Telephonic communications – Telephone line or system combined with diverse electrical...
Reexamination Certificate
1999-04-16
2001-05-22
Chan, Wing F. (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
Reexamination Certificate
active
06236718
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system for transmitting signals between components of a video system over the telephone wiring of a residence.
Until the late 1970's, it was very unusual for ordinary consumers to own electronic devices that generated or supplied video signals. Virtually all video programs viewed on television sets were received “over the air”. This situation changed over the past decade as VCRs, video cameras, cable converters, and home satellite systems became popular.
Currently, many consumers are able to watch video programs at different locations because they own more than one television set. When viewing programs from one of the sources mentioned above rather than those picked up “over the air”, however, it is necessary to convey the signal from the video source to the television set. When source and receiver are located in the same room, connecting the two with a coaxial cable is usually the easiest method. VCRs and cable converters are nearly always connected to nearby television sets in this manner.
When the source and receiver are not located in the same area, a network of coaxial cabling extending through the residence is a fine solution. Most residences, however, are not wired this way, or have networks that do not allow access at all desired locations. Furthermore, most consumers insist that the wiring be neatly installed or kept entirely out of sight, making installation of a network very difficult and unwieldy. This presents a problem when connection between a video source and a television requires wiring that extends between rooms, especially rooms located far from each other, or on different levels.
Today, it is very common for a residence to include a VCR and a television located in a “sitting room”, and a second television located in a bedroom. This has generated an enormous demand for technology that transmits video across a residence without requiring installation of new wires. Possible solutions are to broadcast the signal at low power, or to use power lines or telephone wiring, which are always available, as a conductive path.
Broadcasting is currently not feasible in the U.S. because of FCC regulations, and is not feasible in most other countries for similar reasons. (Several consumer devices that broadcast video at low power have been marketed, however, despite their clear violation of FCC regulations. This testifies to the existence of a large demand for transmission of video over short distances.) In addition to legal obstacles, the possibility of unintended reception of broadcast signals outside residences, and the possibility of interference from other sources broadcasting at the same frequency also present problems.
Regulations covering transmission between source and receiver over conductive paths are much less restrictive, and signals transmitted by this method are much less likely to encounter interference from other signals or be open to interception. Transmission across power wiring is very difficult, however, because appliances typically attached to those networks often impart electrical noise at many different radio frequencies, creating a high potential for interference. Furthermore, a reliable conductive path is not always available across “fuse boxes”, causing problems when source and receiver derive power from different circuits.
The difficulties in transmitting video by broadcasting or by conduction over power lines leave conduction over telephone wiring as the sole remaining option. This technique also involves very serious technological and legal challenges, however, and no solution has been found.
The most obvious difficulties are avoiding interference with telephone communications and conforming with all regulations that govern devices that connect to the public telephone network. Because telephone wiring in the US and many other countries typically includes four conductors, only two of which are used for communications in residences served by a single telephone number, availability of the unused pair would seem to present an interesting opportunity for avoiding these problems. Unfortunately, wiring installers often do not connect the unused pair at the network junctions, leaving breaks in the conductive paths offered by these wires.
The path supplied by the active pair, on the other hand, is guaranteed to be continuous between two jacks as long as telephone devices become active when connected at those jacks. An exception is residences where each jack is wired directly to a central electronic switching unit that provides an interface to the public telephone system. The conductive paths between jacks are likely to be broken across this unit.
There are other technical and legal problems associated with transmission over this wiring beyond those created by the connection to a public or private telephone network. The technical problems derive from the fact that transmission of video was not a consideration when standards for wire properties, installation and connection techniques, and telephone electronics were established. Because these are all factors that can influence the ability of the wiring to reliably transmit high quality RF signals, this environment is poorly suited for transmission of video.
Further legal problems derive from the fact that all RF signals conducted across unshielded wiring will broadcast at least some electromagnetic radiation. (Unlike coaxial cable, telephone wiring is not shielded by a grounded metallic conductor that eliminates radiation.) Because restrictions on RF radiation are very limiting in the US and most other countries, they can potentially defeat any particular electronic technique that could otherwise successfully achieve transmission.
Systems have been developed to transmit video signals over ordinary telephone wiring, but none is practical for the residential application described. Chou (U.S. Pat. No. 4,054,910) discloses a system for transmitting video over an ordinary pair of wires without boosting the video signal in frequency. Video signals transmitted by devices that follow that design, however, would include energy at low frequencies that would interfere with telephone signals.
Tatsuzawa (U.S. Pat. No. 3,974,337) discloses a system that slightly boosts video signals in frequency (by approximately 0.5 Mhz) to prevent conflict with voiceband communications. The system also requires, however, a sophisticated procedure for compressing the bandwidth of the signal so as to avoid use of energies at the higher frequencies, which attenuate quickly. Further, the higher end of the resulting band is “preemphasized”, or amplified more than the lower frequencies, in order to account for the remaining differences in attenuation.
The purpose of the technique disclosed by Tatsuzawa is to allow video signals to travel distances on the order of 1 km or more. The electronics that reduce and expand the signal bandwidth however, are very expensive. There is also a major difficulty in that the preemphasis of the signal must be adjusted depending on the distance between source and receiver. This is of significant inconvenience to a consumer. Further, the system depends on electrical characteristics particular to frequencies between 0 and 4 Mhz, limiting the transmission frequency to that band. This creates legal problems because in the U.S., for example, regulations severely limit the RF energy below 6 Mhz that can be fed to wiring that is connected to the public telephone network. Finally, the restriction to a single band allows for transmission of only a single signal.
There are countless methods for reducing the resolution or the refresh rate of a video signal in order to reduce the bandwidth enough to avoid the problem of attenuation, e.g. Lemelson (U.S. Pat. No. 4,485,400). Current video standards in the U.S. and elsewhere, however, use a refresh rate just quick enough to avoid annoying “flickering” of the picture. Because most consumers have little tolerance for “flickering” or a reduced picture quality, these techniques do not present solutions to the
Chan Wing F.
Fish & Richardson P.C.
Inline Connections Corporation
LandOfFree
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