Worldwide satellite telephone system and a network coordinating gateway for allocating satellite and terrestrial gateway resources

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CROSS-REFERENCE TO RELATED APPLICATION

U.S. patent application Ser. No. 07/678,931 filed Mar. 29, 1991 in the name of one of the co-inventors describes a cellular telephone system wherein orbiting satellites contain controllers for switching and controlling call set-up, in conjunction with a ground-based database management system. The present invention provides an alternate solution.

BACKGROUND OF THE INVENTION

This invention relates to a wireless telephone system for employing one or a plurality of orbiting satellites to allow wireless telephone users (subscribers) communication access to a terrestrial telephone system (whether private, government or common carrier), and particularly to a wireless telephone system, such as a cellular system, which permits subscriber access to terrestrial telephone networks while the subscriber is roaming in areas that do not have cellular telephone services.

There is a need to provide personal communications anywhere on the earth. Current communications systems, for example, cellular telephone systems, require terrestrial cellular relay stations to intercept and link a cellular radiotelephone transmission with conventional switched telephone users and with other cellular telephone users. All of the existing communications systems have limited user range.

Cellular telephone systems have been proposed which account for roamers, i.e., cellular telephone users which roam outside a normal service area. The American Telephone and Telegraph Corp. (AT&T) has proposed an inter-cellular data network for interconnecting terrestrial cellular telephone service areas using a terrestrial packet-switched network that has nodes at the participating cellular telephone service areas wherein packet-switched network data are accumulated in a database of roaming cellular telephone users. The database therein proposed would keep track of roamers and allow terrestrial interconnection of the roamer to the telephone system when the roamer is located in a cellular telephone service area that is remote from a designated home cell. Certain data are collected which would allow routing of calls to the roaming user, allow issuance of billing information, and allow collection of other system operation data.

Efforts are under way to utilize satellite technology in cellular communications. Satellite delivered telephone services to mobile users have been proposed as the Mobile Satellite System (MSS) in the USA. This system is now being implemented by the American Mobile Satellite Corp. (AMSC). It utilizes transceivers in the mobile unit (automobile for example) operating in the L-band (1530-1560 MHz and 1646.5-1660.5 MHz) that communicate to a satellite at geosynchronous orbit. This system is limited to serving just a small portion of the earth. In addition to significant expense to the end user for the transceiver apparatus, the system is subject to noticeable relay delay due to transmission of the signals to and from geosynchronous orbit. Furthermore, the cellular telephone service providers must nevertheless implement a costly additional inter-system network to direct calls to the mobile transceiver apparatus. The current system as envisaged does not have a method for locating the roaming user and directing the call to the user.

U.S. Pat. No. 4,972,456, assigned to GTE MobileNet, discloses a cellular telephone "satellite" roaming system that uses a satellite system to permit access to the cellular telephone system when a user is located in areas outside of cellular telephone system coverage. This system does not contemplate overhead orbiting satellites, but rather the system would employ subsidiary cell sites in a terrestrial-based cellular communications system.

Other patents relate to general information on cellular telephone roaming systems which permit a user of one cellular system to use another cellular system while traveling in areas outside a home cellular system. These patents include U.S. Pat. Nos. 4,901,340; 4,972,460; and 4,833,701.

Motorola, Inc. announced on Jun. 27, 1990 a proposed crosslinked satellite network under the name IRIDIUM. The IRIDIUM system is believed to be described in European Patent Publication EP 365,885, published May 2, 1990, and corresponding to U.S. patent application Ser. No. 263,849 filed 28 Oct. 1988. The IRIDIUM system envisions a constellation of seventy-seven low-earth orbiting satellites in seven circular polar orbits for supporting cellular telephone communications on the earth's surface. In the IRIDIUM system, all handoff and relays of communications traffic are handled in space directly between satellites, so that the terrestrial telephone network is bypassed. However, ground signal processing is required to set up and place calls. Calls originating from outside the satellite service areas must interrogate the home location of the user in order to identify the user. The system requires that all satellites be linked constantly to one another. Each of eleven evenly-spaced satellites sharing an orbit plane is contemplated to project thirty-seven communications cells on the earth's surface. Additionally, each satellite has four intersatellite links, thus forming a geodesic sphere for traffic communication paths. Due to cost and channel limitation, it may be presumed that the IRIDIUM system will not compete with the services provided by terrestrial-based cellular communications systems. A technical description of this invention is believed to be contained under U.S. patent application Ser. No. 263,849 filed Oct. 28, 1988 in the names of Bertiger, Leopold and Peterson.

