HK1074286B - Pre-coordination of return link for hand-off between coverage areas being traversed by a mobile transceiver platform - Google Patents

Description

Pre-coordination of return links for handoff between coverage areas being traversed by a mobile transceiver platform

Technical Field

The present invention relates to ground-to-air communication via satellite communication links, and more particularly to a system for coordinating the handoff of a mobile platform, such as an aircraft, from a first coverage area and into a return communication link of a second coverage area.

Background

To date, broadband data and video services on which our social and economic growth relies are often not readily available on mobile platforms such as airplanes, boats, trains, and automobiles. While technology exists to provide such services to all forms of mobile platforms, past solutions have typically been very expensive, low data rate, and/or only very limited markets for government/military users, as well as some high-end maritime markets (e.g., cruise ships).

Currently, various broadcast Television (TV) services are available to users on land via satellite links. Such services include commercial Direct Broadcast Satellite (DBS) services (e.g., DirecTV ® and EchoStar ®) and customized video such as rebroadcast video over dedicated Fixed Satellite Services (FSS) or broadcast satellite services (BBS) satellites. Data services that may be provided via satellite links include all traditional internet services (e.g., email, web browsing, web conferencing, etc.), as well as Virtual Private Networks (VPNs) for companies and government customers.

Previously developed systems that attempt to provide internet services between a mobile platform and one or more ground-based stations have experienced significant difficulties in maintaining a communication link between the mobile platform and the ground-based station as the mobile platform leaves one coverage area and enters a second coverage area. In such a situation, coordinating the handoff of the communication link from the first ground station to the second ground station is problematic when the mobile platform is required to transition from communication with a first ground-based RF transceiver located within a first coverage area to communication with a second ground-based RF transceiver located within a second coverage area. The first ground station needs to be notified when the mobile platform will leave its coverage area, and with sufficient advance notification, the first and second transceivers associated with both ground stations can coordinate switching the communication link with the mobile platform. More specifically, two ground stations need to communicate with each other and with the mobile station so that the mobile platform can be instructed to relinquish its communication link with the first ground station only after the mobile platform establishes a communication link with the second ground station.

When the handover is completed, it is important to inform both ground-based transceivers. This problem can be exacerbated when the mobile platform involved is an aircraft moving at high speeds. Depending on the distance and area of overlap between the two coverage areas, only a very limited time may be used to establish a new communication link when the aircraft leaves the first coverage area and enters the second coverage area.

In light of the foregoing, it is a primary object of the present invention to provide a system and method for coordinating the interruption of a current return communication link between a mobile platform and a first ground-based transceiver located within a first coverage area, and establishing a new communication link between the mobile platform and a second ground-based transceiver located within a second coverage area, wherein the mobile communication platform is communicating with the ground-based transceiver via satellite transponders orbiting above the first and second coverage areas.

It is another object of the present invention to accomplish handoff of a communication link between a mobile platform and a pair of ground-based transceivers in a relatively short period of time, such as 1 minute, when the mobile platform enters an overlapping region of two coverage areas.

It is a further object of this invention to enable handoff of a communication link from a first ground-based transceiver to a second ground-based transceiver to be accomplished using communication between each ground-based transceiver. The inter-ground based transceiver communication is to deterministically inform the first ground based transceiver that a new communication link has been established with the second ground based transceiver.

Disclosure of Invention

The above and other objects are provided by a system and method for coordinating a return communication link handoff of a mobile platform traveling between a pair of coverage areas. The system and method of the present invention contemplates the use of at least one satellite-based transponder disposed in a geosynchronous or non-geosynchronous orbit on a first coverage area and wherein a first terrestrial-based transceiver is disposed in the first coverage area. At least one second satellite-based transponder is disposed in a geosynchronous or non-geosynchronous orbit and defines a second coverage area, and a second ground-based transceiver is disposed in the second coverage area. The two ground-based transceivers also communicate with each other via a ground-based communication link connection.

