Device and method for linear listener echo cancellation

• US 5,319,636 A
• Filed: 11/14/1991
• Issued: 06/07/1994
• Est. Priority Date: 11/14/1991
• Status: Expired due to Term

• Current Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Original Assignee: Codex Corporation (Motorola Solutions, Inc.)
• Inventors: Eyuboglu, M. Vedat, Long, Guozhu, Ling, Fuyun
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): HOM, SHICK C
• Application Number:
  US07/791,702
• Time in Patent Office: 936 Days
• Field of Search: 370/32.1, 370/32, 375/34, 375/103, 375/119, 375/120, 379/406, 379/407, 379/410, 379/411, 333/18
• US Class Current: 370/291
• CPC Class Codes: H04B 3/232 using phase shift, phase roll or frequency offset correction
• CPC Class Codes: H04B 3/235 combined with adaptive equaliser

Abstract

A device and method utilize a linear feedback/feedforward configuration to estimate and cancel a listener echo wherein equalizer (202) and listener echo cancellation (204 and 208) units are jointly updated, allowing determination of an error signal once (204 and 208), in place of the former method of separate error signal determination for each of an equalizer and a listener echo canceller. An improved phase-correction scheme is utilized to compensate the frequency offset in the listener echo. The relationship between the listener echo and talker far echo is utilized to facilitate the listener echo cancellation.

Claims

1. A listener echo canceller (LECR) for reducing a listener echo interference in a digital communication system having a selected sampling interval, and having an input and an output, said input comprising a sum of a desired signal and a listener echo interference, and said output being free of listener echo interference, said listener echo canceller comprising:

a bulk delay line means, operably coupled to receive and store at least one sample of one of;

the input and the output of said listener echo canceller, to provide a bulk delay line output;

an adaptive listener echo interference estimator means, operably coupled to receive the bulk delay line output for utilizing a listener echo bulk delay relative to the received data signal in place of a talker far echo bulk delay relative to the near echo to generate an estimate of the listener echo interference; and

an interference cancelling means, operably coupled to receive the input of the listener echo canceller and the estimate of the listener echo interference, for producing said output by subtracting said estimate of the listener echo interference from said input of the listener echo canceller,

wherein said adaptive listener echo interference estimator means further includes compensating means, operably coupled to receive the input of the LECR and to receive a phase-corrected listener echo estimate, for compensating a frequency offset in the said estimate of the listener echo interference utilizing a talker far echo frequency offset as an estimate of far echo cancellation, and

wherein the means for compensating the frequency offset includes;

a phase-error estimating means, operably coupled to receive the input of the LECR and to receive a phase-corrected listener echo estimate, for generating a phase error that is a phase difference between the estimate of the listener echo estimate and the said input of the LECR; and

a phase-locked loop, operably coupled to receive the said phase error, for generating a phase correction estimate; and

a phase-correction means, operably coupled to receive the phase correction estimate, for generating a phase-corrected listener echo estimate.

2. The LECR of claim 1, wherein said adaptive listener echo interference estimator means further includes:

a set of filter coefficients and a tapped delay line, operably coupled to receive and store samples of said bulk delay line output; and

wherein the said estimate of the listener echo interference is related to a weighted combination of the stored samples of said bulk delay line output such that the weighting is determined by the filter coefficients, and the said filter coefficients are adaptively adjusted to produce the estimate of said listener echo interference.

3. The LECR of claim 1, wherein the said bulk delay line output is one of:

the input of the LECR, delayed by a selected number of sampling intervals; and

the output of the LECR, delayed by a selected number of sampling intervals;

wherein said selected number of sampling intervals is non-zero.

4. The LECR of claim 1, wherein said adaptive listener echo interference estimator means further includes compensating means, operably coupled to receive the input of the LECR and to receive a phase-corrected listener echo estimate, for compensating a frequency offset in the said estimate of the listener echo interference.

5. The LECR of claim 4, wherein the means for compensating the frequency offset includes:

a phase-error estimating means, operably coupled to receive the input of the LECR and to receive a phase-corrected listener echo estimate, for generating a phase error that is a phase difference between the estimate of the listener echo estimate and the said input of the LECR; and

a phase-locked loop, operably coupled to receive the said phase error, for generating a phase correction estimate; and

a phase-correction means, operably coupled to receive the phase correction estimate, for generating a phase-corrected listener echo estimate.

