KR100556377B1 - Symbol timing restorer - Google Patents

Abstract

The output of the BPF (Band Pass Filter) section can vary from several tens to hundreds of gains, which is not suitable to control with an optimized loop filter in the absence of ghosts.

Therefore, in the present invention, the timing error is adjusted to be close to the normal channel under any channel environment by using a complex normalizer that complex-normalizes the gain so that a constant convergence speed can be obtained regardless of the gain. We want to provide a symbol timing recoverer that allows the filter to operate in an optimized region.

Therefore, using the present invention can achieve a constant convergence rate regardless of the gain size, and in particular, it is possible to improve the initial convergence speed and performance in the channel where frequency selective attenuation occurs.

Timing Restorer, Complex Normalizer, Convergence, Optimization

Description

Symbol Timing Recovery

1 is a block diagram of a general digital TV receiver

2 is a representative structural diagram of a symbol timing recoverer;

3 is a schematic structural diagram of a loop filter of FIG.

4 is a structural diagram of a Gardner type symbol timing recoverer

5 is a structural diagram of a symbol timing recoverer of the conventional OQAM method

6 is a structural diagram of a symbol timing recoverer according to the present invention.

7 is a waveform diagram of a test result of the Gardner type symbol timing recoverer.

8 is a waveform diagram showing the results of testing the performance of the symbol timing recoverer according to the present invention.

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

601: Resampler 602: First OQAM Signal Generator

603: HPF / BPF section 604: squarer / adder

605: BPF section 606: phase separator

607: Complex Normalizer 608: Second OQAM Signal Generator

609: squarer / adder 610: loop filter unit

611: NCO Department

The present invention relates to a broadcast receiver, and more particularly to a symbol timing recoverer capable of providing excellent convergence performance in a frequency selective channel environment.

Hereinafter, the prior art will be described with reference to the accompanying drawings.

1 is a block diagram of a general digital receiver, including an antenna 101, a tuner 102, an analog processing unit 103, an analog / digital (A / D) conversion unit 104, a phase separator 105, Carrier Recovery 106, Symbol Timing Restorer 107, Channel Equalizer 108, Phase Tracer 109, Channel Decoder 110, A / V It consists of an (Audio / Video) signal processing unit 111.

First, the airwave signal received through the antenna 101 is converted into a passband signal of an intermediate frequency (IF) at the tuner 102.

This signal passes through an analog processing unit 103 composed of a SAW filter, a gain control unit (AGC), etc. in order to remove high frequency components generated from adjacent channel interference and tuner 102.

When the fixed oscillator is used, the A / D converter 104 converts the analog signal into a digital signal having a fixed frequency. The passband signal converted into a digital signal is converted into a complex signal through the phase separator 105, and the complex signal is converted into a baseband signal through a carrier recoverer 106.

The signal coming down to the baseband through the carrier decompressor 106 enters the input of the symbol timing decompressor 107 to recover the symbol clock.

The output signal of the symbol timing reconstructor 107 is input to the channel equalizer 108, which removes the inter symbol interference added by the transmission channel. In addition, the residual phase of the carrier that is not removed by the carrier restorer 106 is recovered through the phase tracker 109.

Thus, the phase corrected signal corrects an error generated while passing through the channel through the channel decoder (FEC) 110, and the signal passed through the channel decoder 110 is transferred to the A / V signal processor 111. do.

The A / V signal processor 111 decompresses the video and audio signals processed by the MPEG 2 and Dolby AC-3 schemes and outputs them through the monitor and the speaker 200.

The basic structure of the symbol timing recoverer 107 among the components of the digital broadcast receiver is shown in FIG. 2.

As shown in FIG. 2, the symbol timing recoverer 107 is composed of an interpolator 201, a timing error detector 202, and a loop filter 203.

The signal A / D converted by the A / D converter 104 is input to the interpolator 201 of the symbol timing recoverer 107 via the phase separator 105 and the carrier recoverer 106. The oscillator 201 generates a sample close to the actual symbol timing frequency and phase by generating an intermediate value of the signal sampled by the A / D converter 104.

The output of the interpolator 201 is sent to the timing error detector 202 to extract timing errors by various algorithms. The control signal of the interpolator 201 is obtained by passing the output signal of the timing error detector 202 through the loop filter 203.

3 is a detailed block diagram of the loop filter 203 and shows a structure of a typical secondary loop filter.

