US4987569A — Fast training echo canceller

Claim 1

Independent Claim 96 words

A modem for communicating with a remote device in both directions over a channel, the modem comprising: a. a transmitter for transmitting information over the channel; b. a receiver for receiving a signal on the channel possibly including a real echo signal; c. an echo canceller for estimating the real echo signal, the echo canceller module having variable coefficients; and d. a trainer module for applying a complex training signal sequence to the transmitter and for computing the variable coefficients based upon correlations between the complex training signal sequence and only the corresponding real echo signal.

Claim 2

Dependent Claim 96 words

A modem for communicating with a remote device in both directions over a channel, the modem comprising: a. a transmitter for transmitting information over the channel; b. a receiver for receiving a signal on the channel possibly including a real echo signal; c. an echo canceller for estimating the real echo signal, the echo canceller module having variable coefficients; and d. a trainer module for applying a complex training signal sequence to the transmitter and for computing the variable coefficients based upon correlations between the complex training signal sequence and only the corresponding real echo signal.

Claim 3

Dependent Claim 125 words

A modem for communicating with a remote device in both directions over a channel, the modem comprising: a. a transmitter for transmitting information over the channel; b. a receiver for receiving a signal on the channel possibly including a real echo signal; c. an echo canceller for estimating the real echo signal, the echo canceller module having variable coefficients; and d. a trainer module for applying a complex training signal sequence to the transmitter and for computing the variable coefficients based upon correlations between the complex training signal sequence and the corresponding real echo signal, wherein said complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other so that their cross-correlation is equal to zero.

Claim 4

Dependent Claim 125 words

A modem for communicating with a remote device in both directions over a channel, the modem comprising: a. a transmitter for transmitting information over the channel; b. a receiver for receiving a signal on the channel possibly including a real echo signal; c. an echo canceller for estimating the real echo signal, the echo canceller module having variable coefficients; and d. a trainer module for applying a complex training signal sequence to the transmitter and for computing the variable coefficients based upon correlations between the complex training signal sequence and the corresponding real echo signal, wherein said complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other so that their cross-correlation is equal to zero.

Claim 5

Dependent Claim 16 words

A modem as defined in claim 1 or 2 wherein the complex training sequence is periodic.

Claim 6

Dependent Claim 29 words

A modem as defined in claim 1 wherein the complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other.

Claim 7

Dependent Claim 41 words

A modem as defined in claim 1 or 2 wherein the complex training sequence has the properties that the autocorrelation of the real part is a first impulse train and the autocorrelation of the imaginary part is a second impulse train.

Claim 8

Dependent Claim 50 words

A modem as defined in claim 5 wherein the complex training sequence is periodic with a period of 2L, L being an integer, and of the first and the second impulse trains, one is periodic with a period of 2L, and the other is periodic with a period of L.

Claim 9

Dependent Claim 82 words

A modem as defined in claim 1 or 2 wherein the complex training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is a time index and j is -1, p(n) having the following autocorrelation properties: ##EQU9##

Claim 10

Dependent Claim 122 words

A modem as defined in claim 1 or 2 wherein the training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is a time index and j is equal to -1, p r (n) and p i (n) having the following form: a. for 0≦n<L and i. if L is even, then ##EQU10## ii. if L is odd, then ##EQU11## b. for L≦n<2L, then i. p r (n)=p r (n-L), and ii. p i (n)=-p i (n-L).

Claim 11

Dependent Claim 121 words

A modem as defined in claim 1 or 2 wherein the training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is a time index and j is equal to -1, p r (n) and p i (n) having the following form: a. for 0≦n<L ##EQU12## b. for L≦n<2L i. p r (n)=p r (n-L), and ii. p i (n)=-p i (n-L). where INT[(L-1)/2] is the largest integer which is less than or equal to [(L-1)/2].

Claim 12

Dependent Claim 144 words

A modem as defined in claim 1 or 2 wherein the echo signal includes a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of said training signal sequence, the near echo and the far echo being separated by a delay, BT, and wherein the training sequence is a periodic sequence having a period equal to an integer multiple of a variable L, the modem further comprising: a. a computational element for determining the value of the variable L by: i. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and ii. setting L equal to an integer existing in an interval R which is substantially defined as follows: [(B+N.sub.2)/(k+1)]≦R≦[(B-N.sub.1)/k].

