Modulator/demodulator apparatus

Claim 2

Modulator/demodulator apparatus characterised in first digital signal processor (DSP1) operable in a full duplex mode for providing digital samples to be transmitted to a coder decoder and receiving transmitted digital samples therefrom, the first digital signal processor being responsive to received samples for initiating echo cancellation in the received samples, a second digital signal processor (DSP2) operable to demodulate samples received from the first digital signal processor and outputting demodulated message information therefrom, and an input/output processor (IOP) for initiating operations of the first and second digital signal processor, the input/output processor receiving input information to be transmitted and supplying that information to the first digital signal processor (DSP1) and receiving demodulated message information from the second digital signal processor (DSP2) and outputting the demodulated message information to at least one user device, the input/output processor (IOP) also receiving transmitted digital samples to be demodulated from the first digital signal processor (DSP1) and supplying the transmitted samples to be demodulated to the second digital signal processor (DSP2), the input/output processor being operable in a full duplex mode of operation.

Claim 3

A modulator demodulator apparatus as claimed in Claim 1 characterised in that message information may represent voice and data.

Claim 4

A modulator demodulator apparatus as claimed in claim 1 or 2, characterised in that the first digital signal processor (DSP1) is responsive to received digital samples for initiating an automatic gain control function on the received samples.

Claim 5

A modulator demodulator apparatus as claimed in claim 3, characterised in that the automatic gain control function is implemented prior to echo cancellation.

Claim 6

A modulator demodulator apparatus as claimed in claim 4, characterised in that the automatic gain control function is implemented with negative logarithms.

Claim 7

A modulator demodulator apparatus as claimed in claim 1, characterised in that the first and second digital signal processors (DSP1,DSP2) employ processors capable of performing dot product functions.

Claim 8

A modulator demodulator apparatus as claimed in claim 1, characterised in that the second digital signal processor (DSP2) performs an equalizer function.

Claim 9

A modulator demodulator apparatus as claimed in claim 7, characterised in that the equalizer function is performed using adaptive logic.

Claim 10

A modulator demodulator apparatus as claimed in claim 8, characterised in that the equalizer function includes a plurality of taps on a delay line and the adaptive logic is performed with respect to each of a selected number of taps of the plurality of taps.

Claim 11

A modulator demodulator apparatus as claimed in claim 1, characterised in that the second digital signal processor (DSP2) performs an interpolate function with respect to received baud information.

Claim 12

A modulator demodulator apparatus as claimed in claim 10, characterised in that baud information is loaded into demodulator register means prior to the performance of the interpolate function.

Claim 13

A modulator demodulator apparatus as claimed in claim 11, characterised in a baud servo for controlling the number of bauds processed each frame and the delay imposed by the interpolate function.

Claim 14

A modulator demodulator apparatus as claimed in claim 12, characterised in a predetect baud metric for driving the baud servo during a first mode of operation, a post baud metric for driving the baud servo during a second mode of operation, and means for selecting the predetect baud metric or the post baud metric to baud servo.

Claim 15

A modulator demodulator apparatus as claimed in claim 13, characterised in that the first and second modes are differing transmission rates.

Claim 16

A modulator demodulator apparatus as claimed in claim 14, characterised in that the second digital signal processor (DSP2) performs an equalizer function.

Claim 17

A modulator demodulator apparatus as claimed in claim 15, charcterised in that the equalizer function is performed subsequently to the interpolate function on interpolated samples.

Claim 18

A modulator demodulator apparatus as claimed in claim 16, characterised in that the equalizer function is performed using adaptive logic.

Claim 19

A modulator demodulator apparatus as claimed in claim 17, characterised in that the equalizer function includes a plurality of taps on a delay line and the adaptive logic is performed with respect to each of a selected number of taps of the plurality of taps.

Claim 20

A modulator demodulator apparatus as claimed in claim 1, characterised in the echo cancellation is implemented by injecting a derived echo estimate signal into the received information.

Claim 21

A modulator demodulator apparatus as claimed in claim 19, characterised in that a simple delay line having a plurality of taps, means for developing a column vector as a function of selected transmit samples at the taps correlated with the echo estimate at that sample time, means for obtaining a signal corresponding to the matrix product of the column vector for each tap and the inverse to the transmit autocorrelation matrix to obtain tap values or to adapt the taps, and means for summing the products of the tap values and a sample for each tap to derive an echo estimate signal.

