KR19980028722A - Symbol Interference and Ghost Removable Equalizer and Its Ghost Position Determination Method - Google Patents

Abstract

The present invention relates to a symbol mutual interference and a ghost-removable equalizer and a ghost position discrimination method. In the related art, the symbol reciprocal interference (ISI) and the ghost are removed. There is a problem that can not be removed. Accordingly, the present invention configures a tap update and equalizer 210 for determining the presence or absence of ghosts from an input signal, determining its position in the presence of ghosts, and removing symbolic interference and ghosts using an initial tap coefficient loaded. The initial tap coefficient is set according to the type of ghost to remove various ghosts to increase the adaptability to various ghosts.

Description

Symbol Interference and Ghost Removable Equalizer and Its Ghost Position Determination Method

The present invention relates to a symbol mutual interference and ghost-removable equalizer and a ghost position discrimination method for removing ghosts by adjusting the tap coefficients according to the ghost type by grasping a ghost position when loading the initial tap coefficients. The present invention relates to a symbolic interference and a ghost-removable equalizer and a ghost position discrimination method for removing ghosts that deviate from the total tap coefficient according to and ghost or ghost.

The configuration of the decision feedback equalizer using the conventional Least Mean Symbol (LMS) algorithm includes: a first delay unit 100 for delaying the input ghost signal gn for a predetermined time, as shown in FIG. A first multiplier (110) multiplying the input ghost signal (gn) by a delay signal through a delay unit and outputting a forward tap coefficient; A first adder (120) for adding output values of the multipliers of the first multiplier (110); A detector 130 for detecting a determination value of a symbol from a signal added through the first adder 120; A second delay unit 140 delaying a predetermined time with respect to the determination value detected by the detector 130; A second multiplier 150 for multiplying an output of the second delay unit 140 by a reverse tap coefficient; A second adder (160) for adding the respective multiplier outputs of the second multiplier (150); The output of the first adder 120 is input to the non-inverting terminal (+), the output of the second adder 160 is input to the inverting terminal (-), and the two values are added to the detector 130. It consists of a third adder 170.

Looking at the conventional technology configured as described above are as follows.

Inter Symbol Interference (ISI) is a low-pass filter with ideal characteristics on one channel, which means mutual interference between symbols due to superposition of symbols due to instability of the characteristics.

In addition, the ghost is a component that is generated by different transmission paths, and thus a different time delay occurs for each signal due to different signal transmission paths. That is, the signal transmitted at the same time at the transmitter is received with a slight time error at the receiver, which means an error component that occurs due to mutual interference of these signals.

Likewise, both symbol interference and ghost can be regarded as an error component added to the original signal and should be removed to improve the quality of the received signal. These components are removed by using an equalizer for decision feedback using the LMS algorithm. Let's look at this.

When a signal having a ghost signal gn is input, the signal is received from the first delay unit 100 and delayed for a predetermined time using the delay unit T and output.

The output signal is multiplied by the forward tap coefficients adjusted from the forward tap coefficients C _-M to C _M in the multiplier 110, respectively, and outputted by the first adder 120 and added thereto (U (t)). ) Is output to the third adder 170.

Accordingly, the value V _n added through the third adder 170 is output to the detector 130, and accordingly, the detector 130 determines the determination value of the symbols from the added value V _n . :

Accordingly, the determination value of the symbols detected by the detection unit 130 in the second delay unit 140 ( ), And the second multiplier 150 multiplies the delay value by the reverse taps f _{1 to} f _n to output the result.

When the second delay unit 140 and the second multiplier 150 add the output values multiplied by the reverse tap coefficients by the second adder 16 and output them, the third adder 170 inverts them. The output of the first adder 120, which is added to the terminal (-) and added in the forward direction, is input to the non-inverting terminal (+), and the two values are added to remove the symbol mutual interference (ISI) and the ghost.

In other words, the determination value of the symbols detected through the detection unit 130, that is, Multiplying the past value by the appropriate weight to offset the input value to eliminate ISI and goth.