Claim 13

Dependent Claim 27 words

A modem as defined in claim 10 wherein the integer k is the largest integer that is no greater than (B-N 1 )/(N 1 +N 2 ).

Claim 14

Dependent Claim 21 words

A modem as defined in claim 10 wherein L is selected to be the smallest integer existing in the interval R.

Claim 15

Dependent Claim 14 words

A modem as defined in claim 10 wherein the period is equal to 2L.

Claim 16

Dependent Claim 144 words

A modem as defined in claim 1 or 2 wherein the far echo may have a phase roll, the operation of the echo canceller module is controlled by specifying an estimate of the phase roll frequency and the computed correlations are used to determine a set of variable coefficients in the echo canceller, the modem further comprising: a. a computational element for: i. computing a difference in phase between a first set and a second set of echo canceller coefficients, both sets having been generated by the trainer module, the first set of echo canceller coefficients corresponding to a time T 1 and the second set of echo canceller coefficients corresponding to a later time T 2 ; and ii. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency.

Claim 17

Dependent Claim 33 words

A modem as defined in claim 14 wherein the computed phase difference is a weighted average of the phase differences between corresponding elements of the first and second sets of echo canceller coefficients

Claim 18

Dependent Claim 163 words

A modem for transmitting signals to and receiving signals from a remote device over a channel, the received signal including a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of said training signal sequence, and the near echo and the far echo being separated by a delay, BT, the modem comprising: a. an echo canceller b. a training generator for generating a periodic training sequence to train the echo canceller, the periodic sequence having a period equal to an integer multiple of a variable L; c. a computational element for determining the value of the variable L by: i. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and ii. setting L equal to an integer existing in an interval R which is substantially defined as follows: [(B+N.sub.2)/(k+1)]≦R≦[(B-N.sub.1)/k].

Claim 19

Dependent Claim 163 words

A modem for transmitting signals to and receiving signals from a remote device over a channel, the received signal including a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of said training signal sequence, and the near echo and the far echo being separated by a delay, BT, the modem comprising: a. an echo canceller b. a training generator for generating a periodic training sequence to train the echo canceller, the periodic sequence having a period equal to an integer multiple of a variable L; c. a computational element for determining the value of the variable L by: i. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and ii. setting L equal to an integer existing in an interval R which is substantially defined as follows: [(B+N.sub.2)/(k+1)]≦R≦[(B-N.sub.1)/k].

Claim 20

Dependent Claim 27 words

A modem as defined in claim 16 wherein the integer k is the largest integer that is no greater than (B-N 1 )/(N 1 +N 2 ).

Claim 21

Dependent Claim 21 words

The modem as defined in claim 16 wherein L is selected to be the smallest integer existing in the interval R.

Claim 22

Dependent Claim 14 words

A modem as defined in claim 16 wherein the period is equal to 2L.

Claim 23

Dependent Claim 170 words

A modem for transmitting signals to and receiving signals from a remote device over a channel, the received signal including an echo signal which may have an associated phase roll, and the modem including an echo canceller module the operation of which is controlled by specifying a set of echo canceller coefficients and an estimate of the phase roll frequency, the modem comprising: a. trainer circuitry for generating a set of echo canceller coefficients based upon the echo present in the received signal; b. a computational element for: i. computing the difference in phase between a first set and a second set of echo canceller coefficients, both sets having been generated by the trainer circuitry, the first set of echo canceller coefficients corresponding to a time T 1 and the second set of echo canceller coefficients corresponding to a later time T 2 ; and ii. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency

Claim 24

Dependent Claim 170 words

A modem for transmitting signals to and receiving signals from a remote device over a channel, the received signal including an echo signal which may have an associated phase roll, and the modem including an echo canceller module the operation of which is controlled by specifying a set of echo canceller coefficients and an estimate of the phase roll frequency, the modem comprising: a. trainer circuitry for generating a set of echo canceller coefficients based upon the echo present in the received signal; b. a computational element for: i. computing the difference in phase between a first set and a second set of echo canceller coefficients, both sets having been generated by the trainer circuitry, the first set of echo canceller coefficients corresponding to a time T 1 and the second set of echo canceller coefficients corresponding to a later time T 2 ; and ii. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency

Claim 25

Dependent Claim 33 words

A modem as defined in claim 20 wherein the computed phase difference is a weighted average of the phase differences between corresponding elements of the first and second sets of echo canceller coefficients.

