CA1132243A

CA1132243A - Digital transmission system for television video signals

Info

Publication number: CA1132243A
Application number: CA318,184A
Authority: CA
Inventors: Yukihiko Iijima
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1977-12-20
Filing date: 1978-12-19
Publication date: 1982-09-21
Also published as: US4215369A

Abstract

Abstract A digital transmission system for television video signals is described. The transmitter is of the type which has several input terminals for receiving respective television video signals to be transmitted, several encoding units for encoding the respective video signals into digitized video signals, and multiplexers for multiplexing the respective digitized video signals in a time division manner. The receiver is of the type which has a demultiplexer for receiving the multiplexed video signal from the multiplexer and for separating the multiplexed video signal into the digitized video signals, and several decoding units for decod-ing the digitized video signals into the respective television video signals. The improvement of the invention involves the use of a sync pulse separator for separating sync pulses in the video signal, an encoder responsive to the separated pulses for encoding the video signal into predetermined codes and a generator for generating video-frame-sync codes each indicative of the end of one picture frame. The two coded signals are multiplexed and stored temporarily in a buffer memory. The buffer occupancy rate is measured and a corresponding code generated. The time interval during which the video-frame-sync code is in the buffer is measured.
A second buffer is provided and in the same way as before, the time interval for the second buffer is measured and compared with that for the first buffer. A read-out address signal is controlled according to the result of the comparison.

Description

1~2Z43 .
A Digital Transmission System For Television Video Signals FIELD OF T~E I~VENTION

This lnvention relates to a digital transmission system for television video signals with high transmission efficiency.

BACKGROUND OF THE INVENTION

To improve the transmission efficiency for digitized television video signals, a variable-length code technique has been used in prior arts such as variable-length differential pulse-code modulation systems and predictive encoding transmission systems based on interframe correlation. In either case, video signals to be transmitted are sampled at a sampling rste proportional to s predetsrmined scanning rate. ~owever, since significant information to be transmitted is distributed at random with respect to tlme, s buffer memory for temporarily storing encoded digital signals is needed on the transmitter side to transmit them at a predetermined bit rate.
Correspondingly, another b~ffer memory for temporarily storing the digital~signals transmitted is needed at the receivering end. Also~ it is nscsssary to dscode the received~digital slgDal~s at the same;sampling rate as that in the transmitter so as to avoid ths owerf'ow or underflow of the~buffer memory at the receiver. In order to avoid such an overfIow, the buffer memory of the receiver is requ~red to have s capacity sufflciently lsrger than that of the transmltter.
To remove this restriction imposed on the receiver, a transmission !~
system for digitized video signals has been proposed in the U.S. patènt Uo. 4,027,100 issued May 31, 1977. According to this prlor art, a ~3ZZ43 buffer memory at the transmitter stores synchronization signals produced regularly, signals indicative of a buffer-occupancy state immediately follow-ing the respective synchronization signals~ and information signals produced between each signal indicative of a buffer-occupancy state and'the succeeding synchronization signal unevenly in response to the video signal to be trans-mitted. A buffer memory at a receiver stores the signals transmitted from the transmitter. A decoder coupled to the receiver-side buffer memory de-codes the information signals at a decoding rate controlled with reference to the difference between an actual sum of buffer occupancies of both buffer memories and a value predetermined for the sum. ~lowever, this system can not be applied to the transmission whose transmission speed is constant.
Besides, a television video signal transmission system based on a time-division multiplex technique has been disclosed in "NTC77 Conference Record", volume 3, section No. 41:4. With this prior art, each channel in-formation in one frame is assigned depending on the amount of information to be transmitted. However, beca~se the transmission speed of information is ~- not constant with respect to time, the improved technique disclosed in the United States Patent No. 4,027,100 cannot be adapted to the second prior art.
An object of this~invention is therefore to provide a digital trans-mission system for television video signals.
SUMMARY OF THE INVENTION
The present transmission system comprises a transmitter and a re-` ceiver, said trassmitter comprising a plurality of input terminals for re-ceiving respective television video signals to be transmitted, a plurality of :: :
~ encoding units for encoding said respective video signals ~: :

~;,~ : :
:; ::

, ,, . . . ~ ~ . ~, . .

~3;~243 into digiti~ed video signals, and a multiplexer for multiplexing said respec-tive digitized video signals in a time division manner; and said receiver comprising a demultiplexer for receiving the multiplexed video signal trans-mitted from said multiplexer and for separating the same into said digitized video signals, and a plurality of decoding units for decoding said digitized video signals given from said demultiplexer into said respective television video signals, the improvement wherein:
each of said encoding units comprises a synchronization (sync) pulse separator for separating sync pulses involved in said video signal, an encoder responsive to the separated sync pulses for encoding said television video signal into predetermined codes, a generator for generating video-~: frame-sync codes each indicative of the end of one picture frame of said video signal, first means for multiplexing said video-frame-sync codes and the encoded codes of said encoder, a first buffer memory for temporarily storing the multiplexed codes from said first means, a first read/write con-~ troiler for supplying write-in and~read-out address signals to said first : buffer memory and for measuring a buffer-occupancy state of said first buffer ~:~ memory to produce a buffer-occupancy code, second means for measuring a time interval from a time point when said video-~rame-sync code is written into ;20 said first buffer memory to a time point when read out of said video-frame-; sync code and for produclng a first time-indicating signal representative of said time lnterval, third means for multiplexing the codes read out from said ;. : ` first buffer memory and said first time-indicating code and for supplying the output therefrom to said first multiplexer; and each~of said decoding units comprises a second buffer memory for temporarily storing saididigitized video signal supplied from the correspond-ing encoding unit a second read/write controller for ~ 3 -:: ~
: ~: `: ` ~ : :

~, : ": : . :: . .::: . - :

