MXPA96002753A - Transmission of high-speed isocronic data in mpe type currents - Google Patents

Abstract

The present invention relates to a method for the robust transmission of high-speed isochronous data in a transport stream type MPEG-2, comprising the steps of: providing the isochronous data in a packed elementary stream (PES) having a header PES that precedes a PES load, the PES load includes an isochronous data header followed by a plurality of isochronous data presentation units, align the isochronous data header and the presentation units that follow it within the PES, so that the first byte of the isochronous data header immediately follows the last byte of the PES header, insert a clock increment value in the isochronous data header specifying the ratio of the velocity of the isochronous data to the reference clock speed, the clock increment value allows the isochronous data rate to be derived from see the speed of the reference clock in a decoder, and pack the PES to form a plurality of isochronous data transport packets so that the first load byte of each transport packet is the first byte of a presentation unit of isochronic data and the last byte of an isochronic data unit

Description

TRANSMISSION OF HIGH-SPEED ISOCRONIC DATA IN DATA CURRENTS TYPE MPEG-2 BACKGROUND OF THE INVENTION The present invention relates to a method and an apparatus for communicating data by means of a packet data stream, more particularly it relates to the transmission of high speed isochronic data in a MPEG-2 type data stream. . The invention also provides communication of a data clock increment value towards a decoder in order to provide a more simplified and economical approach for direct digital synthesis (DDS-Direct Digital Synthesis) of a clock frequency necessary to recover, in the data decoder, from the packet data stream. Many standards have emerged for the transport of digital data, such as for digital television data. Examples of these standards include the Motion Picture Experts Group standard referred to as MPEG-2 and the DigiCipher® II standard owned by General Instru ent Corporation of Chicago Illinois, United States of America, the assignee of this invention. . The DigiCipher II standard is similar and includes several aspects of the MPEG-2 standard, which is widely l l ü 8/9 < > MX known and recognized as an audio and video compression specification issued and accepted by the International Standards Organization (ISO) in ISO 12818. In addition to the audio and video compression features, the MPEG-2 specification also contains a " "layer" of systems that provides a coding technique independent of the transmission medium to generate streams of bits containing one or more MPEG programs. The MPEG coding technique uses a formal grammar ("syntax") and a set of semantic rules for the construction of bit streams to be transmitted. The syntax and semantics rules include provisions for the ultiplexing, clock recovery, synchronization and error resilience. For the purposes of this discussion, any data stream that is encoded in a manner similar to that of an MPEG-2 transport stream will be referred to as the "MPEG-2 type transport stream". An example, but by no means the only MPEG-2 transport stream that can exist, is a data stream provided in accordance with the DigiCipher II standard. It is expected that in the future other rules will be enacted. The MPEG-2 transport stream is specifically designed to be transmitted under conditions that can generate data errors. The MPEG transport packets each have a fixed length of 188 bytes. Many programs, each with different components, can be combined into a transport stream. Examples of services that can be provided using the MPEG format are diffusion of television services in terrestrial, cable television and satellite networks, as well as in services based on interactive telephony. The syntax and semantics of the MPEG-2 transport stream are defined in the International Organization for Standardization, ISO / IEC 13818-1, International Standard of November 13, 1994 entitled "Generic Coding of Moving Pictures and Associated Audio: Systems, "(Generic Coding of Films and Associated Audio: Systems, Recommendation H.222.0, and ISO / IEC 13818-2, International Standard of 1995 entitled" Generic Coding of Moving Pictures and Associated Audio: Video, "(Generic Coding of Films and Associated Audio: Video,) recommendation H.262, which are incorporated herein by reference. Multiplexing according to the MPEG-2 standard is achieved by packaging elementary starting currents such as video and audio encoded in packet-based elementary packets (PES-Packetized Elemental Stream) that are then inserted into transport packets. 1'llHH / and MX As noted above, each MPEG transport packet is set at 188 bytes in length. The first byte is a synchronization byte that has a unique eight-bit pattern, that is, 01000111. The synchronization byte is used to locate the start of each transport packet. After the synchronization byte, there is a three-byte prefix that includes an error indicator of the one-bit transport packet, a start indicator of the one-bit load unit, a one-bit transport priority indicator, a 13-bit packet identifier (PID), a two-bit transport mixing control, a two-bit adaptation field control, and a four-bit continuity counter. The use of the synchronization byte and the three-byte prefix leaves 184 bytes of load carrying the data to be communicated. An optional adaptation field may follow after the prefix in order to carry both the information related to the MPEG and the relevant private information for a given transport stream or the elementary stream carried within a given transport packet. The arrangements for clock recovery, for example as a program clock reference (PCR-Program Clock Reference) and splice control, are typical of the information carried in the field of adaptation. By placing this information in a field of PllHH / 'JOMX adaptation, is encapsulated with its associated data to facilitate network re-routing and routing operations. When an adaptation field is used, the load is correspondingly shorter. The PCR is a count that reflects the value of the system chrono-switch (STC) for the associated program at the time when the PCR bytes were inserted into the transport stream. The decoder uses the PCR to synchronize a decoder cronolimitator with the encoder system clock. The lower nine bits of the 42-bit PCR provide a module 300 counter that increments at a clock speed of 27 MHz (the "system clock speed"). In each successive displacement of the module-300, the count in the upper 33 bits increases so that the upper bits represent counts that are presented at 90 kHz speed. This allows the presentation daters (PTS-Presentation Time-Stamps), and the decoding date (DTS-Decoding Time-Stamps) to be compared using the 90 kHz value. As each program or service carried by the data stream can have its own PCR, the programs and services can be multiplexed asynchronously. The synchronization of audio, video and data within a program is achieved using a dater approach.

