llllll|||l|l||llllllllllllll?tlllillggllulllllllllllllllllllllllllll
`
`Unlted States Patent [19]
`Polivka et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,463,656
`Oct. 31, 1995
`
`[54] SYSTEM FOR CONDUCTING VIDEO
`COMMUNICATIONS OVER SATELLITE
`COMMUNICATION LINK WITH AIRCRAFT
`HAVING PHYSICALLY COMPACT,
`EFFECTIVELY CONFORMAL, PHASED
`ARRAY ANTENNA
`
`[75] Inventors; Alan L, Polivka, Palm Bay; Charles
`Zahm, India-antic, both of F1a_
`
`[73] Assignee: Harris Corporation, Melbourne, Fla.
`
`[21] APPL Nu; 146,289
`
`oct- 29, 1993
`[22] Filed:
`[51] Int. Cl.6 ............................ .. H04N 7/167- H04B 1/69
`[52] Us. CL
`3751200 376/18 380/10
`_
`_
`380/13’ 380/19_’ 380/29
`f S
`,
`[58] Field 0 earch ................................. .. 375/1, 370/18,
`380/10’ 13’ 19’ 20
`
`[56]
`
`.
`References Clted
`U_S_ PATENT DOCUMENTS
`
`4’743’906 5/1988 Fullerton ' ' ' ' ' ‘ ' '
`4,901,307 2/1990 Gilhousen et a1.
`5,127,021
`6/1992 Schreiber . . . . . .
`
`' ' ' ' " 375”
`375/1
`. . . . .. 375/1
`
`5,230,076
`
`7/1993 Wilkinson . . . . .
`
`. . . . .. 375/1
`
`.... .. 375/1
`5,285,470 2/1994 Schreiber et a1. .
`5,313,457 5/1994 Hostetter et al. ......................... .. 375/1
`
`Primary Examiner—-David C. Cain
`Attorney, Agent, or Firm—Charles Wands
`
`[57]
`
`ABSTRACT
`
`A system architecture and communication methodology for
`signi?cantly reducing the size of an aircraft antenna required
`to provide full broadcast quality video communications with
`an aircraft via a satellite communications link includes a
`combination of video bandwidth compression, spread spec~
`trum waveform processing and an electronically steered,
`circular aperture phased array antenna, that is conformal
`with an airframe surface of the aircraft. The combination
`provides su?icient signal power to the aircraft, enables
`interference from other satellites to be rejected and main
`‘aims th" Power Spectral density 0f the satellite’s Video
`transmission within FCC requirements. The polarization of
`the receive array is aligned with that of the incoming beam
`from the relay satellite by means of an error signal feed back
`path to control the steering waights Ofthe may Because the
`phased arrays are conformal, it is necessary to modify the
`phase shift settings produced by the antenna steering mecha
`nism executed by the degree of departure of the conformal
`geometry of the array from a planar con?guration. A coor
`dinate transformation look-up table is coupled in the control
`feedback path from the antenna steering mechanism and the
`
`phase shift elements of the phased may‘
`
`29 Claims, 7 Drawing Sheets
`
`COMPRESSED vmto
`OR OTHER DATA
`(FROM IELECONFERENCE
`SHE 14)
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`Petitioners' Ex. 1028 - Page 1
`
`

`
`Petitioners' Ex. 1028 - Page 2
`
`

`
`U.S. Patent
`
`Oct. 31, 1995
`
`Sheet 2 0f 7
`
`5,463,656
`
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`FTC. 2A
`
`Petitioners' Ex. 1028 - Page 3
`
`

`
`US. Patent
`
`Oct. 31, 1995
`
`Sheet 3 of 7
`
`5,463,656
`
`3 a
`
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`
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`COMPRESSED VIDEO (OR OTHER DATA)
`(To TRANSMITTER STAGE 204)
`
`FIG. 2B
`
`Petitioners' Ex. 1028 - Page 4
`
`

`
`U.S. Patent
`
`Oct. 31, 1995
`
`Sheet 4 of 7
`
`5,463,656
`
`2/1}. MONOPULSE COMPARATOR
`
`FIG. 3.4
`
`f 420
`POLARIZATION
`RECEIVER
`(FIG 6)
`
`II
`RECEIVER /230*K
`STAGE
`—\
`(COMPRESSED VIDEO
`FOR TELECONF. OR
`OTHER DATA,
`TELEPHONY ETC.)
