WO1999004575A1 - Method and apparatus for video compression and transmission with reduced delay - Google Patents
Method and apparatus for video compression and transmission with reduced delay Download PDFInfo
- Publication number
- WO1999004575A1 WO1999004575A1 PCT/US1998/014706 US9814706W WO9904575A1 WO 1999004575 A1 WO1999004575 A1 WO 1999004575A1 US 9814706 W US9814706 W US 9814706W WO 9904575 A1 WO9904575 A1 WO 9904575A1
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- video data
- compressed video
- buffer
- rate
- delay
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- 230000006835 compression Effects 0.000 title claims abstract description 41
- 238000007906 compression Methods 0.000 title claims abstract description 41
- 230000005540 biological transmission Effects 0.000 title claims abstract description 29
- 238000000034 method Methods 0.000 title claims description 10
- 239000002131 composite material Substances 0.000 description 8
- 238000010586 diagram Methods 0.000 description 5
- 230000006837 decompression Effects 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 3
- 230000005236 sound signal Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 2
- 238000004891 communication Methods 0.000 description 2
- 230000003139 buffering effect Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000002452 interceptive effect Effects 0.000 description 1
- 238000013178 mathematical model Methods 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 230000002123 temporal effect Effects 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
- H04N19/115—Selection of the code volume for a coding unit prior to coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
- H04N19/152—Data rate or code amount at the encoder output by measuring the fullness of the transmission buffer
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
- H04N19/17—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object
- H04N19/172—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being an image region, e.g. an object the region being a picture, frame or field
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
- H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/90—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using coding techniques not provided for in groups H04N19/10-H04N19/85, e.g. fractals
- H04N19/91—Entropy coding, e.g. variable length coding [VLC] or arithmetic coding
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
- H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
- H04N21/234—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs
- H04N21/23406—Processing of video elementary streams, e.g. splicing of video streams or manipulating encoded video stream scene graphs involving management of server-side video buffer
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N21/00—Selective content distribution, e.g. interactive television or video on demand [VOD]
- H04N21/20—Servers specifically adapted for the distribution of content, e.g. VOD servers; Operations thereof
- H04N21/23—Processing of content or additional data; Elementary server operations; Server middleware
- H04N21/242—Synchronization processes, e.g. processing of PCR [Program Clock References]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
- H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
- H04N19/146—Data rate or code amount at the encoder output
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
- H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards
Definitions
- Video teleconferencing systems significantly increase the effectiveness of personal communication over existing voice-based systems. Often, video sequences
- Video compression technology reduces the channel bandwidth needed to transmit sequences of video information.
- the emerging MPEG2 standard reduces the channel bandwidth requirement by a hundred fold without a significant degradation in video quality.
- the video compression technology reduces the channel bandwidth requirements to a level that is also realistic for transport by the transmission networks
- a conventional video teleconferencing system as shown in FIG. 1 includes four major elements: a video compression unit 10 and a video buffer 12 at a source site 20, a transmission channel 14 connecting the source site 20 to a destination site 22, and a video decompression unit 16 at the destination site 22.
- the video compression unit 10 captures and compresses input video information 8 into a stream 24 of video bits following some type of compression standard such as MPEG2 or H.261.
- the video buffer 12 receives non-constant or bursty data stream 24 from the video compression unit 10.
- the data stream is bursty due to the amounts of temporal and spatial encoding used in compressing the video information.
- the video buffer 12 smooths out the data stream 24 so that a constant rate data stream 26 can be fed into the transmission channel 14.
- the channel 14 delivers the data stream from the source site 20 to the destination site 22.
- the decompression unit 16 decompresses the received data stream 28 to recover the original video information for display. All four elements contribute to an overall system delay. If the system delay increases beyond the human response time, it can significantly reduce the effectiveness of the video teleconferencing system. It is thus important to minimize the delay of each element.
- the present invention is directed to reducing the delay contributed by the video buffer.
- an apparatus for video compression includes a video compressor and a buffer.
- the video compressor compresses an input stream of video data frames at a compression rate to provide compressed video data at an average compressor output rate.
- the buffer receives the compressed video data from the video compressor to provide a compressed video data stream.
- the compressed video data stream is transmitted from the buffer onto a transmission channel at a channel rate greater than the average compressor output rate such that utilization of the transmission channel is less than full. Reducing the channel utilization provides a corresponding reduction in buffer delay which improves end-to-end delay to benefit real-time transmission applications.
- a compression unit includes a video compressor, a buffer and a multiplexer for multiplexing the compressed video data stream with other data streams onto the transmission channel.
