Okamoto, et al.: A Consumer Digital VCR for Digital Broadcasting
`
`643
`
`A CONSUMER DIGITAL VCR FOR DIGITAL BROADCASTING
`Hiroo Okamoto, Hitoaki Owashi, Nobutaka Amada,
`Shigeru Yamazaki, Takaharu Noguchi, and Kuniaki Miura*
`Video & Personal Media Systems Div., Hitachi, Ltd.
`*Multimedia Center, Hitachi Home Electronics America, Inc.
`
`ABSTRACT
`A consumer use digital VCR for the digital
`broadcasting has been developed. This VCR can
`record the compressed digital video signal. The
`maximum recording data rate is 25 Mbps.
`
`successfully developed this new digital VCR using
`various distinctive technologies.
`In this paper, the new digital VCR concept
`and the key technology developed for the digital
`VCR are described.
`
`1. Introduction
`The digital broadcasting service using
`MPEG2 as the picture compression technology
`s t a r t e d in t h e United S t a t e s l a s t year. This
`movement has a momentum spreading to all over
`the world.
`There is a strong demand in the market to
`expect an early appearance of the digital recording
`VCR for the digital broadcasting at a n affordable
`price for c o n s u m e r s . Although t h e d i g i t a l
`broadcasting service has started, this does not
`mean the current analog broadcasting service will
`soon disappear. Instead, it is believed that both
`analog and digital services will coexist for a long
`time.
`
`Furthermore, compatibility of t h e rental
`video t a p e a n d t h e recorded t a p e library is
`essential.
`Based on these market requirements, we
`have concluded the new digital VCR needs to have
`the function of recording the broadcasting signal
`digitally on t h e tape, retaining all t h e analog
`functions current analog VCRs have. We have
`
`2. Basic Concept
`I n order t o keep interoperability a s a n
`analog VCR, the new digital VCR needs to have
`compatibility with conventional VCRs.
`In order to realize a consumer affordable
`price, the specifications of the mechanism, tape
`and heads should be as close to the current analog
`VCR as possible.
`Considering these two conditions, we have
`concluded t h e best solution is t h e bit stream
`recording. The definition of t h e bit s t r e a m
`recording is that it records the input digital bit
`stream digitally on the tape and reproduces the
`same digital bit stream. This is a transparent
`recording and it does not depend on the digital
`broadcasting system, assuring the expandability
`to various multimedia applications.
`The digital VCR records the packet data
`which is transmitted from the receiver, and is sent
`back to the receiver with the same format and the
`same interval as the recording data a t playback.
`Table 1 shows the recording mode of the
`digital VCR. The VCR works a t several recording
`d a t a r a t e modes w i t h o u t c h a n g i n g a d r u m
`
`Manuscript received June 12, 1995
`
`0098 3063/95 $04.00 1995 IEEE
`
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`IEEE Transactions on Consumer Electronics, Vol. 41, No. 3, AUGUST 1995
`
`Table 1 Recording Mode of the Digital VCR
`
`Mode
`I
`JI
`m
`
`t
`
`Recording data rate Maximum recording time
`6.25 Mbps
`8 hours
`12.5 Mbps
`4 hours
`25 Mbps
`2 hours
`
`Recording data
`MPEG b i t stream
`MPEG b i t stream
`ATV b i t stream or
`Time compression data
`
`> Tuner -+ Demod + , ! ~ ~ ~ ~ c t i o n +
`
`Rece i ver
`
`A
`
`Cond i t i ona I
`
`De-
`
`Access + Compression -*
`.
`
`Video
`&
`Aud i o
`
`Digital Interface
`
`t
`
`Record i ng
`
`Reproduced
`Si gna I Processor
`
`Memory
`
`Memory
`
`Analog input
`
`Ana I og Output
`
`Fig. 1 The Digital VCR for The Digital Broadcasting S y s t e m
`
`revolution speed. Therefore this VCR can record
`various digital signals. The mode I is the long play
`mode. The mode 11 is the mode for recording the
`current digital broadcasting signal. And the mode
`I11 is the mode for recording the digital HDTV
`(ATV) b r o a d c a s t i n g signal. T h e m a x i m u m
`recording data rate is 25 Mbps at the mode 111. A
`maximum recording time is eight hours a t the
`mode I.
`
`3. Structure of The Digital VCR
`We have realized the transparent recording
`
`digital VCR using the current analog VCR and the
`digital recording and reproducing circuits. To
`realize the compatibility with the current analog
`VCRs, we have adopted a 1/2-inch oxide tape and a
`drum diameter of 62 mm because they are widely
`used in the current analog VCRs.
