System for, and method of, transmitting and receiving through telephone lines signals representing data
First Claim
1. In combination for transmitting from a transmitter and receiving at a receiver through telephone lines data represented by successive digital signals indicating analog levels in a plurality as increments of data,first means for modulating the successive digital signals with digital signals in a pseudo random code,second means responsive to the digital signals from the first means for converting such digital signals to corresponding analog signals and for introducing the analog signals into the telephone lines for transmission through the telephone lines,third means responsive to the analog signals passing through the telephone lines for converting such analog signals to corresponding digital signals,a linear echo canceller having a first plurality of adjustable coefficients,fourth means, including the linear echo canceller, responsive to the digital signals from the third means and the digital signals in the pseudo random code, adjusted in accordance with the adjustable coefficients in the first plurality, for comparing such digital signals to cancel the digital signals transmitted from the receiver to the transmitter and reflected from the transmitter back to the receiver to obtain resultant digital signals and for adjusting the coefficients in the first plurality in the linear echo canceller in accordance with the results of such comparison,a non-linear echo canceller having a second plurality of adjustable coefficients,fifth means, including the non-linear echo canceller, responsive to the resultant digital signals from the fourth means and the digital signals in the pseudo random code, adjusted in accordance with the adjustable coefficients in the second plurality, for comparing such digital signals to provide an enhanced approximation of the digital signals representing the data and for adjusting the coefficients in the second plurality in accordance with the results of such comparison, andsixth means responsive to the digital signals from the fifth means for processing such digital signals to recover the digital signals representing the data.
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Accused Products
Abstract
Analog signals representing individual digital values (±1, ±3) pass through a telephone line to a receiver. These signals may be first provided in a pseudo random sequence. A linear echo canceller and a first adder eliminate, to an extent, echo signals resulting from second analog signals transmitted on the same telephone line by the receiver. A non-linear echo canceller and a second adder further reduce the echo signals and specifically reduce non-linear components in the echo signals. Adjustable signal delays achieve optimal performance of the linear and non-linear echo cancellers. An equalizer containing four (4) different modules then compensates for signal distortions introduced by the telephone line and minimizes the effect of noise in the telephone line. The equalizer modules are a digital gain control element, a feed forward digital filter and two (2) feedback digital filters. A detector module produces in one of several different ways at the receiver an estimate of the digital data (±1, ±3) transmitted at the other end of the telephone line. The detector either extracts the digital information based on peaks in the received (non-equalized) signal or by adding the equalized signals with preset threshold values. A scrambler-descrambler module locally generates a replica of the digital symbols transmitted in analog form at the other end of the telephone line, based on a limited number (e.g. 23) of correctly detected digital values. The scrambler-descrambler module may also operate as a descrambler to recover data scrambled by the transmitter at the other end.
21 Citations
45 Claims
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1. In combination for transmitting from a transmitter and receiving at a receiver through telephone lines data represented by successive digital signals indicating analog levels in a plurality as increments of data,
first means for modulating the successive digital signals with digital signals in a pseudo random code, second means responsive to the digital signals from the first means for converting such digital signals to corresponding analog signals and for introducing the analog signals into the telephone lines for transmission through the telephone lines, third means responsive to the analog signals passing through the telephone lines for converting such analog signals to corresponding digital signals, a linear echo canceller having a first plurality of adjustable coefficients, fourth means, including the linear echo canceller, responsive to the digital signals from the third means and the digital signals in the pseudo random code, adjusted in accordance with the adjustable coefficients in the first plurality, for comparing such digital signals to cancel the digital signals transmitted from the receiver to the transmitter and reflected from the transmitter back to the receiver to obtain resultant digital signals and for adjusting the coefficients in the first plurality in the linear echo canceller in accordance with the results of such comparison, a non-linear echo canceller having a second plurality of adjustable coefficients, fifth means, including the non-linear echo canceller, responsive to the resultant digital signals from the fourth means and the digital signals in the pseudo random code, adjusted in accordance with the adjustable coefficients in the second plurality, for comparing such digital signals to provide an enhanced approximation of the digital signals representing the data and for adjusting the coefficients in the second plurality in accordance with the results of such comparison, and sixth means responsive to the digital signals from the fifth means for processing such digital signals to recover the digital signals representing the data.
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6. In combination for initially synchronizing transmission through telephone lines of data represented by successive digital signals from a transmitter and reception at a receiver of such data where the digital signals indicate particular ones of analog levels in a plurality as increments of data,
first means at the transmitter for initially providing successive digital signals having a pseudo random code and representing only a limited number of the analog levels in the plurality, second means responsive at the transmitter to the successive digital signals from the first means for converting such signals to corresponding analog signals for transmission through the telephone lines, third means responsive at the receiver to the analog signals transmitted through the telephone lines for converting such analog signals to corresponding digital signals, fourth means responsive to a limited number of the digital signal from the third means at the receiver for providing the successive digital signals having the pseudo random pattern, fifth means responsive at the receiver to a limited number of the digital signals from the third means for generating a sequence of digital signals in the pseudo random code with the limited number of analog levels in the plurality, and sixth means responsive to the signals from the third means and the fifth means for processing such signals to synchronize operation of the receiver with operation of the transmitter.
