Redundantly transmitting message segments over a dual purpose transmission line

摘要

A method of transmitting a message segment on a dual purpose transmission line, such as a power line, on which are liable to occur noise spikes, comprises coding the message segment as components of a burst of carriers of different frequencies, and transmitting on the line two successive bursts encoding the same message segment, preferably within an interval which is substantially less than twice the repetition period of the noise spikes. The message segment is therefore transmitted redundantly to in successive bursts to allow successful reception if one of the bursts is affected by noise spikes. The two bursts may be preceded by a start symbol at the commencement of said interval. The method may include monitoring the transmission line for the occurrence of a noise spike and initiating a transmission of a start symbol and the two bursts on detection of the occurrence of a noise spike.