Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1999-06-25
2001-11-13
Jung, Min (Department: 2663)
Multiplex communications
Communication over free space
Repeater
C370S535000
Reexamination Certificate
active
06317420
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to low-Earth orbit (LEO) satellite communication systems. More specifically, the present invention relates to using spatial multiplexing to increase the bandwidth of the communication links between the satellites and the Earth stations in such a system.
II. Related Art
A typical satellite-based communication system comprises at least one terrestrial base station (referred to as a “gateway”), at least one user terminal (for example, a mobile or hand-held portable telephone), and at least one satellite for relaying communication signals between the gateway and the user terminal. The gateway provides links from a user terminal to other user terminals or communication systems, such as a terrestrial telephone system.
One of the limitations imposed on satellite communications systems is the allocated frequency bandwidth. Various governmental agencies and standards associations allocate bandwidth in the total signal spectrum taking into consideration various political and technical constraints. One type of allocation granted for use in Low Earth Orbit satellite based communications systems is granted by the ITU (International Telecommunications Union) and uses a 200 MHz bandwidth. Given the fixed allocation constraints and an extreme unlikelihood of obtaining additional bandwidth, it is desirable to maximize the capacity of this bandwidth allocation, to thereby maximize the number of users who can utilize a given system at any time.
Conventional satellites use one large beam or beamforming antennas on the communication links between the gateway and the satellite (referred to as a “feeder link”) and between the satellite and the user terminal (referred to as the “user link”). Typically, a single feeder link is used so that a single path couples each satellite with all gateways within view of the satellite. On the user link side, multiple links divide the coverage area of the satellite (referred to as a “footprint”) into a plurality of geographic regions (referred to as “cells”). Each cell is illuminated by one of the user link beams. Each beam uses the full bandwidth allocated to the user link. The resulting bandwidth available for user terminal communication is given by the product of the user link bandwidth and the number of user link beams.
As the demand for such satellite-based communication services increases, so must the capacity of such systems. Given that user bandwidth allocations are at present inflexible, one way to increase the capacity of the user link is simply to increase the number of user link beams. However, any increase in user link capacity must be accompanied by an increase in the capacity of the communication link between the satellite and the gateways.
It is, therefore, desirable to provide a system and method for increasing the capacity of a satellite communications system in which the bandwidth cannot be increased.
SUMMARY OF THE INVENTION
The present invention is suitable for use in a communication system having a plurality of gateways and a satellite that is coupled to the gateways by feeder links and to user terminals by a user link, where the satellite provides a plurality of user beams on the user link.
In one aspect, the present invention provides an apparatus comprising a beamforming antenna that forms a plurality of feeder beams from signals received from the gateways, each feeder beam illuminating one of the gateways and including a plurality of frequency division multiple access (FDMA) channels; a plurality of demultiplexers that separate each of the feeder beams into the FDMA channels; means for combining a first one of the FDMA channels with a second one of the FDMA channels, the first and second FDMA channels comprising signals corresponding to user terminals illuminated by a specific user beam, to produce a user beam signal; and a beamforming user link antenna that forms the specific user beam using the user beam signal.
The user beam signal includes a plurality of frequency bands, and the means for combining comprises a controller that allocates the first and second FDMA channels to the specific user beam and to first and second ones of the user beam signal frequency bands; a first frequency converter that converts the first FDMA channel from the frequency band on which the first FDMA channel was received to the first one of the user beam signal frequency bands; a second frequency converter that converts the second FDMA channel from the frequency band on which the second FDMA channel was received to the second one of the user beam signal frequency bands; a multiplexer that multiplexes the frequency-converted first and second FDMA channels to produce the user beam signal; and a switch that routes the frequency-converted first and second FDMA channels to the multiplexer.
In a further aspect, the present invention provides an apparatus comprising a user link beamforming antenna that forms a plurality of user beams from signals received from the user terminals, each user beam including a plurality of FDMA channels; a plurality of demultiplexers that separate each of the user beams into the FDMA channels; means for combining a first one of the FDMA channels with a second one of the FDMA channels, the first and second FDMA channels comprising signals corresponding to a gateway illuminated by a specific feeder beam, to produce a feeder beam signal; and a user link beamforming antenna that forms the specific feeder beam using the feeder beam signal.
The feeder beam signal includes a plurality of frequency bands, and the means for combining comprises a controller that allocates the first and second FDMA channels to the specific feeder beam and to the first and second ones of the feeder beam signal frequency bands; a first frequency converter that converts the first FDMA channel from the frequency band on which the first FDMA channel was received to the first one of the feeder beam signal frequency bands; a second frequency converter that converts the second FDMA channel from the frequency band on which the second FDMA channel was received to the second one of the feeder beam signal frequency bands; a multiplexer that multiplexes the frequency-converted first and second FDMA channels to produce the feeder beam signal; and a switch that routes the first FDMA channel to the first frequency converter and that routes the second FDMA channel to the second frequency converter.
One advantage of the present invention is that it provides for increased capacity on the feeder link of a communication satellite.
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patent: 4926422 (1990-05-01), Alaria et al.
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patent: 5835487 (1998-11-01), Campanella
patent: 5920284 (1999-07-01), Victor
patent: 6052085 (2000-04-01), Hanson et al.
Jung Min
Ogrod Gregory D.
Qualcomm Inc.
Wadsworth Philip R.
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