Equalizing method and apparatus for single carrier system having an improved equalization performance

Equalizing method and apparatus for single carrier system having an improved equalization performance is disclosed, which includes: a section setting unit for setting filter taps having a predetermined section corresponding to the predicted multi-path; a repeat setting unit for setting filter taps of a repetition section by making the set predetermined section repetitive periodically; and a filter unit for filtering the multi-path by updating the coefficients of the filter taps of the set repetition section. The repeat setting unit sets the filter taps of the repetition section corresponding to an operation characteristic of the filter unit. Accordingly, the apparatus can improve equalization performance by setting filter taps corresponding to the predicted multi-path and updating only the set coefficients of the filter taps. Further, the apparatus can improve equalization performance in dynamic channel circumstances in which the multi-path changes.

This application claims the priority of Korean Patent Application No. 10-2003-0007589 filed 6 Feb. 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to an equalizing apparatus in a single carrier system, and more particularly to an equalizing method and apparatus which can improve equalization performance in dynamic channel circumstances.

2. Description of the Prior Art

As generally known in the art, linear equalizers or decision feedback equalizers are used as equalizing apparatuses in a single carrier system.

FIG. 1is a schematic block diagram regarding a linear equalizer10. A linear equalizer10includes a filter unit11having a FIR-type filter and a switching unit15for operating selectively according to an operation mode of the equalizer. Equalization is performed by repeating a process which obtains an equalization error value corresponding to the operation mode selected by the switching unit15and updates coefficients of all filter taps.

When the operation mode is a blind mode, an error calculating unit17calculates the equalization error value using an output signal of the filter unit11and an output signal of a level decision unit16selected by the switching unit15. Also, when the operation mode is a training mode, the error calculating unit17calculates the equalization error value using the output signal of the filter unit11and a field sync signal selected by the switching unit15.

As described above, the equalization error values obtained from each of the operation modes are inputted to the filter unit11. The filter unit11updates coefficients of all the filter taps using the inputted equalization error values. Accordingly, multi-path of a received signal is removed.

FIG. 2is a schematic block diagram regarding a decision feedback equalizer20. The decision feedback equalizer20includes a FF (feed forward) section21having a FIR-type filter for removing a pre-ghost and post-ghost of a received signal, a FB (feed back) unit23having a IIR-type filter for removing a post-ghost of the received signal and a switching unit25for operating selectively according to an operation mode of the equalizer20, which is either a blind mode or a training mode. An equalization is performed by obtaining an equalization error value corresponding to an operation mode selected by the switching unit25and updating each coefficient of a filter tap of the FF unit21and the FB unit23.

When the operation mode is a blind mode, an error calculating unit27calculates the equalization error value using an output signal of an adder22adding output signals of the FF unit21and the FB unit23and an output signal of a level decision unit26selected by the switching unit25.

Also, when the operation mode is a training mode, the error calculating unit27calculates the equalization error value using the output signal of the adder22adding the output signals of the FF unit21and the FB unit23and a field sync signal selected by the switching unit25.

As described above, the equalization error values obtained from each of the operation modes are inputted to the FF unit21and the FB unit23, respectively. The FF unit21and the FB unit23update coefficients of all the filter taps using the inputted equalization error values. Accordingly, multi-path of a received signal is removed.

The equalization process of a conventional equalizer described above compensates for the channel distortion of the received signal by updating over and over coefficients of all the filter taps of the FF unit and the FB unit on the basis of the equalization error values obtained from each of the operation modes. However, the conventional equalizer is problematic in that equalization speed decreases since the coefficient of the filter tap corresponding to the multi-path as well as the coefficients of all the filter taps are updated.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an aspect of the present invention is to provide an equalizing apparatus and method which can improve equalization performance in dynamic channel circumstances by updating coefficients of filter taps corresponding to a multi-path.

In order to accomplish this aspect, there is provided an equalizing apparatus comprising: a section setting unit for setting filter taps having a predetermined section corresponding to the predicted multi-path; a repeat setting unit for setting filter taps of a repetition section by making the set predetermined section repetitive periodically; and a filter unit for filtering the multi-path by updating the coefficients of the filter taps of the set repetition section.

The repetition setting section, in an exemplary embodiment, sets the coefficients of the filter taps of the repetition section according to the operation characteristic of the filter unit.

The present invention further comprises an error calculating unit for computing an equalization error value on the basis of the output signal of the filter unit, and the filter unit updates the coefficients of the filter taps of the repetition section on the basis of the equalization error value.

