Note: Descriptions are shown in the official language in which they were submitted.
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MOBILE AND HAND-HELD BROADCAST VIDEO
EARTH STATION TERMINALS AND METHODS FOR
COMMUNICATING WITH EARTH TERMINALS VIA SATELLITES
SPECIFICATION
Cross Reference to Related Applications
The present application is a continuation-in-part of U.S. Application Serial
No. 09/503,097, filed February 11, 2000, which is based on United States
provisional
patent applications numbers 60/163,028, filed on November 2, 1999, and
60/142.089,
filed on July 2, 1999, from which priority is claimed.
Background of the Invention
I. Field of the invention.
The present invention relates to techniques for satellite communication of
audiovisual information, and more particularly, to techniques for tracking
earth
orbiting satellites and transmitting real-time, broadcast quality audiovisual
information point-to-point or point-to-multipoint from and toward a small
mobile or
hand-held transceiver unit by way of the tracked satellites.
II. Description of the related art.
Journalistic history is packed with accounts of stories missed for technical
or
logistic reasons. A noteworthy example is the attempted assassination of
former
United States President Ford, which NBC Nightly News missed because it
recorded
the event on photographic film, which had to be processed before it could be
used for
broadcast purposes, rather than on video tape as was done by ABC & CBS. Other
examples include Ross Perot's withdrawal from the 1992 United States
Presidential
race, which NBC missed for want of a satellite truck, and the advent of the
Gulf War,
as to which CNN provided live coverage to the exclusion of its competitors due
to its
unique relationship with Iraqi television. Moreover, television journalism has
often
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been hampered by censorship when local governments which own or control the
satellite uplinks often refuse to transmit programming without editing or, as
in the
Tienanmen Square incident, refuse to transmit it at all.
Since the early nineteenth century, from Julius Reuters pigeons at the battle
of
Waterloo to CNN's satellites at the battle of Baghdad, journalism has moved
closer
and closer to one of its great aspirations -omnipresent immediacy; all the
news -
from anywhere to anywhere - NOW. But even now, with the availability of the
most
advanced equipment, such as flyaway uplinks and satellite trucks, it is still
not
possible to send live transmissions from almost anyplace in the world without
at least
a few days' advance preparation. Satellite trucks move like trucks. The high
cost and
weight of flyaways has made it impossible for even the largest broadcasters to
station
them anywhere except at their network headquarters and at a few of their
largest
bureaus. They rarely are operational in less than 48 hours, and are therefore
almost
always used to cover long running stories like ongoing wars but are generally
not
1 S available to cover fast breaking news events like riots, hurricanes and
earthquakes.
Current systems used in the field of television broadcast journalism are
either
taped or live. Taped systems generally involve a crew of three - a reporter, a
cameraman and an audio or utility technician. The latter two individuals are
directly
responsible for recording the event on videotape or disc for later editing and
transmission to headquarters facilities or studios for inclusion in the
programming of
the network. The equipment is typically a single unit combining a television
camera
and a video recorder, however the camera and recorder may be separate physical
units
connected by a cable. The recorded material is then physically carried from
the scene
of the event to another location to be edited and, if necessary, transmitted
or
physically delivered to headquarters. While taped systems historically were
analog,
recent technology developments have resulted in an increasing use of digital
technology, i.e., the Panasonic DVC-Pro and the Sony Betacam SX.
In most live systems, cameras and microphones are connected by cable to
transmission units. For local coverage, the cameras are connected by cable to
relay
units, most commonly, microwave units. Microwave antennas and transmitters,
costing between $200,000 and $500,000, are generally carried on trucks.
Microwave
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units require a qualified engineer to operate and can only transmit point-to-
point
within line-of sight. Also, frequency coordination and interference can be
major
problems at important events covered by multiple networks. While they are
mobile
within cities, microwave trucks are neither easily transportable to remote
locations,
nor do they have the range required to communicate over distances of more than
a
dozen or so miles, depending on local geography.
For regional coverage, trucks having satellite transmitters and antennas can
drive overland and transmit audiovisual information to communications
satellites.
These units weigh 3.5-10 tons and cost from $350,000 to several million
dollars. An
additional investment of tens of thousands of dollars is required at each
ground station
receiving site. These satellite transmission systems are complex and require
at least
one qualified technician to align the narrow-beam signals to the satellite.
Conventional uplinks require aiming the satellite antenna to within less than
0.5
degrees of accuracy; also, it is difficult to site such uplinks in a place
with clear line-
of sight to satellites over the equator, where look-angles can be less than
10°. These
issues preclude the use of satellite trucks in providing live coverage of many
breaking
news stories and events.
The size and weight of satellite trucks makes long distance deployment of
such equipment via commercial aircraft almost always cost-prohibitive. Indeed,
even
where money is not an issue, such satellite trucks often cannot be deployed in
circumstances where news personnel are not welcomed, e.g., during war
conditions
where one or more parties to the conflict are attempting to cover up war
crimes.
Internationally and nationally, transportable "flyaway" units are ordinarily
deployed only for major stories. While these units are designed to be shipped
in the
cargo holds of airplanes, they cost and weigh nearly the same as the equipment
carried
in the above-mentioned satellite trucks. Specifically, the weight can be
slightly under
a ton to several tons, depending on the amount of production equipment
included.
Weight is such a problem that some manufacturers are currently using aluminum
frames and castings to reduce overall weight, but still the total weight is
many times
more than that of the equipment in accordance with the present invention. The
flyaway unit can take more than 24 hours to assemble and test once it has
arrived at
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the intended destination. Moreover, in terms of power consumption, satellite
trucks
and flyaways typically use between 3 and 7 kilowatts of power, restricting
their usage
to places with compatible power mains available, or requiring a heavy, often
unreliable, generator.
An intermediate technology for transmitting video and audio from remote
locations is the store-and-forward system. The most widely used system of this
type
is manufactured by Toko. The Toko is a portable video and audio transmission
system that can operate wherever the Inmarsat system of satellites provides
service
coverage. It transmits highly compressed (using a proprietary format) video
and
audio in three stages. Stage one is to digitize and compress the video and
audio
signals, at approximately 2 Mbps, and to store it on hard disc. Stage two is
to transmit
this signal via the Inmarsat "B" satellite service at a maximum of 64 Kbps for
storage
on hard disc at the receive site. Stage three entails playing back the
received signal
from hard disc at 2 Mbps. In all it takes 30 minutes to transmit a single
minute of
1 S audio-visual material. The resulting quality falls far below broadcast
standards and is
significantly worse than that obtained using VHS format VCR. For comparison
purposes, digital TV news broadcasts typically require 6-8 Mbps to achieve
video
quality commensurate with news viewer's expectations. In addition, the
Inmarsat "B"
terminal is relatively bulky, weighing around 40-50 pounds and using an
"umbrella"
type antenna.
In the Unites States, this type of low bit rate (2 Mbps) transmission
equipment
is sold by FirstPix and Colby Systems. Both the FirstPix and Colby Systems
units are
designed for use with one or more cellular phones. Utilizing four ordinary
cellular
phone lines simultaneously, these systems require at least six hours to
transmit one
hour of recorded video and audio. Such systems are typically used only in
getting
very limited-duration clips of events transmitted, but are not practical for
sustained,
true broadcast-quality video and audio transmission. Moreover, the store-and-
forward
systems cannot be used for real-time transmission, and are expensive and
bulky.
From the foregoing, it is apparent that a satellite based system is the most
preferable configuration for transmitting television news from a remote
location.
However, before such systems can be utilized to deliver real-time transmission
of
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audiovisual information, particularly of fast breaking news events, several
important
technological obstacles, including the size, weight and complexity of such
systems,
must be overcome. One particularly challenging obstacle lies in the use
alternative of
non-geostationary low earth orbit commercial satellites to transmit
audiovisual
information in real time with a low power transmitter or the effective use of
geostationary high orbit satellites.
There have been several attempts by others to develop systems for
communicating with nongeostationary commercial satellites. In U.S. Patent No.
5,929,808 to Hassan et al. entitled "System and Method For The Acquisition Of
A
Non-Geosynchronous Satellite Signal," a system for communicating with a low
Earth
orbit ("LEO") or middle Earth orbit satellite is described. The system
includes a
satellite antenna which broadcasts a beacon signal, and an earth based station
which
uses the beacon to locate the satellite. The earth based station includes a
directional
antenna, i.e., a phased array antenna having an electronically steerable
receiving and
transmitting beam of variable width and an antenna controller.
In order to locate a satellite, Hassan et al. propose a bottleneck type
searching
algorithm where the search area starts wide and is gradually reduced.
