Adaptive transversal equalizer

Abstract: A processing unit (8) extracts the variance of the output of an adaptive transversal equaliser (1), and the level of the received signal is scaled according to this variance, before being fed to a decision unit (2). The equaliser (1) is updated according to the difference between the input and output of the decision circuit (2).

Description: Background of the Invention Field of the Invention The present invention relates to an automatic equalizer which is caused to converge by a received signal and a data mode convergence method. Description of the Related Art Modems (modulator/demodulator devices) have widely been used for data transmission over voice-grade analog lines. Modems are provided with automatic equalizers, for example, which correct that distortion of the received signal caused by an analog transmission line and establish synchronization of the received data. As is known, when a terminal transmits data to another terminal by using an analog voice line, the terminal on the receiving side performs a preset of an automatic equalizer of the modem of the local apparatus, a reproduction of a timing and a gain control of a gain control circuit based on the training signal, thereby enabling the automatic equalizer to converge so that the distortion of the data is corrected and data can be demodulated. On the other hand in a data transmission system in which a center apparatus and a plurality of terminals are connected to a single transmission line in parallel which is called a multi point system, it is necessary to enable the automatic equalizer to converge by making the center apparatus transmit a training signal every time the terminal diverges, when the automatic equalizer of the modem on the terminal loses its equalizing capability, and the automatic equalizer attempts to converge in accordance with the above method at the time of the divergence of the equalizer of the modem on the terminal. Therefore the above method of enabling the diverged automatic equalizer to converge decreases the efficiency of the data processing operation in the whole system. Therefore, the data mode convergence method for enabling the automatic equalizer to converge with respective terminals receiving data has been proposed and some examples are shown in Japanese Patent early disclosure number 56-78243 and Japanese Patent Application No.1-36284. The conventional data mode convergence method is explained by referring to Figures 1 to 4. In the multi point system, modem 11 to 13 of a plurality of terminals (slave station) 16 are connected to the modem 10 on the master station such as center 15 in parallel through an analog voice line. In this system, the master station modem 10 operates at all times and the slave station modems 11 to 13 have their power sources turned on only when necessary, thereby transmitting the data. The transmission side modulates data when the data transmission is utilizing the analog line, divides the data to be transmitted into groups of predetermined numbers of bits, (for example, three bits in Figure 2A) and assigns the divided data to n, (for example, eight in Figure 2A) signal points on a two dimensional plane. The receiving side demodulates the received data by judging to which signal point chosen out of the n signal points the received signal corresponds based on the coordinate data (this is referred to as receiving on the two dimensional plane), the point in the coordinate data being called the receiving point. Figure 3 is a schematic diagram of a conventional automatic equalizer. In the automatic equalizer the decision section 2 determines the target signal point based on the output of the automatic equalizer (EQL) 1, namely, the coordinate data on the two dimensional plane of the received signal whose gain is controlled by an AGC controller (to be described later) in the automatic equalizer 1. An arithmetic unit calculates the difference between the predecision input (i.e., input signal of a decision means) and postdecision output (i.e., output signal of a decision means), thereby obtaining error data. Multiplier 6 multiplies the error data by a signal designating whether the determined signal point is outside the region surrounded by a dotted line in Figure 2A or inside the region surrounded by the dotted line, (namely, "1" if it is outside the region and "0" if it is inside the region.) If the signal point is located outside the dotted line shown in Figure 2A, multiplier 6 multiplies error data by "1". When the signal point is located inside the dotted line, the multiplier 6 multiplies the data error data by "0". This is because the signal point inside the dotted line in Figure 2A has a high possibility of being mistaken as the distances between signal points are short and the amount of interference between the data is large. Thus the tap coefficients of automatic equalizer 1 are corrected by using error data of the signal points outside the dotted line which have a lower possibility of being mistaken. On the other hand, normalized data NOR from the