KR100556376B1 - Carrier Recovery - Google Patents

Abstract

The present invention relates to a phase correction decision feedback channel equalizer, comprising: a feedforward filter for filtering a signal received from a transmission channel, a feedback filter for removing interference between existing signals using signals detected in the past; An adder that adds an output of a feedforward filter unit and a feedback filter unit, and receives the output signal of the adder and provides a decision signal constellation having a phase equal to that of an input constellation of the feedforward filter unit, It consists of a phase compensator for outputting the corrected output image from which the distortion is removed.

Channel Equalizer, Carrier Phase, Ghost, Phase Compensator

Description

Phase Correction Decision Feedback Channel Equalizer {Carrier Recovery}

1 is a block diagram of a general multi-media digital broadcasting receiver

Figure 2 is a block diagram of a phase correction decision feedback channel equalizer according to the prior art

3 is a block diagram of a digital broadcast receiver equipped with a phase correction decision feedback channel equalizer.

Figure 4 is a block diagram of a phase correction decision feedback channel equalizer according to the present invention

FIG. 5 is a detailed view of the phase corrector in FIG.

6 is a detailed view of the crystalline phase / error / correction phase generator of FIG.

7 is a graph for comparing the ghost performance according to the phase difference of the phase correction decision feedback channel equalizer according to the prior art and the present invention

** Description of the symbols for the main parts of the drawings **

300: preprocessing unit 400: phase correction decision feedback channel equalizer

500: post-processing unit 401: feed forward filter unit

402: feedback filter unit 403: adder

404: phase corrector

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital broadcasting apparatus, and in particular, a phase correction decision feedback channel equalizer capable of providing the same ghost capture / tracking performance regardless of carrier frequency phase and ghost phase and improving ghost cancellation performance. It is about.

Digital broadcasting reception technology, which is currently divided into various media (terrestrial wave, cable, satellite), is being developed as an integrated system structure for integrated digital broadcasting in the future.

In particular, since HDTV transmission system transmits data having a high bit rate of about 20Mb / s or more through a limited band-limit 6MHz, a modulation / demodulation method having good bandwidth efficiency is required. do. In addition, a channel equalizer technique for compensating for non-ideal characteristics of a channel such as symbol / carrier recovery technique for symbol and carrier recovery, multi-path, and Doppler effect This is necessary and an efficient channel decoding method is used for reliable transmission of noise.

The integrated "multimedia digital broadcast receiver" is divided into three reception methods as follows.

1) Terrestrial broadcast reception method:

VSB (Vestigial Side Band, SSB, ATSC, American Style),

Orthogonal Frequency Division Multiplexing (DSB, European Type)

2) Cable broadcasting reception method:

Quadrature Amplitude Modulation (QAM)

3) Satellite broadcasting reception method:

Quadrature Phase Shift Keying (QPSK)

These three reception methods are composed of different element technologies such as analog receiver, signal synchronization, channel equalization, matched filter, and channel decoding.

However, there is a need to perform the development of optimized "multimedia digital broadcast receivers" by selecting functions that can be shared among these element technologies in the future.

In general, a "multimedia digital broadcast receiver" is configured as shown in FIG.

1 is a block diagram of a general multimedia digital broadcasting receiver, comprising: an analog receiver 101 for receiving a radio frequency (RF) signal and converting it into an intermediate frequency (IF) signal, and an analog / analog (A / D) signal; And a digital demodulator 102 for demodulating the digital signal converted using the digital conversion unit 101h.

The analog receiver 101 receives a RF (Radio Frequency) signal of 50 ~ 860MHz by the tuner 101b, converts it into an intermediate frequency (IF) signal, and converts the converted signal into an A / D converter 101h. It converts into a digital signal through the digital demodulator 102 and transmits it.

The analog receiver 101 includes a tuner 101b for converting an RF signal of 50 to 860 MHz received through an antenna 101a into a first intermediate frequency signal of 44 MHz, and a signal output from the tuner 101b. The surface acoustic wave (SAW) filter 101c for filtering the signal, the first oscillator 101d for generating the oscillation frequency for generating the second intermediate frequency signal, and the signal filtered by the SAW filter 101c for the first oscillator Mixer 101e for down-converting to the oscillation frequency generated by 101d and converting it into a second intermediate frequency signal, and compensating for the gain of the second intermediate frequency signal output from the mixer 101e The automatic gain control (AGC) amplifier 101f, the second oscillator 101g for generating the sampling frequency, and the signal amplified by the AGC amplifier 101f are carried out by the second oscillator 101g. A converts into a digital signal according to the sampling frequency generated / D conversion section 101h.

