Real-time satellite communication system using separate control and data transmission paths

A control communication method includes synchronizing a timing in a central earth station and a plurality of remote earth stations such that a predetermined control time period having a plurality of time slots is synchronized among the central earth station and the remote earth stations. The control time period is not longer than a substantially real-time response time period for the remote stations. This method further includes: initiating from a respective remote earth station, and completing, a transmission of control information through a satellite to the central earth station only during one or more of the time slots assigned to the respective remote earth station; receiving the transmission at the central earth station; and sending from the central earth station a separate transmission of data through the satellite to the remote earth station.

BACKGROUND OF THE INVENTION
 This invention relates generally to satellite communication systems and
 methods. It specifically relates to such systems and methods that enable
 real-time high bandwidth communications to occur between a remote location
 and a public access information resource, such as the Internet. This
 invention relates to both geostationary satellites (GEO's) and
 non-geostationary satellites (LEOs).
 Geostationary Satellites (GEO's)
 Satellite communication systems have been used as a high-speed pipeline
 sending many signals in one direction. These signals include various
 information or data such as video signals or telephone signals, typically
 compressed at one site and transmitted to a second site or to multiple
 sites and decompressed.
 In satellite communication systems, a concept called Very Small Aperture
 Terminal (VSAT) permits multiple locations to send small packets of data
 to other locations via the satellite "pipelines." The predominate
 transmission technique uses polling, in which a ground station hub uses a
 satellite transmission to poll one or more remote sites for any data the
 remote sites have to send back to the hub. Data can be sent to the hub,
 analyzed and rerouted. In a polling system, a common return transmission
 path services both polling service requests and impending data transfers.
 The VSAT polling technique entails a complex and costly hub. The technique
 is set up to accommodate many short bursts of return site data. The
 polling methodology is not conducive to provide timely responses in a
 consistent manner to the remote users. It also does not provide for
 deterministic status monitoring and control on a continuous basis of the
 remote terminals.
 Another technique, demand assigned multiple access (DAMA), routes data
 between ground stations without a requirement that it be transmitted to a
 central hub for redistribution with a second satellite transmission. This
 technology is more costly to implement over a large number of remote sites
 than a polled architecture; however, it supports larger bandwidths. If
 available, a transmit channel is temporarily assigned to the remote site
 via a transmission from one of the other sites in the network. The
 channels could be assigned by the site sending the transmission or
 assigned from an available pool by any site in the network. Thus, the DAMA
 technique, as opposed to the polling technique, does not require remote
 transmissions to go to one central hub station for retransmission to the
 destination station. It has been used, for example, in offering digital
 phone and data service in developing countries. With this technology,
 routing and switching are grouped into small earth station clusters, then
 sent to a main earth station where they are transmitted to the end
 destination. Specific application dependent pieces of earth station
 hardware perform the phone switching.
 DAMA and polled satellite communication systems often use a TDMA (Time
 Division Multiple Access) technique. The TDMA technique enables several
 remote sites to share a common channel on a transponder of the
 communication satellite. That is, several remote sites will each transmit
 a fixed length transmission in a predetermined time sequence. Each
 transmission will address the specific channel at a precise time.
 In most VSAT systems (Polled or DAMA) a remote satellite transmission
 contains both data information and status and control information. Because
 of this, neither type of satellite communication system achieves a precise
 predetermined or real time deterministic satellite transmission response
 from a remote terminal station.
 Low Earth Orbital Satellites (LEOs)
 LEOs operate both as single satellites and as part of a constellation of
 many satellites. LEOs operate in assigned non-geostationary polar orbital
 slots that have a much lower altitude than GEO's. GEO's operate at an
 altitude of 22,300 miles above earth whereas LEOs can operate at altitudes
 from 375 to 1,250 miles. Like GEO's, some LEOs are planned to operate with
 comparable size transponders (36 MHz and 54 MHZ transponders). GEO's often
 have 24 transponders and LEOs often have less than one half that number.
 Fewer transponders provide less total satellite bandwidth.
 It takes many non-geostationary LEOs operating in a polar arc above earth
 to fill the needs of a single geostationary earth station operating 24
 hours a day. This is due to the need to have multiple LEOs because of the
 limited time each LEO physically has in orbit while over a specific ground
 station. LEOs are placed in a polar arc and operate at a fixed distance
 from each other. Therefore, a specific LEO satellite passing over an earth
 station is accessible by the earth station for a finite period of time.
 The earth station would therefore be dependent on communicating with many
 LEOs over a 24-hour period in order to maintain continuous communication.
 LEO earth stations addressing the low data rate mobile telephone market
 can use omni-directional antennas to send and receive transmissions from
 the satellite presently orbiting above its ground station. LEOs addressing
 the medium or high-speed data transfer market require the earth stations
 to use one or more mechanical tracking antennas. A new antenna technology
 referred to as a phased array antenna is being developed by others such as
 Motorola to reduce the cost of an earth station that communicates with
 LEOs.
 Satellite to satellite transmissions between several LEOs orbiting in the
 same polar arc are performed by using a processing technique called store
 and forward. LEOs have an onboard microprocessor that can perform limited
 processing functions. The processor can analyze a special packet header on
 a data packet and cause the data packet to be forwarded to an adjacent
 satellite in the polar arc. Special packet headers contained in the front
 of data packets are used for routing the packets between satellites in the
 polar arc. Once a packet is accepted for processing by its intended remote
 earth station site, the packet is processed in a similar manner as a
 packet sent to a remote earth station site from a geostationary satellite.
 A LEO can operate in a message/broadcast or Interactive mode of
 transmission. A message/broadcast mode sends packets to all ground station
 locations simultaneously (point to multipoint); an interactive mode is
 point to point.
 Satellite to satellite transmissions occur via a Ka band or V band
 spectrum. Future developments may replace these links with laser
 communication technology. The present invention is not dependent on either
 type of satellite to satellite transmission technology. LEOs supporting
 voice, interactive multimedia and data applications usually communicate to
 earth stations via the Ka or V band spectrum.
