U.S. patent application number 10/666184 was filed with the patent office on 2004-03-25 for broadband cable television and computer network.
Invention is credited to Klein, Dean A..
Application Number | 20040060072 10/666184 |
Document ID | / |
Family ID | 28792540 |
Filed Date | 2004-03-25 |
United States Patent
Application |
20040060072 |
Kind Code |
A1 |
Klein, Dean A. |
March 25, 2004 |
Broadband cable television and computer network
Abstract
A communication system is provided which may comprise an
upstream source of broadband communications and a downstream local
area network, wherein the upstream source of broadband
communications is coupled to the downstream local area network
through a notch filter. In some embodiments, the upstream source of
broadband communications may be a cable television service
provider, and the local area computer network may use existing
cable television wiring as communication cable.
Inventors: |
Klein, Dean A.; (Eagle,
ID) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
28792540 |
Appl. No.: |
10/666184 |
Filed: |
September 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10666184 |
Sep 17, 2003 |
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08872010 |
Jun 10, 1997 |
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6637030 |
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08872010 |
Jun 10, 1997 |
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08840083 |
Apr 9, 1997 |
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Current U.S.
Class: |
725/127 ;
348/E7.05; 725/149 |
Current CPC
Class: |
H04N 2007/17381
20130101; H04N 7/106 20130101 |
Class at
Publication: |
725/127 ;
725/149 |
International
Class: |
H04N 007/173; H04N
007/16 |
Claims
What is claimed is:
1. A network bus comprising: a notch filter coupled to a coaxial
cable, said coaxial cable routed in a tree configuration to a
plurality of locations of a building, said notch filter configured
to filter out a portion of video signals carried by said coaxial
cable; and a frequency converter, coupled to said coaxial cable,
configured to receive signals from said coaxial cable at a first
frequency and to forward said signals at a second frequency,
wherein said first and second frequencies are within said filtered
out portion.
2. The network bus of claim 1, wherein said frequency converter is
configured to forward said signals via said coaxial cable.
3. The network bus of claim 2, wherein said building comprises a
residential building.
4. The network bus of claim 1, wherein said video signals are
delivered to said coaxial cable from a headend equipment of a
community antenna television system.
5. The network bus of claim 1, wherein said filtered out portion
comprises a frequency range from approximately 50 MHz to
approximately 750 MHz.
6. A local area computer network comprising: a notch filter
configured to receive a signal from a cable television transmission
system and to filter out a portion of said signal in the range of
approximately 50 MHz to approximately 750 MHz to produce a filtered
signal; a community antenna television wire configured to receive
said filtered signal and routed in a tree configuration to a
plurality of locations of a residence, said wire coupled to said
notch filter; a plurality of computers coupled to said wire, each
of said computers having a modem configured to receive and transmit
broadband signals between said computers; wherein said computers
are configured to send and receive communications between different
ones of said computers via said modem by modulating a carrier
having a frequency within said filtered out portion
7. The local area network of claim 6, wherein said personal
computer are configured to send signals to said cable television
transmission system using a carrier frequency in the range of
approximately 0 MHz to approximately 50 MHz.
8. The local area network of claim 7, wherein said modem is
configured to receive a signal at a first frequency and to transmit
said signal at a second frequency.
9. The local area network of claim 8, further comprising a
frequency converter configured to convert signals from said first
frequency to said second frequency.
10. The local area network of claim 9, wherein at least some of
said computers are configured to receive digital data from the
Internet via said wire.
11. The local area network of claim 9, wherein at least some of
said computers are configured to receive FM audio signals via said
wire.
12. The local area network of claim 9, wherein at least one of said
computers is configured to receive signals from said transmission
system using a carrier frequency in the range of approximately 0
MHz to approximately 50 MHz.
13. A method of making a local area network, the method comprising:
routing community antenna television wiring in a tree configuration
to different parts of a structure; coupling a notch filter to said
wiring for filtering out one or more television broadcasts
delivered to said wiring by a service drop of a community antenna
television distribution system; coupling to said wiring a plurality
of computing devices; and configuring at least some of said
computing devices for two-way communication with others of said
computing devices, wherein the two-way communication is carried at
least in part over said wiring at at least one frequency within
said filtered out television broadcasts.
