KR100698207B1 - Equalizer of digital broadcasting receiver - Google Patents

Abstract

A channel equalizer for performing channel estimation and compensation on a signal received through a transmission channel in a digital broadcasting receiver using an OFDM transmission scheme. In particular, the present invention multiplies the phase rotation value according to the variation in the time domain estimated by the fine symbol timing synchronizer by the data input to the time axis interpolator to estimate the channel before the CIR in the channel buffer of the time axis interpolator is reflected. The value has a continuous value with the current channel value reflecting the CIR. Therefore, the performance degradation of estimation and compensation for time-varying and discontinuous channels can be improved to ensure stable quality of service (QOS) of the receiver. In addition, by multiplying the data interpolated in the time domain by the time domain interpolator inversely with the phase rotation value according to the variation in the time domain estimated by the fine symbol timing synchronizer, the performance of the long ghost in the SFN channel can be improved. have.

Equalization, Time Varying Channel, Discontinuous Channel, Time Domain Interpolation, Phase Rotation Value

Description

Equalizer of digital broadcasting receiver

1 is a view showing the structure of a transmission frame of a general DVB method

2 is a block diagram illustrating an embodiment of an equalization apparatus of a conventional digital broadcast receiver.

3 illustrates a channel interpolation process in the time domain

4 is a diagram illustrating an example of time-varying and discontinuous channels in the related art.

5 is a diagram illustrating an example of compensation of a discontinuous channel through phase derotation according to the present invention.

6 is a block diagram illustrating an equalization device of a digital broadcast receiver according to a first embodiment of the present invention.

7 is a block diagram illustrating an equalization device of a digital broadcast receiver according to a second embodiment of the present invention.

Explanation of symbols for main parts of the drawings

211: pilot extractor 212: time base interpolator

213: frequency axis interpolator 214: data buffer

215: channel compensator 610,710: phase derotator

720: phase rotator

The present invention relates to a digital broadcast receiver, and more particularly, to a channel equalization device for performing channel estimation and compensation on a signal received through a transmission channel.

The European Telecommunications Standards Institute (ETSI) has adopted Digital Video Broadcasting Terrestrial (DVB-T) as the standard for airwave channels in European digital TVs. In addition, DVB-H (Handheld) is separately established as a new standard that can satisfy stable reception even in low power for mobile reception and mobile reception, meeting the market demand for digital TV.

The DVB-T and DVB-H adopt an OFDM modulation and demodulation method using multiple subcarriers as a transmission method. The OFDM scheme can extend the symbol period by the number of subcarriers, so that each subcarrier can be equalized by an equalizer using a simple tap. In addition, the OFDM scheme is robust to frequency-selective fading channels by multipath, and is suitable for high-speed data transmission standards of wired and wireless, since only a part of carriers are affected even in narrowband interference signals.

Currently, the OFDM modulation and demodulation method is suitable for digital broadcasting by enabling a single frequency network (SFN) as well as a standard for high-speed wireless LAN of IEEE 802.11a and HIPERLAN / 2, broadband wireless access of IEEE 802.16, and therefore, DAB, DVB-T and DVB. Also adopted as the standard for -H. In addition, the transmission line using the DMT method, which is called a wired OFDM method, is used as the standard in ADSL and VDSL using the existing line, and is also attracting attention as the next generation mobile communication method.

The existing DVB-T supports two transmission modes of 2K and 8K, and the 2K mode has excellent performance of mobile reception, and the 8K mode has robustness against long channel delay in the SFN channel.

However, in case of portable mobile reception, robustness of time-varying channel and consideration of SFN network should be considered at the same time, whereas two modes of DVB-T have mutual weakness. Therefore, the DVB-H supports 4K transmission mode. In addition, the DVB-H supports time slicing to reduce power consumption of the mobile terminal. The time slicing method is a multiplexing method in which a capacity of a transmission path is divided into predetermined time slots and then a packetized broadcast signal is loaded in each time slot.

