Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2000-03-23
2001-12-11
Tweel, John A. (Department: 2632)
Communications: electrical
Systems
Selsyn type
C340S315000
Reexamination Certificate
active
06329905
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to communications, particularly data communications systems and methods over power lines.
BACKGROUND INFORMATION
There are a variety of known applications where it is necessary or desirable to communicate data over power lines. For example, electric power meters for measuring power consumption in a building can advantageously be read remotely over the same power lines to which they are coupled. (See, e.g., U.S. Pat. No. 5,844,949). In another application, appliances within a household, such as a light switch or dimmer, can be controlled by signalling placed on the household power lines.
Conventional power lines, however, typically present a high-distortion, high-noise environment in which reliable and fast data communication is often not possible. In addition to additive white Gaussian noise (AWGN), power lines exhibit noise that is synchronous with the line frequency (e.g., lamp dimmer noise), periodic noise (e.g., motor-generated noise), random noise, radio frequency (RF) noise and interference from other communications devices such as intercoms and security systems. In addition to noise, data signals may also experience substantial attenuation such as when traveling through a transformer from one phase to another. Moreover, notch filters or other frequency-selective attenuation may be coupled to the power lines such as in power supplies for personal computers or power strips.
An additional problem involves voltage transformers, which are inherently inductively coupled and thereby introduce non-linear phase shifts in a signal passing through the transformer. This can lead to substantial signal distortion.
Furthermore, much of the noise on typical household power lines is located at harmonics of the AC line frequency (i.e., 50 or 60 Hz) that extend over large frequency ranges. As such, data communication over virtually any band of frequencies wider than the line frequency will be susceptible to such harmonic noise.
Known power line communications protocols (e.g., X-10, CEBus) often do not provide reliable operation to all outlets in a typical home. Moreover, such known techniques often require costly bridging devices to allow devices coupled to circuits on different phases to communicate with each other.
Complex communications systems are required to perform reliably in the high-noise, phase-distorted power line environment. For example, some of these systems monitor different frequency channels, select an appropriate channel, and then indicate the appropriate frequency to other communicating units. Some systems employ a plurality of signals which are not harmonically related. This requires complicated filtering and signal extraction. (See, e.g., U.S. Pat. No. 5,185,591.) Another scheme, Geometric Harmonic Modulation (GHM) allocates signaling energy into lobes, or tones, at different frequencies being evenly spaced at geometrically increasing multiples of a base frequency. The GHM signaling waveforms are spread spectrum signals in that the signal bandwidth, the bandwidth from the lowest frequency tone to the highest, vastly exceeds the information bandwidth conveyed by the GHM transmission.
Such solutions, however, can be costly to implement and may not ensure fool proof operation, thus rendering them inappropriate for applications where both cost and reliability are motivating considerations such as in household appliance control and communications.
There thus exists a need for a communication system which can reliably yet cost-effectively provide data communications over power lines even under the most adverse conditions.
SUMMARY OF THE INVENTION
The present invention provides a system and method for reliably communicating data over a channel, such as power lines, which channel is characterized by a great deal of harmonic interference, noise and distortion.
An exemplary embodiment of a transmitting device in accordance with the present invention comprises a signal synthesis device which generates a multi-tone signal having a plurality of frequency lobes selected to be positioned away from interference commonly found on power lines. The transmitted signal is generated in accordance with a sample clock signal derived from the line frequency (e.g., 50 or 60 Hz) and thus has a fixed relation thereto. In a preferred embodiment, a modulation device generates first and second tones from prestored waveform samples. The relative phase between the two tones is varied in accordance with the data to be transmitted. The two tones are summed, converted to analog form and applied to the power line for transmission.
The present invention further provides a receiving device for decoding signals generated by the transmitting device. The receiving device comprises a sample clock signal generator which, like the transmitting device, generates a sample clock signal from the line frequency. The modulated signal received from the transmitting sub-system is sampled at the clock frequency by an analog-to-digital converter to digital form and then passed to some form of signal analysis such as a discrete Fourier transform (DFT) device, preferably implemented with a fast Fourier transform (FFT) structure. The DFT device generates the frequency-domain components of the received signals which are then analyzed to extract the base band data encoded in the received signals.
In a preferred embodiment, each symbol of data (e.g., each bit) that is continuously transmitted by the transmitting sub-system until the transmitting sub-system receives from the receiving sub-system an acknowledgment that the symbol of data has been received. Because of the coherency of the receiving and transmitting sub-systems, the receiving sub-system will always properly decode the received signal, given enough samples. This is true even in conditions where the noise power equals or exceeds the signal power.
REFERENCES:
patent: 5185591 (1993-02-01), Shuey
patent: 5777544 (1998-07-01), Vander Mey et al.
patent: 5844949 (1998-12-01), Hershey et al.
patent: 6101214 (2000-08-01), Hershey et al.
patent: 6104707 (2000-08-01), Abraham
patent: 6115429 (2000-09-01), Huang
Kramer Levin Naftalis & Frankel LLP
Thalia Products, Inc.
Tweel John A.
LandOfFree
Power line communication system and method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power line communication system and method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power line communication system and method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582634