MXPA96006364A - Reforming variable speed data paracomunication of speed f - Google Patents

Abstract

The present invention relates to a method for reformatting variable speed data for communication to an external device at a fixed rate, characterized in that it comprises the steps of: recovering fixed-length packets from the variable-speed data of a packet multiplex data, add a packet start byte to the beginning of each of the recovered packets, add filler bits to at least some of the recovered packets if a variable speed data rate is lower than the fixed rate; and provide the recovered packets with the added packet start byte and any padding bits as an output to the external device, at the fi rate

Description

REFORMING VARIABLE SPEED DATA FOR FIXED SPEED COMMUNICATION BACKGROUND OF THE INVENTION The present invention relates to the reformatting of variable speed data for communication with an external device at a fixed speed. The invention has particular application in the provision of an extensible interface for a communications terminal such as a connection box or an integrated receiver decoder (IRD) for digital television, in which the data stream received by the terminal transports the data for use them through an external device ("external data") in addition to television signals and access control signals. The digital transmission of television signals can provide video and audio services of a much higher quality than analog techniques. Digital transmission schemes are particularly advantageous for signals that are broadcast, via cable or satellite television network, to cable television affiliates and / or directly to domestic satellite television receivers. Examples of these schemes are the standard MPEG-2 data transmission and the standard DigiCipher II property of General Instru ent Corporation of P13 < * rK, MX Chicago, Illinois, E.U.A., the assignee of the present invention. The DigiCipher II standard extends the MPEG-2 systems and video standards, which are widely known and recognized as transport and video compression specifications specified by the International Standards Organization (ISO) in the ISO 13818 series document. "layer or stratum" of specification systems MPEG-2 provides a transmission medium independent of the coding technique for assembling bitstreams containing one or more MPEG-2 programs. The MPEG-2 coding technique uses a formal grammar ("syntax") and a set of semantic rules for the construction of bit streams. The. syntax and semantic rules include provisions for demultiplexing, clock recovery, elementary current synchronization, and error handling. The syntax and semantics of the MPEG-2 transport stream are defined in the International Organization for Standardization (ISO / IEC 13818-1, International Standard, 1994 entitled "Generic Coding of Moving Pictures and Associated Audio: Systems," Recommendation H.222 , incorporated herein by reference, it is expected that digital television transmitter and receiver systems will replace existing analog systems in exactly the same way as compact discs.

Digital P1393 / 96MX have largely replaced analog phono recordings in the audio industry. An advantage of digital transmission techniques is that television signals can be compressed using various well-known compression techniques in order to free up the bandwidth in the cable or satellite television spectrum. This bandwidth can be used to provide additional services, such as additional television channels and / or external data communication that may or may not be related to television services. Currently television, telephone, personal computer (PC) and other technologies are beginning to mix. Meanwhile, it is desirable to allow products that use these technologies to communicate with each other through an efficient and low-cost interface. In particular, it would be advantageous to provide an external data interface port in the "connection" boxes that receive television signals from the satellite and cable television system. This interface port would allow the data communication that is made with television program services but that is independent of the services to external peripherals such as a personal computer, a video player / recorder, a video game, or P1393 / 96MX similar. It would be particularly advantageous if this interface port provided data communication to the external peripheral component at virtually any desired fixed rate. Moreover, it would be advantageous for this interface to provide the reformatting of received variable rate data from a cable or satellite television system, into fixed rate data, in an efficient and low cost manner. The present invention further provides an interface having the aforementioned advantages as well as other advantages. In particular, the interface of the present invention allows the emission at a fixed speed regardless of the speed of the information. This feature allows a simple and inexpensive recovery circuit to be implemented using a simple and inexpensive connector, such as a miniature earphone plug or other well-known connector. the circuit is also substantially free of electromagnetic interference (EMI). the data is transported over the interface in a differential mode, providing good noise immunity and a two-wire interface that is not sensitive to the polarity of the wiring. Since the speed of the information is independent of the clock of the receiver that sets the fixed output speed, the transmission speed can be used as a P1393 / 96MX time reference. In this way, the external device can recover the clock very easily despite the variable information speed. Since no DC path is required between the connector and chassis of the receiver, problematic ground circuits are eliminated. Additional advantages will be evident from the following exhibition.