Accordingly,
the controller initially activates only a few elements of the phased array
antenna to
thereby cause a wide beam, e.g., 30 degrees, to be generated. Once the
satellite is
located by the wide beam, additional elements of the phased array antenna are
activated to narrow the beam width and increase the gain of the antenna. This
process
continues until all of the elements of the phased array antenna are activated
to
generate a minimum width beam with the maximum gain directed at the satellite.
Another attempt at providing a satellite communication system is disclosed in
U.S. Patent No. 5,912,641 to Dietrich et al. entitled "Indoor Satellite
Cellular
Repeater System." The system described in Dietrich et al. includes an indoor
terminal, as well as outdoor transmitting and receiving antennas. The outdoor
receiving antenna includes a steerable directional antenna that comprises a
switched,
flat-plate phased array of printed-circuit antenna elements, and is steered by
a
computer in order locate orbiting satellites and to facilitate hard hand-offs.
The
transmitting antenna directs a high-gain beam to the LEOS, either via a
steerable
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beam or an "omnidirectional" transmission, which is inconsistent with "high-
gain."
The patent does not propose any particular steering techniques.
A further attempt to provide a satellite communication system is disclosed in
U.S. Patent No. 5,758,260 to Wiedeman entitled "Satellite Beam Steering
Reference
Using Terrestrial Beam Steering Terminals." Wiedeman discloses a satellite
communication system which generates an altitude correction signal for LEOs.
The
system includes a plurality of satellite beam steering reference terminals
("SBSRTs")
positioned at known locations on the earth's surface. Each SBSRT includes an
antenna, which may be an omnidirectional antenna, to transmit signals to the
LEOs.
In U.S. Patent No. 5,905,466 to Jha et al. entitled "Terrestrial Antennas for
Satellite Communication System," various antennas for transmitting and
receiving
radio signals to and from low Earth orbit satellites are described. Jha et al.
propose
using a steerable antenna which progressively searches for a satellite beacon
to reduce
satellite hand-offs and transmits signals in a wide area, e.g., a conically-
shaped area
measuring 80 degrees across.
Since none of the foregoing prior art utilizes an intelligent steering antenna
which realizes the necessary power management and instantaneous satellite
tracking
from a hand-held transceiver unit, even as that unit changes position,
orientation and
attitude, the prior art fails to provide a commercially viable satellite
communication
system that is able to communicate in real time audiovisual information via
satellites
without expensive and cumbersome uplink equipment. Accordingly, there exists a
need in the art for a technique for tracking geostationary and/or
nongeostationary
satellites and transmitting real-time, broadcast quality audiovisual
information
point-to-point or point-to-multipoint from a small, camera-mounted unit by way
of
the tracked satellites.
Summary of the Invention
An objective of the present invention is to provide the apparatus that can
serve
as a video uplink for real-time broadcast quality transmission from a video
camera via
satellite or other means (e.g., wireline such as fiber) to base stations
anywhere in the
world.
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A second objective of the present invention is to perform the satellite
transmission either directly from the camera or via a local relay in
communication
with the camera by radio or a wireless local area network (LAN) to a portable
uplink
umt.
A third objective of the present invention is to ensure reliable transmission
of
the video and audio signals from the camera to the local relay unit in the
absence of a
line-of sight path between the camera and relay unit.
A fourth objective of the present invention is to allow multiple cameras,
recording, editing, and storage devices to connect to the same relay unit,
with the
relay unit selecting which feeds (one or more) are to be transmitted to the
satellite.
A fifth objective of the present invention is to have a system that is
portable
enough to be carried by one or two people and that will easily fit into an
overhead,
carry-on luggage compartment of commercial airplanes.
A sixth objective of the present invention is to allow the on-camera system to
communicate with the studio and via the satellites through a wide range of
physical
orientations of the on-camera systems, by utilizing an intelligent steering
antenna.
Yet another objective of the present invention is to use an intelligent
steering
antenna so as to minimize the power requirements of the on-camera satellite
transmission unit, thus further enhancing portability.
Still a further objective of the present invention is to provide a system that
can
be operated anywhere in the world at any time by operators who are trained in
its use,
but who are not professional video or satellite engineers.
Yet a further objective of the present invention is to provide a system that
can
be operated with minimal obtrusiveness.
In order to meet these and other objectives which will become apparent with
reference to further disclosure set forth below, the present invention broadly
provides
the apparatus for converting the camera signal to a compressed digital format
and
transmitting the compressed digital signal via satellite or other means
(wireline such
as fiber, etc.) to one or more base stations.
In one embodiment, the satellite uplink - or transmission in general - is
performed directly by a subsystem that is directly attached to the video
camera. In
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another embodiment, a digitized compressed camera signal is relayed to a
remote
local uplink subsystem which performs the satellite uplink or transmission.
Transmission of the compressed camera signal to the remote unit is performed
using a
wireless connection, preferably, IEEE 802.11 wireless LAN, or by cable.
The digitized compressed camera signal is either relayed to the satellite, and
from there to the base station, or transmitted directly to the base stations
using
wireline facilities. At the base station, the audio-visual information
captured by the
camera may be transmitted in real time to television viewers via the
broadcaster's
standard TV distribution facilities. It can also be transmitted to Internet
users via a
broadcaster's web site. The signal can also be decompressed and displayed on a
television monitor for preview purposes. It can also be stored on disk, or
routed (in
either analog or digital form) to other video equipment.
In the disclosure set forth below, emphasis is placed on satellite relay
facilities
since they provide ubiquitous access. Persons skilled in the art can easily
adapt the
design to use wireline facilities.
The accompanying drawings, which are incorporated and constitute part of
this disclosure, illustrate a preferred embodiment of the invention and serve
to explain
the principles of the invention.
Brief Description of the Drawings
Figure 1 is a system diagram illustrating the overall structure of a preferred
embodiment where direct satellite connection is used;
Figure 2 is a system diagram illustrating the overall structure of an
alternative
embodiment of the system where a secondary relay unit is used for satellite
transmission;
Figure 3 is a block diagram of a Camera Unit suitable for use in the
embodiment of Fig. 1;
Figure 4 is a block diagram of a Camera Unit suitable for use in the
embodiment of Fig. 2;
Figure 5 is an illustrative diagram depicting the installation of the Camera
Unit;
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Figure 6 is an illustrative diagram depicting an alternative installation of
the
Camera Unit;
Figure 7 is an illustrative diagram depicting the operation of a circular
buffer;
Figure 8 is an illustrative diagram depicting a secondary relay unit used for
satellite transmission;
Figure 9 is an illustrative diagram depicting the changing orientation and
attitude between an antenna and a satellite due to motion of the antenna;
Figure 10 is an illustrative diagram depicting the design of an active phased
array antenna suitable for use in the embodiments of Figs. 1 and 2;
Figure 11 is a diagram of excitation circuitry suitable for use in the active
phased antenna of Fig. 10;
Figure 12 is an illustrative diagram depicting a tandem tracker pair of
receiving arrays;
Figure 13 is a flow diagram illustrating a preferred processing technique
employed by the tandem tracker;
Figures 14a and b are illustrative diagrams depicting the attachment of an
active phased antenna to a video camera;
Figure 1 S is a functional diagram explaining the operational structure of the
system of Fig.2;
Figure 16 is a legend for software useful in the embodiments of Figs. 1 and 2;
Figure 17 is a software flow diagram for the Camera Unit;
Figure 18 is a software flow diagram for the Satellite Master Control Unit;
Figure 19 is a software flow diagram for the Headquarters Unit.
Figure 20 is a system diagram illustrating the overall structure of an
alternative
embodiment of the present invention;
Figure 21 is an illustrative diagram of an antenna arrangement suitable for
use
in the embodiment of Figure 20; and
Figure 22 is an illustrative diagram of an alternative antenna arrangement
suitable for use in the embodiment of Figure 20.
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Description of the Preferred Embodiments
Referring to Figure 1, one presently preferred embodiment of the invention is
shown. In this preferred arrangement, the system includes Camera Unit 10,
camera
satellite antenna 11, video camera 12, satellite system 30, base or
Headquarters Unit
40, and base satellite antenna 41.
In order to maximize the portability of the system, the video camera 12,
Camera Unit 10 and camera satellite antenna 11 are advantageously integrated
into a
single hand-held unit. In this arrangement, the video camera may be Sony BVW-
D600 digital camera, or a Panasonic DVC Pro digital camera. The Camera Unit 10
10 and antenna 11 may be appropriately mounted on or integrated in the camera
12.
