Apparatus and Method for Transmitting Variable Rate Data According to Multiple Storage State Indicators

The present invention relates to apparatus and method for transmitting data and, more particularly, to apparatus and method for transmitting variable-bit rate data on a digital serial bus having a predetermined transmission rate. The invention also relates to apparatus and method for transmitting variable-bit rate data on a digital serial bus with means for pre-determining the peak bit rate of the variable-bit rate to be transmitted.

As is known, various types of digital video-audio equipment, for example, DVD reproducing devices, digital VTRs, digital televisions, etc., are currently available for consumer use. Several such devices reproduce or receive digital video/audio signals, convert those signals into analog signals, and supply the analog signals to analog-type video/audio equipment. It is also generally desirable to supply from such equipment digital video/audio signals to, for example, a personal computer, a digital television receiver, or other type of digital device.

The communication system IEEE-1394 is a digital serial bus which has been proposed as a means for transmitting such digital video/audio signals between digital devices. Referring to FIG. 1 of the drawings, an exemplary block diagram of an IEEE-1394 system that includes an IEEE-1394 bus 901 and various digital devices 902-907 is shown. In the exemplary block diagram, the IEEE-1394 bus is coupled between a DVD reproducing apparatus 902, a digital VCR 903, a digital broadcasting receiver 904, a digital television receiver 905, a digital television receiver 906 and a personal computer 907. As shown, digital video/audio data is supplied from DVD reproducing apparatus 902 via the IEEE-1394 bus to digital television receiver 906, and digital video/audio data supplied from digital broadcasting 904 is supplied via bus 901 to digital television receiver 905. Given an IEEE-1394 bus with a transmission rate of, for example, 100 Mbps, and video/audio data is organized into "units" of data, then in accordance with IEEE-1394 standard, 4915 units of data can be transmitted during each 125 .mu.sec transmission cycle of the bus. In accordance with this standard, the number of units transmitted corresponds to the bit rate of the signal to be transmitted. For example, to realize a communication speed of approximately 10 Mbps, which corresponds to the mean bit rate of a typical video signal, then approximately 1200 units are needed. However, to realize a communication speed of approximately 2 Mbps, which is the mean bit rate of an audio signal, then approximately 704 units are needed.

One limitation of the above discussed IEEE-1394 standard is that signals are transmitted only after their transmission rate (i.e., bit rate) is determined. However, DVD reproducing devices that employ MPEG encoders/decoders reproduce digital video/audio data at a variable rate and, thus, an IEEE 1394-bus previously has been unable to transmit variable rate data reproduced from such devices.

Therefore, it is an object of the present invention to provide apparatus and method for transmitting digital video/audio data which overcome the shortcomings of the above described system.

Another object of the present invention is to provide apparatus and method which is operable to transmit variable rate digital video/audio data in accordance with the IEEE-1394 standard.

Various other objects, advantages and features of the present invention will become readily apparent to those of ordinary skill in the art, and the novel features will be particularly pointed out in the appended claims.

In accordance with one embodiment of the present invention, apparatus and method are provided for detecting a peak data rate of variable rate data to be transmitted, establishing a rate of transmission of the variable rate data in accordance with the detected peak data rate, and transmitting in accordance with the established transmission rate the variable rate data on a transmission line that requires the transmission rate to be predetermined.

As one aspect of the present invention, a bandwidth of the transmission line that is required to transmit the variable rate data having the detected peak data rate is secured.

As another aspect of the present invention, the reproducing of a signal from a record medium to produce the variable rate signal is controlled in accordance with a control signal, the variable rate signal is processed (e.g., by an MPEG decoder), the control signal is generated in accordance with a condition of processing of the produced variable rate signal, and the variable rate signal is transmitted on the transmission line.

As a feature of this aspect, the transmitted variable rate signal is received and processed in a similar manner as that of the produced variable rate signal (e.g., by a second MPEG decoder), but such second processing does not generate a control signal (similar to the earlier generated control signal) that represents a condition of the second processing.

As a further aspect of the present invention, the transmitted variable rate signal is received by a receiver (e.g., a digital television), the received transmitted variable rate signal is processed, the control signal is generated in accordance with a condition of processing of the received transmitted variable rate signal, and the generated control signal is transmitted back to the transmitting side, wherein the received transmitted control signal is utilized to control the reproducing of a signal from the record medium.