Pll «8 / 9t.MX The presentation daters and the decoding date stamps are inserted in the transport stream to the separate video and audio packages. The PTS and DTS information is used by the decoder to determine when to perform decoding and display an image and when to play an audio segment. As indicated above, the PTS and DTS values are linked to the same clock established by the same PCRs, but are limited by the MPEG-2 standard at a time resolution of 11.1 microseconds. This resolution is limited by the PTS resolution of 90 kHz taps provided by the upper 33 bits of the PCR. This limitation prevents the transport of the generalized "high-speed" data, which is resistant to synchronization errors, for example data rates that are not integer in relation to 90 kbps, using the same approach provided for the video information and audio in a transport stream of the normal MPEG-2 type. MPEG-2 data, such as compressed video and audio data, must be formatted in a packed elementary stream (PES) formed from an association of PES packets. Each PES package includes a header followed by a load. The PES packets are then divided into the loads of the successive fixed-length transport packets.

P1188 / 9bMX PES packets are relatively long and variable in length, and several optional fields, for example presentation daters and decoding daters, can be found after the PES header, when the transport packets are formed from the PES. align with transport packet headers A single PES packet can expand many transport packets and the successions of PES packets must appear in consecutive transport packets of the same PID value.It should be noted, however, that these transport packets can be interleave freely with other transport packets that have different PIDs and that carry data from different elementary streams Video services are carried by placing MPEG video streams encoded in the PES packets, which are then divided into transport packets to be inserted in a transport stream, each PES video package contains the All or part of a coded video image, which we will refer to as "access unit". The PTS and DTS data are placed in the PES packet header that encapsulates the associated access unit. The PTS is used to drive the decoder so that it presents (eg "displays") the associated access unit. The DTS indicates the moment in l'l I H H / '», I? . that the decoder must perform the decoding of the access unit. Audio services are provided in accordance with the MPEG standard using the same specification of the PES pack layer. PTS data is attached to those packages that include audio frame boundaries. These limits are defined by the audio sync words. An audio frame is defined as the data between two consecutive audio synchronization words. In order to reconstruct a television signal from the video and audio information carried in a transport stream of the MPEG-2 type (eg MPEG-2 or DigiCipher II), a decoder is required to process the travel packages to send an output signal to a video decompression processor (VDP) and audio packets to output an audio decompression processor (ADP). It is also possible to transmit other types of data in order to provide services such as teletext, stock quotes and other information that can be carried as separate transport packets derived from a separate packaged elementary stream. Transmission lines for asynchronous data may also be supported; for example, a transmission line would be represented by an RS-232 style output from the decoder, with a Pl l tí? / 'T MX input equivalent to an encoder. These information service transport packets would be multiplexed with MPEG audio and video packets in a final ultiplex transmitted for example via satellite or cable. It would also be helpful to carry data "isochronic" using an MPEG-2 type format. Isochronic data is high-speed data delivered within the limits of a typical clock and is distinguished from "synchronous" pulse data that can arrive at an atypical clock. In this way, the isochronous data carries an instability specification and the clock can be reset with a simple phase latch loop (PLL). In general, an isochronous data component is one in which the data bits are integrated at essentially regular speeds, with an accompanying clock. Any regular or typical (isochronous) speed deviation can be covered by the allowed instability specification. This data can be used for any number of a wide range of "data transmission" applications. An example is the transport of the content of a digital IT data stream (for example a telephone data line). These data streams operate at 1,554 Mbps. Other applications include, without limitation, commercial network data, high-speed general data communications, and P1188 / 9bMX practically any other data service that requires data rates with a constant delay that exceed those that are generally available using asynchronous communication techniques or that are not suitable for the variable delay. These applications are characterized by a general intolerance of "bit slides". That is, errors are tolerated, but resynchronization involving net slippage of the bit streams causes large excesses to the final data synchronization. In the MPEG-2 standard, presentation daters can only indicate presentation units (ie 8-bit bytes of data "presented" to the decoder) at a resolution of 11.1 microseconds. This limitation results from the 90 kHz speed established by the upper bits of the PCR count used to produce the presentation daters. With high speed isochronic data it may be necessary to resolve display units with higher resolution, especially for error recovery purposes. Specifically, it is necessary to be able to present unambiguous presentation units in time to support continuously variable speeds. Therefore, it would be advantageous to increase the resolution time of presentation daters over that provided P118H / 90MX by an implementation of the MPEG-2 standard. For example, it would be advantageous to provide a scheme for increasing the resolution of the PTS time in order to allow the robust transport of isochronous or similar data, at speeds of up to 9.0 Mbps or more. It would also be advantageous to provide a scheme for simplifying a data receiver in order to provide the appropriate clock rates based on a system clock frequency, in order to recover the data from a data stream. In particular, it would be helpful to provide a scheme in which a receiver could provide a clock at any desired information data rate of, for example 19.2 kbps to 9 Mbps, to be used in outputting the isochronous information data, via the DDS . This invention provides a method and an apparatus for transmitting and receiving data in a transport stream type MPEG-2 having the aforementioned advantages as well as others.