~13~:Z~3 producing write-in address signals for writing said multiplexed codes and said time-indicating code into said second buffer memory and for producing read-out address signals for reading out the codes stored in the second buffer me:mory, fourth means for detecting said first time-indicating code involved in said digitized video signal, fifth means for measuring a time interval from a time point when said video-frame-sync code is written into said second buffer memory to a time point when read out of said video-frame-sync code and for producing a second time-indicating code representative of said time interval, and a buffer memory controller for comparing said first and said second time-indicating codes and for control-ling said write-in address signal based on said comparison operation.
According to another aspect of the invention the improve-ment is characterized in that each of said encoding units comprises a synchronization pulse separator for separating synchronization pulses involved in said television video signal, an encoder respon-sive to the separated synchronization pulses for encoding said television video signal into predetermined codes, a generator for generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchronization codes and the encoded codes of said encoder, a first buffer memory for temporarily storing the multiplexed codes from first means, a first read~write controller for supplying write-in and read-out address signals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer occupancy code, a register for storing said buffer-occupancy code at a first predetermined time point, second means fox counting ' ~ -4-~l~ZZ43 the amount of said multiplexed codes read out from said first buffer memory from said first predetermined time point to a second predetermined time point, a subtractor for subtracting the output of said register from the output of said second means, third means for supplying both the output of said subtractor and said codes read out from said first buffer memory to said multiplexer; and each of said decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from the corresponding encoding unit, second read/write controller for pro-ducing write-in address signals for writing sai~ multiplexed codes into said second buffer memory and for producing read-out signals for reading out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, fourth means for detecting and storing the output of said subtractor involved in said digitized video signal supplied from one of said ~;~ encoding units, and a buffer memory controller for comparing said second buffer-occupancy code~with the output on said fourth means :~: to control sald read-out signal based on said comparison operation.
:~:20 According to another aspect of the invention the improve-~; ~ ment is characterized in that each of said encoding units comprises a synchronization pulse separator for separating synchronization pulses involved in sald television video signal, encoder responsive to the separated synchronization pulses for encoding said television video into predetermined codes, a generator generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video~signal first means for multiplexing : said video-frame-synchronization codes and the encoded codes of : 4 "

.. - , .. ,. ., . . . , . , , " ,.,. ~ . . . .

~3Z243 said encoder, a first buffer memory for temporarily storing the multiplexed codes from said first means, a first read/write con-troller for supplying write-in and read-out address s~gnals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer-occupancy code, second means for supplying said first buffer-occupancy code at a first predetermined time point and said multiplexed codes read out from said first buffer memory to said multiplexer; and each of said decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from corresponding encoding unit, second read/write controller for pro-ducing write-in address signals for writing said multiplexed codes into said second buffer memory and ~or producing read-out address signals for readlng out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, third means for detecting and storing said first buffer-occupancy codes involved in said digitized video signal supplied from said corres-ponding encoding unit, fourth means for counting the amount of write-in of said;multiplexed codes from the detection of said first buffer-occupancy code to a second predetermined time point, a:
subtractor for subtracting the output of said third means from the : : .
::~ output of said fourth means, and a buffer memory controller for comparing said second buffer-occupancy code with the output of :~ said subtraotor to control said read-out address signal of said second read/write controller.
According to a further aspect of the invention the improvement is characterized in that each of said plural encoding :: : :

1~3;~Z~3 units comprises a synchronization pulse separator for separating synchronization pulses involved in said television video signal, an encoder responsive to the separated synchronization pulses for encoding said television video signal into predetermined codes, a generator for generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchroniz-ation codes and the encoded codes of said encoder, a first buffer memory~for temporarily storing the multiplexed codes from said first means, a first read/write controller for supplylng write-in and read-out address signals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer-occupancy code, second means for counting the amount of write-in of both said encoded codes of said encoder and said video-frame-synchronization codes into said first buffer memory, a subtractor for subtracti~ng the output of said first read/
write controller from the output of said second means, third means for supplying the output of said subtractor and the multiplexed codes read out from said first buffer memory to said multiplexer;
and each of sald plural decoding units comprises a second buffer memory for temporarily storing said digitized~video signal supplied from corresponding encoding unit, a second read/write controller for producing write-in address signals for writing said multiplexed codes into said second buffer memory and for producing read-out address signals for reading out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, fourth means:for detecting and storing the output of said subtractor -4c-~132;~3 involved in said digitized video signal from said corresponding encoding unit, and a buffer memory controller for comparing said second buffer-occupancy code with the output of said ~ourth means to control the read-out address signals of said second read/write controller.
This invention will now be described in greater detail in conjunction with the accompanying drawings in which:
Fig. 1 is a block diagram of a transmitter for use in first embodiment of this invention;
Figs. 2, 5 and 6 show block diagrams illustrating detailed portions of the transmitter of Fig. l;
Figs. 3a and 3b, Figs. 4a through 4c, Figs. 7a through 7d, and Figs. 8a through 8n show waveforms for explaining the trans-mitter o~ Fig. l;
Fig. 9 is a block diagram of a receiver for use in the first embodiment of this invention;

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~3;Z243 Figures 10 and 11 show block diagrams illustrating detailed por-tions of the receiver of Figure 9;
Figure 12 is a block diagram of a transmitter of a second embodi-ment of this invention;
Figure 13a through 13v show waveforms for explaining the transmit-ter of Figure 12;
Figure 14 is a block diagram of a receiver of the second embodiment of-this invention;
Figure 15 is a block diagram of a third embodiment of this inven-tion; and Figure 16 is a block diagram of a fourth embodiment o~ this inven-tion.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THIS INVENTION
First, a transmitter 100A for use in a first embodiment is de-scribed referring to Figures 1 through 4. A plurality of television video ~signals are given to input terminals 11, 12 --, ln. As shown in Figure 3(a), each of tha video signals comprises vertical sync pulses VO ~odd field) and : VE (even field) at a:regular interval,-horizontal sync pulses ~not shown) ~, equally distribut~ed with respect to time between~two adjacent vertical sync pulses, ànd an analog information signal (not shown) which follows each hor-izontal sync~pulse ànd represents a flow of picture elements along a horizon-: ~ .
tal scanning line. Incidentally, in every drawing hereinafter referred to,thick signal lines represent the paths for parallel binary slgnals and thin :~ signal lines, those for eithèr analog signals or time-serial binary signals.
Further, signal lines and signals may be sometimes represented by the same terms.
: ~ The video slgnals are respectlvely supplied to their corresponding :: : :
encoding units 21 to 2n through input termlnsls 11 to 1 and encoded : _ 5 -:: ~ :

