Patent ID: 6310909
Filing Date: 2001-10-30
Classification: H04L

Abstract:
A method for providing digital communication via twisted pair telephone lines and the like, the method comprising the steps of:defining a frequency spectrum having a predetermined bandwidth within which communication between two transceivers is to be performed, the frequency spectrum comprising a beginning (Fstart) at a low frequency end thereof and an end (Fstop) at a high frequency end thereof;defining at least one channel within the frequency spectrum, the channel having an initial bandwidth which is substantially less than the bandwidth of the frequency spectrum;communicating via the channel while varying the spectral allocation of the channel and while maintaining a constant constellation size;determining a potential bit rate for each of a plurality of the spectral allocations at which communication was performed, the potential bit rate being determined using a potential constellation size for each spectral allocation determined via the measured signal to noise ratio (SNR) for that spectral allocation, a desired minimum signal to noise ratio (SNR) margin, and a given overall target bit rate, according to the formula:potential bit rate=(symbol rate) (FEC payload percentage) log2 (maximum constellation size);wherein the symbol rate is determined by the bandwidth for each spectral allocation; andwherein the constellation size is calculated according to the formula:Constellation size = { 0 if <= (SNR - margin) <10 dB; 4 if 10 dB <= (SNR - margin) <16 dB; 8 if 16 dB <= (SNR - margin) <19 dB; 16 if 19 dB <= (SNR - margin) <22 dB; 32 if 22 dB <= (SNR - margin) <25 dB; 64 if 25 dB <= (SNR - margin) <28 dB; 128 if 28 dB <= (SNR - margin) <31 dB; 256 if 31 dB <= (SNR - margin) }and wherein furthermore for the case where the potential bit rate so calculated is greater than a given overall target bit rate, the constellation size is then subsequently reduced to the smallest value for which the resulting potential bit rate equals or exceeds the overall target bit rate;selecting a spectral allocation having a highest one of the potential bit rates;communicating while using the selected spectral allocation at its corresponding potential constellation size;determining a value of a channel quality criteria;continuing to communicate using the selected spectral allocation at its corresponding potential constellation size when the channel quality criteria indicates that the quality of the channel is above a predetermined threshold; andreducing the constellation size to a new constellation size and determining the potential bit rate for the current spectral allocation and new constellation size when the channel quality criteria indicates that the channel quality criteria is below a predetermined threshold, then selecting a new spectral allocation having a highest one of the potential bit rates and repeating the previous three steps and this step until the channel quality criteria indicates that the channel quality is no longer below the predetermined threshold for the selected spectral allocation, the communicating step being performed with other than the maximum constellation size, when other than the maximum constellation size will result in the maximum potential bit rate and an acceptable channel quality criteria.