decision section 2 and the predecision output are applied to a carrier automatic phase correcting section (CAPC) 5 where a phase correcting quantity is calculated. The output of the automatic equalizing section is multiplied by the phase correcting quantity by a multiplier 3, thereby performing phase correction. At the same time, the phase correcting quantity and the output of the multiplier 6 are multiplied by a multiplier 7 and the result is output to the automatic equalizing section 1 as a tap correcting quantity. In order to enable the automatic equalizer to converge, it is necessary to adjust the output level of automatic equalizer 1 to the optimum value as a first step and to correct the phase of the output of automatic equalizer 1 as a second step. Figure 4 shows an example of an arrangement of the automatic equalizing section 1. The error output of the multiplier 7 (CAPC error) and center tap data are multiplied by a multiplier 103, and the result is then multiplied by a given control coefficient α in a multiplier 104. The result of multiplication is output to an AGC 105 as a reference voltage. The AGC 105 controls the level of an equalized output of an adder 102 according to the reference voltage, outputting the resulting tap coefficient to a multiplier 101. In this way, the automatic equalizer is made convergent while the respective terminals are receiving the data. However, the conventional data mode convergence method has the following drawbacks. (1) The algorithm used in the conventional technique has not been established. In order to accommodate various types of lines, it is necessary to determine the control coefficient α shown in Figure 4 on the basis of experimental results. However, it is 10 difficult to determine the optimum value by experiment because signal points are made multi-valued, and the level adjustment for convergence is difficult. (2) In the prior art, it takes time for the automatic equalizer to change from a state in which it does not completely converge, that is, the receiving points are spread out and distributed around the signal points as shown in Figure 2C, to a state in which the automatic equalizer reaches convergence as shown in Figure 2B where the output level of automatic equalizer 1 is controlled to be constant. (3) Both the phase error and amplitude error are fed back, and thus it takes time to enable the automatic equalizer to converge. JP-A-60-210032 discloses an automatic equalizer according to the preamble of claim 1. More particularly, it discloses an automatic equalizer comprising an equalizer, an AGC (auto gain control circuit), a deciding circuit, and a subtractor. A tap coefficient of the equalizer is controlled by means of an error signal obtained by the subtractor. According to the present invention, there is provided an automatic equalizer comprising: automatic equalizing means; first decision means for deciding a signal point corresponding to an input signal from said automatic equalizing means and error compensating means for obtaining an error signal of an input and an output signal of said decision means, and controlling an equalization characteristic of said automatic equalizing means based on the error signal; characterised by: dispersion extracting means for extracting the degree of dispersion on a two-dimensional plane of the output signal of the automatic equalizing means, and correcting said output signal of said automatic equalizing means to a proper level according to said extracted dispersion; said decision means deciding the signal point based on the signal corrected by said dispersion extracting means. An embodiment of the present invention provides an automatic equalizer which can adjust the level of an input of a decision means and permit convergence in a short time without depending on experiments. Another embodiment of the present invention provides an automatic equalizer which extracts only amplitude errors for speedy convergence. A feature of the present invention resides in an automatic equalizer which makes a decision for an output signal of an equalizing section by a first decision section to obtain received data and corrects tap coefficients of said equalizing section on the basis of an error signal obtained from an input and output of a first decision means with provision of a dispersion extracting section for extracting the dispersion of the output signal of said equalizing section and changing said input signal of the decision means to a proper level according to the extracted dispersion. For example, when a signal point decision is made after the output signal of the equalizing section has been controlled to have a constant level, the dispersion of the signal point decided on becomes large at convergence time and small at divergence time. Therefore, since the input signal of the decision means can be changed to a proper level according to the dispersion, it is possible to prevent the input signal of the decision means from deviating greatly from the optimum level greatly. That is, the convergence can be speeded up. Reference