`
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`
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`
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`
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`
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`DEMODULATOR
`
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`FREQ. SOURCE
`
`TRANSMITTER
`
`1sTACTs
`
`FIG. 3B
`II
`
`'
`
`COMPRESSION/
`RECONSTRUCTION
`UNIT
`
`II
`
`FORWARD ERROR
`CORRECTION
`DECODER UNIT
`
`MUX
`
`VIDEO
`ON BOARD
`—% VIDEO
`RECONSTRUCTION
`UNIT
`MONITOR(S)
`(OECONRRTssIONI
`
`Petitioners' Ex. 1028 - Page 5
`
`

`
`Petitioners' Ex. 1028 - Page 6
`
`

`
`US. Patent
`
`Oct. 31, 1995
`
`Sheet 6 of 7
`
`5,463,656
`
`Petitioners' Ex. 1028 - Page 7
`
`

`
`U.S. Patent
`
`Oct. 31, 1995
`
`Sheet 7 of 7
`
`5,463,656
`
`1
`POLARIZATION
`I
`RECEIVER
`I
`I
`I
`I
`I
`I
`I
`I
`I
`
`COORDINATE
`
`4
`
`*- TRANSTORMATION ‘
`
`II
`
`r431
`LPF
`
`ELEMENT LOCATION
`& ORIENTATION
`
`I
`I
`I
`
`FIG.
`
`Petitioners' Ex. 1028 - Page 8
`
`

`
`5,463,656
`
`1
`SYSTEM FOR CONDUCTING VIDEO
`COMMUNICATIONS OVER SATELLITE
`COMlVIUNICATION LINK WITH AIRCRAFT
`HAVING PHYSICALLY COMPACT,
`EFFECTIVELY CONFORMAL, PHASED
`ARRAY ANTENNA
`
`FIELD OF THE INVENTION
`
`The present invention relates in general to communication
`systems and is particularly directed to system architecture
`and communication methodology that signi?cantly reduces
`the size of the aircraft antenna required to provide full
`broadcast quality video to (or from) an aircraft via a satellite
`communications link.
`
`10
`
`15
`
`BACKGROUND OF THE INVENTION
`
`aperture.
`
`SUMMARY OF THE INVENTION
`
`In accordance with the present, the size of the antenna can
`be signi?cantly reduced, thereby greatly increasing the prac
`ticality of conducting satellite-linked broadcast quality
`video communications with an aircraft, by means of a
`combination of video bandwidth compression, spread spec
`trum waveform processing, forward error correction coding
`and circular aperture phased array antenna technology. By
`combining the signal processing methodologies with a
`phased array antenna, there is realized a communication
`which ensures that sui?cient signal power can be received at
`the aircraft, interference from other satellites can be rejected
`and the power spectral density of the satellite’s video
`transmission can be kept within FCC requirements while, at
`the same time, using a signi?cantly smaller aircraft antenna
`aperture than would otherwise be possible.
`In accordance with the communication mechanism
`employed by the present invention, video signals to be
`transmitted to the aircraft, which can originate on the ground
`from any of a number of potential sources, such as a
`TV-receive only satellite receiver, cable, etc. are initially
`digitized and compressed. The compression operation
`reduces the data rate of the digitized video (which, for
`example, may be on the order of 100 Mb/s) by nearly two
`orders of magnitude (with present day technology), while
`maintaining the full motion and resolution associated with
`broadcast quality video. The video compression reduces the
`information bandwidth which, in turn, reduces the receive
`aperture size required to maintain a given bit error rate
`(assuming all other factors remain the same). The com—
`pressed information bandwidth also improves spread spec
`trum processing gain.
`The digitized compressed video signal can be encoded for
`forward error correction and then spread spectrum-modu
`lated onto a carrier. The use of error correction coding in
`conjunction with eiiicient (e.g. coherent PSK-type or MSK)
`data modulation further reduces the aperture size for a given
`bit error rate.