' ~L3;~ 3 into digitized video signals. Fach of the digitized video signals produced from the encoding units 21 to 2n are supplied to a first multiplexer 12 for multiplexing the digitized video signals depending on their amount supplied.
The multiplexed video signal is given to a receiver over suitable transmis-sion means (not shown). Since the encoding units 21 to 2n are identical to each other, description on only the unit 2l will be made hereafter.
The video signal is supplied through the input terminal 11 to a sync pulse separator 3 used in the encoding unit 21, which separates sync ; puises therefrom. Also, said video signal through the input terminal 11 is given to an encoder 4 responsive to the horizontal sync pulses fed from the separator 3 so that the analog video information can be encoded into predeter-mined codes based on the interframe encoding and variable-length encoding op-erations at a predetermined sampling rate and in synchronism with the hori-zontal sync pulses. For the detail-s of the encoder 4, reference is made to an article titled "Composite Interframe Coding of NTSC Color Television Sig-nals" published in National Telecommunications Conference'i, Vol. 1, pp.
06.4-1 - 4, 1976. A video-frame-sync code generator 14 produces video-frame-.

sync codes 81 each indicative of a picture frame end. A multiplexer 13 is responsive to the odd field vertical sync pulse V0 supplied from the separ-ator 3 to muItIplex the video-frame-sync code 81 and the encoded codes 82 of `~ the encoder 4. The output of the multiplexer i3 is then fed to a first buf-: I .
fer memory 6. Referring to Figure 3b, reference characters P and C designate the video-frame sync code ànd significant codes, respectively.
A read/write controiier 7 of Figure 2 is comprised of a first counter 71 which counts writing pulses 86 supplied through the second multi-plexer 13 from the encoder 4 and produces write-in address signals, and a second counter 72 which counts reading pulses 87 supplied through a third multlplex-er 10 from the first multiplexer 12 and produces read-out address signals, and a subtractor 73 responsive to the output of the first and second counters 71 and 72 to perform a subtraction thereon and thereby to produce a buffer-occupancy code indicative of a buffer occupancy state of the buffer memory 6.
The write-in and read-out address signals given from the counters 71 and 72 are applied to the buffer memory 6. On the other hand, the output of the sub-tractor 73 is fed to the first multiplexer 12.
A video-frame-sync code detector 9 receives the codes read out of the buffer memory 6 to detect the video-frame-sync codes involved therein.
The detection signal 84 fed from the detector 9 is then sent to both a third multiplexer 10 and a timer 8. The timer 8 (not shown in Figure 1) includes a clock generator for generating clock pulses, and a counter for initiating its counting upon receiving the vertical sync pulses 88 obtained from the separ-ator 3 and for terminating it upon receipt of the detection signal 84 given from the detector 9 to produce a code 85 indicative of a time interval there-between. ~The time-indicating code 85 is supplied to the third multiplexer lO
responsive to the signal 84 for multiplexing the codes read out of the buffer ~memory 6 and said time-indicating code 85. The output of the third multiplex-;~ er 10 is applied to the next stage, that is, a parallel/serial converter 11.
Referr mg to Figure 4a corresponding to Flgure 8(g) referred tohereafter, "A'i denotes the time-indicating code 85; "c", a portion of the significant codes C of Flgure 8g; and CHII to CH13, time slots assigned to the codes given from the encoding unit 21. ~ ~ ;

' _ 7 .~.

:

~:~3;~Z~3 Each of the time slots CHll to CH13 has a constant capacity of, for example, 256 bits. Whereas, the totàl bit numher of the codes involved in one picture frame of Figure 3b is, 256 bits in the case of a still pic-ture, and otherwise more than 256 bits. As a result, the time slot CHll usually accommodate a portion c' of the codes of one picture frame and the remaining two time slots CH12 and CH13 (if necessary more than two) shares the other portion.
The multiplexer 12 will be described in more detail in connection with Figures 5 and 8. It is assumed for simplicity of description that the multiplexer 12 is connected to three encoding units 21 to 23. A register 15 responsive to frame sync pulses (Figure 8a) supplied from a multiplexer controller 19 stores first four significant bits of the buffer-occupancy codes 83 given from the read/write controllers 7 of the respective encoding ; units 21 to 23. A channel-assignment-signal generator 16 consisting of an ROM ~read only memory) and coupled to the register 15 produces a channel-assignment signaI (Figure 8b) in response to the output of the register 15.
A counter 18 coupled~to both the multiplexer l9 and a clock generator 20 for generating clock pulses for transmission control, counts the clock pulses and is reset by the frame sync signal (Figure 8a). A read-out signal controller 17 coupled to the channel assignment-signal generator 16 and the counter 18 produces gate pùlses (Figures 8e, 8h and 8k) based on the output thereof.
These gate pulses are then fed to AND gates 21, 22 and 23, respectively, to which the clock pulses ~are applied from the clock genera~or 20. The AND
gates 21 to 23 produce respectively the signals 87, 87' and 87" (Figures if, 8i, and 81) one of which is supplied to tXe read/wri~e controller 7 through the third multiplexer 10. NAND gates~ 24, 25, and 26 receive respectively, at their one input terminals 24a, 25a, and 26a,~ the codes fed from the~par-alleljserial converters 11 ~ ~ 8 :

