DSL rate adaptation

• US 6,310,909 B1
• Filed: 05/11/1999
• Issued: 10/30/2001
• Est. Priority Date: 12/23/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Jones, David
• Primary Examiner(s): Vo, Don N.
• Application Number:
  US09/309,340
• Time in Patent Office: 903 Days
• Field of Search: 375/261, 375/259, 375/285, 375/298, 375/222, 375/265, 375/220, 370/252, 370/468
• US Class Current: 375/220
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04L 5/0064 Rate requirement of the data, e.g. scalable bandwidth, data priority
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04L 5/143 for modulated signals H04L5/1469 takes precedence

Abstract

A method for enhancing the bit rate and/or margin at which quadrature amplitude modulation (QAM) communication is performed includes the steps of varying a spectral allocation and constellation size with which communication is performed, so as to define a combination of spectral allocation and constellation size at which the bit rate and/or margin are enhanced. The spectral allocation can be varied by varying a stop frequency thereof, while maintaining a substantially constant start frequency, so as to mitigate undesirable high frequency content of the bandwidth. Alternatively, both start and stop frequencies may be varied.

Claims

1. 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; and

wherein the constellation size is calculated according to the formula;

2. 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 (constellation size);

wherein the symbol rate is determined according to the formula;

Symbol rate=bandwidth (−

3 dB points); and

wherein the constellation size is set separately for each spectral allocation according to the signal to noise ratio (SNR) for each spectral allocation, the overall target bit rate, and the desired minimum signal to noise (SNR) margin;

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; and

reducing 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.