U.S. patent number RE35,774 [Application Number 08/340,733] was granted by the patent office on 1998-04-21 for remote link adapter for use in tv broadcast data transmission system.
This patent grant is currently assigned to Hybrid Networks, Inc.. Invention is credited to James C. Long, Eduardo J. Moura.
United States Patent |
RE35,774 |
Moura , et al. |
April 21, 1998 |
**Please see images for:
( Certificate of Correction ) ** |
Remote link adapter for use in TV broadcast data transmission
system
Abstract
A hybrid transmission system is provided to transmit and receive
high-speed digital information in the form of variable length
packets using standard television practices and components. The
basic building block of this hybrid digital transmission system is
the device at the remote location that receives the analog
broadcast TV-like signal processed by a standard vestigial sideband
video modulator. This device decodes the digital information from
the signal and then passes it along as digital information to any
form of a data terminal equipment or computer.
Inventors: |
Moura; Eduardo J. (San Jose,
CA), Long; James C. (Sunnyvale, CA) |
Assignee: |
Hybrid Networks, Inc.
(Cupertino, CA)
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Family
ID: |
25046576 |
Appl.
No.: |
08/340,733 |
Filed: |
November 16, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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757151 |
Sep 10, 1991 |
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Reissue of: |
098764 |
Jul 28, 1993 |
05347304 |
Sep 13, 1994 |
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Current U.S.
Class: |
725/118 |
Current CPC
Class: |
H04H
20/30 (20130101); H04H 60/15 (20130101); H04L
12/2801 (20130101); H04L 12/2856 (20130101); H04L
12/2898 (20130101); H04M 11/08 (20130101); H04N
1/00098 (20130101); H04N 7/088 (20130101); H04N
7/173 (20130101); H04H 60/80 (20130101) |
Current International
Class: |
H04M
11/08 (20060101); H04L 12/28 (20060101); H04N
7/173 (20060101); H04H 001/00 () |
Field of
Search: |
;495/4.2,5.1,6.1,6.2,6.3
;348/1,12-13,15,17 ;375/36 ;370/73,76 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 144 801 A3 |
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Jun 1985 |
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EP |
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0 401 873 A3 |
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Dec 1990 |
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EP |
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33 12 723 A1 |
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Oct 1983 |
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DE |
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91/06160 A |
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May 1991 |
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WO |
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WO 94/01280 |
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Jan 1994 |
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WO |
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WO 94/14282 |
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Jun 1994 |
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WO |
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Other References
Descriptive Material Describing Row-Grabbing System of Information
Retrieval Developed by IDR. .
International Business Machines Request for Quotation Dated May 14,
1990. .
Letter from Ed Moura to T. Sappington dated Jun. 5, 1990 (Hybrid
Networks response to IBM Request for Quotation)..
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Primary Examiner: Pham; Chi H.
Attorney, Agent or Firm: Farkas and Manelli
Parent Case Text
This is a continuation of application Ser. No. 07/757,151, filed
Sep. 10, 1991, now abandoned.
Claims
What is claimed is:
1. In a high speed digital information transmission system in which
multi megabit per second digital data is .[.addressably.].
broadcast using .[.contiguous.]. .Iadd.a continuous transmission
that includes address information in .Iaddend.bandwidth in .Iadd.at
least a portion of the spectrum .Iaddend.of a television channel to
a remote site, a remote link adapter comprising
a hybrid interface for .[.receiving.]. .Iadd.detecting .Iaddend.and
demodulating a multi megabit per second digitally encoded signal to
verify an address .Iadd.indicative of said remote link adapter
.Iaddend.and obtain .[.the.]. transmitted digital data .Iadd.in
accordance with detection of said address.Iaddend., said hybrid
interface providing a .[.full duplex.]. .Iadd.two way
.Iaddend.asymmetric network connection which is constructed from
independent forward and return transmission channels in two
directions,
a user interface for providing said digital data to data terminal
equipment, a microprocessor .[.control means.]. .Iadd.controller
.Iaddend.for controlling said hybrid interface in accordance with
protocols for controlling the flow of said digital data and
.[.the.]. addressing in the forward and return transmission
channels, and
a bus interconnecting said user interface, said hybrid interface,
and said microprocessor .[.control means.].
.Iadd.controller.Iaddend..
2. The remote link adapter as defined by claim 1 wherein said
return channel includes a telephone line modem.
3. The remote link adapter as defined by claim 1 wherein said
return channel includes a radio interface.
4. The remote link adapter as defined by claim 1 wherein said
return channel includes a CATV interface.
5. The remote link adapter as defined by claim 1 wherein
said user interface includes an Ethernet interface,
said digital data are broadcast at multi megabit per second data
rates using the frequency spectrum of a 6 MHz television channel,
and
said return channel is provided by an independent transmission path
with data transmission rates of at least 9600 bits per second
whereby said remote link adapter operates in a high speed
asymmetric data transmission system.
6. The remote link adapter as defined by claim 1 wherein said user
interface includes a personal computer bus interface.
7. The remote link adapter as defined by claim 1 wherein said user
interface interfaces with a video game system.
8. The remote link adapter as defined by claim 1 wherein said
hybrid interface includes an RF modem.
9. The remote link adapter as defined by claim 1 wherein said
microprocessor .[.control means.]. .Iadd.controller
.Iaddend.controls the addressing of said hybrid interface and the
flow of data in said bus to any number of multiple users connected
to the user interface. .Iadd.
10. In a high speed digital information transmission system in
which multi megabit per second digital data is transmitted using
continuous transmissions that include address information in any
portion of bandwidth a television channel to a remote site, said
system comprising a remote computer and a remote link adapter for
interconnecting said remote computer to an asymmetric network, said
adapter comprising:
a hybrid interface for demodulating a multi megabit per second
digitally encoded signal to obtain transmitted digital data, said
hybrid interface providing a two way asymmetric network connection
which is constructed of independent transmission channels in two
directions,
a user interface for providing digital data from said digitally
encoded signal to said remote computer,
a microprocessor controller for controlling said hybrid interface
to control the flow of digital data in the transmission
channels,
a bus interconnecting said remote computer, user interface, said
hybrid interface and said microprocessor controller, and
said digitally encoded signal includes address information
associated with said remote computer and said microprocessor
controller controls the flow of digital data in accordance with
said address information. .Iaddend..Iadd.11. A method for
transmitting multi megabit per second digital data in a high speed
digital information transmission system including a microprocessor
connected to control a hybrid interface, the method comprising the
steps of:
transmitting a multi megabit per second digitally encoded digital
data signal to a remote site using continuous transmissions that
include address information in any portion of bandwidth of a
television channel;
forming with the hybrid interface a two way asymmetric network
including independent forward and return channels in two
directions;
demodulating at the remote site said multi megabit per second
digitally encoded data signal transmitted in the forward channel of
the television channel and received by the hybrid interface to
obtain transmitted digital data;
supplying demodulated digital data to data terminal equipment;
and
controlling the flow of digital data in the forward and return
channels in accordance with address information detected in said
digitally encoded data signal, said address information being
indicative of said remote site. .Iaddend..Iadd.12. The method
according to claim 11 in which digital data flows in a return
channel including a selected one of telephone lines, a radio
channel, an Ethernet channel, and a CATV channel.