`The power spectral density of the modulated signal is
`reduced via the spread spectrum processing. Spread spec
`trum processing provides several bene?ts: reduced power
`spectral density (for FCC compliance), privacy (to prevent
`unauthorized users from demodulating the video signal) and
`it enables the receiver on the aircraft to reject interfering
`transmissions from other satellites. Spread spectrum pro
`cessing can take the form of direct PN sequence modulation
`and/or frequency hopping, for example.
`The spread signal is then transmitted from the ground to
`a relay satellite. The relay satellite retransmits the spread
`signal through a transmission zone (e.g. continental US.
`conical coverage) within which the aircraft is travelling. The
`aircraft receives the satellite’s transmission via a compact
`phased array antenna which is preferably conformally con
`?gured so that it may be mounted on the fuselage of the
`aircraft. The phased array antenna provides the required
`amount of antenna gain, while occupying less volume than
`would a purely mechanically steered antenna. The phased
`array antenna may be totally electronically scanned or it may
`only be partially electronically scanned. An example of a
`phased array which is only partially electronically scanned
`is one which scans electronically in one dimension (e.g.
`elevation) and mechanically (e.g. rotational) in the other.
`The face (aperture) of such an antenna may be parallel to the
`
`Conventional schemes for conducting video communica
`tions by way of a satellite link use analog modulation
`formats, which require a very large information bandwidth
`in order to achieve the full motion and resolution that is
`characteristic of ‘broadcast quality’ video. Due to intema
`tional restrictions and FCC regulations placed upon satellite
`transmission power spectral density, it is necessary to use a
`physically large receive antenna with these traditional wide
`band analog modulation formats, in order to achieve the high
`signal-to-noise ratio associated with broadcast quality video.
`Another factor that mandates the use of a physically large
`video receive antenna is the need to reject (interfering)
`transmissions from other satellites which are near the sat~
`ellite sourcing the video. Because commercial satellites can
`be spaced as closely as 2° (in longitude) from one another,
`the antennas utilized in the receive link from these satellites
`are typically designed to have a null-to-null beamwidth of
`less than 4° (+/—2°). Such a narrow beamwidth requires a
`considerably large antenna aperture at the allocated com—
`mercial satellite operating frequencies.
`Unfortunately, the need to install a large geometry
`antenna on the aircraft is one of the greatest obstacles
`incurred to date in attempting to receive broadcast quality
`video from satellites. This has generally rendered the
`antenna, and therefore the communication system, to be
`impractical, because of size, cost, power and/or weight
`constraints associated with the aircraft. Indeed, the use of a
`purely mechanically steered aircraft antenna for this appli
`cation is generally precluded, since most aircraft have lim
`ited space on board and the fact that a mechanically steered
`antenna requires a volume larger than that of the antenna
`itself, in order to accommodate steering over the range of
`pointing angles required to maintain communications during
`normal aircraft flight maneuvers.
`To signi?cantly reduce the volume required and to allow
`placement of the antenna on or near the aircraft’s skin, an
`electronically steered (phased array) antenna (or one that is
`at least partially electronically steered) is preferred. Elec
`tronic scanning, however, affects the antenna aperture area
`required, since the gain of a phased array antenna con?gu
`ration decreases (the bearnwidth widens) as the antenna is
`electronically scanned off-boresight. For example, at a scan
`angle of 60°, the gain may drop by approximately 5 dB from
`what is achievable at boresight. This reduction in gain must
`generally be compensated by an increase in antenna aperture
`area (e.g. by a factor of more than three to recoup the ?ve
`dB loss). Hence, although the phased array antenna occupies
`a much smaller volume than a mechanically steered antenna,
`there is still a strong incentive to reduce the required antenna
`
`20
`
`25
`
`45
`
`55
`
`60
`
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`
`Petitioners' Ex. 1028 - Page 9
`
`

`
`5,463,656
`
`3
`plane of rotation or may be tilted. This architecture still
`provides signi?cant volume reduction as compared with a
`purely mechanically scanned antenna.