 LEOs are divided into three categories: Micro LEOs, Mid LEOs, and Big LEOs.
 The Micro, Mid and Big usually define the physical size of the satellite
 and its overall bandwidth capacity and the amount of earth's surface
 covered by its network of satellites. All three types operate within the
 altitude envelope above earth of 375 to 1,250 miles. If LEOs try to
 operate below 375 miles, they become susceptible to the earth's gravity.
 Most LEOs operate at an altitude of between 435 and 800 miles.
 Big and Mid-size LEOs are being deployed and licensed for global
 communications. Micro LEOs are being deployed and licensed primarily for
 regional communications. Most United States Federal Communications
 Commission (FCC) licenses being granted are for global networks. The first
 global LEO satellite network to reach operational status is used to serve
 the mobile phone market. Medium and big LEOs are usually capable of
 receiving transmissions from high bandwidth transmissions (partial T1 and
 full T1). LEOs usually operate by using one of two techniques FDMA/TDMA,
 or CDMA. LEOs operating with Frequency Division Multiple Access (FDMA) and
 Time Division Multiple Access (TDMA) techniques are applicable to this
 invention.
 LEOs operating with a Code Division Multiple Access (CDMA) technique
 probably are not applicable to the present invention due to their lower
 and limited bandwidth capabilities. CDMA is a technique in which a remote
 earth station uses a spread spectrum modulation and orthogonal codes to
 avoid interfering with other remote earth stations.
 None of the previous GEO/LEO techniques discussed have provided a
 relatively simple and inexpensive way of communicating high-speed
 information that has a time dependency to and from remote site locations,
 especially the ones in which a high bandwidth connectivity infrastructure
 is not available to provide the high-speed information to and from the
 remote locations. Thus, there is the need for an improved and new
 satellite communication system and transmission method to satisfy this
 need.
 SUMMARY OF THE INVENTION
 The present invention overcomes the above-noted and other shortcomings of
 the prior art by providing a novel and improved real-time satellite
 communication system using separate control and data transmission paths.
 It also offers a new art for future designs that require a real time
 predictable response satellite communication system. This includes a novel
 and improved control communication method for a satellite communication
 system, a novel and improved method of providing fast and timely
 information to remote locations, and a novel and improved satellite
 communication system providing real time critical event messaging and
 control with optional follow on timely transmissions of high bandwidth
 data, videoconferencing, or other multimedia data transfers.
 The present invention provides a two-way satellite communication system
 that offers high-speed bandwidths to locations previously lacking high
 bandwidth connectivity. This invention provides real time critical message
 and communication system status and control processing in one dedicated
 transmission path. This enables immediate and continuous responsiveness to
 real time events or to requests for services required from remote
 locations, and thus enables such services as Internet, video conferencing,
 audio conferencing or other standards based communications to be available
 at remote locations.
 High-speed data transfers can take place in an interactive real time
 environment without the bandwidth limitations of a time slot architecture.
 Another advantage of the present invention is that one or more synchronous
 data protocols can be transmitted within the same data stream. This
 capability enables many different types of data protocols to be combined
 to meet application specific requirements. Different protocols can be sent
 in the same data stream.
 Non-limiting examples of where the present invention has particular utility
 include: (1) rural, or isolated, locations that do not have the
 connectivity infrastructure for receiving or transmitting the uncompressed
 and compressed data communicated through the present invention, (2)
 governmental service agencies that desire an alternate communication path
 to secure and rapidly deploy telecommunications, (3) urban and rural
 locations where protocol standards are not compatible with terrestrial
 circuits, and (4) locations with hazardous waste, chemicals or
 contaminants, or locations requesting constant monitoring. Widely
 separated sites can quickly recognize critical events and then conduct
 videoconferences with full-motion video and exchange data simultaneously.
 Interactive communication with remote locations can reduce travel time and
 expense for meetings, consulting or training. Companies can provide their
 staffs with up-to-date information to keep up with advances in their
 fields. Medical facilities in rural, or isolated, areas can enhance the
 quality of health care and limit the cost for their patients by using this
 invention to exchange data and to consult with other health care
 professionals. Patients may receive treatment on-site without the
 inconvenience or potential hazard of extended transport. Interactive
 training in a variety of fields can be provided anywhere a remote station
 can be located in communication with a communication satellite.
 Interactive distance learning courses bring education opportunities to
 remote areas which were previously outside of a high bandwidth
 connectivity infrastructure.
 The foregoing advantages can be achieved with a system having a single
 central earth station providing a single switch for the various
 informational resources desired by the remote locations. This information
 can include a variety of high-speed data such as interactive video
 conferencing and a full range of multi-media capabilities available
 through Internet and Intranet connections.
 In the present invention, each remote earth station operates with dual
 transmission paths to a central station. One transmission path for
 critical real time event and communication status and control uses fixed
 transmission time slots within a channel of a transponder to predetermine
 when a control file of information will be transmitted from a particular
 remote station to the central station. The other transmission path is used
 to transmit synchronous data between remote stations and the central
 station. The status and control file transmitted to the central station
 enables the central station to determine the second path's data
 transmission rates, when to begin the actual data transmission, the
 channel frequency assignment in which to transmit the synchronous data,
 the expected time duration of the transmission, and where to transmit the
 data.
 The present invention works with either geosynchronous or nongeosynchronous
 satellites (e.g. GEOs or LEOs). For example, the present invention can
 work in either a LEO message/broadcast or interactive mode such that
 remote earth stations selectively respond to only those transmissions
 applicable to them. The present invention can be deployed with, for
 example, LEOs using FDMA or TDMA techniques and operate in a similar
 manner as applied to operating GEO satellites.