14. The method of claim 13, wherein each of at least some of said
computing devices comprises a receiver configured to receive video
signals from said headend transmission equipment, a transmitter for
forwarding signals to said headend transmission equipment, and a
modem configured to receive and transmit broadband signals between
said computing devices.
15. The method of claim 13, wherein said computing devices comprise
a computer and a microprocessor controlled appliance.
16. The method of claim 15, wherein said computing devices comprise
an alarm system.
17. The method of claim 13, wherein said filtered out television
broadcasts comprise a portion of the frequency range between
approximately 50 MHz to 750 MHz.
18. The method of according to any of claims 14-17, wherein said
structure comprises a residential building.
19. The method of claim 13, wherein at least some of said computing
devices transmit communications at a first frequency and receive
communications at a second frequency, wherein said first and second
frequency are within said filtered out television broadcasts.
20. A method of networking computing devices, the method
comprising: coupling a notch filter to coaxial wiring carrying
television signals, wherein the coaxial wiring is routed in a tree
configuration to a plurality of locations in a building. filtering
out a frequency band comprising a portion of said television
signals with the notch filter; and establishing two-way
communications between at least two computing devices, wherein said
communications are carried at least in part over said coaxial
wiring utilizing said frequency band.
21. The method of claim 20, wherein said building comprises a
residential building.
22. The method of claim 21, wherein said residential building
comprises a plurality of rooms of a residence.
23. The method of claim 22, wherein said television signals are
delivered to said building via a service drop of a community
antenna television system.
24. The method of claim 20, wherein said frequency band spans the
range from approximately 50 MHz to approximately 750 MHz.
25. The method of claim 23, further comprising blocking at least
some of said communications from being transmitted outside said
local area network via said service drop.
26. The method of claim 20, wherein at least some of said computing
devices transmit said communications at a first frequency and
receive said communications at a second frequency, wherein said
first and second frequencies are in said frequency band.
27. The method of claim 26, further comprising providing a
frequency converter configured to receive said communications at
said first frequency and to forward said communications at said
second frequency.
28. The method of claim 20, wherein one of the computing devices
sends a communication to another of the computing devices at a
first frequency, and wherein said another computing device receives
said communication at a second frequency.
29. The method of claim 23, wherein said computing devices comprise
a network computer.
30. The method of claim 23, wherein said computing devices comprise
a microprocessor controlled appliance.
31. The method of claim 23, wherein said computing devices
comprises an alarm system.
32. The method of claim 20, wherein said computing devices comprise
a network computer and a microprocessor controlled appliance.
33. The method of claim 23, wherein said computing devices comprise
a network computer, a microprocessor controlled appliance, and an
alarm system.
34. A network device comprising: a receiver for receiving a
television signal from a community antenna television system; a
transmitter for transmitting signals to a headend equipment of said
community antenna television system; and a modem configured to
receive and transmit broadband signals between computing
devices.
35. The network device of claim 34, wherein said modem is
configured to receive signals at a first frequency and to transmit
said signals at a second frequency.
36. The network device of claim 34, wherein said receiver is
configured to receive digital data from the Internet.
37. The network device of claim 34, wherein said receiver is
configured to receive FM audio signals.
38. The network device of claim 34, wherein said receiver is
configured to receive signals in the range of approximately 50 to
750 MHz.
39. The network device of claim 34, wherein said network device
comprises a microprocessor controlled appliance.
40. The network device of claim 34, wherein said network device
comprises a computer.
41. The network device of claim 34, wherein said computing devices
comprise a microprocessor controlled appliance and an alarm
system.
42. A method of communicating data between computing devices
comprising: receiving a television signal from a headend
transmission equipment of a cable television transmission system;
filtering out a portion of said television signal in the range of
approximately 50 MHz to approximately 750 MHz to produce a filtered
signal; coupling said filtered signal to unlooped cable television
wiring; coupling a plurality of computing devices to said wiring,
wherein each of at least some of said computing devices comprises a
modem configured to receive and transmit broadband signals between
said computing devices; and establishing two-way communications, at
least in part over said cable television wiring, between different
ones of said computing devices via said modem using at least one
frequency within said filtered out portion.
43. The method of claim 42, wherein each of at least some of said
computing devices comprises a receiver configured to receive
signals from said headend transmission equipment and a transmitter
for forwarding signals to said headend transmission equipment.
