Note: Descriptions are shown in the official language in which they were submitted.
7~
This invention relates to a wide-band communications system ~lith sub-
scriber lines, each comprising two optical wave-gui-les, running betwecn an
exchange and a subscriber-station, for l~ and/or stereo-sound ~lide-l),lr~d sign.lls
on the one hand and, on the other hand, narrow-band digital cornrnlmications
signals such as 64 kbit/s digital telephony s:Lgnals, videotex ~si ~aJs, 8 ~.bit/s
control-signals, an~ program-section signals
In an optical wave-guide wide-band communications system, the
subscriber-lines may each comprise a single optical wave-guide used in both
transmission-directions or two separate optical wave-guides for the two trans-
mission-directions. In the first case, with the existing status of optical
wave-guide technology, only control-signals or relatively simple replies in
interactive services can be transmitted - through an optical wave-guide through
which TV and/or audio wide-band signals are transmitted from the exchange to
the subscriber-station - in a backward channel from the subscriber-station to
the exchange. If, in addition to this, (possibly a plurality of) 64 kbit/s
digital signals and (possibly a plurali~y of) 8 kbit/s digital signals for
digital telephony, videotex, facsimile, and for signalling and synchron-
izing such narrow-band communications services, are to be transmitted between
the subscriber-station and the exchange, or vice-versa, then two optical wave-
guides are provided in each subscriber line, i.e. each transmission-direction
has its own optical wave-guide (ntz 32 (1979) 3, 150 ... 153). Thus video
communication signals may also be passed, if necessary, through the two optical
wave-guides.
Such signal tranmission, through optical wave-guides used in one trans-
mission-direction, requires, for transmission in the direction of the subscriber-
line, grouping of TV and possibly stereo-sound signals, to be distributed within
the scope of unidirectional communication services such as television and radio,
-- 1 --
~A~
with telecommunications signals to be transmitted within the scope of bidirec-
tional communication services such as telephony, teletyping and data-commllnlca-
tLon. This resul.ts :Ln a linking of com~lunicat-Lons serv:Lces of dL~ferent operl-
tors, which may be Imdesirable for pol:i.tlcal or lega:l. reasonC; related to tele-
communications, or also for techni.cal reasons, ~or :Lnstance ln the Ca'-3(' of
analog signals (FM or PPM signa]s) in wide band signals - ln order to avoid the
additional e~pense of decoding at the suhscriber end; analog wide-band signals
must then be grouped with dig-Ltal communications signals and transmitted
through the optical wave-guide from the exchange to the subscriber-station.
This could be accomplished in principal by the combined use of frequency-
division multiplex and time-divisi.on multiplex techniques; in practice,
however, the combination of frequency-division and time-division multiplex
techniques presents problems and demands freedom from distortion and high
linearity from the transmission system.
~ wide-band communications system :Ls known which has subscriber's
stations, each comprising two optical wave-guides running between the exchange
and subscriber's station, for TV and/or stereo sound wide-band signals are
transmitted over the one optical wave-guide from the exchange or distribution
station to the subscriber's station and all digital communica~ions narrow-band
signals, in particular 64 kbit/s digital signals, are transmitted in multiplex
over the other optical wave-guide between the exchange and the subscriber's
station and vice-versa as well as program selection signals from the sub
scriber's station to the exchange or distribution station.
It is the purpose of the invention to provide an advantageous
improvement in such a wide-band communications system.
The invention relates to a wide-band communications system with
subscriberls lines, each comprising two optical wave guides ~unning between the
-- 2 --
exchange and the subscrlber's station, for TV and/or stereo sound wir3e-band
s:ignals, and on the other hand, narrow-band digital communicatlons signal.s in
which only the TV and/or stereo sound wide-band a:Lgna1s are transMltted o~/er
the one optical wave-guide from the exchange or dLstr:Lbution stat:Lon to the
subscriher's stat:Lon and all. digi.tal communl.cations narrow-band si.gna1s> Ln
partLcular 64 kbit/~ dlgital signals, are transmLtted tn multLp1.e~ o~er the
other optlcal wave-guide between the exchange and the subscr:Lber's station and
vice-versa as well as program selectlon signals from the subscriber's station
to the exchange or distributlon station, such a wide-band communicat~ons systern
being characterized according to the invention in that bidirectional video
communications digital signals are also transmitted over the said other optical
wave-guide both between the exchange and the subscriber's station and also
vice-versa.
