Note: Descriptions are shown in the official language in which they were submitted.
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~IGH C~P~TTY r~rr~u~lcATIoNs 8ATELLITE
BACKGROUND OF THE lNV~;N'l'lON
FIELD OF THE lNVl~N'l'lON
The present invention relates to communication
satellites, and in particular, to the provision of a high
bandwidth, high channel capacity, fully switched, fully
interactive communication network in a single satellite.
The inventive system is a high capacity co n; cations
satellite, or HCCS.
DESCRIPTION OF THE RELATED ART
Satellites have been used for communication for years.
One common use of satellites involves distributed
tr~n! i~sion, like the C and Ku band TeleSat, direct
broadcast satellites which have one or two beams. These
satellites, which are in geosynchronous orbit (i.e. their
orbital speed and altitude are such that they seem to hover
over a particular position on the earth's surface,)
broadcast a series of simultaneous "programs" in one
direction to a large number of individual ground stations.
These are not point to point or interactive (2-way)
satellites. However, they do have a fairly wide bandwidth
(typically 100-500 MHz).
Another use for communications satellites is a so-
called point to point gateway type use, in which a
receiving beam is pointed at a large sending dish (for
example, in Europe) and a corresponding transmitting beam
is pointed at a receiving dish in the U.S. (for example,
Intelsat). This system also is geosynchronous and wideband
(100-500 MHz), but has a limited number of beams (for
example, eight beams would be a large number for such a
system). Also, these systems cover only limited areas,
~ allow only limited switching, if any, and handle very few
communication channels.
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Some newer system designs (Iridium, Ellipsat, Calling
Communications) involve a large number (66 to 840) of low
orbit satellites that pass messages among themselves to
create a fully interactive network. These are very
complex, expensive systems limited to low bandwidth (~10
KHz or less) and low capacity (50-200 channels in the
overall system).
Typical satellite communication systems have been
limited by low bandwidth (e.g. 50-500 MHz would handle
only 50-500 channels); switching networks, using stAn~d
video switching capable of inclusion in a satellite, would
handle only 10-100 switched channels. Even the present
nationwide telephone system handles only audio, which has
a much lower bandwidth (~10 KHz), to switch about one
million customers simultaneously. ThLe ground telephone
system contains 10,000-20,000 switching buildings, at a
cost of over $100 billion.
It would be desirable to provide a satellite system
having a large number of channels and high bandwidth, while
providing a fully switched, interactive system. WhLile
optical-based spatial light modulator (SLM) technology is
known, and can be used for transmission through the air, as
evidenced for example in copending Appln. No. 08/133,879,
filed in the name of the present inventor, the application
of SLM technology to provide high capacity satellite
communications has not been known, so far as the present
inventor is aware.
SUMMARY OF THE lNv~N-llON
It is an object of the present invention to create a
c~ ;cation satellite which does not suffer from the
above drawbacks.
It is a specific object of the invention to provide a
system which combines large number of multiple antenna
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beams and a novel optical processing and swit~-hi ng system
utilizing SLM technology.
By utilizing a large number of parallel beams (100 to
4,000) and spatial light modulator (SLM) based optical
processing to distinguish customers within each beam (100
to 1,000 customers/beam) and shift the individual customers
to the appropriate output beam and ouL~u~ frequency, the
present invention allows simultaneous switching of up to
one million simultaneous 1 MHz (full video) signals, thus
yielding a fully interactive video network.
The bandwidth achieved by the invention is 100 times
the bandwidth of the expensive low earth orbit systems, and
hAn~leS five to 20 times the number of simultaneous
customers in a single satellite, in contrast to the 66 to
840 satellites required at present. As a result, the
inventive system is relatively quite low in cost. The SLMs
and beamforming devices are fairly inexpensive single
integrated circuits, enabling a reduction in satellite
weight to be less than half of that of present satellite
designs.
The HCCS system uses from 100-4,000 simultaneous beams
(the baseline design being 1,000). Since it is possible to
reuse the full spectrum in each beam if the beams are coded
properly, it is possible to handle 500 customers per beam
(1 MHz/channel in a total bandwidth of 500 MHz), enabling
total simultaneous usage by about 1 million customers.