6. A device for minimizing a listener echo signal interference in a selectively demodulated communication signal received over a channel having simultaneous transmission and reception, the device comprising;

equalizing means, operably coupled to receive the selectively demodulated communication signal, for providing an equalized signal;

a first correcting means, operably coupled to the equalizing means and to a second correcting means, and being configured for;

receiving the equalized signal;

determining a listener echo estimate; and

combining the equalized signal with the listener echo estimate to provide a first corrected signal;

wherein the second correcting means is operably coupled to the first correcting means and to the equalizing means, and is configured for;

providing a phase correction to the first corrected signal to generate and output a second corrected signal that is an equalized listener echo corrected and phase-corrected communication signal;

providing an error signal to the equalizing means for adjusting an equalization process of the equalizing means and to the first correcting means for adjusting the listener echo estimation; and

providing a rotated reference signal in reference-directed training mode for facilitating an initial training of a listener echo estimation.

7. The device of claim 6, wherein the first correcting means comprises:

(A) primary adding means, operably coupled to the equalizing means and to a listener echo estimating means together with a listener echo phase correcting means that provide a phase-corrected listener echo estimate, for obtaining a difference between the equalized signal and that listener echo estimate, being the first corrected signal;

(B) listener echo estimating means, operably coupled to one of;

the primary adding means in a linear feedback configuration, and

the equalizing means in a linear feedforward configuration; and

further being operably coupled to the second correcting means, for utilizing;

in a data-receiving mode, one of;

the first corrected signal, and

the equalized signal; and

in a reference-directed training mode,

the rotated reference signal;

to determine a first listener echo estimate;

(C) listener echo phase error determining means, operably coupled to the listener echo phase correcting means and one of;

in the data-receiving mode,

the preliminary decision means, and

in the reference-directed training mode,

a reference signal means,

for determining a listener echo phase error;

wherein the listener echo phase-locked loop means is operably coupled to the listener echo phase error determining means for utilizing the listener echo phase error to provide a listener echo phase correction estimate; and

wherein the listener echo phase correction inverse means is operably coupled to the listener echo phase-locked loop means and to the second correcting means that provides an error signal, for utilizing the listener echo phase correction estimate and the second correcting means error signal for providing a rotated error signal for updating the listener echo estimating means.

8. The device of claim 7, further including that the second correcting means comprises:

(A) received data phase correcting means, operably coupled to the first correcting means and to a received data phase-locked loop means, for determining a data phase correction and utilizing that data phase correction to provide a data phase corrected communication signal;

(B) preliminary decision means, operably coupled to the received data phase correcting means, for providing a preliminary estimate of the communication signal transmitted by a remote modem;

(C) received data phase error determining means, operably coupled to the received data phase correcting means and to one of;

in the data-receiving mode,

the preliminary decision means, and

in the reference-directed training mode,

the reference signal means,

for determining a received data phase error α

;

(D) received data phase-locked loop means, operably coupled to the received data phase correcting means and to a received data phase correction inverse means, for providing the received data phase correction estimate φ

(n);

the received data phase correction inverse means being operably coupled to the received data phase-locked loop means and to one of;

the preliminary decision means, and

the reference signal means,

to provide a rotated decision signal;

(E) a combiner, operably coupled to the received data phase correction inverse means and to the first correcting means, for subtracting the first corrected signal from the rotated decision signal to provide an error signal ε

(n).

9. The device of claim 7, further including that the listener echo estimating means includes:

a bulk delay line unit, operably coupled to one of;

in the linear feedback configuration,

the primary adding means, and

in a linear feedforward configuration,

the equalizing means,

and further being operably coupled to the second correcting means, for providing a delay in accordance with a listener echo bulk delay B_L ; and

an adaptive transversal filter unit, operably coupled to bulk delay line unit, whose coefficients are a_k (n), where k=0, 1, 2, . . . , M-1, where M is a number of taps in the transversal filter unit, and whose output is of a form;

##EQU5## where n is a discrete time index and g() is input to the bulk delay line unit.

10. The device of claim 9, wherein B_L is, determined by a talker far echo ranging method.

11. The device of claim 8, further including that the phase-corrected listener echo estimate is of a form:

e_L (n)=p(n)e^jψ

(n), where n is a discrete time index, p(n) is the first listener echo estimate, and ψ

(n) is a listener echo phase correction estimate.

