1. Field of the Invention
The present invention relates to systems and methods for improving the capacity of transmit and receive systems, and in particular to a system and method for improving transmission capacity in satellite broadcast systems.
2. Description of the Related Art
Systems which transmit and receive signals via electromagnetic radiation must deliver those signals to users without interference. Limited available electromagnetic spectrum requires such systems to maximize the use of available spectrum. Often, the optimum solution to maximize spectrum use is driven by the particular application. In addition, the optimum solution may change as the delivered services change. In this case, the problem may be further complicated if maintaining compatibility with heritage devices is desirable.
For mass market broadcast systems, the base of installed receivers represents a significant investment in the system infrastructure. It is extremely important to be able to expand services to receivers at a low cost and with a minimum of disruption.
Current transmit and receive systems, such as those using satellites, often employ a principle of frequency re-use enabled by spatial isolation. A particular channel may only deliver a particular signal to a particular geographic region. A frequency can be used to transmit this signal in one region and simultaneously the same frequency can be “re-used” to transmit a different signal in a different region. No interference will occur as long as there is adequate spatial separation between the signals, i.e. signals intended for reception in one geographical area are not received in other geographical areas.
Spotbeams and frequency re-use techniques can be used to provide unique services to specific coverage regions (e.g. the entire west coast of the United States or only Los Angeles), while services common to all regions are provided via conventional satellite broadcast to multiple geographical areas (e.g. the entire continental United States (CONUS)).
Spotbeam satellite systems thus increase the total capacity transmitted on a given RF frequency channel. However, such systems reduce the capacity delivered to a given user because the total number of RF channels used for CONUS capacity is reduced when channels are assigned to spotbeam use.
There is a need for new systems that can fill this capacity shortfall. There is also a need for systems that can accommodate expanding services (e.g. through the use of spot beams) while maintaining compatibility with the legacy, non-spot beam system receivers. Further, there is a need for devices which allow new services to be implemented with only minor modifications to existing customer installations.
The present invention satisfies these needs.