The invention has the advantage that in the wide-band communications
system the TV and stereo sound-program distributlon on the one hand and the
bidirectional narrow-band digital communications and also video telephony digi-
tal communicat:Lons on the other hand can be realized independently of one
another, if necessary, also consecutively. It is furthermore an advantage that
the technology required for achieving this already meets existing requirements.
2~ Thus, in a further embodiment of the invention the digital communications
signals in the two transmission directions can be transmitted over the said
other optical wave-guide in the separate-time-position process so that in the
optical plane decoupling of the signals in the two transmission directions, for
example by colour filters or high-grade directional couplers, is not needed.
Instead, it is sufficient to provide a simple (for example a 3 db) coupler
between the said other optical wave-guide, on the one hand, and the optical
wave-guide from the relevant electro-optical converter, or a wave gulde leadlng
-- 3
to the relevant opto-electrical converter, on the other hand.
The wide-band signals may be transmitted through the said other
optical wave-guide, preferably on analog-modulated carriers, in Erequency-
division multiplex~ whereas the dlgital commun:lcat-Lons slgnals may be advan-
tageously grouped and transmitted in time-divisLon multlplex through the sald
other optical wave-gulde.
The inventlon is explained hereinafter in greater detail, in con~unc-
tion with the drawlng attached hereto, whereln:
Figures 1 and 3 each show an example of a wide-band communications
system;
Figures 2 and 4 show the timing, for such a wide-band communlcations
system, of a signal transmission in the separate-time-position process.
Figure 1 illustrates d~agrammat:ically, to the degree necessary for an
understanding of the invention, an example of a wide-band communications
system. In this system, a subscriber station TlnSt is connected, through a
subscriber line Al comprising two optical wave-guides Lb, LS - e.g., consisting
of gradient flbres with a core-diameter of 50~m and a casing diameter of
150~ m - to the relevant VSt, it belng indicated ln Figure 1 that the said
subscrlber-station may be set up for digital telephony, facsimlle service,
videotex, touch-tone calling display and for TV and stereo-sound reception.
Only TV and/or stereo-sound wide-band signals are transmitted from
the exchange VSt, through the one optical wave-guide Lb, to the subscr~ber-
station TlnSt. In this connection, Figure 1 shows that the wide-band signals
of the TV program to be transmitted to the relevant subscrlber are passed,
through a wlde-band swltchlng network KFb - for example of the type dlsclosed
in German AS 28 28 662, German OS 29 32 588 or German OS 29 32 587 - and
through a subsequent analog-modulator MOD, for example a frequency-modulator
~ 4
which converts the relevant wide-band signal into an individual carrier-
frequency position, to a wide-band æignal-multiplexer MUX provlded Ln the
exchange for each subscriber and cons:Lst-Lng, ~or exarnple, o~ ban~l-pass ~llters
connected together at the outlet ends, the aaid multiplexer leadLn,, thrr>ll57h an
electro-optical converter E/O, to optlcal wave-gu-Lde Lb; sLmilarly, the wlde-
band signal formed by the stereo-æolmd prograrn sLgnals, is pa~ed, th~ough a
multiplexer STM to be produced with the fre~uency-converters of a carrier-
frequency audio-channel system MStl5, and through an analog-modulator MOD, to
the wide-band multLplexer MUX. The opto-electrical converter 0/~, which closeæ
off the optical wave-guide LD at the subscriber end, iæ followed, in the wide-
band communications system according to Figure l, by a wide-band signal demul-
tiplexer DEMUX to which corresponding TV receiver TV and stereo-sound receiver
STE are connected through corresponding leads tv, st.
All digital communications narrow-band signals are transmitted,
through the other optical wave-guide Ls, from the exchange VSt to the
subscriber-ætation TlnSt and, in the reverse direction, from the subscriber
station to the exchange. In this connection, digital telephony signals (e.g.