is made, by way of example, to the attached drawings in which: Figure 1 illustrates an arrangement of a multipoint system; Figure 2A to 2C are diagrams for use in explanation of an eye pattern; Figure 3 illustrates an arrangement of a conventional automatic equalizer; Figure 4 illustrates an arrangement of the automatic equalizing section of Figure 3; Figure 5 is a diagram for use in explanation of the fundamental principle of the present invention; Figure 6 is a block diagram of an automatic equalizer according to an embodiment of the present invention; Figure 7 illustrates an arrangement of the AGC control section of Figure 6; Figure 8 illustrates an arrangement of the reference value extracting section of Figure 6; Figure 9 illustrates an arrangement of the carrier automatic phase correcting section; Figs. 10A and 10B are diagrams for use in explanation of level adjust operation; Figures. 11A, 11B and 11C are diagrams for use in explanation of amplitude error; and Figure 12 illustrates an arrangement of the amplitude error extracting section of Figure 6. Figure 5 illustrates a basic arrangement of the present invention. According to a first feature (operation mode) of the present invention, a variance (i.e. dispersion) extracting section 8 extracts the variance of an output signal of a transversal automatic equalizing section 1 and changes a predecision input signal level (i.e. signal level input to a decision means) to the optimum level according to the extracted variance. According to a second feature of the present invention, the amplitude error extracting section 9 extracts an amplitude error from a predecision input signal and a postdecision output signal (i.e. signal output from the decision means) and corrects tap coefficients of the transversal automatic equalizing section 1 according to the amplitude error extracted. According to a third feature of the present invention, the variance extracting section 8 extracts the variance of an output signal of the transversal automatic equalizing section 1 and changes a predecision input signal level to the optimum level according to the extracted variance, and the amplitude error extracting section 9 extracts an amplitude error from a predecision input signal at decision 8 and a postdecision output signal (i.e. the output signal from the decision means) to correct the tap coefficients of the transversal automatic equalizing section 1. With the conventional data mode convergence method in which the degree of divergence of the transversal automatic equalizing section 1 is extracted, since when the received signal level becomes small as a result of divergence, the automatic equalizing section 1 makes its output level large, its output value is greatly deviated from the optimum value, thus delaying the convergence. Therefore, it is necessary to multiply the reference signal of the AGC 105 by the control coefficient α. In the first operation mode of the present invention, on the other hand, the variance (i.e., dispersion) of the output signal of the transversal automatic equalizing section 1 is extracted and the predecision input level is changed to the optimum level according to the extracted variance. Therefore, the eye can be changed to the optimum value, the need for control coefficients α is eliminated, and the automatic equalizer is able to converge in a short time. In the conventional method, the error data including both the amplitude and phase error is multiplied by the output data of the carrier automatic phase compensating unit (CAPC) 5 and thus the incorrect phase error is multiplied by the output data, thereby causing the tap coefficients of the transversal automatic equalizer 1 to deviate from the optimum value. The tap coefficient is corrected to an optimum value and thus the automatic equalizer can converge within a short time. In contrast, in the present invention, an amplitude error is extracted from an input and output of a decision means and the tap coefficients of the transversal automatic equalizing section 1 are corrected according to the extracted amplitude error. Therefore, the tap coefficients are corrected based on whether the amplitude error data obtained by decision section 2 is located outside a signal point in which the intra data interference is small or the amplitude error data obtained by the decision section 2 is inside a signal point in which the intra data interference is large. Thus, there is little probability of correcting the tap coefficients according to wrong amplitude error data. This permits the automatic equalizer to converge in a shorter time. In a fourth feature of the present invention, in order to extract the dispersion of the output of the transversal automatic equalizing section 1, a signal point decision is made after the output of the automatic equalizing section 1 is made constant by a first automatic gain control section, the result of the decision is corrected by a second automatic gain control section, and a reference value is obtained from the corrected value. The reference value is output to a third gain