The system is designed to capture live audiovisual information through camera
12 and to transmit real-time, broadcast-quality captured audiovisual
information to the
Headquarters Unit 40 through the satellite system 30. As will be described in
further
detail in connection with Figure 3, this is accomplished by converting the
captured
audiovisual information into a compressed digital stream, preferably an MPEG-2
Transport Stream, and then transmitting the compressed signal in real time via
a
satellite to the Headquarters Unit 40.
In a preferred arrangement, the satellite system 30 is a geostationary
satellite
or a network of Low Earth Orbit Satellites ("LEOS"). As previously noted, a
principal failure of prior art satellite communication systems lies in the
inability to
communicate live audiovisual information with a satellite without expensive
and
cumbersome uplink equipment. LEOS communicate at high frequencies (above 18
GHz), which may permit the use of antenna arrays of smaller dimensions. An
example of such antenna in accordance with the present invention is described
below
in connection with Figs. 9-13
The transmission of the signal at the network layer is preferably accomplished
using the Internet Protocol, offered as a service by the satellite service
provider.
Through the use of Internet Protocol multicasting, it is possible to have
several
Headquarters Units 40 receive the uplinked audiovisual information.
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The present invention provides an improved terrestrial antenna design through
the employment of beam steering that allows further reduction of power
requirements
for reliable transmission, thereby increasing portability. Those skilled in
the art will
appreciate that present invention applies with equal force to other satellite
systems
including geostationary and nongeostationary systems.
In order to accommodate multiple cameras in the field as well as provide more
freedom in the placement of the antenna in the field (e.g., the top floor of a
building),
the Camera Unit 10 can optionally be split into two components: a unit without
the
satellite antenna, and a secondary relay unit that provides satellite
transmission. Such
a configuration is shown in Figure 2.
Referring to Figure 2, an alternative arrangement of the present invention
includes Camera Unit 10, video camera 12, WLAN antenna 13, Satellite Master
Control Unit 20, WLAN PC card and antenna 21, satellite antenna 22, satellite
modem PC card 23, satellite system 30, base or Headquarters Unit 40, and base
satellite antenna 41. It should be noted that like reference numbers are used
in this
specification to indicate like components.
In the arrangement of Figure 2, communication between the Camera Unit 10
and the Satellite Master Camera Unit 20 is performed using a wireless LAN
(WLAN),
which may be a commercially available IEEE 802.11 compliant LAN operating at
11
Mbps, or alternatively, a HiperLan or a Wi-Lan operating at speeds greater
than 20
Mbps. The network layer protocol used is the Internet Protocol. The use of a
packet-
based, shared medium system allows the simultaneous connection of multiple
cameras and playback devices to the same Satellite Master Control Unit 20. The
Satellite Master Control Unit 20 operator can then select the camera input
which
should be relayed to the satellite.
The Camera Unit 10, which is described in further detail in connection with
Figures 3 and 17 below, is a special board appropriately packaged to fit onto
existing
cameras as an accessory. It can also be included in the original configuration
or
custom made camera models designed to include such a board. In case of local
relay,
the Camera Unit 10 reliably (as detailed below) and optionally securely (via
standard
IEEE 802.11 encryption facilities) transmits the audio and video signals from
the
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camera to the nearby Satellite Master Control Unit 20. As mentioned above in
connection with Figure 1, in the case of direct uplink, the Camera Unit 10 and
the
functionality of the Satellite Master Control Unit 20 may alternatively be
integrated
with the camera 12.
The Satellite Master Control Unit 20, which is described in further detail in
connection with Figures 8 and 18 below, is preferably a portable personal
computer
with a WLAN adapter and appropriate control software that receives the digital
video
and audio signal from the Camera Unit 10, and retransmits it to a satellite.
Unit 20
also has the capability of recording audiovisual information to a local mass
storage
device for later preview, editing and/or uplinking. Two-way data and/or audio
communication is also provided between the Satellite Master Control Unit 20,
Camera
Unit 10, and Headquarters Unit 40 to allow command and voice communication
between the unit operators, as well as the station receiving the live feed.
The uplinked signal is routed through the satellite network for eventual
delivery to the Headquarters Unit 40. The Headquarters Unit 40 is preferably a
personal computer with appropriate control software, which can be built in to
conventional broadcast switching equipment (control rooms), and is used for
several
purposes, including decoding the received compressed-domain audiovisual
signals,
displaying decoded video information on a regular television monitor for
preview
purposes, storing received digital signals on a mass storage device, rerouting
the
received signals, in either analog or digital form, to an external device
(e.g., routing
MPEG-2 data to another system through the TCP/IP network), playing back pre-
recorded video from mass storage devices, and most importantly, routing of the
received data to dedicated digital video routers using an appropriate
interface such as
USB or IEEE 1394 for ultimate transmission to television viewers. The software
which provides such functionality is described in further detail in connection
with
Figure 19 below.
The Headquarters Unit 40 is fitted with a commercially available MPEG-2
decoder board (not shown) with analog outputs, a satellite modem card with its
associated satellite receiving antenna 41, and regular TCP/IP connectivity to
other
computing and video equipment in the facility (not shown) via a 100-BaseTX or
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ATM LAN adapter. Additionally, the Headquarters Unit 40 may provide for a
local
audio input (COMS) or communication channel, as well as a pass-through
connection
(additional input that is directly fed back to the Camera Unit 10) for an IFB
channel,
when one is used.
Referring next to Figure 3, a preferred embodiment for the Camera Unit 10 is
shown in greater detail. The Camera Unit 10 is a circuit board measuring
approximately five inches square and 0.5 inches in thickness, and includes
external
connections for the input of S-Video or Composite Video 100, the input of
stereo
audio 110, the input of local monophonic audio 130, and the output of local
monophonic audio 135.
As shown in Fig, 3, captured video information from the camera 12 is received
by the Camera Unit 100 through S-Video or Composite Video input 100 and is fed
to
an NTSC/PAL video decoder 101, which may be a commercially available SAA 7111
decoder. Analog audio information from the camera 12 is received by the Camera
Unit 100 and through the stereo audio input 110 is fed to an audio analog-to-
digital
converter 111, each for conversion into digital data streams. Local monophonic
audio
received at input 130 is converted by audio analog-to-digital converter 131
into a
digital data stream. Local monophonic audio may also be converted by digital-
to-
analog converter 136 into an analog signal for driving a speaker (not shown)
via the
output 135.
In addition to the input/output devices, Camera Unit 10 includes an MPEG-2
encoder subsystem 120, 121, 122, 123, a satellite communications subsystem
180,
and the basic elements of an embedded computing system, including a CPU 150,
local
PCI bus 140, Flash EPROM 141, 8MB DRAM 145, optional 4GB local disk 170,
and a Lithium Ion battery power supply 160. The local bus interconnects via
the
MPEG-2 encoder subsystem 120, 121, 122, 123, the local (monophonic) audio
digital-to-analog (DAC) and analog-to-digital (DAC) converters 131, 136, and
the
communications subsystem 180.
The MPEG-2 encoder subsystem includes an MPEG-2 encoder 120, a serial
EPROM 122, 8MB of SDRAM 121, and a 25 MHz oscillator 123. Digital video
information processed by the auto-sensing NTSC/PAL video decoder 101 and
digital
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stereo audio information processed by analog-to-digital converter (ADC) 111
are
received by the MPEG-2 encoder 120 via video and audio inputs 102, 112.
While the MPEG-2 encoder 120 is shown as a single-chip C-Cube DVxpert
5110, multi-chip solutions as well as software encoders can interchangeably be
used
in the present invention. The MPEG-2 encoder delivers a single data stream of
compressed audio and video information to PCI bus 140 via output 125. This
data is
available through the bus to the host CPU 150, for further processing or
delivery to
the communications subsystem 180.
The structure of the communications subsystem depends on whether the
satellite transmission is performed directly from the Camera Unit 10, as shown
in
Figure 1, or via a Satellite Master Control Unit 20, as shown in Figure 2.
Figure 3
depicts the former configuration.
Referring again to Figure 3, satellite modem interface controller 180 is
connected to the PCI bus 140. Data from the MPEG-2 encoder 120 can be
transmitted to the modem 180 either via the CPU 150, or alternatively via a
DMA
transfer (not shown). Note that the MPEG-2 encoder 120 used in the preferred
arrangement can act as a bus master and can thus initiate its own DMA
transfers. The
satellite modem 180 modulates the digital information for transmission by a
satellite
antenna 11 (to be described below) to the satellite 30, and from there to the
Headquarters Unit 40.