64 kbit/s signals), facsimile sLgnals, control signals (e.g. 8 kbit/s signa]s)
originating from the exchange-control Vs, videotex (Btx) signals, and acknow-
ledgement signals originating from adjusting device Eb in th~ wide-band
switching network KFb, are combined in the exchange VSt, by a narrow-band
switching network KFs - for example of the type disclosed in our Austrian
Patent 354,527 issued January 10, 1980 - in the multiplexer MU~v provided in
the exchanger for each subscriber - together with a corresponding demultLplexer
DEMUXv for example with multiplex units ZD1000 C1 and ZD1000 E10 for a
64 kbit/s multiplex æignal and a multiplex unit DSE 64 k/2 for combining
~4 kbit/s signals into a 2048 Mbit/s multiplex signal - to Eorm a multiplex
_ 5
signal which is then transmitted to the subscriber station TlnSt, in this
example a time-division multiplex si,gnal; a multiplex signa] pasa:l,rls~, In the
opposite transMission-direction, from the subscriber-stat:loll to the exchrlns,~e,
more particularly a tlme-division rnultiplex s:Lgnal, is fanned out, I,n the
corresponding demultiplexer DEMUXv, into correspolld:Lng lnd:ividual a:l,s~rnala,
--5a-
S
such as the (e.g. 64 kbit/s) digital telephony signal and facsimile si ~al,
switched through the narrow-band switching network KFs the (e.g. 8 kbit/s~
control signal to be passed to the exchange-control Vs, the videotex sigrlal,
and the program-selection signal to be passed to the adjusting device Eb in
the wide-band switching network KFb.
A corresponding grouping and degroup:ing of s:ignals takes place - al-
though in the opposite transmission direction - in the subscriber-station TlnSt,
where a corresponding multiplexer MUXt and demultiplexer DEMUXt are provided
for the purpose.
In the exchange VSt, the electrical connection of an electro~optical
converter e/o is connected to the output from the multiplexer ~Xv provided
there for each subscriber; the input to the demultiplexer DEMUXv, provided in
the exchange, is connected to the output from an opto-electrical converter e/o.
The optical connections of these two converters are connected, through a glass-
fibre directional coupler RKv, to optical wave-guide Ls.
In a similar manner, optical wave-guide Ls in the subscriber-station
is connected, through a glass-fibre directional coupler R~t, to the optical
output from an electro-optical converter o/e and to the optical input to an
opto-electrical converter o/e, the electrical input to the electro-optical
converter o/e being connected to the output from the said multiplexer MUXt and
the electrical output from the opto-electrical converter o/e being connected
to the input to the said demultiplexer DEMUXt. The individual narrow-band
communications terminal units and part-units are then connected to the inputs
to the multiplexer MUXt and to the outputs from demultiplexer DEMUXt, which
needs no further explanation at this time.
Glass-fibre directional couplers RK, which also need no further
explanation since they are known per se (e.g. from "nachrichten elektronic"
(1979) 1, 18), need meet no special requirements for the decoupling of multi-
plex signals frorn each other in both transmission-directions :if, as also
i.ndicated in Figure 1, the multiplex signals are transmitted, in both d:irections,
by the separats-time-position p:rocess, through optical wave-guide I,s. Io th:is
end, in the wide-band communicatiorls system il:lustrated i.n l:igure 1, a buffcr-
circuit Zv, obtained for example by means of a shift-rcgister, is provided in
the exchange VSt between multiplexers MUXv and demultiplexers DEMUXv and
electro-optical converter e/o and opto-electrical converter o/e; in a similar
manner, a corresponding separate-time-position buffer-circuit Zt is provided
in the subscriber station TlnSt between multiplexers MUXt and demultiplexers
DEMUXt, on the one handJ and electro-optical converter o/e and opto-electrical
converter o/e on the other hand.
