Mobile and hand-held broadcast video earth station terminals and methods for communicating with earth terminals via satellites

MOBILE AND HAND-HELD BROADCAST VIDEO

EARTH STATION TERMINALS AND METHODS FOR

COMMUNICATING WITH EARTH TERMINALS VIA SATELLITES

SPECIFICATION

0005Cross Reference to Related Applications

0006The 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.

0007Background of the Invention

0008I. Field of the invention.

0009The 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.

0010II. Description of the related art.

0011Journalistic 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 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.

0012Since the early nineteenth century, from Julius Reuter's 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 available to cover fast breaking news events like riots, hurricanes and earthquakes.

0013Current 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.

0014In 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 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.

0015For 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.

0016The 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.

0017Internationally 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 aiφlanes, 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 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 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.

0018In 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 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.

0019There 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.

0020In 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.

0021Another 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 beam or an "omnidirectional" transmission, which is inconsistent with "high-gain." The patent does not propose any particular steering techniques.

0022A 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

0023Satellite 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.

0024Since 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.

0025Summary of the Invention

0026An 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. 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 unit. 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.

0027A 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.

0028A 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.

0029Yet 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.

0030Yet 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 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 802.1 1 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 puφoses. It can also be stored on disk, or routed (in either analog or digital form) to other video equipment.

0031In 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.

0032The accompanying drawings, which are incoφorated and constitute part of this disclosure, illustrate a preferred embodiment of the invention and serve to explain the principles of the invention.

0033Brief Description of the Drawings Figure 1 is a system diagram illustrating the overall structure of a preferred embodiment where direct satellite connection is used;

0034Figure 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 ;

0035Figure 4 is a block diagram of a Camera Unit suitable for use in the embodiment of Fig. 2;

0036Figure 5 is an illustrative diagram depicting the installation of the Camera Unit; Figure 6 is an illustrative diagram depicting an alternative installation of the Camera Unit;

0037Figure 7 is an illustrative diagram depicting the operation of a circular buffer;

0038Figure 8 is an illustrative diagram depicting a secondary relay unit used for satellite transmission;

0039Figure 9 is an illustrative diagram depicting the changing orientation and attitude between an antenna and a satellite due to motion of the antenna;

0040Figure 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;

0041Figure 12 is an illustrative diagram depicting a tandem tracker pair of receiving arrays;

0042Figure 13 is a flow diagram illustrating a preferred processing technique employed by the tandem tracker;

0043Figures 14a and b are illustrative diagrams depicting the attachment of an active phased antenna to a video camera;

0044Figure 15 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;

0045Figure 17 is a software flow diagram for the Camera Unit;

0046Figure 18 is a software flow diagram for the Satellite Master Control Unit;

0047Figure 19 is a software flow diagram for the Headquarters Unit.

0048Figure 20 is a system diagram illustrating the overall structure of an alternative embodiment of the present invention;

0049Figure 21 is an illustrative diagram of an antenna arrangement suitable for use in the embodiment of Figure 20; and

0050Figure 22 is an illustrative diagram of an alternative antenna arrangement suitable for use in the embodiment of Figure 20. Description of the Preferred Embodiments

0051Referring 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.

0052In 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 and antenna 11 may be appropriately mounted on or integrated in the camera 12.

0053The 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.

0054In 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.

0055The 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. 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.

0056In 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.

0057Referring 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.

0058In 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 1 1 Mbps, or alternatively, a HiperLan or a Wi-Lan operating at speeds greater than 20

0059Mbps. 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.

0060The 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 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.

0061The 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 puφoses, including decoding the received compressed-domain audiovisual signals, displaying decoded video information on a regular television monitor for preview puφoses, 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 prerecorded 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.

0062The 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 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.

0063As 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.

0064In 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.

0065The 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 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.

0066While 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.

0067The 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.

0068Referring 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.

0069For 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 multi-frequency time division multiple access (MF-TDMA) for the uplink and asynchronous time division multiplexing (ATDM) for the downlink

0070QPSK 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 well known to persons skilled in the art and may be employed by satellite modem 180 to effect proper communication with the particular satellite.

0071To 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 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 employed.

0072Referring 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 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 puφoses. 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 1 1 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. 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 G.723.1 standard, or alternatively, the GSM standard.

0073As discussed above in connection with Figures 3 and 4, live video information is processed by an NTSC/PAL/SEC AM/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 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.

