Note: Descriptions are shown in the official language in which they were submitted.
`. I I
PHI 80 007 l g-12-1980
"method ox coding a sequence of blocks of binary data bits
into a sequence of blocks of binary channel bits, arrange-
mint for demodulating the data bits coded in accordance
with the method, and recording medium having an information
structure containing sequences of blocks of binary channel
bits."
A. Background of the invention.
A Field of the invention."
The invention relates to a method of coding a
sequence of binary data bits into a sequence of binary
channel bits, the sequence of data wits hying divided into
consecutive and sequential blocks, each comprising m data
bits, these blocks being coded into sequential blocks of
(n1~n2) channel bits nun m), each of these blocks of
channel bits comprising a block of no information bits and
lo a block of no separation bits such that sequential blocks
of information bits are separated by each time one block
of separation bits, two sequential channel bits of` a first
type, the type "1" are separated by at least d sequential
and consecutive bits of a second type, the type I and
'lo the number of sequential and consecutive channel bits of '
the second type being not more than k. The invention further
-
relates to a modulator for carrying out the method of
coding a sequence of binary data bits into a sequence of
binary channel bits; to a conversion circuit comprising the
20 modulator; to a demodulator for decoding the data bits
coded in accordance with the method; to a recording medium
having an information structure comprising sequences of
channel bit cells and to an arrangement for reproducing
information bits derived from a transmission channel, a
25 recording medium in particular.
In digital transmission or magnetic and optical
recording/reproduction systems the information to be trays-
milted or to be recorded is usually in the form of a so-
quince of symbols. These symbols together form the (often
30 binary) alphabet. For the case a binary alphabet is con-
corned (in the further course of this description -this
alphabet is represented by the symbols I and I one
symbol, for example the "1", can be recorded in accordance
I, :
PHI 80 007 2
with the NRZ-mark code as a transition between two states
of magnetization or focus on the magnetic disc, tape or
optical disc. The other symbol, the "C)'7, is recorded by -the
absence of such a transition.
As a result of certain system requirements, con-
straits are imposed in practice on the sequences of sum-
boys which may occur. Some systems are required to be
self-clocking. This implies that the sequence of symbols
to be transmit-ted or to ye recorded should have sufficient
transitions to generate from the symbol sequence a clock
signal which is required for detection and synchronization.
A further requirement may be that certain symbol sequences
must not occur in the information signal as these sequences
are in-tended for special purposes, for example as a sync
chronizing sequence. Imitation of the synchronizing sequence
by the information signal cancels the unambiguity of the
synchronizing signal and consequently, its suitability for
that purpose. It may further be required that the transit
lions do not follow too closely after each other in order
to limit the inter symbol interference.
In the case of magnetic or optical recording this
requirement may also be related to -the information density
on the recording medium, as, when at a predetermined minimum
distance between two consecutive -transitions on the record-
in medium the minimum time interval Twin corresponding
therewith of the signal to be recorded may be increased, the
information density is increased -to the same extent. Also
the required minimum band width Bin is correlated to the
minimum distance Twin between transitions (Bin - 2-T - )
When use is made of information channels which
do not transmit direct current, as is usually the case with
magnetic recording channels this results in the require-
mint that the symbol sequences in -the information channel
comprise the lowest possible (possibly no) direct current
component.
A Description of the prior art.
A method of the type described in -the opening pane-
graph is disclosed in reference Do The article relates
,~, .3
...
57i~
PUKE I 007 3 I 1980
to block codes based on d-, k- or (d, constrained
q-r~ary blocks of symbols which blocks satisfy -the follow-
iIlg requirements:
(a) d~cons-trainto -two Tao symbols are separated by a
run of at least _ consecutive symbols of the "O" -type;
(b) k-constraint: the maximum length of a run of kinesic-
live symbols of -tile type "O" is k.
A sequence of, for example binary data bits is
divided into consecutive and ~ecLuenl-ial block ? each Levine
lo m data bits. These blocks OIL m data bits are coded into
blocks of n information bitts (n m). Since no m, the number
of combinations with n information bits exceeds the number
of possible blocks of data bits (2 ). If, for example, the
constraint requirement is imposed on tile blocks of inform
lo motion bits to be transmitted or -to be recorded, mapping
of -the em blocks of data bitts on-to likewise em blocks of
information bits (out of a possible number of on blocks)
is chosen so that mapping is only carried out on those
blocks of information bits which satisfy the requirement
20 imposed.
