MXPA97001130A - Method and apparatus for transfer of communications between multiple satel systems - Google Patents

Abstract

The present invention relates to a method and apparatus for transferring communications between a primary satellite system (500) and an alternate satellite system (550), which determines (602) when a transfer condition exists for the primary satellite system (500) ). A satellite (604, 904) is determined to be an alternate satellite (552) having a coverage area (554), which is positioned such that the alternate satellite (552) can provide an alternate communications link (556). A transfer between the primary satellite system (500) and the alternate satellite system (550) is then performed (606). When the transfer condition (610) is alleviated, a transfer back to the primary satellite system (550) is effected and normal operations are resumed (60

Description

METHOD AND APPARATUS FOR TRANSFER OF COMMUNICATIONS AMONG MULTIPLE SATELLITE SYSTEMS FIELD OF THE INVENTION This invention relates in general to satellite communications and more particularly to a communication link for transfer between multiple satellite communication systems. BACKGROUND OF THE INVENTION A satellite communications system occasionally experiences conditions that cause the system to provide a lower service to the users of the system. These conditions may include, for example, high traffic congestion in system links and gaps in the communications coverage area of the system. Other conditions that negatively impact the service may include inefficiently directed information and high service costs. In a satellite communication system, one or more satellites act as access points to the system that provide communication channels to ground facilities (eg gates and subscriber units within the system coverage area.) When a satellite system experiences levels not usually high or unusually high traffic on communications links REF: 23918 Within the system, the satellite system may be forced to refuse service to some users, terminate service in process for other users or inefficiently direct traffic through the system. Overly congested links in this way can significantly impact the quality of service that is provided by a satellite system. Gaps in the coverage area of the satellite system can also negatively impact the service that is provided. A system coverage area defines the range of system communications. If an installation on the ground is outside the coverage area, the system is unable to communicate with the installation on the ground. Some satellite systems have coverage areas that normally cover the entire surface of the earth. Other satellite systems have coverage areas that only partially cover the land. During normal operations, a coverage area of the satellite system is defined by the number of satellites in the system, their elevation angles and altitudes, and the types of antennas they employ. Occasionally, an interruption of the satellite service or system failure may affect a coverage area of a system. For example, when a satellite is damaged and is unable to provide access to the system for a ground installation within its normal coverage area, an area of service interruption is likely to result. The typical condition of service interruption continues until the satellite is repaired, replaced or the coverage area of another satellite covers the ground installation. The area within which the satellite system is unable to communicate during normal operations or as a result of a service interruption condition, is referred to here as "coverage gap". The prior art systems do not provide transfer procedures that allow a second satellite system to temporarily provide communications services for a first satellite system. In this way, what is required is a method and apparatus that allows a first satellite system to temporarily transfer communications links to a second satellite or result from conditions (for example, excessively congested links or coverage gaps) that cause the first satellite system provides a service of communications less than optimal. BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 illustrates an area view of a hole Prior art coverage, Figures 2 to 4 illustrate a sequence for an inter-satellite communication link transfer of a satellite system according to the prior art, Figure 5 illustrates a configuration of a primary satellite communication system and alternate according to a preferred embodiment of the present invention; Figure 6 illustrates a flow chart of a method for a ground facility to communicate using an alternate satellite system in accordance with a preferred embodiment of the present invention. Figure 7 illustrates a flow chart of a method for a satellite of a primary satellite system for communicating, using an alternate satellite system in accordance with a preferred embodiment of the present invention; Figure 8 illustrates a flow chart of a method for a satellite in an alternate satellite system that temporarily provides a communications link for a primary satellite system in accordance with a preferred embodiment of the present invention; Figure 9 illustrates a flow chart of a method for a control facility that coordinates the transfer between a primary satellite system and an alternate satellite system in accordance with a preferred embodiment of the present invention; Figure 10 illustrates a block diagram of a ground installation according to a preferred embodiment of the present invention; Figure 11 illustrates a block diagram of a satellite according to a preferred embodiment of the present invention; and Figure 12 illustrates a block diagram of a control installation according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE DIBOJOS The method and apparatus of the present invention allow a first satellite system to temporarily transfer communication links to a second satellite as a result of conditions (eg excessively congested links or coverage gaps) which cause the First satellite system provides communications services less than optimal. Although the description of preferred and alternate embodiments of the invention often employs a coverage gap as a condition for transferring to a second satellite system, the use of a coverage gap is for purposes of illustration and not limitation. The method and apparatus of the present invention can be applied to any condition where a first satellite system wishes to temporarily transfer to a second satellite system.