SUMMARY OF THE INVENTION According to the present invention, a method for the robust transmission of high speed isochronic data in a transport stream type MPEG-2 is provided. The isochronic data provide Pl] 8H / 9t > M / a packed elementary stream (PES) that has a PES header that precedes a PES load. The PES load includes an isochronous data header followed by a plurality of isochronous data display units. The isochronous data header and the presentation units that follow it within the PES are aligned so that the first byte of the isochronous data header immediately follows the last byte of the PES header. A value increment value is inserted into the isochronous data header by specifying the ratio of the velocity of the isochronous data to the reference clock speed. The clock increment value allows the isochronous data rate to be derived from the reference clock speed in a decoder. The PES is packaged in a plurality of isochronous data transport packets, so that a first load byte of each transport packet is the first byte of an isochronous data display unit and a last byte of load in each of the packets in the last byte of an isochronous data presentation unit. An extension of the presentation date (PTS) is provided in the isochronous data header to supplement a PTS of the MPEG-2 standard in the PES header. The combination of the PTS extension with l 1 Mi '/ 9OM? the standard PTS allows the time resolution to be increased to present the isochronous data presentation units in a decoder. In an illustrated embodiment, the PTS extension is provided at the beginning of the isochronous data header. The PTS extension can be derived from the eight most significant bits of the nine bit PCR extension of the MPEG-2 standard. The eight-bit PTS extension can be combined with the PTS of thirty three standard bits of the MPEG to increase the time resolution of the isochronous data display daters from the MPEG-2 standard resolution of 11.1 microseconds (90 kHz) at 74 nanoseconds (13.5 MHz) for the unambiguous determination of the correct start time of the presentation unit with reference to an isochronous data PTS. In the illustrated embodiment, each isochronous data display unit comprises two eight-bit units, so that the display units comprise sixteen-bit words. An increment value may be provided in the isochronous data header by specifying the ratio of the isochronic cough rate to a reference clock rate in the decoder. A method is provided for recovering isochronic data transmitted in accordance with any of the P1188 / 96MX methods mentioned above. A PES header and an isochronous data header are located in a data stream received from isochronous data transport packets. The reference values of the program clock (PCR-Program Clock Reference) are extracted from the isochronous data packets. The PCR values are used to recover the reference clock speed. The clock increment value is extracted from the isochronous data header and used to derive the velocity of the isochronous data from the reference clock speed. Isochronic data is recovered at the speed of isochronic data. The standard PTS is extracted from the PES header. The PTS extension is extracted from the isochronous data header. The extracted standard PTS and PTS extension are used to determine a correct time to initiate the presentation of the isochronous data presentation units contained in the received data stream. In the illustrated embodiment, the PTS extension is provided at the beginning of the isochronous data header, although it may alternatively be provided elsewhere. The PTS extension can be derived from the eight most significant bits of the nine bit PCR extension of the standard MPEG-2.