`In a preferred embodiment where the antenna can be
`mounted conformal with the aircraft surface, the antenna is
`mounted on the top of the fuselage as two phased arrays, one
`on the port side and one on the starboard side of the aircraft,
`so as to provide maximal spatial coverage with the satellite
`regardless of the attitude of the aircraft. A single antenna
`could be used in place of the port-starboard pair in situations
`where a more restricted beam scanning volume is accept
`able. Conformal mounting provides additional bene?ts, such
`as minimal visibility of the antenna, n0 consumption of
`cabin space, minimal aerodynamic drag, etc. The antenna
`aperture is approximately circular so as to reduce the
`antenna sidelobe levels. This minimizes interference with
`respect to satellites that are neighbors to the satellite being
`used.
`A monopulse comparator difference channel is employed
`to control antenna aiming so as to keep the phased array
`pointed at the satellite regardless of the attitude of the
`aircraft. The output of the antenna is despread, demodulated,
`(optionally) decoded and decompressed for use on board the
`aircraft.
`Where the aircraft has an on board video source, such as
`a video teleconference system, the same basic communica
`tion techniques employed for ground-to-air video transmis
`sions are employed for the transmission of video from the
`aircraft. Compression of the video on the aircraft reduces the
`required e.i.r.p. from the aircraft and increases attainable
`spread spectrum processing gain. Spectrum spreading
`reduces the spectral density of the transmitted signal, which
`reduces the transmit antenna’s aperture size required to
`allow the transmitted signal to remain within FCC require
`ments, so as not to interfere with other satellites.
`In addition to maintaining the phased array antenna on
`board the aircraft pointed at the satellite, it is necessary to
`maintain the polarization of the receive and transmit arrays
`aligned with those of the relay satellite. For this purpose the
`output of each antenna element preferably drives a polariz
`ing network containing respective vertical and horizontal
`polarization associated 90° hybrids and two phase shifters.
`The phase shift elements are operative to rotate the polar
`izations of the input waveforms output by the antenna
`elements, so that any linear polarization can be obtained at
`the hybrid outputs. Corresponding ports of each 90° hybrid
`are summed together. The resulting amplitude and phase of
`the summation output is proportional to the sine and cosine
`of the angular error between the phase shifter settings and
`the angular offset of the phased arrays relative to the
`polarization. Other acceptable means of varying the antenna
`polarization include mechanically adjustable polarizers
`(which are especially applicable for the hybrid electro
`mechanical array mentioned previously). The summation
`outputs are demodulated in respective ‘polarization channel’
`and ‘data charmel’ receivers. The ‘data channel’ receiver is
`used to phase lock the ‘polarization channel’ receiver. Func
`tionally, the outputs of the respective receivers are then
`multiplied together in a mixer to derive an error signal which
`is a function of the sine of twice the angular polarization
`error. (In accordance with a preferred implementation, mul
`tiplication is achieved digitally, after matched ?ltering in
`both receivers.) This output of the “mixer” is coupled
`through a lowpass loop ?lter to reduce the noise and to
`provide a zero steady state tracking error. The lowpass
`?ltered signal is used to adjust the settings of the phase shift
`elements of the phased arrays, in accordance with a phased
`
`4
`array weight control mechanism (for steering the beam
`pattern of the phased array) contained within the antenna
`control processor. The transmit array’s polarization angle is
`slaved to that of the receive array. Because the preferred
`phased arrays are conformal or non-planar, it is necessary to
`modify the phase shift settings produced by the antenna
`steering mechanism executed by the control processor
`according to the degree of departure of the conformal
`geometry of the array from a planar con?guration. For this
`purpose, a coordinate transformation look-up table is
`coupled in the control feedback path from the antenna
`steering mechanism and the phase shift elements of the
`phased array.
`In addition to video communications, the present inven
`tion can accommodate other signal formats, such as data
`from terminals, digital telephony, etc. Simultaneous com
`pressed video and data can be transmitted via TDM, FDM,
`CDM or a combination thereof.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 diagrammatically illustrates a communication sys
`tem in accordance with an embodiment of the present
`invention for effecting full motion and resolution broadcast
`quality video communications between a satellite-linked
`earth station and an aircraft;
`FIGS. 2A and 2B, taken together, diagrammatically illus
`trate the system architecture of an earth station for sourcing
`video signals to be transrrritted to an aircraft from a com
`mercial satellite providing one or more channels of com
`mercial television prograrnnring and teleconference video
`signals sourced from a teleconferencing site linked to the
`earth station, the earth station also receiving video etc.
