Telecommunications – Carrier wave repeater or relay system – Portable or mobile repeater
Reexamination Certificate
1997-08-21
2001-03-27
Le, Thanh Cong (Department: 2684)
Telecommunications
Carrier wave repeater or relay system
Portable or mobile repeater
C455S427000, C455S428000, C455S430000, C455S432300
Reexamination Certificate
active
06208836
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a telecommunication system where remote user terminals are in receipt of access to a larger telecommunication system by means of direct access to a satellite which, in turn, is in communication with an earth station. It particularly relates to a system where, potentially, a user terminal can access more than one satellite and where, via a satellite or satellites, can access more than one earth station.
BACKGROUND
First, it is necessary to describe the general terrestrial telephone system. This is the “larger telecommunication system” mentioned above.
The terrestrial telephone system comprises the sum of all of the wire, optical, point-to-point microwave and any other means of conducting signals from one point to another via the surface of the earth, together with their associated switches, amplifiers, encoders, decoders, amplifiers and repeaters. On a national level, the network links all access points in a country. Country is linked to country via international trunk lines. Oceans are spanned by submarine cables. The terrestrial network is a transparent carrier where a signal may be introduced from an access point and routed to another, selected access point elsewhere on the surface of the earth. A subscriber can access the terrestrial system via various gateways. For example, the terrestrial system can be accessed from the public switched telephone network, a public switched data network, an integrated switched digital network, a cellular telephone system, or a satellite telephone system. Each gateway provides a plurality of different access points, which, depending upon the gateway, can range from a simple telephone to a complex data or image source. The subscriber's gateway, at the subscriber's request, commands the terrestrial system to route and carry the message from the subscriber to a selected destination. The message comes in through the subscriber's gateway, passes through the terrestrial system, and exits through the selected destination gateway to reach the access point required. Once the message path is established, two-way communication can commence. This is the way the terrestrial system works. Each gateway is connected to another single gateway. The terrestrial system is not adapted, readily, to switch, during the course of a message, between different source gateways or between different destination gateways.
Each gateway, in what is generally understood to be a telephone system, provides a plurality of access points whereby a subscriber may make or receive calls. Each access point is unique in its identify or location and definitely is unique to its particular gateway. In other words, one access point means one gateway.
Now, satellite systems provide a gateway to the terrestrial system via earth stations, capable of establishing two way contact with a satellite or satellites. In turn, the satellites can communicate with user terminals (portable handsets). The user terminals are thus put in contact with the earth stations which can act as a gateway to the terrestrial system.
Sadly, each earth station is a separate gateway. Generally, the earth stations are widely spread apart. The present invention imagines an earth station density of one, two or just a few earth stations on each continent. Thus, in general, each user terminal will see satellites which are visible only to one earth station. This satisfies the terrestrial network requirement “one access point means just one gateway”, This situation is not a problem. However, there a circumstances, for example, in the middle of the pacific ocean, in the middle of the Sahara Desert, High atop the Andes, where a user terminal may be able to see a satellite or satellites which, in turn, are visible to more than one earth station. This now breaks the rule “one access point means just one gateway”. The user terminal is an access point. Each earth station is a gateway. Now there is the situation “one access point-many gateways”. The terrestrial network is not adapted to respond to multiple gateways. Further, the signals to and from the earth station, satellites and user terminals are forever changing. What was a perfectly good satellite link a moment ago is no longer functional because the satellite has moved, the user terminal has been shielded by a building or other structure, and a host of other reasons. However, one of the other user terminal to satellite to earth station links might still work. How can the switch between earth stations be effected without confusing the operation of the terrestrial network? In particular, how can a call be established between a user terminal and the terrestrial system using the intervening medium of plural satellites and plural earth stations? The present invention seeks to provide a system and a method whereby a user terminal may gain access to the terrestrial system through a single earth station gateway even though alternative earth stations may have to be employed for contact with the user terminal.
SUMMARY OF THE INVENTION
According to one aspect, the present invention consists in a satellite communication system where a user terminal is operative to communicate with each of a plurality of satellites; where each of said plurality of satellites is operative to communicate with each of a plurality of earth stations; where said user terminal is operative to communicate through said plurality of satellites to request service; where said plurality of earth stations comprises a controller; where each of said plurality of earth stations is operative to monitor said satellites, and, in the event of receiving a request for service from said user terminal, is operative to signal said controller, indicatively of having received a request for service from said user terminal; and where said controller is operative, in response to said signal indicative of having received a request for service from said user terminal, to instruct the best placed one out of said plurality of earth stations to service said request.
The first aspect of the present invention further provides a satellite communication system wherein said controller is operative to calculate the position of said user terminal and is operative to select said best placed earth station on the basis of the position of the user terminal, the instant and future positions of the satellites, and the positions of the earth stations.
The first aspect of the present invention yet further provides a satellite communication system wherein said user terminal is operative to request service on a random access channel and wherein each of said earth stations is operative to respond to a request for service on said random access channel.
The first aspect of the present invention yet further provides a satellite communication system wherein said best placed earth station is operative, in response to instruction from said controller, to allocate a frequency for a communication channel for use by said user terminal.
The first aspect of the present invention yet further provides a satellite communication system wherein said controller is operative to instruct said best placed earth station to inform said user terminal of the frequency of said allocated communication channel and wherein said user terminal is operative, in response to said being informed by said best placed earth station to retune to said frequency of said allocated communication channel to communicate with said best placed earth station.
The first aspect of the present invention yet further provides a satellite communication system wherein said user terminal is operative to store the identity of that earth station whereat said user terminal was last registered, and wherein said user terminal is operative to convey said identity to said controller.
The first aspect of the present invention further provides a satellite communication system wherein said controller is operative to command each of said earth stations to inspect the contents of a respective visitor location register to determine whether or
Albuquerque Moraes Jose Luiz
Lu Sze-Ching
Cong Le Thanh
ICO Services Ltd.
McDermott & Will & Emery
Woldetatios Yemane
LandOfFree
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