.Iaddend..Iadd.13. The method according to claim 11 in which in the
step of transmitting, digital data is transmitted at multi megabit
per second data rates using any portion of the frequency spectrum
of a 6 MHz bandwidth of a television channel; and
in the step of controlling, the flow of digital data in the return
channel operates at a rate of at least 9600 bits per second in
asymmetric transmission relative to the rate of digital data in the
forward channel.
.Iaddend..Iadd.14. The method according to claim 11 further
including the steps of:
detecting an address and demodulating digital data; and
transmitting the digital data to at least one data terminal in
response to the address. .Iaddend..Iadd.15. A high speed digital
information transmission system comprising:
a source of multi megabit per second digital data for transmission
to a number of remote sites;
a hybrid transmission facility including a number of video
modulators connected to receive the digital data for encoding the
digital data to produce an analog RF signal for transmission to the
number of remote sites using bandwidth in any portion of a
television channel;
and at each of the number of remote sites;
a remote link adapter including a hybrid interface for detecting
and demodulating said analog RF signal to obtain data from said
source of multi megabit per second digital data, said hybrid
interface providing a two way asymmetric network connection
including independent forward and return transmission channels in
two directions;
circuit connections of the return transmission channel of the
remote link adapter to the hybrid transmission facility;
a user interface for providing digital data to data terminal
equipment;
microprocessor controller for controlling said hybrid interface to
control the flow of digital data in the forward and return
transmission channels; and
a signaling bus interconnecting said user interface, said hybrid
interface and said microprocessor controller. .Iaddend..Iadd.16.
The system according to claim 15 in which the return channel for
digital data includes a selected one of telephone lines, a radio
channel, an Ethernet
channel and a CATV channel. .Iaddend..Iadd.17. The system according
to claim 15 in which digital data is transmitted at multi megabit
per second data rates using the frequency spectrum within a 6 MHz
bandwidth of a television channel; and
the return transmission channel operates at a rate of at least 9600
bits per second in asymmetric transmission relative to the rate of
digital data in the forward channel. .Iaddend..Iadd.18. The system
according to claim 15 wherein the hybrid transmission facility
receives address information for the remote sites, and the
modulators encode the address information and the digital data to
produce said analog RF signal for transmission to at least one of
the remote sites. .Iaddend..Iadd.19. The system according to claim
15 in which the remote link adapter detects an address and
demodulates the digital data for transfer to the data terminal
equipment at the remote site. .Iaddend..Iadd.20. A method for high
speed reception of digital information at a number of remote
locations having hybrid interfaces thereat, the method comprising
the steps of:
receiving a source of multi megabit per second digital data for
transmission to a number of remote sites;
modulating the digital data for encoding the digital data to
produce an analog signal for transmission from a hybrid
transmission facility to at least one of the remote sites using
bandwidth in any portion of a television channel;
forming with the hybrid interfaces a two way asymmetric network
including independent forward and return channels in two
directions;
demodulating the encoded digital data transmitted in the forward
channel on the television channel and received by the hybrid
interface to obtain the transmitted digital data;
supplying the demodulated digital data to data terminal equipment
at the remote site;
supplying digital data over the return transmission channel from a
remote site to the hybrid transmission facility; and
controlling the flow of digital data at the remote site in the
forward and
return transmission channels. .Iaddend..Iadd.21. The method
according to claim 20 in which digital data flows from a remote
site to the hybrid transmission facility in a return channel
including a selected one of telephone lines, a radio channel, an
Ethernet channel and a CATV channel. .Iaddend..Iadd.22. The method
according to claim 20 in which in the step of receiving, digital
data is received at multi megabit per second data rates using the
frequency spectrum within a 6 MHz bandwidth of a television
channel; and
in the step of controlling digital data in the return transmission
channel is controlled at a rate of at least 9600 bits per second in
asymmetric transmission relative to the rate of digital data in the
forward channel. .Iaddend..Iadd.23. The method according to claim
20 in which in the step of receiving, the digital data includes
encoded address data, and the step of demodulating obtains an
address and includes the steps of;
detecting the address with demodulated digital data; and
transmitting digital data to at least one data terminal equipment
in response to the demodulated address data. .Iaddend..Iadd.24. The
method according to claim 20 in which the interfaces detect address
information and demodulate the analog signal for transfer of
digital data to the data terminal equipment at the remote site.