P1188 / 9bMX The apparatus is provided for recovering isochronic data from a MPEG-2 transport packet stream at high data rates in a manner that is rigid with respect to the loss of transport packets due to errors. Means are provided for locating a packed elementary stream header and an isochronous data header in a received isochronous data transport packet stream. Methods for extracting program clock reference values (PCR-Progra Clock Reference) from the stream of isochronous data transport packets are also provided. The means that respond to the PCR values recover a reference clock speed. Means are provided for extracting a clock increment value from the isochronous data header. The extracted clock increment value and the recovered reference clock speed are processed to reproduce the isochronous data rate. The means that respond to the reproduced isochronous data rate recover the isochronic data. Means are also provided for extracting a presentation dater for isochronous data from the PES header and for extracting a PTS extension for isochronous data from the isochronic data header. The 1 HH / 'tnH, means that respond to the PTS extension and the extracted PTS are provided to determine a correct time to start the presentation of the isochronous data presentation units contained in the transport packet flow of received data. In one embodiment of the apparatus, the PTS extension is extracted from the beginning of the isochronous data header, and the isochronous data display units, each, are sixteen bits. The receiving apparatus is provided to recover information data from a data stream. The information is transmitted in the data stream at a speed of information data. A direct digital synthesis clock provides a plurality of reference clock rates based on a frequency of the system clock. Means are provided for locating an information data header in a received information data transport packet stream. Means are provided for extracting a clock increment value from the information data header. The clock increment value specifies the exact ratio of the information data rate to the frequency of a phased system clock. The DDS clock responds to the clock increment value to provide a clock signal at the data rate of the 1 HH / 'IDM information to be used to output the information data. The increment value is given as an integer. The data stream may comprise, for example, a transport packet stream type MPEG-2. In this mode, the nominal system clock frequency is 27 MHz. The increment value is the integer closest to the product of the information data rate and the value of the N module divided by the nominal system clock frequency (that is, 27,000,000). In a specific modality, the value of module N = 536, 868, 000. The integer increments, combined with the 30 ppm variability allowed from the nominal 27 MHz system clock frequency of the MPEG, provide a generator of continuously variable clock to support isochronic data.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic illustration showing how the elementary current data is packaged in support packages; Figure 2 illustrates isochronous data headers and ESPs in relation to Figure 1 in greater detail; Figure 3 is a block diagram of the apparatus P1188 / 96MX encoder for assembling the transport packets referenced in Figure 1; and Figure 4 is a block diagram of the decoding apparatus for recovering the isochronous data carried by the transport packets.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a diagrammatic illustration showing how different digital service components can be multiplexed into a stream of transport packets. Multiplexing is achieved by packing elementary start streams such as video, audio and data encoded in PES packets and then encapsulated in transport packets. The Figure is for illustrative purposes only, since a PES packet, such as pack 12 illustrated, can be translated into more or less seven transport packets 22a-22g illustrated. In the example of Figure 1, an elementary stream generally designated as 10 comprises a serial stream of data bits, like the isochronic data shown. It should be appreciated that other types of data may be provided in the elementary stream to be transmitted according to the present invention. Similar elementary streams will be provided for compressed video and audio data in accordance with the standard P1188 / 96MX transport MPEG-2. The first step in forming a transport packet stream is to encapsulate the elementary stream for each type of data in a corresponding packed elementary stream (PES) formed from successive PES packets, such as packets 12 illustrated. Each PES packet contains a PES header 14 followed by a PES load that contains a series of display units (PU) 18, of fixed length. The load includes the data that will be communicated. The PES 14 header contains useful information in the processing of load data, such as the presentation date (PTS) according to the specifications of the MPEG-2 systems. In accordance with the present invention, an isochronous data header header ISO 16 follows the header PES 14 as part of the load of the PES packet. The presentation units 18 of the load follow the ISO 16 heading. The ISO heading is described in more detail below. The header and load data from each PES packet are divided into individual transport packets 22, 24, 26, of fixed length, each of which contains a transport header 30 and load data 36. The data of Each packet of transport will contain a portion of the load data (it is Pl lHÜ / ObMX say display units 18) of the corresponding PES packets 12 and may also contain the PES header 14 and the ISO 16 header as illustrated in 22a. The transport packet 22d is another isochronous data transport packet in the multiplex 20 of the transport packet. This transport packet includes a transport header 30 as well as a load 36. The load does not include a PES header or an ISO header, since this transport packet is derived from the load data that is subsequent to the PES header and to the header ISO in the PES package. In other words, since there is only one PES header and one ISO header per PES packet, only the first transport packet that is derived from that PES packet will contain the PES header and the ISO header. The load segments of the remaining transport packets that are derived from the PES packet will contain only portions of the actual information data to be transmitted. According to the specifications of the MPEG-2 systems, the packet headers 30 will contain the program identifier (PID) that distinguishes each transport packet stream, such as an isochronous data packet stream, a packet video stream , or an audio packet stream, to Pl 1BH / 91) 11 / from other package streams. In Figure 1, only the derivation of isochronous data transport packets 22 is shown. In order to derive video packets 24 and audio packets 26, the corresponding elementary streams (not shown) are provided encapsulated in PES packets and the transport packets in essentially the same shape as illustrated in Figure 1 with respect to the training of the isochronous data packets 22, except that the isochronous data header 16 of the present invention is not provided in the video or audio transport packets. Each MPEG transport object contains 188 bytes of data, formed from the transport header 30 of at least four bytes and the load data 36 which can be up to 184 bytes. According to the specification of the MPEG-2 system, a field adaptation of, for example, eight bytes, can be provided in the transport medium header 30 and the load 36. The variable length adaptation field may contain, for example, example, the program value reference (PCR) that is used for the synchronization of the system time clock for the decoder. The plurality of isochronous data packets 22b, 22c ... 22g ..., and other packets 24a-f ... and 26a-f ... are '11 '8/9 (, MX multiplex as illustrated in Figure 1 to form the transport stream 20 which communicates on the communication channel from the encoder to the decoder.) The purpose of the decoder is to demultiplex the different types of transport packets from the transport stream, based on the PIDs of the individual packets, and then selectively process each of the isochronous video, audio and data components to be used in the reconstruction of a television signal and recover a data stream represented by the isochronous data Figure 2 illustrates the PES header 14 and the ISO header 16 in more detail The PES header 14 includes various information of length and structure 50 according to the specification of the MPEG-2 systems An optional PTS field 52 must follow the structure and length information 50. In case a PTS is provided, a PTS extension counterpart is provided in the ISO header 16. As illustrated in Figure 2, the PTS extension 54 is preferably provided at the beginning of the ISO 16 header, so that it immediately follows the PTS 52 in the PES header. However, this invention is limited to providing the PTS extension at the beginning of the ISO header. The PTS extension can be provided anywhere else P1188 / 96MX in the ISO header; as long as it can be detected in the decoder to be used to append it to the PTS in order to extend the time resolution to present the isochronous data at the decoder output. By providing eight additional bits, for example in the PTS extension to be added to the thirty three bits provided in the PTS specified for MPEG systems, the standard MPEG-2 resolution of 11.1 microseconds can be extended to 74 nanoseconds for unambiguous determination of the start time of the correct presentation unit in relation to a PTS of extended isochronic data. The ISO header also includes various speed, length and increment information 56. More particularly, the information of speed, length and increment will include a signaling or data rate flag, an isochronous data header length field, a field increment that specifies a ratio between the information data rate (for example the isochronous data rate) with the presence of the system clock. This clock increment value enables a direct digital synthesis clock that is in a decoder, to provide a clock signal at the speed of the information data that is used to output the information data.

