Optimized integrated high capacity digital satellite trunking network

Description of equivalent WO 9955027 A1

Title: OPTIMIZED INTEGRATED HIGH CAPACITY DIGITAL SATELLITE TRUNKING NETWORK

Technical Field This invention relates generally to the field of satellite communication. More specifically the present invention is an optimized integrated high capacity digital satellite trunking network system, otherwise known as the Multipurpose Wideband Communications System (MPWCS) and method for linking multiple earth stations in the same or different antenna transponder footprints of the same satellite at the greatest efficiency in use of power and bandwidth, thereby eliminating the need to reconfigure the satellite transponder based on the desired downlink footprint.

Background Art

Geostationary satellites provide flexible communication relay service using earth stations and satellite transponders, with satellites supporting point-to-multi-point relay service between earth stations. Satellite operators typically lease transponder capacity based upon power, bandwidth, connectivity, and coverage desired by lessees. The leasing of power, bandwidth, connectivity and coverage of the satellite in a non- optimum manner due to the sharing between different user networks results in less than the maximum satellite power and bandwidth being utilized. Further, networks have been historically developed by separate organizations responsible for provision of space segment and earth segment leading to a complex definition of interfaces and less than the highest efficiency in the total capacity which can be derived from the satellite orbit and frequency spectrum which has been assigned. Depending on a number of satellite design parameters (e.g. uplink and downlink frequencies, antenna type, antenna boresight, antenna size, and transmitter power of the satellite) the effective "earth footprint" of a satellite transponder has geographic limits. The geographic limits of the transponder footprint constrain the type of relay service that may be provided.

For two users that are within the same satellite transponder footprint who desire to establish a communication link, a usual and simple form of simplex service requires that the transmitting user point their earth terminal antenna at the relay satellite and transmit on an uplink frequency. Using a satellite antenna whose receive footprint includes the earth station location of the transmitting user, the satellite transponder receives the uplink frequency, translates the frequency to a downlink frequency, amplifies the signal and then re-transmits the translated and amplified signal through the same satellite antenna used to receive the signal. The downlink signal can be received by any earth terminal that is within that satellite antenna footprint. Depending on the downlink frequency, and the previously mentioned physical characteristics of the satellite, the downlink footprint may be as small as a few hundred miles in diameter or up to several thousand miles in diameter. For two users who are within the same satellite antenna footprint, this form of relay service is very effective. For two users who are not within the same satellite antenna footprint, but are within the satellite antenna footprint of another antenna on the same satellite, other techniques are used. One technique involves providing an electronic "cross-strap" between two antennas/transponders on the same satellite. In this arrangement, the uplink signal from the earth transmitting station is received by one satellite antenna and the signal is translated and amplified for re-transmission by another satellite antenna, whose footprint includes the desired receiver. Using this technique, two users who are physically distant from each other and are each within small and different satellite antenna footprints of the same satellite may use a single satellite for relay service.

Various inventions attempt to address different aspects of these problems. Examples include United States Patent No. 5,615,407 to Barkats, United States Patent No. 4,720,873 to Goodman et al . , United States Patent No. 5,283,639 to Esch et al . , United States Patent No. 5,081,703 to Lee, United States Patent No. 5,276,904 to Mutzig et al . , United States Patent No. 5,455,823 to Noreen et al . , United States Patent No. 5,633,891 to Rebec et al . , United States Patent No. 5,424,770 to Schmelzer et al., and United States Patent No. 5,303,393 to Noreen et al .

Disclosure of the Invention

It is therefore an object of the present invention to create a satellite network optimized to use the full power and bandwidth of the constituent satellite, thereby providing highest capacity for operation of a digital trunking network based on the integration of the earth stations and satellite for maximum transmission efficiency.

It is a further objective of the present invention to create a high capacity satellite communications network where usage is measured by time (minutes-of-use) rather than by power or bandwidth leased by a party.

It is yet another objective of the present invention to create a global digital high capacity telecommunications network using the full power and bandwidth of multiple constituent satellites for any communications services within the field-of- view of the satellite network.