Table I on page 439 of reference Do shows how
many different blocks of information bits there are, depend
ding on the length of the block (n) and -the requirement
imposed on d. So, there are 8 blocks of information bitts
25 having a length no at the condition that the minimum
distance do Consequently, blocks of data Boyce having a
length my (23 = 8 data words) could be represented by
blocks of information bits having a length no two cons-
cutive "Taipei symbols in the blocks of information bits
30 being separated by at least one Type symbol. For -this
example, coding -then is ( indicates mapping of one
block onto the other block and vice versa);
000 , 0000
001 ----I 0001
010 0010
01 1 ' -- --I 0100
100 Jo 0101
101 c --------3 1000
C~7~
PHI 80 007 4 9-12-1980
110 4 Jo 1001
1 1 1 '- - - --- '1010
When linking up -the block of information bitts it
is in some cases, however, hot possible to satisfy -the
requirement (in the example the d-con,traint) without
taking further measures In the said article it is pro
posed -to include separation bitts between the blocks of
information bits. or the case of constraint coding one
lock of separation biros, comprising dBase of the "Taipei
10 is sufficient. In the above-mentioned example, where d-1,
one separation bit (one zero) is therefore sufficient. Each
bloat{ of 3 data bitts is then encoded by 5 (4~1) channel
bits.
This coding method has the disadvantage that the
15 contribution of the low frequencies (including d c) to the
frequency spectrum of` the stream of channel bitts is rather
high. A further disadvantage is that -the coding converters
(modulator, demodulator), the demodulator in particular,
are complicated.
As regards the first disadvantage it should be
noted that reference Do indicates that the direct current
unbalance of (d, constrained codes can be limited by
interconnecting the blocks of channel bits by means of a
so-called inverting ox a non-inverting link. Acting thus
25 the sign of the contribution of the instantaneous block of
channel bits to -the direct current unbalance is chosen so
that the direct current unbalance of the preceding blocks
of charnel bits is reduced. However here a (do icon
strained code is concerned whose blocks of information bits
30 can be linked-up without coming into conflict with the (d,
constraint so that the addition of separation bits for
reasons of (d, constraining is not necessary.
By Summary of the invention.
It is an object of the invention to provide a
35 method of the type described in the opening paragraph for
the coding of a sequence of binary data bits into a sequent
go of binary channel bits which improves -the low frequency
spectrum properties of the signal -to be derived from the
Jo
57~
PHI I 007 5
channel bits and which method enables the use of a simple
demodulator.
The method according to the invention is kirk-
terraced in that it comprises the following steps.
1. converting blocks, containing bits of data bits, into
blocks, containing n bits, of information bitts,
2. generating a set of possible sequences of channel bits,
each sequence comprising at least one block of informal
lion bits and one block of separation bits and these
possible sequences each comprising the blocks of inform
motion bits supplemented by one of -the possible bit come
binations of the blocks of separation bits;
3. determining the direct current unbalance of each of -the
possible sequences of channel bitts determined in the
preceding step,
4. determining for each of the possible sequences of channel
bits the sum of the number of separation bits and the
number of consecutive and sequential information bits of
the type "O" which immediately precede a bit of the "1"
type and the sum of the number following after a bit of
the "1" -type, this bit forming part of one of the blocks
of separation bits, and the sum of the number of swooper-
lion bits and the number of consecutive and sequential
information bits of the "O" type immediately preceding
and following after that block of separation bits,
I generating a first indication signal for those sequences
of channel bits the values of the sum determined in the
preceding step of which are higher than Ed and no-t more
than equal to k,
6. selecting from the sequences of channel bits which
resulted in the first indication signal that sequence of
channel bits which minimizes the direct current unbalance
C. short description of the drawings
__ __ _
Embodiments of -the invention end their advantages
will now be further described with reference to -the draw-
inks In these drawings:
Figure 1 shows some bit sequences for 1111istra-t-
in an embodiment of the coding format according lo -the
Puke Jo owe G 9- 1 2-198
invention;
Figure 2 shows stone further embodiments of -the
format of the channel coding to be llSeCI ill the reduction
of the direct current unbalance according -to the invention;
Figure 3 is a flow char-t of` Len embodiment of -the
method according to the invention;
Figure 4 illustrates a block of synchronizing
bitts for use in the method according to the invention;
Figure 5 SWISS alp ~moocliment of` a llemodulator
lo in accordance with the invention for decoding -the data
bits which were coded in accordance with the method;
Figure 6 shows an embodiment of the means for
detecting a sequence of synchronizing bits according -to -the
invention;
lo [I use 7 Chihuahuas an embodiment of a frame - format
for use in the method according -to the invention
Corresponding elements in the Figures have been
given the same reference symbols.
D. References.
-
20 (1) Tang, DOT., Bawl, LO "Block codes for a class of con-
strained noiseless channels". Information and Control,
Vol. 17, no. 5, Dec. 19709 pp.436-461.
(2) Pettily ARM., "Charge-constrained byte-oriented (0,33
code", IBM Technical Disclosure Bulletin, Vow 19, No.