Further, the filter unit includes a FF (feed forward) section for filtering pre-ghosts from among the predicted multi-path and a FB (feed back) section for filtering post-ghosts from among the predicted multi-path. Accordingly, the FF unit updates the coefficients of the filter taps of the repetition section set in accordance with the pre-ghosts, the FB unit updates the coefficients of the filter taps of the repetition section set in accordance with the post-ghosts. In this case, when the FF unit has an overlap operation characteristic, the FF unit updates the coefficients of the filter taps of the repetition section set in accordance with the pre-ghosts and the post-ghosts and performs a filtering operation with respect to the pre-ghosts and the post-ghosts.

Also, in order to accomplish this object, there is provided an equalizing method comprising the steps of: (1) predicting multi-path of a received signal; (2) setting filter taps having a predetermined section corresponding to the predicted multi-path; (3) setting filter taps of a repetition section by making the set predetermined section repetitive periodically; and (4) filtering the multi-path by updating the coefficients of the filter taps the set repetition section.

In an exemplary embodiment, in step3, the filter taps of the repetition section are set according to the operation characteristic of the filter.

The present invention further comprises a step for computing an equalization error value on the basis of the output signal of step4. In step4, the coefficients of the filter taps of the repetition section are updated on the basis of the equalization error value.

Step4comprises the steps of: (a) filtering pre-ghosts from among the predicted multi-path and (b) filtering post-ghosts from among the predicted multi-path. Accordingly, the coefficients of the filter taps of the repetition section set in accordance with the pre-ghosts are updated in step a, and the coefficients of the filter taps of the repetition section set in accordance with the post-ghosts are updated in step b.

Accordingly, the present invention can improve equalization performance by setting the filter tap according to the predicted multi-path and updating only the set coefficients of the filter taps. Further, the present invention can improve equalization performance even in dynamic channel circumstances in which the multi-path changes.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIG. 3is a schematic block diagram regarding a single carrier system employing an equalizer having an improved equalization performance according to the present invention.

A single carrier system includes a RF unit310, an ADC unit (analog to digital converter)320, a synchronizing unit330, an equalizing unit340and a decoding unit350.

The RF unit310tunes a received single carrier signal and converts the tuned signal into a baseband signal. The ADC unit320converts the received analog signal into a digital signal through a digital sampling. The synchronizing unit330compensates for a frequency, a phase and a timing offset of the received signal. The equalizing unit340compensates for channel distortion of the received signal by updating coefficients of the filter taps set in accordance with to multi-path of the received signal. The decoding unit350decodes a data of an input signal equalized by the equalizing unit340.

FIG. 4andFIG. 5are block diagrams showing the exemplary embodiment of an equalizer according to the present invention. The equalizing apparatus of the present invention is described in detail with reference toFIG. 4andFIG. 5.

First,FIG. 4is an embodiment of the equalizing apparatus according to the present invention and is a block diagram regarding a linear equalizer.

The linear equalizer100includes a filter unit110, a multi-path prediction unit120, a section setting unit130, a repeat setting unit140, a level decision unit160, a switching unit150and an error calculating unit170.

The filter unit110has a FIR-type filter and performs a filtering operation with respect to multi-path of an input signal.

The multi-path prediction unit120calculates a correlation value using a correlation relation between a field sync signal and a received signal, then predicts a signal having more than a threshold value as multi-path by means of a predetermined algorithm.

The section setting unit130sets sections of filter taps such that the section of the filter taps includes a predetermined number of the filter taps, by considering the filter taps in which the multi-path of the received signal is filtered and a margin of the multi-path on the basis of the predicted multi-path.

The repeat setting unit140makes the predetermined section set by the section setting unit130repetitive periodically. In this case, the repeated period is set in accordance with an operation characteristic of the filter unit110.

That is, the number of the filter taps in the predetermined section set by considering the margin of the multi-path is m+1 (m is the number of the filter taps which are added according to the margin). When a filter tap corresponding to a location of the multi-path is the nth filter tap fn, the repetition period becomes n-m number of the filter taps. In this case, n is a natural number, which is larger than m.

For instance, when a filter tap corresponding to a main ghost is f0and a filter tap corresponding to a post ghost is f4, the section setting unit130considers the margin of the multi-path. In this case, when the number of the filter taps becomes two, the number of the filter taps of the set predetermined section becomes three. Accordingly, the filter taps of the predetermined section I1regarding the main ghost become f−1, f0and f1, and the filter taps of the predetermined section I1regarding the post ghost become f3, f4and f5. The repeat setting unit140sets an interval between two filter taps (n−m=2) as a period and sets sections of the filter taps which repeat periodically such as f7, f8, f9and f11, f12, f13. (In this case, a previous filter tap of the main filter tap f0is expressed by — and a following filter tap of the main filter tap f0is expressed by +).

The repeat setting unit140provides a predetermined control signal to the filter tap of the repetition section set as described above. Next, the filter unit110compensates for the multi-path, which is the post-ghost, by updating the coefficients of the filter taps of the set filter tap section.

