Data processing: measuring – calibrating – or testing – Measurement system – Measured signal processing
Reexamination Certificate
1998-10-13
2001-03-20
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Measured signal processing
C702S189000, C370S364000, C375S260000
Reexamination Certificate
active
06205410
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of discrete multi-tone (DMT) data communication, and, more particularly, to the field of optimization of the signal-to-noise ratio margin of DMT channels.
BACKGROUND OF THE INVENTION
In data communications using discrete mulitone (DMT) technology, a serial data bit stream to be communicated is distributed among multiple channels and transmitted in parallel from a transmitting modem to a receiving modem. These channels are contained in bandwidth of approximately 1.104 megahertz. Each channel has a bandwidth of 4 kilohertz. The center frequencies of each band are separated by 4.3125 kilohertz.
It is often the case that interference with each channel may vary depending on the precise frequency band occupied by the particular channel. Some channels may experience little or no interference, while the interference on others may be so great as to make that particular channel unusable.
Because interference with individual channels may vary, conventional DMT modems establish a bit loading configuration in which the bit rate of individual channels varies based upon the signal-to-noise ratio of each channel. In order to determine the individual bit rates for each channel, the signal-to-noise ratio for each channel is ascertained. This is typically accomplished at the start up of data communication by transmitting a tone at the center frequency of each channel from the transmitting modem and then measuring the signal-to-noise ratio for each channel at the receiving modem.
After the signal-to-noise ratio is measured for each channel, it is a typical practice to subtract a common margin, typically 6 dB, from the measured signal-to-noise ratio of each channel to obtain a transmission signal-to-noise ratio at which to achieve a bit error rate of approximately 10
−7
. An appropriate bit rate is assigned to the channel based upon the transmission signal-to-noise ratio obtained.
Such conventional approaches suffer from the subtraction of a common margin from all of the measured signal-to-noise ratios of each channel. It is automatically assumed that the common 6 dB margin is appropriate to compensate for the variation in the signal-to-noise ratio for each channel. However, some channels may experience greater variation in the signal-to-noise ratio than others. Thus, in some cases the common margin may be too great, resulting in a bit rate that is unnecessarily slow. In other cases the common margin may be too small, resulting in a bit rate that is too high which translates into an unnecessarily high bit error rate.
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide for a DMT modem which establishes an optimum margin for each DMT channel. In furtherance of this objective, the present invention entails a discrete multi-tone (DMT) transceiver which comprises a processor and a memory. Stored on the memory is operating logic which directs the function of the processor. The operating logic includes bit allocation logic and signal-to-noise (SNR) variation logic. The SNR variation logic determines an variation in the signal-to-noise ratio for each channel. The bit loading logic then determines a bit loading configuration based upon the variation in the signal-to-noise ratio ascertained by the SNR variation logic. The SNR variation logic preferably includes logic to determine the variation in the signal-to-noise ratio by means of statistical analysis, however, other approaches to determining the variation in the signal-to-noise ratio may be employed.
In accordance with another aspect of the present invention, a method is provided for establishing the bit loading configuration of a discrete multi-tone (DMT) transceiver comprising the steps of determining a variation in a signal-to-noise ratio for each of the channels, and, determining bit loading configuration for each of the channels based on the a variation in the signal-to-noise ratio for each of the channels.
Other features and advantages of the present invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional features and advantages be included herein within the scope of he present invention, as defined by the claims.
REFERENCES:
patent: 5521906 (1996-05-01), Grube et al.
patent: 5619505 (1997-04-01), Grube et al.
patent: 6073179 (2000-06-01), Liu et al.
patent: 6075821 (2000-06-01), Kao et al.
patent: 6084906 (2000-07-01), Kao et al.
patent: 6094459 (2000-07-01), Kao et al.
Globespan Semiconductor Inc.
Hoff Marc S.
Thomas Kayden Horstemeyer & Risley
Vo Hien
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