0074Since 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

0075Satellite 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

0076Figure 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).

0077During 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 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.

0078The 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.

0079Areas 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.

0080In 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 puφose computers. Multiple adapters can be used to achieve higher throughputs, using inverse multiplexing.

0081The 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. 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 puφoses.

0082Referring 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.

0083As 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".

0084The 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 puφose, 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 G.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 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.

0085Additional 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 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 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 line of sight path between the camera and base station is a major advantage.

0086Additionally, 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. 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 puφose 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.

0087Because 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 handheld, 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 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.

0088Nevertheless, 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.

0089Referring 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.

0090Some 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.

0091With 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 frequency of about 29 GHz (a wavelength λ = 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 (4π h/ λ) ² = 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.

0092In 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 λ 74π, (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 λ = 1.04 cm, a square array approximately 15 cm on a side of sufficiently densely distributed elements should adequately achieve the required gain.

0093It 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 1 1.

0094Referring next to Figure 1 1 , 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 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.

0095Although 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.

0096The 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 peφendicular 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 φ, where φ = px + qy. (2)

0097A phase detector extracts the phase φ 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 φ . 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 2π 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 are correspondingly scaled. The transmitting array element at (x, y) needs to be excited by a signal of phase θ, where θ = - px - qy. (3)

0098This 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.

0099The 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 2π 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 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. 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 2π radians. By comparing the estimated phases at the large-scale array elements with the measured ones there, the unknown multiples of 2π radians are extracted by rounding to the nearest integer multiple of 2π. These multiples of 2π 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.

0100The details of the tandem tracker algorithm can be expressed as follows. Let 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 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 2π 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, 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)

0101There are four equations for two unknowns in this illustration. The least- squares best estimate for n is given by: n = (s ¹ s^τp, (5) 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:

0102U = round (S (s^τs)-'s^τp - P). (7) Finally, the high-precision, unambiguous, least-squares best estimate of the direction of the satellite is obtained as n = (s^τs + S^TS)-' (s^τp + S^T[P + U]). (8)

0103This 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.

0104With 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 = (s^τs)-' s^τ (9) b = Sa. (10) c = (s^Ts + S^TS)-' (11) d = cs^τ (12)

0105D = cS^T (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 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.

0106In 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 2π radians, these small-scale phases (in the range -0.5 to 0.5) are stored in the 4x1 matrix p (for the illustrative case of four small-scale receptors).

0107In 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 2π 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 2π radians are, of necessity, lost in the phase extraction process. The algorithm restores the missing integers, as follows.

0108In step 430, the 4x1 matrix bp - 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 bp - P should be the missing integers of the ambiguous large-scale normalized phases.

0109However, 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. 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+U) (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.

0110While 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.

0111To conserve power and also to guard against stray radiation that may cause electromagnetic interference, the Earth Station Terminal transmitting subsystem also incoφorates 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.

0112In 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.

0113Referring 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. Use of the pole 500 and backpack 510 is advantageous for the puφoses 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.

0114Referring 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 550.

0115To 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.

0116Referring 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.

0117In 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 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.

0118Finally, 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.

0119According 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 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.

0120Referring next to Figures 16-19, the software components needed to 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 channels) are documented.

0121For the puφose 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 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.

0122Figure 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 main block 650 responsible for coordinating the operation of the different blocks. The operation of the different data flows are now explained. 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 G.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.

0123The 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 G.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 G.723.1 (or GSM) decoder 638, converted to an analog form 632, and played back in the Camera Unit's speakers 639. 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.

0124The 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".

0125The 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.

0126The 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 G.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.

0127Finally, 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.

0128The 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: 1) save the data in a local file, and 2) send the data to a decoder block ("Child Thread 3") for decoding and preview.

0129The 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.

0130The 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.

0131Referring 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 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.

0132Figure 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.

0133Gimbal 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.

0134In 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.

0135Figure 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 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.

0136It will be recognized by those skilled in the art that use of different satellites 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 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. 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 a particular satellite. It has broad applications in television journalism of news and sports events, Internet multicast, as well as coφorate communications and security, where immediate access to live television coverage and other video feeds from anywhere in the world is highly desirable.

0137The invention makes it possible, for the first time, for an ordinary television 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 time without the need for cumbersome and obtrusive ancillary equipment. For the first time the news services will be able to provide live video coverage of breaking stories from most of the earth's surface.

0138In 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.