 More particularly, this invention provides a control communication method
 for a satellite communication system having a central earth station and a
 plurality of remote earth stations linked to the central earth station
 through at least one satellite in orbit above the earth. This method
 comprises synchronizing the timing of the central earth station along with
 the plurality of remote earth stations such that a predetermined control
 time period having a plurality of distinct sequential time slots is
 synchronized among the earth station and the remote earth stations. This
 synchronized timing is necessary to correctly time phase the TDMA remote
 transmission. Preferably, the control time period is cyclical wherein each
 remote site has a cyclical control time. This is the time the remote site
 sends a status and control signal to the central earth station and
 receives its corresponding return transmission acknowledgement. Preferably
 the control time period is not longer than a substantially real-time
 response time period for any one of the remote earth stations. This method
 further comprises initiating from a respective remote earth station. The
 method still further comprises receiving the transmission at the central
 earth station and sending from the central earth station, in response to
 the received transmission, a separate transmission of data through the
 satellite to the remote earth station. This separate transmission
 preferably occurs such that the data is received by the respective remote
 earth station within the predetermined substantially real-time response
 time period or at least within a real-time response period relative to
 such separate data transmissions between the central earth station and the
 respective remote earth station. Synchronizing preferably includes
 receiving in the central earth station and the remote earth stations, a
 timing signal from a source other than the central earth station and the
 remote earth stations (e.g., a timing signal from the Global Positioning
 System). The method can still further comprise obtaining the data from a
 public access information resource containing high bandwidth digitally
 compressed and non-compressed information. A particular resource for
 non-compressed data is the Internet.
 The present invention can also be defined as a method of providing
 information to remote locations. This comprises defining a satellite
 communication group having a central earth station, a plurality of remote
 earth stations each at a respective location remote from the central earth
 station, and a satellite in geosynchronous or nongeosynchronous orbit
 above the earth. This also includes assigning a cyclical control
 communication time period to the defined satellite communication group,
 wherein the control time period is not longer than a substantially
 real-time response time period for any one of the remote earth stations in
 the defined satellite communication group. The method further includes
 determining a transmission time having a duration sufficient for a
 transmission to be sent from any of the remote earth stations and received
 by the central earth station. Also included in this method is allocating a
 specific number of time slots within the control communication time period
 in response to the duration of the control communication time period and
 the determined transmission time. The method further comprises determining
 the number of remote earth stations in the defined satellite communication
 group and the number of time slots. The method also includes assigning
 each remote earth station to at least one respective time slot and to a
 common control transmission frequency if there are not more remote earth
 stations than time slots. If there are more remote earth stations than
 time slots and frequencies to allocate, a remote earth station is assigned
 to an overflow area. The overflow area is designed to allow the remote
 site to operate and transmit, however, the response time can exceed being
 serviced in the basic control time period. The method further comprises
 time synchronizing the central earth station and the plurality of remote
 earth stations such that the control communication time period is
 synchronized among the central earth station and the remote earth
 stations. The method also includes initiating from a respective remote
 earth station, and completing, a transmission of control information
 through the satellite to the central earth station only during a
 respective one or more of the time slots of the control communication time
 period assigned to the respective remote earth station. The method further
 includes receiving the transmission at the central earth station and
 sending from the central earth station, in response to the received
 transmission, a separate transmission of data through the satellite to the
 remote earth station.
 The present invention also provides a satellite communication system
 providing real-time acquisition and transmission of high bandwidth data.
 This system comprises: an information resource providing a high bandwidth
 transmission (e.g., alphanumeric information, video, audio), a satellite,
 and a central earth station. It also includes a remote earth station in
 communication with the central earth station through the satellite to
 transmit control information on a first transmission path through the
 satellite only during the predetermined periodic time slot assigned to the
 remote earth station. In this system the central earth station is
 connected to the information resource to receive the high bandwidth
 transmission and to communicate the high bandwidth transmission on a
 different transmission path through the satellite to the remote earth
 station in response to the control information transmitted by the remote
 earth station. The return data path from the remote earth station to the
 central earth station is on a second transmission path as distinguished
 from the first transmission path on which the control information is sent.

DETAILED DESCRIPTION OF THE INVENTION
 A Description of FIGS. 1-11
 A detailed description of the satellite system of the present invention and
 its implementation are supported by FIGS. 1-11. FIGS. 1-5 are block
 diagrams and schematics of the present invention and FIGS. 6-9 are block
 diagrams and data schematics of an implementation of the present invention
 on a GEO or LEO satellite. FIGS. 10-11 are block diagrams of an
 implementation of the present invention and are specific to a GEO
 satellite or a LEO satellite.
 The Satellite Communication System of the Present Invention
 Referring to FIG. 1, the satellite communication system of the present
 invention includes a satellite 2 which provides transmission paths between
 a central earth station 4 and one or more remote earth stations 6. It is a
 particular aspect of the system of the present invention that the central
 earth station 4 is connected to one or more information resources 8. A
 particularly useful application of the present invention is where high
 bandwidth information resources 8 are required and not otherwise available
 at the remote locations 6.
 An example of high bandwidth information resources for which the present
 invention is particularly adapted include Internet communications, video
 communications (e.g., video conferencing), audio communication (e.g.,
 audio conferencing), and data transmissions. Typically these types of
 resources are packet based and require high bit-per-second transmission
 rates (e.g., 100's of kilobits per second and higher), especially when
 real-time data and/or video communications are to be provided.
 Thus, the satellite communication system of the present invention provides
 high-speed Internet access, video conferencing and multimedia
 capabilities, multiple voice packets and data transmissions, for example,
 anywhere a remote earth station 6 can be set up in communication with a
 communications satellite 2. In particular, the present invention provides
 continuous interactive Internet access and compressed digital two-way
 video, audio and data transfers in real time to users in business,
 industry, government, health care, and education. For example, an
 instructor and/or student in a remote area lacking high bandwidth
 connectivity can conduct either an interactive on line data exchange or an
 interactive videoconference with an instructor in another remote area
 lacking high bandwidth connectivity or in an urban area with network
 connectivity already established.