Claim 26

Independent Claim 81 words

A method for training an echo canceller having variable coefficients which may be set to produce an estimate of a real echo signal, the method comprising: a. applying a complex training signal sequence to a channel; b. receiving a real echo signal on the channel, the echo signal corresponding to the complex training sequence; c. computing correlations between the complex training signal sequence and only the corresponding real echo signal; and d. setting the variable coefficients based upon the computed correlations.

Claim 27

Independent Claim 81 words

A method for training an echo canceller having variable coefficients which may be set to produce an estimate of a real echo signal, the method comprising: a. applying a complex training signal sequence to a channel; b. receiving a real echo signal on the channel, the echo signal corresponding to the complex training sequence; c. computing correlations between the complex training signal sequence and only the corresponding real echo signal; and d. setting the variable coefficients based upon the computed correlations.

Claim 28

Independent Claim 110 words

A method for training an echo canceller having variable coefficients which may be set to produce an estimate of a real echo signal, the method comprising: a. applying a complex training signal sequence to a channel; b. receiving a real echo signal on the channel, the echo signal corresponding to the complex training sequence; c. computing correlations between the complex training signal sequence and the corresponding real echo signal; and d. setting the variable coefficients based upon the computed correlations, wherein said complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other so that their cross-correlation is equal to zero.

Claim 29

Independent Claim 110 words

A method for training an echo canceller having variable coefficients which may be set to produce an estimate of a real echo signal, the method comprising: a. applying a complex training signal sequence to a channel; b. receiving a real echo signal on the channel, the echo signal corresponding to the complex training sequence; c. computing correlations between the complex training signal sequence and the corresponding real echo signal; and d. setting the variable coefficients based upon the computed correlations, wherein said complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other so that their cross-correlation is equal to zero.

Claim 30

Dependent Claim 16 words

A method as defined in claim 21 or 23 wherein the complex training sequence is periodic.

Claim 31

Dependent Claim 29 words

A method as defined in claim 22 wherein the complex training sequence has the property that the real and imaginary parts of the sequence are orthogonal to each other.

Claim 32

Dependent Claim 41 words

A method as defined in claim 21 or 23 wherein the complex training sequence has the properties that the autocorrelation of the real part is a first impulse train and the autocorrelation of the imaginary part is a second impulse train.

Claim 33

Dependent Claim 50 words

A method as defined in claim 26 wherein the complex training sequence is periodic with a period of 2L, and of the first and the second impulse trains, one is periodic with a period of 2L, and the other is periodic with a period of L, L being an integer.

Claim 34

Dependent Claim 82 words

A method as defined in claim 22 or 23 wherein the complex training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is a time index and j is -1, p(n) having the following autocorrelation properties: ##EQU13##

Claim 35

Dependent Claim 122 words

A method as defined in claim 22 or 23 wherein the training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is the time index and j is equal to -1, p r (n) and p i (n) having the following form: a. for 0≦n<L and i. if L is even, then ##EQU14## ii. if L is odd, then ##EQU15## b. for Ln≦n<2L, then i. p r (n)=p r (n-L), and ii. p i (n)=-p i (n-L).

Claim 36

Dependent Claim 121 words

A method as defined in claim 22 or 23 wherein the training sequence has a period of 2L, L being an integer, and said complex training sequence can be written in the form p(n)=p r (n)+jp i (n), where p r (n) is the real part of the n-th complex signal point, p i (n) is the imaginary part of the n-th complex signal point, n is a time index and j is equal to -1, p r (n) and p i (n) having the following form: a. for 0≦n<L ##EQU16## b. for L≦n<2L i. p r (n)=p r (n-L), and ii. p i (n)=-p i (n-L). where INT[(L-1)/2] is the largest integer which is less than or equal to [(L-1)/2].

Claim 37

Dependent Claim 130 words

A method as defined in claim 22 or 23 wherein the echo signal includes a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of the training sequence, the near echo and the far echo being separated by a delay, BT, and wherein the training sequence is a periodic sequence having a period equal to an integer multiple of a variable L, the method further comprising: a. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and b. setting L equal to an integer existing in an interval R which is substantially defined as follows: [(B+N.sub.2)/(k+1)]≦R≦[(B-N.sub.1)/k].

