Method and apparatus for on-board testing of a communication...

Telecommunications – Receiver or analog modulated signal frequency converter – Measuring or testing of receiver

Reexamination Certificate

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C455S067700, C375S224000

Reexamination Certificate

active

06201953

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates generally to earth-orbiting communication satellites and, more particularly, to techniques for testing communication satellites. Typically, communication satellites have multiple independent communication channels, each of which is subject to the introduction of data errors due to faulty components or unwanted signals impressed on the channel. There are basically two ways to test a communication channel: by measuring bit error rates when the channel is carrying selected digital data, and by measuring the channel's response to the introduction of an analog signal.
Prior to this invention, analog or frequency domain testing has been performed by electrical ground support equipment (EGSE) prior to launch of the satellite, and has imposed a significant burden in terms of additional cost and weight. EGSE testing has required the use of multiple test points in the communication system, to make electrical connection with each communication channel. For example, in a 64-channel satellite, an equal number of couplers, attenuators and associated cables are required. The nature of the integration and test procedure is such that, as a practical matter, these additional components must be carried with the satellite into orbit, even though they are only used during testing on the ground. Although bit error rate testing may be performed while the satellite is in orbit, bit error rate testing does not provide a complete and accurate measure of channel quality and cannot reliably predict communication channel errors.
Accordingly, there is a significant need for a technique that allows frequency domain testing of communication satellites, preferably while the satellites are in orbit. The present invention satisfies this need.
SUMMARY OF THE INVENTION
The present invention resides in a method and apparatus for testing communication satellites in orbit or on the ground, but without a significant penalty in terms of additional weight and cost. Briefly, and in general terms, the apparatus of the invention comprises the following onboard components: a processor used for a variety of satellite control and communication functions; a memory for storing a testing module for loading and execution in the processor; a synthesizer for generating test signals under control of the processor when executing the testing module; and a switch controllable by the processor to connect a test signal from the synthesizer to a selected receiver channel to be tested. The selected receiver channel includes an amplifier and an analog-to-digital converter for converting signals received by the receiver channel to digital form for processing by the processor, and the testing module includes a signal analysis sub-module, for analyzing the test signal applied to the receiver channel under test after the test signal has passed through the receiver channel components. Using the apparatus of the invention, each receiver channel in turn can be tested using onboard components.
More specifically, in accordance with one aspect of the invention, the synthesizer is controlled to generate a signal at a frequency normally handled by the receiver channel under test; and the signal analysis sub-module performs a fast Fourier transform (FFT) function to analyze the receiver channel under test in the frequency domain.
In accordance with a related aspect of the invention, the apparatus is also capable of testing a plurality of transmitter channels in the same communication satellite. For this purpose, the apparatus further comprises means for coupling a test signal from the synthesizer to a selected transmitter channel, and means for coupling output from the selected transmitter channel to the processor, for analysis of transmitter channel performance using the signal analysis sub-module.
The invention may also be defined in terms of a novel method for onboard testing of a communication satellite having a plurality of receiver channels. The method comprises the following steps performed on the satellite: storing a testing module in an onboard memory; loading the testing module into a processor used primarily for a variety of satellite control and communication functions; executing the testing module functions in the processor; generating test signals in an onboard synthesizer under control of the processor when executing the testing module; and connecting a test signal generated in the synthesizer to a selected receiver channel to be tested, through a switch controlled by the processor. The selected receiver channel includes an amplifier and an analog-to-digital converter for converting signals received by the receiver channel to digital form for processing by the processor. The method further includes the steps of analyzing, in a signal analysis sub-module, the test signal applied to the receiver channel under test after the test signal has passed through the receiver channel components; and testing each receiver channel in turn, using the foregoing steps of generating test signals, connecting them to selected receivers in turn, and analyzing the test signals after processing by the receiver channels.
More specifically, the step of generating test signals in the synthesizer includes generating a signal at a frequency normally handled by the receiver channel under test; and the step of analyzing in the signal analysis sub-module includes performing a fast Fourier transform (FFT) function to analyze the receiver channel under test in the frequency domain.
The method may also comprise the steps of coupling a test signal from the synthesizer to a selected transmitter channel of the communication satellite; coupling output from the selected transmitter channel to the processor; and analyzing the performance of the selected transmitter channel performance using the signal analysis sub-module.
It will be appreciated from the foregoing that the present invention represents a significant advance in the field of testing communication satellites. In particular, the invention provides a convenient and reliable technique for testing communication satellites in the frequency domain, both on the ground and while in orbit, with little incremental cost or weight penalty. Other aspects and advantages of the invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 5937004 (1999-08-01), Fasulo, II et al.
patent: 6021314 (2000-02-01), Magana et al.

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