44. The method of claim 42, further comprising forwarding a signal
from at least one of said computing devices to said transmission
system using a frequency in the range of approximately 0 MHz to
approximately 50 MHz.
45. The method of claim 42, wherein said wiring is routed in a tree
configuration to a plurality of different locations of a
residential building.
46. The method of claim 42, wherein said wiring comprises coaxial
cable.
47. The method of claim 42, wherein said computing devices comprise
a network computer.
48. The method of claim 42, wherein said modem in configured to
receive communications at a first frequency and to send
communications at a second frequency.
49. The method of claim 42, further comprising coupling a frequency
converter to said wiring, wherein said frequency converter receives
a communication at a first frequency and forwards said
communication at a second frequency.
50. The method of claim 42, wherein said computing devices comprise
a personal computer.
51. The method of claim 50, wherein said computing devices comprise
a microprocessor controlled appliance.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 08/872,010, filed Jun. 9, 1997. The Ser. No.
08/872,010 application is a divisional of U.S. patent application
Ser. No. 08/840,083, filed Apr. 9, 1997, which is now abandoned.
Both of these applications are hereby incorporated by reference in
their entireties herein.
BACKGROUND OF THE INVENTION
[0002] Over the past several years, local area networks (LANs) have
become commonplace in business and manufacturing facilities. In the
residential environment, though, stand-alone computers are common,
but networked personal computers (PCs) have remained relatively
rare. However, as consumers rely more heavily on personal computers
to telecommute, shop, and interact with the ever increasing number
of on-line services, home computer networks will become more
desirable. This trend may be further augmented by the development
of "smart" appliances, alarm systems, etc., which may be controlled
by a home computer system. In addition, "network computers" (NCs),
which are inexpensive networked terminals without significant local
memory or magnetic storage media have recently been introduced.
These devices will make available inexpensive means of accessing
data and programs on a remote personal computer, thereby reducing
the investment in hardware necessary to create a home computer
network.
[0003] Although the utility of home computers is increasing, and
the cost of network hardware is decreasing, another major expense
in the creation of such a home computer network resides in
outfitting the home with network cabling to interconnect the
desired PCs, NCs, appliances, and other network compatible devices.
This expense, of course, is not affected by reductions in the price
of the computer hardware itself. The expense of installing LAN
wiring is generally less of a problem when creating LANs in office
buildings. In the commercial and manufacturing environment, office
facilities are often pre-wired with excess telephone cable. Unused
telephone cable can therefore be used to support, for example, a
10BASET local area network. It has also become more common to
pre-wire business and manufacturing facilities with the dedicated
LAN communication cable necessary to support local computer
networks.
[0004] New residential construction generally does not include any
pre-wiring of LAN cabling, and although telephone wiring is
typically routed to many rooms of the house, there is generally no
excess telephone wiring which can be dedicated to use in a local
computer network. However, over 60% of the homes in the United
States are wired for cable television reception, providing a
wide-band and potentially very high capacity information pipeline
into a majority of American homes. This fact is currently
motivating the development of interactive communication on the
cable television infrastructure. In some cable television
distribution systems, downstream communication from the cable
service provider is carried on 6 MHz channels in the 50-750 MHz
range. Upstream communication from the customer to the cable
service provider is supported on several 6 MHz channels in the 5-42
MHz range. Over these communication channels, interactive services
may be provided which include analog telephone service, as well as
two-way digital communication such as access to the Internet,
electronic shopping, videoconferencing, and other communication
services. Cable modems, commercially available, for example, as the
model CyberSURFER(TM) from Motorola, are designed to implement such
two way digital communication between a consumer's personal
computer and the cable television service provider along the cable
television line. As this trend continues to develop, consumers may
connect more digital computing devices to their cable television
wiring.
[0005] However, the use of this CATV wiring to support a local area
network has not been previously accomplished. As is described in
detail in U.S. Pat. No. 5,255,267 to Hansen et al., it is possible
to inject broadband video channels onto LAN cabling carrying thin
Ethernet baseband communications. However, this requires that
baseband signal energy at frequencies up to 25 MHz be blocked from
entering the broadband video feed by a high pass filter. This
filtering eliminates the possibility of sending upstream messages
from the home to the cable service provider at, for instance, the 5
to 11 Mhz upstream channel currently supported by cable television
service providers. Furthermore, typical baseband transceivers are
designed to operate with twisted pair cable or 50 ohm coaxial
lines, not the 75 ohm coaxial cable pre-installed in homes and used
for cable television delivery.