12. The device of claim 11, further including that ψ

(n) is determined utilizing one of;

(A) a listener echo phase error θ

(n) where ##EQU6## where e_Lr and e_Li are the real and imaginary parts, respectively, of e_L (n), and q_r and q_i are the real and imaginary parts, respectively, of the equalized signal q(n); and

further including that a listener echo phase-locked loop of the first correcting unit determines an estimate of the listener echo frequency offset component f_L (n) and a phase correction estimate ψ

(n) for correcting the phase of the signal p(n), wherein;

space="preserve" listing-type="equation">f.sub.L (n+1)=f.sub.L (n)+b.sub.1 θ

(n), and

space="preserve" listing-type="equation">ψ

(n+1)=ψ

(n)+b.sub.2 θ

(n)+b.sub.3 f.sub.L (n+1),

where b₁, b₂, and b₃ are constants that determine a phase-locked loop characteristic, and f_L (n) may be initialized using a talker far echo frequency offset estimate to facilitate an initial convergence; and

(B) a sign of θ

(n), denoted as s(n);

space="preserve" listing-type="equation">s(n)=sign[e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)],

defining

space="preserve" listing-type="equation">s(n)=1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)>

TH,

space="preserve" listing-type="equation">s(n)=-1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)<

TH, and

s(n)=0 otherwise, where TH is a small predetermined positive threshold value;

and determining f_L (n+1)=f_L (n)+d₁ s(n), and

ψ

(n+1)=ψ

(n)+d₂ s(n)+b₃ f_L (n+1), where d₁ and d₂ are selected constants and f_L (n), an estimate of the listener echo frequency offset component, may be initialized using a talker far echo frequency offset estimate to facilitate an initial convergence.

13. The device of claim 11, wherein the first corrected signal, z(n), is of a form:

z(n)=q(n)-e_L (n), where q(n) is the equalized signal.

14. The device of claim 13, further including that the rotated error input, η

(n) is of a form;

η

(n)=ε

(n)e^-jψ

(n), where ε

(n) is the error signal from the second correcting means.

15. The device of claim 14, further including that φ

(n) is determined utilizing a received communication signal data phase error α

where;

##EQU7## which is used to estimate a frequency offset of a received communication signal f_D (n) and the received data phase correction estimate φ

(n), such that;

space="preserve" listing-type="equation">f.sub.D (n+1)=f.sub.D (n)+c.sub.1 α

(n); and

space="preserve" listing-type="equation">φ

(n+1)=φ

(n)+c.sub.2 α

(n)+c.sub.3 f.sub.D (n+1),

where u(n) is the first corrected signal further phase-corrected by φ

(n), u_r and u_i are the real and imaginary parts, respectively, of u(n), v_r and v_i are the real and imaginary parts, respectively, of v(n), and c₁, c₂, and c₃ are constants that determine a desired phase-locked loop characteristic for a phase-locked loop having an input α

(n).

16. The device of claim 15, further including that the second corrected signal, u(n), is of a form:

u(n)=z(n)e^jφ

(n), n being the discrete time index and z(n) being the first corrected signal.

17. The device of claim 16, further including that a rotated decision signal d(n) is of a form:

d(n)=v(n)e^-jφ

(n), n being the discrete time index, and v(n) being the reference signal r(n) for selection of a reference directed training mode and being a preliminary decision output for selection of a communication signal receiving mode.

18. The device of claim 8, further including:

a noise prediction filter (NPF), operably coupled between the equalizing means and the first correcting means to receive and filter the equalized signal, so that a noise spectrum of the equalized signal is whitened; and

an inverse noise prediction filter (NPF^-1), operably coupled between the second correcting means and the equalizing means, for filtering the error signal from the second correcting means to provide a filtered error signal for updating equalizer coefficients.

