KR20000002886A - Device for synchronized extracting symbol timing and carrier wave frequency using delay combining and method thereof - Google Patents

Abstract

PURPOSE: A device for synchronized extracting a symbol timing and a carrier wave frequency is provided to improve a situation of a noise increase in a high frequency band and a complication of adopting a DFT. CONSTITUTION: A device for synchronized extracting a symbol timing and a carrier wave frequency is produced by; a first delay instrument delaying received data for a symbol period T; a first algorithm instrument providing a compensate conjugation to the delayed signal; a second algorithm instrument multiplying the compensate conjugation provided signal by original received data; a second delay instrument delaying the received data for two times(2T) of the symbol period; a third algorithm instrument providing the compensate conjugation to the two times delayed signal; and a fourth algorithm instrument multiplying the compensate conjugation provided signal by the original received data.

Description

Simultaneous Extraction of Symbol Timing and Carrier Frequency Using Delay Coupling and Its Method

The present invention relates to a data recovery method, and more particularly, to a symbol using a delay combination in which symbol timing and carrier frequency extraction are simultaneously performed to find an accurate sampling point for data received at a synchronous receiver. A timing and carrier frequency simultaneous extraction apparatus and method.

As shown in FIG. 1, a configuration of a digital baseband demodulator for symbol timing error recovery and carrier recovery in a conventional modem is demodulated and applied to an in-phase component and a quadrature component thereof. The frequency discriminator 1 for differentiating the baseband signal to extract the phase of the original signal, and the signal output from the frequency discriminator 1 are extracted only with the signal of the set band to remove noise components and shape the signal. A low pass filter (2) and a fast fourier transform (FFT) fast signal based on a predetermined algorithm for extracting a sync bit from a signal applied through the low pass filter 2 ), A digital / analog converter 4 for converting the digital signal output from the calculator 3 into an analog signal, and the converted analog signal value. A voltage controlled oscillator 5 for fixing the frequency of the received signal and a signal received through the low pass filter 2 in consideration of the residual deviation Δf extracted from the DC term of the FFT-calculated signal. It consists of a judging unit 6 for performing error recovery of the data to be made.

The operation of restoring the symbol timing error and the carrier error in the conventional modem having the above functions will be described below.

Assuming that the received signal r (t) has no distortion due to the channel and pre-detection filtering, Equation 1 below.

In Equation 1, n (t) is an additional band white noise having a spectral density N ₀ existing on only one side, E _b Is a bit energy, T _b Is a bit cycle, ψ _o Is an arbitrary phase, ψ _s (t) Is the frequency modulated phase of the carrier being transmitted.

Also, εT _s Is the time delay caused by channel filtering and assumes the optimal time for the signal to be sampled.

In general, assuming no loss εT _s The range of Limited to

When the noise is ignored in the received signal as defined in Equation 1, the composite baseband signal is represented by a phase component (X) and an orthogonal modulation component (Y), which are represented by Equations 2 and 3 below.

In Equations 2 and 3 above △ _f Is the frequency residual deviation = _F = f _c -f _c ^′ ego, θ Is the center frequency f _c ^′ Frequency residual and phase residual are generated by a voltage controlled oscillator of a receiver with.

Phase component as in Equation 1 and Equation 2 x (t) And quadrature modulation components y (t) Is applied to the frequency discriminator 1 side, the phase of the signal calculated and output through the calculation algorithm of the frequency discriminator 1 φ (t) Is as shown in Equation 4 below.

= 2 π ▵ _f + φ _s (t-εT _s )

As shown in Equation 4, the signal output from the frequency discriminator 1 has the frequency component and noise of the band set through the low pass filter 2 removed, and then the restoration of the data received through the determiner 6 is performed. Proceed.

At this time, the signal output through the low pass filter (2) is extracted by the FFT calculation by the operator (2) of the sync bit detection means, the value for frequency setting is extracted and then the analog by the digital / analog converter (4) After the signal is converted into the oscillation voltage of the voltage controlled oscillator 5, the frequency of the received signal is fixed.

In order to estimate the symbol timing error and the frequency residual deviation at the same time as the reception is performed at the fixed frequency as described above, the calculator 3 performs the FFT operation on the received frequency and then calculates the following equation from the DC term of the FFT converted signal. Frequency residual deviation as shown in 5 ▵f From the phase angle of the FFT transform at the frequency corresponding to the integer multiple of half the bit rate, as shown in Equation 6 below. ε )

As described above, when a synchronous receiver detects a data signal using a discriminator, if the component of noise is assumed to exist, the discriminator uses a derivative so that the noise of the high frequency band is also amplified, which adversely affects the extraction of the received data. This results in a problem of degrading reception quality and requiring a large amount of computation because a DFT operation is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and its object is to provide a differential detection using a product of a received signal and a delayed signal in order to eliminate amplification of a high frequency band noise at a synchronous receiver. In this method, symbol timing recovery and carrier recovery provide reliability in the detection of received data and reduce the amount of computation by improving the complexity of taking a DFT.

1 is a block diagram illustrating a digital baseband demodulator for symbol timing error recovery and carrier recovery in a modem using a conventional discriminator.

2 is a block diagram illustrating an apparatus for simultaneously extracting symbol timing and carrier frequency according to the present invention;

3 is a flowchart for simultaneously extracting symbol timing and carrier frequency in the present invention of FIG.

4 is a graph illustrating a phase output from a modem to which a differential detector is applied according to the present invention.