SUMMARY OF THE INVENTION In accordance with the present invention, a method is provided for reformatting variable speed data for communication to an external device at a fixed speed. Fixed-length packets of variable-rate data are retrieved from a multiplex of data packets, e.g., from an MPEG-2 or Digicipher II data stream. A packet start byte is added to the beginning of each of the recovered packets. If the information speed of the variable speed data is less than the fixed speed at which the data will be communicated to the external device, filler bits are added to each of the recovered packets as necessary in order to preserve the speed fixed to which the output data will be provided to the external device. Although the number of filler bits will be related to the speed of P1393 / 96MX variable speed data information, it is not necessary to specify a fixed relationship between these elements. Instead, a variable amount of padding can be used based on when it carries a real packet that requires filler bits and based on hardware operation (for example, the first-in, first-out record ("FIFO"). ")) that temporarily keeps the packet data and any padding bits before supplying them as output to the external device. As used herein, the "information rate" is the speed of the information carried by the variable-rate data stream as opposed to the velocity of all the data in the variable-rate stream that may also comprise, for example , the parity bits for the error correction advanced. Packets retrieved with the initial byte added from the packet and any padding bits are provided as an output or output to the external device at the fixed rate. The recovered packets can be coded with the initial byte added of the packet and the filler bits before being emitted to the external device, using alternating mark inversion (AI) and eight zero binary substitution (B8ZS) to provide a coded data stream for issue towards P1393 / 96MX external device. The filler bits may comprise, for example, binary pseudo noise (PN) filler bits. Using the AMI coding, the clock information can be embedded in the data stream and a net zero DC component results. In addition, AMI violations can be used for the detection of packet synchronization when the data streams are decoded, without the need for more cables in the interface. The B8ZS encoding reduces DC shift and provides clearly recognizable transitions for clock recovery. Fixed-length packets retrieved during the recovery step may comprise received symbols, in accordance with a multiphase and / or multilevel modulation format, and decoded using an advanced error correction algorithm (FEC) (e.g., the Viterbi algorithm) to obtain the variable speed data. In this mode, the information rate will depend on the symbol symbol speed, the modulation format and a coding rate of the FEC algorithm. In addition, packets can be recovered during the recovery step using a master clock frequency /. The retrieved packets each contain a fixed number B of information bytes plus a fixed number R of parity bytes for P1393 / 96MX error correction. The total length of each packet comprises B + R bytes, where each of the bytes is b-bits in length. The initial byte of the packet may comprise a violation sequence AMI. In particular, the violation sequence may comprise 0 + 0 + -0-0 when the preceding binary "1" closest to the initial byte of the packet in the coded AMI data stream is encoded as an AMI value "+". The violation sequence may comprise 0-0- + 0 + 0 when the preceding binary "1" closest to the initial byte of the packet in the coded data stream AMI is coded as an AMI value "-". a value "+" AMI represents a positive differential output voltage, a value "-" AMI represents a negative differential output voltage and, a value "0" AMI represents a differential output of zero volts. The B8ZS encoding may comprise the replacement of a string of eight zeros with an AMI violation sequence. In particular, the violation sequence used to encode the string of eight zeros can be + 0-00-0 + when the preceding binary "1" closest to the string in the AMI encoded data stream is encoded as a "+" value "AMT. The violation sequence used to encode the string of eight zeros can comprise -0 + 00 + 0- when the preceding 1"binary P1393 / 96MX closest to the initial packet byte in the coded data stream AMI is coded as an "-" AMI value. The apparatus for reformatting the variable speed data is provided for communication to an external device at a fixed speed. A decoder retrieves fixed-length packets of the variable-rate data from a data packet multiplex. An encoder adds an initial packet byte to the beginning of each of the recovered packets. The encoder also adds filler bits to each of the recovered packets if the information rate of the variable rate data is less than the fixed rate at which the data is communicated to the external device. An output port coupled to the encoder provides the recovered packets with the initial byte added from the packet and the padding bits to the external device at the fixed rate. In an illustrated embodiment, the encoder encodes the packets retrieved with the initial packet added byte and the padding bits using alternating mark reversal (AMI) and eight zero binary substitution (B8ZS) to provide a coded data stream for the emission to the external device. The fixed length packages recovered by the P1393 / 96MX decoder may comprise symbols received in accordance with an ultiphase and / or multilevel modulation format and decoded using an advanced error correction algorithm (FEC) to obtain the variable rate data. In this mode, the information rate depends on the symbol symbol speed, the modulation format and a coding rate of the FEC algorithm. The apparatus may further comprise a master frequency clock j_ coupled to the decoder and the encoder. The retrieved packets each contain a fixed number B of information bytes plus a fixed number R of parity bytes for error correction. The total length of each packet comprises B + R bytes, where each of the bytes is b-bits in length. Fill bits are added when necessary to maintain the desired output data rate, despite the variable information rate. The packet start byte may comprise an AMI violation sequence. In addition, the B8ZS encoding can replace a string of eight zeros with an AMI violation sequence.

