MXPA99009041A - Conversion of transportation package regime - Google Patents

Abstract

An outgoing packet stream generator in a remodeler system includes a source of input transport packets and a source of additional packets. A multiplexer is coupled to the current source of input transport packets and to the source of additional packets and generates the output packet stream. A control signal has a variable characteristic having a first state when an input transport packet should be inserted into the output packet stream and a second state when additional packets should be inserted into the stream of output packets. A multiplexer controller conditions the multiplexer to insert an input transport packet into the output packet stream when the control signal has the first state, and an additional packet in the output packet stream when the control signal has a second this

Description

CONVERSION OF TRANSPORT PACKAGE REGIME The present invention relates to a system for converting one stream of transport packets from one packet rate to another packet rate. More and more information is being transmitted digitally, and digital information can be transmitted in the form of a stream of packets carrying the information. For example, current digital television signals are transmitted by packet stream. The packet streams are coded and modulated on carriers that use different modulation schemes. For example, packet streams carrying terrestrial digital television signals in the United States of America are modulated using level 8 vestigial sideband modulation using lattice encoding (8VSB-t). The packet streams carrying digital cable television signals in the United States of America are modulated using 64-level or 256-level quadrature amplitude modulation (64QAM or 256 QAM) or level 16 vestigial side-band modulation (16VSB), The packet streams having satellite television signals are modulated using phase shift manipulation quadrature modulation (QPSK). Each packet stream is specially coded for the modulation it will receive, resulting in different packet rates, and bit rates for respectively modulated packaged bitstreams, ranging from about 19 megabits per second (Mbps) to 8VSB-t to approximately 39 Mbps for 16VSB and 256 QAM. In some applications it is required that particular packages be processed at specific times or over specific time intervals. In particular in television signal transmission systems, it is required that for example image information, in particular packets carrying data of video signals, be displayed at particular relative times. Otherwise, the image will appear too fast, too slow, or shaken due to tremors. To avoid this problem, the information of the time stamp is generated in the place of the transmission and inserted into the packet stream. These time stamps are used to ensure that the images are displayed at the correct times, minimizing the tremor problem described above. Sometimes you want to convert from one modulation format to another. For example, a digital television receiver can receive, decode and display suitably only modulated digital packet streams of 16 VSB or 8 VSB-t. But digital video cassette recorders (DVCR) and / or top box receivers of cable and satellite equipment can receive and process suitably only modulated digital cable packets (64QAM, 256QAM, 16VSB) or satellite ( QPSK). In order for the videocassette recorder and the upper cable and satellite equipment boxes to work properly with this digital television, they must remodulate the signal received in the modulation recognized by the television receiver (16VSB or 8VSB-t). Sometimes you also want to add information to the data stream through the video cassette recorder or the receiver equipment box. For example, displays can be generated on the screen (OSD) to inform the user of the status of the video cassette recorder or the top box of the receiving equipment. Specifically, in a video cassette recorder, a display on the screen with the word "PAUSE" or "REWIND" can be generated as appropriate; or a full map of bits can be displayed. This information can easily be added to a video signal component. However, in digital transmission systems, it is preferred to add display information on the screen as additional packets carrying auxiliary data in packet streams of television programs. The receiver decodes the auxiliary data packets, generates a locally representative signal of screen display and combines that signal with the video signal. However, data streams in television packets generally occur at the maximum data rate, which means that every available bit is used for the digital information that the television program represents. There is no extra capacity available to place additional auxiliary display packages. The above systems provided decoders to completely decode the received packet stream and extract the component signals (i.e. video, audio, data, etc.). These component signals were recorded and re-oped in the desired modulation format. As part of this process, included time stamps were extracted, recalculated and re-inserted into the packet stream. In addition, at this time, auxiliary information was formed, such as on-screen display information, in packets, and combined with the received signal to be recoded and re-modulated. The remodulated signal was supplied, for example, to the television receiver. However, this system required a scrambler, decoder, encoder and full modulator, and a packet maker for auxiliary information. This is expensive, especially since no significant processing is performed on the component signals in the packet stream. U.S. Patent Application Serial No. 09 / 187,318, entitled "Auxiliary Data Insertion in a Transport • Datastream" (insertion of auxiliary data in a transport data stream) filed on November 16, 1998 by Knutson , illustrates another system to convert from one modulation format to another. Patent application 09 / 187,318 illustrates a system in which packet stream in a format at a first bit rate is re-modulated in another format at a second bit rate. In one embodiment, the first and second bit rates are the same, but the bitstream coding changes to erase some of the bits of the error detection code, and replaces the bits deleted with auxiliary information. More specifically, an encoded input packet stream using 8VSB-t, in which the lattice encoding adds a detection bit of. error for every two bits of the packet stream, is remodulated using 8 VSB (no lattice encoding). By erasing the error detection bits added by the lattice encoder, an additional packet can be added for every two packets originally transmitted. These additional packets are used to transmit auxiliary information, or null packets if auxiliary information is not available. In a second embodiment in the application 09 / 187,318, the second bit rate is a multiple of the first bit rate, and the extra bit rate capacity is used to transmit the auxiliary information. More specifically, the input packet stream is encoded using 8VSB-t, while the output packet stream is encoded using 16VSB. The bit rate of the output packet stream is twice the bit rate of the input packet stream. In this way, an additional package can be added for each package originally transmitted. These additional packets are used to transmit auxiliary information, or null packets if auxiliary information is not available. In both cases, the bit rate of the output packet stream is related to the bit rate of the input packet stream by a simple integer ratio: 1: 3 in the first case, and 1: 2 in the second case However, it may be desired to remodulate a stream of packets at a bit rate to another stream of packets at a bit rate that is not necessarily in a single simple proportion with the other. For example, the bit rates of the packet streams modulated by QAM and 16VSB, respectively, are not related by a single simple proportion. Thus, when modulating a packet stream QAM to a packet stream 16VSB is remodulated, it is not possible to simply insert an auxiliary information packet into the stream of output packets every n originally transmitted packets, as in the application 09 / 187,318 , described above. Still further, as described above, the timing of packets in these packet streams can be critical for proper decoding and display of the television picture and sound represented by packet stream, and time stamp information It can be included in the packet stream. In this way, it is important to maintain the proper timing of the packages as much as possible during the demodulation process to ensure that any included time stamps remain accurate. A system that can remodulate a received packet stream signal at a bit rate in a stream of packets at a different bit rate, not necessarily related to the first bit rate by a single full rate, without requiring the complete demodulation, decoding, coding and remodulation of component signals; which allows the insertion of auxiliary data packages (for example, on-screen display data); and which does not interfere with the proper timing of the packages maintained by the time stamps. In accordance with the principles of the present invention, an output packet stream generator in a remodulator system includes a source of an input transport packet stream and a source of additional packets. A multiplexer is coupled to the current source of input transport packets and to the source of additional packets and generates the output packet stream. A control signal has a variable characteristic having a first state when an input transport packet should be inserted into the stream of output packets and a second