As used herein, a "primary satellite system" or "primary system" is a satellite system that has a coverage gap. Similarly, a "primary satellite" is a satellite associated with the primary system. Also as used herein, an "alternate satellite system" or "alternate system" is a satellite system that temporarily provides communications services for a primary system within the primary system coverage gap. Similarly, an "alternate satellite" is a satellite associated with the alternate system. Figure 1 illustrates an aerial view of a coverage gap of prior art 124. The coverage gap condition is used below to describe the advantages of the method and apparatus for the present invention. Each satellite 100-107 of the illustrated satellite system has a coverage area of associated satellites 110 to 117 within which each satellite 100-107 can communicate with land facilities (e.g., a ground facility 120). The total area covered by all satellite coverage areas 110 to 117 represents the system coverage area. A system coverage area typically or occasionally may have gaps, or gaps, within which satellites 100 to 107 can not communicate with ground facilities. Figure 1 illustrates the coverage gap 124 covering the ground facility 120. As a result of the coverage gap 124, the ground facility 120 is unable to gain access to the satellite system 100 to 107. The ground facility 120 for example it can be a switching gate (G). A GW is a switching device that interconnects a satellite system with a land-based communications system such as a public switched telephone network (PSTN) or a land mobile telephone system. Typically, a communication link between a GW and a satellite system has a broad band that allows numerous channels to be supported by the link. The ground facility 120 can also be a fixed or mobile communications unit (CU) which is a radio frequency (RF) device that allows one or more individuals to communicate directly with the satellite system. Typically, a communication link between a CU and the satellite system has a relatively narrow bandwidth that supports one or a small number of channels. Although the term "ground installation" is used, the term is intended to include communication devices or facilities that are not necessarily located on the ground, such as, for example, communications devices on board ships or aircraft. A coverage gap may exist during normal operations of a satellite system, and also during a condition of satellite service interruption, planned or unplanned. A normally existing coverage gap may exist because, for example, the elevation angle of the satellites of a system is relatively low. In this case, the satellites of the system will not travel to higher latitudes in the course of their orbits and thus will be unable to provide coverage at those higher altitudes. At least two coverage gaps will exist within this system: one that encompasses the north pole and one that encompasses the south pole. Another example where a normally existing coverage gap may exist and is in a communications system that uses addressable satellite beams to provide coverage within more populated areas. This system can target its satellite beams only towards populated land regions, for example, while not providing coverage across sparsely populated oceans or regions. In this way, there will be multiple gaps of coverage within the oceanic or sparsely populated regions.

There may also be coverage holes during planned or unplanned satellite service interruption. For example, in Figure 1, a non-functional satellite (not shown) may exist between satellites 103 and 104. The non-functional satellite would be the direct result of the existence of the coverage gap 124 and thus the inability of the installation on land 120 to gain access to the satellite system. A coverage gap can be fixed or mobile. In addition, the coverage gap may be temporary or permanent. In the above-described example of a communication system using satellites having low elevation angles, the coverage gaps at the north and south poles would be both fixed and permanent. Figure 1 illustrates a movable cover gap 124, As the satellites 100-107 travel over orbit paths 130 and 132, the cover gap 124 moves along with them. Eventually, the satellite 103 will substantially encompass the area that previously defines the coverage gap 124 and the satellite 103 will be able to communicate with the installation on the ground 120. The coverage gap 124 may also be temporary, for example when repair or repair is possible. replace the satellite (not shown) which normally serves the area that defines the coverage gap 124.

Although the satellite system illustrated in Figure 1 is unable to communicate with the ground facility 120 at the time illustrated, the method and apparatus of the present invention allow communications with the ground facility 120, by using an alternate satellite system that it temporarily supports a communications link with ground installation 120 for the primary system illustrated in Figure 1. As previously explained, instead of experiencing a gap in coverage as a satellite system it may not be able to communicate with, or it may be capable of only partially communicating with, an installation on the ground due to over-congestion of system links or some other condition that forces the satellite system to provide non-optimal service. The method and apparatus of the present invention allow complete communications with an installation on the ground affected during these other conditions equally. Figures 2 to 4 illustrate a sequence for communication link transfer between satellites 200 to 201 of a satellite system according to the prior art. Figure 1 illustrates the satellites 200 to 201 at a first time (T = l). The satellites 200 to 201 travel on the orbit path 204 and have coverage areas 210 to 211 respectively. At Tl, the satellite 200 communicates with the ground facility 20 (5 over the communications link 220. The direct communications link 220 between the satellite 200 and the ground facility 206 is possible only when the coverage area 210 covers the installation on land 206. In a preferred embodiment, satellites 200 through 201 communicate with each other or over cross link 230. Cross link 230 allows signaling and communications information traffic to be routed through the satellite system over satellites instead of ground links (for example, elbow pipe links) Therefore, the signaling and / or traffic received by satellite 200 through communications link 200 can be disseminated through the rest of the satellite system using cross-links (for example cross-link 230) Although the method and apparatus of the present invention is described predominantly using cross-links, the method and apparatus of the present invention also apply to systems using other types of links (for example, elbow pipe links). Figure 2 illustrates satellites 200 to 201 in a second of time (T = 2) after satellites 200 to 201 have traversed the orbit path 204. At T = 2, both coverage areas 210 to 211 encompass the installation on land 206. However, the coverage area 210 will soon travel beyond the ground installation 206 and thus a transfer between the satellites 200 to 201 is necessary to maintain a continuous link with the ground installation 206. Using a transfer of effected-before- De-interruption, the satellite 200 maintains the communication link 220 until the communication link 221 can be established between the ground installation 206 and the satellite 201. Once the communication link 221 is established, the communications link can be disconnected. 