Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-05-12
2002-03-05
Chan, Jason (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06353490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the transmission of radio frequency (RF) signals over fixed transport mediums and in particular where the bandwidth needed exceeds that currently available over the transport medium. It has particular application to interactive (two-way) cable television (CATV) systems, but is also applicable to other wideband signal transport and distribution systems such as broadcast facilities (studio, exciter, transmitter), telephone public switched networks, local area networks (LANS), wide area network (WANS), medium area networks (MANS), wideband signal transport and distribution corporate/institutional networks, and teleports/antenna farms.
2. Background Information
The Information Revolution is deemed to become the leading economic driving force of the next millennium. Information will be the primary commodity of the 21st century. The ability to store, retrieve, transport and access information will be the dominant measure of success. Although the World Wide Web (www) is being deployed rapidly, access to the Internet is still limited by, and dependent on, the limited bandwidth of the connecting medium which limits access speeds. With the exception of major corporate, institutional and government networks, most users can only tap into this ocean of information using an ordinary analog telephone line, which limits the access rate to less than 56.6 Kbs (typically as low as 14.4 or 28.8 Kbs in remote areas).
As telecommunications systems evolved through the 20th century, multiple transport and delivery mediums have been deployed for disseminating all forms of information; data, audio, telephony and video, for a multitude of users and services. These mediums include the Public Switched Telephone Networks (copper and fiber); Broadcasting (radio, television and wireless communications); Satellite (Geostationary, DBS and LEO's); Terrestrial Microwave; Continental and transoceanic cables (copper, coax and fiber); Cable Television or CATV (coaxial and Cable/HFC); and Wireless Cellular Telephone Networks, both analog (AMPS) and digital (PCS), which use a network of switching cells connected via the public telephone network and direct satellite links.
Since Internet access is basically data transfer over a transport medium, all of these telecommunications networks have the ability to provide Internet access, within specific limitations, and with distinct advantages and disadvantages for each medium. With almost 100% deployment in north America, highly evolved in western Europe and rapidly expanding in developing nations, the Public Switched Telephone Networks commonly referred to as POTS (Plain Old Telephone Service), are today the connection of choice for Internet access. Although major advances are being made in improving the ability of the public telephone networks to carry high speed data, the limiting factor remains the original copper pair connecting most subscribers to the central office, which was historically intended only for narrow band (3 kHz) voice transmission, and the point-to-point architecture of the worldwide telephone network which is not suitable for the point-to-multipoint “broadcasting” of data. Advances in DSL (Digital Subscriber Line) technology greatly increase data delivery rates to subscribers over the existing copper plant, but still limit return bandwidth (subscriber to network) to ISDN rates (128 Kbs max.), and only over very limited distances.
Geostationary communications satellites, especially high power direct broadcast satellites (DBS), are ideally suited for the dissemination of large amounts of information (video, data, audio) to millions of users over large geographic areas, even in underdeveloped, scarcely populated regions. This offers a major advantage over the telephone networks for the high speed delivery of Internet data to subscribers (6 to 8 times faster than telephone lines), but interactive, 2-way communications is still restricted to the bandwidth limitation of a traditional telephone line which must be used for the subscriber's return access to the Internet. A further limitation of Internet access via satellite is the fact that satellites have a limited number of transponders with limited total bandwidth (typically 24 transponders with 36 MHz each). Since their geographical coverage (footprint) is very large, this limited bandwidth becomes rapidly saturated in highly populated areas, even if each subscriber chose to make a major investment in an expensive, private satellite uplink (VSAT).
The third readily available transport medium for high speed internet access are the Cable Television (CATV) networks (both coaxial and Hybrid Fiber/Coax (HFC) systems), widely deployed since the 50's for subscriber based, multi-channel television delivery. Connecting over 70 million homes in the USA today, the world wide subscriber base is projected to grow to some 400 million by 2005. Like satellites, these networks are ideally suited for broadcasting information point-to-multipoint, from the headend directly to subscribers' homes. The bandwidth of these Cable/HFC networks have been continually expanding from an upper limit of 250 MHz to 860 MHz today and beyond. They offer the widest bandwidth direct conduit to the subscriber. Although the expanded bandwidth now available has resulted in many new services being offered by the MSO's (multiple-system operators) they remain largely a unidirectional downstream (headend or hub to subscriber) transport medium (50-750 MHz), with very limited upstream (return path) capabilities (only 5-42 MHz bandwidth). Because these systems have historically been designed primarily to deliver multiple TV channels, the return paths have not been fully implemented, and suffer major noise ingress and interference problems. This limited return path bandwidth was traditionally reserved for system control, performance monitoring and service authorization uses. Although the advanced cable modems currently being deployed in large numbers provide the fastest internet download speed available (20 to 100 times faster than a telephone line), subscriber access in the reverse direction is still predominantly via the limited upstream bandwidth available or the Public Telephone Switched Network, restricting the World Wide Web connection to very high speed data dissemination and low speed access and response by the end user. This today is the major bottleneck in the system, limiting the availability of advanced interactive services such as high speed internet access, video-on-demand, on-screen shopping, banking and brokerage services at home, playing interactive video games, responding to polls, and telephony service over the Cable/HFC plant.
Modem Cable/HFC (hybrid fiber/coax) networks and other telecommunications platforms designed for the transmission and dissemination of high speed data comprising multi-channel, analog and digital television, and advanced interactive internet, e-mail, and other services require very large bandwidth to be shared by multiple users, with 50-750 MHz bandwidth available downstream, and only limit 5-42 MHz available upstream bandwidth.
Typical systems in use today employ optical nodes in the downstream path serving up to 2000 subscribers within a service area, who share the 5-42 MHz return path bandwidth available. Downstream signals are delivered to these nodes by laser transmitters over optical fiber cables. These optical transmissions are converted in the nodes to RF modulated carriers, and delivered to individual subscribers connected to the nodes by coaxial cables. The downstream and upstream signal flows are separated by diplexers with a cross-over frequency at approximately 50 MHz. Typically downstream signals are split into 4 individual outputs, each serving 500 subscribers. The signals from the 4 return inputs are combined (summed), and transmitted back to the headend on a separate fiber.
More advanced services, especially telephony over Cable/HFC networks, also mandate redundant powering of the system via
Krasnikoff Harry
Morales Maximo V.
Singer Samuel
Bello Agustin
Buchanan Ingersoll P.C.
Chan Jason
Quintech, Inc.
LandOfFree
C/N performance of broadband two-way transmission of RF... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with C/N performance of broadband two-way transmission of RF..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and C/N performance of broadband two-way transmission of RF... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2862575