Initially, a ground-based transceiver within a first coverage area periodically receives location information from a mobile platform traveling within the first coverage area. When the mobile platform enters a predetermined overlap region between two coverage areas, the first ground-based transceiver sends a signal to the second ground-based transceiver via a land-based communication link requesting that the communication link be handed off to the second ground-based transceiver. The second ground-based transceiver then selects an assignment for the mobile platform if more than one satellite-based transponder is available within the second coverage area and transmits the assignment back to the first ground-based transceiver. This information is then transmitted to the mobile platform via the first satellite-based transponder. The mobile platform includes an RF transceiver system for communicating with a ground-based transceiver via a satellite-based transponder in each coverage area. The mobile platform then uses its transceiver to acknowledge receipt of the new assignment to the first ground-based transceiver.

The second ground-based transceiver then polls for the presence of the mobile platform. The mobile platform acknowledges the new assignment to the second ground-based transceiver. Upon receiving the acknowledgement, the second terrestrial-based transceiver notifies the first terrestrial-based transceiver via the terrestrial-based communication link that the handoff has been completed. Optionally, but preferably, the first ground-based transceiver then sends an acknowledgement to the second ground-based transceiver, which will then have a communication link with the mobile platform.

Importantly, the above-described handoff needs to be completed before the mobile platform completely leaves the first coverage area. The present invention accomplishes the above-described handoff in less than 1 minute and in many cases about 30 seconds or less. When the mobile platform is an aircraft flying at high speeds, rapid communication link handoff is required. In this case, only a very limited time is available for coordinating the handoff of the communication link with the aircraft from one ground station to another. The above-described system and method accomplish the required handoff of the communication link with the mobile platform in an orderly fashion and without the possibility of ambiguity between two ground-based transceivers when relinquishing the communication link with one ground-based transceiver and establishing a communication link with another ground-based transceiver.

Drawings

The present invention will become more fully understood from the detailed description and the accompanying drawings.

FIG. 1 is a simplified view of the major components and several optional components of the system and method of the present invention, and further illustrates a pair of coverage areas having an overlap region traversed by a mobile platform (e.g., an aircraft), and further illustrates a land-based communication link connecting two ground-based transceivers;

FIG. 2 is a block diagram illustrating a series of communications between a mobile platform and a first ground-based transceiver within an overlap region;

FIG. 3 is a block diagram illustrating a series of communications between a mobile platform and a second ground-based transceiver;

FIG. 4 is a flowchart showing the steps performed in FIG. 2 and the steps of communication between two ground-based transceivers to obtain a new assignment for the aircraft;

FIG. 5 is a flowchart illustrating the steps performed in FIG. 3 for establishing a new communication link between the aircraft and a second ground-based transceiver, in addition to a flowchart illustrating the steps of communicating between two ground-based transceivers in a handoff of the coordinated communication link; and

fig. 6 is a time line illustrating a series of events in performing a handoff from a first terrestrial-based transceiver to a second terrestrial-based transceiver.

Detailed Description

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Referring to fig. 1, an illustration of the method 10 of the present invention and the components and subsystems of the device will be presented in order to provide a framework for the communication link handoff scheme of the present invention. It should be understood that certain sub-components illustrated in connection with fig. 1 are merely optional, yet described and illustrated to allow the reader to understand the flexibility of system 10 in accommodating various existing air-to-ground communication systems.

The system and method 10 of the present invention contemplates managing the communication links of a plurality of mobile platforms 12a-12f as the mobile platforms travel from one different coverage area 14a to another 14 b. A ground portion 16 forming a ground-based Radio Frequency (RF) transceiver is positioned within the coverage area 14 a. At least one satellite 18a, but possibly a plurality of satellites 18a-18c, is arranged in a geosynchronous orbit (GSO) and defines the boundaries of the first coverage area 14 a. At least one satellite 18d, and preferably a plurality of satellites 18d-18f, defines the boundaries of the second coverage area 14 b. The satellites 18d-18f are also in geosynchronous orbit. However, it is understood that non-geosynchronous orbit (NGSO) satellites can also be used in place of geosynchronous orbit satellites.

