Power line communication system utilizing a local oscillator

#MESSAGE COMMUNICATION SYSTEM, Ser. No. 125,844, filed Feb. 29, 1980, now Pat. No. 4,380,009, issued Apr. 12, 1983 invented by Ernest L. Long et al and assigned to the same assignee as the present invention.

#The present invention relates to a power line communication system.

#In a message communication system such as described in the cross-referenced application identified above, there is disclosed therein communications capability in an office environment, utilizing as a transmission medium, in one embodiment, pre-existing conventional AC power lines connected between the various offices in the building. In such an environment, however, a problem which occurs with the transmission of information is the presence of noise, which can seriously affect the capability of detecting and recovering the information transmitted over the power line. Further, as communications traffic increases, problems occur with a system's capability of handling the increased traffic. Typical prior art systems only provide single channel communication while operating with the inherent noise problems described above. There is a need, therefore, for an improved transmission capability which can be utilized in such an environment as described hereinabove and which can overcome the noise problems and can provide multi-channel capability to handle increased communications traffic.

#FIG. 1 depicts a block diagram of a power line transmission system.

#FIG. 2 depicts a more detailed diagram of a transmitter which forms a portion of FIG. 1.

#FIG. 3 depicts a timing diagram for illustrating the operation of the system of FIG. 1.

#Referring now to FIG. 1, a power line communication or transmission system for use in establishing communications over an AC power line is depicted wherein information is transmitted over a conventional AC power line or bus 15, which is connected between a transmitter 10 and a receiver 20. The system depicted in FIG. 1 provides a multi-channel capability with substantial freedom from noise.

#The term "bus" is intended to mean any communication medium for transmitting information. For example, one or more conductors connected in a communication system comprise a "bus". Also typical AC power lines can include 440 volts, 220 volts, 110 volts and three-phase. The present invention is applicable to any type of commercial, industrial and/or residential wiring that carries AC power.

#The system depicted in FIG. 1 utilizes narrow band frequency shift keying (FSK) techniques, a form of frequency modulation in which the modulating wave shifts an output frequency between predetermined values and the output wave generally has no phase discontinuity.