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US 7,352,805 B2Granted
Systems and methods for adaptive VDSL with variable sampling frequency and time-domain equalizer
AssigneeConexant, Inc.
InventorsEhud Langberg, Lujing Cai
Life of this patent
Estimating the term…
Abstract
A method and system for enhancing reach-performance of a multi-carrier VDSL System estimates loop length, estimates maximum available bandwidth that can be utilized at that particular loop length, optimally selects an FFT size and sampling rate, and decides whether to apply a time domain equalization to its receiver and if so, selects a cyclic extension size. To minimize the implementation complexity, the sampling frequencies at receiver and transmitter are lowered to match the actual usable bandwidth. The FFT/IFFT sizes in the implementation are also required to set appropriately accordingly.
Claims15
A method for performing adaptive xDSL communications comprising:
- determining line conditions of a communications channel connecting a transmitter and a receiver, wherein determining line conditions of a communications channel comprises sending a line probing signal from the transmitter to the receiver and estimating a line loop length based on the line probing signal, wherein estimating the line loop length comprises solving the expression Al=−10 Log 10 (Pr/Pt), where Al is the loop attenuation, Pr is the received power estimated at the receiver and Pt is the transmit power, and the Al is indexed against a pre-populated table correlating loop attenuation and loop length;
- estimating a maximum number of usable sub-carrier based on the determined line conditions, wherein the maximum number of usable sub-carrier is indicative of a maximum usable bandwidth spanning from a lowest frequency usable sub-carrier to a maximum frequency usable sub-carrier;
- determining a FFT size based at least on part on the maximum number of usable sub-carriers;
- based at least in part of the determined FFT size, selecting a receiver sampling frequency;
- determining, based at least in part on the line conditions, whether or not to utilize a time-domain equalizer (TEQ), and if so determining the length of the TEQ, and the size of cyclic extension to use;
- and
- communicating from the receiver to the transmitter the size of the FFT, the sampling frequency and, if used, the size of the cyclic extension.
4 more elements
An adaptive xDSL system comprising:
- a first transceiver unit and a second transceiver unit interconnected by a communication channel, wherein the second transceiver is adapted to transmit a training signal to the first transceiver, and the first transceiver is adapted to:
- estimate one or more channel characteristics based on the received training signal, the one or more channel characteristics including at least a channel loop length separating the first and second transceiver units;
- calculate a maximum usable bandwidth between the first and second transceiver over the channel;
- select a minimum size of an FFT to be implemented by the second transceiver unit;
- based on the selected size of the FFT, select a minimum sampling frequency;
- determine whether, based at least in part on the one or more channel characteristics, a TEQ should be used and, if so, selecting a length of the TEQ and a cyclic extension length, and
- transmit to the second transceiver unit determined parameters including the size of the FFT, the sample frequency and, if determined to be necessary, the size of the cyclic extension to use;
- wherein the second transceiver is adapted to set an IFFT having a size corresponding to the FFT size and to transmit data to the first transceiver using the determined parameters.
5 more elements
A chipset for an adaptive VDSL modem comprising:
- circuitry adapted to receive a training signal;
- circuitry adapted to estimate a loop length traveled by the training signal based on estimated properties of the received training signal;
- circuitry adapted to calculate a maximum usable bandwidth over a communication channel traveled by the training signal;
- circuitry adapted to select a sampling frequency based on the maximum usable bandwidth;
- circuitry adapted to select a minimum size of an FFT for transforming a DMT-based signal received over the communication channel based at least in part on the selected sampling frequency;
- circuitry adapted to determine, based on at least in part on the estimated loop length, whether a TEQ should be used on received signals and, if so, to select a TEQ length and a cyclic extension length;
- and
- circuitry adapted to send a signal back to a transmitting device indicative of the selected sampling frequency, FFT size and if determined, the cyclic extension length.
5 more elements
An adaptive xDSL system comprising:
- a first transceiver;
- a second transceiver in communication with the first transceiver over a communication channel to form a transceiver set;
- the transceiver set being adapted to transmit and receive a training signal between the first and second transceivers, and comprising:
- means for estimating one or more channel characteristics based on the received training signal, the one or more channel characteristics including at least a channel communication length separating the first and second transceiver units;
- means for determining a maximum usable bandwidth between the first and second transceivers over the communication channel;
- means for determining a minimum size of an FFT to be implemented by the transceiver set;
- means for determining a minimum sampling frequency based at least in part on the selected size of the FFT;
- means for determining whether, based at least in part on the one or more channel characteristics, a TEQ should be used and, if so, determining a length of the TEQ and a cyclic extension, and
- means for determining an IFFT having a size corresponding to the size of the FFT;
- whereby the transceiver set communicates data using the determined parameters.
7 more elements
Dependencies are inferred from the claim text.