Each satellite 18 includes at least one, and possibly a plurality of, Radio Frequency (RF) transponders. For example, satellite 18a is illustrated as having four transponders 18a₁-18a₄. It will be appreciated that each of the other satellites 18 illustrated can have more than one RF transponder as needed to accommodate the desired number of mobile platforms 12 operating in its coverage area. The transponder 18 provides bent-pipe communication (bent-pipe communication) between the mobile platform 12 and the ground portion 16, after which the mobile platform 12 will be referred to as an airplane. Each aircraft 12 carries a mobile system (i.e., RF transceiver) 20 having transmitting and receiving antennas and a suitable antenna control system for causing the antennas to track satellites within the coverage area over which the aircraft is flying. In a preferred form, the plurality of antennas may each be comprised of an electronically steerable phased array antenna. Each mobile system 20 may also include a plurality of separate RF receivers.

The frequency bands used for these communication links may include any radio frequency band from about 10MHz to 100 GHz. The transponders preferably consist of Ku-band transponders operating in frequency bands designated by the american communications commission (FCC) and the International Telecommunications Union (ITU) for Fixed Satellite Service (FSS) or Broadcast Satellite Service (BSS) satellites. Also, different types of transponders may be employed (i.e., each satellite need not include multiple transponders of the same type), and each transponder may operate at a different frequency. Repeater 18a₁-18a₄Each of which also includes wide area geographic coverage, Efficient Isotropic Radiated Power (EIRP), and high gain noise temperature (G/T).

Referring also to fig. 1, the ground portion 16 includes a ground-based RF transceiver (i.e., a "ground station") 22a in two-way communication with a content center 24 and a Network Operations Center (NOC) 26. The ground station 22a includes a ground-based RF transceiver. A second RF transceiver, which functions as part of a second ground station 22b, is located in a second coverage area 14b, which second coverage area 14b is used to communicate with aircraft 12 operating within the second coverage area 14 b. The second ground station 22b likewise includes a ground-based RF transceiver. Each of the ground stations 22a and 22b is in two-way communication with another ground station and also with a Network Operations Center (NOC) 26. Communication between the two ground stations 22a and 22b is effected via a ground-based communication link 25. Each of the ground stations 22a and 22b may be located anywhere within their respective coverage areas 14a and 14 b.

The content center 24 is in communication with various external data content providers, and the content center 24 controls the transmission of video and data information received by it to the ground station 22 a. The content center 24 may also be in contact with an Internet Service Provider (ISP)30, a video content source 32, and/or a Public Switched Telephone Network (PSTN) 34. Optionally, content center 24 may also be capable of communicating with one or more Virtual Private Networks (VPNs) 36. The video content source 32 can provide live television programming, for example, the United states Cable News Network (CNN)^®) And ESPN^®. The NOC26 performs a variety of functions, one of which is to coordinate the handoff of the communication link between aircraft 12 operating from one of the two coverage areas 14a or 14b to the other. The content center 24a associated with the ground station 22b in the second coverage area 14b is also preferably in communication with the ISP38, and/or the video content provider 40, the PSTN 42 and the VPN 44. An optional over-the-air telephone system 28 may also be included.

A primary advantage of the system and method 10 of the present invention is that the NOC26 is able to coordinate the handoff of communication links between aircraft 12 leaving one coverage area 14a or 14b and entering the other coverage area in any orderly manner and in a short amount of time. Typically, the handoff needs to be completed in about 1 minute, depending of course on the size of the overlap of the two coverage areas 14a or 14 b. In many cases, it is desirable that such a handoff need be completed in about 30 seconds or even less.

Referring to fig. 2, the communication link handoff process of the present invention will be described. Several optional components in fig. 1 have been omitted for simplicity. The same is true. Only two satellites 18 are involvedIllustrated as being used in each coverage area 14a and 14 b. It should be noted that an overlap region 14c exists between the coverage areas 14a and 14 b. The overlap region may vary significantly. However, when a commercial or military aircraft is flying at high speeds, typically in excess of 500mph, the handoff needs to be accomplished in an orderly and very rapid manner so that the aircraft 12 remains in substantially constant communication with one or the other ground stations 22a or 22 b. For purposes of example only, each satellite 18a, 18b, 18c, and 18d will be described as carrying a single transponder 18a, respectively₁、18b₁、18c₁And 18d₁. It should be understood, however, that any one or more of the satellites 18 may readily carry more than one transponder, depending on the amount of traffic desired within the coverage areas 14a and 14 b.