state when additional packets should be inserted into the stream of output packets. A multiplexer controller conditions the multiplexer to insert an input transport packet in the output packet stream when the control signal is in the first state, and an additional packet in the output packet stream when the control signal is in the second state. This system can operate successfully when the bit rate of the output signal is not related by a simple integral ratio to the bit rate of the input signal. In the drawings: Figure 1 is a block diagram of a portion of a remodulation system according to the present invention; Figure 2 is a timing diagram useful for understanding the operation of the system illustrated in Figure 1; Figure 3 is a more detailed block diagram of a numerically controlled oscillator which can be used in the system illustrated in Figure 1; Figure 4 is a timing diagram useful for understanding the operation of the numerically controlled oscillator illustrated in Figure 3; Figure 5 is a more detailed block diagram of a practical embodiment of a numerically controlled oscillator corresponding to that illustrated in Figure 3; Y Figure 6 is a timing diagram useful for understanding the operation of the numerically controlled oscillator illustrated in Figure 5. Figure 1 is a block diagram of a portion of a remodulator system in accordance with the present invention. In the illustrated embodiment, the remodulator is a part of a digital video cassette recorder in which digital signals representing a stream of packets received in a format are recorded and then recovered, and reformatted in a stream of packets in another format However, one skilled in the art will understand that this remodulator system will find use in any system, such as an upper case of digital receiving equipment, where the format of a packet stream must be changed. Only the elements necessary to understand the present invention are illustrated in Figure 1. Other elements and interconnections on the elements are necessary in a complete remodulator system. A person skilled in the art will understand what other elements are necessary, how to design and implement them, and interconnect them with the illustrated elements. One skilled in the art will also understand that other connections, such as status, control and clock signals exist between the illustrated elements but are not illustrated in order to simplify the drawing. In Figure 1, a source (not shown) of an input transport packet stream is coupled to an input terminal of an input packet buffer 10. The input packet stream source may be, for example, a reproduction circuit of a digital video cassette recorder or an upper receiver equipment box. The input transport packet stream source produces a digital signal that carries the transport packets, and the input clock signal synchronized with the input transport packets, in a known manner and supplies both to the buffer input packets 10. A data output terminal of the input packet buffer 10 is coupled to a first data input terminal of a multiplexer (MUX) 20 and an input terminal of a null packet detector 30. An output terminal of the multiplexer 20 is coupled to an input terminal of a re-modulation packet buffer 40. And the output terminal of the re-modulation packet buffer 40 is coupled to an input terminal of a modulator 50. An output terminal of the modulator 50 is coupled to an input terminal of an upstream converter of radio frequency 60. An output terminal of the upstream converter of radio frequency The frequency generates a radio frequency signal at a predetermined frequency (for example channel 3) for reception by, for example, a digital television receiver (not shown). * An auxiliary data source (not shown), which can be a screen display generator, is coupled to an input terminal of an auxiliary packet generator 70. A data output terminal of the auxiliary packet generator 70 is It is coupled to a second data input terminal of the multiplexer 20. An output terminal of a null packet generator 80 is coupled to a third data input terminal of the multiplexer 20. An oscillator 90, which may be an oscillator of voltage controlled crystal (VCXO), has a first output terminal coupled to an input terminal of a state machine 100 and a second input terminal, which carries a packet clock signal, coupled to a clock input terminal of a multiplexer controller 120. The state machine generates control signals to control the operation of the remodulation system illustrated in Figure 1., which is not shown much, in order to simplify the figure. A first control output terminal is coupled to the modulator 50, and a second control output terminal is coupled to an input terminal of a numerically controlled oscillator (NCO) 110. The multiplexer controller 120 controls the operation of the multiplexer 20, as response to the plurality of control signals. A state output terminal from the input packet buffer 10 is coupled to a first input terminal of the multiplexer controller 120 and to an input terminal of an error signal generator 85. An output terminal of the generator of Error signals 85 is coupled to an input input terminal of the oscillator 90. A status output terminal of the auxiliary packet buffer 70 is coupled to a second input terminal of the multiplexer controller 120. An 'output terminal. of the null detector 30 is coupled to a third input terminal of the multiplexer controller 120. A source of a signal indicating whether the bit rate of the input signal is substantially equal to the bit rate of the output signal is coupled to a fourth input terminal of the multiplexer controller 120. An output terminal of the numerically controlled oscillator 110 is coupled to a fifth input terminal of the multiplexer controller 120. An output terminal of multiplexer controller 120 is coupled to a control input terminal of multiplexer 20. Figure 2 is a timing diagram useful for understanding the operation of the remodulator system illustrated in Figure 1. In Figure 2, the time is illustrated in the horizontal direction, and the respective packets in different packet streams are illustrated by different horizontal lines of rectangles. The length of time of each packet is represented by the horizontal size of the rectangle and the temporary place of each packet is represented by the horizontal place of the rectangle. In each of Figures 2a through 2d, an upper line represents the stream of input transport packets and a lower line represents the corresponding output packet stream. In general, the remodulator of Figure 1 operates to convert a stream of input transport packets into one format in an output packet stream modulated in another format. The bit rate of the output packet stream is preferably greater than or equal to the bit rate of the input transport packet stream. It is possible to generate an output packet stream having a lower bit rate than the input transport packet stream only if the input transport packet stream has enough null packets that can be removed to generate the current of output packets at the desired bit rate. If the bitrate of the output packet stream is equal to that of the incoming transport packet stream, the input transport packet stream must contain enough null packets to avoid buffer overflow, as describe later. When the bit rate of the output packet stream is greater than that of the input transport packet stream, additional packets are inserted into the output packet stream to generate the desired bit rate. This situation is illustrated in Figure 2a. In Figure 2a, the bit rate of the input transport packet stream is approximately, but not exactly, 2/3 of that of the output packet stream. Although illustrated as about 2/3, one skilled in the art will understand from the following description, that there needs to be a simple whole relationship between the respective bit rates of the input transport packet stream and the output packet stream . In Figure 2a, there are approximately three packets in the stream of output packets at the time required for two packets in the stream of input transport packets or, put another way, each packet in the stream of output packets takes about 2/3 of the time required by a packet in the stream of incoming transport packets. Additional packets are inserted into the stream of outbound packets at selected times to 'maintain the original temporary locations of the incoming transport packets to the extent possible, as described in more detail below. These additional packages are auxiliary packages that contain auxiliary data (such as on-screen display data) if a package of this auxiliary data is available. For example, Figure 2a, two input transport packets, 1 and 2 are inserted into the stream of output packets as output packets 1 and 2. An additional packet is then inserted into the stream of output packets with the order to temporarily align the next incoming transport packet. In this case, it is assumed that an auxiliary package (screen display) is available. In this way, an on-screen display package, OSD 1, is then inserted into the output packet stream. If an auxiliary data package is not available, then the additional package is a null package. This is illustrated after the inbound transport packet 4. Because no on-screen display package is assumed to be available at this time, a null packet is inserted into the stream of outbound packets as the additional packet. One skilled in the art will understand that the sum of the bit rates of the input transport packet stream and the auxiliary data packet stream must be less than or equal to the bit rate of the output packet stream.