Claim 22

A modulator demodulator apparatus as claimed in claim 20, characterised in that the echo estimate signal is derived in an adaptive manner by repetitively developing the echo estimate signal from received information having the echo estimate signal removed.

Claim 23

A modulator demodulator apparatus as claimed in claim 19, characterised in means for modulating complex baud impulses from transmitter, means responsive to the complex impulse generator means for developing a vector history of information to be transmitted for a plurality of taps, means for storing a plurality of tap adaptation values, means for obtaining a series of dot products of vectors and complex for taps to obtain a series of echo estimate signals, means for dividing received information into a plurality of vectors corresponding to tap values, and means for summing the series of dot products and the vectors to obtain received information samples with the echo estimate removed in a manner minimizing processor load, and means for taking dot products of the vectors and corresponding signals with echo removed for the purpose of initially calculating tap values and subsequently adapting tap values using steepest descent gradients.

Claim 24

A modulator demodulator apparatus as claimed in claim 22, characterised in that the echo estimate signal is derived in an adaptive manner by repetitively developing the echo estimate signal from received information samples with the echo estimate removed.

Claim 25

A modulator demodulator apparatus as claimed in claim 23, characterised in that the plurality of tap adaptive values are periodically updated as part of the adaptive manner of deriving the echo estimate signal.

Claim 26

A modulator demodulator apparatus as claimed in claim 1, characterised in a tone detector for determining presence of a plurality of tones in received information.

Claim 27

A modulator demodulator apparatus as claimed in claim 25, characterised in that the tone detector includes negative logarithm means.

Claim 28

An echo cancellation apparatus for removing echo in received information characterised in a sample delay line having a plurality of taps, means for applying a signal to the plurality of taps, means for developing a transmit signal to echo cross correlation column vector as a function of tap position, means for obtaining a vector corresponding to the dot product function of an inverse transmit auto correlation matrix and the cross correlation column vector, means for summing the vector with the tap vector to obtain more accurate tap values, means for obtaining an initial echo canceler solution, means for summing the products to develop an echo estimate signal, and means for subtracting the echo estimate signal from the received information to develop a modified received information.

Claim 29

An echo cancellation apparatus for removing echo in received information characterised in a sample delay line having a plurality of taps, means for applying a signal to the plurality of taps, means for developing a transmit signal to echo cross correlation column vector as a function of tap position, means for obtaining a vector corresponding to the dot product function of an inverse transmit auto correlation matrix and the cross correlation column vector, means for summing the vector with the tap vector to obtain more accurate tap values, means for obtaining an initial echo canceler solution, means for summing the products to develop an echo estimate signal, and means for subtracting the echo estimate signal from the received information to develop a modified received information.

Claim 30

An echo cancellation apparatus for removing echo in received information as claimed in claim 27, characterised in that the echo estimate signal is derived in an adaptive manner by repetitively developing the echo estimate signal from the modified received information employing the use of a transmit auto correlation matrix as a whitening filter to speed convergence.

Claim 31

An echo cancellation apparatus as claimed in claim 27, characterised in that the means for developing a column vector as a function of tap position comprises, a control processing state for each training phase of the taps, each signal control state having an input and an output, means for applying an adaptation parameter to the input of each signal processing stage, means for applying a tap sample signal associated with that tap to the input of each signal processing stage, and means for developing a column vector for each selected tap at the output of the signal processing stage for that tap.

Claim 32

An echo cancellation apparatus as claimed in claim 29, characterised in that the means for applying an adaptation parameter comprises means for obtaining the product of an adaptive constant and an error signal.

Claim 33

An echo cancellation apparatus for removing echo in received information characterised in a modulator for rotating complex baud impulses from the transmitter, means responsive to the complex signal generator means for developing a vector history of information to be transmitted for a plurality of taps, means for storing a plurality of tap adaptation values, means for obtaining a series of dot products for a vector for tap information and a corresponding tap adaptation value to obtain a series of tap echo estimate signals, means for dividing received information into a plurality of vectors corresponding to tap values to minimize processing load, and means for summing the series of dot products and the vectors to obtain received information samples with the echo estimate removed.