1~3;~:Z~3 of the encoding units 21 to 23, and also receive respectively, at their other input terminals 24b, 25b, and 26b, the signals (Figures 8e, 8h and 8k) given from the read-out signal controller 17. A NAND gate 27 is supplied at its one input terminal 27a with the channel-assignment signal through a parallel/
serial converter 16' from the generator 16, and, at its other input terminal 27b, with an assignment-signal-multiplexing pulse ~Pigure 8c) given from the multiplexer controller 19. On the other hand, a NAND gate 28 receives, at its input terminals 28a and 28b, a frame sync signal (Figure 8d) and the frame-sync-signal-multiplexing pulse (Figure 8a) fed from the multiplexer controller 19, respectively. The output terminals of the NAND gates 2~ to 28 are coupled to the input terminal of another NAND gate 29 which forms an OR gate together with its preceding NAND gates 24 to 28. lhus, the first multiplexer 12 multiplexes the digitized video signals (Figures 8g, 8j and 8m) and the signals (Figures 8b and 8d). The multiplexed video signal appears at the output terminal of the NAND gate Z9.
Referring now to Figures 6 and 7, a detail construction of the multiplexer controller 19 is illustrated together with the clock generator 20. The clock pulses ~Figure 7a) of the generator 20 are applied to a l/N
frequency divider 191 ~where N is an integer equal to the number of clock pulses appearing during one frame time interval from the generator 20) and to four delay circuits 194 to 197 ~the number four comes from the assumption - that the register 15 of Figure 5 stores the four significant bits of the in-coming codes 83). The output of the frequency divider 191 is given to the register 15, the counter 18, and a half-frequency divider 192 as well as the NAND gate 28 as the frame-sync-signal-multiplexing pulse (Figure 7b and Fig-ure 8a). The divider 192 divides the frequency of the frame-sync-signal-multiplexing pulse by 1/2 to produce a channel-assignment-signal multiplex-ing pulse supplied to the NAND gate 27 as the frame sync g _ ~L~3Z243 signal (Figure 7d and Figure 8c). The output of the l/N frequency divider 19 is also fed to the delay circuit 194, the output of which is applied to the next delay circuit 195. The other delay circuits 196 and 197 are responsive to the output of their preceding circuits 195 and 196l respectively. The out-put of the delay circuits 194 to 197 are then supplied to an OR gate 193 to give the channel-assignment-multiplexing pu:Lse (Figure 7c and Figure 8d).
Referring to Figure 9, a receiver 100B used in the first embodiment of this invention is schematically illustrated in a block form. A demultiplex-er 31 is supplied with the multiplexed video signal received from the transmit-ter 100A through an input terminal 30. The demultiplexer 31 functions to sep-arate the supplied multiplexed video signal into n channel (only three chan-nels are shown in Figure 9) digitized video signals which correspond respect-ively to the output of the encoding units 21 to 2n. The demultiplexer 31 sup-plies the n channel digitized video signals to respective decoding units 321 to 32 , each of which serves to decode the received digitized video signal in-to its original vldeo signal. Since theidecoding units 3Zl to 32n are ~denti-cal to each other in their c~rcuit configuration, only the unit 321 will be described hereunder.
A serial/parallel converter 33 converts ~he serial digitized video -, ~ 20 signal of one channel given from the demultiplexer 31 into kime-parallel digit-:
ized video signal. The parallel digitized video s~ignal is then fed to a sec-ond buffer memory 35 ànd temporarily stored therein. A decoder 40 coupled to the second buffer memory 35 is responsive to sampllng pulses supplied from a sampling-clock-pulse~generator 41 for decoding the output of the buffer memory ~35. The decoder 40 wlll be again referred to later by reference to Figure 11.
A video-frame-sync code detector 34 coupled to the converter 33 de-tects the video-frame-sync code involved in the èime parallel dlgitized video signal ~3;2243 to produce a detection signal 89. The signal 89 is supplied to a timer 36 and to a register 38. A read/write controller 42 is identical to the read/
write controller 7 (Figure 2) except that the former is not provided with the subtractor 173. It is therefore understood that the read/write controller 42 responsive to writing pulses supplied through the converter 33 from the de-multiplexer 31 às well as reading pulses from the buffer controller 39 pro-duces write-in and read-out address signals supplled to the second buffer mem-ory 35 for controlling its writing/reading operations. Another video-frame-sync code detector 37 connected to the buffer memory 35 detects the video-frame-sync code read out therefrom to produce a detection signal 88 to be sent to the buffer controller 39. The register 38 responsive to the detection signal 89 stores a first time-indicating code transmitted from the transmitter 100A. The controller 39, which will be described later in more detail by ref-erence to Figure 11, controls both the second buffer memory 35 and the decod-er 40 based on the signals 90 and 95. The video-frame-sync code detect~or 34 or 37 and the timer 36 are identical to their counterparts shown in ~igure 1.
The demultiplexer 31 will be described in more detail referring to Figure 10. A frame-sync-signal detector 43 coupled to the input terminal 30 detects the frame sync signal given from the received multiplexed video sig-2Q cal for produc mg a slgnal 91 to be supplied to a demultiplexer controller 44and to a countar 46. The controller 44 responsive to the si$nal 91 as well as clock pul~ses 95 g~lven from~a clock generator Sl produces a channel-assign- ~;
ment-signal-multiplexing pulse, and consists of the delay circuits 194 to 197 ` and the OR gate l93 shown in Figure 6. The signal 92 is supplied to a regis-ter 45 for storing the channel-assignment signal involved in the received multiplexed video;signal, resulting in p~oducing a signal 93 indicative of the channel-assignment signal. The counter - 1 1 - ~ :