At this time, among the components of the multimedia digital broadcasting receiver, the analog receiver 101 has a structure as shown in FIG. 1 regardless of the demodulation scheme.

On the other hand, the digital demodulator 102 has various forms according to demodulation schemes (VSB, OFDM, QAM, QPSK, etc.), symbol recovery, matched filter, and phase splitter. ), A phase correction decision feedback channel equalizer (Carrier Recovery), a channel equalizer (Channel Equalizer), and a channel decoder (FEC) are used as basic elements.

The symbol recovery unit receives a timing error of current symbols by using a resampler to reduce an error between the digital signal and the signal output from the A / D converter 101h. After interpolation, output to the matched filter part.

The symbol recovery part is an all-digital process that performs A / D conversion of analog data at a fixed frequency and clock recovery of all symbol strings in a resampler, so it does not require an analog device other than an A / D converter, thus simplifying implementation. Noise can be eliminated.

The matched filter filters the signal output in synchronization with the symbol recovery unit, and readjusts the signal to noise ratio (SNR) at the symbol position to be maximum. In the case of the receive filter, it is theoretically impossible to realize the shape of the receive filter having a rectangular band characteristic and an infinite time delay. The detection process in such a system is quite sensitive to very small timing errors. Therefore, the intersymbol effect at the exact sample time can be avoided, but when there is a slight error, symbol mutual interference occurs. Thus, some excess bandwidth is required to realize the system. In order to solve this problem, a matching filter unit is used.

A phase splitter separates the output of the matched filter into an I signal and a Q signal and outputs the same to the phase correction decision feedback channel equalizer.

The phase correction decision feedback channel equalizer (Carrier Recovery) removes the frequency offset and phase noise of the carrier wave by the tuner (101a) and the mixer (101d) of the analog receiver 101, the band pass at the same time It performs the function of digital demodulation, which demodulates a digital signal into a baseband digital signal.

In a digital transmission system such as HDTV, a bit detection error is caused at the receiving side due to distortion caused by a transmission signal passing through a multipath channel, interference by an NTSC signal, distortion by a transmission / reception system, and the like. Inter-Symbol Interference is a cause of bit detection error. Accordingly, the channel equalizer removes the interference between symbols.

In the transmission system, various error correction codes are used depending on the channel environment. In the channel environment, there are various kinds of noises such as condensed noise and scattered noise. In general, the channel decoder (FEC) uses an RS code method and a lattice modulated code method to inter-symbol symbols in the channel equalizer. After removing the scattering noise and the scattering noise existing on the channel included in the interference-removed signal, the baseband signal recovers the synchronization signal inserted during transmission and recovers the received data, that is, the transmission symbol by using the synchronization signals. .

The phase correction decision feedback channel equalizer among the components of the digital broadcasting reception apparatus will be described in detail as follows.

The phase correction decision feedback channel equalizer used in the HDTV transmission system is the receiver side due to the ghost or NTSC signal generated by the transmission signal passing through the multi-path channel and the ghost by the transmission / reception system. In this case, a signal detection error occurs, and in particular, the propagation of a signal through a multipath compensates for the main cause of the bit detection error causing inter-symbol-interference (ISI).

FIG. 2 is a diagram illustrating a structure of a phase correction decision feedback channel equalizer 200 according to the related art. The feedforward filter unit 201 filters and outputs a signal received from the carrier recovery unit 100. A feedback filter unit 202 for removing a portion of interference between symbols from a current estimation generated by previously detected symbols, the feedforward filter unit 201 and the feedback filter unit 202; The adder 203 and the phase corrector 205 add the output of the slicing signal to the feedback filter unit 202 by slicing the signal from which the distortion is removed to generate a crystal signal constellation. Receives the decision signal / error generating unit 204 and the output signal of the adder 203 which are extracted and provided to the feedforward filter unit 201 and the feedback filter unit 202 and are distorted by the phase of the carrier and ghost. Phase to remove It consists of a retainer (205).

The output of the carrier recovery unit 100 is a signal in which a residual carrier phase and a ghost phase exist together, and as shown in the drawing, the shape of the constellation is inclined by the residual phase so that the feedforward of the phase correction decision feedback channel equalizer 200 can be obtained. It is transmitted to the input of the filter unit 201.

On the other hand, the input of the feedback filter unit 202 is a crystal signal constellation slicing the output of the phase corrector 205 through the crystal signal / error generator 202, and the straight constellation without distortion by the phase as shown in the figure Indicates.

