System and method for improving convergence during modem training and reducing computational load during steady-state modem operations
First Claim
1. A method for training echo canceller and equalizer structures of a modem having transmit and receive paths, the method comprising the steps of:
- providing a half duplex training structure including;
an adaptive phase-splitting echo canceller coupled to receive transmit-path samples;
a phase splitting filter coupled to receive receive-path samples; and
an adaptive complex equalizer coupled to the phase-splitting echo canceller and the phase splitting filter to receive a first difference between outputs thereof;
training the phase-splitting echo canceller using the first difference;
decoupling the complex equalizer from the transmit path and thereafter training the complex equalizer using a second difference between an output of the complex equalizer and a reference; and
convolving the trained phase-splitting echo canceller with the trained complex equalizer and convolving the phase splitting filter with the trained complex equalizer to define a trained full-duplex structure, the trained full-duplex structure including;
a trained phase-splitting echo canceller coupled to receive transmit-path samples; and
a trained phase-splitting equalizer coupled to receive receive-path samples.
10 Assignments
0 Petitions
Accused Products
Abstract
A phase-splitting T/3 equalizer and echo canceller structure is computationally efficient because only one point per baud is calculated. However, there are two drawbacks to the structure: (1) since the equalizer performs both the phase-splitting function and channel response equalization, its convergence is slow, and (2) when training the echo canceller during half-duplex training, an answering modem needs an assumed equalizer in its receive path to train its echo canceller, because the adaptive equalizer has not yet been trained; however, after equalizer training the echo canceller needs to be retrained because equalizer coefficients have changed. In contrast, a fixed phase splitting filter can be used during training. The echo canceller and equalizer are each trained with the fixed phase splitting filter thereby improving convergence performance, and after training, the equalizer is convolved with the fixed phase splitting filter to provide the combined phase splitting equalizer and the equalizer is convolved with the echo canceller to provide the combined echo canceller. In this way, computational load is small in steady state and convergence is fast during training. Even though the convergence rate is slower in data mode, it suitable for tracking line variations. An advantage of the transformation from the training structure to the steady-state structure is that a modem or system exploiting the technique provides improved convergence during training while reducing computational load during full-duplex operations. Half-duplex applications, i.e., modem or system operations without echo cancellation, similarly benefit from improved convergence during training and reduced computational load during steady-state operations.
-
Citations
34 Claims
-
1. A method for training echo canceller and equalizer structures of a modem having transmit and receive paths, the method comprising the steps of:
-
providing a half duplex training structure including; an adaptive phase-splitting echo canceller coupled to receive transmit-path samples; a phase splitting filter coupled to receive receive-path samples; and an adaptive complex equalizer coupled to the phase-splitting echo canceller and the phase splitting filter to receive a first difference between outputs thereof; training the phase-splitting echo canceller using the first difference; decoupling the complex equalizer from the transmit path and thereafter training the complex equalizer using a second difference between an output of the complex equalizer and a reference; and convolving the trained phase-splitting echo canceller with the trained complex equalizer and convolving the phase splitting filter with the trained complex equalizer to define a trained full-duplex structure, the trained full-duplex structure including; a trained phase-splitting echo canceller coupled to receive transmit-path samples; and a trained phase-splitting equalizer coupled to receive receive-path samples. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
-
-
12. A method for training a modem having a receive path, the method comprising:
-
providing a half duplex training structure including; a phase splitting filter coupled to receive receive-path samples; and an adaptive complex equalizer coupled to receive an output of the phase splitting filter; training the complex equalizer using a difference between an output of the complex equalizer and a reference; and convolving the phase splitting filter with the trained complex equalizer to define a trained phase-splitting equalizer coupled to receive receive-path samples. - View Dependent Claims (13, 14, 15)
-
-
16. A modem having transmit and receive paths and comprising:
-
a phase splitting filter coupled into the receive path; a first phase splitting T/3 echo canceller coupled between the transmit and receive paths during a transmit-only phase of half-duplex training, wherein coefficients of the first phase splitting T/3 echo canceller are updated during the transmit-only phase to minimize a first difference between outputs of the phase splitting filter and the first phase splitting T/3 echo canceller; a complex T/3 equalizer coupled into the receive path during a receive-only phase of half-duplex training, wherein coefficients of the complex T/3 equalizer are updated during the receive-only phase to minimize a second difference between the output of the complex T/3 equalizer and a reference; a second phase splitting T/3 echo canceller coupled into the receive path during full-duplex operations, the second phase splitting T/3 echo canceller defined by convolution of respective coefficients of the first phase splitting T/3 echo canceller and the complex T/3 equalizer coincident with a cut-over to full-duplex operations; and a phase-splitting T/3 equalizer coupled into the receive path during full-duplex operations, the phase-splitting T/3 equalizer defined by convolution of respective coefficients of the phase splitting filter and the complex T/3 equalizer coincident with the cut-over to full-duplex operations. - View Dependent Claims (17, 18, 19, 20, 21, 22)
-
-
23. An apparatus comprising:
-
a half-duplex training structure comprising; adaptive phase-splitting fractionally-spaced echo canceller means; phase splitting filter means; and adaptive complex fractionally-spaced equalizer means; means for training the adaptive phase-splitting fractionally-spaced echo canceller means during a transmit only phase of half-duplex training; means for training the adaptive complex fractionally-spaced equalizer means during a receive only phase of half-duplex training; and means for converting the half-duplex training structure to a full-duplex structure, the converting means; convolving trained coefficients of the adaptive phase-splitting fractionally-spaced echo canceller means with trained coefficients of the adaptive complex fractionally-spaced equalizer means to define trained fractionally-spaced phase-splitting echo canceller means; and convolving trained coefficients of the phase splitting filter means with trained coefficients of the adaptive complex fractionally-spaced equalizer to define trained phase-splitting fractionally-spaced equalizer means. - View Dependent Claims (24, 25)
-
-
26. A method for providing fast convergence during training of a modem while limiting steady-state computational load of said modem, said method comprising:
-
training a precursor training structure having improved convergence characteristics as compared to a phase-splitting equalizer; after training, transforming from the precursor training structure to a receive path structure including the phase-splitting equalizer structure by convolving filters of the precursor training structure to define the phase-splitting equalizer; and thereafter receiving samples using the receive path structure. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34)
-
Specification