By a document dated Nov. 2, 1990, Ellipsat Corporation made application to the Federal Communications Commission for authority to construct an elliptical orbit satellite system to support, among other things, mobile voice services in the United States through a constellation of six satellites. The service has been presented as complementary of and not competitive with existing and future (terrestrial) cellular telephone services. The system contemplates the use by end users of dual-mode transceivers using Code Division Multiple Access (CDMA) modulation to effect communications with earth satellites in extended-coverage elliptical orbit.

DISCLOSURE OF INVENTION

According to the invention, there is provided a satellite telephone system for communicating with an existing terrestrial telephone system and with a plurality of orbiting satellites as part of a network comprising a plurality of terrestrial gateways. The satellite telephone system includes a master computer coupled to the existing terrestrial telephone system via terrestrial communication links. The system further includes a home user database, a database of roaming users, a route planner, and a gateway controller that are all coupled to the master computer. A telephone interface unit is coupled to the gateway controller and an encoder is coupled to the telephone interface unit. The system further includes a call termination processor coupled to the telephone interface unit and to the encoder; an acknowledge generator coupled to the encoder; a call request processor coupled to the acknowledge generator and to the telephone interface unit; a retry generator coupled to the call request processor; a decoder coupled to the telephone interface unit and to the retry generator; and a modem coupled to the encoder and to the decoder. The system further includes a handoff processor for controlling handoffs between satellites. The handoff processor is coupled to the modem, and an RF power monitor is coupled to the handoff processor. A satellite RF unit is coupled to the RF power monitor and to the modem, and a satellite antenna is coupled to the satellite RF unit. The satellite antenna provides a communication link to the satellites.

The invention will be better understood by reference to the following detailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a figurative illustration of an integrated wireless telephone and orbiting satellite communications system in accordance with the invention.

FIG. 2 is a figurative illustration of the integrated wireless telephone and orbiting satellite communications system showing how a first type of duplex communications circuit may be set up.

FIG. 3 is a figurative illustration of the integrated wireless telephone and orbiting satellite communications system showing how a second type of duplex communications circuit may be set up.

FIG. 4 is a system block diagram according to the invention.

FIG. 5 is a block diagram of a wireless transceiver apparatus for use by an end user.

FIG. 6 is a block diagram of a gateway terminal unit for use in a cellular system according to the invention.

FIG. 7 is a block diagram of a network coordinating gateway for use in a system according to the invention.

FIG. 8 is a block diagram of a network control center for use in a system according to the invention.

FIG. 9 is a block diagram of a satellite system for use in a system according to the invention.

FIGS. 10A-10L together are a flow chart of operation of a specific embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An integrated wireless/satellite communications system 10 according to the invention is shown in FIG. 1. The system 10 may include private, government or cellular telephone systems which themselves comprise gateways 12, 14, 16, 18, each having the means to communicate with the satellite system 10. The gateways may be conventionally-defined metropolitan service areas (MSAs) 12, 14, 16 and rural service areas (RSAs) 18, government telecommunications gateways, or private network nodes. The system 10 may further include according to the invention a network database 20 of users, a satellite communications system with a single one or a plurality of low-earth orbit satellites 22, each of which services a (moving) satellite service area 24, a network control 25, a satellite control center 26, at least one network coordinating gateway 28, a representative roaming end user 30, a packet switched network 32, and a plurality of satellite communications links, including for example satellite telephone communications links 34, 36, a network communications link 38, and a satellite control link 40.

This detailed description uses a cellular terrestrial communications system as an example. As stated above, the invention may alternatively be used with private or government communications systems which may be slightly different than the example given here. In government systems, the communication links may be encrypted. In government and private systems, the ground nodes may be connected only to a private network.

In the exemplary cellular telephone system, there are contemplated existing and future terrestrial wireless telephone systems. Herein they may be collectively referred to as a Terrestrial Service Areas (TSAs).

In accordance with the invention, there is provided a Satellite Service Area (SSA) 24 (which may be moving) having a communications link 34 capable of servicing any roaming user 30 within the SSA 24. The satellite control center 26 is to provide for proper operation of the satellite system 22 by means of Satellite Control Links (SCL) 40 to and from a plurality of satellites which are passing overhead. Other links include the Network Coordinating Link (NCL) 38, the satellite-to-user link 34, and the satellite-to-gateway link 36.

The TSAs are linked by a nationwide packet switched network (NWN) 32 which may be used to establish the network database 20 of users. The NWN 32 may provide the service areas with information necessary to locate roaming users, log in users, log out users, allocate satellite resources, and set up calls.