19. A modem having a linear listener echo cancelling device, the modem being utilized for communicating information with a remote device in both directions over a channel, the modem comprising:

transmission means, operably coupled to receive the information to be communicated, for preparing an analog signal carrying that information for transmission;

hybrid coupling means, operably coupled to the transmission means and to a receiving means, for transmitting the analog signal and for receiving another analog signal from a remote device;

talker echo estimating means, operably coupled to the transmission means, for providing a talker echo estimate to the receiving means; and

the receiving means, operably coupled to the talker echo estimating means and to the hybrid coupling means, for recovering information from the analog signal transmitted by the remote device, said receiving means including one of;

a linear feedback listener echo canceller, and

a linear feedforward listener echo canceller, for reducing a listener echo interference,

encoding means, operably coupled to receive the information to be communicated, for providing an encoded data signal;

modulation means operably coupled to the encoding means, for providing a modulated signal; and

transmission filtering means, operably coupled to the modulation means, for providing a modulated filtered transmission data signal at a desired sampling rate; and

digital-to-analog converting means, operably coupled to the transmission filtering means, for converting the modulated filtered transmission data signal to an analog signal.

20. The modem of claim 19, wherein the talker echo estimating means includes:

talker far echo delay estimating means for estimating a talker far echo delay; and

wherein the listener echo correcting means comprises a bulk delay line whose length is determined by the estimated talker far echo delay, for reducing the listener echo interference.

21. The modem of claim 19, wherein the talker echo estimating means includes:

a far-end echo frequency offset determining means, for estimating a far-end echo frequency offset; and

wherein the listener echo correcting means comprises a frequency offset phase-correcting means for correcting frequency offset in the listener echo estimate, said phase-correcting means further including a phase-locked loop having an initial value determined by the far-end talker echo frequency offset estimate.

22. The modem of claim 19, wherein the receiving means includes:

analog-to-digital converting means, operably coupled to the hybrid coupling means, for converting received analog signals to digital signals at a preselected sampling rate;

first combining means, operably coupled to the talker echo estimating means and to the analog-to-digital converting means, for combining the received digital signal and the talker echo estimate to provide a first talker echo corrected signal;

rate converting means, where desired, operably coupled to the first combining means, for converting the first talker echo corrected signal, being sampled at a transmitter sampling clock, to a second talker echo corrected signal, being sampled at a desired receiver sampling clock;

demodulation means, operably coupled to the rate converting means, for providing a demodulated talker echo corrected signal;

receiving filtering means, operably coupled to the demodulation means, for filtering the demodulated talker echo corrected signal;

equalizing means, operably coupled to the receiving filtering means, for providing an equalized, demodulated filtered talker echo corrected signal;

listener echo cancelling means, operably coupled to the equalizing means, for providing a listener echo corrected, equalized, demodulated, filtered talker echo corrected signal; and

decoding means, operably coupled to the listener echo cancelling means, for decoding the listener echo corrected, equalized, demodulated, filtered, talker echo corrected signal to provide received information.

23. The modem of claim 22, wherein the listener echo cancelling means comprises:

a first correcting means, operably coupled to the equalizing means and to a second correcting means, and being configured for;

receiving the equalized signal;

determining a listener echo estimate; and

combining the equalized signal with the listener echo estimate to provide a first corrected signal;

wherein the second correcting means is operably coupled to the first correcting means and to the equalizing means, and is configured for;

providing a phase correction to the first corrected signal to generate and output a second corrected signal that is an equalized, listener echo-corrected, and phase-corrected communication signal;

providing an error signal to the equalizing means for adjusting an equalization process of the equalizing means, and to the first correcting means for adjusting the listener echo estimate;

providing a rotated reference signal in reference-directed training mode for facilitating an initial training in a listener echo estimation.

24. The modem of claim 23, wherein the first correcting means comprises:

(A) an adding means, operably coupled to the equalizing means and to a listener echo estimating means together with a listener echo phase-correcting means that provide a phase-corrected listener echo estimate, for obtaining a difference between the equalized signal and that listener echo estimate, being the first corrected signal;

(B) listener echo estimating means, operably coupled to one of;

the primary adding means in a linear feedback configuration, and

the equalizing means in a linear feedforward configuration; and

further being operably coupled to the second correcting means, for utilizing;

in a data-receiving mode, one of;

the first corrected signal, and

the equalized signal; and

in a reference-directed training mode,

the rotated reference signal;

to determine a first listener echo estimate;

(C) listener echo phase error determining means, operably coupled to the listener echo phase correcting means and one of;

in the data-receiving mode,

the preliminary decision means, and

in the reference-directed training mode,

a reference signal means,

for determining a listener echo phase error;

wherein the listener echo phase-locked loop means is operably coupled to the listener echo phase error determining means for utilizing the listener echo phase error to provide a listener echo phase correction estimate; and

wherein the listener echo phase correction inverse means is operably coupled to the listener echo phase-locked loop means and to the second correcting means that provides an error signal, for utilizing the listener echo phase correction estimate and the second correcting means error signal for providing a rotated error signal for updating the listener echo estimating means.

