Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-04-12
2002-05-14
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S429000, C455S446000
Reexamination Certificate
active
06389289
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
This invention relates generally to mobile satellite communications systems and, more particularly, to a service area modeling system that supports geographically defined satellite communications service and a method of using the modeling system for rapid identification of the service area in which a mobile user is located.
(b) Description of Related Art
In terrestrial cellular communications systems, a service area is defined as a geographical region within which a communications service provider has made available particular mobile calling services and charges particular billing rates. All mobile callers located within a given service area are treated equally in terms of billing rates (according to subscription) and available services, so it is necessary to determine the service area within which a mobile caller is located in order to be able to properly process a call initiated by the caller.
In the terrestrial cellular communications environment, each stationary cellular tower provides communication services to a geographic region referred to as a cell which is typically about one or two kilometers in diameter and each tower transmits calls at a range of frequencies allocated exclusively to the tower. In addition, each tower is exclusively associated with the service area in which the tower is geographically located such that each tower provides services to the cell in accordance with the service area in which the tower is located. Because each tower transmits at a unique range of frequencies, the transmission frequency of a call may be used to identify the tower that is transmitting the call and, due to the one-to-one correspondence between towers and service areas, once the tower transmitting the call has been identified, the service area is also known. Thereafter, an identifier (“ID”) corresponding to the identified service area is transmitted to a switch that connects the cellular communications network to the public switched telephone network. The switch is programmed to provide the services and billing rates defined for that service area ID so that the call may be properly processed.
This system of call processing in which the call transmission frequency is used to identify the transmitting tower which is then used to identify the service area in which the user is located so that the call may processed accordingly works well in the terrestrial cellular communications environment, in part, because the towers are stationary and the cells (transmitting ranges of towers) are relatively small in size. However, this same call processing system is not suited for the satellite communications environment. In particular, in the satellite environment, the counterpart to the stationary towers of the cellular environment include satellite mounted spotbeam antennas. These spotbeam antennas project ago spotbeams onto the earth and provide communication service to all system users located within the area onto which the spotbeam projects. Thus, the spotbeam may be considered, in some ways, the satellite environment equivalent to the cell of the cellular environment. However, spotbeams project onto geographic regions that are typically on the order of hundreds of kilometers, and, therefore, may encompass a plurality of service areas. As a result, there is not a one-to-one correspondence between spotbeams and service areas. Therefore, in the satellite environment, knowing the identity of the satellite spotbeam transmitting the communications service, e.g., the call, does not enable the identification of a single service area in the cellular environment. In addition, in a non-geo stationary satellite system, low to medium earth orbit satellites are orbiting the earth at rapid speeds so that the spotbeams projected onto the earth's surface by the satellite are also in motion. Thus, the geographic region onto which a satellite cell is projected is changing as the satellite moves, thereby making it impossible to correlate a spotbeam with a single geographically defined service area.
Further, although some satellite systems are equipped to approximate the location of a subscriber unit, the approximation is typically subject to error. This error may span a geographical region that overlaps several service areas and thus is not useful in pinpointing the service area in which the mobile caller is located. In addition, service areas typically have complex geometric shapes as they are often configured to coincide with national or other geopolitical borders so that this error is even less tolerable when the caller is located near an intricate border.
In systems in which the longitudinal and latitudinal coordinates of the subscriber unit can be determined with a satisfactory degree of accuracy, the system could potentially determine the service area of the subscriber unit by identifying the service area corresponding to the coordinate position of the mobile subscriber. However, such a method would require a table in which each of the infinite number of coordinate points on the surface of the earth are associated with a service area. Such an infinitely long list cannot be compiled and would, at any rate, be inefficient and time consuming to search.
Another difficulty is encountered when attempting to model service areas in the satellite communications environment. In particular, geographically defined service areas modeled on the surface of the earth in the satellite environment are three dimensional due to the quasi-spherical shape of the earth. As a result, complex and time consuming three dimensional geometry is required to determine the location of the caller relative to the three dimensional service areas.
Although geographically defined service areas are not an inherent property of mobile satellite communications systems, they are well established in the terrestrial cellular communications system. As a result, existing terrestrial architecture includes equipment adapted to process calls using the geographically defined service areas. In particular, once the service area has been identified for an on-going mobile telephone call, an ID corresponding to the identified service area is transmitted to a mobile switching center. In response, the switch, which has been programmed with the services and billing rates to be provided for the service area, processes the call accordingly. The mobile switching centers used to perform this service area-dependent call processing are complex and costly. Therefore, it is desirable that service areas in a satellite communications system be defined on a regional basis so that the mobile switching centers and other equipment used to process calls in the terrestrial cellular invention may also be used to process calls originating from the satellite environment with little modification.
Thus, there is a need for an improved method of determining, in a satellite communications system, the service area within which a mobile user is located. Preferably, such a method would be efficient, rapid and compatible with the existing geographically defined service area system and associated equipment used in terrestrial cellular communications systems.
SUMMARY OF THE INVENTION
The present invention is embodied in a method of mapping a plurality of geographic regions on the surface of the earth, using the mapping to determine a target geographic region within which a target is located and then providing a service to the target that is associated with the target geographic region. Preferably, the disclosed method may be implemented in a satellite communication system to provide a satellite communication service to a subscriber unit located in a geographical region where a set of previously determined services are readily available such as a particular service area. The method is efficient, rapid and compatible with existing geographically defined service areas systems and associated equipment used in terrestrial cellular communication systems.
In accordance with one aspect of the invention, a method for mapping a plural
Fry John
Mehrotra Asha
Mohebbi Matthew
Voce Daniel A.
Hughes Electronics Corporation
Sales Michael W.
Sobutka Philip J.
Trost William
Whelan John T.
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