As described above, the stream of input transport packets sometimes includes a null packet. When a null packet is detected in the input transport data stream, it can either be erased, passed through to the modulator, or replaced with an auxiliary data packet. If the bit rate of the output packet stream is greater than that of the incoming transport packet stream (Figure 2a), then the presence of null packets can be ignored, and the null packets can be treated like any other input transport packet to be inserted into the stream of output packets. Alternatively, null packets can be detected and replaced by auxiliary data packets. This is illustrated in Figure 2a in which a 'null packet (in the place of the incoming transport packet 3) in the incoming transport packet stream is replaced by an on-screen display packet, OSD 2, in the Output packet stream. The null packet could also have been inserted directly into the output packet stream, as described above. The situation when the bit rate of the input transport packet stream is substantially equal to that of the output packet stream is illustrated in FIGS. 2b to 2d. In general, when the bit rates are equal, packets are inserted into the stream of input transport packets directly into the stream of output packets, as illustrated in Figure 2b. Also, in general, if the stream of input packets contains a null packet, either that null packet is inserted into the stream of output packets, or is replaced by an auxiliary data packet. This is illustrated in Figure 2b in which a null packet (inserted for the incoming transport packet 3) is inserted into the outgoing packet stream, or replaced in a display roll packet, if one is available. If the bit rate of the output packet stream is slightly slower than that of the incoming transport packet stream, as described above, then, the incoming transport packets arrive slightly faster than they exit. the output packages. In this case, the input transport packets accumulate slowly in the input packet buffer 10. Eventually, the input transport packet buffer 10 is filled or almost filled. The input packet buffer 10 conditions its status signal to indicate that it is full or nearly full. In this case, a null packet is erased in the stream of input transport packets to minimize the potential overflow of the input packet buffer. This is illustrated in Figure 2c, in which a null packet (inserted for the input transport packet N + 2) is deleted. This allows the stream of output packets to be temporarily more aligned with the stream of input transport packets. In addition, when the input packet buffer is full or nearly full, the error signal generator 85 responds to the status signal from the input packet buffer 10 by conditioning the oscillator 90 to increase the signal frequency of the signal. exit clock. The clock signal of the oscillator 90 will increase the bit rate of the output packet stream, and will approximate more closely the bit rate of the packet input stream, minimizing the possibility of an overflow of the packet buffer input 10. Similarly, if the bit rate of the output packet stream is slightly faster than that of the incoming transport packet stream, as described above, the output packets will go out faster than incoming transport packages arrive. In this case, the input packet buffer 10 eventually runs out of packets. The input packet buffer 10 conditions its status signal to indicate that it is empty. In this situation, additional packets are inserted, either null packets or auxiliary data packets in the output packet stream, to provide the bits required for the remodulation process. This is illustrated in Figure 2d, in which an N + 2 output packet is required in the output packet stream, but has not yet been received from the input packet stream source. An auxiliary or null data packet (screen display) is inserted into the output packet stream to fill the time for which the N + 2 input transport packet is not yet available. Further, when the input packet buffer is left empty, the error signal generator 85 responds to the status signal from the input packet buffer 10 by conditioning the oscillator 90 to decrease the frequency of the output clock signal. . The clock signal of the oscillator 90 will decrease the bit rate of the output packet stream, and will more roughly match the bit rate of the packet input stream, minimizing the possibility of a subflow of the packets buffer. input 10. If, on the other hand, the input transport buffer 10 is not full or nearly full or empty, and if an auxiliary data packet is available, then the null packet in the incoming transport packet stream is it replaces with an additional package containing auxiliary data if an auxiliary data package is available, as described above with reference to the Figure 2b. If auxiliary data are not available, then a null packet is inserted into the output packet stream. More specifically, in operation, the input packet buffer 10 receives incoming transport packets and smoothes over any data burst from time, and compensates for the trembling in the input packet stream source (not shown). ). Separate input transport packets are provided to the multiplexer 20 and the null packet detector 30. A status signal of the input packet buffer 10 indicates when the input packet buffer is full or nearly full, empty or is operating otherwise in a nominal mode (ie neither empty nor full). A status signal of the null packet detector 30 indicates when the next packet in the input packet buffer 10 is a null packet. The auxiliary data packet generator 70 receives auxiliary data (for example on-screen display data) from the system containing the remodulator illustrated in Figure 1, accumulates the data and forms auxiliary data packets. Auxiliary data packets, when available, are provided to the multiplexer 20. A status signal of the auxiliary data packet generator 70 indicates when an auxiliary data packet is available. The null packet generator 80 continuously generates a null packet, and provides the null packet to the multiplexer 20. The equal speed signal provides an indication of whether the bit rate of the output packet stream is substantially equal to that of the current of incoming transport packages. In a digital television signal, the packets must be present in the packet stream at specific times, or at specific time intervals, in order that the time stamps inserted in the packet stream maintain precise control of the display of the packets. television program carried by the packet stream. In order to preserve this timing during the remodulation process, inbound transport packets must be inserted into the stream of outbound packets in substantially the same temporary places where they are in the stream of incoming transport packets. Additional packets inserted into the packet stream to produce the appropriate output bit rate must be inserted between the inserted input transport packets. Furthermore, this timing must be maintained despite the fact that the bit rates of the input transport packet stream and the output packet stream are not in a single simple proportion.

