JPH0748630B2 - Transversal type automatic equalizer - Google Patents

Description

The present invention relates to a transversal type automatic equalizer generally used in data modems and the like.

[Conventional technology]

Conventionally, this type of transversal type automatic equalizer is composed of an N-tap FIR (finite impulse response) filter and a control means for controlling N tap coefficients of the filter, and a device such as a modem encounters this. It had a tap length sufficient to cope with the worst possible line that would be expected, that is, the line with the longest impulse response in the transmission line, which tap length was device-specific and invariant. Therefore, the delay in the modem device was almost determined by the tap length of this automatic equalizer.

[Problems to be solved by the invention]

Therefore, in the above-mentioned conventional automatic equalizer, the intra-device delay is determined by the worst line as the design target. However, there is a drawback in that it is hard to say that the optimum characteristics are exhibited from a comprehensive viewpoint, such as the delay in the device becomes longer and the throughput of the system including this device is reduced.

An object of the present invention is to provide a transversal type automatic equalizer capable of eliminating the above-mentioned drawbacks, reducing the delay in the above-mentioned apparatus, and improving the throughput of the above-mentioned system.

[Means for solving problems]

According to the present invention, in a transversal type automatic equalizer including an N-tap FIR filter and a control means for controlling N tap coefficients of the FIR filter, the control means has the N tap coefficients. When the numbers are numbered 0, 1, 2, ..., N-1 in order from the one closest to the input of the FIR filter, the absolute values of the 0th to Lth tap coefficients (L <N) are all predetermined. L + 1 to N-
A means for shifting the first tap coefficient as the 0th to NL-2nd tap coefficients, respectively, and setting all the remaining NL-1th to N-1th tap coefficients to zero. A transversal type automatic equalizer is obtained.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the automatic equalizer of the present invention. The input signal is input to the delay device 101 which produces a T second delay. The output D ₀ of the delay device 101 is multiplied by the tap coefficient C ₀ which is the output of the tap coefficient generator 102-0 by the multiplier 103 and input to the accumulator 104. Similarly, delay device outputs D _{1 to} D ₁₉
Is also multiplied by tap coefficients C _{1 to} C ₁₉ and input to the accumulator 104. The accumulator 104 adds all these inputs and outputs it. The tap coefficient output from the tap coefficient generators 102-0 to 102-19 is adjusted by the control unit 106 to optimally equalize the line characteristics. The algorithm for this adjustment is not particularly described, but a well-known gradient method or the like may be adopted.

On the other hand, the tap coefficient output from the tap coefficient generator 102-0 is converted into an absolute value by the absolute value converters 105-0 to 105-19 and input to the control unit 106.

If the values of the tap coefficients C _{0 to} C ₂₀ are expressed by a graph,
It becomes like the figure. Figure 2 (a) is a tap coefficient when the line characteristics are relatively poor, all the tap coefficients to C ₀ -C ₁₉ has a significant value.

Fig. 2 (b) shows the tap coefficients when the line characteristics are relatively excellent, and the nine tap coefficients C _{0 to} C ₈ have very small absolute values of 0.01 or less, so there are almost no tap coefficients. Is the meaning.

By the way, in such a case, the delay from the input of the signal to the automatic equalizer to the output thereof is the time from C ₀ to C ₁₂ having the largest value, that is, 13 × T (seconds).

In the case of the tap coefficient as shown in FIG. 2 (b), since C _{0 to} C ₈ are meaningless, the tap coefficient is shifted as shown in FIG. 2 (c) and the taps of C _{0 to} C ₁₀ are made. The coefficient is C ₉ to C in Fig. 2 (b).
Each equal to the tap coefficients of the _19, the C ₁₁ -C ₁₉ sets zero. Then, since the tap coefficient sequence in FIG. 2 (c) has the same shape as that in FIG. 2 (b), the response to the signal is unchanged, but in FIG. 2 (c), the tap coefficient having the largest value is obtained. Is C ₃ , so the delay in this automatic equalizer is 4 ×
It becomes T (second).

That is, the automatic equalizer having the tap coefficient shown in FIG.
Compared to that of Fig. 2 (b), while maintaining the same characteristics,
The delay is reduced by 9 × T (seconds).

The above control is performed by the control unit 106. Such control is generally performed in a transversal type automatic equalizer including an N-tap FIR filter and a control unit (106) for controlling N tap coefficients of the FIR filter. When the tap coefficients are numbered as 0, 1, 2, ..., N-1 in order from the one closest to the input of the FIR filter, the absolute values of the 0th to Lth (L <N) tap coefficients are all If it is smaller than a predetermined value ε, L + 1 to N−
The control unit is configured to shift the 1st tap coefficient as 0th to NL-2nd tap coefficients, respectively, and set all remaining NL-1th to N-1th tap coefficients to zero. Is achieved by including.

The operation procedure of the control unit 106 for achieving the above series of control operations is shown in the flowchart of FIG.

P01 to P10 represent a total of 11 processes. P01-P03 is C ₀
It is a process of counting the tap coefficient up to which is smaller than ε (= 0.01). P04 to P07 are processes for shifting tap coefficients based on the results of the above-mentioned process, and P08 to P10 are processes for setting the remaining tap coefficients to zero.

The example in which the present invention is applied to the 20-tap automatic equalizer has been described above, but it is obvious that the present invention can be applied to automatic equalizers having other configurations, such as a complex automatic equalizer and a double sampling type automatic equalizer. Is.

〔The invention's effect〕

As described above, the present invention shifts the tap coefficient of the automatic equalizer forward when the line characteristic is excellent,
This has the effect of reducing the delay in the device having this automatic equalizer and contributing to improving the throughput of the system including this device.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of an example of a tap coefficient, and FIG. 3 is a flowchart of a control procedure according to the present invention. 101 ... Delay device, 102-0 to 102-19 ... Tap coefficient generator, 103-0
~ 103-19 ... Multiplier, 104 ... Accumulator, 105-0 to 105-19 ... Absolute value converter, 106 ... Control unit

Claims (1)

[Claims] 1. A transversal type automatic equalizer including an N-tap FIR filter and a control means for controlling N tap coefficients of the FIR filter, wherein the control means includes the N tap coefficients for the N tap coefficients. When numbering 0, 1, 2, ..., N-1 in order from the closest to the input of the FIR filter, the absolute values of the 0th to Lth (L <N) tap coefficients are all predetermined. If smaller than the value, L + 1 to N
A means for shifting the -1st tap coefficient as the 0th to NL-2nd tap coefficients and setting the remaining NL-1th to N-1th tap coefficients to zero. Characteristic transversal type automatic equalizer.