BRIEF DESCRIPTION OF THE DRAWINGS - Figure 1 is a sample waveform that P1393 / 96MX shows an AMI sequence; Figure 2 is a waveform illustrating a first violation sequence AMI; Figure 3 is a waveform illustrating a second violation sequence AMI; Figure 4 is a waveform illustrating a third violation sequence AMI; Figure 5 is a waveform illustrating a fourth violation sequence AMI; and Figure 6 is a block diagram of the apparatus in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an interface for fixed rate data between a communications terminal (e.g., a satellite or cable television connection box) and an external device such as a PC, a recorder / player of video discs, a videotape recorder, a video game or other commercial multimedia devices or for a consumer. The invention is useful in providing an interface for data at any desired speed. In a particular implementation where the high-speed data is transported in a Digicipher II transport stream, the data rate is of the order of P139 Í / 9 (JNX thirty egabits per second (Mbps) These "external data" can be emitted advantageously from an output port as a differential pair of signals, for example, between the signals that make up the differential pair, it can a difference of 0.5 volts from peak to peak is provided In accordance with one embodiment of the invention, the external data emitted is coded using alternating mark inversion (AMI) and the most significant coded AMI bit is first broadcast. translate a binary symbol set into a three-level "ternary" symbol set, encoding the binary zeroes as zero voltage and the binary ones alternately as positive and negative voltage values.MAI coding is well known in the systems art The external data is received at a variable speed and reformatted for communication to an external device at a fixed speed. Fixed speed output taxis are illustrated in Table 1.

P1393 / 96MX TABLE 1 No. of Mnemonic Bits ext_data_sequence (). { for (i = 0; i < N i ++). { ext_data_packet ()} No. of Mnemonic Bits ext_data_packet (). { pkt_start_byte 8 bslbf packet 1880 * 8 bslbf fill n bslbf } The terms used in Table 1 are defined as follows: bslbf - first left bit of the binary string tslsf - first left symbol of the ternary string p_ct_start_byte - one start byte of eight packet packets - a Digicipher II transport packet or 188-byte MPEG-2 fill - a string of n-bit padding bits. Each occurrence of the pkt_start_byte must be one of two symbol sequences of eight AMI. Both sequences will violate the AMI coding rules since P1 393 / 96MX the voltage polarity of adjacent polarities are identical after coding. In an implementation example, the pkt_start_byte patterns are as shown in Table 2.