For example, the modulation technique performed by satellite modem 180 can
be Quaternary Phase Shift Keying ("QPSK") for the uplink and 8-phase PSK for
the
downlink. For both the uplink and the downlink, error control coding is also
performed by satellite modem 180. Resource sharing can be accomplished with a
combination of mufti-frequency time division multiple access (MF-TDMA) for the
uplink and asynchronous time division multiplexing (ATDM) for the downlink
QPSK is a technique for modulating an analog carrier with digital information
suitable for transmission over an analog communications channel. While the
satellite
modem 180 should perform QPSK modulation in order to generate a signal which
ultimately can be relayed by the satellite system, other modulation
techniques, such as
quadrature amplitude modulation ("QAM") or frequency shift keying ("FSK"), are
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well known to persons skilled in the art and may be employed by satellite
modem 180
to effect proper communication with the particular satellite.
To mitigate the effect of noise in the communications channel and the
potential loss of digital information that it can cause, the satellite modem
180 also
5 performs forward error correction ("FEC"). These techniques involve the
addition of
redundant information to the data so that, in the presence of errors, the
original data
can be fully recovered. One example of a FEC technique is Reed-Solomon coding;
several other techniques exist, e.g., block, convolutional and turbo coding,
BCH,
CRC, and parity coding, are well-known to persons skilled in the art and may
be
10 employed.
Referring next to Figure 4, when an Satellite Master Control Unit 20 is used,
the communications subsystem of the Camera Unit 10 is replaced by a PC Card
interface controller 185, to which a wireless LAN adapter (PC Card) 190 is
attached.
The antenna 13 is positioned so that it is exterior to the Camera Unit 10
housing, to
15 minimize interference. In this embodiment, a Lucent Wave LAN Turbo PC Card
is
employed, although any other solution can also be used. The use of a PC Card
allows
easy replacement of the network interface controller in case of malfunction,
as well as
the use of wired communication facilities (e.g., regular 10-Base2 Ethernet)
for testing
and system configuration purposes.
Referring next to Figures 5 and 6, the Camera Unit 10 can either be built-in
to
the body of camera 12 as shown in Figure 5, or be attached to the camera 12 as
an
add-on component as shown in Figure 6. In the arrangement shown in Figure 5,
the
satellite antenna 11 used for direct satellite transmission is shown as being
attached to
the camera 12 above the camera handle. While other designs are also possible,
e.g.,
mounting directly on top of the camera, without a mounting pole, such
positioning
allows effective communication between the antenna 11 and the satellite system
30,
while minimizing exposure of the camera operator to the signal radiated from
antenna
11. In the arrangement shown in Figure 6, the Camera Unit 10 is attached to
camera
12 as an add-on component using a suitable adaptor plate 14 that allows the
placement
of the Camera Unit 10 between the camera 12 and the camera's battery 15.
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The design of the Camera Unit 10 as a regular computer as well as the use of
the Internet Protocol as the underlying communications protocol allows the
Camera
Unit 10 to be accessed from anywhere the satellite network provides
connectivity (in
theory, the entire Internet) for testing, system configuration or upgrade, or
simply
remote operation. This is essential for providing ubiquitous and reliable
service from
the field unit to virtually any place in the world where the unit may be
deployed.
The various external connections of the Camera Unit 10 are connected as
follows. The video input 100 and stereo audio input 110 are connected to the
corresponding outputs of the video camera. In this preferred embodiment, such
inputs
are analog. Persons skilled in the art can easily convert the input subsystem
to
accommodate different formats, including Panasonic's DVC-Pro or Sony's Betacam
SX as well as high-definition ( 16:9) and other standards. For example, C-Cube
already offers a single-chip solution that provides direct DVC-Pro to MPEG-2
conversion in its DVxpress-MX product line.
The local (monophonic) audio input 130 and output 135 are connected to a
microphone and headphones of the camera operator, respectively. They are used
as a
control channel to enable voice communication between the camera operator, the
Satellite Master Control Unit 20 operator (if present), and the persons at
Headquarters
Unit 40 (COMS channel). There may also be provided a second monophonic audio
output (not shown) that contains the Interruptible Feedback Channel (IFB),
providing
a mix of the live program without the camera audio (mix minus one, providing
audio
feedback to the on-site reporter). The source of this signal is the broadcast
studio
located at the Headquarters Unit 40 site. Both the COMS and IFB channels are
low
bit rate using 8 kHz / 8-bit audio, and can be coded using the telephony codec
ITU
6.723.1 standard, or alternatively, the GSM standard.
As discussed above in connection with Figures 3 and 4, live video information
is processed by an NTSC/PAL/SECAM/HDTV video decoder 101, which performs
both demodulation and analog-to-digital conversion, whereas live audio is
converted
by an audio analog-to-digital converter 111. The outputs of the video decoder
101
and the audio A/D converter 111 are fed to the MPEG-2 encoder 120. The codec
has a
direct PCI interface with bus mastering capabilities. The audio and video
signals are
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compressed into a single multiplexed data stream, i.e., an MPEG-2 Transport
Stream,
with a target rate of 6-8 Mbps (rates from 2 to 50 Mbps are possible with the
5110
chip). This rate provides sufficient quality for news use; higher bit rates
can be
immediately used with newer generation wireless LAN, e.g., 100 Mbps, and
satellite
modem products. The stream is made available to the PCI bus for direct
transfer to the
communications subsystem via either DMA or via the host CPU.
Since the communication link may occasionally encounter problems, losses
can be expected in certain situations. With a direct satellite uplinking,
congestion in
the satellite network or atmospheric conditions may prohibit transmission to
the
satellite for some periods of time. Similarly, when a wireless LAN is used
with a
Satellite Master Control Unit 20, various conditions, such as multipath
distortion and
fading, may occasionally disrupt communication. For this reason, the Camera
Unit 10
can optionally be equipped with a hard (or solid state) disk 170 that can be
used as a
circular buffer.
The use of hard disk 170 as a circular buffer is functionally illustrated in
Figure 7. The CPU 150 runs two threads: a writer thread and a reader thread.
The
writer thread maintains a pointer to the buffer. It obtains data from the MPEG-
2
decoder and places them into the buffer, and advances the pointer by as many
positions as the data written. Separately, the reader thread maintains its own
pointers.
It obtains data from the disk starting at the position indicated by the
pointer and sends
it to the communications subsystem. It then advances the pointer by as much
data as
it has retrieved. The reading pointer is always at the same position or
earlier than the
writing pointer. When the end of the buffer array is reached by either
pointer, it loops
around to the beginning of the buffer. The two threads use mutual exclusion
locking
to avoid simultaneous reading and writing of the same buffer position. Also,
the
reading thread always checks that it does not overrun the writing thread (its
pointer
moves ahead of the writing pointer).
During normal operation, the reading thread can be one access behind the
writing thread. When communication problems occur, packet losses will be
occurring
on the link. This can be easily detected by sequence numbering on the packets.
By
keeping an estimate of the packet loss (e.g., a sliding window average), the
receiver
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can automatically request from the sender (the Camera Unit 10) to backtrack so
as to
retransmit the lost data. This means that the reading pointer will move
backwards
into the buffer in order to retransmit information that was distorted or lost.
This can
also be triggered manually by the camera operator, Satellite Master Control
Unit 20
operator, or the Headquarters Unit 40 operator.
The size of the buffer required depends on both the transmitting data rate and
the maximum duration for which transmission problems are expected. With an 8
Mbps stream, 60 MB of data per minute of buffering are required.
Areas of the circular buffer can also be marked by the camera operator,
Satellite Master Control Unit 20 operator, or Headquarters Unit 40 operator,
so that
they are not erased by succeeding passes of the read/write threads. This
allows
material that has been recorded there to be saved for later transmission, and
can be
achieved by using an array of pointers to positions and lengths in the buffer
for which
access is denied. The writing and reading threads examine this array to avoid
overwriting or reading this data.
In operation, the signal from the MPEG-2 encoder is continuously being
written on the hard disk 170. The communications subsystem 180 or 185 obtains
the
data for transmission from the disk 170. When communication problems occur,
the
communication subsystem can backtrack on the circular buffer in order to
ensure that
no information is lost. While this will introduce additional delay, this can
be
preferential to signal loss. The amount of disk space directly determines the
maximum length of communication disruption that the Camera Unit 10 can
tolerate
without loss of captured audiovisual information. With a 4GB disk, 88 minutes
of a 6
Mbps stream can be stored. This is more than enough to cover most cases of
interest.
The communications subsystem simply interfaces the satellite modem or
wireless LAN interface to the bus, and operates in the same way as in general
purpose
computers. Multiple adapters can be used to achieve higher throughputs, using
inverse multiplexing.
The Camera Unit 10 is powered by a Lithium Ion battery pack 160, that allows
increased autonomy and avoids charge memory effects. Depending on camera
features, direct power from the camera's own power supply 15 can be used as
well.