It is a further objective of the present invention to integrate multi-service satellite telecommunications using the full power and bandwidth of constituent satellites for all communications .

It is yet another objective of the present invention to provide voice, data, facsimile, video and general bit stream service using the full power and bandwidth of constituent satellites for all communications.

It is a further objective of the present invention to provide public switched telephone network services using the full power and bandwidth of constituent satellites for all communications . it is yet another objective of the present invention to provide private branch exchange services to selected groups of users using the full power and bandwidth of constituent satellites for all communications.

It is a further objective of the present invention to provide overlay network services to selected groups of subscribers using the full power and bandwidth of constituent satellites for all communications.

It is yet another objective of the present invention to provide domestic and international telecommunications service using the full power and bandwidth of constituent satellites for all communications.

It is a further objective of the present invention to link telecommunication services of the present invention with other communications service providers and carriers.

It is yet another objective of the present invention to link telecommunication services of the present invention with other terrestrial telecommunications providers and carriers.

It is a further objective of the present invention to provide telecommunications services using the full power and bandwidth of constituent satellites for all communications when data being transmitted is either standard or non-standard telecommunications protocols such as but not limited to; ATM, frame relay, Internet, XDSL, IP, and/or mobile telecommunications protocols .

It is yet another objective of the present invention to provide protocol conversion between different standards of communications between countries and within a single country using multiple protocols .

It is therefore an object of the present invention to allow a user within the satellite antenna footprint of one satellite transponder to flexibly communicate with other users who are within the same or other satellite antenna footprints of a single satellite by using the uplink frequency to selectively select between users and satellite antenna downlink footprints without the need to reconfigure the satellite transponders. It is another object of the present invention to provide this flexible communication capability for wideband high data rate communication. The present invention, otherwise known as MPWCS, generally comprises three spacecraft each of which is in a geosynchronous orbit at three orbital locations. Interacting with the three spacecraft are high-capacity digital earth stations. The digital modulation used is phased shift keying (PSK) and specifically 8- PSK modulation for highest bandwidth efficiency. The use of PSK dramatically increases the channel capacity in bits per Hz which can be carried within a given amount of bandwidth.

Relatively large diameter earth station antennas are used to maximize the efficiency with which satellite power is used, for example and without limitation 9 meter antennas are currently used. Further, each earth station has a relatively large high power amplifier to insure communication links are not uplink- power limited, for example and without limitation 350 watt amplifiers are currently used. Digital modems are used for all services to be supported by the system of the present invention. Compression technology is also used within the earth segment to take advantage of; silent periods within a voice conversation, statistical utilization of speech activity among multiple voice channels and redundancy within individual voice channels to allow the available satellite communications bandwidth to be allocated to the largest number of voice channels consistent with maintaining high quality and consistent with meeting national and international standards where appropriate. Finally, protocol conversion is implemented throughout the system so that communications using dissimilar protocols can be converted from one to another. This allows communication from regions or countries using dissimilar protocols to occur in a continuous and seamless manner. Taken together these characteristics result in a high-capacity satellite based digital trunking network.

The present invention overcomes the disadvantages of the prior art through: a) integration of earth and space segments for maximum capacity and efficiency using the available satellite orbit and frequency allocations, and b) providing integrated digital service to users on an end-to-end basis from switching center to switching center location. Further, a combination of multiple antennas and transponders on the same satellite, are linked to hybrid signal combiners, wideband receivers, and hybrid signal splitters on the satellite which are able to use a contiguous portion of both the uplink and downlink frequency spectrum. In one embodiment, the present invention uses two transponders with wideband receivers and two 80 MHZ bandwidth portions of the frequency spectrum separated by 64 MHZ to allow a user to flexibly connect an 80 MHZ bandwidth signal between two satellite antenna footprints. In another embodiment of the present invention, a multiplexer is also used to interconnect multiple transponders, allowing a user to select the downlink footprints of more than two transponders based on the uplink frequency.