The rl ~;n;ng problem is how to switch the 500,000
outgoing channels. As mentioned above, the present phone
system requires 10,000-20,000 buildings to switch the same
number of much lower-bandwidth audio channels; moreover,
the HCCS system must switch the same number of much higher-
bandwidth (1 MHz) video chAnnels within a fairly small
satellite.
Recent developments in SLM using quantum well
technology have created the capability of 1024 x 1024 pixel
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arrays that can be driven at 1 GHz rates from full
reflectance to almost zero reflectance (over 40 dB dynamic
range). While arrays of this size would enable full
implementation of the invention, and would be a preferred
embodiment, as a practical matter at present only smaller
SLMs are available in the necessary quantities and costs.
It is within the contemplation of the invention to use a
larger number of smaller SLMs (perhaps1-wo, four, eight, or
16 or more as desired or necessary) in combination to
provide performance comparable to that achieved by the
larger SLMs.
In accordance with a preferred embodiment of the
inventive switching t~chn;que, first the 500 channels per
beam are encoded by either frequency assignment or
broadband coding. Then, a 1024 x 1024 SLM array (made up
of either a single SLM or multiple smaller SLMs) mixes the
incoming frequencies from the assigned frequencies to
baseband where they are detected and bandpassed.
Alternatively, in the broA~h~n~ coded case, the decoding
signals are multiplied by the input ancl are integrated to
separate the 500 channels per beam. Once separated and
detected, they are remodulated by another set of SLMs to
either move them to the appropriate beam or create the
appropriate wide bandwidth per c,uL~uL beam to retransmit
the information. The entire system takes approximately
seven to 10 1024 x 1024 SLM arrays, a few detector arrays,
and a few linear (1024 x 1) arrays with appropriate optics.
Additional optics to redirect a portion of each beam
back to its same area can also be added to handle the
expected higher volume of local calls.
It also is within the contemplation of the invention
to add special circuitry as necessary to break some
channels down further into over 100 audio channels, or to
combine a number of channels for high definition television
(HDTV) transmission.
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BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the present invention
Will h~c- - more apparent from the detailed description set
forth below when taken in conjunction with the drawings in
which like reference characters correspond throughout, and
wherein:
Figure 1 is an overview of one embodiment of the
invention used as a single communication satellite system.
Figures 2A through 2C are more detailed views of a
series of t~chn;ques for creating a multiple beam antenna
design in accordance with the invention.
Figure 3 is a more detailed view of the structure for
performing optical processing in the first embodiment of
the invention.
Figures 4A and 4B describes a ?c-h~n;sm for
retransmitting a portion of the bandwidth of each beam back
to the same area.
Figure 5 describes an alternative embodiment using
digital coding instead of frequency coding.
Figure 6 is a detailed description of an "arbitrary"
cross bar switch implementation in accordance with a second
embodiment of the invention.
DETATT~n DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 depicts a high capacity communications
satellite system in accordance with the present invention,
in which N beams 2, with M simultaneous customers 1 per
beam, are shown. These M customers would be only a small
fraction of the total customers in the beam. However,
since only approximately 1~ of the customers utilize a
two-way co ln; cation system at any one time, these M
simultaneous users could represent as many as 100 x M
potential customers or ter ;n~l~, each having a small
antenna, a transceiver, and a video camera and TV player~
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The M simultaneous users (where M is from 100 to
4,000; typically 500) would have some low level of near-
lossless video compression to compress each signal to a 1
MHz band (or digital eguivalent), for a total of 500
signals in a typical implementation~ These 500 signals,
each having a bandwidth of 1 MHz, are either frequency
coded or digitally coded to discriminate them from each
other. The signals are received by one of the N parallel
receive beams 3 (typically N = 1000) created by the
multiple beam antenna receiving system on a geosynchronous
satellite (not shown).
on the satellite, the 1000 beams 3 (each cont~ining
500 simultaneous users) are transmitt:ed along N channels 4
to a multiple beamformer 5, using a L x N SLM illuminated
by a laser to form M optical ch~nn~ 6. Each optical
channel 6 is then spread in one ~; ~n~ion using a diverging
cylindrical lens to illuminate a N x M SLM array in an
individual channel resolver 7. The N x M SLM array is
driven by appropriate sinusoidal signals on its backplane
in order to downconvert the desired individual channels to
video. After appropriate detection and filtering, each
channel of each beam is effectively decoded and its signal
is isolated on one pixel of the N x M detector array,
yielding N x M optical channels 8.
