Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-02-11
2001-11-06
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S428000, C455S430000, C455S433000, C455S445000, C455S450000
Reexamination Certificate
active
06314290
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a system and method for implementing a single-hop terminal-to-terminal call in a mobile satellite system and maintaining a signaling path between the mobile terminals and a gateway station during the terminal-to-terminal call.
BACKGROUND OF THE INVENTION
A number of systems exist which provide both mobile terrestrial communication (ie., cellular communication) and mobile satellite communication between terminals. Such a system is hereinafter referred to as an MSAT system. Satellite communication between two terminals is typically implemented via a double-hop, that is, two signal paths. One signal path is from an originating terminal to a ground station via a satellite, and the other signal path is from the ground station to a destination terminal via the satellite. A single-hop, one-way propagation delay can occur which can be on the order of 270 milliseconds (ms). Thus, in a double-hop MSAT system, the propagation delay can be on the order of 540 ms, which can create unacceptable interruptions during calls, particularly voice calls.
A number of single-hop MSAT systems exist; however, these single-hop systems are disadvantageous because signaling paths are terminated once a single-hop satellite signal path is established for a call between two terminals. Without a signaling path during the terminal-to-terminal (TtT) call, no services such as ciphering key exchanges for encryption can be offered within the MSAT system. Thus, callers cannot be guaranteed their privacy during calls within the single-hop MSAT system. A need therefore exists for a single-hop MSAT system which maintains a signaling path during a TtT call for services such ciphering for privacy, among others.
SUMMARY OF THE INVENTION
In accordance with an aspect of the present invention, an MSAT system
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is provided in which single-hop TtT calls can be established. A signaling path is maintained between both the originating terminal and the destination terminal and a gateway station. Thus, a mobile switching center (MSC) can send messages to a terminal via the signaling path when the voice path from the MSC to the terminal is blocked by the satellite in single-hop mode.
In accordance with another aspect of the present invention, the switch interface between gateway station controllers in a gateway station and a GSM-based mobile switching center (DSC) of an MSAT system uses minimal modifications to support single-hop satellite communications with signaling during a TtT call.
In accordance with another aspect of the present invention, an originating terminal and a destination terminal establish radio frequency communication links with at least one gateway station for call establishment. The gateway station assigns satellite channels for communication between each terminal and its corresponding gateway station and allocates satellite channels for a direct satellite link between the terminals and for signaling between each terminal and its corresponding gateway station during a single-hop terminal-to-terminal call.
In accordance with yet another aspect of the present invention, when the originating gateway station differs from the destination gateway station, the originating terminal is reregistered with the destination gateway station. The satellite channels allocated to the originating terminal for the call path and signaling during the terminal-to-terminal call are provided to the destination gateway station.
In accordance with yet another aspect of the claimed invention, a verification signal is transmitted between the terminals via the direct satellite link to verify that it has been established. The verification signal is formatted such that the gateway stations disregard the signal.
In accordance with still yet another aspect of the claimed invention, each gateway station has a traffic control subsystem for managing the allocation of satellite resources to the gateway station. The traffic control subsystems at different gateway stations communicate with each other via an intranetwork communication system. During a terminal-to-terminal call, a destination gateway station can send signals to the originating terminal via the intranetwork communication system and the satellite channels allocated to the originating terminal for signaling.
In accordance with another aspect of the present invention, the system can proceed to implement a double-hop call between the terminals via earlier assigned satellite channels when the direct satellite communication link or associated signaling path fails.
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Joshi Chandra
Noerpel Anthony
Roos Dave
Su Chi-Jiun
Hughes Electronics Corporation
Hunter Daniel
Sales Michael W.
Whelan John T.
Woldetatios Yemane
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