The switching unit150performs a switching operation according to a training mode and a blind mode, which are operation modes of the equalizer.

The level decision unit160determines the output signal of the filter unit110to be a predetermined level and then outputs the level-determined output signal.

The error calculating unit170calculates an equalization error value on the basis of an output signal of the switching unit150, of which the output signal is switched according to the operation mode. That is, the error calculating unit170calculates the equalization error value with respect to the output signal of the filter unit110on the basis of the output signal of the level decision unit160in the blind mode. Further, the error calculating unit170calculates the equalization error value with respect to the output signal of the filter unit110on the basis of a field sync signal in the training mode.

The equalization error values calculated in each of the operation modes as described above are inputted to the filter unit110, the filter unit110updates only the coefficient of the filter tap set over and over on the basis of the predetermined control signal provided from the repeat setting unit140.

FIG. 5is another embodiment according to the present invention and is a more detailed block diagram regarding a decision feedback equalizer.

The decision feedback equalizer200includes a FF unit211, a FB unit213, an adder215, a multi-path prediction unit217, a section setting unit219, a repeat setting unit223, a switching unit225, a level decision unit227, and an error calculating unit229.

The FF (Feed Forward) section211is a filter having a FIR-type filter and removes a pre-ghost from among multi-path. When the FF unit211is an overlapped feed forward filter, it also removes a predetermined number of post-ghosts.

The FB (Feed Back) section213is a filter having an IIR-type filter and removes a post-ghost.

The adder215adds the output signal outputted from the FF unit211and the output signal outputted from the FB unit213and outputs the added signal.

The multi-path prediction unit217calculates a correlation value using a correlation relation between a field sync signal and a received signal, then predicts a signal having more than a threshold value as multi-path by means of a predetermined algorithm.

As described above, the section setting unit219sets a section of filter taps such that the section of the filter taps includes a predetermined number of the filter taps, by considering the filter taps in which the multi-path of the received signal is filtered and a margin of the multi-path on the basis of the predicted multi-path.

The repeat setting unit223makes the predetermined section set by the section setting unit219repetitive periodically. In this case, the repeated period is set in accordance with an operation characteristic of the FB unit211.

That is, the number of the filter taps in the predetermined section set by considering the margin of the multi-path is m+1 (m is the number of the filter taps which are added according to the margin). When a filter tap corresponding to a location of the multi-path is the nth filter tap fn, the repeated period becomes n−m number of the filter taps. In this case, n is a natural number, which is larger than m.

The repeat setting unit223provides a predetermined control signal corresponding to the section of the filter tap set over and over to the FF unit211and the FB unit213, respectively.

That is, the repeat setting unit223provides the FIR filter of the FF unit211with a predetermined control signal corresponding to the section of the filter tap set over and over with respect to the main-ghost and post-ghost from among the predicted multi-path. Then, the repeat setting unit223provides the FF unit211having an overlap characteristic with a predetermined control signal corresponding to the section of the filter tap set with respect to the pre-ghost. Further, the repeat setting unit223provides the IIR filter of the FB unit213with a predetermined control signal corresponding to the section of the filter tap set over and over with respect to the post-ghost from among the predicted multi-path.

Next, the FF unit211and the FB unit213compensates for the multi-path by updating the coefficients of the filter taps of the section of the filter tap set over and over, by means of the predetermined control signal.

The switching unit225performs a switching operation according to the training mode and blind mode, which are the operation modes of the equalizer.

The level decision unit227outputs a signal having a predetermined level determined according to the output signal of the adder215.

The error calculating unit229calculates an equalization error value on the basis of the output signal of the switching unit225which is switched according to the operation mode. That is, the error calculating unit229calculates the equalization error value with respect to the output signal of the adder215on the basis of the output signal of the level decision unit227in the blind mode. Further, the error calculating unit229calculates the equalization error value with respect to the output signal of the adder215on the basis of a field sync signal in the training mode.

The equalization error values calculated in each of the operation modes as described above are inputted to the FF unit211and the FB unit213, respectively, and the FF unit211and the FB unit213update only the coefficient of the filter tap provided from the repeat setting unit223.

Hereinafter, referring toFIG. 6atoFIG. 7c, a process of setting the section of the filter tap is described in detail, which is set over and over by means of the section setting unit219and the repeat setting unit223of the decision feedback equalizer200. The FF unit211described inFIG. 6atoFIG. 7chas a FIR-type filter and an overlap operation characteristic which compensates for a predetermined number of post-ghosts. Further, an equalizing method of an equalizing apparatus according to the present invention is described with reference toFIG. 8.

