WO2003007565A1

WO2003007565A1 - Preprocessing system for communication channel equalization

Info

Publication number: WO2003007565A1
Application number: PCT/KR2001/001334
Authority: WO
Inventors: Chang-Bok Joo; Ki-Yeul Han
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-07-10
Filing date: 2001-08-06
Publication date: 2003-01-23
Anticipated expiration: 2004-01-10
Also published as: KR20030005700A

Abstract

The present invention relates to a preprocessing system for a communication channel equalization which is characterized in that an impulse response characteristic of a channel is enhanced using a difference between filter outputs of different response speeds which represents an gradient of an impulse response function, by removing a negative time portion or a positive time portion for emphasizing a magnitude of a direct wave response portion and suppressing a magnitude of a multi-pass wave response portion in an impulse response of a channel for thereby implementing a channel equalization by forming an absolute value circuit, a LPF and symmetric upper and lower bridge circuits based on the features that an impulse response is represented as a direct wave response portion and a time delayed multi-pass wave response portion in a channel equalization of a wire/wireless communication system.

Description

PREPROCESSING SYSTEM FOR COMMUNICATION CHANNEL

EQUALIZATION

BACKGROUND OF THE INVENTION

TECHNICAL FIELD

The present invention relates to a preprocessing system for a communication channel equalization, and in particular to a preprocessing system for a communication channel equalization which is capable of forming symmetric upper and lower bridge circuits based on an absolute value circuit and a low pass filter(LPF) in a channel equalization of a wire/wireless communication, emphasizing a magnitude of a direct wave response portion and suppressing a magnitude of a multi-pass response portion in a channel equalization pre-stage for thereby implementing a channel equalization with respect to a wire or wireless communication channel in which a channel equalization is not available because an impulse response characteristic exceeds an equalization range of a channel equalizer.

BACKGROUND ART

Generally, as shown in Figure 1 , a wire or wireless communication system includes a transmitter 10, a communication channel 20 which is a signal transmission path and a receiver 30. The receiver 30 includes a channel equalizer 40 for compensating an impulse response characteristic of the communication channel 20 and a signal detector 50 for detecting and recovering a transmitted signal.

In the above wire/wireless communication system, when a transmitted signal of the transmitter 10 is received into the receiver 30 throughout the communication channel 20 without any interference, the receiving signal has a stable transmission signal shape.

However, in the case that the communication channel 20 is formed of a wire, since the receiver 30 receives a direct wave as well as a time delayed multipass wave, namely, a multi-path signal due to a reflection signal effect by various objects, the receiving signal shape may be largely changed. In this case, it is impossible to detect and recover the transmission signal in the receiver 30.

Therefore, in the conventional art, in order to compensate any effects due to the multi-pass wave in the communication channel, various channel equalization algorithms, a plurality of channel equalizers related to the above algorithms, for example, a decision feedback equalizer, an adaptive equalizer and a blind equalizer are introduced.

However, the above-described channel equalizers are designed for the communication channel having a limited characteristic of a certain range.

Namely, the channel equalization is performed with respect to a wire or wireless communication channel in which an impulse response characteristic which represents a signal transmission characteristic of a communication channel is included in an equalization range of a channel equalizer, and the channel equalization is not performed with respect to the wire or wireless communication channel which exceeds the equalization range of the channel equalizer due to a bad communication channel environment. In particular, in the wire/wireless communication system, in order to perform a reliable, high quality and high speed communication, it is needed to effectively control the multi-pass wave. The multi-pass wave which causes a long time delay spread phenomenon due to various reflections of objects and a reflection effect by a load operation or termination based on various electric or electronic equipments makes the communication unavailable in the case of the communication channel like a mobile communication or a power line communication.

DISCLOSURE OF THE INVENTION

Accordingly, it is an object of the present invention to provide a preprocessing system for a communication channel equalization which overcomes the problems encountered in the conventional art. It is another object of the present invention to provide a preprocessing system for a communication channel equalization which is capable of implementing a channel equalization by forming an absolute value circuit , a LPF and symmetric upper and lower bridge circuits based on the features that an impulse response of a communication channel is represented as a direct wave response portion and a time delayed multi-pass wave response portion in a wire/wireless communication system, decreasing a delay spread due to a multipass in a channel equalization pre-stage, largely generating a response speed between the LPF having different frequency bandwidths, namely, an gradient difference of a response function, emphasizing a magnitude of a first response portion corresponding to a direct wave response portion among the impulse responses of the communication channel and suppressing the magnitude of the multi-pass wave response portion for a wire or wireless communication channel in which the impulse response characteristic exceeds an equalization range of the channel equalizer.