The loop filter 203 has two paths. The path filter 1 includes a first multiplier 301 that multiplies a gain K _p by a timing error signal output from the timing error detector 202 to track timing phase errors. a and path 2 is composed of a timing error detector 202, a second multiplier 302 and the gain K _i is the integrator 303, which integrates the timing error signal is multiplied is multiplied by the gain K _i in a timing error signal output from the role It serves to track timing frequency errors. The result obtained through the path 1 and the path 2 is added through the adder 304 to be output as a control signal of the interpolator 201.

Thus, the loop filter 203 can track both timing frequency errors and phase errors.

4 is a view showing the structure of a Gardner symbol timing recoverer, which is widely applied to DTV receivers and other digital communications.

The Gardner symbol timing reconstructor uses only the real part of the complex signal. The symbol timing reconstructor functions to detect a timing error using two samples per symbol, and includes a resampler 401 and a prefilter ( 402, a timing error detector (TED) 403, a loop filter 404, and a NCO (Numerical Controlled Oscillator) unit 405.

The complex signal (I signal + Q signal) from the carrier decompressor 106 enters the input of the resampler 401 to generate a sample corresponding to twice the symbol frequency. In order to reduce the pattern jitter caused by the data by taking only the real part (Q signal), the prefiltering part is prefiltered by using the prefilter unit 402.

Thereafter, the timing error detector 403 detects the timing error and generates a control signal of the resampler 401 after passing through the loop filter unit 404 and the NCO unit 405.

As described above, the Gardner-type symbol timing reconstructor prefilters frequency components at 1/2 of the symbol frequency to reduce pattern jitter, but when the pre-filtered frequency components are attenuated, they do not converge to the symbol frequency. There is a disadvantage that the convergence time is significantly longer.

In addition, a Gardner symbol timing reconstructor using two samples per symbol should be located at the rear end of the carrier reconstructor 106. If the pilot is severely attenuated and carrier recovery is impossible or the residual jitter is severe, a direct influence may be obtained. There are drawbacks to receiving.

In order to overcome the drawbacks of the Gardner type symbol timing recoverer, an application of a timing recoverer using an Offset QAM (OQAM) method has recently been attempted.

The structure of an OQAM symbol timing recoverer is shown in FIG. 5.

Referring to FIG. 5, the symbol timing recoverer of the OQAM method includes a resampler 501, a first OQAM signal generator 502, an HPF / BPF unit 503, a squarer / adder 504, BPF unit 505, phase separator 506, second OQAM signal generator 507, squarer / subtractor 508, loop filter unit 509, and NCO (Numerically Controlled) Oscillator) 510 is configured.

The complex signal from the carrier decompressor 106 enters the input of the resampler 501 and generates a sample corresponding to twice the symbol frequency. The complex output of the resampler 501 is converted into a complex signal that is twice the symbol period in the first OQAM signal generator 502. The output signal of the first OQAM signal generator 502 is converted into DC and data. In order to reduce the pattern jitter caused by the high pass filter and the band pass filter that passes only the signal of the quarter point of the symbol frequency pass through the HPF (High Pass Filter) / BPF (Band Pass Filter) section 503.

In addition, the complex signal from which DC is removed through the HPF / BPF unit 503 is squared / squared with respect to each of the I signal / Q signal in the squarer / adder 504, and thus the influence of the carrier residual phase is increased. Will be removed.

 The output signal of the squarer / adder 504 again has a frequency component corresponding to one-half of the symbol frequency, after which the timing error is obtained using this component.

First, in order to eliminate pattern jitter, only the signal at a point half of the symbol frequency is passed through the BPF unit 505, and then converted into a complex signal again using the phase separator 506, and then the second OQAM signal generator 507 Pass through) to reduce the period of the signal by half.

The converted signal forms a strong tone at a quarter of the symbol's frequency, which is squared by the squarer / subtractor 508 to shift the tone to half the symbol's frequency. This timing signal is used as a control signal of the resampler 501 through the loop filter unit 509 and the NCO unit 510.

The symbol timing reconstructor of the OQAM method can be seen as a way to apply the 4th power timing recovery loop to the limited situation of the VSB receiver. In order to prevent DC increase due to repeated squares, The use of a high pass filter and a band pass filter also affects somewhat in frequency selective fading environments.

The OQAM symbol timing recoverer is severely affected when both sides of the spectrum are attenuated at the same time, but it can compensate to some extent the disadvantage of band edge timing recovery using only one side of the VSB spectrum.

