Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Wireless Data Communications Network and Method for Operating the Data
Communications Network
2 o FIELD OF THE INVENTION
The invention relates to a wireless data communications network in accordance
with the
preamble of claim 1, and a method for operating the data communications
network in
accordance with the preamble of claim 9.
BACKGROUND OF THE INVENTION
It is known in connection with wireless data communications networks to
transmit the data
3 0 to be transmitted without the interposition of a conducting medium, for
example an
electrical conductor or a glass fiber. Here, the data to be transmitted are
forwarded by
means of suitably modulated electromagnetic or optical waves.
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Data transmission methods by means of high-frequency electromagnetic waves are
known in a number of variations and are presently employed in
telecommunications in
particular. For example, telephone calls from the fixed network or mobile
radio network
can be transmitted extra-terrestrially over short to medium ranges. Further
than that, this
data transmission method has been successfully used for over 20 years for
transmitting
information from satellites over long distances. At present, satellite
transmissions are in
particular used for the transmission of radio and broadcast frequencies, but
also for
intercontinental telephone transmissions.
Wireless optical data transmission methods are operated by means of data-
modulated laser pulses. In comparison with high- frequency radio link
connections, the
optical free space connections have been shown to be very advantageous for
data
transmissions for various reasons. For example, because of its extremely short
wavelength, an optical laser beam can be very easily radiated by means of a
relatively
small optical transmission device and therefore at a very small spatial angle.
In contrast
to the above mentioned radio link connections, it is possible because of this
good
focusing ability of the laser beam to employ very small transmitting stations
and receiving
antennas in the course of optical data transmissions. With these minimalized
optical
2 0 antennas considerably larger data rates can be transmitted at a minimal
transmitting
output than it would be possible, for example, with data transmissions by
means of radio
link systems at the same transmitting output. Moreover, optical data
transmission
methods advantageously have almost no background signal noise.
2 5 The good focusing ability, or respectively capability for bundling, of the
optical
transmission beam, however, requires an extremely precise determination of the
direction
of the transmitted beam in the transmitting station, as well as exact tracking
and
alignment of the optical receiver device in the receiving station. Moreover,
the problem
arises in optical free space data communications in particular, that at least
one of these
3 0 stations is arranged freely movable in space, which makes leading the
optical laser beam
in respect to the optical receiver device necessary. A method and an
arrangement for
the disruption- free operation of optical data links between satellites,
wherein a laser
beam is employed for the data transmission between the respective satellites,
is
described in EP 0 876 013 A1.
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Besides a high data transmission rate, the lowest possible energy use of the
transmittinglreceiving stations, and a data transmission as free as possible
of signal
noise, additional requirements are being made on data communications networks
in
accordance with the species, in particular by military air and space
technologies.
For military reconnaissance, or respectively information transmission in
crisis or war
zones, the data communications network employed there must assure the highest
degree
of freedom from interception and interference with the data transmissions.
Although as a
rule an existing communications network is present in such crisis or war
zones, it is not to
l0 be used, especially for reasons of a deficient or lacking interception
security. Up to now a
satellite-supported data communications system had therefore been used as an
obvious
solution, wherein the data to be transmitted are sent from a ground-supported
or aircraft-
supported transmitting station via satellites to the receiving station. In
this case data
transmission occurs via radio signals. However, it was shown that this data
transmission
system is not one hundred percent secure from being intercepted, and that
moreover it
can be interfered with, or respectively disrupted, by third parties in an
undesirable
manner.
It is furthermore of decisive importance that an interception-free
communications
2 0 network can be established very quickly and with simple means. This
communications
network should be operable nearly independently of the existing
infrastructure. Moreover,
a change in the situation can for example make it necessary to change the
structure of
the data communications network, which makes a certain degree of flexibility
of the
network topology used desirable.
Such a data communications network meeting the requirements mentioned could
not
be satisfactorily realized up to now.
Based on this, the object of the present invention is to make available a
universally
3 0 usable data communications network which is secure against interception
and interruption
to the highest possible degree, which moreover is suitable for data
transmissions at a
high information density. Furthermore, it is intended to make available a
method for
operating this data communications network.
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The object in regard to the arrangement is attained in
accordance with the invention by means of a data
communications network.