P1188 / 96MX carried by a data transport stream according to the present invention. In a preferred embodiment of the invention, each isochronous data presentation unit 18 (FIG. 1) is sixteen bits in length, that is, an eight-bit two-byte word. The isochronous data presentation units are aligned with the PES syntax since the first byte of the isochronous data header immediately follows the last byte of the PES header. The isochronous data presentation units are aligned with the transport packet loads so that the first load byte of an isochronous data transport packet is the first byte of an isochronous data presentation unit (which follows any field of adaptation, PES heading and heading of isochronic data). The last byte of the isochronous data transport packet is the last byte of an isochronous data presentation unit. The syntax of the isochronic data according to the present invention is described below using the formal grammar used in the specification of the MPEG-2 systems. The MPEG grammar is a syntax similar to the C language and is a method to describe possibly variable and continuous velocity bit sequences, instead of specifying a program of P1188 / 96MX procedure and its functions as in the case of computer C language. The first column of the syntax contains the syntactic element. The second column gives the length of the syntactic element in bits, and the third column identifies the type of syntax. The types are: bslbf (bit sequence left-most bit first - first the bit furthest to the left of the bit sequence) and uimsbf (unsigned integer most significant bi t first - first the most significant unsigned integer bit). The annotation "isochronous_data_header () { ...}." Indicates that the syntactic elements in brackets are a named game and can be invoked anywhere in the syntax simply by using the designation "isochronous_data_header ()". A conditional appearance of bit structures can be indicated by the typical "if" tests. The familiar and well-known relationship operators in the C language can also be used. Loop structures are possible and use the standard C loop syntax. The syntax box is accompanied by a set of semantics, which provides definitions for each syntax field that has not been previously decided and places restrictions on its use. The syntax of the isochronous data bit stream given below and the semantics of the bitstream represent a preferred embodiment of this invention: PllHH / 'ioMX Isochronous Data Sequence Syntax: Mnemonic Number: Isochronous_data_sequence bit (Isochronous_data_heade () { For (i = 0; KN; 1 ++). {Isochronous_data_presentation_unit 16 bslbf } } Isochronic Data Heading; To restrict each frequency of isochronous data to an even number of bytes, the last field received in the isochronous data header is specified as an even number of bytes. The syntax for the isochronous data headers is: Syntax: Mnemonic number: Isochronous_data_header bits. { pts_ext8 8 bslbf data_rate_flag 1 bslbf reserved 3 bslbf Isochronous_data_header_length 4 uimsbf if (data_rate_flag). { reserved 4 bslbf increment 28 uimsbf} reserved n bslbf } P1188 / 9ÓMX Semantics of Data Bitstream and Synchronous Isochronous Data Sequence: Isochronous_data_presentation_unit - A 16-bit presentation unit of isochronous data where the first (left) bit is presented (output) before the second bit, etc..