220 and the transfer is complete. Figure 4 illustrates the satellites 200 to 201 at a third time (T = 3) after the satellites 200 to 201 have traversed further on the orbit path 204. AT = 3, only the coverage area 211 encompasses the installation in 206. In this way the ground installation 206 is able to communicate with the satellite network only over the communication link 221. This transfer sequence will continue as additional satellite systems (not shown) travel over the ground facility 206 In the event that satellite 201 is unable to establish or maintain communications link 221 with ground installation 206, satellite 200 will not be able to transfer communications with satellite 201 as illustrated in Figures 2 through 3. inability to transfer to satellite 201 will result in a coverage gap that runs over land facility 206. When land facility 206 is a GW, the coverage gap It will probably have significant consequences. All information signaling and communication traffic flows that were routed through the GW to the satellite network will be interrupted. In some cases, a particular GW will be the only interface between the satellite system and terrestrial communications systems within a large geographic area (for example, multiple countries). A gap of coverage that passes over this GW will cause all calls and other communications between the satellite system and terrestrial communications systems to be removed. Although in a non-geo-synchronous system, the coverage gap eventually passes over the GW, and a different satellite will be able to provide service to the GW, the problem will recur as the coverage gap passes over the same GW again or different. The non-functional satellite can take weeks to repair or replace, or in the worst case it can be irreparable or irreplaceable. During that time, service interruptions resulting from the coverage gap will continue to degrade significantly in the performance of the system. When the earth installation 206 is a CU, the consequences of a coverage gap are significant, but not as severe as for a GW. The link that the CU is using will be disconnected as the coverage gap passes over the CU. The user of the CU will have to wait until he is again located within the coverage area of the satellite system and try to establish a communications link at that time. The method and apparatus of the present invention mitigate the adverse consequences that result from a coverage gap, from excessively congested links or from other conditions that degrade the service by temporarily employing an alternate satellite system to provide communications links. The method and apparatus of the present invention apply to satellite systems whose satellite coverage areas move with respect to the surface of the earth, and also to satellite systems whose satellite coverage areas are suntially static with respect to the surface from the earth. In addition, the method and apparatus of the present invention are applicable to any satellite system having one or more satellites that may be in low ground or ground or geo-synchronous orbits or combinations thereof. Figure 5 illustrates a configuration of a primary satellite system 500 and an alternate satellite system 550 in accordance with a preferred embodiment of the present invention. Although the illustrated configuration shows a coverage gap in the coverage area of the primary system resulting from a non-functional system, the configuration is intended for exemplary purposes and is not intended to limit the scope of the invention. As previously explained, a coverage gap may exist normally or as a result of a planned or unplanned satellite service interruption. The primary system 500 comprises the satellites 502 to 504 and the alternate system comprises the satellite 552. The altitudes of the satellites 502 to 504 and 552 may be low earth, middle earth, geo-synchronous or combination thereof. Satellites 502 to 504 and 552 may have the same or different altitudes. The particular altitudes of satellites 502 to 504 and 552 are not crucial to the present invention. As described in conjunction with Figures 2 to 4, during normal operations, satellites 502 through 504 travel over orbit path 506 and provide a continuous communication link with ground facility 520 when transferring from one satellite to another as Coverage areas of satellites 502 through 504 pass over land facility 520. Figure 5 illustrates the method and apparatus of the present invention as it applies when a primary satellite does not operate. The method and apparatus of the present invention can also be applied for example when the links supported by the primary system 500 are over congested or there are other reasons for directing the traffic of the primary system through the alternate satellite 552. The primary satellites 502 and 504 have coverage areas 510 and 512, respectively. Satellite 503, however, has no coverage area illustrated because in this example, satellite 503 does not currently provide communications services. As the satellite 503 passes over the ground installation 520, a condition of service interruption in a prior art system will result. The consequences of this service interruption are described in detail above. In a preferred embodiment, the method and apparatus of the present invention borrow satellite 552 from the alternate satellite system 550. Satellite 552 illustrates that it has a coverage area 554 that encompasses the ground facility 550 at a time when no area of coverage 510, 512 of the primary system covers the ground installation 520. According to the method and apparatus of the present invention, instead of transferring a communication link with the ground installation 520 of the primary satellite 502 to the non-functional primary satellite 503 , the communication link is transferred to the alternate satellite 552. Preferred mode methods for carrying out a transfer to the alternate satellite 552 are described in conjunction with Figures 6 to 9.