In order to achieve the above object, there is provided a preprocessing system for a entire communication channel equalization which is characterized in that the direct wave response portion in an impulse response characteristic of a channel is enhanced using a difference between filter outputs of different response speeds which represents an gradient of a response function, after removing a negative time portion or a positive time portion for suppressing a magnitude of a multi-pass wave response portion and reducing a range of a multipass wave response time portion in an impulse response of a channel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become better understood with reference to the accompanying drawings which are given only by way of illustration and thus are not limitative of the present invention, wherein: Figure 1 is a block diagram illustrating the construction of a transmission system of a communication;

Figure 2 is a view illustrating a channel equalizer which includes a channel equalization preprocessing system;

Figure 3 is a view illustrating the construction of a channel equalization preprocessing system according to the present invention;

Figure 4 is a view illustrating an impulse response characteristic of a channel equalization preprocessing system according to the present invention; Figure 5 is a view illustrating an impulse response of each element of Figure 3 in a communication channel in which a receiving signal detection is impossible;

Figure 6 is a view illustrating an impulse response of each element of Figure 3 in a communication channel in which there is an error when detecting a receiving signal; and

Figure 7 is a view illustrating an impulse response of each element of Figure 3 in a communication channel which has a better impulse response characteristic.

MODES FOR CARRYING OUT THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be explained with reference to the accompanying drawings.

Figure 2 is a view illustrating a channel equalizer having a channel equalization preprocessing system according to the present invention. In the present invention, a channel equalization preprocessing system 400 according to the present invention is installed in the channel equalizer 40 for thereby implementing a channel equalization with respect to a wire or wireless communication channel in which a channel equalization is impossible.

Figure 3 is a block diagram illustrating a channel equalization preprocessing system according to the present invention. As shown therein, there are provided an absolute value circuit 401 for removing a negative time portion or a positive time portion with respect to an input for limiting a multi-pass response portion among the impulse responses of the communication channel 20, a summing unit 404 for summing a response output by a LPF1 402 of a frequency bandwidth f^Hz] and a response output by a LPF2 403 of the same pass bandwidth, an upper bridge circuit 410 for obtaining a difference between an output from the summing unit 404 and a lower bridge circuit which feeds back through a first feedback gain unit 416, passing a response output based on the response output through the LPF having different pass bandwidths, a lower bridge circuit 420 for obtaining a difference between the output from the summing unit 404 and a response output of the upper bridge circuit 410, passing the response output based on the difference through the LPF having different pass bandwidths, obtaining a difference of each response output and providing a gain thereto, and a fifth subtraction unit 430 for obtaining a difference between a response output of the upper bridge circuit 410 and a response output of the lower bridge circuit 420, emphasizing a magnitude of the direct wave response, suppressing a magnitude of a multi-pass wave response and reducing a range of a multi-pass wave response time in an impulse response of a channel and outputting an improved impulse response of the communication channel to the channel equalizer 40.

The upper bridge circuit 410 includes a first subtraction unit 411 for obtaining a difference between an output from the summing unit 404 and a response output of the lower bridge circuit 420 fed back through a first feedback gain unit, a second subtraction unit 414 for inputting an output of the first subtraction unit 411 into a third LPF 412 of the pass bandwidth f^Hz] and the fourth LPF 413 of the pass bandwidth f₂Hz] of the parallel structure and obtaining a difference between a response output of the third LPF 412 and a response output of the fourth LPF 413, a first bridge gain unit 415 for providing an output

of the second subtraction unit 414 with a gain of β and a first feedback gain unit 416 for providing an output of the fourth subtraction unit of the lower bridge circuit

420 with a gain of α and feeding back to the first subtraction unit 411.