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10. In combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels, the digital signals being modulated in accordance with digital signals in a first pseudo random code, the receiver also receiving digital signals modulated in a second pseudo random code different from the first pseudo random code and transmitted from the receiver to the transmitter and reflected from the transmitter back to the receiver,
first means for receiving the analog signals passing through the telephone lines, second means responsive to the analog signals from the first means for converting such analog signals to corresponding digital signals, third means for providing the digital signals in the second pseudo random code, a linear echo canceller having a first plurality of coefficients, the linear echo canceller being responsive to a particular number of the successive digital signals from the third means for modifying such digital signals in accordance with the first plurality of coefficients, fourth means responsive to the digital signals from the second means for modifying such digital signals in accordance with the modified digital signals from the linear echo canceller and for introducing such modified digital signals to the linear echo canceller to obtain modifications in the coefficients in the first plurality in accordance with such modified digital signals, a non-linear echo canceller having a second plurality of coefficients less than the first plurality, the non-linear echo canceller being responsive to the digital signals in the pseudo random code from the third means for modifying such digital signals in accordance with the coefficients in the second plurality, and fifth means responsive to the digital signals from the fourth means for modifying such digital signals in accordance with the modified digital signals from the non-linear echo canceller and for introducing such modified digital signals to the non-linear echo canceller to obtain modifications in the coefficients in the second plurality in accordance with such modified digital signals.
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14. In combination at a receiver for receiving through telephone lines from a transmitter an analog signal corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels, the digital signals being initially modulated in accordance with digital signals in a first pseudo random code in representation of a minimal number of analog levels for facilitating a synchronization in operation of the receiver with the digital signals subsequently passing through the telephone lines to represent data, the receiver also receiving signals transmitted from the receiver to the transmitter and reflected by the transmitter to the receiver and modulated in a second pseudo random code different from the first pseudo random code,
first means responsive to the analog signal for converting such analog signal to digital signals in the first pseudo random code, second means for providing the digital signals in the second pseudo random code with the minimal number of analog levels, third means responsive to the digital signals from the first and second means for operating upon such signals to facilitate the recovery of the digital signals corresponding to the analog signal initially transmitted through the telephone lines with the first pseudo random code, fourth means responsive to the digital signals from the third means for detecting the peaks of such digital signals to provide a first approximation of the digital signals in the first pseudo random code with the minimal number of analog levels, fifth means responsive to the digital signals from the third means for operating upon such digital signals to provide the digital signals corresponding to the individual one of the minimal number of analog levels closest to the analog level of the digital signals from the third means, sixth means responsive to the digital signals from the fourth and fifth means for selectively passing individual ones of such digital signals, seventh means responsive to a limited sequence of the digital signals from the sixth means for producing an extended sequence of digital signals in the pseudo random code representative of the minimal number of analog levels, and eighth means responsive to the signals from a selective one of the sixth and seventh means and to the signals from the third means for indicating when operation of the receiver is synchronized with the digital signals transmitted to the receiver in the first pseudo random code.
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18. In combination at a receiver for receiving through telephone lines from a transmitter an analog signal corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels, the digital signals being modulated in accordance with digital signals in a first pseudo random code,
first means responsive to the analog signal passing through the telephone lines in representation of the data for producing digital signals corresponding to the analog signal, second means for providing digital signals in a second pseudo random code different from the first pseudo random code, the second pseudo random code constituting the code modulating analog signals transmitted from the receiver to the transmitter and reflected by the transmitter back to the receiver, third means responsive to the digital signals from the first and second means for providing at least a partial elimination in the digital signals from the first means of the digital signals modulated in the second pseudo random code and transmitted to the transmitter from the receiver and reflected by the transmitter back to the receiver, fourth means responsive to the digital signals from the second and third means for providing a further elimination, in the digital signals from the third means, of the digital signals modulated in the second pseudo random code and transmitted to the transmitter from the receiver and reflected by the transmitter back to the receiver, and fifth means responsive to the digital signals from the fourth means for recovering the signals representing the data from such signals.
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24. In combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels, the digital signals being initially modulated in accordance with digital signals in a pseudo random code having a minimal number of the analog levels,
first means for receiving the analog signals passing through the telephone lines and modulated in the pseudo random code, second means responsive to the received analog signals for converting such analog signals to corresponding digital signals, third means responsive to a limited number of the digital signals from the second means for generating a pseudo random code corresponding to the pseudo random code at the transmitter, fourth means responsive to the signals from the second and third means for synchronizing operation of the receiver with operation of the transmitter, the pseudo random code constituting a first pseudo random code, the digital signals received by the receiver including digital signals in a second pseudo random code different from the first pseudo random code, the digital signals in the second pseudo random code being transmitted from the receiver to the transmitter and being reflected from the transmitter back to the receiver, fifth means for generating digital signals in the second pseudo random code, and sixth means responsive to the digital signals from the second and fifth means for eliminating, from the digital signals from the second means, the digital signals modulated in the second pseudo random code and transmitted from the receiver to the transmitter and reflected from the transmitter back to the receiver, the fourth means being responsive to the digital signals from the second and sixth means for synchronizing operation of the receiver with operation of the transmitter.