TABLE 2 No. of Mnemonic Bits packet_start_positive (). { 0 + 0 + -0-0 tslsf} No. of Mnemonic Bits packet_start_negative (). { 0-0- + 0 + 0 tslsf} where "0" Represents a differential output of zero volts, represents a differential output of +0.5 volts, and tl_M represents a differential output of -0.5 volts. The packet_start_ positive is issued when the binary one most recently issued, prior to the pkt start byte, was coded as a "+" symbol P1393 / 96MX packet_start_negative when the most recently issued binary one, prior to the pkt_start_byte was coded as a "-" symbol. The AMI coding process is illustrated in Figure 1, which is a random example in which the bit stream 101011000111010 is coded in AMI. As shown in Figure 1, each binary is encoded either as a positive symbol ("+") 50o or a negative symbol ("-") 52. The alternating binaries are coded with opposite polarities, so that a Positive symbol will never be adjacent to another positive symbol and a negative symbol will never be adjacent to another negative symbol. All zeros are coded the same, as indicated by the reference number 54. While Figure 1 illustrates the appropriate AMI coding, Figures 2 and 3 illustrate rape sequences in which the AMI coding rules are violated (which prohibit that the voltage polarity of the adjacent ones is identical). The violation sequence illustrated in Figure 2 is the packet_start_positive violation sequence referred to in Table 2. As is evident from Figure 2, the adjacent ones designated by the reference number r > 6 are both encoded using the same polarity, like the adjacent ones illustrated by the number of P1393 / 96MX reference 58. Similarly, the violation sequence of Figure 3 corresponds to the packet_start_negative sequence referred to in Table 2. Again, the adjacent ones represented by the reference number 60 are both coded with a negative polarity, while the adjacent ones designated by the reference number 62 are both coded with a positive polarity. In addition, to encode the external data using alternate trademark inversion, the preferred embodiment of the present invention uses eight zero binary substitution coding (B8ZS) to avoid problems with the DC offset. In the particular B8ZS coding scheme presented herein, each sequence of eight consecutive bits with zero value of each transport packet is substituted with a violation sequence AMI to increase the transition density. This effectively reduces the DC energy, which is undesirable since the low frequency information can be lost in systems using the transformation coupling. If the low frequency energy is reduced or eliminated using B8ZS coding, loss of data can be avoided. In the present implementation, where, for example, transport packets of 188 bytes are processed, P1393 / 96MX for each sequence of eight consecutive bits with a value of zero, bits with a value of zero are coded as one of two violation sequences. For example, if the most recently encoded binary one was coded as a "+" symbol, then all zero bytes can be coded with the violation sequence + 0-00-0 +, as illustrated in Figure 4. Conversely, if the most recently encoded binary one was coded as a "-" symbol, then all zero bytes can be coded with the violation sequence -0 + 00 + 0- as illustrated in Figure 5. In Figures 4 and 5, the positive AMI symbols are indicated by the reference number 66 and the negative symbols are indicated by the reference number 64. Before the AMI coding, the filler bits can be added to each packet in order to form the external data packets (ext_data_packet) as indicated in Table 1. The number of filler bits, which are advantageously binary pseudo noise (PN) filler bits , depend on the information speed of the multiplex actually acquired. It should be appreciated that this multiplex can normally contain the external data along with other packaged data such as television signal data. Since the number of filler bits required to maintain the output data rate P1393 / 96MX fixed, will depend on the information speed, it will also depend on the symbol speed, the modulation format and the error coding rate advanced. However, there is no need to keep track of these specifications, since the filler bits can be inserted as required, based on real time, in the encoder. For example, after the external data of a packet has been processed for transmission to the external device, the encoder can provide padding bits until it receives the next packet for atteo and transmission. The reception of the next package will be detected when the next package guide arrives. A PN sequence can be generated to produce the filler bits using a four-bit linear feedback shift register (LFSR) as is well known in the art. Figure 6 illustrates the apparatus according to the invention for decoding input packets containing external data received at a variable rate and for reformatting external data for communication with an external device at a fixed rate. Variable