An effective cross bar switch '3 is then applied to
switch any individual channel to any desired output
location. In its simplest embodiment:, this would be done
by encoding the signal at its source, on the ground to
ensure that once detected, it will be in the desired column
to be sent to the desired receive location. This would
require no "intelligence" on the part of the satellite, and
no changes in the satellite's operation.
In a slightly more complex implementation, a "double
hop" capability would be added, in which transceivers on
the ground in selected (or in all) beams could receive a
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signal and re-route it to the desired end points. This
allows for alternative routing, when needed.
In a more general embodiment, selected pixels would be
"remodulated" with arbitrary frequencies (or codes), the
downconverting and detection process being repeated in
either plane. The signal on any pixel could be moved to
any other pixel, to permit fully random cross bar coupling.
once the signals have been decoded and detected, they
are used to modulate another N X M SLM to create N x M
optical signal paths 10. These are then provided to an
individual channel modulator 11, which includes another N
x M SLM whose backplane contains appropriate sinusoidal or
code modulation to "fill" the bandwidth of the retrans-
mitted beams. The signals output over the N x M optical
channels 12 then are provided to a beam combiner 13 which
includes a 1 x N detector array and cylindrical optics,
yielding N optical channels 14. Then, a multiple
beamformer 15 is used to create the appropriate signals 16
to create in turn N retransmitted beams 17 which are
coaxial with the N received beams. These beams (typically
1000) contain the 500 channels each completing the cross
linking of full video, simultaneous c~ -n;cation of one
million customers.
An additional path is created from multiple beamformer
5 by subdividing K direct channels 18. This is done most
easily if the channels are frequency encoded by a simple
filter 19, such as a direct return filter, on each beam.
The filtered channels are added along K direct channels 20
to multiple beamformer 15 to permit a large number of local
video connections within each local beam.
Figures 2A-2C show different methods of creating the
"multiple antenna beams". Figure 2A shows a standard
multiple feed curved re~lector design, commonly called a
Gregorian fed multiple beam antenna. In that antenna, a~5 series of actual RF feeds 21 are located at the focal plane
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of a curved reflector 22 so as to create a series of beams
23 that would cover a large area (like the U.S.) Figure 2B
shows an RF Luneburg lens, a t~chn;que that utilizes a
dielectric sphere 24 that has a variable dielectric
constant as a function of radius so as to focus any
parallel rays to a point on the far side of the sphere. If
M feeds were located on the appropriate locations 25, M
beams 23 covering the desired area would be created.
The above two t~chn;ques are wel] known to ordinarily
skilled artisans in this technological field, and so need
not be detailed any further here. However, these
t~chn;ques do tend to be cumbersome when employed in a
satellite system. A more volume efficient design is shown
in Figure 2C, which shows a Luneburg optical lens approach,
in which M incoming beams 26 are sampled by an RF
multi-element array 27 of appropriate element number and
spacing to create M beams, whose elements are connected in
a pixel to array element manner to an N x M SLM 29. Prior
to ouL~uL to SLM 29, the o~L~uL of array 27 is
downconverted from RF to baseband in downconverter 28. A
laser 30 illuminates the SLM 29 via a~o~iate cylindrical
optics 31 and a half-mirror 32, and the output beam is
focused onto the appropriate M detectors using a variable
dielectric sphere 33 to sample the M beams. M feeds 34
(which can be diode lasers) are collocated to create the
outgoing beams. As can be appreciated, the Figure 2C
embodiment would be quite a bit smaller than those of
Figures 2A or 2B.