These and other objects of the present invention will be apparent to those of ordinary skill in the art after review of the detailed description, the drawings, and the claims.

Brief Description of the Drawings

Figure 1A shows an overview of the present invention. Figure IB shows satellite locations for satellites of the present invention.

Figure 1C shows PSTN backbone service of the present invention.

Figure ID shows the present invention providing dedicated services .

Figure IE shows regional setup of the present invention.

Figure 1 shows a signal flow diagram of the satellite transponder in one embodiment of the present invention. Figure 2 shows an example of the frequency allocation used in one embodiment of the present invention.

Figure 3 shows an example of satellite antenna footprints in one embodiment of the present invention. Figure 4 shows an example of the uplink and downlink signals with users in the same satellite antenna footprint. Figure 5 shows an example of the uplink and downlink signals with users in different satellite antenna footprints .

Figure 6 shows a signal flow diagram of the satellite transponders in another embodiment of the present invention.

Figure 7 shows an example of the frequency allocation used in another embodiment of the present invention. Best Mode For Carrying Out the Invention

Referring to Figure 1A an overview of a single satellite and associated ground stations of the present invention are shown.

Satellite 10 is stationed in a geosynchronous orbit thereby allowing the satellite to be stationary relative to a geographic location on the equator of the earth. The satellite communicates with earth station 12 which has a large diameter antenna designed to maximize efficiency of satellite communications. Connected to antenna 12 is a zone toll switch 14 which meters the usage of the satellite link and is the switch through which communications are made to various local public switched telephone networks, overlay networks, and private networks. The various local access switches 16, 18, and 20 are connected to the zone toll switch 14 and provide the access to various individuals and organizations in the local access area.

Earth station 12 may, for example and without limitation, communicate with earth station 22 which also comprises a relatively large diameter earth station antenna, again maximizing the efficiency and use by the earth station of satellite power. Earth station 22 is further connected to another zone toll switch

24 also connected generally to another public switched telephone network zone. Once again access of local customers is through a series of local access switches 26, 28, and 30.

Referring to Figure IB the satellite field-of-view areas of the three satellites of the present invention and their orbital locations are shown. In general Concept, and without limitation, the present invention requires three satellites for virtually worldwide coverage. The satellites are stationed each in a geosynchronous orbit over ground locations at the equator at 16 degrees West, 77 degrees East, and 167 degrees East Longitude. Referring to Figure 1C the public switched telephone network backbone service is shown. In general concept, and without limitation, four earth stations 32, 34, 36, and 38 are shown.

Again each earth station has a relatively large diameter antenna to maximize the efficiency of communications with the satellites of the present invention. Again each earth station has an associated zone toll switch 40, 42, 44, and 46. Further, trunk switches 48, 50, 52 and 54 are directly connected to each earth station antenna and provide the basis for switching and communications being sent and received over that segment of the digital trunking network. The system of the present invention can also interact with the existing terrestrial backbone 56 thereby providing alternative communication means to the existing terrestrial backbone. Communications can thus be carried over the backbone 56 where appropriate or over the high-capacity digital satellite trunking network of the present invention. A transit switch 58 is also provided to allow communications with PSTN zones 60 and

62 which may be outside the zone of coverage of the present invention, that is, in regions not covered by the satellite footprint . Referring to Figure ID, other dedicated services which can be serviced by the present invention are shown. Satellite earth stations 64, 66, 68, and 70 interact with the satellite of the present invention to provide the high-capacity digital satellite trunking network. Earth station 70 is linked in via its associated trunk switch 72 to various other gateways 74. These gateways provide access to other private communications networks 76. Transit hub 78 provides access to various other local destinations 80 via associated transit and termination units 82. These other domestic destinations 80 may be outside the satellite footprint or simply not be directly connected to an individual earth station of the present invention.

Earth station 68 is connected via its associated trunk switch 84 to a terrestrial fiber-optic or copper transport network 86. Individual private voice 88, a private network 90, or private data access 92 may be connected to this terrestrial network 86.

