System and method for power line communication

1. A method, comprising:

transmitting data in an AC power line signal in a first transmission period, the transmitted data being modulated initially into a first set of time slots dividing the first transmission period; and

responsive to an indication that transmitted data of the first transmission period was not received properly at a receiver, transmitting data in the AC power line signal in a second transmission period according to a modulation scheme in a second set of time slots dividing the second transmission period, the modulation scheme including encoding at least one bit of the data into a greater number of time slots than would occur according to the initial modulation.

2. The method of claim 1 , wherein the first and second sets of time slots include similar time slots in different transmission periods.

3. The method of claim 1 , wherein the first and second sets of time slots include every available time slot within each transmission period.

4. The method of claim 1 , wherein the first and second sets of time slots include different time slots in different transmission periods.

5. The method of claim 1 , wherein a binary frequency shift keying modulation is used in the initial modulation and the modulation scheme.

6. The method of claim 1 , wherein the first and the second sets of time slots are centered around different zero-crossings of the AC power line signal.

7. The method of claim 1 , wherein one bit of the data is initially modulated in each time slot of the first set of time slots.

8. The method of claim 7 , wherein the modulation scheme includes redundantly encoding the at least one bit of the data over a plurality of the second subset of time slots.

9. The method of claim 8 , wherein the modulation scheme includes redundantly encoding the at least one bit of the data over a plurality of the second set of time slots centered around a same zero-crossing of the AC power line signal.

10. The method of claim 8 , wherein the modulation scheme includes redundantly encoding the at least one bit of the data over a plurality of the second set of time slots centered around different zero-crossings of the AC power line signal.

11. The method of claim 1 , wherein the modulation scheme includes redundantly encoding the at least one bit of data using frequency diversity.

12. The method of claim 11 , wherein the redundantly encoded data is encoded in at least one time slot in a plurality of second transmission periods at a different frequency in each of the second transmission periods, each of the second transmission periods having time slots centered around respective zero-crossings of the AC power line signal.

13. The method of claim 1 , wherein the indication is a failure to receive a delivery confirmation from the receiver within a predetermined time.

14. The method of claim 1 , wherein the delivery confirmation is received through a positive acknowledgement protocol.

15. The method of claim 1 , further comprising iteratively transmitting the data into additional sets of time slots with increasing redundancy after the indication occurs at each iteration.

16. A circuit comprising:

a connection to an AC power line signal;

an encoding module to initially modulate data into a first set of time slots dividing a first transmission period of the AC power line signal; and

a processing device to determine whether the initially modulated data was properly received at a receiver, the encoding module modulating data determined to be improperly received into a second set of time slots in a second transmission period, the modulating of improperly received data including encoding at least one bit of the improperly received data into a greater number of time slots than would occur according to the initial modulation.

17. The circuit of claim 16 , wherein the processing device is a microcontroller and the encoding module is part of the microcontroller.

18. A method, comprising:

initially transmitting first data over a plurality of time slots dividing a time period in a power line signal, and

subsequently transmitting second data over a subset of the time slots in a different time period likely to yield least noise based on transmission information received from a receiver pertaining to the initial transmission.

19. The method of claim 18 , wherein the first data is different from the second data.

20. The method of claim 18 , wherein the first data is the same as the second data.

21. The method of claim 18 , wherein the transmission information provides a basis for comparing noise levels over the plurality of time slots.

22. The method of claim 21 , wherein the transmission information identifies the subset of time slots likely to yield least noise.

23. The method of claim 18 , wherein each time period includes a zero-crossing of the power line signal.

24. The method of claim 18 , wherein at least one time period includes a plurality of zero-crossings of the power line signal.

25. The method of claim 18 , further comprising initially transmitting the first data over a plurality of frequencies in the plurality of time slots and subsequently transmitting the second data over a subset of the plurality of frequencies likely to yield least noise based on the transmission information received.

26. The method of claim 25 , further comprising initially transmitting the first data over a plurality of phases in the plurality of time slots and subsequently transmitting the second data over a subset of the plurality of phases likely to yield least noise based on the transmission information received.