KR20000039725A - Recovery device for digital symbol timing - Google Patents

Abstract

PURPOSE: A recovery device for a digital symbol timing is provided to remove information which do not contribute to the recovery of a symbol timing by using a pair of pre-filters, thereby reducing signal interference or jitter due to data pattern. CONSTITUTION: A recovery device for a digital symbol timing comprises an A/D converting unit(10), a re-sampling unit(20) and a symbol timing recovery unit(30). The A/D converting unit(10) samples the receive signals of pass band in which a symbol frequency is used as an intermediate frequency as a quadruple frequency of the symbol frequency. The re-sampling unit(20) generates samples synchronized to a symbol timing from the output samples of the A/D converting unit. The symbol timing recovery unit(30) estimates phase information from the output of the A/D converting unit to output them to the re-sampling unit(20), thereby generating samples synchronized to the symbol timing.

Description

Digital symbol timing recovery device

The present invention relates to a receiver for sampling and demodulating a Quadrature Amplifier Modulation (QAM) signal in a passband, and in particular, digital symbol timing that can reduce jitter due to signal interference or data patterns by using a prefilter pair. It relates to a restoration device.

In general, one of the important technologies that determine the performance of digital data communication technology is the synchronization technology.

In particular, the technique of finding the temporal position of the transmitted data from the received signal is called the symbol timing recovery technique and has been variously developed since it is important enough to influence the performance of the entire system.

FIG. 1 is a block diagram of a conventional symbol timing recovery apparatus using a square method. As shown in FIG. 1, a band-limited baseband pulse amplitude modulation (PAM) signal or a signal in which it is modulated in a pass band is used to obtain a power supply. When the square is taken in 1) and passed through the band pass filter 2, the symbol timing information of the signal is extracted, and when the phase correction loop section 3 corrects the timing more accurately and outputs it, the analog digital converter 4 The analog signal is processed in synchronization with the symbol timing.

However, as the data transmission efficiency needs to be increased, the roll off factor of the band limiting filter is reduced and the number of pulse amplitude modulation (PAM) levels is increased, so that the strength of symbol timing information extracted by the square is gradually smaller. As the influence of jitter due to the data pattern becomes larger, a pre-filter that removes information that does not contribute to symbol timing recovery before symbol timing recovery is used.

As described above, the implementation of the prefilter by analog signal processing in the related art is difficult to control the phase characteristics, which may cause jitter by the prefilter itself. Therefore, there may be an attempt to implement the digital signal processing. There is a problem in that the signal spectrum is doubled by the square, and the interference of the signal after the square is generated in a common case of sampling the signal having the intermediate frequency as the symbol frequency at the quadruple symbol frequency.

Accordingly, the present invention is directed to a receiver for sampling and demodulating a spherical amplitude modulated (QAM) signal in a passband. An object of the present invention is to provide a digital symbol timing recovery apparatus capable of reducing jitter due to signal interference or data patterns by removing information that does not contribute to restoration.

1 is a block diagram of a symbol timing recovery apparatus using a square method;

2 is a block diagram of an embodiment of a digital symbol timing recovery apparatus according to the present invention;

3 is a waveform diagram of a symbol detected during one period in a phase detector;

4 is a block diagram of another embodiment of a digital symbol timing recovery apparatus according to the present invention;

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

10: analog digital conversion unit 20: resampling unit

30: symbol timing recovery unit 31: first pre-filter unit

32: second prefilter 33: multiplier

34 band pass filter 35 phase detection unit

According to one aspect of the present invention, there is provided an analog digital conversion unit for sampling a received signal of a pass band having a symbol frequency as an intermediate frequency at a frequency four times the symbol frequency; A resampling unit which generates a sample synchronized with symbol timing from the output samples of the analog digital converter; It is achieved by constructing a symbol timing recovery unit for estimating phase information from the output of the analog digital conversion unit and outputting the phase information to the resampling unit to generate a sample synchronized with the symbol timing. When described in detail as follows.

2 is a block diagram of a digital symbol timing recovery apparatus according to the present invention. As shown in FIG. 2, an analog digital conversion unit 10 for sampling a received signal of a pass band having a symbol frequency as an intermediate frequency at a frequency four times the symbol frequency is shown. ; A resampling unit (20) for producing a sample synchronized with symbol timing from the output samples of the analog digital conversion unit (10); It is composed of a symbol timing recovery unit 30 for estimating phase information from the output of the analog digital converter 10 and outputting the phase information to the resampling unit 20 to generate a sample synchronized with symbol timing. The operation and operation of the present invention will be described.