- the compression unit further includes a data gate for gating the compressed video data stream into the multiplexer at a multiplexer input rate when the buffer contains compressed video data, wherein the multiplexer input rate is greater than the average compressor output rate.
- the compression unit further comprises a time stamp generator coupled to the multiplexer for generating a time stamp for each compressed video data frame. The time stamp is adjusted by a delay offset value to account for delay due to the buffer.
- the video compressor comprises an
- the time stamp generator comprises a presentation time stamp (PTS) generator for generating a PTS value for each compressed video data frame.
- PTS presentation time stamp
- the PTS value is reduced by a delay offset value to account for delay due to the buffer.
- FIG. 1 is a block diagram of a conventional system for real-time transmission of compressed video information.
- FIG. 2 is a graphical representation of a mathematical model of a video buffer.
- FIG. 3 is a graphical representation of a relationship between maximum buffer delay and channel bandwidth.
- FIG. 4 is a block diagram of a real-time transmission system in accordance with the present invention.
- FIG. 5 is a schematic block diagram of the MPEG2 compressor in FIG. 4.
- FIG. 6 is a schematic block diagram of the PTS generator in FIG. 5.
- a model is first presented to understand how data buffering in the conventional system of FIG. 1 contributes to the overall system delay.
- the video compression unit 10 encodes input data into a format (e.g., MPEG) that is suitable for channel transmission.
- the buffer 12 serves as a temporary storage house for the data coming out of the compression unit 10. This buffer 12 is necessary only because the output of the compression unit 10 is bursty.
- the channel 14 then takes data out of the buffer 12 at a constant rate and delivers it to the video decompression unit 16.
- the following presents output equations for each system element with reference to FIG. 2.
- the video compression unit 10 (FIG. 1) outputs data periodically with a frame period P.
- the frame period P is equal to 33ms for NTSC formatted video and 50ms for PAL formatted video.
- the compressed data A of each frame is sent out within the period P.
- the total data size of each compressed frame is defined by the function f(i), where i is the frame count (i is an integer). Assuming that the video compression unit 10 can only output compressed data at a fixed rate Rep, or zero, the compression unit output data rate, esor(t), which corresponds to data stream 24 (FIG. 1), is then:
- the buffer 12 receives data stream 24 at a rate defined by the function esor(t).
- the buffer 12 outputs the data stream 26 defined by the function buffout(t).
- the buffer 12 outputs data stream 26 at a constant rate of Rch only when there is data within the buffer.
- the fullness of the buffer is given by the function buffievel(t).
- FIG. 2 graphically indicates characteristics of the buffout(t) and bufflevel(t) functions.
- the buffer fullness bufflevel(t) is the difference between the input rate esor(t) (corresponding to stream 24 in FIG. 1) and the output rate buffout(t) (corresponding to stream 26 in FIG. 1):
- buffout(t) is not an easy function to model.
- Tpz(i) a new variable, is defined as the latest time instant in the past when buffout(t) was zero starting from the current frame i. It can be seen in FIG. 2 that the dependency of bufflevel(t) on esor(t) stops at Tpz.
- bufflevel(t) is defined as:
- the channel 14 (FIG. 1) can deliver data at any rate up to a maximum level.
- the video decompression unit 16 (FIG. 1) must receive a full video frame i before it can output a decoded image for display. For this analysis, the time required by the receiver to decode the image is assumed to be zero.
- a delay D(i) is the time it takes to present the i* frame when the i th frame compressed data is available to the buffer 12 (FIG. 1).
- the delay is the time it takes to deliver the last bit of each frame to the destination site 22 (FIG. 1) starting from the first bit going into the buffer 12.
- this delay can be seen graphically in FIG. 2 for value D(4).
- the maximum delay Dmax is inversely proportional to the channel bandwidth Rch, as shown graphically in FIG. 3.
- Imax is the argument of max ⁇ D(i) ⁇ .
- the functions esor, tf, and Tpz are assumed to stay unchanged over the Rch range.
- the plot shows that by increasing the channel bandwidth, Rch, the overall delay decreases.
- the maximum channel bandwidth allowable (Rchmax) is constrained by the physical structure of the channel 14 (FIG. 1).
- FOG. 1 the physical structure of the channel 14
- Utilization is defined here as the ratio of the bandwidth required to the available channel bandwidth.
- the conventional compression unit 10 To achieve 100% utilization of the channel bandwidth, the conventional compression unit 10 (FIG.
- the curve D](Imax) illustrates a system wherein Rchmax crosses the curve where the slope is steep, which translates into a significant delay D A introduced by the buffer unit.
- the present invention provides a method and apparatus wherein the bandwidth utilization is reduced to provide a corresponding reduction in the buffer delay.