speed data, for example, of an MPEG-2 or Digicipher-II data stream, are input to a demodulator 12 via terminal 10. The demodulator demodulates the input modulated data stream for P1 393 / 9ISMX retrieve the data packets and clock information that is sent to an early error correction decoder 14 (FEC). The FEC decoder may comprise, for example, a well-known Viterbi decoder or any other FEC decoder known in the art. The FEC decoder 14 provides the packet data, the initial packet signal and a clock derived from the demodulated data packets to a demultiplexer and a syntax parser 16. This circuit demultiplexes the various types of different packets (e.g. video, audio packets and data packets and parses the demultiplexed data packets in a manner well known in the art The external packet data output from the demultiplexer and the data parser 16 is input to a delay circuit 18 which provides a minimum delay of one data byte (e.g., eight bits) Delayed external data is multiplexed in a selector 20 with a PN 26 generator fill bits at the appropriate time to provide fixed length data packets a fixed data rate The selector 20 is operated to output the PN sequence of the PN 26 generator instead of the external data of the delay circuit 18 by means of a "select PN / packet data" signal issued from the control generator of P1393 / 96MX timing 24. The timing control generator receives the clock and packet start signals from the demultiplexer and the syntax parser 26. Based on the signals, the timing control generator can drive the selector 20 for issue the appropriate number of filler bits at the end of each packet. The timing control generator 24 also emits a signal that allows the PN 26 generator to drive the PN generator to emit the PN sequence. The data and the PN padding bits issued from the selector 20 are encoded by alternate mark inversion in an AMI encoder 22. The encoded AMI output comprises two-bit symbols representing the ternary AMI (three-level) output. A selector 32 outputs either the AMI encoded data or an AMI violation sequence of the B8ZS 30 generator. The selector 32 is operated to output either the encoded AMI data or the violation sequence via a "select B8ZS / data" signal. AMI "of the zero-stripe detection circuit 28. With the detection of a current of eight zeros in the AMI encoded data output from the AMI decoder 22, the circuit 28 will enable the generator B8ZS 30 to emit the violation sequence while, at the same time, it activates the selector 32 to emit the sequence of P1393 / 96MX violation instead of the string of zeros. The timing control generator 24 inhibits the operation of the generator B8ZS 30 via line 40 for the one bit prior to the insertion of a packet start byte in order to avoid the occurrence of a violation sequence AMI B8ZS immediately before the AMI violation sequence used for the packet start byte. In this way, the violation sequence of the packet start byte will always precede a violation sequence B8ZS. The sign (positive or negative) of the last "1" coded in AMI will be detected by the circuit 34 in order to enable the generator B8ZS 30 to insert the correct violation sequence AMI in the data stream issued from the selector 32. The circuit 34 also informs the generator 36 of the initial packet byte of the polarity of the last "1" encoded in AMI. In this way, the generator of the packet start byte will be able to emit the appropriate AMI violation sequence at the beginning of each new external data packet that will be issued from the interface. The generator 36 of the packet start byte receives an enable signal from the start byte coming from the timing control generator 24. This signal indicates the start of a new packet (packet start) and is derived by the control generator from P1393 / 96MX timing 24 by the packet start signal issued from the demultiplexer and the data parser 16. A selector 38 outputs either the AMI encoded data stream of the selector 32 or the AMI violation sequence emitted from the generator 36 of the packet start byte, in response to a "select start / AMI data" signal from the generator of timing control 24. As indicated above, the packet start byte will only be issued at the beginning of each new external data packet. All other times, the selector 38 will broadcast the encoded data in AMI. The output of the selector 38 is communicated by an output port connector (not shown) which may be provided in, for example, a junction box. Any suitable connector can be used, such as a miniature stereo headphone jack, a DIN connector or the like. The external device such as a personal computer, a video game or a video device can be connected to the output port via the coupling connector. In this way, the external device can receive the external data and process it to provide the desired function. For example, external data may comprise text or graphic information that will be reproduced in the external device.