 A significant aspect of the present invention enabling this real time data
 and video conferencing to occur is that it utilizes two principal
 transmission paths. One is a dedicated status and control path, and the
 other is a data transmission path. The remote earth stations 6 use the
 dedicated status and control path to inform the central earth station 4
 that the remote earth station needs something. Both the central earth
 station 4 and the remote earth stations 6 use the data transmission path
 for the high-speed data transmissions for the information from the
 resources 8 and for corresponding transmissions from the remote earth
 station (e.g., interactive videoconferencing). In FIG. 1, the uplink paths
 from each of the remote earth stations 6 for the dedicated status and
 control transmission path are designated by the reference numeral 10, and
 the corresponding downlink to the central station 4 is indicated by the
 reference numeral 12. The high-speed data transmission paths between the
 central earth station 4 and the satellite 2 is designated by the line 14,
 and the corresponding link between the satellite 2 and each remote earth
 station 6 is designated by the reference numeral 16. The use of these
 transmission paths will be described in more detail after the following
 explanation of the satellite 2, central earth station 4, and remote earth
 stations 6, status and control transmission path 10, transmission paths
 from the central earth station 14, and synchronization.
 Implementation of the Present Invention
 The implementation of the present invention implies that the allocated
 satellite space segment in FIGS. 10 and 11 is available for this
 implementation on a 24 hour day, 7 days a week, as a lease or purchase.
 The implementation of this invention for the central earth station (FIG. 6)
 is based on available SCPC MPEG 2 uplink control equipment 110. This SCPC
 MPEG 2 equipment includes the packet multiplexer which outputs a data
 stream. The status and control processor with real time event message
 processing 112 as implemented in this invention includes this invention's
 software, programming logic, file structures, and design logic to provide
 the inputs in real time to the central earth stations packet multiplexer
 110.
 The implementation of this invention for the remote earth station (FIG. 7)
 is based on available hardware components that are integrated into a
 complete uplink system by this invention. The status and control
 workstation 58 provides a complete uplink system via this invention's
 control logic, programming files, data layouts, timing, synchronization,
 data transmission paths, and S & C transmission paths. Therefore, the
 implementation of the present invention establishes a complete operating
 uplink earth station at each remote site capable of receiving and
 transmitting IP (Internet) data, being able to conduct a video conference
 and processing real time events.
 The implementation of the present invention has defined the size of the
 satellite communication system to include one central earth station, 250
 remote earth stations with a provision to add 20+ additional remote earth
 stations. Each remote earth station can process ten 384 KBPS signals, five
 768 KBPS signals, and two 1.544 M/Bit signals. The satellite space segment
 leased or purchased on a GEO satellite is 1/2 of 54 MHZ transponder or 27
 MHZ. The satellite space segment leased or purchased on each LEO satellite
 in this polar arc or constellation is a full 36 MHZ transponder. The
 implementation on a LEO satellite will lease or purchase the same
 transponder on each satellite in the polar arc or constellation of LEO
 satellites. The present invention does not restrict or limit the number of
 transponders, the number of remote earth stations, the type of data or the
 data speed to be transferred. The present invention's implementation as
 shown in FIGS. 6-11 will be described in the following sections;
 satellite, central earth station, remote earth station, status and control
 transmission path and transmission paths from the central earth station.
 Satellite
 A geosynchronous or nongeosynchronous communication satellite can implement
 the satellite 2. Such a geosynchronous satellite has conventional
 transponders known in the art to operate in one or more frequency bands to
 which the satellite has been assigned by the Federal Communications
 Commission (e.g., C band, Ka band, Ku band, S band, X band, or hybrids).
 Such a nongeosynchronous satellite has store and forward capability and
 transponders that typically operate in Ka band, V band or C band. Any
 suitable satellite can be used so long as it provides the necessary
 transmission paths, bandwidths and supports a TDMA architecture. LEOs that
 are designed to rely on a line of site to earth station and operate on a
 multiple frequency or a multiple cell basis (FDMA) and use a Time Division
 Multiple Access (TDMA) are applicable to this invention. The usage of
 multiple frequencies, and/or multiple cells enables the allocated FCC
 frequency spectrum to be divided for status and control satellite
 transmissions. LEOs transmitting higher speed data and operating at Ka
 band or V band and requiring a clear line of site from the satellite to
 the earth station antenna are applicable to this invention. LEOs that only
 operate at lower speeds (2.4-4.8 KBPS) sent over UHF or VHF antennas that
 do not require a clear line of site between the satellite and the earth
 station are not applicable to this invention.
 This invention is applicable to LEOs that have enough bandwidth to support
 high-speed data transfers, are line of site oriented, and also operate
 with a FDMA/TDMA technique. LEOs that offer a combination of phone and
 data or data only with a FDMA and/or TDMA mode of operation are also
 applicable to this invention. This invention can coexist with an existing
 LEO network or it can become inherent in the design logic of a new LEO
 satellite network. LEOs or GEOs (defined as applicable to this invention)
 are not inherently designed for nor are they operationally capable of
 processing critical real time events in a truly deterministic manner. The
 invention dedicates resources for status and control by assigning a fixed
 time slot for each remote terminal station. This assures that within a
 five second interval, or other predetermined period, a satellite
 communication system will recognize and process the time critical event.
 Once a central earth station is aware that a critical situation exists, it
 can control the transmission of the data and/or the compressed digital
 video exchange process on a separate data path.
 The operation of the satellite 2 within the present invention is in its
 conventional manner of receiving uplink transmissions from earth stations
 and retransmitting the signal for reception to earth stations. The
 satellite must accommodate digital transmissions. As in the case of
 geosynchronous satellites, a transponder could be split between one third
 or one half analog and the remainder digital. Non geosynchronous
 satellites are typically designed for digital only transmissions.