The following detailed description, given by way of example and not intended to limit the present invention solely thereto, will best be appreciated in conjunction with the accompanying drawings, wherein like reference numerals denote like elements and parts, in which:

FIG. 1 is a block diagram of a system employing an IEEE-1394 digital serial bus;

FIG. 2 is a block diagram of a data transmission apparatus in accordance with the present invention;

FIG. 3 is a block diagram of a data transmission apparatus in accordance with another embodiment of the present invention;

FIG. 4 is a simplified block diagram of the device shown in FIG. 2;

FIG. 5 is a simplified block diagram of the device shown in FIG. 3;

FIG. 6 is a block diagram of control circuits 301 and 302 in accordance with the present invention;

FIG. 7 schematically illustrates the data structure of an Iso packet; and

FIG. 8 is a schematic illustration of the transmission bandwidth of a digital serial bus that is transmitting data in accordance with the present invention.

FIGS. 2 and 3 illustrate different embodiments of the data transmission apparatus of the present invention, wherein FIG. 2 illustrates a DVD reproducing apparatus 100 that includes an MPEG decoder 6, and FIG. 3 illustrates a DVD reproducing apparatus 100 that does not include an MPEG decoder. As will be discussed, DVD reproducing apparatus 100 shown in both FIGS. 2 and 3 are coupled via an IEEE-1394 digital serial bus 300 to an MPEG decoder 9, included in, for example, a digital television receiver.

Referring first to the embodiment of the present invention shown in FIG. 2, DVD reproducing apparatus 100 is operable to reproduce digital video/audio data from a digital video disk, decode the reproduced data in MPEG decoder 6, and supply the decoded data as respective analog video and audio signals. The analog video and audio signals may be supplied to, for example, an analog television receiver, an analog recording device, etc. DVD reproducing apparatus 100 further is operable to transmit the reproduced digital video/audio data via bus 300 to an external MPEG decoder 9 which decodes the transmitted signal and supplies digital video and audio signals as an output.

DVD reproducing apparatus 100 of the present invention reproduces digital video/audio data from a digital video disk in a reproducing device 1 which supplies the reproduced data via an amplifier circuit 2 to a demodulator 3 which demodulates the reproduced signal. The demodulated signal is supplied to an error correction and memory control circuit 4 which stores the supplied signal in a random access memory 5 and corrects errors in the stored signal in a known manner. The error corrected signal is supplied to MPEG decoder 6 which includes therein a demultiplexer 61, control circuits 62 and 63, and random access memories 64 and 65. The digital signal is supplied to demultiplexer 61 which demultiplexes the signal into its respective video and audio components. The video signal is stored via control circuit 62 in memory 64, and the audio signal is stored via control circuit 63 in memory 65. Control circuits 62 and 63 decode the respective stored video and audio signals in a known manner and the decoded video and audio signals are supplied as, for example, analog video and audio output signals (after digital to analog conversion).

In addition to decoding the stored video and audio signals, control circuits 62 and 63 supply to a system control circuit 7 respective control signals that identify the storage states of the respective memories 64, 65. Similarly, memory control circuit 4 supplies to system control circuit 7 a control signal that identifies the storage state of memory 5. These control signals are sometimes identified as memory occupation data and generally identify how much data is stored in the respective memories. System control circuit 7, in response to the supplied control signals, controls the reproduction of the digital video/audio data by the reproducing device 1 so as to, inter alia, prevent the underflow and/or overflow of the memories.

In accordance with the present invention, DVD reproducing apparatus 100 includes a peak rate setting block 8 which sets the peak rate of the reproduced data for purposes of transmission of the variable-rate data on bus 300 (to be further discussed). DVD reproducing apparatus 100 further includes a control circuit 301 which transmits the error corrected digital signal output by circuit 4 on bus 300 in accordance with the IEEE-1394 standard. In addition to supplying the error corrected digital video/audio signal to MPEG decoder 6, error correction and memory control circuit 4 supplies the error corrected digital video/audio signal to peak rate setting block 8.

As previously mentioned, the mean bit rate of a typical video signal is 10 Mbps, and the mean bit rate of a typical audio signal is 2 Mbps. In accordance with the present invention, peak rate setting block 8 sets the peak rates of the video and audio signals to twice their respective mean bit rates, that is, 20 Mbps and 4 Mbps, respectively. Control circuit 301 calculates from the supplied set peak rate the number of units that are required, and in accordance with the IEEE-1394 standard to provide a total transmission speed of, for example, 100 Mbps on the digital serial bus, 2400 units and 1408 units are required to transmit the video and audio signals, respectively. The transmission band necessary then is said to be "secured" in accordance with the standard.