Pi 3 J / 96MX It will now be appreciated that the present invention provides a method for variable rate data reformatting for communication to an external device at a fixed rate. Retrieving fixed-length packets from the variable-rate data of a data packet multiplex such as an MPEG-2 or Digicipher-II packet stream, adding a packet start byte to each of the recovered packets and adding any bits When necessary, the recovered packages can be issued for use by the external device at a fixed speed. AMI and B8ZS encoding provide robust operation. In addition, the filler bits can be easily added to the packets as needed on a real-time basis to maintain the desired output data rate. In an MPEG-2 or Digicipher-II implementation, a convenient output speed would be the 27 MHz speed that represents the system time clock of a particular service carried by the multiplex. This output speed would enable the receiver to process the external data without the need to locally generate the system time clock using a program clock reference receiver and a phase lock circuit. Although the invention has been described in connection P1 93 / 96MX with a specific embodiment, it will be appreciated that numerous adaptations and modifications can be made thereto without deviating from the spirit and scope of the invention, as set forth in the claims.

P1393 / 96MX

Claims (14)

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 reformatting variable speed data for communication to an external device. at a fixed rate, characterized in that it comprises the steps of: recovering fixed-length packets from the variable-rate data of a multiplex of data packets; add a packet start byte at the beginning of each of the recovered packets; adding filler bits to at least some of the recovered packets if a variable data rate information speed is less than the fixed rate; and provide the recovered packets with the added packet start byte and any padding bits as an output to the external device, at the fixed rate. A method according to claim 1, characterized in that it comprises the additional step of: encoding the recovered packets with the packet start byte and the filler bits added before the P1393 / 96MX step to provide the use of alternate mark inversion (AMI) and eight zero binary substitution (B8ZS) to provide a coded data stream for its emission to the external device. 3. A method according to claim 2, characterized in that the padding bits are pseudo noise (PN) binary bits. 4. A method according to claim 2, characterized in that the packet start byte comprises a violation sequence AMI. 5. A method according to claim 4, characterized in that: the violation sequence is O + OH-0-0 when the preceding binary "one" closest to the packet start byte in the data stream coded in AMI is coded as a value "+" AMI y, the violation sequence is 0-0-1-0 + 0 when the preceding binary "one" closest to the packet start byte in the coded data stream in AMI is coded as a value "-" AMI; where a value "+" AMI represents a positive differential output voltage, a value "-" AMI represents a negative differential output voltage and a value "0" AMI represents a differential output of zero volts. 6. A method according to claim 5, P1393 / 9TMX characterized because the B8ZS coding replaces a string of eight zeros with an AMI violation sequence. A method according to claim 6, characterized in that: the violation sequence used to encode the string of eight zeros is + 0-00-0 +, when the preceding binary "one" closest to the string in the data stream encoded in AMI is coded as a "+" AMI value and, the violation sequence used to encode the eight-zero string is -0 + 00 + 0-, when the preceding binary "one" closest to the packet start byte in the data stream encoded in AMI is encoded as a value "-" AMI. A method according to claim 2, characterized in that the B8ZS coding replaces a string of eight zeros with a violation sequence AMI. A method according to claim 8, characterized in that: the sequence of is + 0-00-0 +, when the preceding binary "one" closest to the string of eight zeros in the data stream encoded in AMI is encoded as a value "+" AMI y, the violation sequence is -0 + 00 + 0-, when the preceding binary "one" closest to the string of eight P1393 / 96MX zeros in the data stream coded in AMI is coded as a value "-" AMI, where a value "+" AMI represents a positive differential output voltage, a value "-" AMI represents a differential output voltage negative and, a value "0" AMI represents a differential output of zero volts. 10. The apparatus for re-rotating variable-rate data for communication to an external device at a fixed rate, characterized in that it comprises: a decoder for retrieving fixed-length packets of variable-rate data from a multiplex of data packets; encoder to add a packet start byte at the beginning of each of the recovered packets; the encoder also adds padding bits to at least part of the retrieved packets when a variable rate data information rate is less than the fixed rate; and an output port coupled to the encoder to provide the recovered packets with the packet start byte and the padding bits added to the external device at the fixed rate. 11. The apparatus according to claim 10, P1393 / 96MX characterized in that: the encoder encodes the packets recovered with the packet start byte and the filler bits added using alternate mark inversion (AM1) and eight zero binary substitution (B8ZS) to provide a stream _ of coded data to emit them to the external device. The apparatus according to claim 11, characterized in that the packet start byte comprises a violation sequence AMI. The apparatus according to claim 12, characterized in that the B8ZS coding replaces a string of eight zeros with an AMI violation sequence. The apparatus according to claim 11, characterized in that the B8ZS coding replaces a string of eight zeros with a violation sequence AMI. P1393 / 9bMX