:: :
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~3Z:~43 46 counts the clock pulses 95 given from a clock generator 51 and is reset by the signal 91. A write-in signal controller 47 consisting of an ROM produces gate pulses in response to the signals 93 and 94 and the clock pulses 95.
The output of the controller 47 is supplied to AND gates 48, 49 and 50 for se-lectively allowing them to pass the clock pulses 95 therethrough. The clock pulses passing through the AND gate 48 are supplied as the writing signals to the read/write controller 42 through the serial/parallel converter 33 as shown in Figure 9, while the remaining clock pulses passing through the AND
gates 49 and 50 are supplied to counterparts (not shown) of the decoding units 322 and 323 of Figure 9.
Figure 11 is a detailed block diagram of the buffer memory control-ler 39 and its known peripheral blocks. The controller 39 comprises a regis-ter 521, two comparators 522 and 523, a buffer control circuit 52 consisting of an ROM, and three NAND gates 54 to 56 functioning as a whole as a single OR gate. The register 521 responsive to the signal 88 supplied from the de-tector 37 stores the first and the second time-indicating codes 85 ('~s) and 90 ('~R)' respectively. The comparators 522 and 523 function to produce sig-nals indicating the following three different formula or conditions depending upon relations between~s + ~R and ~ and Q:

~ ¦~ S ~R ~D ¦ < ~ ............. ;. (~) S + ~R ~D > ~ .... (2) S + ~R `~D <- ~ .... ~3) where Q : a predetermined positive real number; and n : a signal indicative of a predetermlned time ]nterval determined by transmlssion speed over a transmission line used as well as capacities of the buffer memories 6 and 35.

~ ~ X
:: :

~L~3Z243 In response to the signals given from the comparators ;22 and 523, the controller 53 produces binary "1" and/or "O' depending on the abo~e conditions. Specifically, the controller 53 consisting of an RO~ pro-duces the follo~ing logical values depending on the conditions (1) to (3):
(a) If the condition (1) is satisfied, binary "O" appears on the lines 531 and 533, and a binary "1" appears on the line 532;
(b) If the condition (2) is satisfied, a binary "1" appears on ~; all the lines 531 to 533; and (c) If the condition (3) is satisfied, a binary "1" or "O"
appears on the line 531 and binary "O" appears on the lines 532 and 533-`:

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Therefore, the NAND gate 56 produces a binary "1" on its ou~put terminal, if all the input of the N~iD gate 54 are binary "1" or all the input of the N~ND gate 56 are binary "1".
Since the receiver lOOB of Fig. 9 functions in just a reverse manner as the transmitter lOOA e~cept the buffer memory controller 39, for understanding of the operation of the receiver lOOB, the operations limited to the controller 39 ~ill be described in detail hereinafter.
First of all, let us consider the case where the above condition (1) is satisfied, namely, the buffer memory 35 has a proper amount of codes stored so that the decoder 40 is requested to perform its decoding operation. In this case, the controller 53 produces binary "1" on the signal line 532 and binary "O" on the signal lines 531 and 533. For this reason, the decoder 40 receives binary "O" appearing on the line 533, ànd as a result, the decoding operatlon of codes read out from the second buffer m.emory 35 is not prohibited, allowing the request signal fed to ehe input terminal 551 of the gate 55 from the decoder 40 to ~ -become binary "1". On the other hand, since the input terminal 552~ of the gate 55 receives a binary "1" through the signal line 532~ all the input signal to the NAND gate 55 becomes binary "1", so that the N~iD
gate 56 may produce the write signal responsive to the request signal.
Next, considering the case where the~condition (2) is satlsfied.
In this instance, codes more than the predetermined amount are stored in the buffer memory 35. Since binsry "1" appearing on the line 533 makes the decoder 40 stop its decoding operation, the decoder 40 produces binary "O" which is applied to ons input terminal of the N~.ND
gate 55. On the other hand, in response to a oinary "l"~appearing on the lines 531 and 532~the NAND gaCe 54~allows the clock pulses given from the clock generator 41 to pass the NAND gates 54 and 56. Therefore, .

~L1322~3 -- 1~

the write-in signals corresponding to the passed clock pulses are fed to the second buffer memory 35. This means that the codes scored in the memory 35 are read out in response to the applied clock pulses.
The codes thus read out are supplied to the decoder, but no decoding operation can be performed until the condition (1) is satisfied.
This means that the codes are read out in vain from the buffer memory 35 because the rate of the clock pulse generation is greater than the that of the request signal generation.
Finally, let us consider the case where the condition (3) is satisfied, wherein the amount of codes stored in the buffer memory 35 ~ does not reach the predetermined level. It is apparent in this `~ instance that the clock pulses given from the clock generator 41 are . ~
not allowed to pass the NAND gate 56. As a result, the codes stored : ;~ in the memory 35 are not read out therefrom until the first time-indicating signal 90 (~Rj becomes to satisfy the condition (1). While the condition (3? is satisfied, tXe decoder 40 remains in its non-decodlng state ~ithout producing output or, otherwise, it may be designed to produce the preceding picture frame information stored in a frame memory used in the decoder 40. However, this operation of the decoder~40 lS not~directly concerned with thls inveDtiOn, so further description thereof will be omitted.
In~the first embodlment, the supply of the~write-in si~nai or clocks to the second buffer memory 35 is controlled by the time-indlcatlno codes7 s,-ZR, and 7D. However, the suoply of the write-in signal to the second buffer memory 35 can be controlled by the buffer~
occupancy code ~and the read-our signal gsneratioD rates of botD the first and the second buffer memories 6 and 35 and by the write-in rate oP codes into ths first buffer memory 6.

- - . ..... . . .