The satellite system 22 may comprise a single satellite or a constellation of many satellites preferably in low-earth near circular or possibly elliptical orbits. Each satellite is provided with a communications subsystem which is capable of receiving uplink signals, converting them to downlink frequencies, amplifying the signals, and transmitting the signals back to the earth. The satellites do not incorporate satellite-to-satellite links nor serve as bypass to ground-based telecommunications facilities. The satellites are simple "bent-pipe" repeaters, do not perform any on-board signal processing of the communications traffic, and do not have regenerative repeaters. By on-board signal processing (a term commonly used in the satellite industry), it is meant that the satellite brings the RF signals down to bits, and further that the satellite switches or otherwise manipulates the signals. The lack of on-board signal processing of the communications traffic is in sharp contrast to the prior art where on-board signal processing is performed, e.g., Mallinckrodt U.S. Pat. No. 5,073,900 (col. 4 lines 35-39) and European patent publication 0 365 885 to Bertiger (col. 4 lines 7-9). As used herein, "communications traffic" means the voice, data, or other messages that are passed from the user 30 to the caller 107, 108, 50, and vice versa. "Communications traffic" does not include control signals that are sent from the earth to the satellite 22. A regenerative repeater is defined in Sklar, B., Digital Communications (Prentice Hall 1988), p. 232 as one which demodulates and reconstitutes the digital information embedded in the received waveforms before retransmission. A regenerative repeater is defined in Pritchard, W. L. et al., Satellite Communication Systems Engineering (Prentice Hall 2d ed. 1993), p. 401 as follows: " . . . a regenerative repeater, utilizes onboard signal processing of digital signals . . . "

The satellite control link 40 provides remote control of satellite components and configurations. The network coordinating link 38 provides for data transfer to and from a network coordinating gateway 28 for the purpose of establishing communications to and from a roaming user 30, for logging on to the system (registration). The wireless telephone links 34, 36 are used for voice and data communications, position location and other services between the user and various wireless telephone systems. The network control center 25 is used to coordinate between NCGs 28, keep the network database 20 updated to all NCGs 28, collect billing and system information, and coordinate any information from the satellite control center 26 that the NCG(s) 28 might require, such as satellite ephemeris and health.

The wireless telephone user equipment preferably may be any commercially available unit that has the capability of digital signal generation and a compatible modulation scheme with the network into which it is to be integrated, combined with digital and frequency generating equipment compatible with the satellite system. Code Division Multiple Access (CDMA) modulation or other modulation compatible with the satellite relay system is contemplated.

SYSTEM OPERATION:

Operation of the system according to the invention is first described in connection with FIG. 2 and FIG. 3 as follows:

Notification is a first procedure. Each user has a home gateway (HG). Each gateway 12, 14, 16 has a home user database 31 which contains information of all the users for which that gateway is home. Each gateway 12, 14, 16 has a roamer database 27 of all the active roamers in the gateway's service area. The roaming user 30 notifies the system, either by a special control signal to the present satellite system 22 as shown in FIG. 2, by a relay path A-C to a network coordinating gateway (NCG) 28, or, if in service area range, by a special control signal to the nearest service area terrestrial base station 38, that the user 30 desires to use the satellite communications system. The control signal is repeated by all satellites 22 in view of the user 30 to any NCG(s) 28 in view of the satellite(s) 22. The NCGs 28 have algorithms (such as closest to user) to choose between or among NCGs 28. An NCG 28 is selected and takes the request. The special control signal is processed by the NCG 28 and routed outward from the NCG 28 to the packet switched network 32. The NCG 28 selects an Active Gateway (AG) 16, which will handle all calls to and from the user 30 by a system selected method (such as gateway closest to user, or special gateway by request of user). The NCG 28 sends a message to AG 16. The network database 20 is updated to include the user 30 as a roamer in the satellite service area 24. The NCG 28 notes the acceptability of the user 30, and the network database 20 is updated to show the user 30 roaming in the SSA 24. The roamer database 27 of active gateway 16 is then updated to show the user 30 to be in the Satellite Service Area (SSA) 24. The user's home gateway database is updated to show that the user 30 is being serviced by active gateway 16. This condition exists until the user 30 re-enters a service area of the terrestrial cellular system or until the user 30 enters a different satellite service area 24.

There are two kinds of telephone calls: incoming (inbound) to the satellite system and the terrestrial network from the (roaming) user 30; and outgoing (outbound) to the user from the satellite system and the terrestrial network.