Figure 3 describes the internal processing from the
output 6 of the incoming beamformer 5 (N optical channels),
through the input 14 of the outgoing beamformer 15 (N
optical channels) as shown in Figure 1. Referring to
Figure 3, the signals from the incoming beamformer 5 are
constituted by N antenna beam signals on separate signal
paths 100 (typically 1000 paths) each cont~;n;ng M
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frequency or digital coded simultaneous signals (typically
M = 500). These signal paths are connected to a 1 x N SLM
array 101. The array is illuminated by a laser 105 through
a collimating lens 104 and a half mirror 103, the output of
the laser 105 then being focused onto the line array 101 by
a cylindrical lens 102. The lens 102 also spreads each
combined beam reflected signal to cover a complete row of
another SLM array 106. This array has each column
hardwired together and modulated by the same signal within
individual channel resolver 107. The first column is
modulated by a frequency fl, the second by a frequency 2f1,
the third by a frequency 3f1, etc. until the last column is
modulated by a frequency Mf1. Thus the beam, which
contains all frequencies from fl to Mfl, is then multiplied
by the reflectance of each pixel which also is modulated by
f1 to Mf1 according to its position in the row. (The
foregoing procedure actually is carried out in in-phase (I)
and quadrature (Q) steps to cover both ~; ?~ions.) Thus
the frequency effectively is "shifted" such that the
desired channel is shifted or down converted to video. The
array of signals is then bounced off half mirror 103 and
focused by the collimating lens 108 onto
detector/accumulator array 109. This procedure effectively
detects the signal and low pass filters the desired signal
for each pixel.
The detector/accumulator array 109 is connected on a
pixel by pixel basis to another SLM array 110 which is
illuminated by laser 113 through collimating lens 112 and
half mirror 111. At this point, each individual channel
has been fully detected and its signal located on one of
the N x M pixels of the-SLM array 110. The image then is
reflected off SLM array 114 which "remodulates" the
individual signals to "fill" the outgoing beams. At this
- point, the incoming N beams are still spread across the
rows where beam 1 is row 1, beam 2 is row 2, etc. The
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columns now represent the individual customers inside the
beam, column 1 representing customer 1, column 2
representing customer 2, etc. Individual channel modulator
SLM 115, which in this embodiment is iclentical to SLM array
106 but rotated by 90~, takes this demodulated array and
remodulates the signal corresponding to customer 1, beam 1
to frequency f1; customer 1, beam 2 to frequency 2fl, etc.
As with SLM array 106, the procedure is carried out in in-
phase (I) and quadrature (Q) steps. Then, after the
signals are reflected off the half mirror 111, they are
compressed by cylindrical lens 116 into a single pixel
which becomes outgoing beam 1. Each of the beams would be
compressed in this ~nner, and the beams would be output
via 1 x N detector array 117 to the M antenna feeds 118.
This is possible since the remodulation has the effect of
modulating each "customer 1" with a different frequency,
allowing receiving customers to differentiate their
respective calls.
Thus, each customer J from all N beams is remodulated
so as to be separated in frequency and combined optically
to create a new output beam J.
For 1000 simultaneous customers per beam, and 1000
beams, this just-described embodiment would allow one
customer from each beam to call customers in each of the
other beams. Though the system's capability obviously
would be quite large (1 million simultaneous video
circuits), it would not match typical communication usage
very well. This is because typically, a large number of
calls are local and non-local calls, and tend to cluster
into high density areas (e.g., New York City, Washington
D.C.)
One technique to alleviate the call density problem
would be to place repeaters in a large nll~her of suspected
under-utilized regions. These repeaters could use beam K
3S as a stopover between the original point and the desired
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destination. While this approach would use up some of the
capacity of area K served by beam K, it also would provide
significant system flexibility.
Figures 4A and 4B describe two mechAni ~ for
increasing the available number of local (i.e. within beam)
calls by dedicating frequencies fl to fk as "local" calls.