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The total power consumption of the Camera Unit 10 is in the order of 3 Watts,
2
Watts for the transmitter feeding the antenna, and 1 Watt for the other
components,
which is a great improvement over 3,000-7,000 Watts required by a satellite
truck or
flyaway unit.
The Camera Unit 10 runs commercially available TELNET software allowing
remote logins (for configuration, testing and troubleshooting), and also
provides for
downloadable updates of its Flash EPROM for maintenance purposes.
Referring next to Figure 8, the Satellite Master Control Unit 20 is explained
in
greater detail. The signal from the wireless LAN antenna 13 of the Camera Unit
10 is
received by a similar antenna 21 of the Satellite Master Control Unit 20,
which is
relatively close (typically within 0.5 miles) to it.
As shown in Figure 8, the Satellite Master Control Unit 20 is a personal
computer, preferably a commercially available laptop computer including at
least an
Intel 333MHz Pentium II or similar microprocessor with 64 MB RAM, 4 GB disk
space, and two PC Card slots, local analog audio input/output, an audio card
capable
of two-way A/D conversion at 8 bits/8 kHz, and a built-in MPEG-2 decoder. The
Satellite Master Control Unit 20 computer is equipped with a satellite PC Card
modem 21 and antenna, as well as a wireless LAN modem and antenna 23. The
wireless LAN antenna extends on the lateral side of the PC Card adapter. The
satellite
antenna is connected with a cable to the satellite modem in Camera Unit 10.
One
possible antenna configuration can measure 2" x 10" x 10".
The Satellite Master Control Unit 20 receives Internet Protocol packets from
the wireless LAN adapter, and forwards them to the satellite adapter for
relaying
through the satellite network and ultimate reception by the Headquarters Unit
40. For
this purpose, it contains connection control software, to be described below,
that
establishes the connections to the Headquarters Unit 40, and the Camera Unit
10.
The software also provides for two-way voice communication between the
Satellite Master Control Unit 20 and the Camera Unit 10 (COMS channel) using
the
local audio input/output ports. As mentioned earlier, regular telephony-type
coding
can be used for this channel, such as ITU 6.723.1 or GSM. A regular headset
with a
microphone can be attached to these ports, on both the Camera Unit 10 as well
as the
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Satellite Master Control Unit 20. The Satellite Master Control Unit 20 also
relays the
IFB channel, when available, from the Headquarters Unit 40 to the Camera Unit
10.
Additional capabilities of the Satellite Master Control Unit 20 may also
include storage of the data received by the wireless LAN adapter to the local
disk for
5 later transmission or playback, on-screen local preview of the received
video as it is
being relayed to the satellite, switching between the Camera Unit 10 feed and
a local
disk feed under operation control, support for reception from more than one
Camera
Unit 10, and local video editing capabilities using commercially available
software.
In addition to transmissions to satellites, the Camera Unit 10 and the
receiver
10 at the Satellite Master Control Unit 20 have applications wherever there is
a need for
short-distance wireless transmission of broadcast video. Although there are
existing
microwave-based systems for such transmissions, these require that there be a
direct
line-of sight path between the transmitter antenna and the receiver and
require
considerable setup time. The ability to receive digitized video even when
there is no
15 line of sight path between the camera and base station is a major
advantage.
Additionally, the expected price for the equipment disclosed in this
embodiment is
expected to be less than the microwave-based systems. It should be noted that
higher
wireless LAN bandwidths (i.e., 20-100 Mbps) will be required for these
applications
to find widespread acceptance in domains such as sports.
20 Referring next to Figures 9-13, the satellite antenna is now described. As
discussed above with reference to Figure 1, a preferred embodiment of the
invention
provides a satellite antenna attached directly to the camera. The purpose of
the
antenna is to transmit data and/or compressed audiovisual information captured
by the
camera 12 directly to a satellite 30, which may then transmit onward to other
relay
satellites and ultimately, to the base station 40 on Earth.
Because of power limitations at the portable camera, it is not feasible to
irradiate a large portion of the sky and still deliver adequate signal power
to the
satellite. Moreover, the antenna may be mounted on an unstable or unsteady
hand-
held, portable camera platform or a vehicle. Accordingly, in order to overcome
the
disadvantages of cumbersome prior art satellite communication systems, the
radio
frequency (RF) portion of the Earth Station satellite transceiver subsystem
utilizes a
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smart, steerable, low-power antenna 11 or 13, so that reliable transmission
can be
achieved when it is driven by a low power transmitter powered by a lightweight
portable battery 160, and is sufficiently small to be attached to the portable
camera 12.
Nevertheless, the antenna driven by the low power transmitter furnishes
sufficient radiated power density to deliver adequate signal power to the
satellites
receiving antennas, and maintains the transmission link to the satellites
continuously
even if the satellites, such as a LEOS, geostationary and/or non-geostationary
are
apparently changing their relative positions with respect to the camera-
mounted
antenna which is changing its position, orientation and attitude. Accordingly,
as
illustrated in Figure 9, the Earth Station Terminal antenna subsystem in
accordance
with the present invention is able to adapt to changes as the camera mounted
antenna
201, 211 moves and tilts, and as the satellites 200, 210 change their position
relative
to the antenna.
Referring next to Figure 10, one embodiment of the Earth Station Terminal
antenna 11 is shown. In this embodiment, the antenna includes a planar array
of thin
metal layer antenna elements 310, such as microstrip patches formed on a
printed
circuit board and compatible with planar microwave circuit technology.
Some of the antenna elements 301, 302, 303, 304 are receiving elements
dedicated to receiving power-control or beacon signals from satellite 30 and
preserving phase information from the received signals, so that their
direction of
arrival may be analyzed and used to adapt the phasing of the remaining antenna
elements 310, which form a transmitting array. As further discussed below, the
incoming power control signals are additionally used in this invention to
locate the
direction of the satellites and to track them as both the satellites and the
Earth Station
Terminal antenna change position, orientation, and attitude.
With the exception of the dedicated receiving antenna elements 301, 302, 303,
304, the remaining elements 310 of the array 300 act as individually phased
transmitting antennas. In one illustrative embodiment, which is designed for
communication with a constellation of low earth orbit satellites (orbit height
h=700
km), the Earth Station Terminal's transmitting subsystem will operate at the
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frequency of about 29 GHz (a wavelength ~, = 1.04 cm). In order to furnish the
requisite -118 dBW of received power at the satellite receiver when the
satellite is at
its furthest slant range of about 1400 km, which entails free-space loss (4~
h/
~,) Z = 184.4 dB, and accounting for other losses that result in an overall
transmission
loss of 185.5 dB, the Earth Station Terminal transmitter is required to
provide an
equivalent isotropic radiated power (EIRP, the product of the transmitter
power and
the antenna gain) of approximately 34.3 dBW (under clear sky conditions) to
accommodate the required link budget requirements in either two-hop or
multiple-hop
satellite systems. The same principles apply for communication via
geostationary
satellites.
In order to satisfy the required link budget requirements, the Earth Station
Terminal should operate at a power level of approximately 2W, and the antenna
array
should have a gain of G = 31.3 dB. By the universal relation between antenna
gain G
and effective area A,
A = G ~, Z/4~, ( 1 )
this requirement leads to an antenna array effective area of approximately 116
cm2. Even allowing for an antenna efficiency of about 50%, for an uplink
transmitting subsystem operating at or near a wavelength of ~, = 1.04 cm, a
square
array approximately 15 cm on a side of sufficiently densely distributed
elements
should adequately achieve the required gain.
It should be noted that while Figure 10 depicts a 7 x 7 array of patch
elements,
the number of elements shown in the figure, their shape, and their spacing may
be
varied according to principles known in the art. Likewise, although it is
preferable
that four antenna elements are dedicated to receiving satellite signals, other
numbers
of elements may be utilized for this task, provided that a minimum of three
elements
are so dedicated. Moreover, other types of antennas such as nonplanar or
conformal
arrays, traveling-wave antennas, acoustically phased antennas, aperture
antennas, wire
antennas, or open waveguides may be suitable for use as antenna 11.
Referring next to Figure 1 l, the circuitry that controls and excites the
phased
array antenna in the preferred embodiment is shown. A power divider 315 is
driven
by a microwave source 312, which in turn is modulated by the audiovisual
signal
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provided by the modem 180 of camera unit 10. The power divider 315 distributes
power to phase shifters 320, which are controlled individually by the output
of a
phase shift distribution unit 350. Each phase shifter 320 outputs a signal
that is
amplified by a respective power amplifier 330 for application to a
transmitting
antenna element 340. A processing unit 360 receives phase control signals
captured
by receiving elements 301, 302, 303, 304, applies an algorithm to determine
the
excitation phase of each transmitting element, and provides the results to the
phase
shift distribution unit 350.