This process uses an LMS algorithm, which adjusts the tap coefficient in a direction that minimizes the square of the absolute difference between the input signal and the output signal.

If the forward tap coefficient value is C _n and the reverse parallel tap coefficient value is f _n , the error signal e _n is as follows.

e _n = V _n-

= Cg _n -f - ......................................... (One)

Applying Equation (1) to the LMS algorithm results in a tap coefficient expression as shown in the following equation.

C _{n + 1} = C _n- fe _n g _n

f _{n + 1} = f _n + _r e _n ......................................... (2)

here, f and r is the step size parameter of the forward and reverse equalizers, respectively, which controls the convergence speed and stability.

The initial value of the tap coefficient should be given to the equalizer operating in this manner. In general, as shown in FIG. 2A, “1” is given only to C _M and all the rest are set to “0”.

The reason for this is to detect the error component of the signal that is currently input at the beginning of the equalizer's operation. The error component at this moment is larger than the signal after the drive is driven and time passes.

At this time, the forward and reverse tap coefficients are updated by using the LMS algorithm to remove the symbol interference and the ghost on the channel.

Therefore, in Formula (1), Cg _n and fa _n can be expressed as the following equation.

In Equation (3), it can be seen that the error component of the LMS algorithm is extracted from the M signals in the future, the current signal, and the n signals in the past. That is, to eliminate errors between these ranges.

However, in the conventional technology as described above, in the ISI and the ghost is removed, there is a problem in that the ghost is not removed when the former ghost n range and the ghost after the M range.

Therefore, an object of the present invention for solving the conventional problems as described above is to determine the presence or absence of the ghost, whether the ghost or after ghost The present invention provides a method for determining symbol interference and a ghost-removable equalizer and a ghost position determination method for eliminating symbol inter-interference (ISI) for intermediate tap coefficients of which “1” is set, as well as removing ghosts outside the entire tap coefficient. .

1 is a block diagram of an equalizer for the decision feedback method applying the conventional LMS (Least Mean Square) algorithm.

2 is an explanatory diagram showing tap coefficients and set values in FIG.

3 is a schematic diagram of an ISI and ghost-removable equalizer of the present invention.

4 is a detailed view of a ghost discriminating unit in FIG. 3;

5 is an input / output signal diagram for obtaining an autocorrelation function in FIG.

6 is a flowchart illustrating a ghost position determination method of the symbol interfering and ghost-removable equalizer of the present invention.

Explanation of symbols for the main parts of the drawings

200: ghost determination unit 201: autocorrelation function calculation unit

202: threshold determination unit 203: ghost position determination unit

210: tap coefficient update and equalizer

In order to achieve the above object, there is provided a method of determining a ghost position of a symbol mutual interference and ghost-removable equalizer, comprising: a first step of calculating an autocorrelation function from an input signal; A second step of transmitting the portion of the autocorrelation function calculated in the first step above a threshold; The third step of removing the ghost by setting the initial value according to the position of the ghost in the ghost removal range in the portion delivered in the second step.

The symbol interfering and ghost-removable equalizer configuration of the present invention for performing the method consisting of each of the above steps, as shown in Figure 3, to determine the presence or absence of the ghost from the input signal and determine the position of the ghost in the presence And a ghost determination unit 200 for determining an initial tap coefficient to be loaded; It consists of a tap coefficient update and equalizer 210 which removes pawn interactions and ghosts using the position of the ghost input from the ghost determination unit 200 and the initial tap coefficient.

In the above description, the ghost determination unit 200 includes: an autocorrelation function calculation unit 201 that calculates and obtains an autocorrelation function from an input signal; A threshold determination unit 202 for transmitting only a portion of the autocorrelation function calculated by the autocorrelation function calculation unit 201 to a next stage; The ghost position determination unit 203 determines the position of the ghost from the signal passing through the threshold determination unit 202 and determines the initial value at the time of loading.