Figure 5 illustrates a communications link 556 between the alternate satellite 552 and the on-shore installation 520. The alternate satellite 552 also supports cross-links 558 and 560 with the primary satellites 512 and 504, respectively. The cross links 558 and 560 allow the alternate satellite 552 to receive information intended for ground installation 520 of the primary system 500 and also to send information received from the ground installation 520 to the primary system 500. The alternate satellite 552 does not require cross-linking with both primary satellites 502 and 504. in alternative embodiments, the alternate satellite 552 may establish a cross-link with only one primary satellite 502 and 504, with a different primary satellite (not shown) or a ground facility to be interconnected satellite alternate 552 with the primary system 500. In a preferred embodiment, a transfer is coordinated between a primary satellite and an alternate satellite between a ground installation that is transferred, one or more of the primary satellites, one or more of the alternate satellites and a control installation. Figures 6 to 9 illustrate flowcharts of functions performed by each of these devices, respectively in accordance with preferred embodiments of the present invention.

Figure 6 illustrates a flow diagram of a method for an on-ground installation (e.g., ground facility 520, Figure 5) to indirectly communicate with a primary satellite system (e.g., primary satellite system 500, Figure 5) using an alternate satellite system (e.g. alternate satellite system 550, Figure 5) according to a preferred embodiment of the present invention. The method begins when the ground installation maintains normal operations in step 600. By maintaining normal operations, the ground installation communicates directly with a primary satellite in whose coverage area the ground installation is located. Normal operations also include uninterrupted transfers to other primary satellites, when required. In step 602, a determination is made if a condition exists that requires a transfer from the primary system to an alternate system. A transfer condition will exist for example, if a coverage gap is or will soon be in a position such that direct communications with the primary system are not possible for ground installation. The determination if a coverage gap is or will soon be in a position that avoids direct communications between the ground installation and the primary system, can be done in various ways. In a preferred embodiment, the ground installation detects that there is or will soon be a gap in coverage. For example, when the ground installation is a GW, the GW can make the coverage gap determination based on the GW's inability to acquire the next primary satellite for which it is programmed to acquire the GW. When the ground installation is a CU, the CU can make the coverage gap determination based on the inability of the CU to establish a link with any of a number of possible primary satellites to which the CU will be able to transfer. In an alternate mode, the ground installation may receive a message from another device (eg a control facility) indicating that a coverage gap is or will soon be in a position such that direct communications with the primary system are not possible. As previously explained, another transfer condition can be excessive congestion in the links of the primary system. If there are no transfer conditions, the procedure iterates as illustrated in Figure 6, and normal operations continue. In a preferred embodiment, if a transfer condition exists, the ground installation determines, in step 604, an alternate satellite that can temporarily employ the ground facility to indirectly maintain a link with the primary system. In a preferred embodiment, this determination will include an evaluation of the coverage areas of alternate systems for one or multiple alternate systems. When an alternate satellite has a coverage area encompassing an installation on the ground, the alternate satellite can potentially support a communication link with the ground installation during the interruption of the primary system service. In an alternate modality, the knowledge of which alternate satellite will be used in the case of a service interruption can be pre-determined. This pre-determination can be feasible for example when the alternate satellite is geo-stationary and has a coverage area that is essentially fixed with respect to the surface of the earth. After an alternate satellite is determined, the ground installation switches to the alternate satellite in step 606. In a preferred embodiment, the ground installation switches from the primary satellite to the alternate satellite using a perform-before-interrupt transfer sequence. . The installation on the ground synchronizes with the alternate satellite before interrupting the communications link with the primary satellite. Once the alternate link to the alternate satellite is achieved, the ground installation disconnects from the primary satellite.