This can be done on a beam-to-beam basis by direct
filtering -- a t~chn;que which will be described with
reference to Figure 4A -- or by filtering all f1 to fk
signals after they have been filtered spatially -- a
technique which will be described with reference to Figure
4B. Figure 4A describes an electronic (signal filter
bypass) solution, while Figure 4B describes an optical
solution, involving an optical alteration of N x M array
115 to accomplish a partial bandwidth bypass. In Figure
4A, an incoming signal 200 is divided into two signals by
divider 201. One of the signals continues onto the 1 x N
SLM array 101 for processing as described before. The
other channel is filtered in hAn~pA~s filter Z02 and
combined directly with the output signal coming from the 1
x N detector array 117. These signals are summed in summer
203 to provide a summed signal, which is used to drive the
output beam 204 corresponding to the same input beam.
Figure 4B describes an optical solution to the same
problem. The signal coming through half mirror 111 is
partially interrupted by a full mirror 205 oriented at 45~
which reflects off the vertical mirror 206 and another 45~
mirror 207 to image what is in region a to region b. Note
that region b is rotated by 90~ with respect to region a.
After appropriate modulation, the output beam contains
frequencies fl to fk that are identical to the frequencies
fl to fk sent up in the same beam.
Figure 5 describes an alterative embodiment that
replaces the downconversion SLM 106 and the remodulation
SLM 115 with digital code multiplication. The nomenclature
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used in this Figure indicates that different codes can be
used in commùnicating in the two directions. As shown,
frequency fl is replaced with code K + 1, frequency f2 is
replaced with code K ~ 2, and so on for the downconversion
process, and frequency fl is rep]aced with code 3,
frequency f2 is replaced with code 2, and so on for the
remodulation process. The reflective signal is then
integrated to decode the desired signals. This t~chnique
will allow for many more channels to be contained in a
given bandwidth, as is conventional in code division
multiple access (CDMA) systems.
The simplest embodiment, even with the inbeam
repeaters and the Partial Bandwidth B~pass to increase the
available local calls, would have difficulty handling a
large number of calls between two separate beams. Using
the repeater technique uses up one additional channel per
extra call. Thus, for example, 10 c<~lls between Beàm 10
(Los Angeles) and Beam 342 (Washington, D.C.) would take 19
total channels. A fully arbitrary cross bar switch, an
embodiment of which is shown in Figure 6, would handle that
problem easily.
The arbitrary cross bar switch implementation of
Figure 6 includes all of the structure of Figure 3, but
adds optical elements between N x M ';LM array 110 and an
additional detector/accumulator 109 and SLM array 110. The
first detector/accumulator 109 and SLM array 110 identify
each incoming customer by column and each beam by row. The
optical signal out of SLM 110 is diverted by a half mirror
300 through half mirror 301, and is focused by lens 302
onto an N x M arbitrary modulator SLM array 303 (arbitrary
modulator ~1). This array 303 is a complex N x M array
that allows for any frequency f1 - Mflt:o modulate any pixel
in the N x M array. With the arbitrary modulator ~1, each
pixel can be multiplied by an arbitrary Kfl that can be
different for each pixel.
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The reflecte,d arbitrarily modulated signal from array
303 then is focused to a line by the first cylindrical lens
304 and is spread by the second cylindrical lens 304
through half mirror 305 to another SLM array 306 which
downconverts each pixel to its fl - Mfl position. The image
output by array 306 then is reflected by half mirror 305
through half mirror 307 to a second N x M arbitrary
modulator SLM array 308 (arbitrary modulator #2) which
multiplies each pixel by an arbitrary value Lfl which is
different for each pixel. The output of SLM array 308 is
reflected off half mirror 307 and passed through first and
second cylindrical lenses 309, 309, similarly to the
handling of the output of SLM array 303. Thus each pixel
is downconverted to its fl to fN position onto SLM array
311.
The first SLM array 306 effectively moves the signal
in plane #1 - the second SLM array 311 effectively moves
the signal in plane #2, which is orthogonal to plane #1.
The signal is then re-detected (as done by a
detector/accumulator 109) and used to modulate another SLM
array (like SLM array 110) and combined with the original
signal from SLM array 110. Thus any signal from any beam
can be moved to be like any other signal from any other
beam, yielding a great deal more flexibility.
While the invention has been described in detail with
reference to preferred embodiments, various changes and
modifications within the scope and spirit of the invention
will be apparent to those of working skill in this
technological field. Thus, the invention is to be
considered as limited only by the scope of the appended
claims.