Incoming calls initiated by the user 30 begin with a request to access the public switched telephone network (PSTN). The AG 16 processes the request and checks its databases 27, 31 for the user 30. Depending on ephemeris, satellite resources, gateway resources and call destination, the call is accepted by the AG 16. If necessary, the AG 16 requests satellite resources from an NCG 28. The AG 16 could be a user's HG or any remote TSA. The call is set up, for example as shown in FIG. 2, via path A-B, under database control of the designated NCG 28 and the selected TSA 16. The remote TSA 16 (the AG) then acknowledges the request and processes the call to the call destination 50 through a public switched circuit 17. Channels and/or codes are assigned by the AG 16 assisted by the designated NCG 28; and the gateway roamer database 27 at the AG 16 is updated to show that the user equipment is busy. A handoff processor 33 at the AG 16 is updated to enable handoff from one satellite to another if required. The AG 16 notifies the designated NCG 28, via the packet switched network 32, that the call is in process and states the satellite resources that are being used, to allow the NCG 28 to note in its database 20 that the user 30 is busy. The home user database 31 of the user's HG is updated to show the user 30 as busy and to show the user's AG 16.

Subsequent to call setup, the user 30 and the call destination 50 are connected via two-way wireless (cellular) telephone communications links A-B, as shown in FIG. 2. These communications may be carried out using spread spectrum modulation techniques and Code Division Multiple Access (CDMA) channels, or other modulation compatible with the satellite system, using equipment located at the user 30 position, and equipment located at the remote TSA 16 in the satellite service area (SSA) 24. The CDMA or other modulation signal is converted to a voice signal at both the user 30 end and the remote TSA 16. At the user 30 end, the signal is converted either to an analog signal for voice and sent to a loudspeaker or headphones, or converted to a digital signal and sent to another device for further processing of data. At the remote TSA end 16 the signal is received by antenna 38, converted to either a voice signal or digital data, and sent via a PSTN switch (not shown) for further routing via the public switched telephone network 17 to the call destination 50. After communications is ended, a signal from either end 30, 50 of an "on-hook" condition signifies end of communication.

The call termination processes proceed as follows: the AG 16 notifies the designated NCG 28 of call termination and that the channel is free. The network database 20 is notified of call termination and billing information, and is updated to show the user 30 as not busy. The AG 16 updates its roamer database 27 and resets handoff processor 33. The AG 16 notifies the user's HG via packet network 32 that the user 30 is not busy. The HG updates its home user database 31 to show user 30 not busy.

Consider the situation where a remote location called the "caller" 50 desires to make a telephone call to a cellular telephone user 30 that is roaming and is not located in a terrestrial cellular telephone service area (TCTSA). The call is initiated as shown in FIG. 3. The caller 50 uses the PSTN 21 to call the user's wireless (cellular) telephone number at the user's HG 12 or perhaps some other equivalent location. The call is transferred by the PSTN switch to the user's HG 12. The HG 12 equipment 23 processes the call and, by accessing the home user database 31, finds that the user 30 is roaming in the satellite service area 24 and thereby knows to route the call to the AG, which, for this example, we assume is the same as HG 12. The HG equipment 23 then routes a request for route planning to the route planner 25. The route planner 25 routes the call to the AG 12. In this example, the AG 12 is the HG 12, so no more call routing is required. The home TSA 12 makes a call setup notification to the designated NCG 28 via packet network 32. The AG 12, upon receiving the request signal, checks its database 31 for user status, processes the information, and based on the information in its database 31, satellite resources and AG 12 resources, accepts or rejects the call.

If the AG 12 is another GTSA (not the user's HG), such as equipment 16, HG 12 requests a call setup to the AG 16 via the packet network 32. The AG 16 checks satellite 22 channel capacity and requests satellite 22 resources from the designated NCG 28 if necessary via the packet network 32. The AG 16 hails the user 30 and transmits call setup information via the satellite 22. The ACG 16 notifies the HG 12 to route the call to the AG 16 and to update its home user database 31 to show the user 30 is busy. The call setup is as described above for the home TSA 12.

If it accepts a call for connection, the AG 12, 16 sets up the call. The AG 12, 16 transmits the request for access to the user 30 through satellite 22. If accepted by the user 30, an acknowledgment is transmitted to the AG 12, 16 through satellite 22. The AG 12, 16 updates the database 31 to show the user 30 to be busy, and signals the designated NCG 28 to update the network database 20 to show the user 30 to be busy.

Subsequent to call setup, the user 30 and the caller 50 are connected via two-way wireless telephone communications links via path A-D, as shown in FIG. 3. The AG 12, 16 notifies the designated NCG 28 that the call is in progress and states the satell