Modem equalizer training using previously stored parameters

• US 4,621,366 A
• Filed: 02/22/1984
• Issued: 11/04/1986
• Est. Priority Date: 02/22/1984
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Universal Data Systems Incorporated
• Inventors: Cain, Roger W., Harris, Norman R.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US06/582,453
• Time in Patent Office: 986 Days
• Field of Search: 333/18, 375/8, 375/11, 375/12, 375/13, 375/14, 375/97, 375/106, 370/17, 371/22, 340/825.06, 340/825.14, 340/825.15
• US Class Current: 375/222
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

A high-speed modem which acquires receiver operating parameters and equalizer coefficients, stores the parameters and coefficients after an initial modem communication having an initial training sequence, and reinitializes the modem equalizer and receiver at the beginning of subsequent modem transmissions with the previously stored coefficients and parameters to be followed by a shortened training sequence. The modem according to the present invention acquires the above-mentioned parameters and coefficients with improved accuracy by extending the initial training period before the transmission of data. The particular stored receiver parameters include carrier frequency offset and data timing frequency offset parameters. According to the present invention, an additional Δ parameter is determined and stored which optimizes the receiver timing according to a difference between parameters acquired at different portions of the initial training sequence. During subsequent modem transmissions and after restoration of several of the previously used equalizer coefficients and receiver parameters, the modem further acquires the remaining receiver parameters during a very brief training period. The parameters acquired during the brief training period are adjusted by the previously determined Δ parameter to achieve a high data accuracy with a minimum (brief) training period, which maximizes data transfer during the subsequent transmissions.

Claims

1. A method of equalized modem training between at least two modems comprising the steps of:

receiving a long train sequence of training signals having strong spectral components at the band edges of the transmission spectrum and a subsequent pseudorandom sequence;

acquiring a first set of modem parameters including a timing difference parameter for the difference between the optimum timing of said strong spectral components and said pseudorandom sequence

storing at least one of said modem parameters in a memory;

transferring a block of data between said modems;

terminating the transmissions;

reinitiating the transmissions;

receiving a short sequence of training signals;

acquiring subsequent receiver parameters including a short train timing parameter;

reloading at least one of said stored modem parameters from said memory;

adding said timing difference parameter to said short train timing parameter; and

transferring a subsequent block of data.

2. In a modem receiving a training sequence, a method of modem adjustment comprising the steps of:

receiving a first segment having strong spectral components at the band edges of the transmission spectrum;

acquiring a preliminary data timing parameter therefrom;

receiving a second segment having a pseudorandom sequence;

adjusting the preliminary data timing to provide a final data timing parameter according to the received pseudorandom sequence;

detecting a data timing difference parameter according to the difference between said preliminary and final data timing parameter;

transferring data;

storing the data timing difference parameter;

terminating the data transfer;

providing a training sequence to reorganize said preliminary data timing parameter;

combining the stored data timing difference parameter and said preliminary data timing parameter to restore said final timing parameter; and

transferring subsequent data.

3. The method of claim 2, wherein the first segment comprises a pattern of alternating signals, and the second segment comprises an equalizer conditioning pattern.

4. A communications system including a communication channel and a plurality of corresponding modems wherein one of said modem includes;

means for selectively transmitting a long training sequence, a short training sequence, and data signals on said communication channel;

wherein

the corresponding modem includes;

means for receiving said transmitted signals from said communication channel, including;

means for equalizing the received signal from said communication channel, having selectable equalizer coefficients;

means for detecting a long train sequence from the received signal;

means for detecting the timing from the received signal;

means for acquiring modem parameter values during said long train sequence from said means for equalizing and said means for detecting the timing, including a revised timing epoch value acquired at the end of said long train sequence;

means for storing said parameter values from said means for acquiring, including the equalizer coefficients selected according to said timing epoch;

means for receiving a block of data thereafter from the received signal;

means for detecting a short train sequence from the received signal;

means for restoring said revised timing epoch from the received signal and said means for storing;

means for restoring said equalizer coefficients from said means for storing; and

means for receiving data from the received signal after the parameters are restored.

5. For use in a data communication system having a training signal sequence preceding the transmission of data, a modem comprising:

means for establishing a channel and receiving a signal;

means for detecting a training sequence on said channel, said training sequence having predetermined training signals of at least two distinct segments;

means for acquiring receiver parameters on said channel according to said detected training sequence including a timing signal derived from at least two of said distinct segments;

means for storing said receiver parameters from said means for acquiring receiver parameters;

means for restoring said receiver equalizer and timing parameters from said means for storing after said means for detecting indicates a subsequent training sequence, wherein a subsequent training sequence is shorter than the initial timing sequence, and said receiver parameters being fully restored after said subsequent training sequence;

means for measuring an initial timing parameter;

means for measuring a revised timing parameter; and

means for determining the difference between said timing and revised parameter, wherein said difference parameter is stored in said means for storing.

6. The modem of claim 5, further including

means for equalizing the received signal according to said training sequence.

7. The modem of claim 6, wherein said means for restoring includes

means for adding the initial timing parameter to said stored difference parameter to provide a revised timing parameter.

8. The modem of claim 7, further including

channel equalizer means for improving the quality of said channel, having parameters selected according to said revised timing parameter.

9. The modem of claim 8, wherein said receiver parameters further include said equalizer coefficients.

10. The modem of claim 7, wherein

said training sequence comprises a first and a second part,

said means to acquire provides said initial timing offset parameters during the first part, and adjusts said initial timing offset parameter to form said revised timing offset parameter at the end of said second part.

11. The modem of claim 5, wherein said receiver parameters include:

a timing frequency offset parameter; and

a carrier frequency offset parameter.