.Iaddend..Iadd.25. A two way interactive communication system
comprising:
a host computer and a remote user station wherein said host
computer includes a source of data for being transmitted to said
remote user station;
an asymmetric network interconnecting communication paths of said
host computer and said remote user station, said asymmetric network
comprising a high speed forward channel and a lower speed return
channel, said forward and return channels cooperatively providing
interactive two way communication between said host computer and
said remote user station in accordance with a forward channel
protocol and a return channel protocol;
a host interface connected with said host computer, said host
interface including:
a controller for receiving data from said source of data and for
effecting multi megabit per second transfers of data from said host
interface in accordance with said forward channel protocol;
a modulator connected with said controller for modulating a
broadband signal with said multi megabit per second data;
and a transmitter connected with said modulator for transmitting a
broadband signal carrying said multi megabit per second data over
the forward channel of said asymmetric network; and
a remote interface connected with said remote user station, said
remote interface including:
a broadband receiver for receiving said broadband signal
transmitted over said forward channel;
a demodulator for demodulating said broadband signal thereby to
extract data from said broadband signal that carries said multi
megabit per second data; and
a controller connected with said demodulator for producing
representations of data transmitted from said host computer in
accordance with said
forward channel protocol. .Iaddend..Iadd.26. The two way
interactive communication system as recited in claim 25,
wherein
said remote interface further includes a modulator for modulating
data transmitted from said remote user station, a transmitter
connected with said modulator for supplying a return signal to said
return channel of said asymmetric network, and a microprocessor
that controls the transfer of data from said remote user station to
said return channel in accordance with said return channel
protocol, and
said host interface further includes a receiver that receives
information from said remote user station transmitted over said
return channel, a demodulator connected with said receiver for
demodulating information transmitted over said return channel, and
controller of said host interface includes a microprocessor that
produces representations of data transmitted over said return
channel from said remote user station in accordance with said
return channel protocol. .Iaddend..Iadd.27. The interactive
communication system as recited in claim 25 wherein the forward
channel and the return channel of said asymmetric network are
independent in a common physical transmission medium, and wherein
said controller of said host interface defines the forward protocol
in the forward channel and said controller of said remote user
station defines the return channel protocol of said asymmetric
network. .Iaddend..Iadd.28. The interactive communication system as
recited in claim 27 wherein each of the forward and return channels
of said asymmetric network physically reside on a selected one of a
CATV cable channel, an over-the-air radio channel and a broadcast
satellite channel. .Iaddend..Iadd.29. The interactive communication
system as recited in claim 25 wherein said asymmetric network
comprises at least two physically separate media and said
controller of said host interface defines said forward channel
protocol in one direction on a first of said media and said
controller of said remote user station defines said return channel
protocol in an opposite direction on a second of said media.
.Iaddend..Iadd.30. The interactive communication system as recited
in claim 29 wherein each of the forward and return channels of said
asymmetric network physically resides on a selected one of a CATV
cable channel, an over-the-air radio
channel, and a broadcast satellite channel. .Iaddend..Iadd.31. The
interactive communication system as recited in claim 25 wherein
said controller of said host interface that defines a forward
channel protocol provides for assembling a series of data packets
including source data from said host computer and for effecting the
transmission of said series of data packets over said forward
channel, said series of data packets comprising a main menu packet
that identifies the nature of information contained in a subsequent
data packet, and said controller of said remote interface being
responsive to said menu packet and user selection criteria thereby
to select information contained in said subsequent data packet.
.Iaddend..Iadd.32. The interactive communication system as recited
in claim 25 wherein said remote interface has a unique address and
said controller of said host interface transmits data packets
having address information that is recognized by said remote
interface for reception of information. .Iaddend..Iadd.33. In an
interactive communication system for providing two way
communications between a host computer and a remote user station,
said remote user station including a remote interface associated
therewith that includes a broadband receiver for detecting multi
megabit per second data transmitted over a forward channel in a
broadband signal, a demodulator for demodulating said broadband
signal, and a controller connected with said demodulator for
producing representations of at least a portion of data transmitted
from said host computer, the improvement comprising:
an asymmetric network that includes a high speed forward channel
and a lower speed return channel wherein said forward and return
channels cooperatively provide two way interactive communication
between said host computer and said remote user station in
accordance with a forward channel protocol and a return channel
protocol,
a host interface including a controller for receiving data from a
source of data and for effecting multi megabit per second transfers
of data originating from said host computer over said forward
channel in accordance with said forward channel protocol, a
modulator connected with said controller for modulating a broadband
signal with said multi megabit per second data, and a transmitter
connected with said modulator for transmitting a modulated
broadband signal over the forward channel of said asymmetric
network, and
said remote user station further includes unique address
information associated therewith and said controller of said remote
interface operates to detect said unique address information by
demodulating a broadband signal carrying multimegabit per second
data. .Iaddend..Iadd.34. In an interactive communication system for
providing two way communications between a host computer and a
remote user station, the improvement comprising:
an asymmetric network including a high speed forward channel and a
lower speed return channel wherein said forward and return channels
cooperatively provide two way interactive communication between
said host computer and said remote user station in accordance with
a forward channel protocol and a return channel protocol,
a host interface including a controller for receiving data from a
source of data and for effecting multi megabit per second transfers
of data originating from said host computer in accordance with said
forward channel protocol, a modulator connected with said
controller for modulating a broadband signal with said multi
megabit per second data, and a transmitter connected with said
modulator for generating a broadband transmission carrying multi
megabit per second data for transmission over the forward channel
of said asymmetric network, and
a remote interface including a broadband receiver for detecting
said broadband transmission carrying multi megabit per second data
transmitted over said forward channel, a demodulator for
demodulating said broadband transmission, and a controller
connected with said demodulator for producing representations of
data originating from said host computer and transmitted over said
forward channel in accordance with said forward channel protocol.
.Iaddend..Iadd.35. A method of providing two way interactive
communication between a host computer and a plurality of remote
user stations across a broadband communication medium which
includes independent forward and return channels in an asymmetric
network configuration, wherein at least one of said remote user
stations has a unique address, said method comprising the steps
of:
transmitting over said medium a broadband signal carrying
multimegabit per second data in said forward channel of said
asymmetric network from said host computer to a remote user station
in accordance with a forward channel protocol;
transmitting return channel signals over said medium from at least
one of said remote user stations to said host computer in
accordance with a lower speed return channel protocol,
controlling the transfer of data between said host computer and
said at least one of said remote user stations in accordance with
said forward and return channel protocols, said controlling
including the steps of:
generating a data packet containing source information to be
transferred from said host computer and address information which
identifies a unique one of the remote user stations,
broadcasting said data packet over said forward channel, and
detecting said data packet at a uniquely addressed remote user
station and selecting source information contained in said packet.
.Iaddend..Iadd.36. A method of providing two way interactive
communication between a host computer and a plurality of remote
user stations across a broadband communication medium which
includes independent forward and return channels in an asymmetric
network configuration, wherein at least one of said remote user
stations has a unique address, said method comprising the steps
of:
transmitting over said medium a broadband signal carrying multi
megabit per second data in said forward channel of said asymmetric
network from said host computer to said plurality of remote user
stations in accordance with a forward channel protocol,
transmitting return channel signals over said medium from said
plurality of remote user stations to said host computer in
accordance with at least one lower speed return channel protocol,
and
controlling the transfer of data between said host computer and
said remote user stations in accordance with said forward and
return channel protocols, said controlling including the steps
of:
generating a multibit data packet containing source information to
be transferred from said host computer, address information which
identifies a unique one of the remote stations and variable length
information defining the length of source information contained in
said data packet,
broadcasting said data packet over said forward channel, and
detecting said data packet at a uniquely addressed remote user
station and selecting information contained in said packet in
accordance with length
information provided in said data packet. .Iaddend..Iadd.37. The
method as recited in claim 35 further comprising the step of
providing said medium from a selected one of an over-the-air
broadcast medium, a CATV cable medium, a coaxial cable and a fiber
optic cable as the broadband communication medium.