`signals from the aircraft;
`FIGS. 3A and 3B, taken together, show the system archi
`tecture of the video transceiver on board an aircraft;
`FIG. 4 diagrammatically shows fuselage-mounted con
`formal phased array antenna comprising two separate pairs
`of transmit and receive phased arrays, one of which is
`mounted on the port side of the top of the fuselage of the
`aircraft and the other of which is mounted on the starboard
`side of the top of the aircraft fuselage;
`FIG. 5 shows a low pro?le, conformal con?guration of a
`transmit, receive phased array pair formed of a laminate
`structure having a top layer that contains a two-dimensional
`array of antenna elements and a bottom layer through which
`a transmission line interconnect is distributed; and
`FIG. 6 shows the polarization tracking mechanism asso
`ciated with the antenna elements of a respective conformal
`phased array comprised of a two-dimensional distribution of
`dual polarization antenna elements.
`
`DETAILED DESCRIPTION
`
`Before describing in detail the satellite-linked video com
`munication system in accordance with the present invention,
`it should be observed that the present invention resides
`primarily in what is effectively a novel combination of
`conventional signal processing and communication circuits
`and components and not in the particular detailed con?gu
`rations thereof. Accordingly, the structure, control and
`arrangement of these conventional circuits and components
`have been illustrated in the drawings by readily understand
`able block diagrams which show only those speci?c details
`that are pertinent to the present invention, so as not to
`obscure the disclosure with structural details which will be
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`Petitioners' Ex. 1028 - Page 10
`
`

`
`5,463,656
`
`15
`
`25
`
`5
`readily apparent to those skilled in the art having the bene?t
`of the description herein. Thus, the block diagram illustra
`tions of the Figures do not necessarily represent the
`mechanical structural arrangement of the exemplary system,
`but are primarily intended to illustrate the major structural
`components of the system in a convenient functional group
`ing, whereby the present invention may be more readily
`understood.
`FIG. 1 diagrammatically illustrates a satellite-to-aircraft
`communication system in accordance with an embodiment
`of the present invention for effecting full motion and reso
`lution broadcast quality video communications between a
`satellite-linked earth station 11 and an aircraft 12. Video
`signals to be transmitted to the aircraft may originate from
`a variety of sources, such as a TV-receive only satellite
`receiver, CATV, etc. For purposes of presenting an exem
`plary embodiment, the video signals will be assumed to
`include both commercial television programming down
`linked from a commercial satellite 13, as well as private
`teleconference video signals sourced from a teleconferenc
`ing site 14, which is linked to earth station 11 by land lines,
`microwave or ?ber-optic links, shown generally at 15.
`The video signals received by earth station 11 are pro
`cessed for transmission to aircraft 12 by way of a transmit!
`receive antenna dish 16. Antenna 16 uplinks an RF carrier
`upon which the video has been modulated to a relay satellite
`23. The video processing mechanism, to be described more
`fully below with reference to FIGS. 2A and 2B, involves
`digitizing the video signals to a prescribed data rate and then
`compressing the digitized video to a prescribed data rate
`(e. g. aT1 data rate of 1.544 Mb/s). The compressed digitized
`video signal can be subjected to (optional) forward error
`correction encoding and spread spectrum-modulated onto a
`carrier for transmission to relay satellite 23. Spread spec
`trum-modulation of the signal reduces its power spectral
`density. The spread signal is transmitted via uplink channel
`21 (e. g. Ku band) to relay satellite 23. Relay satellite 23 then
`retransrnits the spread signal over a downlink transmission
`channel 31 (e.g. Ku-band) to aircraft 12.