This flexible connection to terrestrial fiber-optic or copper transport networks can be duplicated at any other ground station location. Thus a second terrestrial network 94 may also have private voice 96, private network 98, private data 99, connected to it. Thus the present invention allows data, private networks or any other communications to be connected across broad geographic areas to other terrestrial fiber-optic copper or copper transport networks.

Referring to Figure IE a typical configuration at any given communication region of the present invention is shown. This is the type of installation that is associated with a ground station in communication with a satellite of the present invention.

Earth station 150, with its large diameter antenna is connected to a trunks switch multiplexer 152. This multiplexer allows communications from a variety of different sources to be multiplexed and transmitted over the earth station to maximize utilization of bandwidth. A private network 168 may be directly connected to the trunk switch multiplexer. It should be noted that in this specific example no protocol conversion is needed between the private network or end-user and the trunk switch multiplexer. However the system of the present invention is capable of protocol conversion in situations where communications are coming from other countries, or other regions which simply use different protocols. For example, communications via toll switches 162,164, and 166 may occur from a given PSTN zone 160. These communications are transmitted through a zone switch 158 to the earth station or over the terrestrial backbone. If the protocol is not the same, protocol converter 154 converts the incoming communications having a different protocol. Thereafter signals in communications are connected to the trunk switch multiplexer and are transmitted over the high-capacity digital satellite trunking network of the present invention.

Each regional earth station also incorporates a redundant call logger 156 which allows the transmission of billing information regarding utilization of the network to the hub station. This billing information is also transmitted at various times, and on a non-interference basis with communications being transmitted over the network.

Referring to Figure 1, a signal flow diagram of the satellite transponders in one embodiment is illustrated. Two independently steerable satellite antennas 101, 103 are provided which can be boresighted to provide different earth footprints. The received signal from each satellite antenna is amplified by a low noise amplifier (LNA) 105, 107 prior to signal combination in a hybrid signal combiner 109. The combined signal is then filtered 110 and input to a wideband receiver 111 where the uplink frequency is shifted or translated to the downlink frequency. The translated frequency is then split by a hybrid signal splitter 113 into two signal paths before each is amplified by a high power amplifier (HPA) 115, 117. Each signal is then filtered 119, 121 and passed to the corresponding satellite antenna 101, 103 for re-transmission on the corresponding downlink frequency.

Referring to Figure 2, an example of frequency allocation for one embodiment is illustrated. Two 80 MHZ uplink frequency bands 201, 203 are shown, with a 64 MHZ separation frequency band 205. Two 80 MHZ downlink frequency bands 207, 209 are also shown, with a corresponding 64 MHZ separation frequency band 211. The downlink frequency for antenna 101, in Figure 1, is the lower 80 MHZ band 207 ( approximately 12.512 to 12.592 MHZ) while the downlink frequency for antenna 103 is the upper 80 MHZ band 209 (approximately 12.656 to 12.736 MHZ). Referring now to Figure 3, examples of satellite antenna footprints for different transponders are illustrated. The footprint for one antenna (101 in Figure 1) covers one geographic area 301, while the footprint of the other antenna (103 in Figure

1) covers another geographic area 303. Using this embodiment of the present invention, a first user, located within satellite antenna footprint 301, can communicate with a second user also located in satellite antenna footprint 301. Alternatively, a first user, located within satellite antenna footprint 301, can communicate with a third user located in satellite antenna footprint 303.

Referring now to Figure 4, examples of the uplink and downlink signals are shown for users who are both in satellite antenna footprint 301 (Figure 3) of satellite antenna 101 (Figure

1) . Here, the uplink signal is in the lower of the two 80 MHZ bands 201 (approximately 14.744 to 14.824 MHZ) and the downlink signal is also in the lower of the two 80 MHZ bands 207

(approximately 12.512 to 12.592 MHZ).