Isochronic Data Header: pts_extß - The 8-bit field that extends to the PTS transported in the PES header of this PES. This field corresponds to the 8 most significant bits of the 9-bit PCR extension defined in the specification of the MPEG-2 systems, and is used according to the present invention to extend the resolution time of the isochronic data PTS from from the specification resolution of the MPEG-2 systems from 11.1 microseconds (90 kHz) to 74 nanoseconds (13.5 MHz) for the unambiguous determination of the correct start time for the presentation unit referred to as data PTS isochronic data_rate_flag - a flag or signaling of a bit that, when set to "1" indicates that an increment field is present in the isochronic data header.

Pl 188/9 () MX isochronous_data_header_length - a 4-bit field that indicates the number of words (16 bits) of the isochronous data header that follows this field, including the reserved words, (the 16-bit units require that the isochronous data header is an even number of bytes which, coupled to the isochronous data presentation units, to the adaptation fields and to the PES header also form an even number of bytes, and allows isochronous data transport packets they are generated without any byte filling or useless, and therefore with a higher efficiency. increment - a 28-bit field that indicates the clock increment value of the isochronous data and takes a value that describes the exact ratio of the isochronous data rate to the reference clock engaged in phase (for example a reference of 27 MHz of MPEG-2 In a preferred embodiment, the increment is: increment = NINT (isochronous data rate * 536,868, O00 / nominal_system_clock_frecuency), where nominal_system_clock_frecuency is specified by MPEG as 27 MHz and "NINT" means "the whole closest. "As mentioned before, MPEG allows a variability of 30 ppm from the nominal system clock sequence P1188 / 96MX reserved - A field of n-bits of reserved words of which the decoder does not assume a particular value .

The block diagram of Figure 3 illustrates a possible encoder for implementing the present invention. Isochronous data (for example, from stream 10 - Figure 1) are input via terminal 60 to a header insertion step 62 that inserts the data required to assemble the ISO 16 header. This data is obtained, for example , from a system microprocessor not shown. The ISO data with the inserted ISO header are received by step 66 of the PES packer which inserts the PES header 14 that has been assembled from the PES header data entry via terminal 68; as with the ISO header data, the PES header data can be obtained from a system microprocessor or from another data source, as is well known in the art. An isochronous data clock signal is input via the terminal 65 to a phase locked loop (PLL) 67 of the encoder of Figure 3. The PLL can, for example, comprise a 27 MHz oscillator and a DDS circuit to latch to the input clock signal, using the nearest increment value P1188 / 9 MX as calculated before. The PCR values are then generated by the PCR generator 69. The PCR values are entered as still packaged transport adaptation data 70 of the transport packet, described in more detail below. Once the ISO header and the PES header have been inserted into the elementary stream of isochronous data, the subsequent load data input via terminal 60 is segmented to follow the header in the form of fixed length display units. The result is an association of PES packages 12 that leave the PES 66 packer to step 70 of the transport packet packer. At this point, the data needed to assemble the transport header is received by terminal 72 in a conventional manner and assembled in a transport header, to which the counterpart load data is appended. The load data comprises the following data portion (ie the PES header data, the ISO header data and / or the presentation units) from the current PES packets. The output of the packaging 70 is a series of isochronous data transport packets 22 where each will comprise a transport and load header, and may or may not include the PES header and the P1188 / 96MX isochronous data header information as part of the load. The isochronous data packets from the packer 70 can be multiplexed or with compressed inputs of audio packets and video packets to a multiplexer 74 by means of: terminals 76 and 78, respectively. The audio and video packages are provided in accordance with the specifications of the MPEG-2 systems, as is well known in the art. The multiplexer 74 assembles the transport packets in a stream of transport packets 20 (as shown in Figure 1). The transport packet stream is modulated in a conventional modulate 80 and transmitted by a conventional transmitter 82 via a communication channel via satellite, via cable or by other known means. Figure 4 illustrates a receiver ("decoder") for the output of transmission multiples from the encoder of Figure 3. The transmitter multiplex enters a decoder 92 via terminal 90 and is odulated in a conventional demodulator 94. A demultiplexer 96 retrieves audio packets, video packets and isochronous data packets from the stream of demodulated transport packets. Isochronous data packets are entered P1188 / 96MX to a header processor 98 which may comprise a conventional microprocessor programmed to retrieve the PES header and the ISO header from the stream of isochronous data packets. The PST is extracted from the PES header in a PTS extraction stage 102. The PTS extension that is provided according to the present invention is extracted from the ISO header by a step 104 of extracting the PTS extension. The PTS extension and the PTS are combined in a combiner 106 to provide the isochronous data of the PTS which allows the high speed isochronic data to be presented accurately in time. A PTS decoder 108 extracts the synchronization information from the PTS output of the extracted isochronous data that comes from the combiner 106. This timing or synchronization information is input to an isochronous data extractor 110 that also receives the isochronous data packets from of the demultiplexer 96. The system synchronization information from the header processor 98 allows the extraction stages 102, 104, the PTS decoder 108 and the isochronous data extractor 110 to be properly located and process the data presented in each stage. The ISO 110 data extractor responds to the PTSs from the PTS decoder 108 in order to present the P1188 / 96MX individual isochronous data display units (the "ISO data" recovered) at the appropriate time. The ISO data presented comes from the ISO 110 data extractor to be used to provide a desired service based on the information incorporated in the data. The decoder of Figure 4 also includes a DDS clock 100 which is used to provide a plurality of reference clock rates used by the header processor and / or by other decoder components. The system synchronization output from the header processor 98 is based on one or more of the reference clock rates provided by the DDS clock. These reference clock rates are based on a system clock frequency, for example the system clock frequency of 27 MHz set in the specification of the MPEG-2 systems. In order to process the PCRs to generate the system clock frequency for use by the DDS, the decoder includes a PCR 97 parser that extracts the PCR values from the isochronous data transport packets. The extracted PCR values are used to latch a phase 99 latch loop that generates the system clock (for example 27 MHz). The clock of Pll 88 / 96MX system enters the DDS 100 clock to be used in the generation of reference clock speeds, which are described in the foregoing. In order to simplify the decoder, a clock "increment" is provided in the isochronous data header to specify the ratio of the isochronous data rate to the system clock frequency. This increment is recovered by the header processor 98 and enters the DDS clock 100, which uses the increment to provide a clock signal at the isochronous data rate for use in the presentation of isochronous data. The provision of a clock increment in the isochronous data header avoids the need for the decoder to compute this increment on its own. In conventional systems using a direct digital synthesis clock, the decoder receives a required clock frequency indicator with the data to be recovered. The clock frequency indicator specifies the current clock frequency to be synthesized by the DDS clock. As the DDS clock scales an existing system clock in order to produce various fixed clock frequencies, conventional decoders must first determine the desired clock rate ratio with respect to the clock.

