Communications: electrical – Systems – Selsyn type
Reexamination Certificate
2001-05-23
2003-08-19
Tweel, John (Department: 2632)
Communications: electrical
Systems
Selsyn type
C375S267000
Reexamination Certificate
active
06608552
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a system for transmitting data over power-carrying wires and, more particularly, to a system, for carrying commands and control signals over power-carrying wires to lamp controllers, that is relatively immune to disturbances prevalent on such wires.
In a controlled lighting system, such as deployed particularly in commercial and industrial premises, there are typically a plurality of lamp clusters, each controlled by a controller, and one or more command stations, from which various lighting functions may be controlled by users. Usually the lamps are of the fluorescent type and a controller includes an electronic ballast—to stabilize the light. An important lighting function is dimming, that is—controlling the light level of each lamp cluster. Commands for changing the light level or for setting it at a desired value are usually issued by the user by means of a command station. Such commands may also be issued by a computer or by some appliance control center (such as deployed in a home). In some systems there are also deployed light level detectors—for monitoring the actual light level at certain points and issuing feedback control signals to the controllers, so as to maintain some predetermined light level.
All such command—and control signals must be transmitted from their respective sources to one or more of the lamp controllers. Such transmission may be effected either by wireless means, or over a pair of wires, dedicated to the purpose, or over wires that primarily serve for the transmission of power and that usually must also be connected to the controllers and to the various command-issuing units. Wireless transmission requires relatively expensive transmitting and receiving equipment for reliable operation, especially for systems with large spatial extent. Transmission over dedicated wires requires that such wires be specially installed; such installation may be relatively expensive, especially in older premises. On the other hand, power mains are ubiquitous in most buildings and easily accessible from all units; moreover, in many lighting systems full power wiring may already exist prior to the installation of the control features and components and thus represents a readily available conduit for the control signals.
The present invention is primarily concerned with method and apparatus for transmitting lighting control signals over power-carrying wires. However, while the invention will be described in terms of an embodiment within a lighting control system, it should be understood to apply, with obvious modifications, also to other systems that require transmission of data or control signals over power-carrying wires, such as heating- and cooling systems, industrial production lines or home appliance control systems.
From the point-of-view of signal transmission, power lines are electrically very noisy, that is—they carry, in addition to the power (at a frequency of 50 or 60 Hertz, and its harmonics), randomly varying voltages of relatively large magnitude. Part of such noise comes over the mains from outside the controlled system and part of it may be generated within the system —e.g., by switching power supplies, electronic ballasts, motors, lamp instabilities etc. The time variation of the noise voltages may be categorized into three groups: (1) continuous wide-band random variation (akin to “white” noise), (2) continuous narrow-band disturbances (about distinct frequencies) and (3) randomly occurring narrow pulses. In order to reliably transmit data in the presence of such noise and disturbances, the transmission method (that is —the characterization of the signals and the manner in which data is encoded onto them and decoded from them) must be optimally designed. Moreover, the impedance of power lines is generally not constant, but rather frequency dependent and variable with time.
Another important characteristic of power-line transmission systems, especially when serving power control signals, is the relatively low rate at which data need generaly be transmitted. Effective data rates of less than a thousand bits per second are usually sufficient. A third, related, characteristic is that the controlled system, with its power wiring, has a limited spatial extent and that the power transmission medium may generally be regarded as dedicated to the system.
An important requirement from most practical power-line transmission systems is that the necessary hardware components, especially those associated with the controlled devices (and thus usually functioning as signal decoders) carry a low cost. This is due to the fact that most of such devices, such as motors, lamp ballasts and regulators, themselves carry relatively low costs.
Most methods of prior art for transmission over power lines have been largely based on methods for transmission over other media, such as wire pairs, coaxial cables and wireless transmission channels. Such methods, well known in the general fields of communications and data transmission, are optimized for transmission conditions on such other media and particularly—for their noise characteristics. The latter are, in most cases, of the wide band type, but in certain systems, one of the other two types mentioned above (continuous distinct frequencies or impulses) may be predominant and the transmission methods optimized for the relevant one of them. Generally, however, few of the known transmission methods is specifically designed to overcome all three mentioned types of disturbances (noise), characteristic to power lines, simultaneously.
Moreover, traditional transmission systems are designed for relatively high rates of data. Although various spectrum-spreading methods are utilized, the available bandwidth generally limits the spread ratio. On the other hand, as has been mentioned hereabove, power system control signal are of relatively low rate and thus it stands to reason to simply modify a known method so as to spread the spectrum widely enough to reliably overcome all noise types prevalent on power lines. In practice, this proves to yield insufficient reliability vs. the achieved transmission rate.
Finally, the hardware components required by systems based on current transmission methods are relatively expensive. Even components currently offered commercially, specifically for power-line communication, are too expensive for most practical lighting systems. The following examples may serve as an indication of typical costs: In a “X-10” system, a remote unit (i.e. one attached to a controlled device) costs about $20. A power-line modem is offered by Echelon Corp. at about $120 and by Intellon Corp.—for $100-200. By contrast, the present invention aims at enabling a remote reception component to sell for between $1 and $10.
U.S. Pat. No. 5,579,335 discloses apparatus and method for decoding signals transmitted over power lines, using band-splitting filters, delay-line correlators, which operate on two separate frequency bands, and further signal processors. The method enables transmission rates in the order of 100 kb/s (which is much higher than required in practical control systems), but the apparatus is inherently expensive.
U.S. Pat. No. 5,448,593 discloses a system for network communication over power lines, which uses two-frequency FSK modulation and an error coding system to control reception quality; upon analyzing errors in the received signal, receiver gain is modified or different frequency pairs are selected for keying or the transmitted bit rate is adjusted. The transceiver apparatus for such a system is, again, inherently expensive and has additional drawbacks in that it (a) assumes stationary noise conditions over a certain period, which is not always the case (especially with impulse-type noise), and (b) requires a reverse transmission path (and thus—additional transmission apparatus), which otherwise is not necessary and further increases system cost.
U.S. Pat. No. 5,448,593 discloses a system for transmitting and detecting signals over power lines to
Fogel Meir
Raviv Dov
Rubin Daniel
Wulich Dov
Friedman Mark M.
Systel Development & Industries Ltd.
Tweel John
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