Apparatus and method for adaptively optimizing equalization delay of data communication equipment

• US 4,811,360 A
• Filed: 01/14/1988
• Issued: 03/07/1989
• Est. Priority Date: 01/14/1988
• Status: Expired due to Fees

• Current Assignee: PC-TEL Incorporated
• Original Assignee: General DataComm, Inc. (General DataComm Industries, Inc.)
• Inventors: Potter, William J.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US07/144,534
• Time in Patent Office: 418 Days
• Field of Search: 375/11, 375/12, 375/13, 333/18, 333/28 R, 333/28 T, 364/724
• US Class Current: 375/231
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

A data communication equipment equalizer which minimizes the total training time delay (RTS-CTS) is disclosed. The total RTS-CTS delay of the provided equalizer consists of a delay due to a minimal training sequence required for the equalizer coefficients to converge given a low distortion channel, plus whatever delay is necessary for the equalizer coefficients to converge given the particular channel. The equalizer of the invention preferably comprises: first and second FIRs each having a plurality of taps for storing data signal samples over time, a plurality of tap gain for multiplying the equalizer coefficients with the stored data samples, a coefficient update for comparing the sum of the tap gain products to an ideal value and for changing equalizer coefficients accordingly, and a processor for processing the communications data according to the adapted equalizer coefficients; a buffer delay for receiving and storing the communications data transmitted after the completion of the training sequence and before the equalizer coefficients have been sufficiently adapted to allow substantially error free transmission; and a data decision for deciding what ideal data value to assign a processed data sample. While the training sequence length is minimized for an optimal channel, no communications data is lost in a non-optimal channel as the buffer delay stores the communications data while the FIRs use the communications data to continue to adapt the equalizer coefficients.

Claims

1. A data communication equipment equalizer which is arranged to receive and process data which has been sent over and distorted by a channel, said equalizer comprising:

(a) a first impulse response means having a coefficient update means, wherein said first impulse response means is arranged to obtain at least a first group of said data, and to adapt equalizer coefficients of said coefficient update means based on said at least first group of obtained data at least until said equalizer coefficients are sufficiently adapted to allow substantially error free data transmission;

(b) a buffer delay means for receiving at least a second group of said data and for delaying at least said second group data until said equalizer coefficients of said first impulse response means have been sufficiently adapted to allow substantially error free transmission of at least said second group data, and for providing delayed data, after said equalizer coefficients are sufficiently adapted to allow substantially error free transmission, to an impulse response means which processes at least said delayed second group data according to said adapted equalizer coefficents and provides therefrom processed data samples; and

(c) data detector means for receiving said processed data samples and determining what data values to assign to said processed data samples.

2. A data communication equipment equalizer according to claim 1, wherein:

said first group datfa comprises training sequence data followed by communication data, and said second group data comprises at least said communication data, such that said first and second groups at least partially intersect,

said training sequence data comprises a substantially minimal training sequence based on a low distortion channel,

said buffer delay means receives at least said communications data transmitted after completion of said minimal training sequence and before said equalizer coefficients have sufficiently adapted, and

a total training time delay of said equalizer for said channel is substantially minimized and comprises a delay due to said substantially minimal training sequence, plus a delay necessary for said channel to permit said equalizer coefficients to sufficiently adapt.

3. A data communication equipment equalizer according to claim 2, wherein:

all said communications data is maintained as said buffer means stores said communications data while said equalization means uses said communications data to continue to adapt said equalizer coefficients.

4. A data communication equipment equalizer according to claim 1, wherein:

said first impulse response means further comprises

(1) a plurality of data tap means for storing samples of at least said first group data over time,

(2) a plurality of tap gain means which multiply a plurality of said equalizer coefficients with said stored as least first group data samples to obtain a plurality of products,

(3) a summing means for summing said products and producing an output therefrom, and

(4) said coefficient update means for comparing said output to an ideal value, for changing said equalizer coefficients accordingly, and for determining whether said equalizer coefficients are sufficiently adapted to allow substantially error free transmission.

5. A data communication equipment equalizer according to claim 4, wherein:

upon equalizer coefficients being sufficiently adapted to allow substantially error free transmission, said buffer means is arranged to provide a predetermined plurality of at least second group data samples to a predetermined number of said plurality of tap means during one cycle, and thereafter to provide one said second group data sample per cycle to one of said plurality of tap means.

6. A data communication equipment equalizer according to claim 4, further comprising:

(d) a plurality of switching means for controlling flow of said data into, through, and out of said equalizer, at least one of said plurality of switching means coupled to said channel.

7. A data communication equipment equalizer according to claim 6, wherein:

said impulse response means which processes said at least second group delayed data is said first impulse response means, and

said plurality of switching means comprises a first switching means for connecting said channel directly to said buffer delay means, a second switching means for disconnecting said channel from at least one of said plurality of data tap means to which it may be connected, a third switching means for connecting an output of said buffer delay means with at least one of said plurality of data tap means once said equalizer coefficients are sufficiently adapted to allow substantially error free data transmission, and a fourth switching means for connecting an output of said data detector means to a data terminal equipment.

8. A data communication equipment equalizer according to claim 4, wherein:

said impulse response means is a finite impulse response filter, and said buffer delay means comprises a RAM.