P1 1 88/9 ?, MX system clock frequency from which the desired clock frequency will be derived. The processing equipment necessary to carry out this function adds cost and complexity to the decoder. In a digital television decoder, the cost must be kept to a minimum since a separate decoder will be required for each of the potential millions of television sets in the field. By providing the decoder with an increment that can be used directly by the DDS clock to produce the desired frequency the complexity and cost of the receiver are reduced. In the system of the present invention, the computation of the increment necessary to provide the desired frequency is done centrally in the encoder, which serves the millions of decoders in the field. The decoders therefore do not need to perform this computation. It should now be appreciated that this invention provides a method and apparatus for communicating information data, for example isochronous data, in a transport stream of the MPEG-2 type. The isochronic data follows a PES header on the load portion of a packed elementary stream. The PES load starts with an isochronous data header that is followed by the data presentation units P1188 / 96MX isochronic. In the preferred embodiment, the display units are sixteen bits in length. The presentation units are aligned with the packed elementary stream, with the first byte of the isochronous data header following the last byte of the PES header. The isochronous data presentation units also align with the transport packets that carry them. In particular, the first loading byte of a transport packet is the first byte of a presentation unit. The last byte of a transport packet is the last byte of a presentation unit. A unique isochronous data bit stream syntax is provided to implement the present invention. The syntax provides a clock increment in the isochronous data header to describe the ratio of the isochronous data rate to a system reference, thus providing additional information to the decoder that allows the complexity and cost of the receiver to be reduced . Although the invention has been described in connection with a preferred embodiment, it should be appreciated that many modifications and adaptations may be made thereto without departing from the spirit and scope thereof as set forth in the appended claims.

