Error detection/correction and fault detection/recovery – Pulse or data error handling – Digital data error correction
Reexamination Certificate
2001-08-07
2003-05-20
Moise, Emmanuel L. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Digital data error correction
C714S752000, C714S776000, C370S474000
Reexamination Certificate
active
06567948
ABSTRACT:
BACKGROUND
Today, the availability of powerful digital computational tools has yielded the ability to present information in forms that go far beyond text and numbers. There now exists the capability to create and share data in more complex multimedia forms, using graphics, audio, still images and moving images (video), as well as combinations of those forms. This data may be a well-defined group of bits, such as a graphics/text file, an audio file or a still image file. The data may also be a real-time or near real-time bit stream of bits, such as that generated by live video, audio, or financial data.
Whether in file or stream format, however, multimedia data generally is far larger in size than text data. For example, whereas a conventional text file usually occupies less than 50 Kilobytes (Kbyte), just one minute of compressed video requires up to 10 Megabytes (Mbyte), almost 200 times larger in size. The presentation of information in multimedia form therefore creates two problems—storage and communication. Storage has improved dramatically over the past few years. For example, personal computers (PCs) can now store inexpensively many Gigabytes (Gbyte) of data, and the cost-per-Gbyte is becoming less expensive every day.
Communications, however, remain a problem. Historically, the oldest method of distributing large amounts of information has been printed material, usually in the form of magazines and books. However, this method is relatively expensive, takes days to complete, is limited to presenting data in text, pictorial or graphic form, and is difficult to update or change. Distribution of information via audio cassette or video cassette, while less costly and allowing information to be presented in audio and video form, is still relatively slow in that shipment of the physical item containing the information must take place, the cassette itself still makes it relatively difficult to update and change the information, and is incapable of communicating live video and audio.
More practical than printed material and cassettes, graphics, music and other information may be digitized into computer data files, referred to as “large digital objects,” which in turn may be transferred from a host computer to a potentially large number of subscriber computers. One common way of transferring data files is via a public or private computer network, in which the data files are transmitted by the host computer and received by the subscriber computers over phone lines via a modem. Although distribution via modems may work well for multi-Kbyte files, transmitting multi-Mbyte data files is impractical even when using the fastest modems, because the transmission speed of modems is constrained by the relatively low bandwidth of the telephone lines. For example, reliably retrieving just one large data object using the Internet, or other public or private networks, even when using ISDN lines, may take many minutes to many hours, and is relatively expensive.
To avoid overloading expensive private networks, many companies distribute large text files and other large digital objects using CD-ROM disks, each of which can hold, for example, up to 660 Mbytes of data. While the cost of distribution is moderate in comparison to using a network, the distribution of CD-ROM disks suffers from one major drawback shared by the oldest methods of information distribution—it can take one or more days, in comparison to the theoretically near-instantaneous communication potential that digital information should enjoy. Further, to update this CD-ROM based information, new CD-ROMS must be provided, usually from every three months to a year.
Moreover, none of the above-described communication methods can be used to communicate quickly, efficiently and reliably streams of live data. For example, video may be stored on videotape prior to broadcast (“tape delay”). This is not acceptable, however, when users require the video immediately. Digital communication of live video or audio via the Internet is slow, unreliable and unwieldy. Traditional analog communication methods such as TV and radio, as well as the proposed digital TV, although quick and efficient, are very susceptible to noise and interference.
To overcome some of the problems associated with the above methods of distribution, distributors of large data files or long data streams are turning to satellite broadcasting. Satellite broadcasting provides not only distribution over large geographical areas, for example, the entire United States and Canada, but potentially has the high bandwidth capacity required to transmit large amounts of data at high speeds, thus reducing the transmission time to seconds. Moreover, the cost of satellite broadcasting, on a per-user basis, is comparatively less than the respective costs of the above methods.
One type of satellite broadcasting is one-way satellite broadcasting. A one-way broadcast satellite system, shown in
FIG. 7
, transfers data from a host computer to a satellite transmitter device
2
. The satellite transmitter device
2
in turn transmits, through an uplink antenna
4
, the data to a satellite
5
using digital modulation techniques well-known in the art. The satellite
5
retransmits the data to one or more downlink antennas
6
and satellite receiver devices
7
. The satellite receiver device
7
transfers the data to the subscriber computer
8
.
One notable drawback of one-way satellite broadcast systems, however, as compared to some other methods of information distribution such as the above-described computer networks, is the inability of the subscriber computers to inform the host computer that a reception error has occurred. For example, if the information is live video, the display of the receiver will simply “freeze up” if an error is encountered, unable to continue until a correct frame of video is received. Thus, it is essential that the transferred data files or streams be received in perfect condition, or capable of being reconstructed to be in perfect condition, at all the subscriber computers.
The above drawback of one-way satellite broadcasting is further compounded, however, by the greater vulnerability of the broadcast signal to various forms of noise interference present in the transmission channel. One form of noise that is always present in the channel is “white” noise. For example, white noise is introduced in the satellite channel by the thermal radiation of the gaseous constituents of the earth's surface. The strength and frequency of this noise varies, and it sometimes overpowers the transmitted signal causing it to be received erroneously. Because of white noise, a transmitted binary “zero” bit is occasionally received erroneously as a binary “one” bit, and vice-versa. Such errors are known as bit errors. White noise generally tends to cause isolated bit errors in a transmitted message. Although these bit errors are usually spread out throughout the message, they can be easily detected and corrected, because they are isolated. In contrast with white noise, “impulse” noise tends to wipe out long sequences of consecutive bits. Such errors are known as “burst” errors. Their duration varies from a few milliseconds to a few seconds, but certain phenomena, such as rainstorms or sunspots, can cause burst errors of even longer duration such as a few minutes. Unlike bit errors due to white noise, burst errors are not distributed over the entire message, but only a portion thereof. However, burst errors are more difficult to detect and correct, because they wipe out so many consecutive bits of data.
Well-known error detection and correction (EDAC) schemes are used to reduce the effects of errors caused by white noise. EDAC generally operates at the bit level by adding enough redundant data bits to the data to detect and correct the received data. In practice, EDAC can only detect and correct a limited amount of bit errors. The redundant data added to the original data, however, obviously increases the amount of data to be transmitted and thus the transmission bandwidth and transmis
Fischer Michael
Paleologou Sophia
Steele William E.
Fitzpatrick ,Cella, Harper & Scinto
KenCast, Inc.
Moise Emmanuel L.
LandOfFree
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