When a signal subjected to spherical amplitude modulation (QAM) is received by wire or wirelessly, an intermediate frequency signal having a symbol frequency as a center frequency is passed through a tuner (not shown) and an analog preprocessor (AFE, not shown). ) Is entered.

At this time, since the clock used for sampling in the analog digital converter 10 is not synchronized with the symbol timing of the received signal S (t), the clock is re-generated to generate data samples in phase synchronized with the symbol timing. The sampling unit 20 is necessary.

The resampling unit 20 is a kind of low pass filter that obtains the phase information of the sample to be output with respect to the phase of the input sample by filter processing from the input samples.

The symbol timing recovery unit 30 performs a function of estimating symbol timing phase information based on these samples from samples not synchronized with the symbol timing so that the resampling unit 20 generates samples synchronized with the symbol timing. to be.

Here, the symbol timing recovery unit 30 includes a first pre-filter unit 31 which passes a lower sideband component among frequency components of a sample output from the analog digital converter 10; A second prefilter unit 32 which passes an upper sideband component among frequency components of a sample output from the analog digital converter 10; A multiplier (33) for multiplying the outputs of the first and second prefilters (31, 32); A bandpass filter unit 34 for passing only a symbol frequency component among frequency components of an output sample of the multiplier 33; The first and second prefilters 31 and 32 are called sideband prefilter pairs. The first and second prefilters 31 and 32 are referred to as pairs of sideband prefilters. It serves to reduce jitter caused by the data pattern of the signal.

When the outputs of the sideband prefilter pairs are multiplied by each other in the multiplier 33, a tone is formed at a symbol frequency position along with a component in which a signal is distorted in the frequency spectrum.

In this case, when the sideband prefilter pair is used, the signal spectrum is limited to within 2 times the intermediate frequency compared to the case of obtaining the symbol timing information by taking the square of the received signal. In the case of a digital demodulator which is commonly used, a signal interference problem does not occur.

Fig. 3 is a waveform diagram of a symbol detected for one period in a phase detector, in which the output of the bandpass filter 34, which appears as a tone at the symbol frequency position in the frequency domain, is viewed in the time domain. The cosine waveform, which is synchronized with the symbol phase, is clocked out of four symbols per period with a clock that is not synchronized with the symbol frequency.

Thus, the phase detector 35 can estimate the symbol timing from four consecutive sample inputs.

That is, since the sample string of the output of the bandpass filter 34 changes from a negative value to a positive value every four times on average, the symbol timing of the received signal is based on the magnitude ratio of the negative value and the positive value. Can be estimated.

4 is a block diagram of still another embodiment according to the present invention. As shown in FIG. 4, an analog digital converter 10 sampling a received signal of a passband having a symbol frequency as an intermediate frequency at a frequency four times the symbol frequency is shown. ; A resampling unit (20) for producing a sample synchronized with symbol timing from the output samples of the analog digital conversion unit (10); The embodiment of FIG. 2 is composed of a symbol timing recovery unit 30 which estimates phase information from the output of the resampling unit 20 and outputs the phase information to the resampling unit 20 to generate a sample synchronized with the symbol timing. The difference is that the phase estimation operation of the symbol timing recovery unit 30 is obtained from the output of the resampling unit 20. The phase detection unit 35 accumulates the residual phase error obtained from the output of the bandpass filter 34. Gradually, the symbol timing of the received signal is approached.

As described above, the digital symbol timing recovery apparatus of the present invention uses a prefilter pair to remove information that does not contribute to symbol timing recovery before symbol timing recovery, thereby preventing jitter due to signal interference or data pattern. have.

Claims (3)

An analog digital conversion unit for sampling a received signal of a pass band having a symbol frequency as an intermediate frequency at a frequency four times the symbol frequency; A resampling unit which generates a sample synchronized with symbol timing from the output samples of the analog digital converter; And a symbol timing recovery unit for estimating phase information from an output of the analog digital conversion unit and outputting the phase information to a resampling unit to generate a sample synchronized with the symbol timing. 2. The apparatus of claim 1, wherein the symbol timing recovery unit comprises: a first prefilter unit configured to pass a lower sideband component of frequency components of a sample output from the analog digital converter; A second prefilter unit configured to pass an upper sideband component among frequency components of a sample output from the analog digital converter; A multiplier for multiplying outputs of the first and second prefilters; A bandpass filter for passing only a symbol frequency component among frequency components of an output sample of the multiplier; And a phase detector for obtaining and outputting a phase of symbol timing from an output of the band pass filter. 2. The apparatus of claim 1, wherein the symbol timing recovery unit estimates phase information from an output of the resampling unit and outputs the phase information to the resampling unit to generate a sample synchronized with symbol timing.