Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1999-03-19
2001-08-14
Marcelo, Melvin (Department: 2733)
Multiplex communications
Communication over free space
Repeater
C370S319000, C455S013300
Reexamination Certificate
active
06275479
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to satellite communication systems and, in particular, to a communication satellite with communication signal amplifiers that are multiplexed to transmit simultaneously communication signals to different geographic regions and/or communication signal receivers that are multiplexed to receive simultaneously communication signals for different geographic regions.
BACKGROUND AND SUMMARY OF THE INVENTION
A conventional communication satellite in geosynchronous orbit has a communication signal receiving system and a communication signal transmitting system. The receiving system includes a satellite receiving reflector that receives multiple communication uplink signals from one or more terrestrial transmitting stations and concentrates the signals at corresponding ones of multiple receiving horns, which pass the communication uplink signals through an input filter system to a satellite low noise amplifier (LNA) and downconverter system.
A communication multiplexer system receives the low noise amplified and frequency converted uplink signals and channelizes and routes the signals to the transmitting system for transmission to terrestrial recipient stations. The transmitting system typically includes an amplifier system, which may include traveling wave tube (TWT) amplifiers, to provide high reliability, high power output amplification. The outputs of the high power amplifier system are connected through an output filter system to one or more transmit horns for transmission as downlink signals via a satellite transmit reflector. Communication satellite systems have limited bandwidth and power for transmitting downlink communication signals. The amount of effective bandwidth in a communication satellite system directly corresponds to the amount of traffic that can be carried (i.e., the satellite's capacity). Typically, satellite downlink communications are transmitted over a wide area, which may be covered by an array of narrow zone or “spot” beams to make maximal use of the physical or actual bandwidth that is allocated. This is called frequency re-use and it allows the frequency band of the actual bandwidth to be used multiple times and thereby increase the effective bandwidth for satellite communications.
Each spot beam is associated with a geographic region called a cell. Each spot beam typically includes two communication signals, one each of two opposite polarizations (e.g., horizontal/vertical or right-/left-circular). The satellite includes a TWT amplifiers for each communication signal for each cell. As the number cells increases, the number of TWT amplifiers required on the satellite increases at a 2:1 ratio (i.e., two TWT amplifiers for each cell). Due to the power, size, and weight requirements of TWT amplifiers, practicable satellites can carry only a limited number of TWT amplifiers. As a consequence, the one-to-one relationship between communication signal (e.g., TWT) amplifiers and transmitted can severely limit the total capacity of the system. Moreover, the amplification power of each TWT amplifier is limited to practical levels and cannot be increased arbitrarily.
In accordance with the present invention, therefore, a communication satellite transmitting system includes communication signal amplifiers (e.g., traveling wave tube (TWT) amplifiers) with outputs that are multiplexed among multiple transmit horns, each of which transmits a downlink communication signal to a corresponding geographic cell.
In one implementation, each TWT amplifier is multiplexed among at least three transmit horns. With the communication signal amplifiers employing frequency re-use, such as if each amplifier employs common frequency sub-bands for each of multiple communication signals, the 3-to-1 multiplexing allows signals to be transmitted to the geographic cells without any immediately adjacent cells corresponding to the same frequency sub-band. This reduces interference and cross-talk between the signals transmitted to adjacent cells.
As another aspect of this invention, amplification power can be allocated dynamically between the communication signals as they are transmitted to compensate for signal degradation that can be caused by, for example, rain or communication channel traffic. The amplification power can be allocated either between the communication signals amplified by a single amplifier or between the communication signals amplified by different amplifiers. In accordance with the allocation of amplification power, amplification power may be allocated preferentially to cells in regions that are characterized as receiving relatively heavier rains.
As another aspect of the present invention, a communication satellite receiving system includes communication receivers with inputs that are multiplexed among multiple receive horns, each of which receives an uplink communication signal for a corresponding geographic cell. In one implementation, each receiver is multiplexed among at least three receive horns.
The multiplexing of TWT amplifiers and receivers can significantly reduce the numbers TWT amplifiers and receivers required for a given number of geographic cells. This has the advantage of reducing the cost and weight of a satellite and allowing the satellite to provide communications to a greater number of cells. In some prior communication satellite designs, the number of cells to which a satellite could provide communications was limited by the size and weight of the required TWT amplifiers. The multiplexing provided by the present invention can increase the overall capacity of a satellite while simultaneously reducing the cost to manufacture and launch it.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.
REFERENCES:
patent: 4599619 (1986-07-01), Keigler et al.
patent: 4706239 (1987-11-01), Ito et al.
patent: 5033108 (1991-07-01), Lockood
patent: 5924015 (1999-07-01), Garrison et al.
Snell William L.
Thompson Mark D.
Ipsolon LLP
Marcelo Melvin
Spacecode LLC
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