The conventional DVB-H and DVB-T receivers perform channel estimation using a scattered pilot arranged in a predetermined pattern in the frequency domain.

The distributed pilot consists of pseudo random binary sequences (PRBS) known to each other in a transmitter and a receiver, and is transmitted at a power that is 4/3 times larger than that of a data signal.

1 shows the pattern of the distributed pilot. The distributed pilot has a structure that is repeated every 12 in one OFDM symbol, and the next OFDM symbol has a structure in which the positions of the first distributed pilot are shifted to the right by three positions compared to the previous OFDM symbol. Therefore, the same distributed pilot pattern has a structure that is repeated every 4 OFDM symbols.

The distance between the distributed pilots located in the frequency domain determines the delay range of the ghost that can be estimated in the channel. Therefore, if the time domain interpolation is performed on four consecutive OFDM symbols, the distance between the distributed pilots located in the frequency domain is reduced to 1/4, and the channel estimation performance can be improved for the SFN channel in the wide area. In addition, when interpolation is performed in the time domain, adaptive channel estimation for time-varying channels is possible.

Therefore, in performing channel estimation, first, interpolation of the distributed pilot is performed in the primary time domain, and then interpolation in the frequency domain may be performed using the distributed pilot interpolated in the time domain.

FIG. 2 is a block diagram illustrating a structure of a conventional equalizer, and includes a pilot extractor 211, a time axis interpolator 212, a frequency axis interpolator 213, a data buffer 214, and a channel compensator 215. It is composed of

In the equalizer structure as shown in FIG. 2, time-base interpolation using pilots should be performed first. Therefore, an input data buffer 214 corresponding to OFDM four symbols and a four-symbol pilot channel in the time-base interpolation unit 212 used for channel estimation are used. You need a buffer.

That is, OFDM symbols received through the transmission channel are simultaneously provided to the pilot extractor 211 and the data buffer 214. The pilot extractor 211 extracts a distributed pilot from an OFDM symbol through zero forcing estimation and outputs it to the time base interpolation unit 212.

If the interpolation order is increased, more optimal performance can be obtained. However, interpolation in the time domain increases the number of OFDM symbols to be stored in the channel buffer and increases the complexity of channel estimation. Accordingly, the time axis interpolator 212 performs channel estimation of the time domain through linear interpolation for every four OFDM symbols in which the same distributed pilot is located.

That is, the time base interpolator 212 stores the channel buffer through zero forcing at the distributed pilot position after the equalizer starts channel estimation, and then performs interpolation on OFDM symbols having the same pattern as the fourth one. .

The interpolated signal in the time domain is input to the frequency axis interpolator 213 to interpolate in the frequency domain. The interpolation is performed to the channel compensator 215 which is interpolated in the frequency domain in the time domain.

Meanwhile, the data buffer 214 extracts distributed pilot signals from the pilot extractor 211, the time axis interpolator 212, and the frequency axis interpolator 213, and inputs the time required to perform time and frequency axis interpolation. The OFDM symbol is delayed and output to the channel compensator 215.

The channel compensator 215 divides the output of the frequency axis interpolator 213 by the output of the buffer 214 to compensate for a signal distorted by the channel. That is, after the seventh OFDM symbol is received, the estimation of the channels of all bands ends, and the estimated channel at this time is an estimate of the fourth received symbol.

FIG. 3 is a diagram illustrating a channel interpolation process in a time domain, and illustrates a progress of a memory (ie, a channel buffer) according to channel estimation.

In the case of the DVB-T and DVB-H receivers, the reception channel is generally time-varying. In addition to the time-varying characteristics of the channel, impulse noise generated from the peripheral electric devices brings discontinuity of the channel in the time domain. In addition, if there is a residual frequency offset in the estimation and compensation of the sampling frequency offset of the receiver, samples within a symbol are lost or added after a predetermined time.