In an alternate mode, a communication link can be established between the ground installation and the alternate satellite. Typically, the prior establishment of the communications link is more feasible for a geo-stationary alternate satellite. A previously established alternate link will not be used until it is required and in this way messages will not normally be sent through the alternate link. However, when the alternate satellite is required to provide a link to the ground facility, messages can then be sent through the alternate link. This alternate mode can eliminate the need to configure and disarm an alternate link each time a transfer condition occurs. In step 603, the ground facility sends and receives signaling information and communications traffic through the alternate satellite, thereby indirectly communicating with the primary satellite system. As previously explained, the ground installation can send information to the primary system by sending it through the alternate link to the alternate satellite which in turn sends the information to the primary system through one or more cross links with the primary satellites. The ground installation receives information from the primary system when the primary system sends the information to the alternate satellite over the one or more crossed links and the alternate satellite in turn sends the information to the ground installation over the alternate link. A determination is made in step 610 if the condition requiring a transfer in step 602 has been alleviated. When the transfer condition was a coverage gap, the transfer condition will be alleviated when the primary system has re-established coverage of the area where the installation is located on the ground. The primary system can re-establish coverage, for example, when another primary satellite has moved in its orbit in such a way that the coverage area of the satellite covers the ground installation. Alternatively, the non-operational satellite can be repaired or replaced, thus providing coverage back to the area occupied by the ground installation. When the transfer condition was over congested links with the primary satellite system, the transfer condition will be alleviated when the links approximate an acceptable operational capacity. As previously explained, other transfer conditions may also occur. When the transfer condition is not alleviated, the procedure iterates as illustrated in Figure 6. When the transfer condition is alleviated, the ground installation switches back to a primary satellite in step 612, and normal operations are resumed in step 600. In a preferred embodiment, switching back to the primary satellite will require the ground facility to acquire and synchronize communications with the primary satellite. In an alternate mode, a link that does not carry traffic with the primary satellite can be previously acquired and switched back to the primary system, which involves starting to transmit and receive communications traffic on the previously acquired link. Figure 7 illustrates a flow chart of a method for a satellite of a primary satellite system (e.g. system 500, Figure 5) to communicate with a ground facility using an alternate satellite system in accordance with a preferred embodiment of the present invention. The method begins when the primary satellite conducts traffic as usual in step 700. Directing traffic as usual includes directing traffic over cross links to other primary satellites and over downlinks to ground facilities. In step 702, the primary satellite receives one or more instructions to start directing messages destined for particular identified ground facilities (hereinafter "identified ground facilities") through an alternate satellite. The instruction may include a runtime, for example, which indicates that the primary satellite will have to start directing through the alternate satellite at a future time indicated by the execution time. Alternatively, the instruction can be a real-time instruction to be executed by the primary satellite upon reception. Alternatively, the instruction may include some other execution condition that must be met before the primary satellite begins to steer through the alternate satellite (for example, a condition that the primary satellite must reach a certain location before executing the instruction). After receiving the instruction, the primary satellite establishes a cross-link with the alternate satellite in step 704. As previously explained, the cross-link allows the alternate satellite to send information received from a ground facility to the primary system, and also receives information intended for ground installation of the primary satellite. More than one cross link between the primary satellites and the alternate satellite can be established. After the cross link is established, in step 706, the primary satellite sends traffic destined for the ground facilities, identified through the alternate satellite and receives information from the identified ground facilities through the alternate satellite. In an alternate mode, the primary satellite can direct traffic through the alternate satellite, based on a geographic location and a destination ground facility, rather than on the basis of an identity of the ground facility. In a preferred embodiment, a determination is made in step 708 if an instruction to normally route by the primary satellite has been received. Similar to the instruction received in step 702, the instruction to address normally may be in real time, have an associated runtime or have some other execution condition indicating when the instruction should be carried out. If a direction instruction has not been normally received, the procedure iterates as illustrated in Figure 7, and the primary satellite maintains the cross-link with the alternate satellite. In a preferred embodiment, if an instruction has been received to direct normally, at the time when the instruction is to be executed, the primary satellite interrupts communications with the alternate satellite in step 710 and begins to direct traffic as is usual in the stage 700. In a preferred embodiment, interrupting communications will involve disconnecting the cross link with the alternate satellite. In an alternate mode, the primary satellite can maintain a synchronized cross-link with the alternate satellite, but interrupting communications will involve the failure to transmit or receive messages on the cross-link. Figure 8 illustrates a flow chart of a method for a satellite in an alternate satellite system (e.g. system 550, Figure 5) temporarily to provide communication service for a primary satellite system according to a preferred embodiment of the present invention. The method begins when the alternate satellite receives one or more instructions, in step 800, which indicate that the satellite will provide service for a primary satellite system. The one or more instructions can be in real time, have an associated execution time or have an execution condition as previously explained. In a preferred embodiment, the alternate satellite establishes an alternate link, in step 802, with one or more ground facilities that the alternate satellite has been designated to support. In a preferred embodiment, establishing an alternate link will be made upon acquisition and synchronization with a ground facility. In an alternate mode, the alternate link may be pre-established but will not transport messages until required. In step 804, the alternate satellite establishes one or more cross links with the primary satellites. As previously explained, cross-links allow the alternate satellite to direct information between the primary system and the ground facilities that maintain the alternate satellite. In an alternate mode, the one or more cross links may be pre-established but will not transport messages until required. The sequence of steps 802 and 804 is not crucial to the present invention. In alternate modes, steps 802 and 804 may be performed simultaneously or in a reverse order of that illustrated in Figure 8. In step 806, the alternate satellite directs signaling information and communications traffic received on the alternate link from the installation of ground to the primary system over the cross link. In step 808, the alternate satellite directs signaling information and communications traffic received on the cross link from the primary system to the ground facility on the alternate link. The steps 806 may be performed simultaneously or in reverse order of that illustrated in Figure 8. A determination is made in step 810, whether an instruction has been received for the alternate satellite to stop the service supply between the ground facility and the primary system. The instruction can be in real time, have an associated execution time or have an associated execution condition. When an instruction to stop the service supply has not been received, the procedure iterates as illustrated in Figure 8. When an instruction has been received to stop the service supply, the alternate satellite interrupts the service between the primary system and the ground installation of step 812. In a preferred embodiment, the alternate satellite interrupts the service by disconnecting the alternate link and the one or more cross links. In an alternate mode, when the alternate link and / or cross-links are previously established, the alternate satellite interrupts the service when it does not send or receive more messages about the alternate link and / or cross-links. Then the procedure ends. Figure 9 illustrates a flow chart of a method for a control facility that coordinates the transfer between a primary satellite system and an alternate satellite system in accordance with a preferred embodiment of the present invention. In a preferred embodiment, a control facility regulates the routing of information through the primary satellite system. When the primary satellite system wishes to use an alternate satellite system to help sustain communications links, the control facility is responsible for controlling the transfer of communication links between the two systems.