Although the phase shifters are the primary elements that control the steering
of the beam radiated by the phased array of antenna elements 310, it may be
advantageous to control the shape of the beam as well. This may be
accomplished by
varying the amplifier gains for each array antenna element individually.
The algorithm that extracts the direction of the incoming satellite signal and
develops the appropriate phasing of the transmitting elements will next be
described.
Let the wave vector k of the incoming plane wave have the components p and q
in the
perpendicular x, y directions, respectively, when projected onto the plane of
the array.
Then the receiving element at (x, y) picks up a signal of phase cp, where
~P = px + qy. (2)
A phase detector extracts the phase cp for the element at (x, y). As there is
a
plurality of receiving elements, we have a plurality of known values of x and
y, as
well as of cp . The two unknown values p, q can then be estimated, by a least-
squares
algorithm, or any similar calculation that generates values of p, q that best
fit the data.
Ambiguities in phase by multiples of 2~ may need to be resolved by using more
receiving elements or reconfiguring them.
For the transmitting array to radiate its beam in the direction from which the
satellite signal is coming, it is necessary to generate a wave along the array
surface
with the opposite phase constants, -p and -q. The physics of electromagnetic
radiation
then guarantees that the direction of the emitted beam is that of -k, if the
frequency of
the emission is the same as that of the received signal. If it is not the same
frequency,
the phase constants axe correspondingly scaled. The transmitting array element
at (x,
y) needs to be excited by a signal of phase 8, where
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8=-px-qy. (3)
This applies to each of the plurality of transmitting elements at the known
coordinates (x, y). The phase shift distribution unit 350 allocates the
appropriate phase
to each transmitting element of the array.
To avoid grating lobes in the radiation from the phased array antenna 300, the
element spacing needs to be kept less than a wavelength in all directions, say
1 cm for
the 29 GHz satellite system example. It is desirable to make the radiation
pattern of
any single transmitting element nearly isotropic, so that the beam strength
remains
relatively constant as the beam is steered. The precise shape, such as
rectangular or
circular patches, of each transmitting element affects this individual
radiation pattern;
the number of elements needed depends on the gain to be achieved.
The design constraints imposed by the stringent requirements of small size and
low power for the Earth Station Terminal antenna lead to solutions that
involve arrays
of both transmitting and receiving elements, to allow for tracking of the
satellite and
the beaming of the radiation to it, in directions relative to the antenna that
are
randomly time varying. This, in turn, leads to a dilemma regarding the spacing
of the
array elements used for tracking. That spacing should be large enough in order
to
achieve adequate accuracy, yet it should also be small enough to avoid the
tracking
ambiguities associated with grating lobes of the radiation pattern.
Specifically, if the
tracking elements are spaced many wavelengths apart to gain precision, the
resultant
phase measurements will be ambiguous by many multiples of 2~ radians,
representing
many grating lobes and spurious directions of the satellite. If the elements
are spaced
less than a wavelength apart, the grating lobes are avoided but the precision
may be
unacceptably poor.
Referring next to Figure 12, a highly preferred embodiment of the satellite
antenna 11, 22, which takes into account the above noted difficulties, is
shown. The
tandem tracking antenna 350 combines two receiving antenna arrays, one large-
scale
array 301, 302, 303, 304 for high accuracy, and a small-scale array 305, 306,
307,
308, to resolve phase ambiguities.
Two goals are achieved by means of a tandem tracking antenna and an
algorithm to control the antenna. The first step of the algorithm extracts the
phases of
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the small-scale receiving subarray, for which the maximum element spacing is
less
than a wavelength and is therefore immune to the phase ambiguity or grating
lobe
problem. A least-squares calculation yields a best, but low-precision,
estimate of the
direction of the incoming control signal from the satellite.
5 Next, the phases at the large-scale receiving subarray are calculated
assuming
the best estimate is correct. While these phases are imprecise because they
arise from
an estimate derived from a small-scale array, they resolve the ambiguities of
integer
multiples of 2~ radians. By comparing the estimated phases at the large-scale
array
elements with the measured ones there, the unknown multiples of 2~ radians are
10 extracted by rounding to the nearest integer multiple of 2~. These
multiples of 2~ are
then added to the measured phases at the large-scale array elements to resolve
the
ambiguities and, combined with the unambiguous phases at the small-scale array
to
give a more accurate least-squares estimate of the direction of the satellite.
The details of the tandem tracker algorithm can be expressed as follows. Let
15 the antenna array be in the xy-plane and let the direction of the satellite
with respect to
the normal to the array be denoted by a unit vector whose components in the
array
plane are elements of a 2x1 column matrix n; this is the unknown to be
estimated. Let
the locations of the small-scale array elements be given by the matrix s; in
the
illustrative example depicted in the figure, this is a 4x2 matrix (the number
of rows is
20 the number of elements; the columns give the x and y components of the
element
locations, measured in wavelengths at the receiver frequency). Let the
measured
phases at the small-scale array elements be given by the matrix p in units of
2~
radians; in the illustrative example, this is a 4x1 matrix. For the small-
scale array, the
elements are less than a wavelength of the received signal apart (in the
illustration,
25 this refers to the separation along the diagonal of the small square
subarray), and there
is no ambiguity in the phases (the entries in p are limited to the range -0.5
to 0.5).
The relationship among these matrices is expressed by the equation:
p = sn. (4)
There are four equations for two unknowns in this illustration. The least-
squares best estimate for n is given by:
n = (sTS)-' sTP~
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where "T" indicates the transpose of the matrix. This estimate suffers from
low
precision. For the large-scale array, the corresponding matrices are S and P,
but P is
ambiguous to the extent that additive integers are lost in the measurements of
the
phases. The relationship among the large-scale matrices is given by:
Sn=P+U (6)
where the entries in the U matrix are unknown integers. The phase measurements
furnish only P, whose entries are in the range -0.5 to 0.5. The tandem tracker
algorithm finds the unknown integers in U by rounding to the nearest integers:
U = round (S (sTS)-'sTp - P). (7)
Finally, the high-precision, unambiguous, least-squares best estimate of the
direction
of the satellite is obtained as
n = (STS + STS)' (sTp + ST[P + LT]). 8
This direction in the array plane is then used directly in the phasing of the
transmitting
array elements, at the transmitting frequency, to aim the Earth Station
Terminal
transmitting antenna beam in the current direction of the satellite.
With reference to the flow chart contained in Figure 13, the Tandem Tracker
Algorithm, which is preferably implemented by software executing on central
processing unit 360, is described as follows. In step 410, the matrices a, b,
c, d, and
D are precalculated as follows:
a = (sTS)-' sT (9)
b = Sa. (10)
C = (STS + STS) ' ( I I )
d = csT (12)
D = cST (13)
The matrices b, d, and D are stored for later use in the processor unit 360.
As
indicated in the flow chart, these matrices are based on the geometrical
matrices s and
S, which contain the list of pairs of coordinates of each receiving element,
in units of
the wavelength of the signal received from the satellite power control or
beacon
transmission. The matrix s holds the locations of the small-scale receiving
array
elements; S has the locations of the large-scale array elements. For a planar
receiving
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array, there are two coordinates for each element; in the illustrative example
that uses
four small-scale elements, the s matrix is 4x2 and if the large-scale array
has four
elements as well, S is also 4x2. In that case, a will be 2x4, b will be 4x4, c
will be
2x2, d will be 2x4, and D will be 2x4.
As discussed above, the receiving elements of the Earth Station Terminal
antenna 300 receive a control signal or beacon transmission from the
satellite, which
is in the direction of the unit vector n with respect to the orientation of
the Tracker
array. For a planar array, only the two components of n within the plane are
needed;
these form the 2x1 matrix that is sought as the output of the Tandem Tracker
to locate
the direction of the satellite.
In step 420, the Tandem Tracker extracts the phase of the incoming signal at
each element of the small-scale array; these phases are unambiguous but also
of low
accuracy, by virtue of the small separation of the array elements. After
normalizing to
2~ radians, these small-scale phases (in the range -0.5 to 0.5) are stored in
the 4x1
1 S matrix p (for the illustrative case of four small-scale receptors).
In step 421, which is preferably performed simultaneously with step 420, the
Tracker extracts the phase at the elements of the large-scale array,
normalizes to 2~
radians, and stores these phases in the 4x1 matrix P. Although obtained with
greater
precision from the large-scale array, these phases are also in the range -0.5
to 0.5
because integer multiples of 2~t radians are, of necessity, lost in the phase
extraction
process. The algorithm restores the missing integers, as follows.