Referring to FIG. 8, prior to each 125 .mu.sec transmission cycle of the IEEE-1394 bus 300 during which the video and audio signals are transmitted, the required transmission band is secured by control circuit 301, such transmission band being represented by the dashed rectangular portion in each cycle in FIG. 8. That is, the regions surrounded by the dashed rectangular portions are said to be "secured" for the data that is to be transmitted by DVD reproducing apparatus 100 of the present invention. The hatched portion of each secured rectangular portion of each cycle represents that portion of the secured transmission band that is actually utilized, i.e., the hatched portions represent the variable rate data itself. The unsecured transmission band corresponds to those regions beyond the dashed rectangular portions and are usable by other devices, for example, digital VCR 903 shown in FIG. 1.

Control circuit 301 secures the necessary transmission band and subsequently transmits the digital signal (video and audio) supplied from error correction and memory control circuit 4 on the secured transmission band of bus 300. The digital signal is transmitted to a control circuit 302 which operates to control the bus communication in accordance with the IEEE-1394 standard, which control circuit 302 being included in, for example, a digital television receiver 200 that includes an MPEG decoder 9. Therefore, and in accordance with the present invention, variable bit rate data reproduced by DVD reproducing apparatus 100 is transmitted on a digital serial bus in accordance with the IEEE-1394 standard.

The transmitted video/audio data is supplied from control circuit 302 to MPEG decoder 9 which has a structure similar to that of MPEG decoder 6, but control circuits 92, 93 do not produce control signals that identify the storage state of memories 94, 95. The digital video/audio signal is supplied to a demultiplexer 91 which demultiplexes the signal into its respective video and audio components which are then stored via control circuits 92 and 93 in random access memories 94 and 95, respectively. The respective digital and audio signals are decoded by control circuits 92 and 93 and the decoded video and audio signals are supplied as, for example, respective digital video and audio signals.

As previously mentioned, control circuits 92 and 93 do not generate control signals that identify the storage states of memories 94 and 95. DVD reproducing apparatus 100 operates to MPEG decode the reproduced signal in MPEG decoder 6 and simultaneously transmit the reproduced signal on bus 300. Since MPEG decoder 9 is equivalent to MPEG decoder 6, and since control circuits 62 and 63 generate respective control signals representing the storage states of memories 64 and 65, which in turn controls the reproduction of the data from the digital video disk, it is unnecessary for control circuits 92 and 93 to generate controls signals that identify the respective storage states of memories 94 and 95. In other words, the storage states of memories 64 and 65 should be substantially equivalent to the storage states of memories 94 and 95, respectively and, thus, proper control of the reproduction of the digital video/audio data from the digital video disk is provided solely by MPEG decoder 6.

As previously mentioned, MPEG decoder 6 may supply as outputs respective analog video and audio signals and such signals may be supplied on an analog signal line 400 to an analog television receiver 500, such as shown in FIG. 4.

In accordance with the present invention, as discussed above, the storage states of memories 64 and 65 are detected and the reproduction operation of DVD reproducing apparatus 100 is controlled in accordance with such storage states thus preventing underflow and overflow of memories 64 and 65. By the use of MPEG decoder 6, a separate MPEG decoder 9, that is coupled to DVD reproducing apparatus 100 of the present invention via digital serial bus 300, does not need to determine whether an underflow or overflow condition of memories 94 and 95 exists. Furthermore, by detecting the peak rate of the supplied digital video/audio signal periodically in peak rate setting block 8, variable rate data may be transmitted on a digital serial bus in accordance with the IEEE-1394 standard, even when such standard requires that the transmitted bit rate be known.

Referring next to FIG. 3 of the drawings, a block diagram of apparatus for transmitting digital video and audio data in accordance with another embodiment of the present invention is shown. FIG. 5 also illustrates the present embodiment, wherein DVD reproducing apparatus 100 is coupled to a digital television 200 including therein a display unit and MPEG decoder 9. Referring back to FIG. 3, DVD reproducing apparatus 100 includes a DVD reproducing device 1, an amplifier 2, a demodulator 3, an error correction and memory control circuit 4, a random access memory 5, a peak rate setting block 8, a system control circuit 7 and a control circuit 301 and thus is similar to DVD reproducing apparatus 100 shown in FIG. 2, except the DVD reproducing device of the present embodiment does not include an internal MPEG decoder 6. In the present embodiment, circuits 1-5 operate in a manner identical to that of circuits 1-5 shown in FIG. 2, wherein digital video/audio data is reproduced from a digital video disk, demodulated, stored in memory 5, error corrected in circuit 4 and supplied as an error corrected digital video/audio signal to control circuit 301 via peak rate setting block 8. Peak rate setting block 8 operates in the same manner as that described above with respect to the embodiment shown in FIG. 2 and, therefore, further description thereof is omitted herein. Also, like the embodiment shown in FIG. 2, control circuit 301 shown in FIG. 3 secures the necessary bandwidth in accordance with the peak rate detected by peak rate setting block 8 and transmits on bus 300 the error corrected digital video/audio signal in accordance with the IEEE-1394 standard, all as previously discussed.