The method begins when the control facility detects a need to transfer communication links to the alternate system in step 900. As previously described, the need to transfer communication links may arise for example due to various types of transfer conditions. For example, a need for a transfer may occur when a gap in the coverage area of the primary system exists or is imminent. Other transfer conditions may include the need for the primary system to derive traffic from its satellites due to over-congestion or other reasons such as efficiency or cost of addressing. A need for transfer due to a gap in coverage can be detected, for example through satellite telemetry (for example, a satellite fails to report status and thus is considered inoperable) or through orbit dynamics calculations. A need for transfer due to over-congestion in the primary system links can be detected, for example, by checking traffic levels over cross-links and downlinks and assessing whether traffic levels are close to or exceed pre-determined traffic thresholds. .

When a need is detected by transfer, the control facility forecasts a time when the transfer will occur. For example, when the transfer condition is a coverage gap, and a communication link with an alternate satellite is not previously established, the transfer time will be a time that allows an alternate satellite to establish an alternate link with a ground facility before the primary system interrupts its communications link with the ground installation. In step 904, the control installation determines one or several alternate satellites that can be temporarily used by the ground installation, to maintain an indirect link with the primary system. In a preferred embodiment, this determination will include an evaluation of the coverage areas of one or more alternate satellites for one or more alternate systems. An acceptable alternate satellite is an alternate satellite that has a coverage area that encompasses the ground installation such that the alternate satellite can sustain an alternate link with the ground installation for the period of time required by the primary system the alternate link . In some situations, multiple alternate satellites may be required to provide alternate service for the entire period of time when the alternate link is required. For example, the satellites of an alternate system can be satellites of low terrestrial orbit that change rapidly position with respect to the surface of the earth. Alternate service may be necessary for a period of time that exceeds the capacity of a single alternate satellite to provide service (ie the satellite would not be in the range of the ground installation for the entire period). In this case, a first alternate satellite will have to transfer to another alternate satellite of the alternate system or other satellites of the alternate system (for example a geo-synchronous satellite) in order to provide an alternate link for the entire period. In a preferred embodiment, in step 904, the control facility determines the multiple alternate satellites that will be required to provide alternate service for the entire period of time, when alternate coverage is required. In an alternative mode, the knowledge that alternate satellites or satellites will be used in the event that alternate service is required, can be pre-determined. This prior determination will be feasible for example when the satellite or alternate satellites are geo-stationary and have coverage areas that are essentially fixed with respect to the surface of the earth. In step 906, the control facility generates instructions for carrying out the transfer between the primary system and the alternate system. These instructions can be in real time, have an associated runtime or have an associated execution condition, for example. In a preferred embodiment, the instructions will inform the satellites and ground facilities when to establish / disconnect communication links in order to transfer to the alternate satellite. In an alternate mode, when alternate links and cross-links have been pre-established, the instructions will inform the satellites and ground facilities that start sending and receiving messages about the pre-established links. In step 908, the control facility sends the instructions to the satellites and ground facilities that will be affected for transfers. This includes instructions for the alternate satellite. Satellites and ground facilities do not use the instructions to perform the transfer procedure. In step 910, the control facility determines whether the need for the alternate system support has ended. The need for the support of the alternate system will be terminated, for example when the primary system has resumed coverage on the affected ground facilities or when the primary system links are no longer excessively congested. If the need for alternate system support has not yet been completed, the procedure iterates as illustrated in Figure 9 and steps 904 to 908 are repeated. Steps 904 to 908 should be repeated occasionally because different alternate satellites and / or transfer instructions may be necessary for the duration of the alternate system support, for example when available resources and / or physical orientation of satellites and ground facilities change with e-1 time. When the control facility determines that the need for support of the alternate system is over, the control facility generates instructions in step 912 for the satellites and ground facilities to resume normal operations (ie operate the alternate system without assistance). These instructions can be in real time, have associated execution time or have associated execution conditions. In step 914, the control facility sends the instructions to the affected satellites and ground facilities which in turn use the instructions to resume normal operations. In an alternate mode, the control facility may have a determined time when the alternate satellite support is no longer required near the time when the control facility performs step 912. In another alternate mode, the control facility may have determined the duration of time when alternate satellite support is required. It is no longer required to know the time when the alternate satellite support or the duration of support will allow the control installation to generate commands to resume normal operations and send those