Referring to Figure 5, examples of the uplink and downlink signals are shown for users who are in different satellite antenna footprints. In this example, the transmitting user is in the satellite antenna footprint 301 (Figure 3) of antenna 101

(Figure 1) , while the receiving user is in the satellite antenna footprint 303 (Figure 3) of antenna 103 (Figure 1) . Here, the uplink signal is in the upper of the two 80 MHZ band 203 ( approximately 14.888 to 14.968 MHZ) and the downlink signal is in the upper of the two 80 MHZ bands 209 (approximately 12.656 to 12.736 MHZ) . Referring back to Figures 1 and 2, in this embodiment, both antennas (101, 103 in Figure 1) and LNAs (105, 107 in Figure 1) have sufficient bandwidth to pass both 80 MHZ bands (201, 203 in

Figure 2) in addition to a 64 MHZ band separation (205 in Figure 2) into the hybrid signal combiner (109 in Figure 1) . This approximately 224 MHZ bandwidth output of the hybrid signal combiner (109 in Figure 1) is processed by a wideband receiver

(111 in Figure 1) , which performs a frequency translation from the uplink to downlink frequency. The translated frequency output of the wideband receiver is then split into two 80 MHZ downlink signals (207, 209 in Figure 2) before amplification by two HPA's (115, 117 in Figure 1) and transmission through the two antennas (101, 103 in Figure 1) . In this example, one transponder downlink antenna (101 in Figure 1) uses the lower frequency band (207 in Figure 2) of the two 80 MHZ bands, and the other transponder downlink antenna (103 in Figure 1) uses the upper frequency band (209 in Figure 2) of the two 80 MHZ bands.

Both transponders are thus able to receive both 80 MHZ bands (201, 203 in Figure 2) . Completing the example, a transmitting user in the satellite antenna footprint of one transponder (301 in Figure 3) who wants to communicate with another receiving user also in the satellite antenna footprint of the same transponder (301 in Figure 3) will uplink in the lower frequency band (201 in Figure 4) of the two 80 MHZ uplink bands. When the uplink frequency is translated to the downlink frequency, the downlink frequency will also be in the lower frequency band (207 in Figures 2 & 4) of the two 80 MHZ downlink bands. Alternatively, a transmitting user in the satellite antenna footprint of the first transponder (301 in Figure 3) who wants to communicate with a second receiving user who is in the satellite antenna footprint of the second transponder (303 in Figure 3) will uplink in the upper frequency band (203 in Figures 2 & 5) of the two 80 MHZ uplink bands. When the uplink frequency is translated to the downlink frequency, the downlink frequency will now be in the upper frequency band (209 in Figures 2 & 5) of the two 80 MHZ downlink bands. This will have the same effect as "cross-strapping" the two transponders would have in the traditional method of operation.

Referring now to Figure 6, the signal flow of another embodiment of the present invention is illustrated. This arrangement uses the transponder pair of the first embodiment 600 and adds another transponder pair 602 and further allows users to cross signals between the transponder pairs 604. In this configuration, a multiplexer, IMUX 601, 603 is interposed in the signal path between the antenna 103, 605 and the low noise amplifiers 107, 607. The IMUX provides an alternative signal path that allows signals to be crossed between the transponder pairs 600, 602. After frequency splitting by the IMUX 601, 603, the signal path is similar to the first embodiment . Specifically, the signal is amplified by an LNA 609, 611, followed by a receiver 613, 615 which translates the uplink frequency to the downlink frequency. The frequency translated signals are then amplified by an HPA 617, 619 prior to another multiplex operation OMUX 621, 623 and final transmission by the respective antennas 103, 605.