Referring to fig. 2 and 4, the aircraft 12 passes through an assigned "return link" transponder 18b carried by a satellite 18b via its mobile system 20₁Signals are sent to periodically report their location in coverage area 14 a. The term "return link" is used to denote communication from the aircraft 12 back to the ground station 22a via one of the satellites 18. The term "forward link" is used to refer to any communication from one of the ground stations 22a or 22b to the aircraft 12. The aircraft 12 also operates in coordination with the assigned forward link and return link channels when operating within a given coverage area 14a or 14 b. Preferably, the mobile system 20 of the aircraft 12 is also provided with a "public key" so that an appropriate encryption scheme may be employed in connection with the data content transmitted between the ground stations 22a, 22b and the aircraft 12.

With further reference to fig. 2 and 4, the first step in initiating a handoff of the communication link of the aircraft 12 from zone 14a to 14b includes having the ground station 22a request a handoff from the NOC26, as shown at step 50 in fig. 4. This step also includes having the ground station 22a request the required public key to decrypt the information transmitted by the ground station 22b if the data content transmitted by the transceiver 22b uses encryption. When the ground station 22a detects that the aircraft 12 has entered the overlap region 14c of the two coverage areas 14a and 14b, the ground station 22a initiates a handoff request.

Next, as shown in step 52 of FIG. 4, when the NOC26 starts the transponder 18c corresponding to satellites 18c and 18d₁And 18d₁In communication, it selects the forward link and return link assignments that the aircraft 12 will use, which also includes causing the ground station 22b to send a "service key" packaged in the platform public key to the ground station 22a via the NOC26 if encryption is used. (an explanation for inserting an additional "service key").

Once the ground station 22a receives the forward link and return link transponder assignments from the ground station 22b, the ground station 22a transmits this information to the aircraft 12 via the satellite 18a, as indicated by arrows 54a and 54b, and also as indicated by step 56 of fig. 4. The aircraft 12 then passes through a return link transponder 18b from its mobile transceiver 20 via satellite 18b₁A signal is sent to acknowledge the new allocation as shown by step 58 in fig. 4 and arrows 55a and 55 b.

Referring now to fig. 3 and 5, the steps for establishing a new communication link between the aircraft 12 and the ground station 22b of the area 14b will be described. Initially, the NOC26 begins polling for the presence of a new user (i.e., aircraft 12), as shown at step 60 of fig. 5. This polling is accomplished by a signal sent to a designated forward link transponder, in this example a transponder 18c carried by a satellite 18c₁. Arrows 62a and 62b represent the forward communication link signals.

Once the aircraft 12 receives the polling signal from the ground station 22b, it sends an acknowledgement signal back to the ground station 22b that acknowledges the new return link and forward link assignments, as shown at step 64 of fig. 5. The confirmation signal is sent via an assigned return link transponder, which in this example comprises a transponder 18d carried by a satellite 18d₁. This return link is also designated in fig. 3 by arrows 66a and 66 b.

Once the ground station 22b receives the acknowledgement from the aircraft 12, the ground station 22b sends a signal to the NOC26 via the land-based communication line 25 indicating that the handoff has been completed, as shown in step 68 of fig. 5. NOC26 then forwards the information to ground station 22 a. Subsequently, the ground station 22a sends an acknowledgement to the ground station 22b via the land-based communication line 25 and the NOC26 confirming that the ground station 22b is now in communication with the aircraft 12, as shown at step 70. Once this occurs, NOC26 adds aircraft 12 to the list of active mobile platforms in communication with ground station 22b, as shown at step 72. Finally, NOC26 removes aircraft 12 from the list of active mobile platforms in communication with ground station 22 a.