control section which changes the output of the automatic equalizing section 1 to a proper level according to the reference value. In a fifth feature of the present invention, the energy at a receiving point is calculated using secondary approximation, and an amplitude error is calculated from the difference in energy between points of reception. The use of the secondary approximation, which is simple in operation, for calculating energy at points of reception permits the amplitude error to be calculated easily. Hereinafter, a specific arrangement of the automatic equalizer of the present invention will be described with reference to Figure 6. In Figure 6, like reference numerals are used to denote blocks corresponding to those in the conventional automatic equalizer shown in Figure 3. The variance extracting section 8 extracts the variance of the equalized output of the transversal automatic equalizing section 1. The amplitude error extracting section 9 extracts an amplitude error from the absolute value |Ref| of a vector at a signal point and the predecision input signal. The variance extracting section 8 comprises a first automatic gain control section 80 for holding the amplitude of the equalized output of the automatic equalizing section 1 substantially constant, a decision section 81 for allocating the output signal of the first automatic gain controller 80 to a signal point, a second automatic gain control section 82 for holding the amplitude of the signal-point output of the decision section 81 substantially constant, a reference value extracting section 83 for extracting a reference value from the AGC controlled variable from the second automatic gain control section 82, and a third automatic gain control section 84 for holding the equalized output of the transversal automatic equalizing section 1 substantially constant according to the reference value extracted by the reference value extracting section 83. The decision section 81 is equipped with a ROM storing a table which makes coordinate data of each of signal points arranged on a two-dimensional plane correspond with the decision result for the signal point, the distance |Ref| between the signal point and the origin, and data (1 or 0) indicating whether the signal point exists in the inside area (called the dead zone) in which the amount of interference between data is large or in the outside area in which the amount of interference between data is small. When the real part and imaginary part of a receiving point are obtained, a reference is made to the coordinate data in the table to decide the signal point closest to the coordinate data of the receiving signal on the two dimensional plane, so that the decision result, the distance |Ref| and the 1/0 data for the signal point are output. The 1/0 data indicates whether the decided signal point exists in the outside area or the inside area. Reference will now be made to figure 7 to describe the arrangement of the second automatic gain control section 82. This section comprises a squarer 820 which squares its input to calculate the input energy, an adder 821 which subtracts the output of the adder 820 from the input energy calculated from the reference value, a multiplier 822 which multiplies the output of the adder 821 by a coefficient α, a tap section 823 for delaying the adder output, an adder 824 which adds the output of the multiplier 822 and the output of the tap section 823, a multiplier 825 for multiplying the adder output by a coefficient b, an adder 826 which adds a coefficient c to the output of the multiplier 825, and a multiplier 827 which multiplies the input to the automatic gain control section 82 by the output of the adder 826. The output signal of the adder 824 is output to the reference value extracting section 83 as an AGC control signal. The first and third automatic gain control sections 80 and 84 are also configured as shown in Figure 7. The reference value extracting section 83 is constructed, as shown in Figure 8, from a polarity conversion section comprising a multiplier 830 which multiplies the AGC control signal output from the second automatic gain control section 82 by a coefficient d of negative polarity and an adder 831 which adds a coefficient f to the output of the multiplier 830, thereby outputting the reference value to the third automatic gain control section 84. The carrier automatic phase correcting section 5 is constructed, as shown in Figure 9, from a multiplier 50 for multiplying the predecision input and the decision result NOR from the decision section 2, a first integrator 51 for integrating the output of the multiplier 50 to calculate its average component, an adder 53 for adding the output of the multiplier 50 and the output of the first integrator 51, and a second integrator 54 for integrating the output of the adder 53. The output of the second integrator 54 is multiplied by the equalized output of the automatic equalizing section 1 in the multiplier 3, thereby correcting the phase error component of the output signal from automatic equalizer. Also, in