To control this, the combination of the oscillator 90, the state machine 100 and the numerically controlled oscillator (NCO) 110 produces a bistate control signal having a first state for the times when the input transport packet must be inserted in the output packet stream, and a second state times when an additional packet (either auxiliary or null) must be inserted, in a manner that will be described in more detail below. A signal generated in this way can be controlled to make the duty cycle substantially adequate for any proportion of bit rates. The "input / additional" signal is supplied to the multiplexer control circuit 120. The multiplexer control circuit 120 operates as a response to these status signals, and to the packet clock signal received from the oscillator 90, to provide a signal of control to multiplexer 20. In response to this control signal, multiplexer 20 operates to selectively couple either an input transport packet, an auxiliary data packet or a null packet to its output terminal, in a manner described in more detail. Further on, the multiplexer 20 generates from this mode an output packet stream having a bit rate required by the desired modulation technique. The packet stream of the multiplexer 20 is accumulated by the remodulation pack buffer 40 to standardize any timing tremors. The modulator 50 formats the digital packet stream of the remodulation packet buffer 40 in a suitable manner to produce a data stream in the previously determined modulation bit rate., and modulates the formatted data stream. In the illustrated embodiment, the packet stream is modulated by 16 VSB, as described above and has a bit rate of approximately 39 Mbps. It is possible for the output packet stream to be modulated according to any modulation scheme, for example. example, either 16 VSB or 8 VSB. The control signal from the state machine 100 controls the modulation scheme used by the modulator 50, while other control signals control the bit rate of the output packet stream to conform to the selected modulation scheme. The modulated packet stream of the modulator 50 is then converted upwards by the upward converter of radio frequency 60 to a desired radio frequency, for example, the frequency of the channel 3 which can be received by a digital television receiver. Referring now to the operation of combining the multiplexer 20 and the multiplexer controller circuit 120, there are five basic functions that can be performed: 1) inserting an input transport packet into the output packet stream; 2) insert a null packet in the output packet stream; 3) inserting an auxiliary data packet into the output packet stream; 4) delete a null packet from the stream of incoming transport packets; and 5) replacing a null packet of the input transport packet stream with an auxiliary data packet in the output packet stream (which is a combination of (3) and (4)). The function performed is controlled by the multiplexer control circuit 120 in response to the status signals, as described above. As described above, the transport / additional status signal of the numerically controlled oscillator 110 indicates the times when an incoming transport packet should be placed in the next packet slot in the output packet stream and the times when a packet should be placed. additional package (auxiliary or null) in the next packet slot in the stream of output packets. This status signal is always set to "transport" when the bit rate of the input transport packet stream is equal to that of the output packet stream. When the packet clock signal of the oscillator 90 indicates the occurrence of the next output packet slot, an input transport packet is inserted into the output packet stream if this status signal indicates that a packet of packets is required. transport, and either an auxiliary or null packet is inserted into the output packet stream if the status signal indicates that an additional packet is required. The null detection signal of the null detector 30 indicates that the next input transport packet in the input packet buffer is a null packet. If the bitrate of the output packet signal is greater than that of the incoming transport packet stream, then this signal can be ignored, and the null packet treat like any other packet in the transport packet stream of input.- If the bit rate of the output packet stream is substantially equal to that of the input transport packet stream, then the null detection signal is processed as follows: if the input packet buffer 10 is full or almost full, as indicated by its status signal, then the detected null packet is erased. If the input packet buffer 10 is not full, and an auxiliary data packet is available, as indicated by the status signal of the auxiliary packet generator 70, then the auxiliary data packet can be replaced by the null packet. . Otherwise, the null packet is inserted into the output packet stream.