Leakage and addition of samples in this time domain appear as an FFT window slip phenomenon and cause phase rotation on the CTF (Channel Transfer function), which is a response in the frequency domain. Since the slip phenomenon of the FFT window causes a continuous flow of time, the performance of the estimated ghost range is degraded, so fine symbol timing synchronization is performed in the DVB-T and DVB-H receivers. FSTS requires continuous tracking.

4 is a diagram illustrating a case in which a general time-varying and discontinuous channel appears, and shows an example in which time-varying and discontinuous channels are generated in a channel for an i-1 th symbol.

At this time, the change in the channel reflected by the receiver by the time-varying and discontinuous channels as shown in FIG. 4 and the sampling frequency offset is performed in the fine symbol timing sync block. However, in this process, a channel reflecting a CIR different from a channel in which an offset exists previously is input to the time base interpolation unit 212 of the equalizer, thereby having discontinuities.

That is, in the case of time-varying or discontinuous channel conditions as shown in FIG. 4, the fine symbol timing sync block of the receiver tracks the channel estimation within the offset. Therefore, the measured channel impulse response (CIR) is reflected for accurate FFT window section estimation. However, in this case, since the time domain interpolator 212 performs a time domain interpolation between the channel estimate with the offset of the channel buffer and the CIR and compensates the channel estimate, the wrong estimation is performed. Compensation cannot be made correctly until the channel value estimated at.

Therefore, in the receiver, it is difficult to expect the performance improvement of the receiver because wrong estimation and compensation corresponding to 7 symbols are performed every minute when the fine symbol timing sync block reflects the correct value of the symbol timing sync. In other words, during the seven symbols inputted to the time axis interpolation unit 212, the discontinuous channel is incorrectly interpolated, that is, channel estimation, and thus channel compensation is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an equalization device for improving channel estimation and compensation performance in time-varying and discontinuous channel situations.

In order to achieve the above object, the equalizer of the digital broadcast receiver according to the first embodiment of the present invention comprises: a fine symbol timing synchronizer for estimating and outputting a phase rotation value according to a variation in a time domain; A phase derotator for multiplying a signal received through a transmission channel with a phase rotation value output from the fine symbol timing synchronizer; An interpolator for extracting a distributed pilot from the phase derotated and output data and interpolating the time-domain and the frequency domain; A data buffer configured to delay and output the data output by being phase-rotated for the processing time of the interpolator; And a channel compensator for performing channel compensation by dividing the output data of the interpolator by the output data of the data buffer.

An equalization apparatus of a digital broadcast receiver according to a second embodiment of the present invention includes a fine symbol timing synchronizer for estimating and outputting a phase rotation value according to a variation in a time domain; A phase derotator for multiplying a signal received through a transmission channel with a phase rotation value output from the fine symbol timing synchronizer; An interpolator configured to extract a distributed pilot from the data that is output by the phase derotation, interpolate the time domain, and inversely multiply the interpolated data by a phase rotation value output from the fine symbol timing synchronizer; A data buffer for delaying and outputting a signal received through a transmission channel for the processing time of the interpolator; And a channel compensator for performing channel compensation by dividing the output data of the interpolator by the output data of the data buffer.

The interpolator may include a pilot extractor configured to extract a distributed pilot from data output by the phase derotation; A time axis interpolator for interpolating the distributed pilot signal extracted by the distributed pilot extractor into a time domain; A phase rotator for multiplying the data interpolated by the time axis interpolator inversely with a phase rotation value output from the fine symbol timing synchronizer; And a frequency axis interpolator configured to interpolate the phase rotated output data to a frequency domain.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described. At this time, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, by which the technical spirit of the present invention and its core configuration and operation is not limited.

The same components as in the related art are denoted by the same names and the same reference numerals for convenience of description, and detailed description thereof will be omitted.

The present invention is to improve the performance of the equalizer degraded due to time-varying and discontinuous channel conditions and sampling frequency offset.