instructions, with execution times associated with the satellites and ground facilities before, during or after transfer. After the instructions for resuming normal operations have been sent, the procedure ends. Preferred embodiments of the apparatuses employed to carry out the method of the present invention are described in conjunction with Figures 10 to 12. Figure 10 illustrates a block diagram in the land installation 1000, according to a preferred embodiment of the invention. present invention. In a preferred embodiment, the ground facility 1000 comprises the processor 1002, primary system transceiver 1004, and alternate system transceiver 1006. In an alternate mode, a single transceiver (not shown) can be used instead of the separate primary system transceiver 1004 and the alternate system transceiver 1066. The primary system transceiver 1004 interconnects the ground installation 1000 with the primary system satellites. The primary system transceiver 1004 is typically used during normal operations with the primary system. The alternate system transceiver 1006 interconnects the ground installation 1000 with alternate system satellites. The alternate system transceiver 1006 is typically employed when an alternate satellite provides a communication interface between the ground facility 1000 and the primary system. The processor 1002 sends and receives messages to and from the primary system transceiver 1004 and the alternate system transceiver 1006 and performs most of the functions described in conjunction with Figure 6. Figure 11 illustrates a block diagram of the satellite 1100 in accordance with a preferred embodiment of the present invention. The satellite 1100 comprises the processor 1102, cross link transceiver 1104 and downlink transceiver 1106. Satellite 1100 may be a primary system satellite or an alternate system satellite. When the satellite 1100 is a primary system satellite, during normal operations, the cross link transceiver 1104 is used to support one or more cross links with other primary system satellites. The downlink transceiver 1106 is used to support communication links with ground facilities. When an alternate system satellite is employed to provide service for the primary system, the cross link transceiver 1104 may be used to support one or more cross links with alternate system satellites. The downlink transceiver 1106 may or may not continue to be used to support communication links with ground facilities. The processor 1112 is used to perform most of the functions described in conjunction with Figure 7. When the satellite 1100 is an alternate system satellite, the cross-link transceiver 1104 is used to support one or more cross-links with system satellites. primary. The downlink transceiver 1106 is used to support communication links with ground facilities that hold the alternate system satellite for the primary system. The processor 1102 is used to perform most of the functions described in conjunction with Figure 8. Figure 12 illustrates a block diagram of the control installation 1200 according to a preferred embodiment of the present invention. The control facility 1200 comprises the processor 1202 and the transceiver 1204. The transceiver 1204 is used to receive telemetry of primary system satellites and also to transmit instructions either directly or indirectly to primary system satellites, alternate system satellites and facilities in land that are affected by an inter-system transfer. Processor 1202 performs most of the functions described in conjunction with Figure 9.

In summary, the method and apparatus of the present invention allow a transfer to be made between a primary satellite system and an alternate satellite system, when the primary satellite system has a condition where the transfer is necessary to avoid interruption or corruption of communications systems services. While the principles of the invention have been described above in connection with a specific apparatus, it will be clearly understood that this description is made only by way of example and not as limitation in the scope of the invention. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (10)

1. CLAIMS 1.- Method for transferring a communication link from a primary satellite system, the method is characterized by the steps of: (a) determining that a transfer condition exists within the primary satellite system, when the satellite system experiences a condition that the primary satellite system wishes to alleviate when using communications services from an alternate satellite system; (b) establishing an alternate communication link with the alternate satellite system, wherein the alternate satellite system is capable of supporting the alternate communications link that can alleviate the transfer condition; and (c) send traffic to and receive traffic from the alternate satellite system over the alternate communications link.
2. 2. Method according to claim 1, wherein the transfer condition is that there is a gap of coverage area within the primary satellite system and the step of determining that the transfer condition exists is characterized by the steps of: (a) detect by ground installation that the gap of a coverage area exists within the primary satellite system because the communication link can not continue to be maintained with the primary satellite system; and (a2) determining that the transfer condition exists based on the detection stage.
3. 3. - Method according to claim 1, wherein the transfer condition is that at least one communications link supported by the primary satellite system is over-congested, and the step of determining that the transfer condition exists is characterized by stages of: (a) receiving an instruction from a communications gate that the CU must switch to the alternate satellite system instead of within the primary satellite system.
4. 4. Method according to claim 1, further characterized by the steps of: (d) deciding if the transfer condition for the primary satellite system has been overcome in such a way that the ground installation can communicate with the system of primary satellite; (e) when the transfer condition has been alleviated, interrupting the sending of traffic to and receiving traffic from the alternate satellite system over the alternate communications link; and (f) start sending traffic to and receive traffic from the primary satellite system over the communications link.
