Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-11-04
2001-03-27
Olms, Douglas W. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S498000
Reexamination Certificate
active
06208666
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the delivery of digital video and data, and more particularly, to a system and method for maintaining timing synchronization in a digital video network.
BACKGROUND OF THE INVENTION
The delivery of digital video signals to a subscriber has been accomplished via many ways. For example, compressed digital video using the motion picture experts group (MPEG-2) compression/decompression methodology can be delivered using a variety of media including coaxial cable, fiber optic cable and satellite. Some of these delivery systems are considered “video-on-demand”, or “near video-on-demand” in that a user, or subscriber, may select from a plurality of offerings and view a particular program as desired from time to time. In video-on-demand systems, a user may select a program for viewing at any arbitrary time. In near video-on-demand systems, a user is typically given a choice of programming available at repeated specific times. Furthermore, broadcast video applies to programming that occurs with a daily or weekly schedule and is delivered to a wide number of subscribers at the same time.
These systems typically make available to the user all channels of programming from which the user selects the desired program, typically through the use of some sort of converter or decoder box located near a television set. For example, in a typical cable television system, all available programming is delivered to a user via a coaxial cable that terminates near the user's premises. The programming made available to each particular user is determined by the insertion of a filter, or a scrambler, between the supply cable and the user's premises. In this manner, the selection available to a user is controlled. In these cable television systems, a “pay-per-view” system is also available through the use of the converter box. If the user desires a particular program, the user contacts the cable service provider ahead of time in order to purchase that particular program.
In satellite digital video delivery systems a user, or subscriber, installs a small parabolic reflector and special electronics at the premises. These systems use the direct broadcast satellite “DBS” spectrum to deliver digital video signals to a user. In these systems, all of the available programming content is transmitted directly to all users from specialized satellites in geosynchronous earth orbit. Geosynchronous orbit refers to an orbit in which a satellite orbiting the earth remains in a fixed position relative to a point on the earth. A receiver unit located at the user premises decodes the data stream in order to extract the desired programming.
Each of the aforementioned digital video delivery systems have drawbacks. For example, in cable television systems, it is relatively easy to steal, or pirate, the signal from the cable located near the user premises. This allows an unauthorized user access to all programming available on the cable. Furthermore, historically, cable television systems suffer from reliability problems.
A satellite delivery system also has drawbacks. Because all of the available programming is simultaneously beamed to all subscribers, bandwidth allocation, and therefore, channel capacity, becomes critical. For example, during times when many sporting events or high action programming that contain fast motion are broadcast simultaneously, such as on Sunday afternoons during football season, additional bandwidth must be made available to certain channels. Because the amount of available bandwidth is fixed, this necessitates the reduction of bandwidth available for other channels. In addition, satellite delivery systems rely upon the proper installation of the parabolic reflector, which must have an unobstructed line of sight to the transmitting satellite or satellites, and suffer from signal degradation in inclement weather. Furthermore, as in cable television systems, or in any system in which all channels are delivered to all customers, it is possible to obtain unauthorized channels.
Other available systems make a number of video programs available to an end user by employing an asynchronous transmission network (ATM) over which a particular program may be delivered to an end user. Unfortunately, ATM systems are costly to implement and because these systems employ an ATM switching fabric, they can easily become overloaded if, for example, a large number of users chose to view a wide variety of programs.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.
SUMMARY OF THE INVENTION
The present invention provides a system and method for maintaining timing synchronization in a digital video network.
Briefly described, in architecture, the system can be implemented as follows. A system for maintaining timing synchronization in a digital video transport system comprises a filter configured to receive a program group containing a plurality of programs and isolate at least one of the programs, a buffer in communication with the filter, a program clock reference (PCR) extractor in communication with the filter, a counter in communication with the PCR extractor, and a multiplexer in communication with the counter and configured to receive an output of the buffer and the counter.
The present invention can also be viewed as providing a method for maintaining timing synchronization in a digital video transport system. In this regard, the method can be broadly summarized by the following steps: receiving in a filter a digital video transport stream having a timing reference value and comprised of a plurality of packets and containing a plurality of programs, filtering the transport stream to obtain at least a desired one of the plurality of programs, supplying the desired program to a buffer and monitoring the desired program to detect the presence of the timing reference value within any of the packets that is valid. Also performed are the steps of copying the timing reference value into a counter, incrementing the counter by an amount equal to the time the desired program resides in the buffer, supplying the timing reference value to a multiplexer, and overwriting the timing reference value into the desired program after the desired program leaves the buffer.
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Dunn Bryan W.
Eshleman Matthew A.
Lawrence Peter H.
Geogia Tech Research Corporation
Olms Douglas W.
Pizarro Ricardo M.
Thomas Kayden Horstemeyer & Risley, L.L.P.
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