`The aircraft 12 receives the satellite’s downlink channel
`retransmission via a compact phased array antenna 35,
`which may be totally electronically scanned or it may only
`be partially electronically scanned. As noted above, a phased
`array which is only partially electronically scanned is one
`which scans electronically in one dimension (e.g. elevation)
`and mechanically in the other (e. g. rotational). In a preferred
`embodiment of the invention, phased array antenna 35 is
`con?gured so as to be conformal with the aircraft surface,
`for example, on the top of the fuselage as two sets of
`transmit and receive phased arrays, one transmit, receive
`pair on the port side and the other on the starboard side of
`the aircraft. Alternatively, transmit and receive functions
`may be combined into a single array, although generally at
`the expense of increased aperture size due to additional
`losses and/or half duplex duty cycle. This port/starboard
`separation provides approximately full hemispherical cov
`erage with the satellite regardless of the attitude of the
`aircraft. A single antenna may be used in place of the
`port-starboard pair in situations where a more restricted
`beam scanning volume is acceptable. Mounting the antenna
`on the top of fuselage not only saves cabin space, but,
`because of its relatively thin, conformal con?guration, mini
`mizes antenna visibility and reduces drag. In addition to
`occupying less volume than would a purely mechanically
`steered antenna, such a compact phased array antenna 35
`provides the required amount of antenna gain.
`Uplink transmissions received at the aircraft from relay
`
`6
`satellite 23 are processed through a data recovery receiver,
`which despreads and demodulates the received signal. The
`demodulated video is then reconstructed for distribution to
`a variety of terminals and monitors on board the aircraft.
`Downlink transmissions from the aircraft may include both
`data and telephony transmissions, including control and
`overhead signalling, such as that employed for channel
`selection, and also video signalling in the case that telecon
`ferencing capability is provided.
`FIGS. 2A and 2B, taken together, diagrammatically illus
`trate the system architecture of earth station 11 for the
`present example of sourcing video signals to be transmitted
`to aircraft 12 from both commercial satellite 13, which
`provides commercial television programming, as well as
`private teleconference video signals sourced from telecon
`ferencing site 14 linked to the earth station. In the present
`example, commercially broadcast television signals are
`derived via a TV receive-only (e.g. C-band or Ku-band)
`satellite receiver 201 which is coupled to receiving antenna
`17, to which satellite 13 downlinks the analog FM television
`programming (eventually to be replaced with digital trans
`mission), selected channel(s) of which are forwarded by
`earth station 11 to aircraft 12. Receiver 201 outputs base~
`band analog video signals received by antenna 17, which are
`then processed for transmission via antenna 16 to relay
`satellite 23.
`The processing mechanism employed in accordance with
`the present invention initially involves digitizing (via an
`A-D converter, included in video compression unit 203) the
`television channel(s) supplied by receiver 201 to a pre
`scribed data rate and compressing the digitized television
`signal(s) by way of video compression unit 203. For this
`purpose, video compression unit 203 may comprise a Rem
`brandt II/VP compressor/decompressor unit the CTX PlusTM
`algorithm, manufactured by CM (Compression Labs Inc.).
`Compressing the video reduces (e. g. by nearly two orders of
`magnitude) its data rate which, for example, may be on the
`order of 100 Mb/s, while maintaining both full resolution
`and motion associated with broadcast quality television
`signals. Since the video compression operation e?ectively
`narrows the information bandwidth, it inherently contributes
`to a reduction in the receive aperture size required to
`maintain a given bit error rate. The compressed information
`bandwidth also facilitates spread spectrum processing to be
`subsequently performed.
`The compressed digitized television signal produced by
`video compression unit 203 is supplied to transmit stage
`204-1. Additional transmitter stages 204 may be included
`which are controllably tunable to respective ones of a
`plurality of video channels that are available for transmis—
`sion to the aircraft and are operative to place compressed
`video (or auxiliary data and telephony) signals onto a carrier
`for transmission to the relay satellite 23.
`For this purpose each modulation stage 204-i has a
`multiplexer 205, to a first input 202 of which a compressed
`video channel (or other data) of interest is coupled. As set
`forth above, the video channel may be derived either from
`the downlinked channels output by TVRO receiver 201,
`from one or more teleconferencing sites 14 served by earth
`station 11, or any other desired data source. The output of
`multiplexer 205 is coupled to (an optional) forward error
`correction unit 207. Error correction unit 207 may comprise
`an STEL-2020 Convolutional Encoder Viterbi Decoder
`manufactured by Standford Telecommunications, Inc.