[0006] The creation of a home personal computer network has thus
entailed a significant amount of cable routing through interior
walls of the household, which is a time consuming and expensive
procedure. What is needed therefore, is a system and method of
creating a home personal computer network without the necessity of
installing dedicated network cabling.
SUMMARY OF THE INVENTION
[0007] In one embodiment, the present invention includes a
communication system comprising an upstream source of broadband
communications and a downstream local area network. The upstream
source of broadband communications is coupled to the downstream
local area network through a notch filter. Other embodiments of the
present invention include a local-area-network of computing devices
comprising a notch filter comprising a first port and a second
port, wherein the first port is coupled to a first cable and the
second port is coupled to a second cable. In addition, the first
port comprises an input port for signals carried by the first
cable, and the second port comprises an output port coupling notch
filtered signals to the second cable. A plurality of computing
devices are coupled to the second cable.
[0008] The invention also comprises methods of interconnecting
computing devices. One method comprises receiving a signal
comprising a plurality of cable television channels from a first
coaxial cable, filtering out a portion of that signal to produce a
filtered signal, and coupling the filtered signal to pre-installed
cable television wiring. A plurality of computing devices are
coupled to the pre-installed cable television wiring, which then
communicate messages by modulating a carrier having a frequency
within the filtered out portion.
[0009] A notch filter comprising a first port adapted for
connection to a video distribution system and a second port adapted
for connection to a local-area-network are also provided by the
invention, as are new computing devices. Such computing devices may
comprise first and second receivers, each configured to receive a
broadband signal in the frequency band from approximately 50 to 750
MHz. Also, the computing devices may comprise first and second
transmitters, wherein the first transmitter is configured to
transmit a broadband signal in the frequency band from
approximately 5 to 42 MHz, and the second transmitter is coupled to
transmit a broadband signal in the frequency band from
approximately 50 to 750 MHz.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a block diagram illustrating the basic components
of a cable television distribution system.
[0011] FIG. 2 is a graphical representation of the signals
comprising a standard 6 MHz broadcast or cable television
channel.
[0012] FIG. 3 is a system level block diagram of a LAN implemented
on cable television wiring inside a residence.
[0013] FIG. 4 is a graphical representation of the signal
attenuation produced by the notch filter of FIG. 3.
[0014] FIG. 5 is a block diagram of a preferred computing device
for coupling to the LAN of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0015] Embodiments of the invention will now be described with
reference to the accompanying Figures, wherein like numerals refer
to like elements throughout. The terminology used in the
description is intended to be interpreted in its broadest
reasonable manner, even though it is being utilized in conjunction
with a detailed description of certain specific embodiments of the
invention. This is further emphasized below with respect to some
particular terms used herein. Any terminology intended to be
interpreted by the reader in any restricted manner will be overtly
and specifically defined as such in this specification.
[0016] As discussed above, one expense involved in the
establishment of a local-area-network of computing devices is the
provision of suitable interconnecting wiring. One aspect of the
present invention mitigates this expense by using existing
"community antenna television" wiring (or "CATV" or cable
television wiring) within a structure to support not only cable
television reception, but also network communications between
computing devices within the structure. Referring now to FIG. 1, a
cable distribution system comprising headend transmission equipment
10 operated by the cable television service provider is
illustrated. As is known in the art, the "headend" of the cable
transmission system is the point where UHF/VHF/FM and/or satellite
television signals are fed into the system. The headend 10 is
coupled to a distribution cable 12 that runs on a pole or
underground through a neighborhood which receives cable television
service. The individual residences 14 each receive the television
signal, which may of course comprise both video and audio signals,
from the distribution cable 12 via service drops 16.
[0017] The service drops 16 typically comprise 75 ohm coaxial
cable, and extend onto the premises as a 75 ohm coaxial cable bus
or tree configuration 18 internal to each residence 14. The
on-premises cabling 18 is generally routed to several rooms of the
residence 14, including the living and family rooms, as well as the
bedrooms, where it is connected to one or more television receivers
20.