 An implementation of a channel map for this invention is represented by
 FIGS. 10 and 11. In this implementation, satellite transponder space
 segment is allocated on two different size transponders. A GEO satellite
 is based on a 54 MHZ transponder 310 (FIG. 10) and a LEO, a 36 MHZ
 transponder 375 (FIG. 11).
 Information or data is transmitted to the satellite in kilobytes per second
 (KBPS) or megabits per second (MBPS). The transponder, however, allocates
 space segment in megahertz. It is therefore necessary to convert from
 kilobits and megabits to megahertz. This conversion is performed in
 establishing the size of the transport data stream 340 (FIG. 10). The
 status and control (S & C) return remote path 330 was converted in FIG. 8
 (292). The remote return data path 335 conversion calculation is not
 shown, therefore, the conversion to required is 384 KBPS.times.1.33=0.511
 KHZ or 0.6 KHZ.
 FIG. 10 requires 17 MHZ of space segment 320 to accommodate the central
 station 325, the S & C return path 330 and twenty-eight channels of 384
 KBPS each 335 and 350. The 17 MHZ of a transponder 315 is 1/2 of the
 entire transponder of 54 MHZ 370. The S & C remote return path of 0.7 MHZ
 comprises both permanently assigned time slot TDMAs and their respective
 non-permanently assigned overflow area 345.
 FIG. 11 requires the entire transponder of 36 MHZ 325. Within the 36 MHZ,
 of transponder, the central station requires 12.0 MHZ 360, the S & C
 return path 0.7 MHZ 365, and the return data path for a 384 KBPS of data
 to be transferred each or 23.3 MHZ to transfer 38 separate data transfers
 of 384 KBPS each, 377.
 Central Earth Station
 Referring to FIG. 2, the central earth station 4 includes information input
 and processing circuitry 18. The circuitry 18 connects to the information
 resources 8 in any suitable manner. For example, connection can be by
 copper or optical fiber cable, which can be supplied by a telephone
 communication service provider 38. This connection at a central earth
 station site can be to a DS3 line, a T1 line, an ATM line or an ISDN line.
 Further packets of data protocols are removed and inserted into the
 interconnecting earth station equipment by a router or gateway.
 The information to be transmitted by the central earth station 4 over the
 data transmission uplink 14 is provided to a time sync circuit 20 and to a
 packet multiplexer 24.
 The time sync circuit 20 is synchronized in the illustrated embodiment by
 the atomic clock from the government operated Global Positioning System
 (GPS) as designated by the reference numeral 22 in FIG. 2. A commercial,
 off the shelf, GPS receiver with antenna is used at each central or remote
 site to provide an actual precise coordinated time.
 Non-geosynchronous satellites have an embedded level of header protocol
 processing in the satellite that is not found in geosynchronous
 satellites. To communicate with the non-geosynchronous satellites requires
 a header protocol applied in the packet multiplexer 24 preceding each
 multiplexed packet. This header format is the same for all LEO
 transponders that have the same transponder number. As it relates to this
 invention, header format can be used to send a common message to all
 remote earth stations in the polar arc or send data to only one remote
 earth station. This message feature will be used by the central earth
 station of the invention to transfer a transport data stream 14 to all
 remote earth stations 6 simultaneously.
 The ability of the header to identify and to transmit data to a specific
 location will be used by the remote earth station of this invention to
 transfer to both the primary S & C path and the secondary data path to the
 central earth station 4.
 The output from the packet multiplexer 24 with or without the packet header
 24 is input to a modulator 26. The modulator 26 takes the data stream
 input from the packet multiplexer 24 and through a technique referred to
 as phase shift keying creates a modulated signal with forward error
 correction. There are different modulation techniques, some of which are
 more power efficient. The most common types of modulation are BPSK and
 QPSK. Modulated signals use forward error corrections that can be 5/11,
 1/2, 3/5, 2/3, 3/4, 4/5, 5/6 and 7/8. Some of the modulation schemes are
 BPSK, quadrative phase shift keying or (QPSK), DEBPSK or Differential
 Encoding Modulation, OKQPSK Quadraphase Modulation, DBPSK or Differential
 Phase Modulation. The most common LEO or GEO modulation scheme for
 high-speed data is QPSK with 3/4 forward error correction.
 The output from the modulation circuit 26 is provided to a transceiver 28.
 The transceiver 28 transmits the amplified signal to an input port of a
 feed assembly of a satellite antenna 30. GEOs and LEOs use one of three
 different types of feed horns to transmit and receive: prime focus, offset
 or gregorian type. The feed horn transmits the amplified signal of the
 transceiver 28 to the reflector 30, which in turn sends the amplified
 signal to the satellite 36 (corresponding to satellite 2 in FIG. 1).
 Larger earth station antenna reflectors 30 create more signal gain and
 therefore require less signal power from the transceiver 28 to reach the
 satellite 36.
 In a particular embodiment the antenna reflector size for a typical GEO
 system is 3.7 meters at the central site and 1.8 meters or 2.4 meters at
 the remote site. The antenna reflector size for a LEO system depends on
 the particular technology. At a specific site, an antenna typically is one
 of two types: either a phased array antenna (re "under development") or a
 mechanical antenna. Both types of antennas track the LEO satellite. The
 phased array antenna tracks each satellite by using microelectronics that
 follow the satellite as it moves through the polar arc. The actual
 tracking electronic mechanism can be accomplished through patched arrays.
 The antenna size is targeted to be less than 0.7 meter by 0.7 meter.
 Mechanical antennas are based on existing technology. Two antennas with
 polar arc tracking capabilities track both the leading satellite and the
 trailing satellite as they travel through the arc. Mechanical antenna
 sizes in a particular implementation typically range from one to two
 meters for central earth station antenna 30 and &lt;1 meter for remote earth
 station antenna 50.