25. The modem of claim 23, further including that the second correcting means comprises:

(A) a received data phase correcting means, operably coupled to the first correcting means and to a received data phase-locked loop means, for determining a data phase correction and utilizing that data phase correction to provide a data phase corrected communication signal;

(B) a preliminary decision means, operably coupled to the received data phase correcting means, for providing a preliminary estimate of the communication signal transmitted by a remote modem;

(C) received data phase error determining means, operably coupled to the received data phase correcting means and to one of;

in the data-receiving mode,

the preliminary decision means, and

in the reference-directed training mode,

the reference signal means,

for determining a received data phase error α

;

(D) received data phase-locked loop means, operably coupled to the received data phase correcting means and to a received data phase correction inverse means, for providing a received data phase correction estimate φ

(n);

the received data phase correction inverse means being operably coupled to the received data phase-locked loop means and to one of;

the preliminary decision means, and

the reference signal means,

to provide a rotated decision signal;

(E) a combiner, operably coupled to the received data phase correction inverse means and to the first correcting means, for subtracting the first corrected signal from the rotated decision signal to provide an error signal ε

(n).

26. The modem of claim 24, further including that the listener echo estimating means includes:

a bulk delay line unit, operably coupled to one of;

in the linear feedback configuration,

the primary adding means, and

in a linear feedforward configuration,

the equalizing means,

and further being operably coupled to the second correcting means, for providing a delay in accordance with a listener echo bulk delay B_L ; and

an adaptive transversal filter unit, operably coupled to bulk delay line unit, whose coefficients are a_k (n), where k=0, 1, 2, . . . , M-1, where M is a number of taps in the transversal filter unit, and whose output is of a form;

##EQU8## where n is a discrete time index and g() is input to the bulk delay line unit.

27. The modem of claim 26 wherein B_L is, where desired, determined by a talker far echo ranging method.

28. The modem of claim 24, further including that the phase-correction listener echo estimate is of a form:

e_L (n)=p(n)e^jψ

(n), where n is a discrete time index, p(n) is the first listener echo estimate, and ψ

(n) is a listener echo phase correction estimate.

29. The modem of claim 28, further including that ψ

(n) is determined utilizing one of;

(A) a listener echo phase error θ

(n) where ##EQU9## where e_Lr and e_Li are the real and imaginary parts, respectively, of e_L (n), and q_r and q_i are the real and imaginary parts, respectively, of the equalized signal q(n); and

further including that a listener echo phase-locked loop of the first correcting unit determines an estimate of the listener echo frequency offset component f_L (n) and a phase correction estimate ψ

(n) for correcting a phase of the signal p(n), wherein;

space="preserve" listing-type="equation">f.sub.L (n+1)=f.sub.L (n)+b.sub.1 θ

(n), and

space="preserve" listing-type="equation">ψ

(n+1)=ψ

(n)+b.sub.2 θ

(n)+b.sub.3 f.sub.L (n+1),

where b₁, b₂, and b₃ are constants that determine a phase lock loop characteristic and f_L (n) is initialized, where desired, utilizing a talker far echo frequency offset estimate to facilitate an initial convergence; and

(B) a sign of θ

(n), denoted as s(n);

space="preserve" listing-type="equation">s(n)=sign[e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)],

defining

space="preserve" listing-type="equation">s(n)=1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)>

TH,

space="preserve" listing-type="equation">s(n)=-1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr n)q.sub.i (n)<

TH, and

s(n)=0 otherwise, where TH is a small predetermined positive threshold value;

and determining f_L (n+1)=f_L (n)+d₁ s(n), and

ψ

(n+1)=ψ

(n)+d₂ s(n)+b₃ f_L (n+1), where d₁ and d₂ are selected constants.