5. 5. Method according to claim 1, wherein a primary satellite of the primary satellite system transfers a communication link between the primary satellite and an installation on the ground to the alternate satellite system, the alternate satellite system is capable of supporting an alternate communications link with the ground facility that can alleviate the transfer condition, and the method is further characterized by the steps, performed by the primary satellite, of: (d) receiving a first instruction to transfer the communication link with the alternate satellite of the alternate satellite system, instead of transferring the communication link within the primary satellite system; (e) establish a link - crossed with the alternate satellite as a result of the first instruction; (f) interrupting the sending and receiving of ground installation traffic through the communication link with the ground installation, and (g) sending and receiving ground installation traffic through the alternate satellite over the cross link.
6. 6. - Method according to claim 1, wherein an alternate satellite of the alternate satellite system provides an alternate communication link with a ground installation for the primary satellite system, the alternate satellite system is capable of supporting the link of alternate communications that can alleviate the transfer condition and the method is further characterized by the steps performed by the alternate satellite, of: (d) receiving a first instruction to provide communications services with the ground facility using the communications link alternate with ground installation; (e) direct traffic from the ground installation intended for the primary satellite system through at least one cross-link with at least one satellite of the primary satellite system, where at least the cross-link allows the satellite to send at least traffic to and receive traffic from the ground installation through the alternate satellite; and (f) direct traffic from the satellite as a minimum, intended for ground installation through the alternate communication link with the ground facility.
7. 7. Method according to claim 1, wherein a control facility initiates transfer of a communication link from the primary satellite system to the alternate satellite system, the alternate satellite system is capable of supporting an alternate communications link with a ground installation that can alleviate the transfer condition and the method is further characterized by the steps, performed by the control facility, of: (d) detecting that the transfer condition exists when a need arises to transfer from the system from primary satellite to alternate satellite system; (e) forecast a transfer time when the primary satellite system should transfer to the alternate satellite system; (f) generate at least one instruction, which directs at least one satellite of the primary satellite system that transfers to the alternate satellite system at the time of transfer, where after transfer, the instruction will at least cause the satellite to send at least traffic and receive traffic from the alternate satellite system; and (g) send the instruction at least to the satellite at least before the transfer time.
8. 8. Method according to claim 1, wherein a ground facility that is capable of communicating with the primary satellite system and the alternate satellite system is characterized by: a processor to determine that the transfer condition for the system of primary satellite exists, and to establish the alternate communication link with the alternate satellite system, wherein the alternate satellite system is capable of supporting the alternate communication link and to transfer a communication link with the primary satellite system to the alternate satellite system when sending traffic to and receiving traffic from the alternate satellite system over the alternate communication link; a primary system transceiver coupled to the processor, the primary system transceiver to communicate with the primary satellite system over the communication link; and an alternate system transceiver coupled with the processor, the alternate system transceiver to communicate with the alternate satellite system over the alternate communication link.
9. 9. - Method according to claim 1, wherein a primary satellite of the primary satellite system is capable of maintaining a communication link between the primary satellite and a ground installation and the primary satellite is characterized by: a processor for receiving a first instruction to transfer the communication link to an alternate satellite of the alternate satellite system, instead of transferring the communication link to another primary satellite of the primary satellite system, where the instruction that is received after the primary satellite system experiences the transfer condition, the alternate satellite system is capable of supporting the alternate communication link that can alleviate the transfer condition and the processor is also used to establish a cross-link with the alternate satellite, interrupting the sending of traffic to the installation in ground over the communication link with the installation in tie and send the traffic destined for installation on the ground to the alternate satellite on the cross link; a downlink transceiver coupled to the processor, the downlink transceiver maintains the communication link with the installation on the ground; and a cross-linked transceiver coupled with the processor, the cross-linked transceiver maintains the cross-link with the alternate satellite.
10. 10. Method according to claim 1, wherein an alternate satellite of the alternate satellite system is characterized by: a processor for determining that the primary satellite system requires the alternate satellite to provide the alternate communications link with a ground installation, When the primary satellite system experiences the transfer condition, where the alternate satellite system is capable of providing the alternate communications link that can alleviate the transfer condition, the processor also directs the traffic from the installation on land destined for the primary satellite system through at least one cross-link with at least one satellite of the primary satellite system, where at least the cross-link allows the satellite to at least send the traffic to and receive the traffic from the installation on the ground through of the alternate satellite, the processor also directs traffic from the minimum satellite intended for ground installation through the alternate communications link with the ground installation; a downlink transceiver coupled with the processor, the downlink transceiver maintains the alternate communication link with the ground installation, and a cross-link transceiver coupled with the processor, the cross-link transceiver maintains the cross-link at least with the satellite as a minimum of the primary satellite system.