Telecommunications – Transmitter – With electrical protection of transmitter circuit or operator
Reexamination Certificate
1998-09-18
2001-08-07
Trost, William (Department: 2683)
Telecommunications
Transmitter
With electrical protection of transmitter circuit or operator
C455S026100, C455S067150, C455S092000, C455S013400, C455S405000, C455S427000, C455S522000, C340S600000
Reexamination Certificate
active
06272325
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to communications systems and, in particular, to satellite communications systems wherein a plurality of user terminals are in bi-directional wireless communication with a terrestrial communications network via a gateway and at least one satellite.
BACKGROUND OF THE INVENTION
Existing regulations specify a total amount of exposure to RF energy, above a threshold power density, that a user of a wireless terminal can be exposed to within a predetermined interval of time (e.g., averaged over one half hour).
One technique to determine the user's exposure would be to monitor the radiated power within the user's terminal and average over time the radiated power that exceeds the threshold. If the threshold level is exceeded within the specified interval of time, the user terminal could be rendered inoperable, thereby removing the user from the transmitted RF energy.
However, this approach could result in user terminals being modified or manufactured so as to defeat this function. Although the convenience to the user of always having the terminal available for use could be assured, the user may be exposed to relatively high levels of RF energy. Furthermore, a user terminal that is manufactured to operate with a specified allowable average power density could be rendered obsolete if the threshold level is later changed. As such, providing this function in the user terminal has a number of drawbacks.
Some user terminals are capable of operating with both a wireless terrestrial communications system as well as with the satellite communications system. In this case it can be appreciated that the user may experience, during a given period of time, different amounts of RF exposure in each system. These exposures may be cumulative if they occur within some predetermined period of time, such as when the user makes a call on the terrestrial system and then makes a call using the satellite system. However, at present there is no known mechanism for accounting for the user's RF exposure in each system.
OBJECTS OF THE INVENTION
It is a first object of this invention to provide an improved method and system for remotely monitoring a user's exposure to transmitted RF energy, and for terminating a connection or call if the user's exposure will exceed a predetermined threshold limit.
It is a further object of this invention to provide an improved method and system for refusing service to a user terminal identified as one which may cause a user to experience exposure to RF energy that would exceed a specified threshold amount.
It is a another object of this invention to provide an improved method and system for accounting for a user's RF exposure when using two or more wireless communications systems, such as a terrestrial cellular system and a satellite-based system.
It is a another object of this invention to provide an improved method and system for accounting for a user's RF exposure and for also actively controlling a selection of a user's communication link parameters, such as an assigned frequency channel, time slot, and/or data rate, so as to reduce the user's RF exposure.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by a method wherein a system gateway (GW) determines, from closed loop power control information, a power density at an antenna of a user terminal. The GW also maintains a record of a duration of time that the power density exceeds a specified threshold. The GW determines if an averaged transmitted power density associated with the antenna of the user terminal will equal or exceed at least one of a predetermined threshold level, within a specified period of time, or an absolute threshold level. If the GW determines that a threshold will probably be exceeded if the call connection is maintained, the GW terminates the connection prior to a time that the user terminal averaged transmitted power density level equals or exceeds the predetermined or absolute threshold level.
In accordance with an aspect of this invention, when making the threshold determination the GW also considers the cumulative RF exposure of the user terminal in at least one another wireless communications system.
If it becomes apparent that an over-threshold amount of exposure will occur, the GW preferably informs the user via a tone or a visual indicator that a current connection or call will be terminated. Thereafter, and assuming that the user is still connected, the GW automatically terminates the connection, and refuses to service the user again until after enough time has elapsed so that the exposure threshold will not be immediately exceeded. Provisions are made for allowing predetermined types of calls (e.g., emergency calls) to be made during the cutoff period.
It within the scope of the invention to perform the power density monitoring function also within the user terminal. In this case information may be transferred to the GW over a return link, and majority voting or some other technique can be employed by the GW before terminating the connection. In this case the power density determination made at the GW has priority over that made in the user terminal to prevent a user terminal from intentionally or inadvertently defeating the power density monitoring function. The monitoring function may also be performed in whole or in part within the satellite.
Prior to terminating a call or refusing to service the user terminal, and in accordance with a further aspect of this invention, the GW may take steps to reduce the user's RF exposure by actively modifying one or more user terminal RF power influencing parameters, such as one or more of the transmitted data rate, frequency channel assignment (in a FDMA system), and/or time slot assignment (in a TDMA system).
This invention thus pertains, in a preferred but not limiting embodiment, to a satellite communication system that includes at least one earth orbiting satellite, at least one terrestrially located user terminal, and at least one terrestrially located gateway. The gateway includes circuits and the like for conveying a bidirectional wireless communication connection between a terrestrial communications system and the at least one user terminal through the at least one satellite. At least one of the at least one gateway, the at least one satellite, and the at least one user terminal includes circuitry and the like for determining, at least during a connection, if a cumulative RF exposure of a user associated with the terminal, when operating in a plurality of wireless communications systems, will equal or exceed a threshold level. Also provided is a mechanism for controlling the wireless connection to prevent an RF exposure of the user from equaling or exceeding the threshold level.
In accordance with an aspect of this invention a method is disclosed for operating a communications system. The method includes steps of establishing a wireless connection with a user terminal through a forward link and a return link; determining, during the connection, if an averaged transmitted power density associated with an antenna of the user terminal will equal or exceed, relative to a user of the terminal, at least one of a predetermined threshold level, within a specified unit of time, and an absolute threshold level; and taking action to reduce or eliminate the transmitted power of the user terminal at a time prior to or when the averaged transmitted power density level equals or exceeds the threshold level. The step of determining includes a step of considering an amount of power radiated by the user terminal in a satellite communications system as well as in a terrestrial communications system.
The step of determining includes a preliminary step of receiving information from another communications system for indicating an amount of power radiated by the user terminal in the other communications system, and may weight this information differently than the information derived in the communi
Monte Paul A
Sites Michael J
Wiedeman Robert A
Globalstar L.P.
Ohlandt Greeley Ruggiero & Perle L.L.P.
Sobutka Philip J.
Trost William
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