30. The modem of claim 23, wherein the first corrected signal, z(n), is of a form:

z(n)=q(n)-e_L (n), where q(n) is the equalized signal.

31. The modem of claim 24, further including that the rotated error signal, η

(n), is of a form;

η

(n)=ε

(n)e^-jψ

(n), where ε

(n) is the error signal from the second correcting means.

32. The modem of claim 25, further including that the received data phase correction estimate φ

(n) is determined utilizing a received communication signal data phase error α

where;

##EQU10## which is used to estimate a frequency offset of a received communication signal f_D (n) and the received data phase correction estimate φ

(n), such that;

space="preserve" listing-type="equation">f.sub.D (n+1)=f.sub.D (n)+c.sub.1 α

(n); and

space="preserve" listing-type="equation">φ

(n+1)=φ

(n)+c.sub.2 α

(n)+c.sub.3 f.sub.D (n+1),

where u(n) is the first corrected signal further phase-corrected by φ

(n), u_r and u_i are the real and imaginary parts, respectively, of u(n), v_r and v_i are the real and imaginary parts, respectively, of v(n), and c₁, c₂, and c₃ are constants that determine a desired phase-locked loop characteristic for a phase-locked loop having an input α

(n).

33. The modem of claim 23, further including that the second corrected signal, u(n), is of a form:

space="preserve" listing-type="equation">u(n)=z(n)e.sup.jφ

(n).

34. The modem of claim 25, further including that a rotated decision signal d(n) is of a form:

d(n)=v(n)e^-jφ

(n), n being the discrete time index, and v(n) being the reference signal r(n) for selection of a reference directed training mode and being a preliminary decision output for selection of a communication signal receiving mode.

35. The modem of claim 23, further including:

a noise prediction filter (NPF), operably coupled between the equalizing means and the first correcting means to receive and filter the equalized signal, so that a noise spectrum of the equalized signal is whitened; and

an inverse noise prediction filter (NPF^-1), operably coupled between the second correcting means and the equalizing means, for filtering the error signal from the second correcting means to provide a filtered error signal for updating equalizer coefficients.

36. A method for minimizing a listener echo signal interference in a selectively demodulated, equalized communication signal received over a channel having simultaneous transmission and reception, said method comprising the steps of:

receiving said selectively demodulated communication signal, for providing an equalized signal;

determining a listener echo estimate; and

combining said equalized signal with said listener echo estimate to provide a first corrected signal;

providing a phase correction to said first corrected signal to generate and output a second corrected signal that is an equalized, listener echo-corrected and phase-corrected communication signal;

providing an error signal for adjusting said equalization signal and said listener echo estimate;

providing a rotated reference signal in a reference-directed training mode for facilitating an initial training of said listener echo estimate.

37. The method of claim 36, further including the steps of:

(A) obtaining a difference between said equalized signal and that listener echo estimate, being said first corrected signal;

(B) selecting one of;

said first corrected signal,

said equalized signal, and

said rotated reference signal,

as a first selected signal;

(C) utilizing said first selected signal to determine a first listener echo estimate;

(D) providing a listener echo phase correction estimate and combining said first listener echo estimate and said listener echo correction estimate to provide the phase-corrected listener echo estimate;

(E) utilizing said equalized signal and said phase-corrected listener echo estimate to provide a listener echo phase error;

(F) utilizing said listener echo phase error to provide a listener echo phase correction estimate; and

(G) providing an error signal and utilizing said listener echo phase correction estimate and said error signal for providing a rotated error signal for updating said first listener echo estimate.

38. The method of claim 37, further including the steps of:

(A) determining a data phase correction and utilizing that data phase correction to provide a data phase corrected communication signal;

(B) providing a preliminary decision output signal of the communication signal transmitted by the remote modem;

(C) selecting one of;

the preliminary decision output signal, and

a reference signal,

as a second selected signal;

(D) determining a received data phase error α

;

(E) providing a received data phase correction estimate φ

(n);

(F) providing a rotated decision signal; and

(G) substantially subtracting the first corrected signal from the rotated decision signal to provide an error signal ε

(n).

39. The method of claim 38, further including the steps of:

utilizing a bulk delay unit to provide a delay in accordance with a listener echo bulk delay B_L ; and

utilizing an adaptive transversal filter unit whose coefficients are a_k (n), where k=0, 1, 2, . . . , M-1, where M is a number of taps in the transversal filter unit, and whose output is of a form ##EQU11## where n is a discrete time index and g() is input from the first switching unit.