When described in detail with respect to the operation and effect of the present invention configured as described above. When a signal is input to the equalizer, the ghost determination unit 200 and the tap update and equalization unit 300 receive and process the same. First, the ghost determination unit 200 will be described with reference to FIG. 4.

When a signal is input, the autocorrelation function is calculated by the autocorrelation function calculation unit 201, and the obtained autocorrelation function is transmitted to the ghost position determination unit 203 of the next stage only the portion exceeding the threshold of the threshold determination unit 202. .

After all, the part that goes beyond the threshold is where ghosts exist.

Here, the equation for the autocorrelation function is as follows.

_aa (n) = e {a (i) a (i + n)}

Here, e means the average of the formula in parentheses.

If a ghost such as a dotted line exists with respect to the input signal indicated by the solid line as shown in FIG. 5A, the autocorrelation function is output as shown in FIG. 5B.

Then, the threshold determination unit 202 determines the position of the ghost by comparing a value greater than or equal to a threshold value by applying a threshold value of an appropriate value to the signal output as shown in FIG. 5B.

That is, if the position of the ghost transmitted through the threshold determination unit 202 exists between -M and n in FIG. 2, the ghost position determination unit 203 sets the tap coefficient C _M as shown in FIG. The initial value is set to 1 ”, and if it is out of this range, it moves to the next stage.

Where M and n are the number of tabs defined, M is the number of forward taps, and n is the number of reverse taps.

In the next stage, if the ghost is a post-ghost between-(M + n) and -M, the initial value of the reverse tap coefficient f _n is set to “1” as shown in FIG. In the next step, if the ghost position is n to n + M, the initial tap coefficient C _-M is set to "1" as shown in FIG. 2B.

If it is out of the ghost removal range as described above, the initial tap coefficient C _M is set to “1” as shown in FIG. 2A.

The initial value set in the same manner as described above is output from the ghost determination unit 200 to the tap coefficient update and equalization unit 210.

Then, the tap coefficient update and equalizer 210 removes the ghost using the initial value transmitted from the ghost determination unit 200.

As described above, the present invention has an effect of increasing the adaptability to various ghosts by setting the initial tap coefficient according to the type of ghost to remove the various ghosts.

Claims (5)

Ghost determination means for determining the presence or absence of a ghost from an input signal, determining its position in the presence of a ghost, and determining an initial tap coefficient to be loaded; And a tap updating and equalizing means for removing symbol interference and ghost using the position of the ghost inputted from the ghost discrimination means and the initial tap coefficients. 2. The apparatus according to claim 1, wherein the ghost discriminating means comprises: an autocorrelation function calculating means for calculating an autocorrelation function from an input signal; Threshold determination means for transmitting only a portion of the autocorrelation function calculated by the autocorrelation function calculating means to a next stage; And a ghost position discriminating means for discriminating a ghost position from the signal passing through the threshold determining means and determining an initial value at the time of loading. A first step of calculating an autocorrelation function from an input signal; A second step of transmitting the portion of the autocorrelation function calculated in the first step above a threshold; The ghost of the symbol mutual interference and ghost remover equalizer, characterized in that the third step to remove the ghost by setting the initial value according to the position of the ghost in the ghost removal range in the portion delivered in the second step Position determination method. 4. The method of claim 3, wherein the initial value setting in the third step comprises: a first step of setting the forward tap coefficient C _M to 1 when the ghost position exists between -M and n; A second step of setting the reverse tap coefficient f _n to 1 if the ghost position exists between-(M + n) and -M; A third step of setting the forward tap coefficient C _-M to 1 when the ghost position exists between n and n + M; The ghost position discrimination method of the symbol mutual interference and the ghost can be removed, characterized in that the fourth step of setting the tap coefficient to 1 in the above process is set to 0. 4. The symbol mutual interference of claim 3, further comprising a fourth step of setting a forward tap coefficient C _M to an initial value when the position of the ghost does not correspond to a ghost removal range in a third step. And a ghost position determination method of the ghost removable equalizer.