[0018] Initially, cable television service included only
communication of television channels in a downstream path 22 to
subscribers. Currently, downstream communication is accomplished in
the frequency band between approximately 50 and 750 MHz. This
provides sufficient bandwidth for dozens of television channels,
each occupying a 6 MHz wide portion of the spectrum. Furthermore,
spectral efficiency can be improved by a factor of about three with
the implementation of currently available digital transmission
techniques, so that delivery of hundreds of television channels can
be expected in the future.
[0019] Many cable distribution systems have now been configured to
also support upstream communication to the cable television service
provider. This upstream communication path 24 has typically been
performed on the frequency band between approximately 5 and 42 MHz,
comprising a bandwidth of approximately six standard television
channels. One use of this upstream communication capacity is the
consumer issuance of pay-per-view signals to the cable service
provider. This communication occurs generally in an upstream band
from approximately 5 to 11 MHz. As will be explained below, it is
one aspect of the present invention that the on-premises cabling 18
can be used to support a local area computer network in addition to
cable television service by utilizing a portion of the downstream
spectral bandwidth 22 for LAN communication. Using the methods and
apparatus of the present invention, this is accomplished without
interfering with the upstream communication path 24.
[0020] The downstream bandwidth of 50 to 750 MHz is partitioned
into several 6 MHz wide channels which are grouped into sets of
adjacent channels with unused bands provided between different
channel sets. One such channel is illustrated in FIG. 2. The
television signal comprises a luminance signal 30 modulated onto a
carrier 32 which is 1.25 MHz above the lower band edge. A
chrominance signal 34 is transmitted on a sub-carrier at about 3.58
MHz above the luminance carrier 32. Finally, an FM modulated audio
signal 38 is provided on a carrier at about 4.5 Mhz above the
luminance carrier 32. Adjacent luminance carriers 32 are assigned
to frequencies which are spaced 6 MHz apart, thereby creating
frequency division multiplexed channels of 6 MHz width. Almost all
of the energy transmitted for a given channel is confined to the 6
MHz channel width to eliminate unacceptable adjacent channel
interference.
[0021] With a downstream bandwidth of approximately 700 MHz, it can
be appreciated that a very large number of 6 MHz wide channels can
be supported, which number will only increase with the
implementation of digital television transmission. It can therefore
also be appreciated that in any given residence, many of these
available channels will be either (1) unprogrammed by the cable
service provider, (2) comprise premium channels to which the
consumer does not subscribe, or (3) be channels which are simply
not watched to an appreciable extent. Thus, a significant amount of
available spectrum is not efficiently utilized.
[0022] Referring now to FIG. 3, a residence 14 is shown which
illustrates the implementation of a LAN that communicates over this
under-utilized bandwidth on the cable television infrastructure. As
was described with reference to FIG. 1, the residence 14 is
supplied with cable television service via a service drop 16 which
supplies cable television signals to a bus or tree configuration of
on-premises 75 ohm coaxial cable. Preferably, the service drop 16
passes through a notch filter 40 which isolates a segment 42 of the
service drop from selected frequency bands which are defined by the
stop bands of the notch filter 40. In some configurations, the
isolated segment 42 has been wired to several rooms of the
residence to supply cable television to those areas of the
household where television reception may be desired. More specific
characteristics of the isolation provided by the notch filter are
described in more detail below with reference to FIG. 4. Briefly,
the notch filter 40 effectively blocks selected bands of
frequencies within the total 50 to 750 MHz downstream bandwidth
from entering the residence in the downstream direction. The notch
filter 40 also prevents upstream transmission out of the residence
14 in the same selected band. As is set forth in detail below, the
notch filter clears a portion of the downstream spectrum for use as
LAN bandwidth. The notch filter also helps ensure privacy of
network communication because LAN signals are blocked from exiting
the residence and being coupled to the cable television
distribution network. The notch filter 40 may comprise a body
having two ports. One port is adapted for connection to a video
distribution system through, for example, a service drop 16. The
second port is adapted for connection to a local-area-network
through, for example, a segment of cable 42 inside a residence, as
will be described in more detail below. It can be appreciated that
a notch filter circuit, or two or more notch filter circuits, may
be incorporated into other electronic devices currently used in
communication systems such as cable distribution amplifiers,
splitters, set-top converters, or even cable ready television sets.