`The main issue of the transparent recording
`is that the VCR must transmit the reproduced
`packet data with the same timing as the received
`data. Therefore we regenerate the interval of the
`reproduced packet d a t a using t h e time stamp
`which is added to the received packet data.
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`Okamoto, et al.: A Consumer Digital VCR for Digital Broadcasting
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`
`Fig. 1 shows a block diagram of the digital
`VCR and the digital broadcasting receiver.
`At recording, the receiver sends the packet
`data to the VCR through the digital interface. Fig.
`2 shows the configuration of the recording packet
`data. The packet data is transmitted with the
`packet time stamp which indicates the interval of
`the packets.
`The recording signal processor converts the
`received packet data into track format data of the
`VCR. The track format comprises several blocks.
`These block data are recorded on the tape by the
`rotary heads.
`At playback, the VCR corrects the errors
`which occurred a t reproducing and converts the
`data back into the packet format. After that, the
`interface circuit of the VCR regenerates the
`interval of the reproduced packet data using
`t h e time s t a m p and sends it back to t h e
`receiver through the digital interface.
`The receiver decompresses the received
`packet d a t a to the video signal and audio
`s i g n a l t h e s a m e a s t h e c a s e t h a t
`decompresses the broadcasting signal.
`Furthermore, this VCR can record and
`reproduce t h e analog video signal like a
`current VCR.
`
`TIME
`STAMP
`
`PACKET DATA
`
`Fig. 2 Packet Configuration
`
`4. Synchronization at Recording
`To regenerate the interval of t h e packet
`d a t a , t h e recording r a t e of t h e VCR must be
`synchronized with the packet transmission rate.
`Therefore the VCR synchronizes the recording
`r a t e a n d t h e d r u m s p e e d w i t h t h e p a c k e t
`transmission rate using the time stamp.
`Fig. 3 shows the recording circuit of the
`digital VCR.
`At first, the interface circuit detects the
`time stamp in the received packet data and sends
`
`Packet
`
`Rece i ved
`Packet
`
`1 track-
`
`_ _ _ _ _
`
`<-
`m 121
`I
`/
`
`
`Recording
`Data
`
`I
`
`1
`
`_ _ _ _ _
`
`n
`
`I
`
`output
`Packet
`
`_ _ _ _
`
`Fig. 4 Packet Transmission Timing
`
`Drum
`Servo
`
`Master
`
`Record i ng
`Signal
`
`Counter
`
`PLL
`
`f
`
`Memory
`
`Time
`Stamp
`
`-
`
`Digital
`Input
`
`Fig. 3 Recording Circuit of the Digital VCR
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`it to the PLL circuit. The PLL circuit generates
`the recording master clock for the recording signal
`processor and the drum servo circuit using this
`time stamp. This master clock is synchronized
`with the packet time stamp rate. Therefore
`the recording signal processor and the drum
`rotation of the VCR are synchronized with the
`transmission rate of the packet.
`Fig. 4 shows the transmission timing of
`the packet. The packets data received in the
`half rotation of the drum is recorded in one
`track.
`At playback, the interface circuit of the
`VCR r e g e n e r a t e s t h e i n t e r v a l of t h e
`reproduced packet data using the time stamp
`and the local oscillator which oscillates the
`same frequency as t h e t i m e s t a m p r a t e .
`T h e r e f o r e t h e t r a n s m i s s i o n t i m i n g i s
`completely regenerated t h e s a m e a s t h e
`received timing.
`
`4. Recording Format
`The configuration of the packet d a t a
`depends on the digital broadcasting system.
`Therefore t h e VCR adopts several packet
`configurations. I n case t h a t the size of the
`packet is 188 b y t e s , one p a c k e t d a t a is
`allocated in two blocks. And, in case that the
`size is less than 140 byte, two packet data is
`allocated in three blocks. Fig. 5 shows the
`block configuration. The block consists of sync.
`code, I D code, t h e packet d a t a a n d error
`correction codes.
`Fig. 6 shows the error correction code
`configuration. At the MPEG data recording
`system, a n error correction capability is very
`important. Because, if a n uncorrectable error
`is occurred in the intra frame data at playback,
`several frames of the data can not be decoded.