.Iaddend..Iadd.38. The method as recited in claim 36 further
comprising the step of providing said medium from a selected one of
an over-the-air broadcast medium, a CATV cable medium, a coaxial
cable and a fiber optic cable as the broadband communication
medium. .Iaddend..Iadd.39. The method as recited in claim 35
further comprising the steps of providing the forward channel from
a selected one of an over-the-air broadcast medium, a CATV medium,
a coaxial cable and a fiber optic cable; and providing the return
channel from another selected one of an over-the-air broadcast
medium, a CATV medium, a coaxial cable and a fiber optic cable.
.Iaddend..Iadd.40. The method as recited in claim 36 further
comprising the steps of providing the forward channel from a
selected one of an over-the-air broadcast medium, a CATV medium, a
coaxial cable and a fiber optic cable; and providing the return
channel from another selected one of an over-the-air broadcast
medium, a CATV medium, a coaxial cable, and a fiber optic cable.
.Iaddend..Iadd.41. A communication system for providing two way
interactive communication between a host computer and a plurality
of remote user stations wherein at least one of said remote user
stations has a unique address, said system comprising:
a broadband communication medium which includes independent forward
and return channels in an asymmetric network configuration,
a multi megabit per second forward channel protocol defined in the
forward channel of said asymmetric network for carrying information
signals in a broadband signal transmitted over said broadband
communication medium from said host computer to said plurality of
remote user stations,
a lower speed return channel protocol defined in said return
channel of said asymmetric network for transferring data from at
least one of said plurality of said remote user stations to said
host computer,
a controller for controlling the transfer of information signals
between said host computer and at least one of said remote user
stations in accordance with said forward and return channel
protocols, said controller including circuitry for generating a
multibit data packet containing source information to be
transferred from said host computer and address information which
identifies a unique one of the remote user stations, and
said remote user station including circuitry for detecting said
data packet at a uniquely addressed remote user station.
.Iaddend..Iadd.42. A communication system for providing two way
interactive communications between a host computer and a plurality
of remote user stations wherein at least one of said remote user
stations has a unique address, said system comprising:
a broadband communication medium which includes independent forward
and return channels in an asymmetric network configuration,
a multi megabit per second forward channel protocol defined in the
forward channel of said asymmetric network for carrying information
signals in a broadband signal transmitted over said broadband
communication medium from said host computer to said plurality of
remote user stations,
a lower speed return channel protocol defined in said return
channel of said asymmetric network for transferring information
signals from at least one of said remote user stations to said host
computer,
a controller for controlling the transfer of data between said host
computer and at least one of said remote user stations in
accordance with said forward and return channel protocols, said
controller including circuitry for generating a multibit data
packet containing source information to be transferred from said
host computer, address information which identifies a unique one of
the remote stations and length information which defines the length
of information contained in said data packet, and
at least one of said remote user stations including circuitry for
detecting said data packet at a uniquely addressed remote user
station and for selecting source information contained in said
packet in accordance with length information provided in said data
packet. .Iaddend..Iadd.43. The communication system as recited in
claim 41 wherein said broadband communication medium is a medium
selected from one of a cable network, an over-the-air RF signal and
a direct satellite broadcast signal. .Iaddend..Iadd.44. The
communication system as recited in claim 42 wherein said broadband
communication medium is a medium selected from one of a cable
network, an over-the-air RF broadcast medium, and a direct
satellite broadcast medium. .Iaddend..Iadd.45. The communication
system as recited in claim 41 wherein each of the forward and
return channels of said asymmetric network is a selected one of a
cable network, an over-the-air broadcast network and a direct
broadcast satellite network.
.Iaddend..Iadd.6. The communication system as recited in claim 42
wherein each of the forward and return channels of said asymmetric
network is a selected one of a cable network, an over-the-air
broadcast network and a direct broadcast satellite network.
.Iaddend..Iadd.47. A multi-user computing system including an
asymmetric network for providing two way interactive communication
and that enables multi megabit per second transfers of data to a
plurality of remote user stations connected to said asymmetric
network, said system comprising:
a provider site,
a plurality of remote user stations,
a broadband CATV transmission facility including:
a cabling network for transferring information packets between said
provider site and the remote user stations,
a high-speed link for connection with the provider site,
a digital signal encoder for converting digital signals from the
provider site into standard baseband video input signals, and
a video modulator for receiving said baseband input signals thereby
to produce a broadcast signal on a selected broadcast channel that
is transmitted by said CATV transmission facility to said remote
user stations,
wherein at least one of said remote user stations includes:
a computing system,
an RF modem including a TV tuner for receiving and automatically
synchronizing to a selected broadcast channel of the video
modulator of said broadband CATV transmission facility, and
an interface that interconnects said RF modem and said computing
system, said interface including a microprocessor controller for
defining a protocol for receiving information packets transmitted
in a forward channel from said provider site to at least one of
said remote user stations, for monitoring incoming information
packets for a unique address associated with said remote user
station, for forwarding information packets to said computing
system for further processing upon detection of said unique
address, and for transferring information from said remote user
station to said provider site over a narrow band return channel
that comprises a selected one of a telephone line, an over-the-air
broadcast channel and a selected narrowband channel of said CATV
transmission facility. .Iaddend..Iadd.48. In combination with a
multi-user computing system that includes an asymmetric network for
providing two way interactive communication between a provider site
and multiple remote user stations wherein at least one of said
remote user stations has a unique address associated therewith and
includes a computing system, the improvement comprising:
a broadband CATV transmission facility including:
a cabling network for transferring information packets between said
provider site and the remote user stations,
a high-speed link for connection with said provider site,
a digital signal encoder for converting digital signals from the
provider site into standard baseband input signals, and
a video modulator for receiving said baseband input signals thereby
to produce a broadcast signal on a selected broadcast channel that
is transmitted by said CATV transmission facility to said remote
user stations, and
wherein at least one of said remote user stations includes:
an RF modem including a TV tuner for receiving and automatically
synchronizing to a selected broadcast channel of the video
modulator of said broadband CATV transmission facility, and
an interface that interconnects said RF modem and said computing