In step 430, the 4x1 matrix by - P is calculated. Because both the small-
scale and the large-scale arrays receive the satellite signal from the same
direction n,
the calculated 4x1 matrix by - P should be the missing integers of the
ambiguous
large-scale normalized phases.
However, these will not be precisely integers, because of inaccuracies of the
phase extractions, noise, or other random disturbing effects. Thus, in step
440, the
Tracker rounds these numbers to the nearest integers and forms the 4x1 matrix
of
integers U that resolves the phase ambiguities.
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Finally, in step 450, the least-squares best estimate of the direction of the
satellite is calculated as the 2x1 matrix n at the output of the Tandem
Tracker, in
accordance with the following:
n = dp + D(P+ZT) (15)
Note that the matrix operations entail only sums of products of numbers, so
that the
tracking calculations can be done virtually instantaneously. The direction of
the
satellite, given by n, can then be used by the Earth Station Terminal
transmitting array
to beam its signal to the satellites.
While the tandem tracker algorithm has been described with respect to a
planar array antenna, other types of array antennas such as non-planar arrays
may be
employed. A planar array is two dimensional, a non-planar array is three
dimensional.
To conserve power and also to guard against stray radiation that may cause
electromagnetic interference, the Earth Station Terminal transmitting
subsystem also
incorporates means for ensuring that it emits radiation only when its tracking
system
has captured the receiving satellites. If the incoming signals from the
satellites are
absent or too weak for the system to recognize the power control signal or
beacon, the
software will not allow power to be fed to the transmitting array. The
transmitting
array will be energized only when the signals from the satellites are
detected, the
system recognizes it as a valid power control or beacon signal, and the
algorithm
furnishes the direction of the satellites.
In addition, the antenna will not be energized if the user has not extended
the
platform that holds the shielded antenna unit to a suitable height above the
camera.
To allow for intermittent loss of contact, the system will be capable of
storing the
signals to be transmitted, in the buffer described above, and emitting them,
typically
(but not necessarily) in bursts, when contact is reestablished.
Referring next to Figure 14a, an alternative embodiment of the invention is
shown where the antenna 300 is attached to video camera 12 by means of a pole
500,
and where the pole is attached to a backpack 510 which carries the camera unit
10.
The height of the antenna 300 is adjustable by extending or retracting the
antenna pole
410.
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Use of the pole 500 and backpack 510 is advantageous for the purposes of
positioning the antenna 300 significantly above the camera operator to
considerably
reduce health-related concerns regarding radiation emitted by the antenna 300,
as well
as to provide for a more balanced combination of the camera 12 and camera Unit
10.
An additional benefit of this configuration is that it allows larger antenna
sizes, thus
significantly improving the antenna's receiving and transmission
characteristics. It
also allows for a larger camera unit 10 which may be less expensive to
manufacture.
Referring next to Figure 14b, another alternative embodiment of the invention
is shown where the antenna 300 is attached to the top of video camera 12 by
means of
a telescoping stand 550. The height of the antenna 300 is adjustable by
retracting or
extending the stand 5 S 0.
To protect the user from the microwave radiation emitted by the antenna, it
can be shielded on the sides and below with a metal shield 560, leaving only
the top
surface exposed. Microwave radiation will not penetrate even a thin metal
shield, so
its thickness is only a matter of adequate structural integrity. As shown in
Figure 14b,
the standard mechanical telescoping platform 550 may be used to ensure that
the
exposed top of the antenna be above the level of the user's head when the
camera is
on his shoulder.
Referring next to Figure 15, the operation of the system depicted in Figure 2
is
now described. A camera operator controls the Camera Unit 10 which is
recording
video and audio content captured by the camera 12 (shown in Fig. 15 as a
personal
computer). This content is transmitted to the Headquarters Unit 40 through the
Satellite Master Control Unit 20. A reporter gets an IFB (Interruptible
Feedback
Broadcast) signal back from the Headquarters Unit 40 (which may be a broadcast
studio), that contains the broadcast mix minus his or her own voice (mix-minus-
one).
The producer can optionally interrupt the IFB channel and communicate with the
reporter.
In the return direction, from the studio toward the camera operator, the
camera
operator has a data control channel and needs only a low-quality, low bit rate
audio
connection with the Satellite Master Control Unit 20 operator (COMS channel).
The
Satellite Master Control Unit 20 has its own operator, who has the capability
of
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communicating via the low-quality, low bit rate audio connection with either
the
Camera Unit 10 or the Headquarters Unit 40. The selection is performed by a
software
switch.
Finally, the Headquarters Unit 40 has its own operator, who is able to
communicate with the Satellite Master Control Unit 20 and Camera Unit 10
operators
through the COMS channels.
According to normal use of the system, the operators would exchange setup
information (positioning for better reception, better reporter coverage,
proper shot
angle and overall framing, etc.) through the COMS channels whereas the primary
10 video and audio content would be transmitted through the main wireless LAN
channel. The IFB is used so that the reporter is kept informed of what occurs
in the
studio, as well as to provide a voice communications path with the production
crew at
the home station.
Referring next to Figures 16-19, the software components needed to
15 implement the Camera Unit 10, Satellite Master Control Unit 20, and
Headquarters
Unit 40 systems are now described. Figure 16 is a legend for the following
diagrams.
Figures 17 through 19 document the software modules of the Camera Unit 10,
Satellite Master Control Unit 20, and Headquarters Unit 40 subsystems
respectively.
Both the primary data paths (video) as well as secondary data paths (IFB and
COMS
20 channels) are documented.
For the purpose of describing the different modules of the system software, a
block-based diagram, where each block corresponds to a coding unit or thread,
is
illustrated. As shown in Figure 16, a block indicates in its various areas (i)
the type of
the block, i.e., if it is a parent (master) or child thread, or of it is a
hardware-based
25 operation (ii) the data flow (input, output and control) of the block,
(iii) a brief
description of its functionality, and (iii) a brief description of its
implementation.
Figure 17 depicts the software flow diagram for the Camera Unit 12. There are
three data flows on the Camera Unit 12: a broadcast MPEG-2 flow 610, an IFB
channel data flow 620, and a COMS channel data flow 630. In addition, there is
a
30 main block 650 responsible for coordinating the operation of the different
blocks. The
operation of the different data flows are now explained.
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The broadcast data flow 610 starts with the "MPEG-2 Encoder" 611. This is a
hardware-based operation, which is controlled by the "Main Frame" block. This
block
encapsulates functionality that is provided by the program's user interface
(e.g., a
start/stop button). The data produced at the encoder is read continuously by
the
"Child Thread 1" 612, and is placed in the circular buffer 613. A second
thread,
"Child Thread 2" 614, is responsible for reading data from the circular buffer
and
sending it to the Satellite Master Control Unit ("SMCU") encapsulated in RTP
packets. Again, the control of the sending operation is performed by the "Main
Frame" block 650.
The "Main Frame" block 650 exchanges messages with the SMCU in order to
establish connections, prepare the communication channel for the broadcast
data flow,
setup the COMS channel, etc. The IFB data flow 620 starts at the Head Quarters
Unit
("HQU"), where the audio of the broadcast is mixed, excluding the audio
provided by
the Camera Unit feed (mix minus one). As explained earlier, the IFB can be
interrupted by the produced at the HQU site in order to communicate with the
reporter
at the Camera Unit site. The data coming from the HQU are first routed to the
SMCU, which in turn forward them to the Camera Unit. The "Child Thread" 621 is
reading the data as UDP (or RTP) packets from the network, and places them in
the
input buffer 622. Then, the 6.723.1 (or GSM) module 623 receives them and
decodes
them. It then forwards them to the "Sound Card 1" 624 for conversion to an
analog
form and playback to the system's speakers 625.
The COM channel data flow is bi-directional between the Camera Unit and the
SMC. At the Camera Unit end, a microphone picks up the voice of the Camera
Unit
operator. The data first undergoes A/D conversion within "Sound Card 1" 632,
and
then it is forwarded to an 6.723.1 (or GSM) encoder 633. The encoded data is
placed
in the output buffer 634, and from there it is transmitted to the network via
"Child
Thread" 635. Similarly, data from the SMC COMS channel is received by the
"Child
Thread" 635, placed in the input buffer 637, read by the 6.723.1 (or GSM)
decoder
638, converted to an analog form 632, and played back in the Camera Unit's
speakers
639.
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Figure 18 depicts the data flows of the SMC. As with the Camera Unit, there
is a "Main Frame" block 750 which encapsulates the functionality of the GUI,
as well
as messages and commands originating from the HQU and/or Camera Unit.