The output of the adder 203, which is a part of adding the two constellations, causes distortion of the constellations because the signals to be added have different phases, and deteriorates the ghost performance of the phase correction decision feedback channel equalizer 200. Will result.

The constellation degraded by the residual phase exhibits a constellation substantially similar to the residual phase of the phase correction crystal feedback channel equalizer 200, and the recovery of the residual phase is corrected by the phase compensator 205 and is straightened as shown in the drawing. A constellation with a shape can be obtained.

However, the input constellation of the feedback filter unit 202 generates a phase error equal to the output constellation and the residual phase of the feedforward filter unit 203, and thus adds two constellations having this phase error. The crystal feedback channel equalizer 200 exhibits different ghost capturing / tracking performances according to the phases and also deteriorates the ghost removal ability.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the ghost signal is fixed regardless of the frequency phase and ghost phase of the carrier by making the phase of the decision signal property of the feedback filter equal to the phase of the input signal property of the feedforward filter part. Its purpose is to provide a phase-corrected decision feedback channel equalizer that can provide tracking performance.

Another object of the present invention is to improve the ghost removal performance of the phase correction decision feedback channel equalizer.

The phase correction decision feedback channel equalizer according to the present invention includes a feed forward filter unit for filtering a signal received from a transmission channel, a feedback filter unit for removing interference between existing signals using signals detected in the past, and the feed. An adder that adds an output of a forward filter unit and a feedback filter unit, and receives the output signal of the adder and provides a decision signal constellation having a phase identical to a phase of an input constellation of the feedforward filter unit and distorted by phase And a phase compensator for outputting the removed corrected output constellation.

Preferably, the phase compensator provides a phase tracker for generating the corrected output constellation using the output constellation of the adder, and provides a decision signal constellation having the same phase as an input constellation of the feedforward filter section. And a crystalline phase / correction phase / error generator for generating a crystalline phase, a correction phase, and an error.

Preferably, the phase tracker is configured to multiply a conjugation value of the adder phase with the output constellation of the adder to produce a corrected output constellation.

The crystal constellation phase corrector may be configured to provide a crystal signal constellation obtained by multiplying the crystal constellation and the correction phase value to the feedback filter unit.

Preferably, the crystal phase / correction phase / error generator includes a crystal for receiving the corrected output constellation and generating a crystal constellation, and a phase generator for generating a correction phase by multiplying a conjugation value of the crystal phase in the corrected output constellation. And an error generator for generating an error by subtracting the crystalline phase from the corrected output constellation.

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, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

3 is a block diagram of a digital broadcast receiver equipped with a phase correction decision feedback channel equalizer. The baseband digital signal generated by the pre-processing unit 300 is a phase correction decision feedback channel equalizer 400. Referring to FIG. A baseband digital symbol, which is used as an input and is an output of the phase correction decision feedback channel equalizer 400, is used as an input of a post-processing unit 400.

Figure 4 is a block diagram of a phase correction decision feedback channel equalizer 200 according to the present invention, a feedforward filter unit 401 for filtering and outputting a signal received from the preprocessor 300, and A feedback filter unit 402 which removes a portion in which interference between symbols is generated from a current estimation generated by the symbols detected at the output of the feed forward filter unit 401 and the feedback filter unit 402. adder 403, and a crystal having the same phase as the phase of the input constellation (y _n = y _'n e ^jφn) of the adder 403, the output signal received by the phase correction decision feedback channel equalizer 200, the adding A signal output (a _n = a ' _n e ^{j φ} _n ) is provided to the feedback filter unit 402, and a corrected output constellation (r _n = r' _n e ^{-j φ} _n ), which corrects distortion due to phase, is applied to the post processor 500. ) Is configured as a phase corrector 404 for outputting.

The input constellation generated by the pre-processing unit _{(300) (y n = y} 'n e jφn) is, the carrier phase and the phase e ^jφn by the phase correction decision feedback channel in twisted state equalizer by the ghost, as shown in Figure 4 The determination signal constellation (a _n = a ' _n e ^{j φ} _n ) inputted to the 400 and input to the feedback filter unit 402 is also distorted by e ^jφ _n by the phase corrector 404 to the feedback filter unit 402. It is input, and is added through the adder 403 to generate the output constellation (Z _n = Z ' _n e ^{j φ} _n ).

That is, the output constellation (Z _n = Z ' _n e ^{j φ} _n ) is ^removed from the input constellation (y _n = y' _n e ^{j φ} _n ) received from the preprocessing unit 300. holding, it is reflected input constellation _{(y n = y 'n e} jφn) is left as it is.