I 7. Dec. 19769 pp.2715-2717.
E. Desert lion of` the embodiments.
P
Figure 1 shows some bit sequences to illustrate
the method of coding a run of binary data bits (Figure pa)
into a run of binary channel bitts (Figure 1b). The run of
30 data bits it divided in-to consecutive and sequential blocks
BY. Each block of data bits comprises m data bits. By way
of example, the choice m - 8 will be used in the further
course of this description and in the Figures. The same
applies, however for any other value of m. A lock of m
35 data bits BDj generally comprises one of` the 2 possible
bit sequences.
Such bit sequences are not so suitable for direct
optical or magnetic Al recording and -that for several reasons.
i. .
Pluck 80 007 7
When namely -two data symbols of the ~]_11 type, which are for
example recorded on the recording medium as a -transition
from one magnetizing direction to the other or as a -tray-
session to a pit, immediately follow after each another,
then these transitions must not be too close to each other
in view of their mutual interaction Issue limits the inform
motion density. it the same time the minimum band width
B which is required to transmit or record the bit stream
men
is increased when the minimum distance 'Mooney between cons-
eutive transitions (Bin 1/(2Tmjn)re~uirement which is often imposed on data transmission
and optimal or magnetic Al recording systems is that the
bit sequences must have sufficient transitions to recover
from the transmit-ted signal a clock signal with which sync
ehronization can be carried out. A block having m zeroes,preceded in worst case situations by a block ending in a
number of zeros and followed by a block beginning with
a number of zeros, would endanger the dock extraction.
Information channels which do not transmit Doherty
current, such as magnetic recording channels must Earthier
satisfy the requirement that the datcl stream to be recorded
comprises a direct current component which is as small as
possible. With optical recording it it desirable that the
low-frequeney portion of the data spectrum is suppressed
to the best possible extent, -this in view of the servo
controls. In addition, the demodulation is simplified when
the direct current component is relatively small.
For the above and other reasons a so-called
channel coding is performed on the data bits before they
are transmitted v the channel or before they are recorded.
In the case of block coding (reference Do the blocks of
data bits which each contain m bits are coded as blocks of
information bits which each comprise no information bitts.
Figure 1 shows how the block of data bits Bid is converted
into a block of information bits Byway By way of example
the choice no - I will be used in the further course of
this description and in the Figures. us no is greater
than m, no-t all -the combinations which can be formed
_
PHI 80 007 8
with no bits are utilized those combinations which do not
fit in well with -the channel -to be utilized are not used
So, in -the example given only 256 word, need to be selected
from -the more than 16.000 possible channel words for the
required one-to-one mapping of data words on-to channel
words. Consequently, some requirements may be imposed on
the channel words. One requirement is that between two con-
secutive information bits of a first -type, the "1" type,
at least d sequential and consecutive information bits of
one type, the 'JO" -type are situated within the same block
of no information bitts. Table I on page 439 of reference
Do shows how many such binary words there are, depending
on -the value of d. It appears from the table that for
no = 14 -there are 277 words with a-t least -two do bitts
of the "O" -type between consecutive bits (of -the "1" type.
When coding blocks of eight data bits of which there may
be 2 = 256 combinations, as blocks of 14 channel bitts the
requirement do can therefore be amply satisfied.
Catenation of the block of information bits Bit
is, however, not possible without further measures when
the same requirements of d constrained is no-t only imposed
within a block of no bits but also extends over the bound
defy between two consecutive blocks. To -this end, reference
Do proposes (page 451~ -to include one or more separation
bits between the blocks of channel bits. It can be easily
seen that when a number of "O" type separation bits at
least equal to d is included, that the d-constraint is
satisfied. Figure 1 shows that a block of channel bitts BCi
consist of the bloc of information bits Bit and a block of
separation bits BSi. The block of separation bits comprises
no bits so that the block of channel bitts BCi comprises
no no bits. By way of example the choice no = 3 will be
used in the further course of the description and in -the
Figures, unless indicated differently.
In order -to make -the clock generation as reliable
as possible a further requirement may be that -the maximum
number of "O" -type bitts which may occur uninterruptedly
between two consecutive "1" type hits within one block of
I
PI 80 007 9
information bits is limited to a predetermined value k. In
the example where my and nl=14 it is possible to eliminate
from the 277 words which satisfy do those words, for
example which have a very high value for k. It appears
that k may be limited to 10. Consequently, a set of 28
(in general em) blocks of data bits of 8 bits each (in
general m) is mapped onto a set of also 28 (in general em)
blocks of information bits/ which information bits have
been selected from 214 (in general 2nl) possible blocks of
information bits, which is partly the result of the fact
that the following requirements have been imposed: do and
k=10 (in general do k-constrained). It is still at one's
option which one of the blocks of data bits is to be also-
elated with one of the blocks of information bits. In the
above-mentioned reference (Do) a number translation from
data bits to information bits is unambiguously determined
in a mathematically closed form. Although this translation
can, in principle, be used, preference is given to a
different association as will be further explained herein-
after.