- the bandwidth utilization is reduced by effectively reducing the average bit rate Avbr of the compression unit relative to the channel rate Rchmax.
- the curve D 2 (Imax) illustrates a system for which the utilization value has been reduced. It can be seen that for the same value of Rchmax, the corresponding delay D B is reduced.
- the relationship between the channel utilization and the reduction in buffer delay depends on the function esor(t), which is compression algorithm dependent.
- the present invention provides flexibility to balance tradeoffs between video quality and video delay. In video teleconferencing applications where both the video quality and the video delay are important, this flexibility becomes very valuable.
- FIG. 4 an exemplary embodiment of a real-time video transmission system according to the present invention is shown.
- the system includes the following elements: a composite camera 100, an MPEG2 compressor 104, a modulator 108, a satellite repeater 110, a demodulator 112, an MPEG2 video decompressor 116 and a composite video display 120.
- the composite camera 100 captures motion information into an analog composite format following a conventional video standard such as NTSC or PAL.
- the MPEG2 compressor 104 receives this analog signal and compresses it following the MPEG2 standard.
- the MPEG2 compressor 104 generates a smooth output stream into the modulator 108.
- the modulator 108 modulates the digital bit stream from the compressor 104 into a suitable radio frequency signal for transmission via the satellite 110.
- the demodulator 112 demodulates an RF signal received from the satellite 110 to recover the compressed digital bit stream.
- the MPEG2 decompressor 116 decodes the compressed digital bit stream following the MPEG2 standard and outputs an analog composite signal following the NTSC standard.
- the composite video display 120 then displays the images represented by the composite signal.
- a video digitizer 200 converts composite analog video signals (e.g., NTSC or PAL standard) into CCIR-601 digital format.
- a video preprocessor 204 performs real time filtering on the CCIR-601 digital video signal to increase compression efficiency.
- a video compressor 214 compresses the preprocessed digital video signal to provide an elementary video stream 232 following the MPEG2 video standard (ISO/TEC 13818-2).
- An audio digitizer 202 converts analog audio signals into digital audio signals following the AES/EBU standard (ANSI 4.40 - 1992).
- An audio compressor 208 compresses the digital audio signals to provide an elementary audio stream 235 following the MPEG2 audio standard (ISO/IEC 13818-3).
- a data compressor 210 compresses data following a custom-defined compression technique to provide an elementary data stream 237.
- a table generator 212 generates transport tables 239 following the MPEG2 system section standard (ISO/IEC 13818-1).
- a multiplexer 236 multiplexes the video, audio and data elementary streams along with the transport tables into a single transport stream 241 following the MPEG2 system section standard (ISO/IEC 13818-1).
- a physical layer interface 220 converts the transport stream 241 into an analog signal suitable for transmission over various different physical media (e.g. RS422, DS3, G.703, ASI).
- a data timing manager 226 generates time stamps and system clocks to the various elements to ensure that the transport stream complies with the MPEG2 system section standard (ISO/IEC 13818-1).
- a system controller 222 initializes, monitors, and periodically updates each of the elements within the compressor 104.
- a front panel 224 and a network management interface 225 provide user access to customize the compressor configuration.
- the low delay aspect of the present invention is implemented in the exemplary embodiment using a video buffer 216, a compress data gate 228 and a PTS generator 230.
- the buffer 216 receives a video data stream from the video compressor on line 232 at a compressed video output clock rate on line 234.
- the output clock rate is typically set not to exceed 54MHz. This output clock rate corresponds to the instantaneous or peak rate for the function esor(t) defined in the model above (FIG. 2).
- the buffer has a buffer depth that is deep enough to handle the maximum variable buffer verifier (VBV) buffer size as defined by MPEG2 and set within the video compressor 214.
- VBV buffer size is set at 9.1 Mbits.
- the data gate 228 gates the data output from the buffer 216 and into the multiplexer 218.
- the gate 228 provides a multiplexer clock input signal 238 that clocks data to the multiplexer 218 at a rate of Rg bits per second when there is data in the buffer, and 0 bits per second when there is no data.
- the gate 228 is implemented by generating a clock pulse at a gate rate of Rg when the buffer is not empty as indicated by the status of a buffer empty flag 237.
- the gate rate Rg corresponds to the channel rate Rchmax (FIG. 3). As noted above, it has been found according to the present invention that a reduction in the channel bandwidth utilization provides a corresponding reduction in buffer delay.
- the gate rate Rg is 20% larger than the average compressor output rate Avbr.
- corresponding ratios for Rg/Avbr can be empirically determined to provide a desired reduction in buffer delay.