40. The method of claim 39, wherein B_L is determined by a talker far echo ranging method.

41. The method of claim 36, further including that the listener echo estimate is of a form:

e_L (n)=p(n)e^jψ

(n), where n is a discrete time index, p(n) is the first listener echo estimate, and ψ

(n) is a listener echo phase correction estimate.

42. The method of claim 41, further including that ψ

(n) is determined utilizing one of;

(A) a listener echo phase error θ

(n) where ##EQU12## where e_Lr and e_Li are the real and imaginary parts, respectively, of e_L (n), and q_r and q_i are the real and imaginary parts, respectively, of the equalized signal q(n); and

further including that a listener echo phase-locked loop of the first correcting unit determines an estimate of the listener echo frequency offset component f_L (n) and a phase correction estimate ψ

(n) for correcting a phase of the signal p(n), wherein;

space="preserve" listing-type="equation">f.sub.L (n+1)=f.sub.L (n)+b.sub.1 θ

(n), and

space="preserve" listing-type="equation">ψ

(n+1)=ψ

(n)+b.sub.2 θ

(n)+b.sub.3 f.sub.L (n+1),

where b₁, b₂, and b₃ are constants that determine a phase lock loop characteristic and f_L (n) is initialized utilizing a talker far echo frequency offset estimate to facilitate an initial convergence; and

(B) a sign of θ

(n), denoted as s(n);

space="preserve" listing-type="equation">s(n)=sign[e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)],

defining

space="preserve" listing-type="equation">s(n)=1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)>

TH,

space="preserve" listing-type="equation">s(n)=-1 for e.sub.Li (n)q.sub.r (n)-e.sub.Lr (n)q.sub.i (n)<

TH, and

s(n)=0 otherwise, where TH is a small predetermined positive threshold value;

and determining f_L (n+1)=f_L (n)+d₁ s(n), and

ψ

(n+1)=ψ

(n)+d₂ s(n)+b₃ f_L (n+1), where d₁ and d₂ are selected constants and f_L (n) is initialized using a talker far echo frequency offset estimate to facilitate an initial convergence.

43. The method of claim 36, further including that the first corrected signal, z(n), is of a form:

z(n)=q(n)-e_L (n), where q(n) is the equalized signal.

44. The method of claim 37, further including that the rotated error signal, η

(n), is of a form;

space="preserve" listing-type="equation">η

(n)=ε

(n)e.sup.-jψ

(n), where ε

(n) is the error signal.

45. The method of claim 38, further including that the received data phase correction estimate φ

(n) is determined utilizing a received communication signal data phase error α

where;

##EQU13## which is used to estimate a frequency offset of a received communication signal f_D (n) and the received data phase correction estimate φ

(n), such that;

space="preserve" listing-type="equation">f.sub.D (n+1)=f.sub.D (n)+c.sub.1 α

(n); and

space="preserve" listing-type="equation">φ

(n+1)=φ

(n)+c.sub.2 α

(n)+c.sub.3 f.sub.D (n+1),

where u(n) is the first corrected signal further phase-corrected by φ

(n), u_r and u_i are the real and imaginary parts, respectively, of u(n), v_r and v_i are the real and imaginary parts, respectively, of v(n), wherein v(n) is the reference signal r(n) for selection of a reference directed training mode and being the preliminary decision output for selection of a communication signal receiving mode, and c₁, c₂, and c₃ are constants that determine a desired phase-locked loop characteristic for a phase-locked loop having an input α

(n).

46. The method of claim 36, further including that the second corrected signal, u(n), is of a form:

space="preserve" listing-type="equation">u(n)=z(n)e.sup.jφ

(n).

47. The method of claim 38, further including that the rotated decision signal d(n) is of a form d(n)=v(n)e^-jφ

(n), n being the discrete time index.

48. The method of claim 38, further including the steps of:

utilizing a noise prediction filter (NPF) to receive and filter the equalized signal, so that a noise spectrum of the equalized signal is whitened; and

utilizing an inverse noise prediction filter (NPF^-1) for filtering the error signal to provide a filtered error signal for updating equalizer coefficients.