Catenation of the furthermore k-constrained chant
not words It is only possible, which also applies for the
d-constrained blocks, when separation blocks have been
arranged between the blocks of information bits Bit. In
principle the same separation blocks of no bits each can
be used for this purpose as the requirements d-constrained
and k-constrained are not each others opposite, but are
rather complementary. when, consequently, the sum of the
number of bit values of the "O" type preceding a given
separation block exceeds the number of values following
after that separation block and the no bits of the swooper-
lion block itself exceed the value _, -then at least one
of the bit values of the "O" type of the separation block
should be replaced by a bit value of the "l" type in order
to split the sequence of heroes into sequences which are
each not more than k bits long.
In addition to their function of ensuring that
the requirements of (d, constraint are satisfied the
I
PHI 80 007 10
separation blocks can be dimensioned so that they can also
be utilized for minimizing the direct current unbalance.
This is cased on the recognition of -the fact that for some
catenations of blocks of information bits a predetermined
format of the block of separation bits is indeed prescribed
but that in a large number of cases either no requirements
or only limited requirements are imposed on the format of
the block of separation bits. The degree of freedom
created thus is used for minimizing the current unbalance.
The coming into existence and the growth of the
direct current unbalance can be explained as follows. The
block of information bits Boil as shown in Figure lb is rev
corded on the recording medium, for example in the form of
a NRZ-rnark format. With this format a "1" is marked by a
transition at the beginning of the relevant bit cell and
becomes a "O" when no transition is recorded. The bit
sequence shown in Boil then assumes a shape which is denoted
by WE, in which shape this bit sequence is recorded on the
recording medium. This sequence has a direct current us-
balance as for the present sequence the positive level has length which is longer than the negative level A measure
which is often used for the direct current unbalance is the
digital sum value, abbreviated to d.s.v. Assuming the levels
of the wave form to be WE + 1 and -1, respectively, the
d.s.v. is then equal to the running integral of the wave
form WE and is IT in the example shown in figure 1 , T
being the length of one bit interval. When such sequences
are repeated, the direct current unbalance will grow.
Generally, this direct current unbalance results in a base
line movement and reduces the effective signal-to-noise
ratio and, consequently, the reliability of the detection
of the recorded signals
The block of separation bits BSi is used as
follows to limit the direct current unbalance. At a given
instant a block of data bits Bid is supplied. This block
of data bits Bid is converted into a block of information
bits BIT for example by means of a liable stored in a store.
Thereafter, a set of possible blocks of channel bits/ con-
7~3
PHI 80 007 11
twining (no + no) bits is generated. All these blocks come
prose the same block of information bitts (bit cells 1 to
14, inclusive, Figure lo supplemented by the possible bit
combinations of the no separation bits (bit cells 15, 16
and 17~ Figure lb). Consequently in the example shown in
Figure lb a set consisting of on _ 8 possible blocks of
channel bits is produced. rrhereafter the following pane-
meters are determined from each of the possible blocks of
channel bits, in principle in an arbitrary sequence:
I a) it is determined for the relevant possible block of
channel bits, in view of the preceding block of channel
bits, whether the requirement of d-cons-trained and -the
requirement of k-constrained do not conflict with the
format of the present block of separation bits;
d) determination of the d.s.v. for the relevant, possible
block of channel bits.
A first indication signal is generated for those
possible blocks of channel bits which do not conflict with
the d-constraint and k-constraint requirements. The choice
of the coding parameters guarantees that such an indication
signal is generated for at least one of -the possible blocks
of information bits. Finally, from the possible blocks
of channel bits for which a first indication signal has
been venerated that block of channel bits is, for example,
selected which has in an absolute sense the lowest d.sAv~
However, a still better method is the accumulation of the
d.s.v. of the preceding blocks of channel bits and to
select from the blocks of channel bits which are eligible
for -the next-coming transmission that block which will
cause the absolute value of the accumulated d.s.v. -to
decrease. The word selected thus is transmitted or recorded.
An advantage of this method is that the separation
bits which are already necessary for other purposes can now
also be utilized in a simple manner for the limitation of
the direct current unbalance. An additional advantage is
that the intervention in the signal to be transmit-ted is
limited to -the blocks of separation bitts and does no-t ox-
tend to the blocks of information bitts (ignoring -the
PHI 80 00~ 12
polarity of the wave form to be -transmitted or recorded).
The demodulation of the read, recorded signal -then only
relates -to the information bitts, eye separation bits may
be left out of consideration.