FIG. 6a-6care views illustrating a case in which only pre-ghosts exist.FIG. 6ais a view illustrating multi-path predicted by the multi-path prediction unit217using a correlation relation between a received signal and a field sync signal, with respect to the received signal having a main-ghost (0Ts, 0dB) and a pre-ghost (−32Ts, −3dB) in step811.

In step813, the section setting unit219considers a corresponding filter tap and filter tap margin according to the multi-path on the basis of a location of the multi-path predicted as shown inFIG. 6a, and sets the filter tap section (I1) having a predetermined section as shown inFIG. 6b. In step815, the repeat setting unit223sets the filter tap sections (I1) having a predetermined section so that the filter tap sections (I1) are periodically repeated (P1).

Typically, the FF unit211has a FIR-type filter and removes ghosts by reducing the ghosts gradually. The compensation characteristic of the filter having the FIR-type filter is that the filter sets a latency time for a main-ghost as a period and performs a filtering operation with respect to the ghosts while reducing the size of the ghosts gradually.

That is, the repeat setting unit223sets the filter tap for filtering the ghost which occurs periodically by means of the FIR-type filter, by setting the filter tap section having a predetermined section, which repeats periodically.

In step815, the repeat setting unit223provides a predetermined control signal ‘1’ to the periodically repeated filter taps from among all filter taps of the FF unit211as shown inFIG. 6b, and provides a predetermined control signal ‘0’ to the rest of the filter taps.

Accordingly, the FF unit211updates the coefficient of the filter tap set on the basis of the equalization error value calculated by the error calculating unit229in order to perform an equalization in step817.

Also, since the post-ghosts do not exist as shown inFIG. 6a, the repeat setting unit223provides a predetermined control signal ‘0’ to all filter taps of the FB unit213. Accordingly, the FB unit213does not update the coefficients of all the filter taps, that is, the FB unit213does not operate.

Accordingly, the present invention can improve an equalization speed by setting only minimum filter taps having an effect on an equalization performance for the multi-path of the received signal and updating the set coefficient of the filter tap.

FIG. 7a-7care views illustrating a case in which only post-ghosts exist.FIG. 7ais a graph of illustrating multi-path predicted by the multi-path prediction unit217using a correlation relation between a received signal and a field sync signal, with respect to the received signal having a main-ghost (0Ts, 0dB) and a post-ghost (32Ts, 3dB) in step811.

In step813, the section setting unit219considers a corresponding filter tap and filter tap margin on the basis of a location of the multi-path predicted as shown inFIG. 7a, and sets filter taps having a predetermined section (12) as shown inFIG. 7b. In step815, the repeat setting unit223sets the filter tap sections (I2) having a predetermined section such that the filter tap sections (I2) are periodically repeated (P2).

The FF unit211compensates for post-ghosts having a predetermined section according to an overlap characteristic. Then, the repeat setting unit223sets the filter taps having a predetermined section corresponding to the post-ghosts such that the filter taps having a predetermined section are periodically repeated.

The repeat setting unit223provides a predetermined control signal ‘1’ to filter taps having a predetermined section set over and over corresponding to the main-ghost and post-ghost from among the all filter taps.

Also, as shown inFIG. 7c, the repeat setting unit223provides a predetermined control signal ‘1’ to filter taps having a predetermined section (I2) set periodically (P2) corresponding to the post-ghost.

That is, when the pre-ghosts do not exist, the FF unit211updates coefficients of filter taps compensating for the main-ghost and coefficients of filter taps compensating for the post-ghost according to an overlap operation characteristic from among all filter taps.

Next, the FF unit211and FB unit213update the coefficient of the filter tap set in accordance with the multi-path set by the repeat setting unit223as shown inFIG. 7bandFIG. 7c, on the basis of the equalization error value obtained by the error calculating unit229, and thus perform an equalization in step817.

Accordingly, the present invention can improve an equalization speed by updating the part of the filter taps set in accordance with the multi-path from among all filter taps of the FF unit211and FB unit213. Further, the present invention can improve equalization performance in dynamic channel circumstances in which the multi-path changes.

According to the present invention, the received multi-path is predicted and the filter taps are set in accordance with the predicted multi-path, and the set coefficients of the filter taps are updated. Accordingly, the present invention can improve equalization speed than the prior equalizer updating all the filter taps and equalization performance in dynamic channel circumstances in which the multi-path changes.

Further, the present invention can prevent a possible reduction of a performance by setting the filter taps having a predetermined section after considering not only the filter taps corresponding to the predicted multi-path, but also the margin of the multi-path, and setting the filter taps having a predetermined section over and over after considering the operation characteristic of the FIR-type filter.

Accordingly, the present invention can improve equalization performance in dynamic channel circumstances in which the multi-path changes.