`Therefore we adopt the triply encoded Reed-
`
`Solomon code for error correction. The C1 code
`consists of one block data. The C2 code consists of
`one track data. And the C3 code consists of 12
`tracks data. Fig. 7 shows the error correction
`
`I S Y N C l l D I
`
`PACKET DATA
`
`Ici PARITY~
`
`Fig. 5 Block Configuration
`
`<-'
`
`1 block .->
`
`T
`I 1 track
`
`Cl
`PAR I TY
`
`Fig. 6 Error Correction Code Configuration
`
`1 E+OO
`
`1 E-05
`
`1E-10
`
`1E-15
`
`1 E-20
`
`1 E-25
`
`1 E-30
`
`1 E-35
`
`1 E-40
`
`0. 1
`
`0. 01
`Byte Error Rate
`
`0.001
`
`Fig. 7 Error Correction Capability
`
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`Okamoto, et al.: A Consumer Digital VCR for Digital Broadcasting
`
`647
`
`MARGIN
`
`AUX
`
`GAP
`
`DATA
`
`Fig. 8 Track Format
`
`probability of the random error. An uncorrectable
`error probability of less than 1 X lo-'' has been
`obtained w h e n a byte e r r o r r a t e is 1 X lo-'.
`Furthermore a burst error of 0.67 track can be
`corrected.
`Fig. 8 shows t h e t r a c k format. A track
`consists of the auxiliary data area, the packet data
`area and the subcode data area. This track data
`are modulated based on scrambled NRZI. Total
`recording bit rate after modulation is 19 Mbps per
`channel.
`
`5. Specifications of The VCR
`Table 2 shows t h e specifications of t h e
`digital VCR. This VCR h a s three modes. In any
`mode, a d r u m speed is 1800 revolutions per
`
`minute.
`The mode I is the long play mode. At this
`mode, a t a p e speed is 16.68 mm/s. T h e VCR
`records two tracks per two drum revolutions. A
`maximum recording rate is 6 . 2 5 Mbps a n d a
`maximum recording time is 8 hours.
`The mode I1 is the mode for the current
`digital broadcasting system. At this mode, a tape
`speed is 33.35 mm/s. The VCR records two tracks
`per one drum revolution. A maximum recording
`rate is 12.5 Mbps and a maximum recording time
`is 4 hours.
`The mode I11 is the mode for the HDTV
`digital broadcasting system like the ATV system.
`At this mode, a tape speed is 66.7 mm/s. The VCR
`records four tracks per one drum revolution using
`
`Table 2 Specifications of the Digital VCR
`
`Item
`
`Mode I
`
`Mode ID
`
`Tape
`
`Drum Speed
`Tape Speed
`Number of Heads
`Transmi ss i on Rate
`Error Correct i on Code
`Modu I a t i on Method
`Record i ng B i t Rate
`Track Pitch
`Minimum Wave Length
`
`1/2
`
`Mode II
`inch Oxide Tape
`1800 m i n-'
`33.35 mn/s
`
`16.68 mn/s
`
`66.70 mn/s
`4
`2
`2
`25.0 Mbps
`12.5 Mbps
`6.25 Mbps
`Tr i p I y Encoded Reed-So I Omon Code
`S-NRZ I
`19 Mbps/ch
`29 , u m
`0.63 ,u m
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`4 heads. A maximum recording rate is 25 Mbps
`and a maximum recording time is 2 hours.
`A track pitch is 29 p m. A minimum wave
`length is 0.63 p m.
`
`6. Recording and Reproducing
`Characteristics
`Fig. 9 shows the power spectrum of the
`reproduced signal. Fig. 9(a) shows the power
`spectrum of the system noise. Fig. 9(b) shows the
`power spectrum of the reproduced signal when a
`signal of 4.75 MHz (2T pattern) is recorded. Fig.
`9 ( c ) s h o w s t h e p o w e r s p e c t r u m of
`t h e
`reproduced signal when S-NRZI modulated
`signal is recorded. A head width is 40 p m . A
`signal-to-noise ratio of 26 dB (Spp/Nrms, Signal
`frequency = 4.75 MHz) has been obtained.
`Fig. 10 shows t h e eye p a t t e r n of t h e
`reproduced signal.
`A byte error rate of less than 5 X 10.’ has
`been obtained.
`
`7. Conclusions
`A digital VCR for the digital broadcasting
`has been developed. The new VCR has realized
`the transparent digital bit stream recording by
`u s i n g t h e newly-developed d i g i t a l s i g n a l
`processor and additional heads.
`The maximum recording rate is 25 Mbps
`and maximum recording time is 8 hours a t the
`recording rate of 6.25 Mbps.