Figure 2 shows some further embodimerlts of -the
method. Figure pa shows schematically -the sequences of
blocks of channel bitts .,,, Boil BCi, Boil ..., these
blocks comprising a predetermined number of (no + no) bits.
Each block of channel bits comprises blocks of information
bits consisting of no bits) and blocks of separation bits...
Boil Boil BSi, Boil ,,., each consisting of no bits,
In this embodiment -the direct current unbalance
is determined across several blocks for example as shown
in Figure pa across two blocks of channel bits BCi and
Boil The direct current unbalance is determined in a
similar manner as described for the embodiment of Figure
1, on the proviso that the possible formats of super blocks
are generated for each super block SBCi, that is to say the
blocks of information bits for block BCi and blocks Boil
are supplemented by all the possible combinations which can
be formed with the no separation bits of blocks BSi and
block Boil That combination which minimizes the direct
current unbalance is thereafter selected from this set.
This method has the advantage -that the remaining direct
current unbalance has a more uniform character as it is
considered more than one block of channel bits in advance
which intervention is optimum.
An advantageous variant of this method has -the
distinctive feature that the super block SBCi (Figure pa)
I is shifted one block of channel bits only after the direct
current unbalance has been minimized. This means that
block BC'i (in Figure aye, which is part of the super block
SBCi, is processed and that the subsequent super block
SBCi+1 (not shown) contains the blocks Boil and BC'i~2
(not shown) for which the above-described direct current
unbalance minimizing operation is performed. So the
block BCi+1 is part of both the super block SBCi end the
subsequent block SAC It is theft perfectly possible
HO 80 007 aye
that the (provisional) choice for the separation bits in
block Boil made in super block SBCi differs from the
ultimate choice made in super block SBCi+l. As each block
is assessed several times (twice in the present example)
the direct current unbalance and consequently the noise
contribution is further reduced
Figure 2b shows a further embodiment in which
the direct current unbalance is determined for several
blocks simultaneously (SBCj), for example as shown in Figure
lo 2b for four blocks of channel bits BCj(ll, BCj~2), BCj(3)
and BCj(4). Each of these blocks of channel bits comprises
a predetermined number of no information bits. However,
the number of separation bits comprised in the blocks of
separation bits BSj(1~, BSj(2), BSj(3) and BSj( ) is not the
same for each block of channel bits. The number of inform
motion bits may, for example, amount to 14 and the number of
separation bits for the blocks BSjl1), BSj~2) and BSj(3)
ox - r
PHI 80 007 13
may be 2 for each block and 6 for block BSj(4~. Deter-
mining the direct current unbalance is carried out in a
similar manner as described for the embodiment of figure
pa.
In addition -to the advantages already mentioned
in the foregoing and which also apply here, this method
has the advantage -that the availability of a relatively
long block of separation bits increases the possibilities
of reducing the direct current unbalance More specifically,
the remaining direct current unbalance of a sequence of
channel bits in which each block of channel bits comprises
an equal number of, for example, 3 bits is larger than the
remaining direct current unbalance of a sequence of channel
bits -the blocks of separation bits of which comprise an
average of 3 bits, divided however into 2-2-2-6 bits.
It should be noted that the described -time so-
quinces of functions and associated states of the method
can be realized by means of universal sequential logic
circuits such as commercially available microprocessors
with associated stores and peripheral equipment Figure 3
shows a flow Hart of such an implementation. The following
explanatory texts are associated with the legends of the
geometrical figures which illustrate, time-sequentially,
the functions and states of the coding method. Callahan A
shows the reference symbol, B the legend and column C -the
explanatory text associated with the relevant geometrical
Figure
A B C
1 DISC :=0; the digital sum value (d.s.v) of
age.
it the preceding blocks of channel
bits is given -the value zero at
the start of the method. The first
data word BY is given the number
it Proceed the geometrical
figure 2;
2 Bid The block of data bitts of m bitts
of the number i is selected from
a store. Proceed to geometrical
I
PHI 80 OWE 14 9-l2-1980
figure 3;
3 Bit (Bid) The block of data bits having numb
bier i (Bid) -is converted into a
block of informatioIl bits consist
tying of no bits (Bit) by means of
a Table stored in -the store; pro-
aced -to geometrical Figure 4;
4 joy A parameter is initiated at a
value O; -the parameter l is the
number of one of the blocks of
channel bits consisting of` n1~n2
bits which is possibly eligible
for transmission or recording; pro-
aced to geometrical Figure 5;
lo 5 j:=j+1 The parameter l is increased by 1;
proceed to geometrical Figure 6.
6 j I? When the relevant parameters have
been determined of all the q posy
sidle blocks of channel bitts,
operations are continued by the
operation indicated by geometrical
Figure 13. In geometrical Figure 6
this is indicated by the link N.