In these cases, of course, the device may include additional ports
adapted for connection to other pieces of equipment.
[0023] Inside the residence 14, several television receivers may be
coupled to the isolated segment 42 of the cable television wiring.
The television receivers 20 may include upstream transmitters which
operate in the 5 to 42 MHz upstream channels for the transmission
of pay-per-view or other signals supported by the cable television
service provider. Also coupled to the isolated segment of cable
television wiring are a plurality of computing devices 44, 46, and
48. Although illustrated as PCs in FIG. 3, it can be appreciated
that these computing devices 44, 46, 48 can be of many different
types, including network computers, microprocessor controlled
appliances, alarm systems, and the like. Because one or more bands
of frequencies have been notched out of the cable wiring 42 by the
notch filter 40, the computing devices 44, 46, and 48 can
communicate in the notched out bands using known LAN configurations
described below.
[0024] LAN physical layers can be broadly grouped into two
different classes: baseband and broadband. A baseband network
transmits data as alternating positive and negative voltage levels
on the LAN interconnecting cable. A broadband network encodes data
as phase, amplitude, and/or frequency shifts onto a sine wave
carrier. Industry standard physical layers of both types have been
defined in two standards promulgated by Institute of Electrical and
Electronic Engineers (IEEE). These standards are set forth in
ANSI/IEEE 802.3, 1996 Edition and IEEE 802.4-1990, which
publications are well known to those of skill in the art. These two
IEEE standards are hereby incorporated by reference in their
entirety.
[0025] Baseband communication between the computing devices 44, 46,
48 includes serious disadvantages because of the desire to preserve
the availability of the 5 to 42 MHz band for upstream
communications to the cable service provider. Accordingly, the
residence computing devices 44, 46, 48 may utilize broadband
communication. This is compatible with the pre-installed 75 ohm
coaxial cable, and also allows signal energy to be contained within
the bands of frequencies notched out by the filter 40. Furthermore,
this configuration prevents LAN interference with those downstream
cable television channels which are not notched out by the filter
40, and also prevents interference with upstream communications in
the 5 to 42 MHz band. Specific LAN physical layers which may be
implemented include the 10BROAD36 configuration defined in IEEE
802.3 and the broadband token passing networks defined in IEEE
802.4. Device interface hardware for establishing communication
over these broadband networks is well known to those of skill in
the art.
[0026] The broadband LAN of FIG. 3 may be a single cable
configuration utilizing two frequency bands for communication, as
only a single cable is generally strung within the residence to
distribute cable television signals. In such single cable broadband
networks, the networked devices receive data at one carrier
frequency and transmit data at a second carrier frequency.
Accordingly, the LAN of FIG. 3 may include a headend frequency
converter 50. This device receives inbound communications from each
device 44, 46, 48, in a first frequency band, and converts them to
outbound communications in a second frequency band which are
received by the computing devices. It is, of course, preferred for
both transmit and receive frequency bands to be within notched out
frequency bands created by the notch filter 40.
[0027] Referring now to FIG. 4, the characteristics of the notch
filter 40 will be described. The notch filter 40 may be of active
or passive configuration, and may further be made tunable.
Electrically, the notch filter 40 defines a response curve 60 of
gain as a function of frequency. The filter 40 may exhibit a signal
attenuation which reduces the incoming cable television signal
strength within two selected bands 62, 63 to below a noise floor of
approximately -30 dBmV/14 MHz. In one embodiment, the center
frequencies 64, 65 of the two bands are approximately 192.25 MHz
apart, to be compatible with the transmit/receive band separation
adopted in IEEE 802.3 and 802.4. It can be appreciated that deeper
attenuation of the downstream signal will improve the internal
broadband network signal to noise ratio.