In accordance with this, a wireless data communi-
cations network is provided, wherein a plurality of flying
objects capable of changing their positions are located in
a common, limited area in the earth's atmosphere or at the
distance of the earth atmosphere from the surface of the
earth, can be connected with each other by means of an
optical transceiver station in each flying object, each of
which can be connected interference-free by means of first
wireless data links which are designed at least partially
as laser-optical data links using a broadband laser beam
having a minimal angle of divergence to assure an
interruption secure and interference secure data, and by
the network having at least one fixed station on or near
the ground, which can be connected with at least one
transceiver station via second wireless links wherein:
at least one of the transceiver stations is designed
for bi-directional data transfer and has an optical
receiving unit and an optical transmitting unit for this
purpose,
the optical transmitting unit containing means for
optical data modulation, a laser unit and an optical output
amplifier for transmitting data-modulated laser signals and
the optical receiving unit having a reception amplifier and
means for optical data modulation,
the transceiver stations having means for position
stabilization and means for tracking the optical beam and
at least one of the transceiver stations is seated freely
pivotable in space in such a way that this transceiver
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station can be coupled via first data links with any
arbitrary transceiver station.
The object is regard to the method is attained by a
method for operating a data communications network which
includes the following method steps:
(a) a data transfer is performed between at least two transceiver stations,
each
provided in flying objects, via the first data links, wherein an optical laser
signal is used at
least in sections for the data transfer,
(b) then a wireless data transfer between at least one transceiver station and
a
station on near the ground takes place via the second data links, wherein a
data signal is
received-f~om the respective transceiver station andJor is transmitted to the
respective
transceiver station.
The dependent claims are directed to preferred embodiments and further
developments of the invention.
Tile present invention describes an optical data communications network, which
is
based on fixed stations on, or near the ground, and non-stationary flying
objects, which
are connected~with each other via wireless~data links and therefore constitute
a
communications network which is freely configurable over a wide range. This
data
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communications network meets the demands mentioned at the outset, which are
made
on data communications particularly in crisis or war zones, and permits a
linkage of the
input and output signals of the data communications network which is free of
electrical
feedback.
The proposed concept is essentially based on interruption- free optical laser
communications between different flying objects operating above the cloud
tops. These
laser-optical data links offer the greatest amount of interception security,
and can
furthermore be advantageously established, or changed very rapidly. This data
1 o communications network, which is a competitor of satellite-supported
communications
networks, can, in contrast to the latter, be installed with comparatively
simple and cost-
effective means. Only at least two flying objects are required for the build-
up of such a
data communications network, besides the stations on or near the ground. Since
the
individual flying objects, each of which represents the network linkages of
the data
communications network, can operate independently of the other within wide
limits, a
maximal autonomy of the network linkages can be assured. In particular, by
means of
this the data communications network can be very rapidly reconfigured and
adapted to
changes in this way. By employing additional flying objects it is also
possible to generate
redundancy, and therefore greater flexibility in the topology of the data
communications
2 0 network.
Further details and advantages of the invention will be explained in what
follows by
means of two exemplary embodiments. The invention will be explained in greater
detail in
what follows by means of the exemplary embodiments represented in the
drawings.
2 5 Shown are here in:
Fig. 1, a first exemplary embodiment of a data communications network in
accordance with the invention,
3 o Fig. 2, a second exemplary embodiment of a data communications network in
accordance with the invention,
Fig. 3, a diagram indicating the maximum track distances as a function of the
cloud
tops and the flight level of the aircraft.
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Equal or functionally equal elements are provided with the same reference
numerals
in all drawing figures.
Fig. 1 represents a first data communications system in accordance with the
invention, which is built up by means of aircraft. Two aircraft flying at high
altitude are
identified by 11, 12 in Fig. 1. Optical receiver stations 21, 22 have been
installed in each
aircraft 11, 12. The transceiver stations 21, 22 are directly coupled with
each other by
means of an optical data link 31. Furthermore, a base station 61, which is
arranged on
the surface 51 of the earth, is provided which, in the present case, is
connected via a
1 o further data link 71 with an aircraft 11.
An interruption-free optical data link 31 is essential for this coupling of
the transceiver
stations 21, 22. For this reason, the two aircraft 11, 12 and the data link 31
connecting
them, have been arranged above the cloud tops in the present example. Here,
the flight
level of the aircraft was identified as d3, the distance of the aircraft from
each other as d1,
and the cloud tops as d2.