When j Q, operations are con-
tinted by the operation indicated
by geometrical Figure 7;
7 BCi:=BIi+BSj The jut possible block of channel
bitts BCi is formed by supplement
tying -the block of information bits
Bit by the jut combination ox the
block of separation bits BSJ; pro-
aced to geometrical Figure 8;
8 DSVj=? The d.s.v. of -the jth possible
block of charnel bitts is determined
proceed to geometrical Figure 9;
9 kj ? It is checked whether the jut posy
sidle block of channel bits on
catenation with -the preceding blocks
S; I
PHI 80 007 15 9-12-1980
ox channel bitts BCi 1 satisfies
the k-constraint requirement, If
this requirement is satisfied
operations are continued by the
operation indicated in geometrical
Figure 10 (link N). If this require-
mint is not satisfied, then the
following step is the operation
indicated by geometrical Figure
lo 11 (link Ye.
10 Ed? It is checked whether -the j
possible block of channel bits on
catenation with -the preceding block
ox channel bits Sue 1 satisfies
the d-constraint requirement. If
this requirement is satisfied the
following step is the operation
indicated by geometrical Figure 12
(link N). When this requirement is
not satisfied, then the operation
is continued by the step indicated
by geometrical Figure 11 (link Y);
11 DSV~J):=max The d.s.v. of the jth block ox
channel bits is given such a high
value (Max) that this block can
definitely not be selected; pro-
aced to geometrical Figure 12;
12 DS~(Ci) -DSV(j)~ The d.s.v. ox the j block of
DSVaCc channel 'bits (dsv~i) is added to
the accumulated dsv (DSVacc) of
-the preceding blocks of channel
bits to obtain a new accumulated
value of the d.s.v. (DSV(J); pro-
aced to geometrical Figure 5;5 13 mix /DSV:=DSV(e) The minimum value ox the dsv ox
the q possible 'blocks of channel
bits is determined. This appears
to be the d.s.v. ox the first
Puke 80 007 IT I 19~0
bleakly of` channel bits (Proceed to
gnome t Rockwell Figure I
lo BY The first block of channel bitts is
selected from the q possible bloats;
proceed to geometrical figure 15;
DS~Tacc ~DSV( ) The accumulated value ox` the d so
(DSVacc) is made equal to the
accumulated -value of the do of
the selected first block owe inform
motion bitts; proceed -to gnome Roy-
eel Figure 16;
16 it 1 The number of the blocks of data
and information Boyce is increased
by one. Proceed to geometrical
Figure 2; the cycle is now repeated
for -the next, the it block of
data bits.
The slow chart shown above is applicable to the
embodiment shown in Figure 1. For the embodiments ox Figure
the corresponding flow charts hold, talking the modifica-
lions already described into consideration.
In order to enable a distinction when demodulate
in the transmitted or recorded stream of channel bits be-
tweet the information bits and the separation bits (n3+n4)
25 namely no synchronizing information bits and nil swanker-
sizing separation bitts, are included in the stream of
channel bits blocks. A block of synchronizing bits is, for
example, inserted after each predetermined number of blocks
of information and separation bits. After detection of this
30 word it can then be unambiguously determined in which bit
position information bits and in which bit positions so-
parathion bits are present. Measures should therefore be
-taken to prevent the synchronization word from being
imitated by certain bit sequences in the information and
35 separation blocks. To this end a ionic block owe swanker-
sizing bits, that is to say synchronizing bits which are
not present in information and separation bit sequences
can be chosen. Sequences which do no-t satisfy the require-
Al
PI-IQ 80 007 17 9-12-l~80
rent of being d-constrained or k-constrained are not so
attractive or this purpose as the information density or
the self clocking properties are when affected negatively.
However the choice is very loomed WE -thin the group of
sequences itch satisfy -the (d, k)-coIlstraint requirements.
different method is therefore proposed. The
block of synchronizing bits includes, or example, at
least two times in succession and consecutively a sequence
which comprises S bits of the "Taipei between -two sequent
trial bits of the "Taipei. Preferably, S is equal to k.
Figure 4 shows a bloclc of synchronizing bits SUN. The block
comprises two times in succession and consecutively a so-
quince (10000000000, 1 followed by 10 zeros) denoted by
SUE and SUNUP respectively. This sequence may also be
15 present in -the channel bit stream, namely for sequences
where h-10. ivory, to prevent the sequence from occurring
two times in succession and consecutively outside the block
of synchronizing bits, the first indication signal is
suppressed when the sum of the number of separation bits
20 and the number of sequential and consecutive information
bits of the "0" type immediately proceeding a bit of the
"1" type, the latter forming part of the block of separation
bits, is equal to k and also equal to the sum of the number
of consecutive and sequential information bits of the "0"
25 -type which immediately follows after the said bit of the
"1" type of the block of separation bits. The other, at-
ready indicated way to prevent imitation would be to use
two times in succession the sequence 100000000000 thus 1,
followed by 11 zeros.