`Using error correction coding in conjunction with eflicient
`(e.g. coherent PSK-type or MSK) data modulation further
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`reduces the aperture size for a given bit error rate. A second
`input 206 of multiplexer 205 is derived from an earth station
`control processor 210 through which the operation of earth
`station 11 is controlled. Control processor 210 may comprise
`a processor-based transceiver controller, such as an LCP HI
`Local Control Processor manufactured by TelMac., the
`supervisory functionality is effected by means of a resident
`communication control program, such as a System 90,
`manufactured by CCS (Corporate Computer Systems). The
`second input provides data/overhead signalling capability
`customarily employed for communication system control
`functions. The output of forward error correction unit 207 is
`coupled to a PSK/Spread Spectrum modulator 216, such as
`an STEL-2173 NCO in conjunction with an STEL-1032
`PRN Coder, manufactured by Standford Telecommunica
`tions, Inc. (or a CD7000 cellular telephone by Qualcomm),
`which performs initial carrier modulation of the compressed
`video along with PN spreading onto an IF carrier.
`Spread spectrum modulation reduces the spectral density
`of the modulated signal. The spread spectrum processing
`performed by unit 213 can take the form of direct PN
`sequence modulation and/or frequency hopping, for
`example. As described previously, spread spectrum process
`ing reduces power spectral density for FCC compliance,
`prevents unauthorized users from demodulating the video
`signal and enables the receiver on the aircraft to reject
`interfering transmissions from other satellites.
`The spread IF signal is coupled to an up-converter 217,
`which up-converts the spread IF by mixing it with the output
`of frequency synthesizer 214, such as that used in the
`CV-121 Ku-band SATCOM transmitter manufactured by
`Comstream Corp., which is referenced to a stable frequency
`source 215. The synthesizer frequency is selected by control
`processor 210. The level of the resulting spread RF signal
`may be (optionally) adjusted by a variable attenuator 219 for
`application to one port of a summing unit 222, the output of
`which is supplied to high power ampli?er 221. The output of
`high power ampli?er 221 is coupled to input port 223 of a
`diplexer 225.
`Summing unit 222 is coupled to receive the outputs of the
`respective signal transmitter stages 204-1 . . . 204~N. The T1
`data rate information channels that are coupled to modula
`tion stages 204, may include teleconference and data chan
`nels, as discussed above. The resulting multi-channel sum~
`mation signal from summing unit 222 is coupled from
`diplexer 225 to antenna 16, which outputs the multi-channel
`signal over uplink channel 21 to relay satellite 23. Relay
`satellite 23 then retransmits the combined channels over a
`downlink channel 31 to aircraft 12.
`The receiver section of earth terminal 11, shown in FIG.
`2B, includes a low noise ampli?er 231 which is coupled to
`an output port 232 of diplexer 225. The output of low noise
`ampli?er 231 is coupled to a power divider 233, which has
`a plurality of outputs coupled to respective inputs of a set of
`receiver stages 234-1 .
`.
`. 234-M. Within a respective
`receiver stage 234, its power divider input is coupled to an
`RF-IF down-converter 236, followed by a despreading
`demodulator unit 238. Under the control of a frequency
`synthesizer 237, such as that used the DER-401 Ku-band
`SATCOM receiver manufactured by Comstrearn Corp.,
`down-converter 236 reduces the carrier frequency of the
`spread signal to IF. The IF signal is then despread in
`despreading demodulator 238, such as that used in the
`Qualcomm CD7000 cellular phone hand set, where the
`original PSK modulation is also removed to recover infor
`mation signals (which may include video, such as telecon
`ference signals) sourced aboard the aircraft.
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`The output of despreading demodulator 238 may be
`coupled to an optional FEC decoder 24 and then to a
`demultiplexer 243, which extracts the compressed inforrna~
`tion (e.g. video) signal on a ?rst output channel 244 and
`overhead, control and data on a second output channel 245.
`Output channel 244, which may contain compressed video
`that has been sourced from the aircraft 12 is coupled to a
`remote site teleconference system 14. Output channel 245
`may contain channel request information from the aircraft
`that instructs the control processor 210 to effect a change in
`the selected television broadcast channel, as will be
`described below with reference to FIGS. 3A-3B.
`Referring now to FIGS. 3A and 3B taken together, the
`system architecture of the video transceiver aboard the
`aircraft 12 is shown as comprising a physically compact,
`phased array antenna 35, which is preferably confonnally
`con?gured, so that it may be mounted atop the fuselage of
`the aircraft. In accordance with a preferred embodiment of
`the invention, phased