An example frequency allocation that corresponds to this other embodiment is illustrated in Figure 7. In addition to the technique of the first embodiment, using an orthogonal polarization, the uplink antenna (103 in Figure 6) is able to receive and pass two 80 MHZ bands 701, 703, with a 64 MHZ separation band 705. These two 80MHz bands are received and translated to the downlink frequencies 707, 709 as in the first embodiment. However, the bandwidth that is passed through the uplink antenna (103 in Figure 6) to the IMUX (601, 603 in Figure 6) also includes a 34 MHZ band 711 in addition to a 10 MHZ frequency separation band 713. In this example, this 268 MHZ wideband signal (34+10+80+64+80 MHZ) is divided by the IMUX (601,

603 in Figure 6) into two signal paths. One signal path, the upper 224 MHZ, is handled as in the first embodiment. The other signal path, the lower 34 MHZ 711, is crossed to the other transponder pair (602 in Figure 6) . This 34 MHZ signal 711

(14.700 to 14.734 MHZ) is processed by the LNA (611 in Figure 6) and the frequency is translated to the downlink frequency by a receiver (615 in Figure 6) . In the example, the 34 MHZ uplink frequency 711 is translated to the 34 MHZ downlink frequency 715

(11.057 to 11.091 MHZ) before it is amplified by the HPA (617 in

Figure 6) and multiplexed with other signals by the OMUX (621 in

Figure 6) and finally transmitted through the antenna (605 in Figure 6) .

The signal flow for transmission from the satellite antenna footprint of satellite antenna 605 to the satellite antenna footprint of satellite antenna 103 is similar to that from satellite antenna 103 to satellite antenna 605. However, the example frequency allocation is different. Referring to Figure 7, the uplink frequency 717 (approximately 15.216 to 15.247 MHZ) and the downlink frequency 719 (approximately 12.769 to 12.803

MHZ) are 34 MHZ wide.

For a transmitting user in the satellite antenna footprint of satellite antenna 605 who wants to transmit to a receiving user in the satellite antenna footprint of satellite antenna 625, the uplink frequency will be 721 (approximately 15.130 to 15.180

MHZ) and the downlink frequency will be 723 (approximately 10.977 to 11.027 MHZ). A transmitting user in the satellite antenna footprint of satellite antenna 625 who wants to transmit to a receiving user in the satellite antenna footprint of satellite antenna 605, the uplink frequency will be 725 (approximately 15.271 to 15.321 MHZ) and the downlink frequency 727 (approximately 11.121 to 11.171 MHZ).

Referring again to Figure 1, the hardware to accomplish the present invention must have certain capabilities. The independently steerable satellite antenna 101, 103, must each have sufficient pointing accuracy to track and maintain boresight at sufficient gain to provide the required performance. The low noise amplifier 105, 107 must have a flat response across the desired spectrum with sufficient gain to provide the required performance. The hybrid signal combiner 109 must be capable of receiving two signal sources and suitably combining them into a single composite signal (without adverse noise, attenuation or artifacts) sufficient to provide the required performance. The filter 110 must have suitable cut-off and selectivity to provide the required performance. The wideband receiver 111 must be capable of translating the input signal frequency to the desired output signal frequency with sufficient gain to provide the required performance. The hybrid signal splitter 113 must be capable of dividing a single signal with specified bandwidth into multiple signals of specified bandwidth without adverse attenuation or artifact. The high power amplifiers 115, 117 must be capable of amplification across the input frequency spectrum with flat response. Finally, the filters 119, 121 must have suitable cut-off and selectivity to provide the required performance .

Referring again to Figure 6, the hardware to accomplish the other embodiment of the present invention must have certain capabilities. The additional independently steerable satellite antenna 625, 605, must each have sufficient pointing accuracy to track and maintain boresight at sufficient gain to provide the required performance. The input multiplexer, IMUX 601, 603 which is interposed in the signal path after the antenna 103, 605 must have sufficient bandwidth to provide the required performance. The low noise amplifier 107, 607, 609 and 611 must have a flat response across the desired spectrum with sufficient gain to provide the required performance. The wideband receiver 613, 615 must be capable of translating the input signal frequency to the desired output signal frequency with sufficient gain to provide the required performance . The high power amplifiers 617, 619 must be capable of amplification across the input frequency spectrum with flat response. Finally, the output multiplexer, OMUX 612, 623 must have bandwidth to provide the required performance . An optimized integrated high capacity digital satellite trunking network has been described. Those skilled in the art will appreciate that minor variations may be made to the system described without departing from the scope of the invention as disclosed.