[0028] In the above described embodiment, the attenuation is
sufficient to reduce the signals within the selected bands of
frequencies to at or below the maximum cable noise levels allowed
by IEEE 802.3. However, signal attenuation this great may not be
necessary to implement a LAN in accordance with the present
invention. What is important is that the attenuation be sufficient
for broadband communication between the on-premises networked
devices 44, 46, 48 to occur on carriers within the notch filter
stop bands 62, 63 with reasonable reliability. For some broadband
networks connected to some standard cable television signals, a 20
dB or greater signal attenuation provides sufficient rejection of
the cable television signal to allow reliable internal broadband
communication over the cable wiring 42 at carrier frequencies
within the rejected bands, and in some cases, the required
attenuation may be less. One possible situation where notch filter
attenuation may not need to be particularly deep is where the stop
bands of the notch filter reside in regions of the downstream
spectrum that are not being utilized by the cable television
service provider to deliver downstream signals. In this case there
is no downstream signal requiring attenuation, thereby reducing the
need for deep notch filter attenuation. It may be noted however
that some notch filter attenuation may still be desirable to
prevent excess LAN signal energy from exiting the residence and
being coupled to the cable drop 16 and then to the rest of the
upstream distribution system.
[0029] In the embodiment illustrated in FIG. 4, the notch filter
"stop bands" 62, 63 comprise the frequency bands for which the
signal level of the downstream cable television signals is reduced
to at least below -30 dBmV/14 MHz noise level. In this embodiment,
these frequencies are considered "rejected," and the cable on the
other side of the filter 40 is considered isolated from these
frequency bands. In accordance with the above discussion, however,
a "stop band" does not necessarily require this level of
attenuation, and the term "stop band" is not intended to be defined
by specific numerical attenuation values. Rather, "stop band" is
intended to denote that band of frequencies for which the
attenuation of the notch filter is sufficient to allow broadband
LAN communication within the stop band on cable coupled to the
output of the notch filter. As used herein, such a stop band
defines a band of "rejected" frequencies, and cabling coupled to
the output of the notch filter is isolated from those rejected
frequencies. It can be appreciated therefore that the notch filter
40 attenuation required to create a stop band will vary from system
to system, and will depend on the nature of the LAN being used in
the residence, the strength of the incoming cable television
signal, as well as many other factors. Appropriate notch filter
attenuation values may be readily determined by those of skill in
the art for specific implementations of the invention.
[0030] In addition to the depth, the widths 66, 67 of the stop
bands may also be variable, as well as the center frequencies 64,
65. These values may be chosen in accordance with the nature of the
incoming television signal and the nature of the LAN being
implemented on the output of the notch filter 40. The center
frequencies 64, 65 of the stop bands may be in the cable television
downstream communication band somewhere between approximately 50
and 750 MHz, with the value selected to provide minimal
interference with the consumer's reception of desired cable
television channels. Compatibility with IEEE 802.3 requires the
stop band center frequencies to be 192.25 MHz apart, with the lower
frequency band 62 being dedicated to transmission of messages by
the computing devices 44, 46, 48, and with the higher frequency
band 63 being dedicated to reception of message by the computing
devices 44, 46, 48. In one embodiment, the transmit stop band
resides from 53.75 MHz to 71.75 MHz, and the receive stop band
resides from 246 to 264 MHz. These bands coincide with certain
transmit and receive channels for a broadband network compatible
with IEEE 802.3. Of course, different carrier frequencies can be
chosen, being selected to produce stop bands which attenuate only
cable television channels which the user is not reluctant to lose.
In some cases, it will be desirable to raise the stop band
frequencies and corresponding LAN carrier frequencies because the
transmit bands allocated by IEEE 802.3 reside in the Low Band (i.e.
channels 2-6) of the incoming cable television service, and a
consumer may prefer not to notch these particular channels out.
[0031] The widths 66, 67 of the stop band should be wide enough to
accommodate the bandwidth requirements of the LAN being
implemented. For the embodiment discussed above, 18 MHz bandwidth
(including a 4 MHz collision enforcement band) is used for each of
the transmit and receive bands. Generally, bandwidth requirements
decrease with decreasing desired LAN data transfer rate. A 1 Mb/sec
broadband LAN may require only 1-2 MHZ of bandwidth, whereas a 10
Mb/sec broadband LAN may require 12 or more MHz of bandwidth. In
the residential environment, 1 Mb/sec internal communication data
rate may often be sufficient, and in this case, each stop band can
reside entirely within a single 6 MHz cable television channel. The
center frequencies 64, 65 of the stop bands may then be chosen to
be approximately centrally located within downstream cable
television channels. Higher speed LANs, like the 10BROAD36 of IEEE
802.3 which requires a total of 36 MHz bandwidth, will require stop
band widths that reject several incoming cable television channels.