In addition, since the influence of the carrier frequency can be eliminated under the influence of the squarer / multiplier 504, the performance of the timing recoverer does not deteriorate even in a situation where the carrier restorer cannot converge.

However, despite these advantages, if the frequency component corresponding to the pass band is severely attenuated in the band pass filter due to the limitation of applying the band pass filter (BPF) periodically, the gain may become small and fail to converge.

The present invention has been made to solve the above problems, and an object thereof is to provide a symbol timing recoverer capable of improving initial convergence speed and performance in a frequency selective channel and a multi-interference channel environment.

The symbol timing reconstructor according to the present invention receives a complex signal and generates a sample corresponding to twice the symbol frequency, and a first sample for converting the complex output of the resampler into a complex signal that is twice the symbol period. Squares an HPF / BPF unit for removing pattern jitter by DC and data from an OQAM signal generator, the signal converted by the first OQAM signal generator, and an I signal and a Q signal from which DC is removed through the HPF / BPF unit, respectively. A squarer / adder for removing the influence of the carrier residual phase by adding a squared value, a BPF section for bandpass filtering the output signal of the squarer / adder at a half point of the symbol frequency, and the BPF section A phase separator for receiving an output signal and converting the signal into a complex signal, a complex normalizer for complex normalizing the output of the BPF unit having passed through the phase separator, and a period of the complex normalized signal A second OQAM signal generator that is lowered to 1/2, a squarer / subtractor that squares an output signal of the second OQAM signal generator and converts it into a timing signal having a strong tone at a half point of a symbol period, and the square And an NCO unit and a loop filter for generating a control signal of the resampler using the output of the pre-subtractor.

)을 구하는 제곱근기와, 상기 위상 분리기로부터 수신한 I 신호 및 Q 신호를 각각 상기 제곱근기의 출력값으로 나누는 제 1, 제 2 나눗셈기로 구성되는 것을 특징으로 한다.Preferably, the complex normalizer may include first and second squarers that square the I and Q signals received from the phase separator, an adder that adds output values of the first and second squarers, and an output value of the adder. Square root (

And a first divider and a second divider for dividing the I signal and the Q signal received from the phase separator by the output value of the square root, respectively.

Preferably, the complex normalizer is implemented using a ROM.

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.

6 is a structural diagram of a symbol timing recoverer according to the present invention. The complex normalizer 607 performs complex normalization of a gain so that a constant convergence speed may be represented regardless of a gain size in a conventional symbol timing recoverer of an OQAM method. ) Is an additional configuration.

As shown in FIG. 6, the symbol timing recoverer receives a complex signal from the carrier recovery unit 106 to generate a sample corresponding to twice the symbol frequency, and the resampler. A first OQAM signal generator 602 for converting the complex output of the device 601 into a complex signal that is twice the symbol period, and a pattern formed by DC and data in the OQAM signal converted by the first OQAM signal generator 602. HPF / BPF unit 603 for performing high pass filtering and band pass filtering at a quarter of symbol frequency, and I-signal with DC removed through the HPF / BPF unit 603. A squarer / adder 604 that squares each of the Q signals and adds the squared value to remove the influence of the carrier residual phase, and the output signal of the squarer / adder 604 at a point half of the symbol frequency. A BPF unit 605 for performing band pass filtering; Complex normalization for complex normalizing the output of the BPF unit 605, which receives the output signal of the BPF unit 605 and converts it into a complex signal, and the BPF unit 605 converted into a complex signal through the phase separator 606. 607, a second OQAM signal generator 608 that lowers the period of the complex normalized signal by half, and a second OQAM signal generator 608 that forms a strong tone at a quarter of the symbol frequency. A squarer / subtractor 609 that squares an output signal of the squareband and converts the output signal of the squarer / subtractor 609 into a timing signal having a strong tone at a half point of a symbol period. A loop filter 610 and an NCO unit 611 for generating a control signal of the device 601.

The complex signal received from the carrier recovery unit 106 is generated as a sample corresponding to twice the symbol frequency through the resampler 601, and the complex output is generated through a symbol period through the first OQAM signal generator 602. It is converted into a complex signal which is twice as large as.

Subsequently, the converted signal is removed from the pattern jitter due to DC and data through the HPF / BPF unit 603 and the influence of the carrier residual phase is removed through the squarer / multiplier 604.