amplifier 7 the output of the second integrator 54 is multiplied by the product obtained by multiplying the amplitude error extracted from the amplitude error extracting unit 9 by 1/0 data representing whether the signal point is outside the dotted line shown in Figure 2A or inside the dotted line shown in Figure 2A. The tap coefficients of the automatic equalizer 1 can be corrected based on the output of the amplifier 7. Next, the operation of the automatic equalizer at the time of extraction of the variance will be described. When the output of the automatic equalizing section 1 is input to the first automatic gain control section 80 for level control, since the average level of the equalized output of the equalizing section 1 is low at divergence time, the output of the first automatic gain control section 80 is greater than the optimum level. In this state, the decision section 81 performs decision operation and assigns the received signal whose level is corrected by the first automatic gain control unit 80 to corresponding to a signal point on the two-dimensional plane and then upon at divergence, the received signal is subjected to a normalized distribution with the origin point of the two dimensional plane at its center of the divergence and thus more received signals are assigned to the signal point which is closer to the origin point in the two dimensional plane as shown by a black circle in Figure 2A. As a result, at divergence, the signal point at the center of the two dimensional plane is high in density and the distribution of the signal points is biased, thereby making the distribution smaller. In contrast at convergence, the received signal is distributed uniformly at respective signal points on the two dimensional plane, the received signal can be assigned to respective signal points as shown in Figure 10A and thus the divergence of the signal point becomes large. At this time, the average density of the signal points at divergence is lower than the average density of the signal points at convergence. As a result, the average level of the input signal to the second automatic gain controller 82 becomes large at convergence and becomes small at divergence. Therefore, the tap output of the automatic gain controller 82, namely, the AGC control signal becomes large at divergence and becomes small at convergence. That is, the AGC control signal indicates the degree of the variance of output of the automatic equalizing section 1. When the variance is great (at convergence time), the AGC control signal is small, otherwise it is great (at divergence time). In order to make the output of the automatic equalizing section 1 close to the optimum level, it is necessary to set the reference value of the third automatic gain control section 84 to be large at convergence time and small at divergence time. To this end, the reference value extracting section 83 multiplies the AGC control signal output from the second automatic gain control section 84 by a negative coefficient d (for example, -1/4) to convert the polarity and make the controlled variable small. This is output as the reference value for the third automatic gain control section 84. Figure 10B is a diagram for use in explanation of the operation when the AGC control signal is multiplied by -1/4 in the multiplier 830. When the AGC control signal is +2, the output of the multiplier 830 is -0.5. When the AGC control signal is -2, the multiplier output is +0.5. As a result, the third automatic gain control section 84 corrects the output of the automatic equalizer 1 so that the output levels does not become excessive divergence and so that the output level does not become too small at convergence, thereby outputting the corrected output as the predecision input to the decision section 2. By extracting divergence at signal point obtained when the output of the automatic equalizer 1, namely, the received signal subjected to the AGC control is assigned to the corresponding signal point and controlling the reference value for the third automatic gain control section 84 so that it may become large at convergence time and small at divergence time, the prior art problem that the output level of AGC controller becomes excessive at divergence and, deviates from an optimum value greatly and becomes difficult to converge is avoid, thereby enabling the automatic equalizer to converge within a short time. Next, a method of obtaining amplitude errors will be described. As shown in Figure 11A to 11C, when each of vectors (error components at received points) directed from received points r to signal points (indicated by black dots) is split into a component (amplitude component) directed to the origin and a component (phase component) orthogonal to the amplitude component, the amplitude components are substantially the same at any point, but the phase components differ in direction. If, therefore, only amplitude errors are extracted to pull in received data, data will be permitted to converge in a shorter time. Supposing here a vector at a received point to be |r|e jw and a vector at a signal point to be |Ref|, then the amplitude error will be represented by e jw (|Ref| - |r|) = |r|e jw (|Ref|/|r| - 1) In equation (1), |r|ejw indicates a vector at a signal point as described above and |Ref| indicates the absolute value of a vector at a signal point, which is obtained by the decision section 2. Thus, it is only required to obtain 1/|r|. 