)을 이용하여 시간축 보간부의 채널 버퍼에서 채널이 서로 불연속성을 가지지 않도록 함으로써, 등화기의 채널 추정 및 보상 성능을 개선할 수 있다. 또한 상기 시변 및 불연속성의 채널 상황으로 인해 추정 가능한 고스트 범위의 감소를 막도록 함으로써, SFN 채널 에서 롱 고스트(long ghost)에 대한 성능을 개선시킬 수 있다. To this end, the present invention provides a pre-phase derotation according to the shift in the time domain estimated in the fine symbol timing sync block;

) To improve channel estimation and compensation performance of the equalizer by preventing the channels from having discontinuities in the channel buffer of the time base interpolator. In addition, by preventing the reduction of the estimated ghost range due to the channel condition of the time-varying and discontinuous, it is possible to improve the performance for long ghost in the SFN channel.

In other words, the reflection of the exact value of the fine symbol timing synchronization is a compensation for the shift in the time domain, so that an error in channel estimation due to such a shift may result in a phase rotation prior to time axis interpolation. Will be compensated first.

Therefore, the channel estimation value before the CIR is reflected in the channel buffer of the time base interpolator has a continuous value with the current channel value reflecting the CIR, and can eliminate errors in channel estimation and compensation caused by discontinuities. do.

5 is a diagram illustrating an example of removing channel discontinuities for an i th symbol before a CIR and an i + 1 th symbol after being reflected.

The structure of the equalizer according to the present invention for discontinuous channel compensation as shown in FIG. 5 will be described by dividing into first and second embodiments.

FIG. 6 is a block diagram illustrating an equalization apparatus according to a first embodiment of the present invention, in which a phase derotator 610 is placed at the front end of both the pilot extractor 211 and the data buffer 214. It is equipped structure.

)을 입력되는 OFDM 심볼에 곱하여 파일럿 추출부(211)와 데이터 버퍼(214)로 출력함에 의해 현재 데이터와 채널 추정값을 같이 보상시킨다. That is, the phase derotator 610 is a phase rotation value according to the variation in the time domain estimated by the fine symbol timing sync block (

) Is multiplied by the OFDM symbol to be output to the pilot extractor 211 and the data buffer 214 to compensate for the current data and the channel estimate.

The time axis interpolation unit 212 performs channel estimation of the time domain through linear interpolation for every four OFDM symbols in which the same distributed pilot extracted by the pilot extraction unit 211 is located.

Accordingly, since the channel estimation value before the CIR is reflected in the channel buffer of the time base interpolator 212 has a continuous value with the current channel value reflecting the CIR, the error of channel estimation and compensation caused by discontinuity is eliminated. You can do it.

Detailed descriptions of the frequency axis interpolation unit 213, the data buffer, and the channel compensator 215 will be omitted since they will be described with reference to FIG. 2.

However, in the case of the first embodiment described above, although compensation and estimation of a channel due to discontinuity are possible, there is a disadvantage in that the range of ghost that can be estimated in the frequency axis interpolation process is reduced. That is, current DVB-T and DVB-H receivers allow estimation of long ghosts existing in SFN channels of Tu / 6 or lower, but in this case, due to phase rotation for compensation due to discontinuities, There is a disadvantage in that the range of the value modulated by the ghost is reduced, thereby lowering the estimation performance of the frequency interpolation unit 213.

FIG. 7 is a block diagram illustrating an equalization apparatus according to a second embodiment of the present invention. In addition to discontinuous channel compensation, FIG. 7 improves performance of an estimated ghost range in an SFN channel.

Referring to FIG. 7, a phase derotator 710 is provided at a front end of the pilot extractor 211, and a phase rotator is provided between the time axis interpolator 212 and the frequency axis interpolator 213. 720 is provided. In this case, data input to the data buffer 214 is data that does not pass through the phase derotator 710.

That is, OFDM symbols received through the transmission channel are simultaneously provided to the phase derotator 710 and the data buffer 720. The phase derotator 710 performs phase derotation on the channel value of the CIR reflected by the fine symbol timing sync block and outputs the phase derotation to the pilot extractor 211. In this case, data input to the data buffer 214 is data for which phase derotation has not been performed.