Referring now to fig. 6, a time line for the handoff sequence described with respect to fig. 2-5 is illustrated. The timeline illustrates the approximate time to complete each step of the handoff sequence described above. Requesting forward link and return link assignments from the ground station 22b of the area 14b takes approximately 2 seconds or less, as indicated by time interval 76. The steps of causing the ground station 22b to transmit the Forward Link (FL) and Return Link (RL) assignments to the ground station 22a via the land-based communication line 25, and causing the ground station 22a to transmit these assignments to the aircraft 12, comprise about 5 seconds or less, as indicated by time interval 78. In about 10 seconds or less, the aircraft 12 locks onto the forward link and return link assignments, as shown by time interval 80. The ground station 22b then receives an acknowledgement from the aircraft 12 via the assigned return link, and when the NOC26 deletes the aircraft from its list of valid mobile platforms, the ground station 22a relinquishes the communication link with the aircraft 12. This occurs in about 5 seconds or less as shown by time interval 82. Thereafter, the aircraft 12 begins transmitting its position data to the ground station 22 b. Thus, the entire handoff sequence is completed well within 30 seconds from the time the aircraft 12 enters the overlap region 14c between coverage areas 14a and 14 b.

The apparatus and method 12 of the present invention thus provides for ensuring orderly delivery of communications from a first ground station located within a first coverage area to a second ground station located within a second coverage area as a mobile platform leaves the first coverage area and enters the second coverage area. Although the foregoing example is described in terms of an aircraft, it should be understood that the handoff sequence could just as easily be used on a ship or any other mobile platform that requires travel in two or more adjacent coverage areas. Importantly, the handoff scheme provided by the present invention enables communication of the aircraft to be accomplished in a very short time frame. The acknowledgement signal transmitted by each of the ground stations 22a and 22b also ensures that the existing communication link with the aircraft 12 will not be abandoned until an RF connection is made between the aircraft and the ground station of the new coverage area into which it is entering.

Those skilled in the art can now appreciate from the foregoing description that the broad techniques of the present invention can be implemented in a variety of forms. It is also to be understood that variations of the preferred embodiments in certain embodiments herein can be readily implemented in other embodiments. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.

Claims (17)

1. A method for coordinating handoffs of communications from a mobile radio frequency transceiver on a mobile platform leaving a first coverage area to communicate via a second satellite-based transponder with a second base station located in a second coverage area from being in communication with the first satellite-based transponder and simultaneously with the first base station, the method comprising the steps of:

defining an overlap region between the first and second coverage regions;

determining, using the first base station, when the mobile platform has entered the overlap region;

obtaining a communication link allocation from the second base station using the first base station and forwarding the communication link allocation to the mobile platform via the first satellite-based repeater; and

causing the mobile platform to transmit a signal to the second base station via the second satellite-based transponder confirming receipt of the communication link allocation before the first base station releases the communication resources allocated to the mobile platform.

2. The method of claim 1, further comprising the step of:

causing the second base station to send a signal to the first base station, the signal informing the first base station that the handoff is complete.

3. The method of claim 1, further comprising the step of:

causing the mobile platform to send a signal to the first base station, the signal confirming receipt of the communication link assignment.

4. The method of claim 1, further comprising the step of:

connecting the first base station and the second base station via a land-based communication line.

5. The method of claim 1, wherein the handoff is completed in less than 60 seconds after the first base station requests the second base station to provide the communication link allocation.

6. The method of claim 1, wherein the step of the second base station providing the communication link allocation comprises providing a public key for decrypting encrypted information subsequently transmitted from the first base station.

7. A method for coordinating a handoff of a communication from a mobile radio frequency transceiver traveling on a mobile platform within a first coverage area to a second ground based transceiver deployed within a second coverage area via a second satellite transponder from communicating with the first ground based transceiver via the first satellite transponder when the mobile platform leaves the first coverage area and enters the second coverage area, the method comprising the steps of:

(a) defining the first coverage zone;

(b) defining the second coverage zone such that an overlap region exists between the first and second coverage zones;

(c) placing the first and second ground-based transceivers in communication with each other via a land-based communication line;

(d) causing the mobile platform to periodically report its position to the first ground-based transceiver;