1/|r| can be calculated by equation (2) using a secondary approximation. 1/|r| = g(|r| 2 ) 2 +h(|r| 2 ) 2 +k Since |r| 2 can be expressed by equation (3), equation (2) can be rewritten as equation (4). |r| 2 = (r r 2 +r i 2 ) 1/|r| = g(r r 2 +r i 2 )+h(r r 2 +r i 2 )+k Figure 12 shows an example of an arrangement of the amplitude error extracting section 9 which implements the above arithmetic operation. The amplitude error extracting section 9 comprises a squarer 90 which squares a predecision output (received point) r to calculate energy, a squarer 91 which squares the output of the squaring section 90, a multiplier 92 which multiplies the output of the squarer 91 by a coefficient g, a multiplier 93 which multiplies the output of the squarer 90 by a coefficient h, an adder 94 which adds the outputs of the multipliers 92 and 93 together, an adder 95 which adds a coefficient k to the output of the adder 94, a multiplier 96 which multiplies the output of the adder 95 by the absolute value |Ref| of the signal point vector, an adder 97 which adds a coefficient m to the output of the multiplier 96, and a multiplier 98 which multiplies the predecision output by the output of the adder 97. That in, a signal input to the amplitude error extracting section 9 is squared by the squarer 90 and then multiplied by the coefficient h by the multiplier 93, and the output of the squarer 90 is squared by the succeeding squarer 91 and then multiplied by the coefficient g by the multiplier 92. The outputs of the multipliers 93 and 92 are added together by the adder 94. The coefficient k is added to the output of the adder 94 by the adder 95. Thereby, the operation of 1/|r| = g (|r 2 |) 2 + h (|r| 2 ) 2 + k is performed. Subsequently, the output of the adder 94 is multiplied by |Ref| by the multiplier 96 and then m = -1 is added to the output of the multiplier 96. Thereby, the operation of (|Ref| / |r| - 1) is performed. When the result of the above operation and the input signal |r|e jw is multiplied by the multiplier 98, the amplitude error represented by equation (1) is obtained. The amplitude error output and an outside signal point decision output (1 or 0) from the decision section 2 are multiplied by the multiplier 6 (refer to Figure 6), and the output of the multiplier 6 is multiplied by the output of the carrier automatic phase correcting section 5 by the multiplier 7. The output of the multiplier 7 is applied to the automatic equalizing section 1 to correct its tap coefficients. In this way, data convergence can be speeded up by extracting the amplitude error of a received signal and correcting the tap coefficients of the automatic equalizing section 1 according to the amplitude error. The present invention may be modified as follows. (1) In addition to the above method of calculating the energy at receiving points as the method of extracting the amplitude error, the receiving point is normalized to the signal point with phase 0° and only the real component (the amplitude component) of the error is extracted and thereafter the real component of the error may be reversely rotated to the signal point corresponding to the receiving point, namely, it may be assigned to the signal point corresponding to the receiving point. (2) Alternatively, after the amplitude component of the error is obtained by moving the receiving point along the circumference of a circle with radius 1 and then the amplitude component of the error is normalized by the magnitude of the signal point and thereafter the signal point is subtracted from the receiving point, thereby obtaining the amplitude error. Although the preferred embodiment of the present invention has been disclosed and described, it is apparent that other embodiments and modifications are possible. According to the present invention, since the divergence of the signal point subject to the decision is extracted and the gain of the AGC is controlled based on the divergence, a proper AGC control is applied to the received signal, thereby speeding up the convergence of the automatic equalizer. By extracting only the amplitude error from the error data between the receiving point and the signal point, and by correcting the tap coefficients of the transversal automatic equalizer using the amplitude error, the tap coefficients can be controlled at the maximum value, thereby speeding up the convergence of the automatic equalizer. The data mode convergence method of the present invention does not use control coefficient α and does not require a determination of the control coefficient α for particular lines through experimentation. Further am the convergence of the automatic equalizer is speeded up, the line cost can be reduced.