The transceiver stations 21, 22 can be designed for bidirectional or
unidirectional
data transfer, i.e. for transmitting and/or receiving optically modulated
data, wherein the
2 0 data to be transmitted are modulated in the form of a broadband laser
beam. The optical
transmitting unit of a transceiver station 21, 22 designed for transmitting
contains means
for the optical transmission of the data, a laser unit and an optical output
amplifier. As a
rule, an optical receiving unit of a transceiver station 21, 22 designed for
receiving has a
reception amplifier and means for optical data transfer. Furthermore, the
transceiver
stations 21, 22 have means for position stabilization, as well as means for
tracking the
optical beam. By means of this it is possible to assure that an interruption-
free data link
31 is assured in case of slight vibrations, or respectively relative movements
of the
transceiver stations 21, 22 in respect to each other. The optical transmitting
and
receiving devices of a transceiver station 21, 22 are advantageously arranged
so they are
3 0 freely pivotable in space, so that they can build up interruption-free
data links with other,
also freely movable transceiver stations 21, 22.
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The structure and functioning of such transceiver stations is exactly
described in EP 0 847 150 A1 and EP 0 863 627 A1.
The functioning of the data communications network from Fig. 1 will be
briefly described in what follows.
The first aircraft 11 in the example shown is located above a partial area 52
of the surface of the earth, while the second aircraft 12 is located above an
area
far distant from the partial area 52. The partial area 52 can be, for example,
a
crisis or war zone, above which the first aircraft 11 flies for the purpose of
aerial
reconnaissance. The data obtained from this aerial reconnaissance are
l0 transmitted from the first transceiver station 21 to the second transceiver
station
22 in the second aircraft 12 via a broadband data-modulated laser beam. It is
advantageously possible to transmit data at transmission rates far above 100
Mbic/sec by means of this broadband laser beam. The data-modulated laser
beams have a minimal angle of divergence and prevent therefore an undesired
radiation. It is possible to assure by means of this type of data transmission
that
an interception-secure and interference-secure data transmission takes place
at
least above the partial area 52.
The demodulated data can be transmitted from the second aircraft 12 via a
further
20 data link 71 to the station 61 on or near the ground. The data transmission
via the
second data link 71 can take place by means of radio signals, since in the
case shown the
ground station is located far outside the partial area 52, so that here a
reduced
requirement for interFerence, or respectively interception security of the
data transmission
results. However, an optical data transmission between the aircraft 12 and the
station 61
on or near the ground would be conceivable.
Fig. 2 shows a second exemplary embodiment of a data communications network in
accordance with the invention. Here, three aircraft 11, 12, 13 are provided,
whose
transceiver stations (not represented in Fig. 2) are respectively connected
with each other
via data links 31, 32. Two ground stations (or stations near the ground) 61,
62 are
additionally represented, which are respectively connected with one of the
aircraft 11, 12
via further data links 71, 72. A closed data communications network can
therefore be
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created in the example represented in Fig. 2, wherein a completely
interception-secure
and interference-secure data transmission between two ground stations 61, 62
is possible
over very large distances.
Figs. 1 and 2 show that it is possible to create any arbitrary data
communications
networks in accordance with the invention in that any arbitrary number of
aircraft 11, 12,
13 and ground stations 61, 62 are suitably connected by means of laser-
optical data
links. As already mentioned, an interruption-free optical data link 31, 32 is
essential for
the functioning of the data communications network. An optical link which is
interruption-
l0 free over great distances, can typically, but not necessarily, be assured
above the cloud
tops 41. For this reason the aircraft 11, 12, 13 connected with each other via
data links
31, 32 must fly at least high enough that the respective data links 31, 32
between them
are dependably arranged above the cloud tops 41 (d4 > d2).
Fig. 3 shows a diagram indicating the maximum track distances (d1 ) between
two
aircraft as a function of the flight level (d3) and the cloud tops (d2). It
turns out that, with
assumed cloud tops at 12 km and a flight level of 16 km, a maximum distance of
approximately 500 km results between the two aircraft, while at a flight level
of 30 km the
free distance nearly doubles.
To create the data communications network in accordance with the invention,
aircraft
11, 12, 13 were used in Figs. 1 and 2, which are designed for flying at great
altitude.
Such high- altitude aircraft, which as a rule are jet-propelled, have a
service ceiling which
mostly lies high above the maximum cloud tops. However, in every case the
aircraft
2 5 should have a ceiling of more than 12,000 m. It would also be conceivable
to use captive
balloons in place of aircraft. Very great altitudes, as far as up into the
stratosphere, can
be attained by means of captive balloons.
However, these aircrafts can also be designed as so-called unmanned drones,
such
3 o as are often employed for reconnaissance purposes in crisis zones.
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