In addition, the lower bridge circuit 420 which is symmetric with respect to the upper bridge circuit 410 includes a third subtraction unit 421 for obtaining a difference between an output from the summing unit 404 and a response output of the upper bridge circuit 410 which is fed back through the second feedback gain unit, a fourth subtraction unit 424 for inputting an output from the third subtraction unit 421 into a fifth LPF 422 of the pass bandwidth f^Hz] and a sixth LPF 423 of the pass bandwidth f₃[Hz] of the parallel structure, a second bridge gain unit 425

for providing an output of the fourth subtraction unit 424 with a gain of β, and a second feedback gain unit 426 for providing an output from the second subtraction

unit 414 of the upper bridge circuit 410 with a gain of α and feeding back to the third subtraction unit 421.

Here, the relationship of f^Hz], f₂[Hz] and f₃[Hz] is f₂< f,< f₃, and the magnitude of the gain of the first and second feedback gain units 416 and 426 is

α and α<1 , and the magnitude of the gain of the first and second bridge gain units

415 and 425 is β and β»1.

The channel equalization preprocessing system according to the present invention removes a negative time portion or a positive time portion from the impulse response of the communication channel and reduce the range of the multi-pass response time portion for thereby decreasing a delay spread due to the multi-pass.

The magnitude of the first response portion corresponding to a response portion of the direct wave from the impulse response of the communication channel by largely generating a response speed difference of the upper and lower bridge circuits 410 and 420, namely, an gradient difference of the impulse response function through the symmetric upper and lower bridge circuits 410 and 420 formed of the third LPF 412 and the fourth LPF 413 having the different pass bandwidths f^Hz] and f₂[Hz] and the fifth LPF 422 and sixth LPF 423 having different pass bandwidths f^Hz] and f₃[Hz].

As shown in Figure 4, the channel equalization preprocessing system according to the present invention formed using the absolute value circuit and the LPF for reducing the range of response time portion of the multi-pass wave and the magnitude thereof using a response speed difference between the filters having different pass bandwidths implements a channel equalization in the channel equalizer with respect to the communication channel in which the range of the channel equalization is exceeded by the impulse response characteristic. In addition, since the channel equalization preprocessing system according to the present invention uses a response speed difference between the filters having different frequency bandwidths, the band pass filter(BPF) may be used instead of the first through sixth LPF 402 through 423.

The operation of the channel equalization preprocessing system according to the present invention will be explained with reference to the accompanying drawings.

First, the absolute value circuit 401 for reducing the range of the multi-pass wave response portion among the impulse responses of the communication channel inputted through the communication channel 20 of the wire/wireless communication system removes a negative time portion or a positive time portion.

In addition, a sum value of a response output based on the first LPF 402 having a pass bandwidth of f^Hz] which passes an output of the absolute value circuit 401 through the first summing unit 404 and a response output based on the second LPF 403 having the same pass bandwidth f^Hz] as the first LPF 402 which passes an impulse response of the communication channel is obtained.

In order to emphasize the magnitude of the direct wave response portion, the upper and lower bridge circuits 410, 420 are operated.

Namely, when the output from the summing unit 404 is outputted to the second and fourth subtraction units 411 and 421 of the upper and lower bridge circuits 410 and 420, in the case of the upper bridge circuit 410, the first subtraction unit 411 obtains a difference between an output from the summing unit 404 and an output of the fourth subtraction unit 424 of the lower bridge circuit 420 fed back through the first feedback gain unit 416. Here, the first feedback gain unit 416 provides an output from the fourth

subtraction unit 424 of the lower bridge circuit 420 with a gain of α and feeds back to the first subtraction unit 411.

A difference between a response output based on the third LPF 412 having a pass bandwidth of f^Hz] which passes an output of the first subtraction unit 411 through the second subtraction unit 414 and a response output based on the fourth LPF 413 having a frequency bandwidth of f₂[Hz] of the parallel structure which passes the output of the first subtraction unit 411 , and the output obtained based on the difference is outputted to the first bridge gain unit 415.

Therefore, the first bridge gain unit 415 provides an output from the second

subtraction unit 414 with a gain of β and outputs to the fifth subtraction unit 430. The lower bridge circuit 420 having the structure symmetrical to the upper bridge circuit 410 operates in the same method as the upper bridge circuit 410. Namely, a difference between an output from the summing unit 404 and an output of the second subtraction unit 414 of the upper bridge circuit 410 fed back through the second feedback gain unit 426.