Claim 38

Dependent Claim 27 words

A method as defined in claim 31 wherein the integer k is the largest integer that is no greater than (B-N 1 )/(N 1 +N 2 ).

Claim 39

Dependent Claim 21 words

A method as defined in claim 31 wherein L is selected to be the smallest integer existing in the interval R.

Claim 40

Dependent Claim 14 words

A method as defined in claim 31 wherein the period is equal to 2L.

Claim 41

Dependent Claim 133 words

A method as defined in claim 21 or 23 wherein the far echo may have a phase roll, the operation of the echo canceller is controlled by specifying an estimate of the phase roll frequency and the computed correlations are used to determine the echo canceller coefficients, the method further comprising: a. computing the difference in phase between a first set and a second set of echo canceller coefficients, both sets having been generated by the trainer module, the first set of echo canceller coefficients corresponding to a time T 1 and the second set of echo canceller coefficients corresponding to a later time T 2 ; and b. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency.

Claim 42

Dependent Claim 33 words

A method as defined in claim 35 wherein the computed phase difference is a weighted average of the phase difference between corresponding elements of the first and second sets of echo canceller coefficients.

Claim 43

Independent Claim 134 words

A method for computing a period used to construct a periodic training sequence for training an echo canceller, the training sequence being applied to a channel and resulting in a corresponding echo signal including a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of the training sequence, and the near echo and the far echo being separated by a delay, BT, the method comprising: a. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and b. setting the period equal to an integer multiple of an integer existing in an interval R which is substantially defined as follows; [(B+N.sub.2)/(k+1)]≦R≦[(B'N.sub.1)/k].

Claim 44

Independent Claim 134 words

A method for computing a period used to construct a periodic training sequence for training an echo canceller, the training sequence being applied to a channel and resulting in a corresponding echo signal including a near echo having a span of about N 1 T and a far echo having a span of about N 2 T, N 1 and N 2 being integers and T being the symbol time interval of the training sequence, and the near echo and the far echo being separated by a delay, BT, the method comprising: a. selecting an integer k which is no greater than (B-N 1 )/(N 1 +N 2 ); and b. setting the period equal to an integer multiple of an integer existing in an interval R which is substantially defined as follows; [(B+N.sub.2)/(k+1)]≦R≦[(B'N.sub.1)/k].

Claim 45

Dependent Claim 27 words

A method as defined in claim 37 wherein the integer k is the largest integer that is no greater than (B-N 1 )/(N 1 +N 2 ).

Claim 46

Dependent Claim 21 words

A method as defined in claim 37 wherein L is selected to be the smallest integer existing in the interval R.

Claim 47

Dependent Claim 15 words

A method as defined in claim 37 wherein the integer multiple is equal to 2.

Claim 48

Independent Claim 127 words

A method for estimating a phase roll of an echo signal received by a modem, the modem including an echo canceller the operation of which is controlled by specifying a set of echo canceller coefficients and an estimate of the phase roll frequency, the method comprising: a. generating a first and a second set of echo canceller coefficients based upon the received echo signal, the first set corresponding to time T 1 and the second set corresponding to a time T 2 ; b. computing the difference in phase between the first set and the second set of echo canceller coefficients; and c. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency.

Claim 49

Independent Claim 127 words

A method for estimating a phase roll of an echo signal received by a modem, the modem including an echo canceller the operation of which is controlled by specifying a set of echo canceller coefficients and an estimate of the phase roll frequency, the method comprising: a. generating a first and a second set of echo canceller coefficients based upon the received echo signal, the first set corresponding to time T 1 and the second set corresponding to a time T 2 ; b. computing the difference in phase between the first set and the second set of echo canceller coefficients; and c. dividing the computed phase difference by the time difference, T 2 -T 1 , to arrive at the estimate of the phase roll frequency.

Claim 50

Dependent Claim 33 words

A method as defined in claim 41 wherein the computed phase difference is a weighted average of the phase differences between corresponding elements of the first and second sets of echo canceller coefficients.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1994-01-21	1994-07-23	1995-01-22	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1998-01-21	1998-07-23	1999-01-22	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2002-01-21	2002-07-23	2003-01-22	$7700.00	Window Closed / Lapsed

Fast training echo canceller

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