The broadcast flow 710 start at the "Child Thread 1" 711 where data is read
from the network in the form of RTP (or UDP) packets. Alternatively, and
according
to an option set by the "Main Frame", the date source may be the Hard Disk
Drive
(HDD). The data read (either from the network of from the disk) is placed in
the
Memory Module 712 (circular buffer). "Child Thread 2" 713 then reads the data
and
performs one or more of the following operations: 1 ) transmit the data to the
HQU via
the network, 2) save the data as a local file, and 3) decode the data through
an
additional block 714 ("Child Thread 3") and display it in the local SMC
screen. Any
combination of these operations can be performed; the desired configuration is
determined by options set at the "Main Frame".
The IFB channel data flow 720 is very simple: data from the HQU is read
from the network 721, placed in a buffer 722, and then rerouted through the
network
723 to the Camera Unit.
The COMS channel configuration 730 is slightly more involved in that the
network communication block has a selector (controlled by the "Main Frame")
that
determines whether or not the data will be sent to the HQU or the Camera Unit.
As
with the Camera Unit, the COMS data originate at the microphone 731, through
the
analog to digital converter 732, to the 6.723.1 (or GSM) encoder 733, to the
output
buffer 734, and from there to the network communication block 735. According
to the
setting provided by the "Main Frame", the data is sent via the network either
to the
HQU or the Camera Unit. The received data follow the exact path in reverse,
through
input buffer 737, decoder 738, D/A converter 732, and speaker 739.
Finally, Figure 19 depicts the data flows in the HQU. Again, the overall
operation is determined by the "Main Frame", which encapsulated the GUI and
commands received from the SMCamera Unit.
The broadcast flow 810 starts with "Child Thread 1" 811 which either receives
data from the network or reads it from a hard disk drive (HDD). The data is
placed in
a buffer 812. From there, "Child Thread 2" 813 will do one or more of the
following:
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1 ) save the data in a local file, and 2) send the data to a decoder block
("Child Thread
3") for decoding and preview.
The IFB data flow 820 starts at the microphone 821 in the master console. It
undergoes analog-to-digital conversion 822, encoding (G.723.1 or GSM) 823,
buffering 824 and transmission 825 to the Camera Unit via the SMC. The COM
channel 830 is completely symmetric with one in the Camera Unit, described
above.
The foregoing merely illustrates the principles of the invention. Various
modifications and alterations to the described embodiments will be apparent to
those
skilled in the art in view of applicants' teachings, herein. Thus, although
the shown
embodiments utilize LEOS, the present invention will also function with a
variety of
geostationary and/or nongeostationary satellites and other wireline (e.g.,
fiber)
networks with appropriate modifications, such as SONET and SDH products
including T3, and OC-3. Moreover, while the foregoing has been described with
respect to live audiovisual information captured by camera 12, the invention
applies
with equal force to the compression and real-time transmission of pre-recorded
audiovisual information, e.g., by replacing camera 12 with a variety of
playback
devices such as the portable Sony SX-225 edit pack, digital servers, DVD
players, or
laptop computers (not shown). It will thus be appreciated that those skilled
in the art
will be able to devise numerous systems and methods which, although not
explicitly
shown or described herein, embody the principles of the invention and are thus
within
the spirit and scope of the invention as defined by the appended claims.
Referring to Figure 20, there is shown an alternate arrangement of the
invention wherein the camera 12, Camera Unit 10 and antenna 300 are
permanently or
temporarily mounted on an automobile 904, such as an SUV. Antenna 300 is
arranged at the top of pole 92, which is mounted to the exterior of automobile
904.
Camera 12 may be mounted together with Camera Unit 10, or may be separate
therefrom and connected by cable. Preferably camera 12 can be easily
dismounted
and carried away from vehicle 904 and linked to Camera Unit 10 by cable or LAN
as
described above. Alternatively, a playback machine 905 may be placed in the
vehicle
and linked, e.g., by cable, to the antenna 300 for transmission of recorded
audiovisual
information back to a headquarters station. The arrangement of Figure 20 may
be a
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permanent installation on a vehicle for local news coverage having significant
reduced
cost compared to a truck installation with a terrestrial microwave link, or
may be a
temporary installation, as on a rented vehicle.
Figure 21 shows a gimbal arrangement that can be used with antenna 300, and
which has particular advantage when antenna 300 is mounted on a hand-held unit
or
on a vehicle, as shown in Figure 20. Providing a gimbal arrangement as shown
in
Figure 21 facilitates use of the vehicle mounted system while the vehicle is
in motion,
and provides some compensation for vehicle angle changes (such as going over
rough
terrain), thereby reducing the burden on the electronic beam steering system
for
tracking geostationary and/or nongeostationary satellites.
Gimbal unit 920 is arranged to be mounted on brackets 922 which may be
separately mounted to a vehicle or antenna stand. Unit 920 is connected by
arms 928
and 930 to brackets 922 using respectively gimbal bearings 924 and 926. Unit
920
additionally includes arms 932 and 934 which are connected to antenna 30 by
bearings 938 and 936 respectively. Accordingly antenna 300 may pivot about two
axes to change orientation with respect to mounting brackets 922.
In a hand-held or vehicle mounting configuration antenna 300 may be
arranged to have a center of gravity that is below bearings 924, 926, 936 and
938.
Thus as the angle of the camera or vehicle changes, antenna 30 will remain
horizontal
by force of gravity. Alternately, bearings 924, 926, 936 and 938 may be
provided
with resistance such that antenna 300 can be set and maintained at a desired
fixed
angle with respect to mounting brackets 922. This arrangement can be used to
approximately point the broadside of antenna 300 at a geostationary satellite
and
thereafter allow the electronic circuitry to refine the pointing angle of the
angle of the
antenna beam. In a still further arrangement servo motors may be provided to
turn
antenna 300 about the bearings, for example to stabilize the antenna on a
moving
vehicle using a gyroscopic sensor.
Figure 22 shows an alternate gimbal, which is arranged as a frame 950
surrounding antenna 300. Bearings 954, 956 pivotally connect frame 950 to
brackets
952, and bearings 958, 960 connect frame 950 to antenna 300. Brackets 950 are
connected to mounting pole 902 below antenna 300. In a still further
arrangement of
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coarse antenna pointing, only a single set of bearings 954, 856 are provided
to connect
antenna 300 directly to bracket 952, to point the antenna in elevation and
bracket 952
is arranged to pivot about pole 92 to point antenna 300 in azimuth.
It will be recognized by those skilled in the art that use of different
satellites
5 operating on different frequency bands will change the requirements of
antenna 300.
For example, the present International Telecommunication Union recommended
Fixed Satellite Service frequency bands include three frequency bands, Ka-band
(20/30 GHz), Ku-band (11/15 GHz) and C-band (4/6 GHz). For each satellite and
each frequency band the size (and consequently the gain) of the antenna must
be
10 selected to provide sufficient radiation power level at the satellite for
the signal to be
effectively received at the satellite. Further, array antennas are subject to
"steering
loss" when they are not pointed directly toward the satellite. Those skilled
in the art
are capable of computing the power budget for providing the required wide
bandwidth
signal according to the distance and receiver requirements of the satellite
being used.
1 S The present invention provides a system for transmitting real-time,
broadcast
quality audio visual information point-to-point or point-to-multipoint from a
very
small, camera-mounted or vehicle-mounted Earth Station Terminal unit using
satellite
facilities. Such a unit can be used for performing video and audio
transmission with
minimal preparation, from anywhere in the world but within the footprint
coverage of
20 a particular satellite. It has broad applications in television journalism
of news and
sports events, Internet multicast, as well as corporate communications and
security,
where immediate access to live television coverage and other video feeds from
anywhere in the world is highly desirable.
The invention makes it possible, for the first time, for an ordinary
television
25 news camera to feed directly to a satellite without (in its preferred
configuration) the
use of any intermediary system. Thus for the first time networks, news
services,
broadcast and cable stations will be able to deploy television cameras with
direct links
to satellites in virtually any location around the world where live television
coverage
is desired. They will be able to feed from every one of their news cameras in
real
30 time without the need for cumbersome and obtrusive ancillary equipment. For
the first
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time the news services will be able to provide live video coverage of breaking
stories
from most of the earth's surface.
In remote areas this camera unit will make live transmissions possible for the
first time ever. One briefcase added to an ordinary camera unit will enable
the
journalist to feed live television coverage within minutes after he or she
arrives at the
scene of a newsworthy event. In short, the invention ends most of the
logistical
problems of live television journalism and lets journalists do what they do
best: cover
the story.