 The central earth station 4 can also receive signals from the remote
 stations. This is accomplished by integrated receiver decoders 32,34 that
 will take either the status and control signal or the data signal from a
 remote station 6. One integrated receiver decoder is required to process
 the control signal with BPSK modulation 34 and one integrated receiver
 decoder is required to process the data signal with QPSK modulation 32
 Satellite receivers demultiplex the modulated signals.
 A particular implementation of the central earth station 4 is shown in FIG.
 6. This illustrates an FCC-licensed central earth station 4 in a
 particular location, such as to connect to a Telco 118 providing access to
 the information resource(s) 8. This central earth station 4 can
 communicate such resources to remote earth stations 6 located anywhere
 within the footprint of the particular satellite or satellites 2 with
 which the particular central earth station 4 communicates. In this
 particular implementation, compressed digital media (H323) 116 and
 Internet Protocol (IP) applications 114 can be communicated. These
 resources can be obtained by connecting the central earth station 4 to the
 local telecommunications carrier (Telco) 118. This can be by way of a
 copper connection or by a high bandwidth fiber connection or other
 suitable means. The Telco 118 provides the IP 130 connectivity to the
 world wide web 120 or in the case of H323 video 116 through a gateway
 (H323/H320) 128 to an ISDN connection (frame relay) 122. IP 114 or H323
 116 traffic from other remote earth stations can also be received and
 rerouted 124, 130. Telco communications are two-way so that communications
 can be provided back to the information resources 8 (e.g., a responsive
 e-mail on the Internet IP; return video and audio in a two-way video
 conference H323).
 In the particular implementation illustrated in FIG. 6, a satellite
 transponder 36 is leased or assigned for use by the central earth station
 4 on a seven-day, 24-hour basis. In the United States, a single carrier
 license from the FCC is sufficient for this. This allows the uplinking of
 one channel of multiplexed data to the leased transponder on the satellite
 on a single carrier during a single transmission 110. The uplink and
 downlink frequencies of either the central or the remote sites can be
 altered by the central site as long as they are within the designated
 segment of a leased or assigned transponder 36.
 Remote Earth Stations
 Referring to FIGS. 3, 4, 5 each remote earth station 6 includes
 conventional equipment such as either two tracking antennas (LEO) 50 or a
 stationary antenna (GEO) 50 communicating with the satellite 2 (36 in FIG.
 2) and circuitry 52 such as containing a transceiver, and two modems. One
 modem 78 operates at an input data rate of 9.6 kilobits per second and
 uses a BPSK modulation scheme and a second modem 102 operates at rates of
 384 KBPS, 768 KBPS and 1.544 Mbytes per second. The modem 102 operates
 with a QPSK modulation scheme. The modem 102 accepts variable data rates,
 but only operates with one data rate during a single transmission at a
 time. The output of the modems are combined 80 before entering the
 transceiver 86. The transceiver outputs two separate modulated carriers.
 The status and control workstation 58 determines the frequency and power
 level of the transceiver 86. The transceiver frequency and power can be
 adjusted up or down by the output of the modem 66. By varying the output
 of the 70 MHZ signal from the modem 66 the transceiver's frequency can be
 adjusted up or down. By varying the IF signal from the modem the power
 level in the transceiver 86 can be adjusted. The S & C remote workstation
 58 sequences the S & C transmission with the data transmission so that
 both modulated carriers will not overlap. The remote station 6 is designed
 to only put up one carrier at a time and therefore not violate the FCC
 license. Since the S & C signal is deterministic and must transfer at a
 predetermined time, it has transmission priority over the data transfer.
 The S & C carrier is up for one second or less. This has a minimum effect
 on data transfer capability.
 This equipment can communicate with an Internet server 54 that connects to
 a local area network 60 and/or a personal computer 62 such as at a
 classroom in a school, for example. The equipment 52 can also communicate
 such as with video conferencing equipment 64 that might also be provided
 in the classroom.
 Equipment in the remote earth station 6 that is provided by or modified by
 the present invention is the status and control logic in the workstation
 58. The logic, as shown in an implementation of the invention, operates on
 information contained in FIG. 9. FIG. 9 is a totally self contained file
 providing all the information necessary at each remote site to define the
 processing necessary by the S & C workstation 58.
 The remote earth station 6 uses two transmission paths. It uses the status
 and control path by initiating transmissions out through the antenna 50
 for uplink to the satellite 2 and then downlink to the central earth
 station 4. The remote earth station 6 also handles two-way communications
 through the return data transmission path which also occurs through the
 antenna 50. Each of these will next be described.
 Status and Control Transmission Path
 The status and control transmission path is dedicated solely for the
 communication of a respective status and control file as implemented
 (FIGS. 9A-9E) from each of the remote earth stations 6. A maximum time
 period is defined within which all of the remote earth stations 6 must
 complete their status and control communications. Furthermore, each
 communication must be initiated and completed within a respective time
 slot of the overall response time period.
 The overall total time period is defined as the maximum duration based on
 the criticality of the particular application to which the present
 invention is being applied. For example, if a particular system is
 installed to provide communications with hospitals, each remote earth
 station must be able to provide its status and control information to the
 central earth station within a very short period of time. Other
 applications requiring real time or substantially real time communication
 must also have short time periods. An implementation of this invention,
 FIG. 8 defines the time period as a maximum of five seconds. The five
 second maximum was only selected as a reasonable limitation. Although all
 the communications need to occur within this implemented time period, the
 time period is cyclical in that such communication availability recurs
 every five seconds.
 To accommodate many remote earth stations, the present invention permits
 transmissions to occur on different frequency channels or sub-channels
 within the overall dedicated bandwidth. For example, one remote earth
 station would be assigned to one of five implemented slots having a
 predetermined transmission frequency. Another five remote earth stations 6
 would be assigned to the same five time slots, but these transmissions
 would occur at a different transmission frequency within another
 sub-channel bandwidth. This can be continued for additional remote earth
 stations up to the maximum allowed bandwidth for the dedicated status and
 control transmission space segment assignment allocated for permanent
 allocation.