In addition, the block of synchronization bits
also comprises a block of synchronization separation bits.
The function of the block of separation bits is exactly
the same as the function described in the foregoing of the
block of` separation bits between the blocks of information
35 bits. (consequently they have for their purpose to satisfy
the (d, constraint and a limited direct current unbalance
requirement. The measures which are taken -to prevent the
synchronizing pattern frombeiIlg imitated yin the run of
lo A So
PHI 80 007 18 I 1980
channel bits as it occllrs -Tao telex in succession and con-
secutively, these same measures also pronto this pattern
from occurring three times before or after the block of
synchronizing bits.
The above-described method, Thigh may also be
referred to as modulating or encoding, is of a considerably
simpler character in the opposite direction, -that is -to
say during demodulation or decoding. Limitation of -the
direct current unbalance is effected without affecting the
lo blocks of information bits, so that the information in
-the separation blocks is irrelevant for demodulating the
information In addition, the choice taken at the modulator
end which m bit long block of data bits is associated with
which no long block of information bit is of importance
15 not only for the modulator but also for the demodulator.
Amelia the complexity of the demodulator depends on this
choice. In magnetic recording systems -the complexity of
modulator and demodulator are of equal importance as they
are in general both present in -the apparatus. In systems
20 for optical record ng3 the recording medium is of the "read-
only" type so that the consumer equipment need only comprise
a demodulator. So in this latter case it is particularly
important to reduce the complexity of the demodulator as
much as possible even at the cost of the complexity of the
25 modulator-
Figure 5 shows an embodiment of a demodulator which demodulates the blocks of 8 data bitts from blocks of
14 information bitts. Figure pa shows the block schematic
circuit diagram of the demodulator. The demodulator
comprises AND-gates 17-0 to 17~51, inclusive, each having
one or more inputs. One of the 14 bitts of the blocks of
information bits is applied -to each input, which are of
the inverting or non inverting -type. Figure 5b shows in
35 column Of how -this is carried out. Column 1 represents
the least significant bit position C1 of the 14 bit inform
motion block, column 14 the most significant bit position
CLUE and the intermediate columns 2 to 13, inclusive no-
pi
PUKE 80 007 19 ~12-1980
present the remailing, corresponding Will tile bit position
significant bit positions. The lines O owe I inclusive
relate to -the number of -the AND-gate, thaw is -to say line
O relates -to the input format of AND-gate -lo O, line 1
relates to the input format of Andante '17-19 etc. A
symbol 1 in the i column of line I signified that the
j l~ND-gate 17 is supplied via a ilon~inverting input with
-the content of -the i bit position By. A symbol O in the
i column of line i signifies that the j Date -lo
is supplied via an inverting input with the content of the
i bit position (Of). Consequently, (line 0)9 an inverting
input of Agate 17-0 is connected to -the i bit position
(C1), and a non-inverting input is connected to the 4
bit position (CLIP); (line 1) a non-inverting input of ED-
5 gate 17-0 is connected to the 3 bit position, C3); etc.
The demodulator further _olnprises 8 Orates
18-1 -to 18-8~ inclusive, the inputs o-f which are connected
to the outputs of the AND gates 17-0 -to 17-51, inclusive.
no 5b shows ion column At ho this is realized. Column
20 Awl relates to AND-gate 18-1~ column A relates to AND-
gate 18-~, ... and column A replates -to Date 18-8, A.
locator A in the it column of the jth line inducts that
the output ox AND-gate 17-j is connected to the input of
OR-gate 18-i.
For the AND-gates 17-50 and 17-51 the circuit is
modified as follows. An inverting output of both AND-gate
17-50 and 17-51 are each collected to an input of a further
~UND-gate 19. An output of OR-circuit 18-4 is connected to
a further input ox Negate 19.
Each output of the OR-gates 18-1 9 18-2, 18-3 and
18-5 to 18-8, inclusive, and an output of AND-gate 19 are
connected to an output 20~i. The decoded block of 8 data
bits is consequently available in parallel fornl at this
output.
The demodulator shown in logger pa may, alter-
natively be in the form of a so-called ELLA (field pro-
grumble logic array), for example the Signetics 'bipolar
PLY type 82S100/82S10l. The Table shown in Eigllre 5 is the
PUKE I 007 ''I 9-12-1980
programmable table for this array.
The lemodulator shown in Logger is, because
of its simplicity eminently suitably for optical record
ding systems ox the "read-only" type.
