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A communication system for a power line is described. A transmission system of the communication system divides the time axis into a number of time slots synchronized such that one time slot can start about a zero crossing of the power line signal. These time slots may be referred to as channels. Da

A communication system for a power line is described. A transmission system of the communication system divides the time axis into a number of time slots synchronized such that one time slot can start about a zero crossing of the power line signal. These time slots may be referred to as channels. Data may initially be modulated into at least one of these time slots over a first transmission period according to a modulation scheme. The time slots and/or modulation scheme used in subsequent transmission periods may be adjusted depending on transmission feedback relating to prior modulated data.

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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; andresponsive to an indication that transmitted data of the first transmission p

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; andresponsive 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; anda 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, andsubsequently 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.