system, said interface including a microprocessor controller for
defining a protocol for receiving information packets transmitted
in a forward channel from said provider site to the remote user
station, for monitoring incoming packets for a unique address
associated with said remote user station, for forwarding said
information packets to said computing system for further processing
upon detection of said unique address, and for transferring
information from said computing system to said provider site over a
narrow band return channel that comprises a selected one of a
telephone line, an over-the-air broadcast and a selected
narrowband
channel of said CATV transmission facility. .Iaddend..Iadd.49. A
multi-user computing system including an asymmetric network for
providing two way interactive communication, said system
comprising:
a provider site,
a plurality of remote user stations,
a broadband CATV transmission facility including:
a cabling network for transferring information packets between said
provider site and the remote user stations wherein said information
packets include destination address information indicative of
unique ones of said remote user stations,
a high-speed link with said provider site,
a digital signal encoder for converting digital signals from the
provider site into standard baseband input signals,
a video modulator for receiving said baseband input signal thereby
to produce a broadcast signal on a selected broadcast channel that
is transmitted by said CATV transmission facility to said remote
user stations,
return channel communication equipment for receiving information
from at least one of said remote user stations and for transmitting
at least some of said information to said provider site,
at least one of said remote user stations including,
a computing system,
an RF modem including a TV tuner for receiving and automatically
synchronizing to a selected broadcast channel of the video
modulator of said broadband CATV transmission facility, and
an interface that interconnects said RF modem and said computing
system, said interface including a microprocessor controller for
defining a protocol for receiving and selecting information packets
transmitted in a forward channel from said provider site to the
remote user station, and for transferring information from said
computing system to said provider site over a narrow band return
channel that comprises a selected one of a telephone line, an
over-the-air broadcast and a selected narrow band
channel of said CATV transmission facility. .Iaddend..Iadd.50. A
multi-user computing system including an asymmetric network for
providing two way interactive communication, said system
comprising:
a provider site,
a plurality of remote user stations wherein at least one of said
remote user stations has a unique address,
a broadband CATV transmission facility including:
a cabling network for transferring information packets between said
provider site and the remote user stations wherein said information
packets include destination address information indicative of
unique ones of said remote user stations and packet length
information indicative of the length of said information
packet,
a high-speed link with said provider site,
a data encryption system associated with the provider site,
a digital signal encoder for converting digital signals from the
provider site into standard baseband input signals,
a video modulator for receiving said baseband input signal thereby
to produce a broadcast signal on a selected broadcast channel that
is transmitted by said CATV transmission facility to said remote
user stations,
return channel communication equipment for receiving information
from at least one of said remote user stations and for transmitting
said information to said provider site,
at least one of said remote user stations including,
a computing system,
an RF modem including a TV tuner for receiving and automatically
synchronizing to a selected broadcast channel of the video
modulator of said broadband CATV transmission facility,
an interface that interconnects said RF modem and said computing
system, said interface including
an encryption chip set for encrypting and decrypting
information,
a microprocessor controller for defining a protocol for receiving
information packets transmitted in a forward channel from said
provider site to the remote user station, for instructing the tuner
to monitor incoming packets for a unique address associated with
said remote user station, for forwarding said information packets
to said computing system for further processing upon detection of
said unique address, and for transferring information from said
computing system to said provider site over a narrow band return
channel that comprises a selected one of a telephone line, an
over-the-air broadcast and a selected narrowband channel of said
CATV transmission facility. .Iaddend..Iadd.51. A multi-user
computing system including an asymmetric network for providing two
way interactive communication that enables multi megabit per second
transfers of data in an asymmetric network, said system
comprising:
a provider site,
a plurality of remote user stations,
a broadband transmission facility including:
a signal transmission network for transferring information packets
between said provider site and the remote user stations,
a high-speed link for connection with the provider site,
wherein at least one of said remote user stations includes:
a computing system,
a high speed modem for receiving multi-megabit per second
information transfers, and
an interface that interconnects said high speed modem and said
computing system, said interface including a microprocessor
controller for defining a protocol for receiving and selecting
information packets transmitted in a forward channel from said
provider site to the computing system, and for transferring
information from said computing system to said provider site over a
narrow band return channel that comprises a selected one of a
telephone line, an over-the-air broadcast and a selected
narrowband
channel of said broadband transmission facility. .Iaddend..Iadd.52.
In combination with a content provider site and at least one remote
user station that includes a high speed modem for detecting data in
multi megabit per second transfers of data in a broadband signal, a
sending and receiving interface that enables communication between
said high speed modem and a computing system, said interface being
operative with a controller for effecting communication in a
forward channel and a return channel in accordance with predefined
protocols:
a broadband communication system for enabling two way interactive
communication between said provider site and said at least one
remote user station, said broadband communication system
including
a high-speed link for connection with said provider site,
an asymmetric network for enabling two way communication in an
asymmetric network configuration that enables multi megabit per
second transfers of data to said at least one remote user station
in accordance with a multi megabit per second forward channel
protocol and that enables a lower speed transfer of data from said
at least one remote user station in accordance with a lower speed
return channel protocol, and
said at least one remote user station including an associated
unique address and an associated demodulator which operates to
detect said associated unique address by demodulating said
broadband signal carrying
multi megabit per second data. .Iaddend..Iadd.53. The method as
recited in claim 12, wherein the digital data flows through a
router which is not a hybrid interface. .Iaddend..Iadd.54. The
system as recited in claim 16, where the return channel includes a
router other than the remote link adapter. .Iaddend..Iadd.55. The
method as recited in claim 21, wherein the digital data flows from
a remote site to the hybrid transmission facility through a router
which is not a hybrid interface. .Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to data transmission by television
(TV) broadcast, and more particularly the invention relates to a
remote link adapter for use in receiving broadcast data.