- video quality and video delay There is, of course, a tradeoff between video quality and video delay. That is, in order to reduce the delay, the video quality is reduced since the average compressor output rate Avbr is below the value that corresponds to 100% utilization. In general, setting the ratio Rg/Avbr too high can lead to unacceptable video quality.
- the total video system delay is determined by time stamps that are included at the beginning of each compressed video frame. More specifically, the MPEG2 system section standard (ISO/IEC 13818-1) specifies a PTS field within a packetized elementary stream (PES) header at the beginning of the compressed video frame, which determines the time elapsed from the time the uncompressed frame is captured (e.g., in MPEG2 compressor 104, FIG. 4) to the time the uncompressed frame is displayed at the video decompressor output (e.g., MPEG2 decompressor 116, FIG. 4).
- PTS packetized elementary stream
- an offset value of 100ms has been determined empirically for the IBM model ME31 video compressor that effectively reduces the overall system delay by that amount. It should be noted, however, that for other video compressors, corresponding PTS offset values can be empirically determined to account for the reduction of the delay required by the buffer 216 (FIG. 5). While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
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Abstract
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Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AU84897/98A AU8489798A (en) | 1997-07-18 | 1998-07-16 | Method and apparatus for video compression and transmission with reduced delay |
EP98935710A EP0995318A1 (en) | 1997-07-18 | 1998-07-16 | Method and apparatus for video compression and transmission with reduced delay |
CA002296375A CA2296375A1 (en) | 1997-07-18 | 1998-07-16 | Method and apparatus for video compression and transmission with reduced delay |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US5302897P | 1997-07-18 | 1997-07-18 | |
US60/053,028 | 1997-07-18 |
Publications (1)
Publication Number | Publication Date |
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WO1999004575A1 true WO1999004575A1 (en) | 1999-01-28 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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PCT/US1998/014706 WO1999004575A1 (en) | 1997-07-18 | 1998-07-16 | Method and apparatus for video compression and transmission with reduced delay |
Country Status (4)
Country | Link |
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EP (1) | EP0995318A1 (en) |
AU (1) | AU8489798A (en) |
CA (1) | CA2296375A1 (en) |
WO (1) | WO1999004575A1 (en) |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1993015571A1 (en) * | 1992-01-29 | 1993-08-05 | Bell Communications Research, Inc. | Smoothing delay-sensitive traffic offered to atm networks |
US5535202A (en) * | 1994-03-16 | 1996-07-09 | Mitsubishi Denki Kabushiki Kaisha | Priority processing of ATM cells using shift register stages |
GB2306073A (en) * | 1995-10-03 | 1997-04-23 | Nec Corp | VBR MPEG video encoding for ATM networks with dynamic bandwidth renegotiation |
EP0782137A2 (en) * | 1995-12-27 | 1997-07-02 | Sony Corporation | Digital signal multiplexing and recording |
-
1998
- 1998-07-16 EP EP98935710A patent/EP0995318A1/en not_active Withdrawn
- 1998-07-16 CA CA002296375A patent/CA2296375A1/en not_active Abandoned
- 1998-07-16 WO PCT/US1998/014706 patent/WO1999004575A1/en not_active Application Discontinuation
- 1998-07-16 AU AU84897/98A patent/AU8489798A/en not_active Abandoned
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1993015571A1 (en) * | 1992-01-29 | 1993-08-05 | Bell Communications Research, Inc. | Smoothing delay-sensitive traffic offered to atm networks |
US5535202A (en) * | 1994-03-16 | 1996-07-09 | Mitsubishi Denki Kabushiki Kaisha | Priority processing of ATM cells using shift register stages |
GB2306073A (en) * | 1995-10-03 | 1997-04-23 | Nec Corp | VBR MPEG video encoding for ATM networks with dynamic bandwidth renegotiation |
EP0782137A2 (en) * | 1995-12-27 | 1997-07-02 | Sony Corporation | Digital signal multiplexing and recording |
Non-Patent Citations (1)
Title |
---|
LAUDERDALE J ET AL: "A NEW TECHNIQUE FOR TRANSMISSION OF PRE-ENCODED MPEG VBR VIDEO USING CBR SERVICE", 23 June 1996, 1996 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC), CONVERGING TECHNOLOGIES FOR TOMORROW'S APPLICATIONS DALLAS, JUNE 23 - 27, 1996, VOL. VOL. 3, PAGE(S) 1416 - 1420, INSTITUTE OF ELECTRICAL & ELECTRONICS ENGINEERS, XP000625043 * |
Also Published As
Publication number | Publication date |
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EP0995318A1 (en) | 2000-04-26 |
CA2296375A1 (en) | 1999-01-28 |
AU8489798A (en) | 1999-02-10 |
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