Claim 34

An echo cancellation apparatus for removing echo in received information characterised in a modulator for rotating complex baud impulses from the transmitter, means responsive to the complex signal generator means for developing a vector history of information to be transmitted for a plurality of taps, means for storing a plurality of tap adaptation values, means for obtaining a series of dot products for a vector for tap information and a corresponding tap adaptation value to obtain a series of tap echo estimate signals, means for dividing received information into a plurality of vectors corresponding to tap values to minimize processing load, and means for summing the series of dot products and the vectors to obtain received information samples with the echo estimate removed.

Claim 35

An echo cancellation apparatus as claimed in claim 31, characterised in that the echo estimate signal is derived in an adaptive manner by repetitively developing the echo estimate signal from received information samples with the echo estimate removed.

Claim 36

A tone detector for detecting energy level associated with a plurality of tones characterised in means for receiving samples of information, means for converting each sample into a vector representation related to each of the plurality of tones to be detected and obtaining a summation for a plurality of vectors each related to one of the plurality of tones to be detected, means for summing products of each vector related to one of the plurality of tones to be detected with the product of a previous vector, means for obtaining the negative logarithm of the absolute value of the products summed, means for obtaining a sum log quantity for the negative logarithms obtained, means for comparing the sum log quantity with a background level, the means for comparing indicating the presence of differing ones of the plurality of tones, and means for counting the successful detects and determining when sufficient confidence has been achieved to set a detect flag.

Claim 37

A tone detector for detecting energy level associated with a plurality of tones characterised in means for receiving samples of information, means for converting each sample into a vector representation related to each of the plurality of tones to be detected and obtaining a summation for a plurality of vectors each related to one of the plurality of tones to be detected, means for summing products of each vector related to one of the plurality of tones to be detected with the product of a previous vector, means for obtaining the negative logarithm of the absolute value of the products summed, means for obtaining a sum log quantity for the negative logarithms obtained, means for comparing the sum log quantity with a background level, the means for comparing indicating the presence of differing ones of the plurality of tones, and means for counting the successful detects and determining when sufficient confidence has been achieved to set a detect flag.

Claim 38

An automatic gain control for received information provided to a modem characterised in a variable attenuation device, an a to D converter connected to the variable attenuator device, a MU-LAW to linear converter connected to the A to D converter, the MU-LAW to linear converter having an output, means for multiplying the output of the MU-LAW to linear converter by a selected quantity, and means for modifying the selected quantity and the variable attenuation device until the negative logarithm of received information energy falls within prescribed boundaries.

Claim 39

An automatic gain control for received information provided to a modem characterised in a variable attenuation device, an a to D converter connected to the variable attenuator device, a MU-LAW to linear converter connected to the A to D converter, the MU-LAW to linear converter having an output, means for multiplying the output of the MU-LAW to linear converter by a selected quantity, and means for modifying the selected quantity and the variable attenuation device until the negative logarithm of received information energy falls within prescribed boundaries.

Claim 40

Modulator/demodulator apparatus employing distributed processor control for a two wire full duplex modulation/demodulation communications channel characterised in a transmission digital signal processor means operable in a full duplex mode for providing digital information to be transmitted to a coder decoder and for receiving information therefrom, the transmission signal processor including echo cancellation means responsive to received information to provide echo cancellation to the received information, automatic gain control means coupled to the echo cancellation means and responsive to the echo cancellation to provide automatic gain control to the received information as echo cancelled, tone detection means responsive to received information for detecting tones associated therewith to determine service requests for the two-wire communications channel, a receive digital signal processor means responsive to the digital information from the transmission digital signal processor and operable to demodulate the information for outputting demodulated message information, the receive processor including interpolation means for providing an outputted message at a new data rate and coupled to baud sync means for synchronizing the interpolated data to the received data, wherein the outputted message is to be directed to at least one user device, an input/output processor means coupled via control channel means to the transmit and receive digital signal processor means to provide high level control of the processor means wherein a first control channel means is operative to control the echo cancellation means in the transmission processor, and a second control channel means is operative to control the automatic gain control means and a third control channel means is operative to control the tone detection means and a fourth control channel means is operative to control the interpolation means of the receive processor means according to the information received from either the transmit or receive processors in a full duplex mode.