At the present time there is no cost effective method of delivering
at high-speed packets of digital information to remote locations
like homes and mobile vehicles. As used herein, digital information
are packets that may contain multimedia data (sound, pictures,
text, graphics, video) or executable computer code in addition to
addressing status and protocol data. The existing telephone
circuits, cellular systems and radio systems are just too slow to
be practical and useful in an ever increasing number of digital
multimedia applications including graphics, imaging, animation or
remote windows. High-speed leased telephone lines and/or high-speed
broadband switched digital service, offered by the telephone
companies, are too expensive or not yet available to any average
user (consumer) or potential user and do not address the needs of
mobile users. In addition, all other existing forms of digital
transmission techniques to the remote location (also known as the
last mile) within any particular metropolitan area are too
expensive and impractical to be useful at the present time. Most of
these existing forms of high-speed digital transmission to the
remote location are well known in the prior art but none of them
attempt to use a low-cost, high-speed hybrid transmission scheme as
described herein.
There are some existing forms of encoding digital information into
the vertical blanking intervals (VBI) of a standard NTSC baseband
TV signal, but again, these techniques provide severe difficulties
with synchronization and the reception of digital information when
it is delivered in the form of variable length data packets. These
difficulties translate into higher costs at the receiving site,
making those techniques those techniques also impractical when used
to broadcast high-speed (greater then 10 Mbps) digital information
in the form of variable length packets (also referred to herein as
"addressable broadcasting" digital service) at very low cost.
This present invention relates to a very cost effective method of
diverting high-speed (e.g., 10 Mega bits per second, Mbps, or
higher) digital information in the form of packets to any remote
location such as a home, school, office or mobile vehicle using
standard TV practices and components and as part of a very
comprehensive hybrid transmission system. More particularly, the
invention provides a device for receiving broadcast data,
transmitting the data to the end user, and communicating as
necessary with the information provider.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is a practical method of
transmitting and receiving high speed digital information at remote
sites.
Another object of the invention is an adapter for receiving
broadcast data.
Briefly, in accordance with the invention, a hybrid transmission
system transmits and receives high-speed digital information in the
form of .[.variable length.]. .Iadd.data .Iaddend.packets using
standard television broadcast practices and components. The basic
building block of this hybrid digital transmission system is the
remote link adapter device at the remote location that receives the
analog or digitally encoded broadcast signal processed by a
standard television vestigial sideband video modulator. The device
decodes the digital information from the signal and then passes it
along as digital information to any form of a data terminal
equipment or computer.
The remote link adapter includes a hybrid interface, a user
interface, and a control means. The hybrid interface includes a
radio modem for receiving the broadcast channel, and an optional
return channel having a telephone modem, a radio link interface or
a CATV interface for use in an on-demand addressable broadcast
system. The user interface can include an Ethernet interface, a
personal computer interface (e.g. PC/AT or MAC), or a direct bus
into a video game system such as the Nintendo NES or Super NES. The
control means includes a microprocessor, memory, and a stored
control program.
The invention and objects and features thereof will be more readily
apparent from the following detailed description and appended
claims when taken with the drawings.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a functional block diagram of a data transmission system
employing remote link adapters in accordance with the
invention.
FIG. 2 is a functional block digram of a remote link adapter as
used in the system of FIG. 1.
FIGS. 3-5 are functional block diagrams of three different
embodiments of the remote link adapter illustrated in FIG. 2.
FIG. 6 is a functional block diagram of the RF portion of the data
transmission system of FIG. 1.
FIG. 7A is a schematic of a data scrambler and FIG. 7B is a
schematic of a data descrambler as used in FIG. 6.
FIG. 8A is a schematic of a three level decoder, and FIG. 8B is a
schematic of a three level decoder as used in FIG. 6.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
FIG. 1 is a functional block diagram of a data transmission system
for broadcasting data to remote locations and employing remote link
adapters in accordance with the invention. The system includes an
Information Provider site 10, a Hybrid Transmission facility (HTF)
12, a CATV head-end or TV broadcast site 14 which transmits the
data over a standard 6 Mhz television channel, and the Remote sites
which receive the incoming digitally encoded broadcast signal.
The central site data communications equipment (DCE) at the
Information Provider's site sends a high-speed digital signal to
the Hybrid Transmission Facility (HTF) via any suitable high-speed
line or media. In the case where the Information Provider's site is
co-located with the HTF, the connection between the central site
DCE and the HTF can be a short piece of coaxial cable.
The HTF receives the incoming high-speed digital signal, combines
it with other incoming high-speed digital signal (using local area
network-LAN-based fast-packet switching techniques) to the
appropriate outgoing port for broadcasting purposes. The signal is
then transmitted to the appropriate head-end location or
over-the-air TV broadcast site either as an analog signal or as a
digital signal. Again, the head-end site or TV broadcast site could
be co-located with the HFT.
Before the digital signal is broadcast over the air or transmitted
downstream throughout a cable television (CATV) network, the
digital signal is first encoded into a standard 1 volt
peak-to-peak, baseband input into a standard video modulator. The
signal is then processed by the video modulator just like it
processes a standard 1 volt peak-to-peak baseband television input
signal and is then transmitted over a standard 6 Mhz television
channel.
The Remote Link Adapter (RLA) at the remote site receives the
incoming TV-like analog signal using a built-in standard TV
tuner/receiver. After processing the signal, the RLA presents the
resulting digital signal to the data terminal equipment (DTE)
interface. When a return channel is present, the RLA also forwards
digital information (packets) to the central site using the return
channel. The return channel(s) can be a standard public switched
network telephone line(s) operating at a different speed from the
forward broadcast channel or any other available channel, such as a
radio channel, or the CATV system itself.
Finally, if a remote channel is present, the central site DCE will
receive the incoming digital information (packets) from the return
channel and forward them to the central network interface to
complete the circuit. However, if a return channel is not present,
the RLA simply selects digital information (packets) from the
high-speed forward broadcast channel based on a specific selection
criteria defined by software. A hybrid system as described herein
without a return channel is also known as a "selectable addressable
broadcast system". A hybrid system as described herein with a
return channel is also known as a "on-demand addressable broadcast
system." One of the unique characteristics of the hybrid system is
that the forward broadcast channel is completely independent from
any form of a return channel. This feature allows each channel to
be optimized independently from the other.
FIGS. 2-5 are functional block diagrams of embodiments of the RLA.
The RLA receives the high-speed analog signal from the 6 Mhz
broadcast TV channel, processes the signal and then delivers the
resulting digital signal to a specific DTE interface. Physically,
the RLA will either be a small standalone box or a printed circuit
card (PC board) that can be mounted inside any number of DTE units
including computers, workstations, home computers, interactive
graphics terminals or simple video game machines.
