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Single-event noise type can be easily overcome, by simply repeating the data packet. However, the situation is more complex with line-synchronized noise type, because this type of noise can introduce one (or more) error 120 times per second. If the data transmission process lasts more than 1/120 second (or 8.33 msec), errors will likely occur, and packets will be lost. In many circumstances, it is unlikely that repeating the packet will circumvent the problem. Breaking the data packet into smaller segments lasting less than 8.33 msec, and transmitting these segments between noise bursts is also impossible, because the transmitter could have a local noise source, different from the noise source at the receiver.
In other words, in any PLC system, one should assume that noise at the receiver is unknown to the transmitter. Consequently, it could be difficult (if not impractical) for an intelligent transmitter to analyze the power line noise characteristics and adapt its transmission strategy, because noise at the receiver end is very likely to be different from noise measured at the transmitter. Moreover, such an intelligent transmitter could not broadcast messages to N receivers, each receiver having its own and different local noise characteristics.
Local noise is not the sole source of communication errors. Sudden impedance variation can also induce similar effects. Different loads (some compact fluorescent lights, personal computer power supplies, switching power supplies) are known to make the impedance of the communication link change abruptly with time, generally synchronously with the power line frequency. (These loads generally offer a higher impedance level around the zero crossing of the power wave.) For the same reasons as above, impedance variations at the receiver end is almost undetectable at the transmitter location, making adaptive algorithms difficult to implement. The same principles apply to impedance variation: more severe effects are generally observed when the impairment source is close to the receiver, and the impedance between the receiver and the transmitter is high. Once again, repeating a greater than 8.33 msec packet will likely not overcome line synchronous, impedance variation related error bursts.
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