9. A data communiction equipment equalizer according to claim 1, further comprising:

(d) a second impulse response means comprising said impulse response means which processes said at least second group delayed data according to said adapted equalizer coefficients determined by said first impulse response means, wherein said coefficient update means to which said second group delayed data is provided by said buffer delay means is said second impulse response means.

10. A data communication equipment equalizer which is arranged to receive and process data which has been sent over and distorted by a channel, said equalizer comprising:

(a) a first impulse response means having a coefficient update means, wherein said first impulse response means is arranged to obtain at least a first group of said data, and to adapt equalizer coefficients of said coefficient update means based on at least said first group of obtained data;

(b) a buffer delay means for receiving at least a second group of said data, and for delaying at least said second group data until said equalizer coefficients of said first impulse response means have been sufficiently adapted to allow substantially error free transmission of at least said second group data,

(c) a second impulse response means for receiving at least said second group delayed data from said buffer delay means after said equalizer coefficients of said first impulse response means are sufficiently adapted to allow substantially error free transmission, said second impulse response means comprising at least a processing means for processing at least said second group data according to said adapted equalizer coefficients to provide processed data samples, wherein at least one of said first and second impulse response means includes means for determining whether said equalizer coefficients are sufficiently adapted to allow substantially error free transmission; and

(d) data detector means for determining what data values to assign said processed data samples.

11. A data communication equipment equalizer according to claim 10, wherein:

said first and second impulse response means are finite impulse response filters, and said second finite impulse response filter is coupled to an output of said buffer delay means to receive said at least second group data and to process said second group data with said equalizer coefficients determined by said coefficient update means of said first finite impulse response filter.

12. A data communication equipment equalizer according to claim 11, wherein:

said data detector means of said equalizer is coupled to an output of said second finite impulse response filter such that determined data values may be sent to a desired data terminal equipment.

13. A data communication equipment equalizer according to claim 10, wherein:

said first impulse response means comprises;

(1) a plurality of data tap means for storing samples of at least said first group data over time,

(2) a plurality of tap gain means which multiply a plurality of said equalizer coefficients with said stored at least first group data samples to obtain a plurality of products,

(3) a summing means for summing said products and producing an output therefrom, and

(4) said coefficient update means for comparing said output to an ideal value, and for changing said equalizer coefficients accordingly.

14. A data communication equipment equalizer according to claim 13, wherein:

said second impulse response means further comprises,

a plurality of second tap means for storing samples of at least said first group data over time,

a plurality of second tap gain means for multiplying second equalizer coefficients with said at least first group data samples to produce a second plurality of products,

a second summing means for summing said second plurality of products and producing a second output therefrom, and

second coefficient update means for comparing said second output to said ideal value, for changing said second equalizer coefficients accordingly, and for determining whether said second equalizer coefficients are sufficiently adapted to allow substantially error free transmission wherein

said adapted equalizer coefficients of a first of said first and second impulse response means are available to the other of said first and second impulse response means.

15. A data communication equipment equalizer according to claim 11, wherein:

said first group data comprises training sequence data followed by communication data, and said second group data comprises at least said communication data, such that said first and second groups at least partially intersect,

said training sequence data comprises a substantially minimal training sequence based on a low distortion channel,

said buffer delay means receives at least said communications data transmitted after completion of said minimal training sequence and before said equalizer coefficients have sufficiently adapted, and

a total training time delay of said equalizer for said channel is substantially minimized and comprises a delay due to said substantially minimal training sequence, plus a delay necessary for said channel to permit said equalizer coefficients to sufficiently adapt.

16. A data communication equipment equalizer according to claim 15, wherein:

all said communications data is maintained as said buffer delay means stores said communications data while said equalization means uses said communications data to continue to adapt said equalizer coefficients.

17. A data communication equipment equalizer according to claim 14, wherein:

upon said equalizer coefficients being sufficiently adapted to allow substantially error free transmission, said buffer delay means is arranged to provide a predetermined plurality of said second group data samples to a predetermined number of said plurality of second tap means during one cycle, and thereafter to provide one said second group data sample per cycle to one of said plurality of second tap means.

18. A data communication equipment equalizer according to claim 14, wherein:

upon equalizer coefficients being sufficiently adapted to allow substantially error free transmission, said buffer delay means is arranged to provide one said second group data sample per cycle to one of said plurality of second tap means.

19. A method for adaptively optimizing equalization delay in an equalizer of a modem provided with at least an impulse response means having a coefficient update means with equalizer coefficients, and a buffer delay means, comprising:

(a) sending data over said channel to said modem;

(b) using at least a first group of said data to adapt said equalizer coefficients;

(c) storing at least a second group of said data in a buffer delay means while said at least first group data is being used to adapt said equalizer coefficients;

(d) upon said equalizer coefficients being sufficiently adapted to allow substantially error free transmission, processing in an equalizer having said adapted coefficients at least said second group of data stored in said buffer delay means and providing therefrom processed data samples; and

(e) from said processed data samples, determining what data values were sent over said channel.

20. A method according to claim 19, wherein:

said first group of data uses at least training sequence data of substantially minimal length and communications data, and said step of storing said second group of data uses at least said communications data, said first and second groups of data at least partially intersecting wherein said minimal length is defined by a length of time required to permit said equalizer of said modem to adapt said equalizer coefficients so as to allow substantially error free data transmission given a low distortion channel, and

said second group data stored in said buffer delay means comprises at least communications data received while said equalizer coefficients are being adapted, wherein at least samples of said communications data are used to adapt said equalizer coefficients.