The available auxiliary data signal from the auxiliary data packet generator 70 indicates that an auxiliary data packet is available. If the transport / additional status signal indicates that an additional packet is required, and the available auxiliary data signal indicates that an auxiliary data packet is available, then the auxiliary data packet is inserted into the output packet stream. Or, if the bit rate of the bits of the input transport packet stream is substantially equal to that of the outgoing packet stream, the next packet in the incoming transport packet stream is a null packet and the Incoming packet buffer is not full or nearly full, then the auxiliary data packet is inserted into the stream of output packets. The status signal of the input packet buffer 10 indicates whether the input packet buffer 10 is full or nearly full, empty, or otherwise nominally operable (ie neither full nor empty). If the buffer is full or nearly full, then any null packet detected in the stream of input transport packets, as indicated by the status signal of the null detector 30, is cleared. If the buffer is empty, then additional packets (either auxiliary or null packets) are inserted into the stream of output packets. If the buffer is operating nominally, then none of these actions takes place. The equal speed signal indicates whether the bit rate of the output packet stream is substantially equal to that of the input packet stream. The response of the multiplexer control circuit 120 to this signal has been described above. The multiplexer control circuit 120 generates the control signal for the multiplexer 20. This signal can have three binary signals: a first one for conditioning the multiplexer 20 for coupling an input transport packet of the input packet buffer 10 to the buffer memory of remodulation packets 40; a second to condition the multiplexer 20 to couple an auxiliary data packet of the auxiliary packet generator 70 to the remodulation packet buffer 40; and a third to condition the multiplexer 20 to couple a null packet of the null packet generator 80 to the packet buffer remodulation 40. Alternatively, the control signal could be a binary bit encoded signal having a value indicating which of the previous actions will be carried out. The multiplexer control circuit 120 can be designed and implemented with wired logic, either combinatorial or sequential, or as a software program executed on a microprocessor. One skilled in the art will understand how to design and implement this control circuit 120 in any form. The state machine 100 controls the overall operation of the remodulator illustrated in Figure 1. One skilled in the art will understand the sequencing and control signals required to properly time the operation of the remodulator illustrated in Figure 1, and will understand how to design and implementing a state machine 100 to generate these control signals. Figure 3 is a more detailed block diagram of a numerically controlled oscillator 110 which can be used in the system illustrated in Figure 1, and Figure 4 is a timing diagram useful for understanding the operation of a numerically controlled oscillator. illustrated in Figure 3. In Figure 3, the lines represent lines that carry digital signals, and the thicker lines represent digital signals of multiple bits that have more bits than thinner lines. In Figure 3, a signal representing the difference in time duration between the input and output transport packets, tm- - tout, is coupled to a first data input terminal of a multiplexer (MUX) 202. A signal representing the negative of the time duration of the outbound transport packet, -tout, is coupled to a second data entry terminal of the multiplexer 202. An output terminal of the multiplexer 202 is coupled to a first input terminal of an adder 204. An output terminal of the adder 204 is coupled to an input terminal of an insurer 206. A terminal The output of the insulator 206 is coupled to a second input terminal of the adder 204. The insulator 206 is clocked by the clock signal of the output packet. The combination of adder 204 and insurer 206 forms an accumulator. The output terminal of the insulator 206 is coupled to an input terminal of a comparator 208. An output terminal of the comparator 208 generates the transport / additional signal, described above, which is also coupled to an input terminal of the multiplexer 202 The transport / additional signal has a logical value 'l' at times when a packet of the incoming transport packet stream is to be inserted into the stream of output packets, and a logical value '0' times when an additional package (auxiliary or null) is going to be inserted into the stream of output packets. This is further indicated by the horizontal line on "additional" in Figure 3. The transport / additional signal is coupled to the multiplexer control circuit 120 (of Figure 1). In general operation, the value of the signal at the output of the insurer 206 (ie, the output of the accumulator) represents the amount of time in which the current of the transport packet is ahead of the current of the output packet. When this value is less than the time duration of a packet of the output packet stream, then the input transport packets must be inserted into the stream of output packets because there is no time for an additional packet in the packet. Output packet stream. However, when this value becomes greater than the time duration of a packet of the output packet stream, this indicates that there is time for an additional packet to be inserted into the output packet stream. When this happens, the time duration of an output packet is subtracted from this value to form the additional packet inserted in the stream of output packets and the operation continues, all as described in more detail below. The comparator 208 compares the value of the signal from the insurer 206 with a value representing the time duration of the output packet tout. If the value of the output signal of the insurer 206 is less than the value of the time duration of the output packet tout, then the comparator 208 generates a logical signal 'l', indicating that a transport packet of entry in the stream of output packages. If the value of the output signal of the insurer 206 is greater than the value of the time duration of the output packet tout, then the comparator 208 generates a logic signal 'O', which indicates that an additional packet is to be inserted. in the stream of output packets. Referring to Figure 4, the start time of packet 1 in the input transport packet stream is temporally aligned with the start time of packet 1 in the output packet stream. At this time, and under this condition, the value at the output terminal of the insurer 206 is 0. This is less than the value of the time duration of the output pack tout and the comparator 208, thereby generating a signal logic 'l'. This indicates that an input transport packet is to be inserted into the output packet stream, and conditions the multiplexer 202 to couple the time different signal tjn-tout to the input of the adder 204, whose output now has the value from tjü - tout. The insurer 206 is clocked at the final time of the output pack 1, and the output signal of the insurer 206 becomes t-tout. In the illustrated embodiment, this is less than the time duration of the output packet tout so that the output of the comparator 208 is still a logical signal 'l'. The multiplexer 202, thus, continues to couple the time difference signal tn-tout with the input of the adder 204, whose output now has the value of 2 (tjn-tout).