(e) determining when the mobile platform has entered the overlap region using the first ground-based transceiver and requesting a handoff of communications with the mobile transceiver from the first ground-based transceiver to the second ground-based transceiver from the second ground-based transceiver;

(f) transmitting transponder assignment information regarding the second satellite transponder to the first ground-based transceiver using the second ground-based transceiver;

(g) transmitting the allocation information to the mobile platform via the first satellite transponder using the first ground-based transceiver;

(h) polling the mobile platform using the second ground-based transceiver to verify the presence of the mobile platform within the overlap region; and

(i) in response to the polling, using the mobile radio frequency transceiver to send an acknowledgement to the second ground-based transceiver via the second satellite transponder to acknowledge receipt of the allocation information, the mobile platform then communicating with the second ground-based transceiver instead of the first ground-based transceiver.

8. The method of claim 7, further comprising the step of:

after receiving the allocation information from the first terrestrial-based transceiver, causing the mobile transceiver to transmit a signal back to the first terrestrial-based transceiver confirming receipt of the allocation information.

9. The method of claim 7, further comprising the step of:

notifying the first ground-based transceiver that the handoff is complete using the second ground-based transceiver after receiving the acknowledgement from the mobile transceiver on the second ground-based transceiver.

10. The method of claim 9, further comprising the step of:

causing the first ground-based transceiver to send an acknowledgement signal to the second ground-based transceiver confirming that the second ground-based transceiver has taken over communication with the mobile transceiver.

11. The method of claim 7, wherein step (f) includes the step of transmitting a public key to the mobile radio frequency transceiver; and

wherein the public key enables the mobile radio frequency transceiver to decrypt encrypted data subsequently transmitted from the second ground-based transceiver via the second satellite transponder.

12. A method for coordinating handoffs of communications from a first base station to a second base station for communications of a mobile radio transceiver on a mobile platform as the mobile platform travels from a first coverage area to a second coverage area, the method comprising the steps of:

defining an overlap region between the first and second coverage regions;

causing the second base station to send a new communication link assignment to the first base station via a land-based communication line connecting the base stations when the mobile platform enters the overlap region;

forwarding, using the first base station, the new communication link allocation to the mobile radio frequency transceiver via a first satellite-based transponder that is orbiting within the first coverage area; and

causing the mobile transceiver to transmit an acknowledgement signal to the first base station via a second satellite-based transponder orbiting within the second coverage area, the acknowledgement signal confirming that the mobile platform has received the new communication link assignment.

13. The method of claim 12, further comprising the step of:

causing the mobile platform to periodically report its location to the first base station.

14. The method of claim 12, further comprising the step of:

causing the mobile radio frequency transceiver to send an acknowledgement signal to the second base station acknowledging receipt of the new communication link assignment.

15. The method of claim 14, further comprising the step of:

and after receiving the confirmation signal from the mobile radio frequency transceiver, the second base station sends a return confirmation signal to the first base station.

16. The method of claim 15, further comprising the step of:

causing said first base station to send a response acknowledgement to said second base station confirming that said handoff has been completed.

17. A system for enabling a handoff of a communication from a mobile platform communicating with a first base station in a first coverage area via a first satellite-based transponder to a second base station in a second coverage area via a second satellite-based transponder, the system comprising:

a radio frequency transceiver configured on the mobile platform;

a first base station having a radio frequency transceiver and located within the first coverage area;

a second base station having a radio frequency transceiver and located within the second coverage area;

a land-based communication line for connecting the first base station and the second base station;

a network operation center in communication with each of the base stations via the land-based communication lines, an

Wherein the network operations center coordinates handoff of communications between the mobile platform and the first base station to the second base station by:

detecting when the mobile platform enters an overlap region between the coverage areas;

causing the second base station to transmit allocation information related to a repeater to the first base station;

causing the first base station to forward the allocation information to the mobile platform via the first satellite-based repeater;

causing the second base station to poll the mobile platform;

causing the mobile platform to reply to the poll via the second satellite-based transponder to acknowledge receipt of the assignment information; and

causing the second base station to notify the first base station that a communication link has been established with the mobile platform.