The shift of the actual directional separation from the optical plane
into the electrical ~and digital) plane obtained in this way has the advantage
that the separate-time-position control-circuits Zv, Zt may follow conventional
IC technology (or example, using shift-registers). The fact, associated with
the use of the separate-time-position process, that the bit-sequence frequency
in signals "bursts" in the lead amounts to a multiple of the useful-bit rate
is better disregarded when used with optical wave-guide Ls since, on the one
hand, there is no radiation interference (reradiation) here and, on the other
hand, line-loss in the optical wave-guide does not increase with increasing
bit-rate, and the range thereof is not affected as it is in a copper line.
In determining the parameters for separate-time-position transmission, for
example "burst"-length and "burst"-pause, it is therefore desirable to base this
upon the maximal possible range obtainable in the transmission of signals
through an opti.cal wave-guide.
~igure 2 gives a corresponding example of the chronological pat-tern
-- 7 --
of the burst transmission. According to this example, a maximal signal-
transit-time of 1001us in each transmission-direction is available for a
digital-signal-~lock lasting 25/us~ corresponding to an optical wave-guide
length of about 20 km. In this connection it is assuMed that, as kno~m per se
(from German AS 25 11 619), bursts with digital-signal words in each o~ t~lo
consecutive (125 lus) pulse-frames are transmitted in both directions If one
also uses, in this connection, the 2048 Mbit/s pulse, which is in any case pre-
sent in digital switching, as a bit-sequence pulse in the bursts, this produces,
in the case of the assumed burst-length of about 251us, a transmission-capacity
of about 3 x 64 kbit/s, i.e. a capacity to transmit, for example, two 64 kbit/s
digital-communications channels (for example for digital telephony and facsi-
mile~ and eight 8 kbit/s digital-communications channels (for signalling,
synchronizing and data-transmission).
Figure 3 shows a further example of a wide-band communications system
according to the inventionj which provides not only the communications services
provided by the system according to Figure 1, but also digital video-telephony,
bidirectional video-communications digital signals being transMitted between
the exchange and the subscriber station, and vice-versa, through optical wave-
guide Ls through which digital communica~ions narrow-band signals are transmitted
in both directions.
'rhe diagram in Figure 3 is based upon that in Figure 1, and the fore-
going explanations relating to Figure 1 therefore apply to Figure 3 also and
need not be repeated, but Figure 3 also shows that the subscriber station also
comprises a video-communications unit VKA with a camera and a video-terminal
and is thus also set up for bidirectional video-communication (video-telephony).
Video-communications unit VKA is connected, in the transmitting direction,
through an analog-digital converter D/A, to one input to multiplexer MUXt and,
in the receiving direction, through a digital-analog converter D/A, to one out-
put from demultiplexer DEMUXt. According to l~'igure .S, one input to a video-
communications switching network KFB is connected, in the exch.mgc VSt, to one
output from multiplexer MIIXv, while a relevant output frolll the said switchins~
network is connected to one input to mult:iplexcr DMlJXv, the said switching nct-
work being also controllcd by exchange-contro] Vs. 'I'hc video connections are
a]so connected through the said switching network K~B.
In addition to 64 kbit/s telephony signals, facsimile signals and
(e.g. 8 kbit/s) control signals, multiplex signals which group video-telephony
signals, for example in the form of 8 Mbit/s digital signals, are transmitted
through wave-guide Ls in both directions, to which end the multiplexers and
demultiplexers may also consist of multiplex units DSMX2/8 (in the case Df an
8 Mbit/s digital signal) and DSMX8/34 (in the case of a 34 Mbit/s digital signal).
An example of the chronological pattern of a corresponding burst
transmission is given in Figure 4. In this case~ a maximal signal-transit-time
of 40 ~us in each transmission-direction is available for a digital-signal-block
(burst) lasting 80 ~s, corresponding to an optical wave-guide length (range)
of about 8 km; within each burst, 8 kbits, for example, can be transmitted
at a transmission-velocity of 100 Mbit/s, for example.
In conclusion, it should be pointed out that the video switching net-
work KF~ - and also the wide-band switching network KFb - shown in Figure 3 may
comprise cross-point circuits which use ECL technology, the said circuits being
formed by controllable multiplexers connected together into multi-stage cross-
point pyramids, as already indicated elsewhere (German Patent 3 204 900.5).
_ 9 _
