Forward error correction at MPEG-2 transport stream layer

Details Forward error correction at MPEG-2 transport stream layer Forward error correction at MPEG-2 transport stream layer

1998-12-23

2002-08-06

Kizou, Hassan (Department: 2662)

Multiplex communications

Diagnostic testing

Of a repeater

C370S475000

Reexamination Certificate

active

06430159

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to techniques of forward error correction with a communications protocol, and in particular, relates to forward error correction of MPEG-2 at the transport stream layer.
BACKGROUND OF THE INVENTION
Digital video includes the steps of the encoding of moving pictures into a digital signal, broadcasting the digital signal, and decoding the digital signal into a viewable format such as a television screen or a computer monitor. With the rapid improvements in computer technology, digital video is now readily available for computer systems, etc. and will soon be widely available for broadcasting. As digital video can also incorporate the transmission of audio signals, it is believed that this technology will eventually replace current television technology (analog video), and will have broad application in many areas such as the Internet and telecommunications in general.
Because of the broad application of digital video, the International Organization For Standardization (ISO) formed ISO/IEC JTC1 SC29 WG11, more commonly known as the Motion Pictures Expert Group 2 (MPEG-2) to generate standards for broadcast quality digital video. (An earlier committee was ISO CD 11172, or MPEG-1, which created the first generation of digital video standards, which are optimised for CD-ROM. Another variant under development is MPEG-4 for low bandwidth video telephony.) In particular, MPEG-2 defines a compressed bit stream, but the actual implementation of the compression operations are up to individual manufacturers of digital video equipment.
MPEG-2 is a standard (“MPEG-2 standard”) with various parts at different levels of completion. Of particular interest are:
ISO/IEC DIS 13818-1 Information technology—Generic coding of moving pictures and associated audio information: Systems
ISO/IEC DIS 13818-2 Information technology—Generic coding of moving pictures and associated audio information: Video
ISO/IEC 13818-3:1995 Informationtechnology—Generic coding of moving pictures and associated audio information—Part 3: Audio and the contents of each of these references are incorporated herein by reference. The MPEG-2 standard addresses the combining of one or more elementary streams of video, audio and other data into single or multiple streams which are suitable for storage or transmission. In very general terms, the MPEG-
2
standard for transmitting digital video and associated audio and other information involves the following steps: first, a digital video signal (from a digital camera or from an analog to digital converter) is compressed by analyzing and encoding the signal using spatial and temporal redundancy. Spatial redundancy refers to the redundant information inside one video frame while temporal redundancy refers to the redundant information between consecutive frames. This process generates: Intra-frames (I-frames), which contain all of the information in an entire image; Predicted frames (P-Frames), which have some compression as they are predicted based on past I-frames and/or other P-frames; and Bi-directional predicted frames (B-frames), which are the most compressed images as they are predicted from past and future I-Frames and P-Frames, Next, an audio signal is compressed by removing low power tones adjacent high power tones. Removal of these tones does not affect the signal, because the high power tones tend to mask the lower power tones, making them inaudible to the human ear. Finally, the compressed video signals, audio signals and related time stamps of those signals are assembled into packets and inserted into a Packetized Elementary Stream (PES). Each packet in a packetized elementary stream contains overhead information such as a start code, stream id, packet length, optional packetized elementary stream header and stuffing bytes, in addition to the actual packet bytes of video and audio data.
It will be apparent from the foregoing that the packetized elementary stream contains encoded video and audio data for storage or transmission. In order to multiplex several streams of packetized elementary streams, a Programme Specific Information (PSI) table is also created, which includes a series of tables to reassemble specific packetized elementary stream within multiple channels of packetized elementary streams. Thus, the packetized elementary stream and program specific information form the basis for constructing either a Program Stream (PS) or a Transport Stream (TS) of packetized elementary stream and program specific information packets, which are particularly defined in ISO/IEC International Standard 13818-1.
The Program Stream is generally suitable for communicating or storing one program of coded data and other data in error free environments, such as an optical storage device, and where processing of system coding is a major consideration. In contrast, the Transport Stream is suitable for storing or communicating one or more programs in environments where significant errors can occur, such as packet-switched networks, etc. These errors can be manifested as bit value errors within a packet, or the loss of one or more entire packets.
However, while the transport stream was intended to protect data within the transport stream from corruption in error-prone environments, the transport stream has been found to be less than satisfactory in this regard and it remains difficult to ensure reliable transmission of the transport stream through these environments. These difficulties are more particularly explained in “Protecting MPEG-2: FEC schemes in DVB-C,S,T”, (“Protecting MPEG-2”)© Copyright 1994-1998 Hewlett-Packard Company, the contents of which are incorporated herein by reference, and a copy of which is available at:
http://www.tmo.hp.com/tmo/pia/component_test/PIAApp/Notes/English/MPEGpaper2.html.
An example of error prone environments in which the transport stream can be broadcast are the various Digital Video Broadcasting Project (DVB) formats, such as Direct Broadcast Satellite (DBS), terrestrial cable networks (including coax and fibre optic etc.) or terrestrial broadcasts. In order to protect the transport stream and to achieve a Bit Error Ratio (BER) of no more than 10
−11
, Forward Error Correction (FEC) is now often added to protect the transport stream during transmission. In simple terms, the method of correcting in these formats is as follows: the original transport stream is inserted into a forward error correction encoder; the resulting signal is broadcast over the environment to a receiver; and the transport stream is recovered from the received signal by a symmetric forward error correction decoder.
Generally, a different forward error correction encoder and decoder is required for each DVB format, and this requires that each receiver have a symmetric forward error correction decoder. Variations between forward error correction encoding techniques, such as Reed-Solomon (RS), include the actual amount of error correction code added to the end each transport stream packet, whether the forward error correction packets are interleaved or spliced, and whether viterbi convolutional coding is performed. In addition to the necessity of a symmetric forward error correction decoder, it will be apparent that the addition of error correction code to the end of each packet effectively adds another layer to the protocol stack and this new layer is specific to the transmission architecture and not subject to the MPEG-2 standard. Thus, a broadcaster must ensure that each intended receiver has a symmetric forward error correction decoder.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a novel forward error correction method and system to protect a digital transport stream which obviates or mitigates at least one of the disadvantages of the prior art.
In a first aspect of the present invention, there is provided a method of creating a portion of an enhanced MPEG compatible data stream with optional forward error correction information included therein, the method comprising the steps of:
receiving an

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