Here, the second feedback gain unit 426 provides an output from the

second subtraction unit 414 of the upper bridge circuit 410 with a gain of α and feeds back to the third subtraction unit 421.

A difference between a response output based on the fifth LPF 422 having a frequency bandwidth of a f^Hz] which passes through an output of the third subtraction unit 421 through the fourth subtraction unit 424 and a response output based on the sixth LPF 423 having a pass bandwidth of a f₃[Hz] of the parallel structure which passes through an output of the third subtraction unit 421 is obtained. An output based on the difference is outputted to the second bridge gain unit 425. When the operations of the upper and lower bridge circuits 410 and 420 are completed, the fifth subtraction unit 430 obtains a difference between a response output outputted through the first bridge gain unit 415 of the upper bridge circuit 410 and a response output outputted through the second bridge gain unit 425 of the lower bridge circuit 420 and largely emphasize a magnitude of the response output corresponding to a direct wave response portion in the impulse response of the communication channel and outputs an impulse response of the communication channel which suppressed the magnitude of a multi-pass wave response portion and reduced the range of a multi-pass wave response time portion in an impulse response of a channel to the channel equalizer 40.

The impulse responses generated from each element of the channel equalization preprocessing system in the case that the channel equalization preprocessing system according to the present invention having an impulse response characteristic shown in Figure 4 is adapted will be explained with reference to Figures 5 through 7.

Figure 5 is a view illustrating a response output of each element of Figure 3 in the case that the communication channel which can not detect a receiving signal since the equalization range of the channel equalizer is largely deviated, Figure 6 is a view illustrating an impulse response of each element of Figure 3 in a communication channel in which there is an error when detecting a receiving signal, and Figure 7 is a view illustrating an impulse response of each element of Figure 3 in a communication channel which has a better impulse response characteristic. At this time, (a) of each of Figures 5, 6 and 7 represents an impulse response of a corresponding communication channel, (b) of each of the same represents a response output of the first LPF 402, (c) of each of the same represents a response output of the second LPF 403, (d) of each of the same represents an output of the summing unit 404, (e) of each of the same represents an output of the second subtraction unit 414 of the upper bridge circuit 410, (f) of each of the same represents an output of the fourth subtraction unit 424 of the lower bridge circuit 420, and (g) of each of the same represents a last impulse response outputted from the fifth subtraction unit 430. As shown in (d) of Figure 5, a negative time delay portion is removed as a result of the check of the impulse response outputted from the summing unit 404, and as shown in (g) of Figure 5, the direct wave response portion among the impulse response of the communication channel is clear as a result of the check of the last impulse response outputted from the fifth subtraction unit 430 and the magnitude of the same is emphasized, and the magnitude of the multi-pass response portion is largely suppressed.

Therefore, it is possible to obtain a certain channel equalization in the channel equalizer.

As shown in (d) of Figure 6, a negative time delay portion is removed as a result of the check of the impulse response outputted from the summing unit 404 like the embodiment of Figure 5, and the direct wave response portion among the impulse response of the communication channel is clear as a result of the check of the last impulse response outputted from the fifth subtraction unit 430 as shown in (g) of Figure 6, and the magnitude of the same is emphasized, and the magnitude of the multi-pass response portion is largely reduced.

As shown in (g) of Figure 7, the direct wave response portion among the impulse response of the communication channel is more clear as a result of the check of the last impulse response outputted from the fifth subtraction unit 430 like the embodiments of Figures 5 and 6 for thereby obtaining a typical impulse response characteristic of the communication channel.

As described above, in the channel equalization preprocessing system according to the present invention, it is possible to implement a channel equalization with respect to the wire/wireless communication channel in which the channel equalization is impossible since the impulse response characteristic largely exceeds the equalization range of the channel equalizer by forming the absolute value circuit and upper and lower symmetric bridge circuits with LPF having different frequency bandwidth, emphasizing the magnitude of the direct wave response portion in the channel equalization pre-stage and suppressing the multi-pass wave response portion and reducing the range of the multi-pass wave response time portion.