The insurer 206 is now clocked at the end time of the output pack 2, and the output signal of the insurer 206 becomes 2 (tl 111 'OUt In the illustrated mode, this is greater than the duration of the output packet time The comparator 208 thus generates a logic signal '0.' This indicates that an additional packet is to be inserted into the output packet stream, and conditions the multiplexer 202 to couple the output - tout with the input of the adder 204, whose output now has the value of 2 (t¡n -tout) -tout.This represents the time in which the input transport packet stream remains ahead of the output packet stream after the packet additional has been inserted into the outgoing packet stream The insurer 206 is time again at the end of the additional packet time 0SD1, and the output signal of the insurer 206 becomes 2 (t¿n - tout) - tut. This is less than the time duration of the output packet tout so that the output of the comparator 208 becomes a logical signal 'l'. In response, the multiplexer 202 couples the time difference signal tu-tout to the input of the adder 204, and an input transport packet is inserted into the stream of output packets. The operation described above is repeated continuously, inserting additional packets into the stream of output packets when there is sufficient time to accommodate them between the input transport packets. The circuit illustrated in Figure 3 can operate for durations of any time for the input and output packets. More specifically, these durations of time do not have to be in an entire proportion. Figure 5 is a more detailed block diagram of a practical embodiment of a numerically controlled oscillator 110 corresponding to that illustrated in Figure 3. In Figure 5, elements that are the same as those illustrated in Figure 3 are designated with the same reference numbers and are not described in detail later. In Figure 5, two adjustments are made to the circuit illustrated in Figure 3. First, the numbers that represent values are kept as binary fixed point numbers that have the bit format "SI.FFF ..." where S represents a signal bit, I represents an integer bit and F represents fractional bits, all in a known manner. The precision with which the numerically controlled oscillator 110 operates depends on the size of these numbers. In a preferred embodiment these numbers have a width of 24 bits. Second, the values of the different parameters are normalized to the time duration of the output packets tout. That is, the time duration parameters are all expressed as fractions of time duration of the output packet tOUt 'In addition, the packet time duration values are replaced by the corresponding packet rate values, as described in more detail. detail later. These adjustments make the implementation of the numerically controlled oscillator 110 easier to practice and more efficient to operate. More specifically, the different parameters are normalized by dividing them among tout in a known manner. In addition, the packet time duration parameters are replaced by packet speed parameters: the packet transport transport speed is designated rv, and is equal to l / tjn; the output packet speed is designated rt and is equal to l / tout. '111 OUt CV = OUt -? N OUt Consequently, the time difference parameter -? n -ouf coupled to the first input terminal of the multiplexer 202, is normalized to a control value CV as illustrated in equation (1). The control value CV is coupled to the numerically controlled oscillator 110 from the state machine 100 (of Figure 1). The signal tout supplied to the second input terminal of the multiplexer 202 (of Figure 3) is normalized to a value of -1, and the compared value of the comparator 208 (of Figure 3) is normalized to a value of 1. Because the comparator 208 (of Figure 3) compares the value of the output signal of the insurer 206 with 1, and because the values are represented by fixed point binary numbers, the comparator 208 can be implemented by a port And 208 ', of two inputs, negative input, which responds to the two most significant bits (S and I) of the output of the insurer 206, which represent the entire portion and the sign of the exit value of the insurer. Port Y 208 'generates a logic signal' l 'when the value of both two bits is logic' 0 ', which indicates a value less than 1. If any of these bits is logical' l ', a value is indicated greater than 1, and then port Y 208 'generates a logical signal' 0 '. The remainder of the circuit illustrated in Figure 5 operates as described above with reference to Figure 3. Figure 6 is a useful time diagram for understanding the operation of the numerically controlled oscillator illustrated in Figure 5. In Figure 6, the two upper lines represent the input transport packet stream and the corresponding output packet stream as illustrated in Figure 2a. The third waveform represents the clock of the packet supplied to the multiplexer controller 120 from the oscillator 90. Each leading edge of the packet clock identifies the start of the packet slot in the stream of output packets. At the start of each packet slot in the output packet stream (ie at the front edge of the packet clock) the transport / additional signal is sampled. If it is a logical 'l', then an incoming transport packet is inserted into the output packet stream. If it is a logical '0', an additional package (auxiliary or null) is inserted into the output packet stream, all as described in more detail. The input data stream may have a QPSK modulation format or a QAM modulation format (64-QAM or 256-QAM), while the current of. data may present a VSB modulation format (8-VSB or 16-VSB), for example. Other input / output modulation formats are also possible.