~132:ZA3 ~ lore specifically, it will be understood that the folloT~ing equations are given:

Vs(t) = V2(tl,0 ................... (4) WS(t) = WR(tt;~ ................... (S) where Vs(t): the read-out rate of the codes given from the first buffer memory 6;
VR(t): the write-in rate of the codes into the second buffer memory 35;
: delay time tsecond) of signal transn.ission over a ~; 10 transmission line;
Ws(t): the ~.~rite-in rate of the codes into the first buffer memory 6;
WR(t): the read-out rate of the codes from the second bufLer memory 35;
G~ : delay time (second) from the write-in operation of the codes into the first buffer memory 6 to the read-out operation of the codes given from the second bufer memory 35, wherein ~ ~~ t d ( ~ is therefore equal to the sum of respective delay times of the codes passing through the two buffer memories 6 and 35.) On the other hand, the amount of codes stored in the first buffer memory 6 at a given time t can be expressed by t~ ~ ~
BS(t) ~ J ~Ws(r) - Vs(~) d~ ~ --------- (6) Like~ise, the amount of codes s~ored 1~ .ne second buffer memory 3~ a~
25 a given tlme t can be expressed by ~ ;

~: :
..
. ~
: .
:

~3;~:243 r t BR(t) = J [VR(~) - WRf~l)] d~ ................................................................ (7) Under the conditio~s given by the equations (4) and (5), ~ rt +
BR(t + ~) =J [VR(I) ~ WRt~)] d~

~t +~
-I EVs(~ ~~) ~ t~s(~ ~~)l d~
J
rt +~
=J :Vs(~)d - BS(t) ...,,, (8) t ~ ~
= ~ VR('T)dt - BS(t) ...... (9) J(t ~
; From the equations (6) and (7), ~e obtain B5(t)+~R(t+d) = J-t[~s(~)-vs(~)]d~ [VR(~)-wR(~]

t-~WS(~)d ~ ~ :
: : : t : .: BR~t +d^ ~ = Ws (~d - BS (t) . . ., (10) ~ In the case ~.~here the transmission speed i8 a function of time, if :
delay time from ehe Nrite-in operation of codes into the first buffer : ~e ry 6 to the read-out operation~of~the~same frorn th2 second buffe : ::~ : -memor,~35 is O~(constant), the equatiorls (8), (9) and (10) are 15 : satisfied. It is therefore understood that lf the read-out timiDg at . the buffer memory 35 is so controlled as to satisfy the equations (8), (9) and (10~, ~the above delay timeO~ is made constant.
~,:

~ :: ~: ~ : : : :

~3Z243 The following three embodiments of this invention are respectively constructed based on the equations (8) to ~10), wherein their parts correspond-ing to those in the first embodiment of Figures 1 to 11 are designated by like reference characters.
Referring to Figures 12 and 13, a transmitter 200A used in a second embodiment of this invention comprises a plurality of encodi~g units (only one unit 53 is shown) and a multiplexer 62. An encoder 4 is supplied, at an input terminal 11, with the video signal for encoding into a digitized video signal.
The output of the encoder 4 is applied to a buffer memory 6 for temporary stor-age. A register 60 responsive to a first control signal 93 (Figure 13(p)) sup-plied from the multiplexer 62 stores a buffer-occupancy code indicative of a buffer-occupancy state of the buffer memory 6. A counter 59 responsive to the first control signal 93 as well as a second control signal 94 (Pig. 13(o)) com-mences and terminates its counting of write-in pulses 94' supplied through an-other multiplexer 10 fed from the multiplexer 62, respectively. The output of the counter 59, therefore, indicates the amount of codes;read out of the buffer memory 6 during the time interval defined by two applications of the first and the second control signals 93 and 94 to the counter 59. The output of the ~counter 59 and the register 60, which respectively correspond to JV5(l)d and to B ~t) of the equation (8), are applied to a subtractor 61 for performing a sub- -~: ~ S
traction thereon. The output 102 of the subtractor 61 is supplied to the multi-plexer 10 responsive to the second control signal 94 for multiplexing the output code 102 and the codes read out of the buffer memory 6. The multiplexer 62 multiplexes the output of the plurality of encoding units as mentioned previous-ly. First control signals of a second and a third encoding unlts (not shown) are depicted by Figures 13r and 13t, respectively, and on the other hand, sec-ond control signals of the second~and the third encodlng unlts by Figures 13q and 13s, respectively. The muItiplexer 62 operates in the same manner as the ~32~43 multiplexer 12 of Figure 1 except for the generations of the first and the sec-ond control signals 93 and 94, and the other blocks such as a read/write con-troller 7 and a parallel/serial converter 11 are identical in their functions to their counterparts. The first and the second control signals can be obtained by adding an ROM to the block diagram of Figure 5, which is controlled by the output signal (used as an address) of the half-frequency divider 19.
Referring to Figure 14, a receiver 200 B for the second embodiment comprises a demultiplexer 63 and a decoding unit 66l. The demultiplexer 63 is supplied, at an input terminal 30, with the multiplexed video signal transmittedfrom the transmitter 200A, so that the multiplexed video signal can be demulti-plexed into plural digitized video signals, and the digitized video signal transmitted from the encoding unit 581 of Figure 12 can be applied to the decod-er 661. The demultiplexer 63 supplies a third control signal 95 to another de-multiplexer 64, which sign~l 95 is indicative of the position of the output 102 supplied from the subtractor 61. I'he demultlplexer 64 responslve to the third control signal 95 separates the code 102 from the multiplexed video signal sup-plied through a serial/parallel converter 33 from the demultiplexer 63. The separated code 102 is then stored in a register 65 in response to the third control signal 95. A buffer controller 39 i5 supplied with the output code 102 of the register 65 as well as the output code 96 of a read/write controller 42 corresponding to the left side of the equation (83, and controls the buffer memory 35 so as to satisfy ~he equation (8). The function of the controller 39 is similar to that mentioned to in connection with Figure ll. The demultiplexer ;
63 has the same functions as~the demultiplexer 31 of Figure 9 except for produc-tion of the third coDtrol slgnal 9S. The signal 95 can be readily generated by ~: ~ combination of a frequency dlvider and an ROM (not shown in Figure 14).
Referring to Figure 15, a transmitter 300A and a receiver 300B for use in a third embodiment based on the equation (9), are schematically illus-: : - 19 - ~ :