The block of synchronizing bits can be detected
with the means shorn in Figure 6. The transmitted or read
recorded signal is applied to an input terminal 21. The
signal is in the (ark) format. This signal is applied
directly to a first input of an OR-gate ''2 and -to a second
lo input of OR-gate 23 via a delay clement 23. A so-called
NAZI signal is then available at the output of` OR gate
22, which is connected to the input of a shift register
24. The shift register comprises a number of sections,
each having a tap, which number is equal to the number of
I bits comprised in the block of synchronizing bits. In the
example used in the foregoing, the shift register must have
23 sections a namely in order to be able -to contain the
sequence 10000000000100000000001. Each tap is connected to
an input of an AND-gate 25, which input is either an in-
20 venting or a non-inverting input. When the synchronization
sequence is present at the inputs of Negate 25, a signal
will then be generated at an output 26 of this AND-gate
which may be used as an incaution signal for the detection
of the synchronizing pattern. By means of this signal the
25 bit stream is divided in two blocks of (n1-~n2) bits eke
These blocks of channel bits are shifted, one after the
other, in a further shift register. The most sifnigicant
no bits are read in parallel and applied to the inputs of
the AND-gates 17, as shown in Figure pa. The least sign-
30 ficant no bits are irrelevant for the demodulation.
The coded signal is, for example, recorded on antiquely recording medium. The signal has a form denoted by
IF in Figure 1b The signal is applied on the recording
medium in a helical information structure The information
35 structure comprises a sequence of a number of super blocks,
for example ox the type shown in Figure 7. A super block
Ski comprises a block of synchronizing bits Sync, this
block being implemented as shown ill Fig ire 4, and a number
PI 80 007 I
(33 in the embodiment) of blocks of channel bits, each
having (nl-~n2) bits BCI, BC2, ... BC33. A channel bit of
the "1" type is represented by a transition in the record-
in medium, for example a transition from no-pit to pit; a
channel bit of the "O" type is represented on -the record
in medium by the absence of a transition. The helical
information track is subdivided into eliminator cells, the
bit cells. On the recording medium these bit cells form a
spatial structure, which corresponds to a subdivision in
the time (period time of one bit) of -the stream of channel
bits.
Independent of the content of the information and
separation bits, a number of details can be distinguished
a-t the recording medium. For the medium the k-constraint
implies that the maximum distance between two consecutive
transitions is clue bit cells. The longest pit (or no-pit)
has therefore a length of (clue) bit cells. The d-constraint
implies that the minimum distance between the two kinesic-
live transitions is do The shortest bit (or no-pit) has
therefore a length of do bit cells. Furthermore, at
regular distances, there is a pit of the maximum length
followed by (or preceded by) a no-pit of the maximum
length. This structure is part of the block of the sync
chronization bits.
In a preferred embodiment k=10, do and a super-
block Ski comprises 588 channel bit cells. The super block
Ski comprises a block of synchronization bits of 27 bit
cells and 33 blocks of channel bit cells, each having 17
(14+3) channel bit cells.
A modulator, a transmission channel, for example
an optical recording medium, and a demodulator may together
be part of a system, for example a system for the conversion
of analog information (music, speech) into digital inform
motion, which information is recorded on an optical record-
in medium. The information recorded on the recording
medium (or a copy thereof) can be reproduced by means of an
arrangement which is suitable for the reproduction of -the
type of information which has been recorded on -the
"1~3
PHI 80 007 22
recording medium
The conversion circuit comprises in particular
an analog-to--digital converter for converting the analog
signal music, speech) to be recorded into a digital sign
net of a predetermined format (source kidding In add-
lion, the conversion circuit may include a portion of an
error-correction system, In the conversion circuit the
digital signal is converted into a format by means of
which the errors which particularly occur during reading
of the recording median can be corrected in the arrange-
mint for the reproduction of the signals. An error eon-
reaction system which is suitable for this purpose is disk
closed in Applicant's Canadian Patent No. 1,163,3~1
issued March 6, 19~4.
The digital, error-protected signal is there-
after applied to -the modulator described in the foregoing
(channel coding) for conversion into a digital signal
which is adapted to the channel properties. In addition
the synchronization pattern is supplied and the signal is
brought -to a suitable frame format, The signal thus
obtained is used to generate a control signal, for example
for a laser (N~Z-mark format) by means of which a helical
information structure is applied on the recording medium
in the form of a sequence of pits/no pits of a predator-
mined length
The recording medium or a copy thereof can bread by means of an arrangement for the reproduction of
the information bit derived from the recording medium.
To this end the arrangement comprises a modulator, which
has already been described in detail, the decoder portion
of the error correction system and a digital/analog con-
venter for reconstituting a replica of the analog signal
which is applied to the conversion circuit.
I