Claims: An automatic equalizer comprising: automatic equalizing means (1); first decision means (2) for deciding a signal point corresponding to an input signal from said automatic equalizing means (1); and error compensating means (9) for obtaining an error signal of an input and an output signal of said decision means (2), and controlling an equalization characteristic of said automatic equalizing means (1) based on the error signal; characterised by: dispersion extracting means (8) for extracting the degree of dispersion on a two-dimensional plane of the output signal of the automatic equalizing means, and correcting said output signal of said automatic equalizing means (1) to a proper level according to said extracted dispersion; said decision means (2) deciding the signal point based on the signal corrected by said dispersion extracting means (8). The automatic equalizer according to claim 1, wherein said dispersion extracting means (8) comprises: a first automatic gain control means (80) for changing the output signal of said automatic equalizing means (1) to a proper level, a second decision means (81) for deciding a signal point corresponding to the output signal of said first automatic gain control means (80), a second automatic gain control means (82) for outputting a signal indicating the degree of dispersion on the two-dimensional plane of the signal point decided by said second decision means (81), a reference value extracting means (83) for extracting a reference value from the signal indicating the degree of dispersion; and a third automatic gain control means (84) for changing the output signal of said automatic equalizing means (1) to a proper level according to said reference value. The automatic equalizer according to claim 1, wherein said automatic equalizing means (1) comprises a transversal automatic equalizer; said error compensating means (9) obtains an amplitude error signal from the input and the output signal of said decision means (2), and outputs a signal for changing a tap coefficient of the transversal automatic equalizer based on the amplitude error signal. The automatic equalizer according to claim 3, wherein said amplitude error compensating means (9) calculates energy at a receiving point by secondary approximation and extracts an amplitude error from a difference in energy between the receiving point and a signal point decided. The automatic equalizer according to claim 3, wherein said amplitude error compensating means (9) extracts the amplitude error by normalizing the receiving point by the signal point decided and then rotating in reverse the error which consists of the real component extracted toward the signal point decided. The automatic equalizer according to claim 3, wherein said amplitude error compensating means (9) extracts the amplitude error by moving a receiving point onto the circumference of a circle of radius 1, normalizing the receiving point by the magnitude of the signal point decided and then subtracting the receiving point. The automatic equalizer according to claim 3, wherein said first decision means (2) outputs to said amplitude error compensating means (9) a signal indicating whether or not a signal point decided is a signal point where the amount of interference between data is small, and said amplitude error compensating means (9), when the signal point decided is a signal point where the amount of interference between data is small, corrects the tap coefficients of said automatic equalizing means (1) according to an amplitude error extracted and to a signal outputted by said first decision means (2). The automatic equalizer according to claim 3 and 4, wherein said amplitude error compensating means (9) comprises: a first squarer (90) for squaring the output signal of said automatic equalizing means (1), a second squarer (91) for squaring an output signal of said first squarer (90), a first multiplier (93) for multiplying an output signal of said first squarer (90) by a predetermined value h, a second multiplier (92) for multiplying the output signal of said second squarer (91) by a predetermined value g, a first adder (94) for adding an output signal of said first multiplier (93) and an output signal of said second multiplier (92), a second adder (95) for adding a predetermined value k to an output signal of said first adder (94), a third multiplier (96) for multiplying an output signal of said second adder (95) by the absolute value of a signal point, a third adder (97) for adding a predetermined value m to an output signal of said third multiplier (96), and a fourth multiplier (98) for multiplying a predecision input signal by an output signal of said third adder (97). The automatic equalizer according to claim 1, wherein said error compensating means (9) obtains an amplitude error signal from the input and the output signal of said first decision means (2), outputs the amplitude error signal to said automatic equalizing means (1), and controls an equalization characteristic of said automatic equalizing means (1). The automatic equalizer according to claim 1, wherein said dispersion extracting means (8) comprises: first automatic gain control means (80) for changing the output signal of said automatic equalizing means (1) to a proper level; second decision means (81, 82) for deciding a signal point corresponding to an output signal of said first automatic gain control means (80), and outputting the signal indicating the degree of dispersion on the two-dimensional plane of the decided signal point; and second automatic gain control means (84) for correcting a level of the output signal of said automatic equalizing means (1) based on the signal indicating the degree of dispersion, which is output from said second decision means (81, 82). The automatic equalizer according to claim 10, wherein said automatic equalizing means (1) comprises a transversal automatic equalizer, and changes a tap coefficient of said transversal automatic equalizer based on the amplitude error signal output from said error compensating means (9).

Inventors: HIRAO KYOKO, KAKU TAKASHI, HIRAO, KYOKO, KAKU, TAKASHI, HIRAO, KYOKO, C/O FUJITSU LIMITED, KAKU, TAKASHI, C/O FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1993
Main classification: H04L25
IPC codes: H03H15, H04B3, H04L25, H03H17, H03H21