' . ,; . : : ., ,, ., . , . , ~ , . ~ , .
- . ,: -, ~ . . ~ , ,, ~3ZZ43 trated in a block diagram. The transmitter 300A comprises a plurality of en-coding units (only one unit 671 is shown) and a first multiplexer 68. An en-coder 4 receives, at an input terminal 1l, the television video signal and en-coding it into digitized video signal. The sync pulse separator 3 is also sup-plied with the video signal for separating the sync signals involved therein.
A second multiplexer 13 is responsive to the sync pulses. The read/write con-troller 7, which is coniigured in the same manner as shown in ~igure 2, pro-duces the buffer-occupancy codes 83 which are supplied to the third multiplexer 10. The multiplexer lO responsive to a ourth control signal 96 supplied from the first multiplexer 68 multiplexes the codes 83 and the codes read out from the first buffer memory 6. The multiplexer 68 receives the output of the third multiplexer lO through the serial/parallel converter 11 in order to multiplex the digitized video signal fed :Erom the other encoding units (not shown), and then to transmit the multiplexed video signal to the receiver 300B.
The receiver 300B comprises a demultiplexer 69 and a plurality of de-coding units only one of which is depicted by reference numeral 701. The de-multiplexer 69 is supplied, a* the input terminal 30, with the multiplexed :
video signal transmitted from the transmitter 300A, so that the multiplexed video signal can~be demultiplexed into plural digitized video signals corre-sponding to the output of said encoding units. The demultiplexer 64 respons-ive to a fifth control signal 97 supplied from *he demultiplexer 69 separa~es the buffer-occupancy code 83 from the digitized vldeo slgnal fed from the encoding unit 67. A register~72 stores this signal 83 also in response to the signal 97. A co~nter 71 responsive to the control signal 97 starts to count the write-in clock pulses supplied to the buffer memory~35 and terminates the counting upon receipt of a sixth control signal 98 supplied from the demultiplexer 69 for counting the amount~of write- m clock pulses~supplied to the buffer memory 35 durinA the time in~r~al. The output of ~he cou~ter 71 and the regi=ter 72 :~, : , " . . , ,~ , , ~13~ 3 are supplied to a subtractor i3 which performs a subtraction thereon to pro-duce a signal indicative of the difference. The output of the subtractor 73 corresponds to the right side of the equation (9). The buffer memory control-ler 39 receives the output of the subtractor 73 and the output of the control-ler 42 corresponding to the left side of the equation (9) so as to control the buffer memory 35 based on the received signals in the same manner as mentioned in connection with Figure ll.
In Figure 16, the fourth embodiment of this invention functions to satisfy the equation (10) and comprises a transmitter 400A and a receiver 400B.
It is noted that the transmitter 400A differs from 300A (Figure 15) in that a counter 75 and a subtractor 76 are added to the former. Whereas, the receiver 400B, unlike 300B (Figure 15), is not provided with any counter as well as sub-tractor.
First, description on the transmitter 400A will be given in detail.
The counter 75 responsive to seventh and eighth control signals 99 and 100 both supplied from a multiplexer 77 initiates and terminates its counting of the ; write-in pulses for use in writing the codes from the second multiplexer 13 into the first buffer memory 6. The read/write controller 7~produces the buf-fer-occupancy code 83. The buffer-occupancy code 83 and the output of the counter 75 are supplied to the subtractor 76 to perform a subtraction thereon.
The output 104 of the subtractor 76 corresponds to the right side of the equa-~; tion (lO)~and is multiplexed at the multiplexer lO together with the codes read out fFom~the buffèr memory 6. The receiver 400B is supplied with the multi-plexed video signal from the transmltter 400A. A ninth control signal 101 indi-~`~ cates or specifies a position of the output 104 of the subtractor 76. A regls-ter 80 responsive to the control signal lOl supplied from a demultiplexer 78 ~, stores the output 104. The output of the register 80, that is, 104 and an out-put 105 (corresponding to the left side of the equation (10)) are fed to the :

~13;~Z43 buffer memory controller 39 whlch controls the operation of the second buffer memory 35 so as to satisfy the equation (10).
Since functions of the other blocks have been described in detail by reference to the preceding drawings, further description thereof will be omit-ted.
Although only embodiments of this invention are described and illus-trated hereinbefore, various modifications can be made by those skilled in the art without departing from the subject matter of this invention.

,~ I .
:
. ~ , ., :

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a digital transmission system for television video signals, which comprises a transmitter and a receiver, said transmitter comprising a plurality of input terminals for receiving respective television video signals to be transmitted, a plurality of encoding units for encoding said respective television video signals into digitized video signals, and a multiplexer for multiplexing said respective digitized video signals in a time division manner;
and said receiver comprising a demultiplexer for receiving the multiplexed video signal transmitted from said multiplexer and for separating the same into said digitized video signals, and a plurality of decoding units for decoding said respective digitized video signals given from said demultiplexer into said respective television video signals, the improvement wherein:
each of said encoding units comprises a synchronization pulse sep-arator for separating synchronization pulses involved in said television video signal, an encoder responsive to the separated synchronization pulses for en-coding said television video signal into predetermined codes, a generator for generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchronization codes and the encoded codes of said encoder, a first buffer memory for temporarily storing the multiplexed codes given from said first means, a first read/write controller for supplying write-in and read-out address signals to said first buffer memory and for measuring a buf-fer-occupancy state of said first buffer memory to produce a buffer-occupancy code, second means for measuring a time interval from a time point when said video-frame-synchronization code is written into said first buffer memory to a time point when read out from the first buffer memory and for producing a first time-indicating code representative of said time interval, third means for multiplexing the codes read out from said first buffer memory and said first time-indicating code and for supplying the output therefrom to said first multiplexer; and each of said decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from the correspond-ing encoding unit, a second read/write controller for producing write-in ad-dress signals for writing said multiplexed codes and said time-indicating code into said second buffer memory and for producing read-out address signals for reading out the codes stored in said second buffer memory, fourth means for de-tecting said first time-indicating code involved in said digitized video sig-nal, fifth means for measuring a time interval from a time point when said video-frame-synchronization code is written into said second buffer memory to a time point when read out of the second buffer memory and for producing a sec-ond time-indicating code, and a buffer memory controller for comparing said first and said second time-indicating codes and for controlling said read-out address signal based on the comparison operation.