 If there are no S & C time slots available for permanent allocation, then
 slot numbers are assigned on a temporary basis from 20 temporary slots
 FIGS. 8A-8B. The time slots operate in the following manner. The twenty
 slots are assigned on a first come, first served basis. If more than
 twenty time slots are needed, then the same slot number is assigned to the
 next twenty, however, the transmission time assignments are altered by
 additional time for each group of twenty slots that are assigned. Everyone
 gets serviced: in the implementation shown in FIG. 8, the envelope in
 which a S & C return path is available exceeds the five second window by
 an additional five seconds every time a group of twenty temporary
 assignments are made. In other words, more bandwidth will not be
 allocated, only the response time will be lengthened.
 The file sizes are shown in FIGS. 9A-9E. All files are defined digits or
 characters. It is possible to transfer only the fields within the files
 that have actually changed. For simplicity the size of a file to be
 transferred have not been optimized. If a particular remote earth station
 needs a faster S & C capability then the remote could have another time
 slot within the five second time slot. More than two time slots may impact
 the ability of the second data transfer path unless the remote station is
 dedicated to performing S & C functions (e.g. critical or real time event
 status monitoring/control and reporting and not being dependent on the
 second data path). The S & C file is designed to recognize a problem,
 effect a control solution and transmit the real time or time critical
 event along with the control logic and what IP to effect the control or
 take further action. For example, if a remote earth station is located at
 an electric utility power distribution substation; and a critical event at
 this site needs to reduce or increase power consumption on a power grid
 leading into the electronic power distribution substation, then the need
 can be identified. The required change can be specified for an associated
 location in the electronic utility power grid. This change can be sent by
 a remote earth station's S & C control transmission to the central earth
 station and then to a corresponding Telco connection to the internet
 location along with a control command specifying the action required.
 An example of the S & C file (FIG. 9) shows that status and control
 information from the remote needs to be transmitted at a rate of 9.6 KBPS
 . This 9.6 KBPS for a file transfer in conjunction with the propagation
 time from the remote earth station to the satellite and down to the
 central earth station and return would take about 11/2 seconds (includes
 propagation time) for a GEO and about 1-second for a LEO.
 FIG. 9 identifies an implementation approach to a detached file approach by
 providing a description of: remote earth station address, status codes,
 operation codes, required response times, data requests, data transfer
 types, data transfer speeds, the quality of the transfers,
 encrypting/scrambling needs, location, demand status, receive and transmit
 frequencies, authorization codes, uplink install date, uplink last
 maintenance date, date site entered into service, other data and messages
 150. FIG. 9 also shows a central station file transfer size of 2,060
 digits 230 and a remote station file transfer size of 602 digits 230. With
 each transport data stream from the central earth station 2,060 digits 230
 will be sent to each remote earth station. Only one remote earth station
 site will accept and use the file information.
 The above has been described with regard to designating each time slot by
 the time a remote earth station 6 uses a transponder as it transmits to
 the central earth station 4. If fixed transmission packets and times are
 defined, each time slot can be shortened to the length of the size of the
 transmission packet with each remote earth station being able to
 immediately follow the transmission of a preceding remote earth station.
 That is, one remote earth station could transmit status and control
 information within the fixed packet size at its respective transmission
 start time and a second remote earth station could immediately commence
 transmission of its status and control packet at its assigned start time
 coinciding with the end of the transmission of the packet from the first
 station. If a transmission has errors, there is a provision in the
 implementation to retransmit the packet.
 An implementation of the status and control transmission path consists of
 applying the block diagram in FIG. 4 to an implementation of the invention
 to define structures, file sizes and file contents as shown in FIGS.
 9A-9E. FIG. 4 of the invention establishes the logic flow that creates a
 status and control file 46 containing information as shown in FIGS. 9A-9E.
 This consists of information from transmissions and operational
 information S & C 150, 175 and critical real time events S & C 185, 175,
 and the data-second path 195, 200, 175 and 195, 210, 175, and 195, 220,
 175.
 In the creation of the remote file 46 inputs from critical events 74, the
 central file transferred to the remote 76 and session requests from
 terminals or workstations 70 are processed by 72. The central file
 transferred 76 consists of information from transmissions and operational
 S & C 150, 170, and critical real time events S & C 185, 170, and the data
 second path 195, 200, 170 and 195, 210, 170 and 195, 220, 170.
 If the S & C remote file is being processed for a LEO transmission, then a
 special header is required 82. The information for the header is available
 from the central station S & C file transfer 76. After the nature of the
 satellite is determined, the frequency and power level are set 66 from
 input available from the central station S & C file transfer 76. The
 transfer start time 68 is set from input available from the central
 station S & C file transfer 76.
 At a precise time as determined by 69 the file data is modulated by a BPSK
 modem 78 and combined with a null input from the QPSK modem and sent to
 the transceiver for the uplink antenna 50.
 An implementation of the invention as to the precise time a remote site
 will transmit a status and control file is defined by FIGS. 8A-8B. FIGS.
 8A-8B defines a structure for allocating time slots on a permanently
 assigned basis as well as a structure for handing time slots when the
 permanent area is totally assigned. This provision is referred to as an
 overflow area.
 In this implementation, channels one through fifty 250 represent
 permanently assigned space segment. Channels fifty-one through fifty-four
 285 represent an overflow area in which a remote station would be assigned
 on a temporary basis.
 Each channel requires 12.8 KHZ 200 of space segment times fifty-four
 channels equals 0.7 MHZ of space segment 300.
 A channel can process one remote a second 275 and if five seconds are
 allocated before the channel is processed a second time, then the five
 remotes can be processed within the 12.8 KHZ of space segment. This
 enables the permanently assigned channel area to accommodate 250 remote
 earth stations 50.times.5=250 and the overflow area to accommodate twenty
 remote earth stations 5.times.4=20 295.