In these cases, finding several unutilized or underutilized
channels should not be difficult. The design and construction of
notch filter circuits which produce stop band depths, widths, and
center frequencies suitable for use with the present invention is
well known to those of skill in the art, and the details of the
notch filter 40 circuit are accordingly not further described
herein.
[0032] To take full advantage of the communication paths of the
invention, a computing device may incorporate a plurality of
receivers and transmitters. Such a computing device is illustrated
in FIG. 5. In this embodiment, the coaxial cable 42 is coupled to
the computing device 44, and is routed to a first tunable
receiver/demodulator 70 having a frequency range of approximately
50 to 750 MHz. This receiver additionally may comprise one or more
demodulators for retrieving NTSC or PAL encoded video from the
cable television service, FM audio signals, and also for recovering
digital data from, for example, cable service provided Internet
access. The computing device may also comprise a modulator and
transmitter 72 coupled to the cable 42 for transmitting upstream
signals to the cable television service provider. This transmitter
72 may operate in the 5 to 42 MHz band currently supported by many
cable television providers. Furthermore, for on-premises
communication of internal data with other computing devices within
the residence, the computing device 44 additionally may comprise a
dual frequency modem 74 coupled to the cable 42 for transmission
and reception of broadband signals on the LAN inside the residence.
The modem 74 may operate at a transmission frequency f.sub.1 and a
receiving frequency f.sub.2 which are each within a stop band of
the notch filter 40.
[0033] As with the circuitry for the notch filter 40, suitable
transmitters, receivers, modulators, and demodulators for
communicating as described above may be produced by those of skill
in the art without undue experimentation or further inventive
contribution, and further details of their construction is not
described herein. These individual components of the above
described system have been commercially made and used in other
broadband communication systems such as LAN equipment compatible
with the broadband specifications of IEEE 802.3 and 802.4, as well
as in television set top converters and cable modems.
[0034] The expense and difficulty of installing a home personal
computer network is significantly reduced with the invention
because existing wiring in the residence is also utilized to
support a LAN. This is accomplished by utilizing existing cable
television wiring as LAN interconnecting cable. Implementation of
such a system provides many advantages over the creation of a
separate in-home computer network. In addition to the fact that
installation is relatively inexpensive because the cable is already
installed, the cable itself supports very high data rates and
produces comparatively low levels of electromagnetic interference.
Furthermore, the computers on the network are coupled to the cable
television service and are therefore, able to receive all of the
video or data services available from the cable television service
provider.
[0035] The foregoing description details certain embodiments of the
invention and describes the best mode contemplated. It will be
appreciated, however, that no matter how detailed the foregoing
appears in text, the invention can be practiced in many ways. For
example, many different types of broadband LANs can be supported by
cable television wiring which use different modulation and medium
access control techniques. Furthermore, LANs which may not be
classified as "broadband" may be used in the system of the present
invention as long as the signal energy of the LAN communication can
be confined to a selected portion of the available spectral
bandwidth of the cable. It will also be appreciated that the
specific carrier frequencies and communication frequency bands
discussed above are currently preferable because of compatibility
with certain standards and cable distribution systems currently
developed. The invention, however, is not limited to these
frequencies and frequency bands. In addition, although the system
has been described in the context of the delivery of cable
television to residential buildings, the invention is not limited
to this environment, and may be utilized in any communication
system where it is desirable to more efficiently use available
bandwidth and/or to avoid the expense of installing additional LAN
cabling. As is also stated above, it should be noted that the use
of particular terminology when describing certain features or
aspects of the present invention should not be taken to imply that
the broadest reasonable meaning of such terminology is not
intended, or that the terminology is being re-defined herein to be
restricted to including any specific characteristics of the
features or aspects of the invention with which that terminology is
associated.
[0036] The invention may be embodied in other specific forms
without departing from its spirit or essential characteristics. The
described embodiment is to be considered in all respects only as
illustrative and not restrictive, and the scope of the invention
is, therefore, indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning
and range of equivalents of the claims are to be embraced within
their scope.
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