`We have confirmed t h a t it is possible to
`produce a digital VCR which has a n outstanding
`digital quality, a t a consumer affordable price,
`r e t a i n i n g a l l t h e a n a l o g f u n c t i o n s of t h e
`conventional analog VCR.
`
`Tp = 29 p m , T w = 40 pm
`
`10 dB/div
`
`SPAN 20 MHz. CENTER 10 MHz
`
`Fig. 9 Power Spectrum of The Reproduced
`Signal
`
`Fig, 10 Eye Pattern of The Reproduced
`Signal
`
`H i t a c h i , L t d . f o r t h e i r a s s i s t a n c e i n t h e
`development of this VCR.
`
`Acknowledgment
`The a u t h o r s would l i k e t o t h a n k t h e
`members of Multimedia Systems R 8z D Division,
`
`References
`[l] M. S . Deiss, “A DBS Television System using
`M P E G C o m p r e s s i o n a n d H i g h P o w e r
`
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`
`Okamoto, et al.: A Consumer Digital VCR for Digital Broadcasting
`
`649
`
`Transponders", 1994 ICCE, TUPM 5.6, J u n e
`1994.
`[2] R. Hopkins, "Digital Terrestrial HDTV for
`North America", IEEE Trans. on Consumer
`Electronics, CE-40, No.3, pp. 185-198, August
`1994.
`[3] H. Okamoto, e t al, "A Consumer Digital VCR
`for Advanced Television", IEEE T r a n s . on
`Consumer Electronics, CE-39, No.3, pp. 199-
`204, August 1993.
`
`Biographies
`
`Hiroo Okamoto is a Senior
`Engineer in the Development
`D e p a r t m e n t a t Video &
`P e r s o n a l Media S y s t e m s
`D i v i s i o n , H i t a c h i L t d . ,
`Y o k o h a m a , J a p a n . H e
`received the B.S. degree and
`t h e M . S . d e g r e e f r o m
`Kumamoto University in 1980.
`Since then, he has been with
`Hitachi and engaged in the
`development of digital audio
`and video products, especially
`i n t h e f i e l d of s i g n a l
`processing circuits.
`
`Hitoaki Owashi is a Senior
`Engineer in the Development
`D e p a r t m e n t a t Video &
`P e r s o n a l M e d i a S y s t e m s
`D i v i s i o n , H i t a c h i L t d . ,
`Y o k o h a m a , J a p a n . H e
`received his B.S. and M.S.
`degrees from Tokyo Institute
`of Technology, in 1980. Since
`then, he has been engaged in
`the research and development
`of home use and broadcast use
`VCRs.
`
`Nobutaka Amada i s a n
`Engineer in the development
`d e p a r t m e n t a t V i d e o &
`P e r s o n a l Media S y s t e m s
`D i v i s i o n , H i t a c h i L t d . ,
`Y o k o h a m a , J a p a n . H e
`graduated from Wakayama
`Technical College in 1974.
`Since then, h e has been with
`Hitachi and engaged in the
`development of digital audio
`and video products.
`
`Shigeru Yamazaki i s a n
`Engineer in the development
`d e p a r t m e n t a t Video &
`P e r s o n a l Media S y s t e m s
`D i v i s i o n , H i t a c h i L t d . ,
`Y o k o h a m a , J a p a n . H e
`g r a d u a t e d f r o m O s a k a
`Prefectural Technical College
`i n 1975. Since then, he has
`b e e n w i t h H i t a c h i a n d
`engaged in the development of
`d i g i t a l a u d i o a n d v i d e o
`products, especially i n the
`field of magnetic recording
`technology.
`
`Takaharu Noguchi i s a
`S e n i o r E n g i n e e r i n t h e
`development department a t
`Video & P e r s o n a l M e d i a
`Systems Division, Hitachi Ltd.,
`Y o k o h a m a , J a p a n . H e
`received the B.S. degree from
`Hiroshima University in 1973.
`Since then, he has been with
`Hitachi. Since 1979, he has
`b e e n e n g a g e d i n t h e
`development of digital audio
`and video products.
`
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`IEEE Transactions on Consumer Electronics, Vol. 41, No. 3, AUGUST 1995
`
`Kuniaki Miura is a General
`M a n a g e r of M u l t i m e d i a
`C e n t e r , H i t a c h i H o m e
`Electronics America, Inc.,
`Norcross, Georgia, USA. He
`received the B.S. degree from
`Tokyo University in 1973.
`Since then, he has been with
`Hitachi and engaged in the
`development of t h e signal
`processing a n d recording
`technology of video products.
`He is currently i n charge of
`multimedia business.
`
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