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27. In a combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels and modulated in a first pseudo random code involving the analog levels, the digital signals being initially provided in a second pseudo random code representing a minimal number of analog levels for facilitating synchronization of operation of the receiver with operation of the transmitter,
first means responsive to the analog signals for converting such analog signals to corresponding digital signals, second means responsive to the digital signals from the first means for eliminating from such digital signals the digital signals previously transmitted from the receiver to the transmitter and reflected by the transmitter back to the receiver, third means at the receiver responsive to the digital signals from the second means for eliminating from each of such digital signals the effects of delays in previous digital signals from the second means, fourth means responsive to the digital signals from the third means for detecting the peaks of such digital signals, fifth means responsive to the digital signals from the third means for converting such digital signals to digital signals representing the analog levels closest in the plurality to the analog values of the digital signals from the third means, sixth means responsive to the digital signals from the fourth and fifth means for prioritizing such digital signals in a particular relationship and for passing such prioritized digital signals, seventh means responsive to the prioritized digital signals passed by the sixth means for generating, during production of the second pseudo random code at the transmitter, signals in a pseudo random code dependent initially upon a limited number of the prioritized digital signals generated in the second pseudo random code by the transmitter and thereafter upon an increased number of the prioritized digital signals in the second pseudo random code generated by the transmitter, and eighth means responsive to the digital signals from the fourth means and the seventh means during the production of the second pseudo random code for synchronizing operation of the receiver with operation of the transmitter.
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31. In combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels and modulated in a first pseudo random code involving the plurality of analog levels, the digital signals being initially provided in a second pseudo random code representing a minimal number of the plurality of analog levels for facilitating synchronization of operation of the receiver with operation of the transmitter,
first means responsive to the analog signals for producing digital signals representative of the analog signals, second means responsive to the digital signals from the first means in the second pseudo random code for recovering such digital signals, such code third means having a plurality of successive positions, the third means being responsive to a limited number of the digital signals from the second means for transferring such digital signals progressively to the successive positions in the third means, fourth means responsive to the digital signals shifted to the progressive positions in the third means for tapping such digital signals at particular ones of such progressive positions, fifth means responsive to the tapped digital signals and the digital signals from the second means for operating upon such digital signals in a particular relationship to obtain digital signals for introduction to the third means, and sixth means responsive to the digital signals from the second means and the digital signals from the fifth means for synchronizing the operation of the receiver with the operation of the transmitter.
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36. In combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels and modulated in a first pseudo random code involving the plurality of analog levels,
first means for receiving the analog signals transmitted from the transmitter and the analog signals transmitted from the receiver to the transmitter and reflected from the transmitter back to the receiver and modulated in a second pseudo random code different from the first pseudo random code, second means responsive to the analog signals received by the first means for converting such analog signals to digital signals representing the analog signals, third means for providing digital signals in the second pseudo random code, fourth means defining a first echo canceller having a first plurality of terminals with first adjustable coefficients, the fourth means being responsive to the digital signals from the third means for adjusting such signals in accordance with such first adjustable coefficients, fifth means responsive to the digital signals from the second means and the fourth means for comparing such digital signals and for adjusting the coefficients at the first plurality terminals in the fourth means in accordance with the results of such comparison, sixth means defining a second echo canceller having a second plurality of terminals, less than the first plurality of terminals, with adjustable coefficients, the sixth means being responsive to the digital signals from the third means for adjusting these digital signals in accordance with such adjustable coefficients, and seventh means responsive to the digital signals from the fifth means and the sixth means for comparing such digital signals to produce resultant signals and for adjusting the coefficients in the sixth means in accordance with such resultant signals.
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41. In combination at a receiver for receiving through telephone lines from a transmitter analog signals corresponding to digital signals representing data in accordance with individual ones of a plurality of analog levels, the digital signals being initially modulated in accordance with digital signals in a pseudo random code having a minimal number of analog levels,
first means responsive to the analog signals for producing digital signals representing the analog signals, second means including a plurality of registers responsive to a limited number of the digital signals from the first means for generating a sequence of digital signals in the registers in accordance with the pseudo random code, third means responsive to the sequence of signals from the registers for producing resultant digital signals for introduction to the second means, fourth means responsive to the digital signals from the first means and the resultant digital signals from the third means for synchronizing operation of the receiver with operation of the transmitter, fifth means, including the plurality of registers, responsive to the sequence of the digital signals from the first means for passing such digital signals when the receiver is receiving the analog signals representing the data, and sixth means responsive to the sequence of the digital signals from the fifth means for recovering the data when the receiver is receiving the digital signals representing the data.
Specification