Accordingly, since the channel estimation value before the CIR is reflected in the channel buffer of the time base interpolator 212 has a continuous value with the current channel value reflecting the CIR, the error of channel estimation and compensation caused by discontinuity is eliminated. You can do it.

The channel estimate value interpolated in the time domain by the time axis interpolator 212 is input to the phase rotator 720. The phase rotator 720 reversely compensates the phase value compensated by the phase derotator 710 with respect to the output data of the time axis interpolator 212 and outputs it to the frequency axis interpolator 213. That is, the phase rotator 720 inversely multiplies the data interpolated in the time domain by the time domain interpolator 212 with the phase rotation value according to the variation in the time domain estimated by the fine symbol timing synchronizer, thereby in the SFN channel. This will improve performance for long ghosts.

Detailed descriptions of the frequency axis interpolation unit 213, the data buffer 214, and the channel compensator 215 will be omitted since they will be described with reference to FIG. 2.

As such, when the channel is estimated through the phase derotation and rotation processes, the error that is broken by the discontinuity with the channel reflected by the FSTS can be eliminated, and the estimation range for the long ghost that can be obtained in the compensation process in the frequency domain is obtained. Is not reduced to allow for improved channel estimation and compensation in the SFN channel.

On the other hand, the terms used in the present invention (terminology) are terms defined in consideration of the functions in the present invention may vary according to the intention or practice of those skilled in the art, the definitions are the overall contents of the present invention It should be based on.

The present invention is not limited to the above-described embodiments, and as can be seen in the appended claims, modifications can be made by those skilled in the art to which the invention pertains, and such modifications are within the scope of the present invention.

The effects of the equalizer of the digital broadcast receiver according to the present invention described above are as follows.

First, the present invention multiplies the data inputted to the time axis interpolator and the data buffer by the phase rotation value according to the variation in the time domain estimated by the fine symbol timing synchronizer so that the CIR in the channel buffer of the time axis interpolator is reflected. The previous channel estimation value has a continuous value with the current channel value reflecting the CIR. Therefore, the performance degradation of estimation and compensation for time-varying and discontinuous channels is improved, thereby ensuring a stable receiver quality of service (QOS).

Second, by multiplying the data interpolated in the time domain by the time domain interpolator inversely with the phase rotation value according to the variation in the time domain estimated by the fine symbol timing synchronizer, the performance of the long ghost in the SFN channel is improved. It works.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

Claims (3)

A fine symbol timing synchronizer configured to estimate and output a phase rotation value according to the variation in the time domain; A phase derotator for multiplying a signal received through a transmission channel with a phase rotation value output from the fine symbol timing synchronizer; An interpolation unit for extracting a distributed pilot from data derotated and output from the phase derotator and interpolating the time domain and the frequency domain; A data buffer configured to delay and output data derotated from the phase derotator for a processing time of the interpolator; And And a channel compensator for performing channel compensation by dividing the output data of the interpolator into output data of the data buffer. A fine symbol timing synchronizer configured to estimate and output a phase rotation value according to the variation in the time domain; A phase derotator for multiplying a signal received through a transmission channel with a phase rotation value output from the fine symbol timing synchronizer; A distributed pilot is extracted from the data derotated and output from the phase derotator and interpolated in the time domain. The interpolated data is multiplied inversely with the phase rotation value output from the fine symbol timing synchronizer. Cadre; A data buffer for delaying and outputting a signal received through a transmission channel for the processing time of the interpolator; And And a channel compensator for performing channel compensation by dividing the output data of the interpolator into output data of the data buffer. The method of claim 2, wherein the interpolation unit A pilot extractor extracting a distributed pilot from data derotated and output from the phase derotator; A time axis interpolator for interpolating the distributed pilot signal extracted by the distributed pilot extractor into a time domain; A phase rotator for multiplying the data interpolated by the time axis interpolator inversely with a phase rotation value output from the fine symbol timing synchronizer; And And a frequency axis interpolator for interpolating the data rotated and output by the phase rotator in a frequency domain.

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