Pulse or digital communications – Transceivers – Modems
Reexamination Certificate
1999-12-06
2002-05-14
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Transceivers
Modems
C375S225000, C375S227000, C370S252000, C370S465000, C455S069000
Reexamination Certificate
active
06389065
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to XDSL communication systems and, more particularly, to a rate adaptive XDSL communication system and method.
BACKGROUND OF THE INVENTION
In XDSL communication systems, there can be provisions made for adapting the rate at which data is communicated across the XDSL link. Rate Adaptive DSL (RADSL) is one example of such a system. In general, the data rate across an XDSL link is determined by the baud rate and the number of bits per symbol, or constellation. Thus, the data rate can be adjusted by adjusting either the baud rate or the size of the constellation.
Typically, conventional XDSL chip sets implement rate adaptive algorithms that provide a choice of rate based solely upon the signal-to-noise ratio (SNR). However, these schemes typically take too long to functions. Further, they often do not work because a given signal-to-noise ratio does not guarantee the desired performance (e.g., 10
−7
bit error rate) at the desired rate. This is true in part because the chip set is assuming performance based upon relatively constant noise, when, in fact, real world physical connections do not typically experience constant patterns of noise. Thus, the conventional rate adaptive algorithms are incorrect on some types of noise models and do not accurately select the appropriate rate.
SUMMARY OF THE INVENTION
In accordance with the present invention, a rate adaptive XDSL communication system and method are provided that provide significant advantages over conventional XDSL communication systems.
According to one aspect of the present invention, a rate adaptive digital subscriber line (XDSL) communication system and method train an XDSL link for XDSL equipment at a data rate set by a baud rate and a constellation size. Actual operating characteristics of the XDSL equipment are then obtained from parameters for the trained XDSL link. One or more rate adaptive data tables storing empirical data for performance of the XDSL equipment are accessed. Then, it is determined whether the trained data rate will provide a desired bit error rate using the actual operating characteristics and the empirical data from the accessed one or more of the rate adaptive data tables. In one embodiment, if the trained data rate will not provide the desired bit error rate, a new data rate is selected using the empirical data and the actual operating characteristics. Then, the XDSL link is trained using the new data rate, and the process is repeated. Further, in one embodiment, the actual operating characteristics used comprise the actual receiver gain and signal-to-noise ratio, and the empirical data comprises specified receiver gains, signal-to-noise ratios, baud rates and constellation sizes used to achieve a desired bit error rate.
It is a technical advantage of the present invention to use receiver gain and signal-to-noise ratio (SNR) together to choose a data rate. This selection makes the communication immune to characteristics of the noise because, for a given signal to noise ratio and receiver gain, the performance of the XDSL transceiver can be empirically determined and stored in rate adaptive data tables.
It is another technical advantage of the present invention that the rate adaptive data tables can be derived from a whole end-to-end system with simulated noise. This means that the performance of the system is known for a given signal-to-noise ratio and receiver gain and that time consuming bit error rate tests based upon a known bit test pattern do not have to be used.
It is a further technical advantage of the present invention to allow the communication system to verify the current data transfer rate and to use the rate adaptive data tables to estimate the actual signal-to-noise ratio margin and to modify the amount of margin available.
Additional technical advantage of the present invention should be apparent from the drawings and specification.
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Baker & Botts L.L.P.
Cisco Technology Inc.
Le Amanda T.
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