Wireless communication systems, such as satellite communication systems, provide a means by which data, including audio, video, and various other sorts of data, may be communicated from one location to another. Information originates at a first station, such as a first ground-based station, and is transmitted to a wireless relay, such as a communication satellite. Information received by the wireless relay is retransmitted to a second station, such as a second ground-based station. In some wireless relay communication systems, either the first or second station (or both) are mounted on a craft, such as an aircraft, watercraft, or landcraft. Information may be transmitted in just one direction (e.g., from a first ground-based station to a second ground-based station only) or may be transmitted in both directions (e.g., also from the second ground-based station to the first ground-based station).
In a wireless relay communication system in which the wireless relay is a satellite, the satellite may be a geostationary satellite, in which case the satellite's orbit is synchronized to the rotation of the Earth, keeping the coverage area of the satellite essentially stationary with respect to the Earth. In other cases, the satellite is in an orbit about the Earth that causes the coverage area of the satellite to move over the surface of the Earth as the satellite traverses its orbital path.
The signals that are directed to or from a first station may be directed by using an antenna that is shaped to focus the signal into a narrow beam. Such antennas typically have a paraboloid shaped reflector to focus the beam.
In some cases, a beam may be formed electronically by adjusting the gain and phase (or time delay) of signals that are transmitted, received, or both from several elements of a phased array antenna. By properly selecting the relative phase and gain transmitted and/or received by each element of a phased array antenna, the beam may be directed. In most cases, all of the energy being transmitted from a ground-based station is intended to be received by one wireless relay. Similarly, information received by the second station is typically received from one wireless relay at a time. Therefore, it is typical that a transmit beam that is formed to transmit information to the wireless relay (whether by use of electronic beamforming or by use of an antenna with a shaped reflector) is relatively narrow to allow as much of the transmitted energy as possible to be directed to the wireless relay. Likewise, a receive beam that is formed to receive information from the wireless relay is typically narrow to gather energy from the direction of the wireless relay with minimal interference from other sources.
In many cases of interest, the signals that are transmitted from the wireless relay to the first and second stations are not directed to a single station. Rather, the wireless relay is able to transmit signals over a relatively large geographic area. For example, in one satellite communication system, a satellite may service the entire continental United States. In such a case, the satellite is said to have a satellite coverage area that includes the entire continental United States. Nonetheless, in order to increase the amount of data that may be transmitted through a satellite, the energy transmitted by the satellite is focused into beams. The beams may be directed to geographic areas on the Earth.
Reference designators (e.g., 100) are used herein to refer to aspects of the drawings. Similar or like aspects are typically shown using like numbers. A group of similar or like elements may be referred to collectively by a single reference designator (e.g., 200), while individual elements of the group may be referred to by the reference designator with an appended letter (e.g., 200a, 200b).
The figures are not intended to be exhaustive or to limit the claimed invention to the precise form disclosed. The disclosed method and apparatus may be practiced with modification and alteration, and that the invention is limited only by the claims and the equivalents thereof.