FIG. 2 illustrates the basic building blocks for the RLA. As
illustrated, the overall RLA design consists of three basic parts:
(1) The User Interface 20 which is also sometimes referred to as
The DTE Interface, (2) The Hybrid Interface 22 which includes the
forward broadcast channel and an optional return back channel, and
(3) The control means or The Engine 24 which includes the
microprocessor, memory, control and optional security portions of
the RLA.
FIG. 3 illustrates the implementation of a fully configured RLA. In
this implementation, the user interface 20 is Ethernet, the hybrid
interface 22 is a high-speed (approximately 10 Mbps) RF modem used
to receive the forward broadcast channel and a built-in 9600 bps
telephone modem used to transmit the return channel. The engine 24
of the RLA is a standard Intel microprocessor with associated read
only memory (ROM), random access memory (RAM) and a digital
encryption standard (DES) co-processor chip-set used to decipher
the incoming distal information from the broadcast channel. This
RLA device is a small standalone box with an Ethernet interface, an
RF "F" connector interface to receive the high-speed broadcast
channel, and an RJ-11 telephone jack used for the return
channel.
FIG. 4 illustrates the implementation of the RLA for use with a
personal computer bus. In this case, the user interface 20 is a
direct computer bus interface. The hybrid interface 22 of this
embodiment is identical to the implementation of FIG. 2 but the
engine 24 is a less capable microprocessor with a smaller amount of
ROM and RAM and no encryption co-processor.
This RLA device is a PC board form factor product that interfaces
directly with either a PC-AT bus (model 200-001), a MacII bus
(model 200-002) or a PS/2 bus (model 200-003). The PC board also
provides an RF "F" connector to receive the high-speed broadcast
signal and an RJ-11 telephone jack for the return channel.
FIG. 5 illustrates the implementation of the RLA for use with a
video game machine such as the Nintendo NES or Super NES. This
implementation is the lowest cost implementation of the RLA. The
user interface 20 is a direct bus interface into the NES or Super
NES. In this implementation, the memory and memory control portions
of the RLA are implemented in the form of a standard NES or Super
NES video game cartridge. The memory control function 24 uses a
single VLSI custom chip. The hybrid interface is a very low-cost
high-speed (approximately 10 Mbps) RF modem, with no return channel
and the engine is another single VLSI custom integrated circuit
(IC). Finally, an optional expansion interface is also provided in
case a future return channel upgrade is required. The same
expansion port may also allow for the attachment of an external
printer or an external bulk storage device or other peripherals.
This RLA device is packaged in a small plastic enclosure that
connects directly to a Nintendo NES or Super NES video game
machine. The device provides an RF"F" connector to receive the
high-speed broadcast channel and an optional expansion port. A
return channel will normally not be available in this RLA
implementation.
The RLAs described in accordance with this invention are designed
to operate in a hybrid transmission system with a specific forward
broadcast ("IN Channel") protocol. The IN Channel protocol
specifies the rules used by the RLAs to receive and filter the
relevant digital information (packets) flowing in the forward
broadcast channel. Each RLA has a unique digitally encoded address.
RLAs are capable of receiving broadcast packets, multicast packets
(packets addressed to groups of users/RLAs) and packets
specifically addressed to them. The forward broadcast channel (IN
Channel) is a shared channel. Many RLAs may share the same channel
to receive digital information. When an RLA is powered up and the
RF modem is appropriately tuned to a particular IN Channel (6 Mhz
broadcast TV Channel), the RLA modem automatically synchronizes to
the incoming high-speed data being broadcast and starts monitoring
(receiving) the incoming signal. The RLA firmware, after its
initial power-up and self test sequence, instructs the RLA to look
for a particular address or set of addresses (e.g., broadcast
packets). Once packets with these addresses are detected, the RLA
then forwards the appropriate incoming packets to the DTE for
further processing.
Selectable Broadcast--All RLA units receive the main-menu packet
from the channel. Then, based on user selections, the RLA units
filter the appropriate broadcast packets from the channel in the
next broadcasts. Broadcasts are repeated periodically. Based upon
the nature of the digital data, certain packets are re-broadcast
approximately every other second while other packets are
re-broadcast approximately every minute. The information contained
in a particular broadcast cycle (sequence of packets) will also
change with time.
On-Demand Broadcast--Users request a particular set of information
(packets) in accordance with any given data communications protocol
supported by The IN Channel. The RLA will support most standard and
defacto protocols that run over a standard IEEE-802.3 Ethernet
local area network. The following are the different types of
on-demand calls that can be set-up using The IN Channel:
a. Broadcast/Multicast--The Information Provider broadcasts or
multicasts the information to the particular user or group of
users. No call set-up is required. The request for information is
completely asynchronous from the delivery of information;
b. Secure Sessions--This is the most complex procedure since it
involves the distribution of encryption keys;
c. Non-secure sessions--This procedure is identical to the
procedures currently used by existing network applications. The IN
Channel is transparent to most LAN-based network applications;
d. Interactive sessions for the Consumers--The procedures are
determined by the different information Providers, who decide to
use the IN Channel to deliver their services.
For on-demand applications--The RLA shown in FIG. 3 goes through an
initial call set-up/security procedure before it becomes
operational. First, the user dials a particular telephone number.
Dial-back security and user authentication will be optional at this
stage. Once the central site DCE (located at the Information
Provider's site) answers the call, the RLA goes through a security
protocol (encryption key distribution) if used in the system. Next
a link layer connection is established between the central site DCE
and the remote RLA. This connection remains transparent to the
applications running above. The hybrid connection looks like a
transparent remote Ethernet bridge and, therefore, is compatible
with all upper layer protocols (e.g., TCP/IP, AppleTalk, ISO,
DECNET, etc.) that can run over Ethernet. Once the connection is
established, the remote user can now run standard network
applications just as if the user were located at the central site
local area network. The hybrid connection is terminated by hanging
up the telephone side of the connection (the return channel).
The RLA shown in FIG. 4 series also goes through an initial call
set-up procedure before it becomes operational. Again, first, the
user dials a particular telephone number. Dial back security and
user authentication will be optional at this stage. Once the
central site DCE answers the call, a link layer connection is
established between the central site DCE and the remote RLA. Since
the remote RLA is a PC board that fits inside a particular personal
computer, specific network driver software is required by the RLA.