Namely, in the channel equalization preprocessing system according to the present invention, it is possible to perform a reliable and high quality high speed power line communication and mobile communication in which the impulse response characteristic of the communication channel is bad due to the multi-pass wave by improving the impulse response characteristic of the communication channel having the multi-pass wave. In addition, the present invention may be well adapted to various wire/wireless transmission apparatus and system, a high speed power line transmission apparatus, a home network system, etc.

As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be 5 understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be constructed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore l o intended to be embraced by the appended claims.

Claims

1. A channel equalization preprocessing system characterized in that an impulse response characteristic of a channel is enhanced using a difference between filter outputs of different response speeds which represents an gradient of a response function, by removing a negative time portion or a positive time portion for emphasizing a magnitude of a direct wave response portion in an impulse response of a channel.

2. The system of claim 1 , wherein said an absolute value circuit is used for removing a negative time portion or a positive time portion for suppressing a multipass wave response portion.

3. The system of claim 1 , wherein an absolute value circuit and a low pass filter are used for removing a negative time portion or a positive time portion for suppressing a multi-pass wave response portion of a delay time.

4. The system of claim 1 , wherein a difference of the outputs of the symmetric upper and lower bridge circuit is obtained when using a response speed difference of a filter for emphasizing a magnitude of a direct wave response portion.

5. The system of claim 2, wherein a sum of an input and a response output which passed through the absolute value circuit is inputted into the symmetric upper and lower bridge circuits which emphasizes the magnitude of the direct wave response portion.

6. The system of claim 3, wherein a sum of an input and a response output of the low pass filter of the same frequency bandwidth as the response output based on the absolute value circuit and the low pass filter is inputted into the symmetric upper and lower bridge circuits which emphasizes the magnitude of the direct wave response portion.

7. The system of claim 6, wherein a sum of the response outputs based on the band pass filter instead of the low pass filter is inputted into the symmetric upper and lower bridge circuit which emphasizes the magnitude of the direct wave response portion.

8. The system of claim 1 , further comprising: a summing unit for summing a response output based on the absolute value circuit and the low pass filter of the pass bandwidth f^Hz] and a response output based on the low pass filter of the same pass bandwidth; an upper bridge circuit which includes: a first subtraction unit for obtaining a difference between an output from the summing unit and a response output of the lower bridge circuit fed back through the feedback gain unit; a second subtraction unit for inputting an output from the first subtraction unit into the LPF of the pass bandwidth f^Hz] and the LPF of the pass bandwidth f₂[Hz] of the parallel structure and obtaining a difference of the response outputs; and a bridge gain unit for providing an output of the subtraction unit with a gain; a lower bridge circuit which includes: a third subtraction unit for obtaining a difference between an output of the summing unit and a response output of the upper bridge circuit fed back through the feedback gain unit; a fourth subtraction unit for inputting an output of the third subtraction unit into the LPF of the pass bandwidth f^Hz] and the LPF of the pass bandwidth f₃[Hz] of the parallel structure and obtaining a difference of the response outputs; and a bridge gain unit for providing an output of the subtraction unit with a gain; and 5 a fifth subtraction unit for obtaining a difference of the response outputs of the upper and lower bridge circuits and outputting the difference to the channel equalizer.

9. The system of claim 8, wherein said symmetric upper and lower bridge o circuits are formed of the band pass filters having different response speeds.

10. The system of claim 1 , wherein an impulse response function of the channel equalization preprocessing system is discrete-processed base on time using a difference between the filter outputs of the different response speeds after 5 removing a negative time portion or a positive time portion of the impulse response, and the discrete-processed value is used as a coefficient of the filter.

11. The system of claim 1 , wherein a negative time portion or a positive time portion of the impulse response is removed, and a difference of the filter outputs 0 of the different response speed is used.

12. The system of claim 1 , wherein the impulse response function of figure 4 of the channel equalization preprocessing system which is capable of enhancing an impulse response characteristic of the channel using a difference of the filter 5 outputs of the different response speeds which represent the gradient of the response function is discrete-processed based on time, and the discrete- processed value is used as a coefficient of the filter.

13. The system of claim 1 , wherein a parallel or a cascade forming of the channel equalization preprocessing system are used for enhancing an channel impulse response characteristic.