FIG. 5 is a detailed view of the phase corrector 404 in FIG. 3. The phase corrector 404 includes a phase tracker 404a for generating a corrected output constellation (r _n = z _n e ^-jφn ) and a phase correction determination. the decision to provide the input constellation (y _n = y _'n e ^jφn) and determining a signal constellation (a _n = a has the same phase' _n e ^jφn) to the feedback filter part 402 of the feedback channel equalizer 200 and the aqueous phase corrector (404b), is configured to determine the aqueous phase (a _'n), the correction phase (e ^jφn), the error (e (n)) determines the aqueous phase / phase correction / error generator (404c) for generating a.

The phase tracker (404a) is output aqueous phase _{(Z n = Z 'n e} jφn) correction phase (e ^jφn) conjugated (conjugation) value (e ^-jφn) for multiplying the distortion is removed by the phase-corrected output of the Generates the constellation (r _n = z _n e ^-jφn ).

In addition, the decision aqueous phase corrector (404b) determines the aqueous phase (a _'n) corrected phase (e ^jφn) for multiplying the input constellation (y _n = y in' _n e ^jφn) and integrity signal constellation is corrected to have the same phase (a _n = a _'n output ^jφn e), and the aqueous phase decision signal (a _n = a' is used as input for the _n ^jφn e) is a feedback filter section 402.

The error e (n) generated by the crystalline phase / correction phase / error generator 404c is transmitted to the feedforward filter unit 401 and the feedback filter unit 402.

FIG. 6 is a detailed view of the crystalline phase / corrected phase / error generator 404c of FIG. 4, which determines the signal of the corrected output constellation r _n = z _n e ^-jφn to generate a crystalline constellation a ' _n . And a phase generator 42 for generating a correction phase e ^jφn by multiplying the ^condensed value of the crystal phase a ' _n by the corrected output phase r _n = z _n e ^-jφn . And an error generator for generating an error e (n) of the phase correction decision feedback channel equalizer 200 by subtracting the crystalline phase a ' _n from the corrected output phase r _n = z _n e ^-jφ n. It consists of 43.

7 is a graph for comparing the ghost performance according to the phase difference of the phase correction decision feedback channel equalizer according to the prior art and the present invention, respectively, when the ghost phase is 0 °, 90 °, 180 °, 270 ° Simulation results.
In general, the simulation may be performed at the algorithm level or by incorporating hardware. However, FIG. 7 showing the simulation result of the present invention is a result of using the hardware, which is applied by the channel equalizer of the present invention to a ghost simulator. The results obtained are shown.
The ghost simulator plays a role of putting a ghost into a channel. The ghost simulator measures a change in amplitude and phase for each tap, and FIG. 7 shows a result measured at 30 positions.

In the channel where the residual carrier phase and the ghost phase exist together, the conventional phase correction decision feedback channel equalizer shows that the ghost capture / tracking performance differs according to the ghost phase values as shown in graphs A, B, C, and D. It can be seen that the ghost removal performance is poor.

On the other hand, the phase correction channel feedback channel equalizer according to the present invention as shown in the graph E can be seen that always capture / track a constant ghost irrespective of the phase of the ghost, and it can be seen that the ghost removal performance is also improved.

As described above, the phase correction crystal feedback channel equalizer of the present invention can provide a constant ghost capture / tracking performance regardless of the frequency phase of the carrier and the ghost phase, and can improve the ghost removal ability.

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 examples, but should be defined by the claims.

Claims (5)

A feedforward filter unit for filtering a signal received from a transmission channel; A feedback filter unit for removing interference between existing signals using signals detected in the past, An adder for adding outputs of the feedforward filter unit and the feedback filter unit; A phase tracker for generating the corrected output constellation using the output constellation of the adder; A crystal constellation phase corrector for providing a crystal signal constellation having the same phase as an input constellation of the feedforward filter unit; And a phase corrector comprising a crystalline phase, a corrected phase, and a crystalline phase / corrected phase / error generator for generating an error. delete The method of claim 2, The phase tracker And a phase correction decision feedback channel equalizer configured to multiply a conjugation value between the output phase of the adder and the correction phase to produce a corrected output phase. The method of claim 2, The crystalline phase compensator And providing a decision signal property obtained by multiplying the crystal shape and the correction phase value by a feedback filter unit. The method of claim 2, Crystalline phase / correction phase / error generator A determiner for receiving the corrected output constellation and generating a crystal constellation; A phase generator for generating a correction phase by multiplying a conjugation value of a crystalline phase by the corrected output phase; And an error generator configured to generate an error by subtracting the crystalline phase from the corrected output constellation.

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