Claim 41

Modulator/demodulator apparatus employing distributed processor control for a two wire full duplex modulation/demodulation communications channel characterised in a transmission digital signal processor means operable in a full duplex mode for providing digital information to be transmitted to a coder decoder and for receiving information therefrom, the transmission signal processor including echo cancellation means responsive to received information to provide echo cancellation to the received information, automatic gain control means coupled to the echo cancellation means and responsive to the echo cancellation to provide automatic gain control to the received information as echo cancelled, tone detection means responsive to received information for detecting tones associated therewith to determine service requests for the two-wire communications channel, a receive digital signal processor means responsive to the digital information from the transmission digital signal processor and operable to demodulate the information for outputting demodulated message information, the receive processor including interpolation means for providing an outputted message at a new data rate and coupled to baud sync means for synchronizing the interpolated data to the received data, wherein the outputted message is to be directed to at least one user device, an input/output processor means coupled via control channel means to the transmit and receive digital signal processor means to provide high level control of the processor means wherein a first control channel means is operative to control the echo cancellation means in the transmission processor, and a second control channel means is operative to control the automatic gain control means and a third control channel means is operative to control the tone detection means and a fourth control channel means is operative to control the interpolation means of the receive processor means according to the information received from either the transmit or receive processors in a full duplex mode.

Claim 42

An apparatus as claimed in claim 35, characterised in that the input/output processor means directs the control of the automatic gain control means in the transmission processor via the first control means including means for calling up automatic gain control subroutines based on energy levels received from either the transmission or receive processors by means for implementing negative logarithms including means for implementing antilog routines to provide relatively constant signal levels for transmission and reception by the transmission and receive processors.

Claim 43

An apparatus as claimed in claim 35, characterised in that the echo cancellation means is a sample rule echo canceler.

Claim 44

An apparatus as claimed in claim 35, characterised in that the echo cancellation means is a baud rate echo canceler.

Claim 45

An apparatus as claimed in claim 37, characterised in that the echo cancellation means includes a plurality of echo cancellation taps, means responsive to received information to provide an echo estimate for the information, and means for providing an inverse auto correlation matrix to achieve a convergence for the plurality of echo cancellation taps.

Claim 46

An apparatus as claimed in claim 39, characterised in means responsive to the transmit to receive cross correlation function and the inverse auto correlation matrix to provide the convergence value for the taps.

Claim 47

An apparatus as claimed in claim 38 characterised in that the baud rate canceler includes complex vector generation means for rotating and storing baud vectors each indicative of an echo cancellation value.

Claim 48

An apparatus as claimed in claim 35, characterised in that the echo cancellation means includes controlled feedback means for providing discrete timing signals for the equalization taps.

Claim 49

An apparatus as claimed in claim 35, characterised in that the tone detection means includes a plurality of sine-cosine FIR filter means each for measuring tone energy at associated discrete frequencies indicative of desired tones with each filter in the plurality operative to reject all tones except the associated tone.

Claim 50

An apparatus as claimed in claim 35, characterised in that the receive digital signal processor means includes buffer means coupled to the input/output processor means to load received samples from the input/output processor means, interpolation means coupled to the buffer means to interpolate the samples to define the correct baud position of the samples, equalizer means coupled to the interpolation means to equalize the corrected samples according to an equalizer angle, conversion means coupled to the equalizer means to convert the equalized corrected samples to polar coordinates, means coupled to the conversion means and the equalizer means to subtract a carrier angle from the equalized angle to obtain a modulation angle, means responsive to the modulation angle to subtract the angle from an ideal modulation angle to obtain an error signal, a phase locked loop responsive to the error signal for providing at an output a corrected carrier signal.

Claim 51

An apparatus as claimed in claim 44, characterised in means responsive to a first and a second modulation angle to provide a control signal at an output indicative of the difference therebetween.

Claim 52

An apparatus as claimed in claim 44, characterised in means for generating the ideal modulation angle by quantizing means operative to quantize the modulation angle to a given significant number of bits.

Claim 53

An apparatus as claimed in claim 44, characterised in means for generating the ideal modulation angle by replacating means responsive to a synchronized information signal to obtain an expected data pattern indicative of the modulation angle including means to synchronize GPA or GPC pattern with the mode message for a smooth rate transition.

Claim 54

An apparatus as claimed in claim 44 further including means to derive equalizer error signals ( X, Y) from equalizer angle O and the error angle.