The transmitted digital video/audio signal is supplied to a control circuit 302 included in digital television receiver 200 which supplies the received signal to an MPEG decoder 9 which includes therein a demultiplexer 91, control circuits 92 and 93, and memories 94 and 95. Demultiplexer 91 demultiplexes the transmitted signal into its respective video and audio components, and stores the video data via control circuit 92 in memory 94 and stores the audio data via control circuit 93 in memory 95. Control circuits 92 and 93 MPEG decode the respective video and audio data to produce respective digital video and audio signals.

In accordance with the present invention, control circuits 92 and 93 detect the storage states (conditions) of memories 94 and 95, respectively (like control circuits 62 and 63 in FIG. 2), and generate therefrom respective control signals that are supplied to control circuit 302. Also in accordance with the present invention, the control signals supplied from control circuits 92 and 93 to control circuit 302 are transmitted from control circuit 302 on digital serial bus 300 to control circuit 301 in DVD reproducing apparatus 100.

In accordance with the IEEE-1394 standard, control circuits 301 and 302 each have a block structure as shown in FIG. 6, wherein each control circuit includes an Iso packet transmitting and receiving block 310, a bus control block 311, an information signal processing block 312 and a plug control register 313 located within bus control block 311. Iso packet transmitting and receiving block 310 performs isochronous communication for transmitting the video signal data and audio signal data, and bus control block 311 performs asynchronous communication for transmitting control signals. Data is transmitted between the Iso packet transmitting and receiving block 310 and information signal processing block 312 within each control circuit 301 and 302. In accordance with the IEEE-1394 standard, the Iso packet that is transmitted between control circuit 301 and 302 has the data structure as shown in FIG. 7.

Referring to FIG. 7, each Iso packet is formed from "quadlets" of data, each quadlet consisting of four bytes of information. The Iso packet includes a header, which includes therein the data length that is provided in the so-called first quadlet. The Iso packet header further includes in the second quadlet cyclic redundancy check (CRC) codes for the information of the first quadlet. As shown, the packet header is comprised of the first and second quadlets, such packet header being transmitted at the beginning of packet transmission. A data field follows the packet header, and the cyclic redundancy check codes for the data field follows that data field.

Bus control block 311 of each control circuit 301 and 302 receives from the respective information processing block 312 the control signals that identify the storage states of memories 94 and 95. Such information is transmitted from one control circuit to another control circuit utilizing asynchronous communication. Typically, control circuit 302 transmits such control signals asynchronously to control circuit 301 which subsequently supplies the transmitted control signals to system control circuit 7. As previously mentioned, bus control block 311 of each control circuit 301, 302 includes a respective plug control register 313. Plug control register 313 sets values stored therein in accordance with the transmitted information, for example, the transmitted signals, and the various information generated by the particular equipment utilized, and Iso packet transmitting and receiving block 310 of the respective control circuit 301, 302 is controlled in accordance with the values stored in plug control register 313.

Finally, the control signals transmitted to system control circuit 7 from control 301 operate to control the reproducing operation of DVD reproducing circuit 1 in order to prevent underflow and overflow of memories 94 and 95.

Like the first embodiment previously discussed with reference to FIG. 2, the embodiment of FIG. 3 is operable to transmit variable rate data across a transmission line, for example, IEEE-1394 bus 300, which has a predetermined rate of transmission. Referring again to FIG. 8, the transmission band is secured prior to the transmission of the digital video/audio data and, as previously discussed, the hatched portion of the secured bandwidth of each cycle represents the variable rate data itself supplied by DVD reproducing apparatus 100, and the unsecured transmission band corresponds to those regions beyond the dashed rectangular portions and are usable by other devices.

While the present invention has been particularly shown and described in conjunction with preferred embodiments thereof, it will be readily appreciated by those of ordinary skill in the art that various changes may be made without departing from the spirit and scope of the invention. For example, the present invention, although described with reference to the IEEE-1394 standard and the use of MPEG decoders, is not limited to this standard and/or the use of MPEG decoders, but may be applied to other standards and/or other types of coders/decoders that produce/decode variable-rate data.

Therefore, it is intended that the appended claims be interpreted as including the embodiments described herein, the alternatives mentioned above, and all equivalents thereto.