2. In a digital transmission system for television video signals, which comprises a transmitter and a receiver, said transmitter comprising a plurality of input terminals for receiving respective television video signals to be transmitted, a plurality of encoding units for encoding said respective tel-evision video signals into digitized video signals, and a multiplexer for multiplexing said respective digitized video signals in a time division manner, said receiver comprising a demultiplexer for receiving said multiplexed video signal transmitted from said multiplexer and for separating the same into said digitized video signals, and a plurality of decoding units for decoding said respective digitized video signals given from said demultiplexer into said re-spective television video signals, the improvement wherein:
each of said encoding units comprises a synchronization pulse separ-ator for separating synchronization pulses involved in said television video signal, an encoder responsive to the separated synchronization pulses for en-coding said television video signal into predetermined codes, a generator for generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchronization codes and the encoded codes of said encoder, a first buffer memory for temporarily storing the multiplexed codes from first means, a first read/write controller for supplying write-in and read-out ad-dress signals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer-occupancy code, a register for storing said buffer-occupancy code at a first predetermined time point, second means for counting the amount of said multiplexed codes read out from said first buffer memory from said first predetermined time point to a second predetermined time point, a subtractor for subtracting the output of said register from the output of said second means, third means for supplying both the output of said subtractor and said codes read out from said first buf-fer memory to said multiplexer; and each of said decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from the correspond-ing encoding unit, second read/write controller for producing write-in address signals for writing said multiplexed codes into said second buffer memory and for producing read-out signals for reading out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, fourth means for de-tecting and storing the output of said subtractor involved in said digitized video signal supplied from one of said encoding units, and a buffer memory controller for comparing said second buffer-occupancy code with the output on said fourth means to control said read-out signal based on said comparison operation.

3. In a digital transmission system for television signals, which com-prises a transmitter and a receiver, said transmitter comprising a plurality of input terminals for receiving respective television video signals to be transmitted, a plurality of encoding units for encoding said respective tel-evision video signals into digitized video signals and a multiplexer for multi-plexing said respective digitized video signals in a time division manner, said receiver comprising a demultiplexer for receiving the multiplexed video signal transmitted from said multiplexer and for separating the same into said digitized video signals, and a plurality of decoding units for decoding said respective digitized video signals given from said demultiplexer into said respective tel-evision video signals, the improvement wherein:
each of said encoding units comprises a synchronization pulse separ-ator for separating synchronization pulses involved in said television video signal, encoder responsive to the separated synchronization pulses for encoding said television video into predetermined codes, a generator generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchronization codes and the encoded codes of said encoder, a first buffer mem-ory for temporarily storing the multiplexed codes from said first means, a first read/write controller for suppling write-in and read-out address signals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer-occupancy code, second means for supply-ing said first buffer-occupancy code at a first predetermined time point and said multiplexed codes read out from said first buffer memory to said multiplex-er; and each of said decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from corresponding en-coding unit, second read/write controller for producing write-in address signals for writing said multiplexed codes into said second buffer memory and for pro-ducing read-out address signals for reading out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, third means for detecting and storing said first buffer-occupancy codes involved in said digitized video sig-nal supplied from said corresponding encoding unit, fourth means for counting the amount of write-in of said multiplexed codes from the detection of said first buffer-occupancy code to a second predetermined time point, a subtractor for subtracting the output of said third means from the output of said fourth means, and a buffer memory controller for comparing said second buffer-occup-ancy code with the output of said subtractor to control said read-out address signal of said second read/write controller.

4. In a digital transmission system for television video signals, which comprises a transmitter and a receiver, said transmitter comprising a plurality of input terminals for receiving respective television video signals to be transmitted, plural encoding units for encoding said respective television video signals into digitized video signals, and a multiplexer for multiplexing said digitized video signals in a time division manner, said receiver comprising a demultiplexer for receiving said multiplexed video signal transmitted from said multiplexer and for separating the same into said digitized video signals, and plural decoding units for decoding said respective digitized video signals into said respective television video signals, the improvement wherein:
each of said plural encoding units comprises a synchronization pulse separator for separating synchronization pulses involved in said television video signal, an encoder responsive to the separated synchronization pulses for encoding said television video signal into predetermined codes, a generator for generating video-frame-synchronization codes each indicative of the end of one picture frame of said television video signal, first means for multiplexing said video-frame-synchronization codes and the encoded codes of said encoder, a first buffer memory for temporarily storing the multiplexed codes from said first means, a first read/write controller for supplying write-in and read-out address signals to said first buffer memory and for measuring a buffer-occupancy state of said first buffer memory to produce a first buffer-occupancy code, sec-ond means for counting the amount of write-in of both said encoded codes of said encoder and said video-frame-synchronization codes into said first buffer mem-ory, a subtractor for subtracting the output of said first read/write controller from the output of said second means, third means for supplying the output of said subtractor and the multiplexed codes read out from said first buffer memory to said multiplexer; and each of said plural decoding units comprises a second buffer memory for temporarily storing said digitized video signal supplied from corresponding encoding unit, a second read/write controller for producing write-in address signals for writing said multiplexed codes into said second buffer memory and for producing read-out address signals for reading out the codes stored in said second buffer memory and for measuring a buffer-occupancy state of said second buffer memory to produce a second buffer-occupancy code, fourth means for de-tecting and storing the output of said subtractor involved in said digitized video signal from said corresponding encoding unit, and a buffer memory control-ler for comparing said second buffer-occupancy code with the output of said fourth means to control the read-out address signals of said second read/write controller.