Network applications need to be ported to the hybrid network driver
in order to be able to run over the hybrid connection.
The RLA shown in FIG. 5 normally does not go through a call set-up
procedure since no return channel is used. This embodiment operates
in accordance with the IN Channel protocol.
The IN Channel uses a protocol that controls the flow of
information and the addressing in the channel. All RLAs will have a
unique address. In addition, the RLAs will also be able to receive
broadcast and multicast messages (packets). The following is a list
of the different types of packets that can flow in the IN
Channel:
1. Broadcast packets (including selectable broadcast packets)
2. Multicast packets
3. On-Demand Addressable packets
Secure Packets
Non-secure Packets
Network Management Packets
4. Addressable video frame packets (followed by one or more NTSC
video frames)
The channel transports variable length data packets. Packet
multiplexing techniques are primarily based on a FIFO (first in
first out) scheme as a direct feed from a LAN Switch port. A
priority scheme is given to certain packets, including selectable
broadcasts and some network management packets. The IN Channel
operates in a synchronous mode. Both on-demand and selectable
broadcast traffic is transported in the IN Channel at the same
time. Bandwidth management is performed by the equipment at the
Hybrid Regional Distribution Centers.
The digital information (packets) carried by The IN Channel ate
transparent to the applications. Standard upper-layer protocols
such as: TCP/IP, NFS, X-Windows, AppleTalk, Netware and ISO will be
able to run unchanged over the IN Channel. However, upper-layer
protocol optimization and/or new upper-layer protocols may be used
for consumer-based applications.
The information flowing in The IN Channel is packaged in packets.
Each packet contains the address of the subscriber (destination
address) and the source address (optional). LAN-based fast packet
switching and multiplexing techniques will be used to process and
transport information in the channel. Off-the-shelf packet
switching equipment can be used at the regional distribution
centers.
The hybrid data transmission system return channel is optional. It
needs to be used, however, when running real-time interactive
applications. The return channel protocol provides data compression
needed to improve the performance of high-speed interactive
applications.
The packet-data delivery via The IN Channel has a specific error
rate. The IN Channel is a datagram, packet-based transport system.
This system relies on the bandwidth and services provided by the
CATV (cable or wireless) operators. Error recovery is achieved by
the end-to-end transport layer protocol running in the data
terminal equipment (DTB). A good example here is TCP/IP. For
selectable traffic, packets with CRC errors will be dropped. They
will be received by the RLA on the next re-broadcast.
FIG. 6 shows the signal path from the head end cable TV transmitter
site to a typical terminal. The system translates between NRZ
baseband digital stream at the input to a modulation form suitable
for use on a standard CATV head end modulator, and translates the
received signals from a standard TV tuner connected to a cable TV
network to baseband NRZ data stream and a regenerated clock. A TV
tuner containing only those features required for receiving the
digitally modulated CATV signal is used. The design is adaptable to
a range of bit rates.
The data source 50 can be any baseband NRZ data stream. The clock
52 can be part of the system or supplied by the data source. The
scrambler 54 takes a data stream supplied by the user and
exclusively ORs the stream with a pseudorandom pattern which is a
function of the past data. This breaks up periodic bit patterns
which would degrade the bit synchronizer functioning.
The 3 level encoder 56 takes in a NRZ bit stream and clock and
converts it to a more bandwidth efficient class IV partial response
3 level format. The output is not bandwidth limited because the
CATV modulator contains SAW filters that produce the bandwidth
limiting without any added phase distortion. A format that does not
contain spectral terms at DC is used so that the CATV modulator and
tuner not having a frequency response down to DC will not be a
hindrance. The TV transmitter 58 is a standard unit commonly used
in CATV or over the air TV systems. It takes a baseband video
signal and converts it to any commonly used TV format or digitally
encoded vestigial sideband signal.
The TV distribution network 60 can be any distribution system used
to distribute TV signals. It can be electrical cable, optical
cable, or over the air radio or microwave or direct broadcast
satellite. The broadcast signal containing the data is converted to
baseband by a TV tuner 62 with only those portions necessary to
receive the digitally modulated signal from the TV distribution
network and produce a baseband video output consisting of the 3
level baseband signal. The 3 level decoder 64 takes the 3 level
signal from the video output of the TV tuner 62 and converts it
into two level NRZ data using a clock produced by the bit
synchronizer 66. The bit synchronizer 62 regenerates the data clock
from the video output of the TV tuner. The descrambler 68 takes in
the data stream from the scrambler (after being modulated,
transmitted, received, and demodulated by the RF components) and
recovers the original data stream.
FIG. 7A is a schematic of one embodiment of the scrambler. The
scrambler takes input data and XORs the data with a 23 bit PRNG
sequence to make it more random. The circuit is designed as a two
port network. Clock and data go to the input, and clock and
scrambled data come from the output which matches the inputs on the
3 level encoder. The circuit performs an additional function as a
test pattern generator. The pull up resistor on the data input
provides all ones which produces a PRNG output.
The descrambler shown schematically in FIG. 7B performs the inverse
function of the scrambler. It is designed as a two port network
with clock and scrambled data going in the input, and clock and
data coming from the output.
FIG. 8A is a schematic of the three level encoder. It uses class 4
duobinary encoding format created by subtracting a 2 bit delayed
version of the input from itself. A zero input produces a middle
level output and a one input produces one of the extreme levels.
The second and subsequent one in a sequence keeps the output at the
same level as caused by the first one.
FIG. 8B is a schematic of the three level decoder. It uses
comparators to detect the three levels. The voltage levels for
comparison are set by a combination of two items. The first is a
factory set trimpot. Small adjustments around this value are set by
a feedback network that tries to make the two extreme voltage level
outputs (ones) occur 25% of the time. This is the situation that
exists with random data such as produced by scrambled data. The
data is sampled at the proper time by a locally regenerated
clock.
There has been described a Remote Link Adapter used to receive high
speed data transmitted by television broadcast. The RLA can be
employed in interfacing with a LAN, an individual personal
computer, or a video game machine. While the invention has been
described with reference to specific embodiments, the description
is illustrative of the invention and is not to be construed as
limiting the invention. Various modifications and applications may
occur to those skilled in the art without departing from the true
spirit and scope of the invention as defined by the appended
claims.
* * * * *