frames are unacknowledged.

14. The method of claim 11 further comprising programming the external device to monitor the quality of a communications channel by determining if the frame error rate exceeds a threshold value.

15. The method of claim 11 further comprising programming the implantable and external devices to cycle among designated control channels after a specified period time if the devices are unable to establish communications over the designated control channel farthest away in frequency from the selected data channel that failed.

16. The method of claim 11 further comprising programming the external and implantable devices to attempt to re-establish communications over another designated data channel after reverting to one of the designated control channels upon a failure in the selected data channel.

17. The method of claim 16 further comprising programming the external device to searching for an available data channel by checking the data channels for activity.

18. The method of claim 17 further comprising programing the external device to listen to a particular data channel for a valid preamble known to be transmitted by all devices during the transmission of data frames and regard the data channel as unused if no such preambles are detected over a specified time period.

19. The method of claim 17 further comprising programming the external device to measure the signal strength of a particular data channel over a specified period of time and regard the channel as unused if the peak signal strength over specified period of time is less than a specified value.

20. The method of claim 17 further comprising programing the external device to:

listening to a particular data channel for a valid preamble known to be transmitted by all devices during the transmission of data frames;

measuring the signal strength of the particular data channel over a specified period of time; and,

regarding the data channel as unused if no such preambles are detected over a specified time period and if the peak signal strength over specified period of time is less than a specified value.