Claims (23)

1. In a remodulator system, a generator of an output packet stream having a first rate, comprising: a source of an input transport packet stream having a second rate; a source of additional packages; a multiplexer, coupled to the current source of input transport packets and the source of additional packets, to generate the output packet stream, - a source of control signals, which responds to the first and second speeds, to generate the control signal having a first state when an input transport packet should be inserted into the stream of output packets and a second state when additional packets should be inserted into the stream of output packets; and a multiplexer controller, coupled between the control signal source and the multiplexer, for conditioning the multiplexer for inserting an input transport packet into the output packet stream when the control signal has the first state, and for inserting a additional packet, in the output packet stream when the control signal has the second state.

The system of claim 1 wherein the control signal source accumulates the amount of time that the input transport packet stream is ahead of the output packet stream, and generates the control signal that the second packet has. state when the accumulated time is greater than a time duration of each output packet, and that the first state has otherwise.

The system of claim 2 wherein when the source of control signals generates the control signal having the second state, the duration of time of an output packet decreases from the accumulated time.

The system of Claim 1, wherein the source of control signals comprises: an accumulator for generating the signal having a value representing the time when the input packet stream is ahead of the output packet stream; a comparator for comparing the output signal of the accumulator with a signal representing a time duration of the output packet, and if the value represented by the output signal of the accumulator is less than the value represented by the time duration of the pack of output, generate the control signal having the first state, and if the value represented by the output signal of the accumulator is greater than the value representing a time duration of the output packet, generate the control signal that has the second state.

The system of claim 4 wherein the source of control signals further comprises: a time difference signal source having a value representing the difference in the time duration of the input packet and the time duration of the exit package; a source of a time signal of the output packet having a value representing the time duration of an output packet; and the accumulator responds to the time difference signal and the time signal of output packets, to increase the value of the time difference signal when the control signal has the first state, and to decrease the value of the signal of output packet time when the control signal has the second state.

6. The system of claim 5 wherein: the source of the time difference signal generates a CV signal having the value: rt CV = - 1 where the value rv is the speed of the input transport packet and rt is the speed of the output packet; the time signal source of the output packet generates a signal that has the value -1; and the comparator compares the accumulated time signal with a signal having the value 1.

The system of claim 5 wherein the accumulator further comprises: a multiplexer, having a first data input terminal coupled to the source of time difference signals, a second data input terminal coupled to the output signal time source, a control input terminal that responds to the control signal, an output terminal; an adder, having a first input terminal coupled to the output terminal of the multiplexer, a second input terminal, and an output terminal; and an insurer, having an input terminal coupled to the output terminal of the adder, and an output terminal coupled to the second input terminal of the adder and the comparator.

The system of claim 1 wherein: the system further comprises a source of an output packet clock signal indicating when an output packet is to be inserted into the stream of output packets; and the accumulator further samples the control signal in response to the clock signal from the output packet and inserts an input transport packet into the output packet stream in response to the output packet clock signal when the output signal The sampled control has the first state, and inserts an additional packet in the output packet stream in response to the output packet clock signal when the sampled control signal has the second state.