The signal passed through the squarer / adder 604 has a frequency component corresponding to one-half of the symbol frequency, and then the timing error is obtained using this component.

First, the output signal of the squarer / adder 604 is removed from the pattern jitter through the BPF unit 605 and converted into a complex signal using the phase separator 606.

Depending on the channel characteristics, the output of the BPF unit 606 may have a difference of up to several tens or hundreds of gains, which is not suitable for controlling by using a loop filter optimized for a ghost-free situation.

Thus, by using the complex normalizer 607 to adjust the gain of the timing error close to the normal channel under any circumstances, the timing recoverer operates in the optimized region of the loop filter 610.

This not only improves the speed of convergence but also acts as a factor to increase the possibility of convergence.

6 illustrates an implementation of the complex normalizer 607, and a ROM may be used in actual hardware implementation.

)을 구하는 제곱근기(607d)와, 위상 분리기(606)로부터 수신한 복소 신호(I 신호, Q 신호)를 각각 상기 제곱근기(607d)의 출력값으로 나누어 출력하는 제 1, 제 2 나눗셈기(607e)(607f)로 구성된다.The complex normalizer 607 includes first and second squarers 607a and 607b that square the complex signals (I and Q signals) from the phase separator 606, respectively, and the first and second squares. An adder 607c that adds a squared value by the steps 607a and 607b, and a square root of the output value of the adder 607c.

The first and second dividers 607e for dividing and outputting the square roots 607d for obtaining?) And the complex signals (I signals, Q signals) received from the phase separator 606 by the output values of the square roots 607d, respectively. 607f).

7 and 8 are simulation results for comparing the performance of the conventional Gardner symbol timing restorer and the timing restorer proposed in the present invention under a single ghost environment.

The simulation environment assumes that there is no AWGN (Additive White Gaussian Noise) and that the carrier restorer is perfectly convergent.

In the case of the Gardner method, as shown in FIG. 7, when the ghost causes interference in phase with 0 degree delayed by 1 symbol, the gain of the prefiltered timing signal is too small to converge to the timing frequency offset. If it does not occur (② signal).

This phenomenon can be observed even when a 0 dB ghost with 2 symbol delay interferes with a 180 degree phase difference (5) signal. In this case, since both gains of the pilot signal and the timing signal are weakened, carrier recovery and symbol timing recovery are difficult.

On the other hand, when applying the method proposed in the present invention as shown in Figure 8, it can be seen that almost all of the single ghost converges at a constant speed.

Of course, even if the gain is increased when AWGN is severely applied, a slight performance degradation is expected due to the amplification of noise, but it can be seen that the convergence performance is superior to that of Gardner and the conventional OQAM timing restorer in most DTV reception environments.

In particular, performance improvement is noticeable in channels with ghosts of less than 10 dB.

The symbol timing recoverer of the present invention as described above has an effect of improving initial convergence speed and performance in a channel in which frequency selective attenuation occurs by limiting gain variation of a timing error signal using a complex normalizer.

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 (3)

A resampler for receiving a complex signal and generating a sample corresponding to twice the symbol frequency; A first OQAM signal generator for converting the complex output of the resampler into a complex signal that is twice the symbol period; An HPF / BPF unit for removing pattern jitter by DC and data from the signal converted by the first OQAM signal generator; A squarer / adder for removing the influence of the carrier residual phase by adding squared and squared values of I and Q signals from which DC is removed through the HPF / BPF unit; A BPF unit for band-pass filtering the output signal of the squarer / adder at a point half of a symbol frequency; A phase separator for receiving the output signal of the BPF unit and converting the signal into a complex signal; An adder for adding the first and second squarers, each of which squares the I and Q signals received from the phase separator, and an output value of the first and second squarers, and a square root of the output value of the adder (

And a first divider and a second divider for dividing the I and Q signals received from the phase separator and the output values of the square root, respectively, and complex normalizing the output of the BPF portion passing through the phase separator. With a complex normalizer, A second OQAM signal generator for lowering the period of the complex normalized signal by 1/2; A squarer / subtractor which squares an output signal of the second OQAM signal generator and converts the output signal of the second OQAM signal into a timing signal having a strong tone at a half point of a symbol period; And a NCO unit and a loop filter for generating a control signal of the resampler using the output of the squarer / subtractor. delete The method of claim 1, The complex normalizer Symbol timing recoverer, characterized in that implemented using a ROM (ROM).

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