 An implementation of the remote earth stations secondary data path is
 described in FIG. 5. The secondary data path operates only when authorized
 to start a transfer 90. This authorization is contained in the central
 station S & C file 76, also contained in this file is the information to
 set the transceiver frequency 92, and the transfer end time 94.
 The number of input data packets to be processed by time synchronous input
 data packets 96 is determined by the central station S & C file 76 (FIG.
 4) as well as when to start to transfer 98. Unlike the implementation of
 the status and control files from a remote which only sends a fixed file
 at a specific predetermined reoccurring time, the secondary path is
 structured to continually transmit as packets are received until the
 transfer end time equals the GPS clock 98 or interrupted by S & C files
 being transferred 97. The type of data transfers, their frequency, power
 level, the number of workstations or terminals to be transferred, and the
 transfer rate are preset and pre authorized by the central station S & C
 file 76.
 Workstations and terminals can be added or deleted via the S & C path to
 the central earth station. FIGS. 9A-9E Category A Item 10 can request
 these changes. The data line multiplexer 100 will place multiple data
 packets into a single data stream to be modulated by the QPSK modem 102.
 Both the S & C primary path and the data secondary path will use a common
 transceiver 86 and antenna or antennas 50.
 Transmission Paths from the Central Earth Station
 When the central earth station 4 receives a status and control transmission
 from a remote earth station 6, the central earth station 4 begins a
 response. It analyzes the file just received in the context of the other
 work it is processing for other remote earth stations, appropriately
 retrieves the requested information from the information resources 8, and
 appropriately packages and transmits the information to the respective
 remote earth stations through the data transmission path having the uplink
 14 and the downlinks 16 as represented in FIG. 1. Transmissions over this
 path occur in a conventional manner. FIG. 2 indicates that such a
 conventional manner includes a MPEG 2, DVB, or ATSC transport data stream
 18. Such a data transmission path permits synchronous data transmissions
 from 386 KBPS to 28 megabits per second (MBPS), an implementation of this
 invention is shown as 7.0 MBPS (FIG. 10) and 9.0 MBPS (FIG. 11). Various
 types of IP application data and (H323) protocols are indicated by the
 non-limiting examples designated on the attached FIGS. 6-8.
 Upon receipt of a data transmission from the central station, the receiving
 remote station demultiplexes any combined multiplexed transmissions and
 routes the packet as appropriate.
 Synchronization
 As apparent from the foregoing, synchronization of the central earth
 station and all the remote earth stations 6 is important to proper
 functioning of the present invention. An implementation (FIGS. 6, 7) of a
 two-way TDMA VSAT satellite system of the present invention is
 synchronized by an external clock 22 that has precise timing. An example
 of such a precise external clock is the atomic clock of the United States
 Global Positioning System (GPS). This clock signal or time is received by
 available off the shelf equipment and is used by suitable equipment in the
 central earth station 4 and each of the remote earth stations 6. The
 external time 22 is used to synchronize the status and control
 transmission 58, and it is also used to synchronize the data transmissions
 58.
 This invention separates the usage of the TDMA principle between the status
 and control and the actual data transfers. TDMA specified channel of a
 transponder. The information data and media in this secured transfer can
 usually contain both compressed media and non-compressed data. In a
 particular implementation, for example, the information data is defined as
 an Internet Protocol Application (IP) and the media as H323 Protocols
 (H323). Thus, this approach enables one or more time slots to be dedicated
 for use by a remote terminal to send a status and control file on a
 continues cyclical basis. It also defines the data/media transmission as a
 second transmission path. This second transmission path delivers a
 compressed and non-compressed time synchronized data stream, for example.
 The TDMA status and control transmission file transfers occur within a
 predetermined amount of time that preferably enables real-time
 responsiveness (e.g., in five seconds or less). An event driven real time
 message can be transmitted within the communication status and control
 transmission file. Event driven real time messages can be used for
 national or local security breaches, notification of terrorist attacks,
 fire alarms, seismic events, or any other type of real time event that
 requires immediate acknowledgement and action. Critical or real time
 events in the status and control transmission file received from a remote
 terminal site can be sent by the receiving ground station to the Internet.
 The status and control transmission file can contain programming to
 operate a PLC (Programmable Logic Controller) or other similar type of
 programmable logic control device.
 Upon an acknowledgement from a central site that a critical or real time
 event occurred at a remote site, the remote site can begin to transmit and
 receive high-bandwidth transmissions (e.g., H323 compressed media video,
 audio & data) on a separate channel. The second transfer, or data
 transfer, can send packets of compressed media (H323) along with Internet
 Applications (IP), for example. Different protocols based on the same
 transport standard can be multiplexed into a single data stream and
 modulated. The data is then transmitted over a non-TDMA satellite channel.
 Upon receipt of the non-TDMA satellite transmitted data at a central site,
 the data is demultiplexed. The transmission from the central site is in a
 single multiplexed data stream and sent to all remote sites
 simultaneously. Upon receipt at a remote site, data packets are
 demultiplexed and checked for addresses. Only those packets belonging to a
 particular remote site and its terminals or workstations are kept. A
 server, a router, or other applicable type of interconnectivity equipment
 performs the validation of address. Thus, the satellite communication
 system supports instant event status, instant event messages, and
 communication status and communication system control as well as follow on
 two-way interactive compressed video/audio/data (H323) and non-compressed
 data transmissions (IP).
 Thus, the present invention is well adapted to carry out the objects and
 attain the ends and advantages mentioned above as well as those inherent
 therein. While preferred embodiments of the invention have been described
 for the purpose of this disclosure, changes in the construction and
 arrangement of parts and the performance of steps can be made by those
 skilled in the art, which changes are encompassed within the spirit of
 this invention as defined by the appended claims.