The system of claim 1 wherein the source of control signals comprises a variable duty cycle oscillator that generates the control signal having a service cycle having an "on" time representing the fraction of time in that the incoming transport packets should be inserted into the stream of outgoing packets, and an 'off' time representing the fraction of the time in which additional packets should be inserted into the packet stream.

The system of claim 9 wherein the variable duty cycle oscillator comprises: an accumulator, having an input and output terminal, 'for increasing the value of the signal at the output terminal by the value of the signal at the input terminal; a control signal generator, coupled to the accumulator output terminal, for generating the control signal; a multiplexer, coupled to the input terminal of the accumulator and responding to the control signal, for coupling a control value to the input terminal of the accumulator when the control signal has the first state and for coupling a constant value to the Accumulator input terminal when the control signal has the second status.

The system of claim 10 wherein the generator of the control signal comprises circuits for generating the control signal having the first state when the value at the output terminal of the accumulator is less than a predetermined value and which has the second state otherwise.

The system of claim 10 wherein - the input transport packet stream has a first bit rate and the output packet stream has a second bit rate, - and the control value has the CV value : CV 1 where rv is the bit rate of the input packet stream and rt is the bit rate of the outgoing transport packet stream.

The system of claim 1 wherein: the source of additional packets comprises: a source of auxiliary data packets, responding to an auxiliary data source, which generates a status signal indicating that a data packet is available auxiliaries; and a source of null packets; and the multiplexer controller further responds to the status signal of the auxiliary packet source, to insert an auxiliary data packet into the output packet stream as an additional packet if the auxiliary data packet is available, and insert a null packet in the output packet stream as an additional packet if a data packet is not available.

The system of claim 1 wherein: the input transport packet stream has a first bit rate and the output packet stream has a second bit rate equal to the first bit rate; the stream of incoming transport packets comprises null packets; the input transport packet stream source comprises an input packet buffer, which generates a status signal indicating whether the buffer is full or nearly full, and the multiplexer controller also responds to the status signal of the packet. the input packet buffer to condition the multiplexer to clear a null packet from the stream of input transport packets if the input packet buffer is full or nearly full.

The system of claim 14 wherein: the source of additional packets comprises: a source of auxiliary data packets, responding to an auxiliary data source, which generates a status signal indicating that a data packet is available auxiliaries; a source of null packets; the system further comprises a null packet detector, coupled to the transport packet stream source, for generating a status signal indicating whether a next incoming transport packet is a null packet; and the multiplexer controller also responds to the status signal of the auxiliary packet source and to the status signal of the null packet detector, to replace an auxiliary data packet with a null packet in the input transport packet stream if it is If an auxiliary data packet is available, replace a null packet from the source of null packets with the null packet in the stream of input transport packets if an auxiliary data packet is not available.

The system of claim 14 wherein: the system further comprises a source of a signal indicating whether the predetermined first bit rate is equal to the second predetermined bit rate; and the multiplexer controller responds to the status signal of the input pack buffer and the signal indicating whether the predetermined first bit rate is the same as the second predetermined bit rate for conditioning the multiplexer to clear the null packet from the output packet stream if the first predetermined bit rate equals the second rate of default bits and the input packet buffer is full or almost full.

The system of claim 1 wherein: the input packet stream has a first bit rate and the output packet stream has a second bit rate greater than the first bit rate; the source of additional packets further comprises: a source of auxiliary data packets, responding to an auxiliary data source, which generates a status signal indicating that an auxiliary data packet is available; a source of null packets; the system further comprises a null packet detector, coupled to the source of the incoming transport packet stream, to generate a status signal indicating whether the next incoming transport packet is a null packet; the multiplexer is also coupled to a source of auxiliary data packets and to the source of null packets, and the multiplexer control circuit responds 'to the status signal of the auxiliary data packet source, to condition the multiplexer to insert an auxiliary data packet into the output packet stream as an additional packet if an auxiliary data packet is available, and otherwise Insert a null packet into the stream of output packets as an additional packet.

18. The system of claim 17 wherein: the input transport packet stream contains null packets; the system further comprises a null packet detector, coupled to the input transport packet stream source, for generating the status signal indicating whether the next input transport packet is a null packet; and the multiplexer controller further responds to the status signal of the auxiliary packet source and to the status signal of the null packet detector, to replace an auxiliary data packet with the null packet in the output packet stream.

19. The system of claim 1 further comprises a modulator, coupled to the multiplexer, for modulating the output packet stream.

The system of Claim 1 wherein: respective packets in the stream of input packets are assumed to be transmitted at the corresponding predetermined times; and the multiplexer controller conditions the multiplexer to insert the respective input transport packets in the output packet stream at substantially the corresponding times.

The remodulator system of claim 1, wherein: the format of the input packet stream is compatible with one between a QAM or QPSK modulation format; and the format of the output packet stream is compatible with a modulation format 8 -VSB or 16-VSB.

22. The remodulator system of claim 8, wherein: the source of the incoming transport packet stream represents auxiliary disp(OSD) dispinformation.

23. The remodulator system of claim 8, wherein: the input packet stream format is compatible with one of the modulation formats QAM, QPSK or VSB modulation formats; and the output packet stream format is compatible with a different one of the QAM, QPSK or VSB modulation formats.