P1188 / 96MX

Claims (22)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A method for the robust transmission of high-speed isochronic data in a current of MPEG-2 transport type, comprising the steps of: providing the isochronous data in a packed elementary stream (PES) having a PES header preceding a PES load, the PES upload including an isochronous data header followed by a plurality of isochronous data presentation units; align the isochronous data header and the presentation units that follow it within the PES, so that the first byte of the isochronous data header immediately follows the last byte of the PES header; insert a clock increment value in the isochronous data header specifying the ratio of the speed of the isochronous data to the reference clock speed, the clock increment value allows the isochronous data rate to be derived from the speed of the clock P1188 / 96MX reference, in a decoder; and packaging the PES to form a plurality of isochronous data transport packets so that the first load byte of each transport packet is the first byte of an isochronous data display unit and the last byte of load of each of the packets is the last byte of an isochronous data unit.
2. 2 . A method according to claim 1, further comprising the steps of: providing a presentation dash extender (PTS) in the isochronous data header to supplement a standard MPEG-2 PTS provided in the PES header, the combination of the extension PTS with the standard PTS allows the time resolution to be increased to present the isochronous data presentation units in the decoder.
3. 3. A method according to claim 2, characterized in that the PTS extension is provided at the beginning of the isochronous data header. A method according to claim 3, characterized in that the PTS extension is an eight-bit extension derived from the eight most significant bits of the nine-bit PCR extension of the standard MPEG-2. P1188 / 96MX 5. A method according to claim 4, characterized in that the eight-bit PTS extension is combined with a standard 33-bit PTS to increase the time resolution from about 11.1 microseconds to about 74 nanoseconds. 6. A method according to claim 5, characterized in that the isochronous data display units, each one, are sixteen bits in length. 7. A method according to claim 1, characterized in that the isochronous data display units are each sixteen bits long. 8. A method for recovering isochronous data transmitted in accordance with the method of claim 1, comprising the steps of: locating a PES header and an isochronous data header in a data stream received from the isochronous data transport packets; extract program clock reference (PCR) values from the isochronous data transport packets; use the PCR values to recover the reference clock speed; extract the clock increment value from the isochronous data header; use the extracted increment value P1188 / 9b X to derive the isochronous data rate from the reference clock speed; and recover the isochronous data at the isochronous data rate. A method according to claim 8, characterized in that before the transmission of the high-speed isochronous data in the transport stream type MPEG-2, a presentation dash extender (PTS) is provided in the isochronic data header for supplement a standard MPEG-2 PTS provided in the PES header, the combination of the PTS extension with the standard PTS allows the time resolution to present the isochronous data presentation units in the decoder to increase, the method to recover the Isochronous data also include the steps of: extracting the standard PTS from the PES header; extract the PTS extension from the isochronous data header; and using the extracted standard PTS and the PTS extension to determine a correct time to start the presentation of the isochronous data presentation units contained in the received data stream. P1188 / 96MX 10. A method according to claim 9, characterized in that the PTS extension is provided at the beginning of the isochronous data header. A method according to claim 10, characterized in that the PTS extension is derived from the eight most significant bits of the standard 9-bit MPEG-2 PCR extension. 12. A method according to claim 11, characterized in that the isochronous data display units are each sixteen bits long. A method according to claim 1, characterized in that it further comprises the step of inserting the PCR values to form isochronous data transport packets that are used by the decoder to recover the reference clock speed. 14. An apparatus for recovering isochronous data carried at an isochronous data rate in a transport stream type MPEG-2, comprising: means for locating a packed elementary stream (PES) header and an isochronous data header in a stream received from isochronous data transport packets; a means for extracting program clock reference (PCR) values from the stream of isochronous data transport packets; P1188 / 96MX a means that responds to the PCR values to recover a reference clock speed; means for extracting a clock increment value from the isochronous data header; a means for processing the extracted clock increment value and the recovered reference clock rate in order to reproduce the isochronous data rate; and a means responsive to the isochronous data rate reproduced by the processing means to recover the isochronous data. 15. An apparatus according to claim 14, further comprising: means for extracting a presentation dater (PTS) for isochronous data from the PES header; a means to extract an extension PTS for isochronous data from the isochronous data header; and a means that responds to the PTS and the extracted PTS extension to determine a correct time to start the presentation of the isochronous data presentation units contained in the received data transport stream. 16. An apparatus according to claim 15, characterized in that the PTS extension is extracted from P1188 / 96MX of the start of the isochronous data header. 17. An apparatus according to claim 15, characterized in that the isochronous data display units are each sixteen bits long. 18. A decoding apparatus for recovering information data from a data stream, the information is transmitted in the data stream at an information data rate, characterized in that it comprises: a direct digital synthesis clock (DDS) to provide a plurality of reference clock rates based on a frequency of the system clock; means for locating an information data header in a received stream of information data transport packets: and a means for extracting a clock increment value from the information data header, the specified clock increment value the ratio of the information data rate to the frequency of the system clock; wherein the DDS clock responds to the clock increment value to provide a clock signal at the information data rate to be used in the output of the information data. P1188 / 9bM? 19. An apparatus according to claim 18, characterized in that the increment value is an integer. 20. An apparatus according to claim 19, characterized in that the data stream is a transport stream type MPEG-2; the clock frequency of the system is approximately 27 MHz; and the increment value is the integer closest to the product of the information data rate and a value of module N divided by 27, 000,000. 21. An apparatus according to claim 20, characterized in that the value of module N = 536,868,000. 22. An apparatus according to claim 18, characterized in that: the clock frequency of the system has a tolerance range that allows the DDS clock to generate a substantially continuous range of reference clock rates, from a system clock, to retrieve information at any information rate within the substantially continuous range. P1188 / 96MX