In the baseband data signal recovery apparatus, a complex conjugate signal of a signal obtained by delaying a received signal by a symbol period T is multiplied by the received signal, and the received signal is symbolized. The present invention provides a synchronous data recovery apparatus that multiplies a complex conjugate signal of a signal delayed by a period of 2T and a received signal to simultaneously perform symbol timing and carrier frequency extraction of a received signal.

In recovering the baseband data signal using the modem, if the reception of the data is detected, delay the symbol period T and twice the symbol period by 2T through the respective delay means, and to the signal output through the respective delay means. Take the complex conjugate and multiply it with the received signal, extract the carrier frequency with the set algorithm using the signal calculated by delaying 2T of symbol period, and from the signal calculated by delaying by symbol period T Using the extracted carrier frequency, the phase DC term caused by the carrier frequency is removed, and only the component of the DFT corresponding to half the bit rate is extracted.

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

As shown in FIG. 2, the apparatus for extracting the symbol timing and the carrier frequency at the same time includes the first delay circuit unit 11, the first operator 12, the second operator 13, the second delay circuit unit 21, and the third. It consists of an operator 22, a fourth operator 23, a carrier extractor 24, a compensation circuit 31, a DFT narrowband frequency extractor 32, a symbol timing error extractor 33 and a determiner 34. , The first delay circuit section 11 is a received signal r (t) Delays the symbol period T and then delays the signal r (t-T) Outputs

The first operator 12 is a signal that is delayed through the first delay circuit unit 11 applied r (t-T) Take a plural conjugate to the signal r ^* (t-T) Outputs

The second operator 13 is delayed by a symbol period T and then the received data and the received original data in which the plural conjugates are taken. r (t) Multiply the signal s (t) Outputs

The second delay circuit unit 21 is received data r (t) Delay the signal by twice the symbol period, or 2T r (t-2T) Outputs

The third operator 22 is a signal that is delayed through the second delay circuit unit 21 is applied r (t-2T) Take a plural conjugate to the signal r ^* (t-2T) Outputs

The fourth operator 23 delays the symbol period 2T and then receives the received data and the received original data in which a plurality of conjugates are taken. r (t) Multiply by c (t) Outputs

The carrier extracting unit 24 is a signal that is calculated and applied by the fourth operator 23 c (t) Carrier frequency from f _c Extract

The compensation circuit unit 31 is a carrier frequency extracted from the carrier extraction unit 24 is applied f _c The signal applied from the second operator 13 using s (t) Compensate for the phase DC component by the carrier frequency of.

The DFT narrowband frequency extractor 32 compensates for the phase component by eliminating the DC term and extracts only a Discrete Fourier Transform (DFT) component corresponding to half of the symbol rate.

The symbol timing error extractor 33 extracts a symbol timing error by using a DFT frequency component corresponding to half of the symbol rate as differential detection means and outputs a signal thereof.

The determiner 34 recovers data received from the extracted symbol timing error and carrier frequency and outputs the recovered data.

An operation of performing symbol timing error recovery and carrier recovery in the present invention having the above-described function will be described with reference to the flowchart of FIG. 3.

Data signal through wired / wireless communication furnace r (t) Is received (step 110), the first delay circuit section 11 receives the received data. r (t) Delayed by the symbol period T (step 120), and then the delayed signal r (t-T) Is applied to the first operator 12 side.

The first operator 12 is applied to the delayed signal r (t-T) Take a plural conjugate to r ^* (t-T) After the signal is formed (step 121) and applied to the second operator 13 side, which is a multiplier, the second operator 13 receives the plural conjugation and is applied. r ^* (t-T) Signal and original data received r (t) Computed by multiplying s (t) Is applied to the compensation circuit section 31 (step 122).

In addition, the data signal r (t) When receiving the second delay circuit unit 21 receives the received data signal r (t) Delay the signal by twice the symbol period, or 2T r (t-2T) Is applied to the third operator 22 side (step 130).

The third operator 22 is a delay applied signal r (t-2T) Take a plural conjugate to r ^* (t-2T) It forms as a signal and applies it to the 4th operator 23 side which is a multiplier (step 131).

The fourth operator 23 is applied to take a plurality of conjugates r ^* (t-2T) Signal and original data received r (t) Computed by multiplying c (t) Is applied to the carrier extraction section 24 (step 132).

The carrier extracting unit 24 is a signal that is calculated and applied by the fourth operator 23 c (t) Is calculated by the following equation (7) carrier frequency f _c The result of the calculation of the second operator 13 after extraction s (t) Is applied to the side of the compensation circuit section 31 to which it is applied (step 133).

The compensation circuit unit 31 is a carrier frequency extracted from the carrier extraction unit 24 is applied f _c The signal applied from the second operator 13 using s (t) By calculating as shown in Equation 8 below, the phase DC term due to the carrier frequency is removed to compensate only the phase component to determine whether the restoration of the carrier frequency is completed (step 134).

s (t) ⋅ e ^{-j 2 π f c T}

When the restoration of the carrier frequency is completed through the operation of step 134, the compensation circuit unit 31 applies the restored carrier frequency to the DFT narrowband frequency extractor 32, and the DFT narrowband frequency extractor 32 is applied. The extracted carrier frequency is extracted using only the DFT frequency component corresponding to half of the symbol rate by using a discrete Fourier transform (DFT), and the extracted signal is applied to the symbol timing error extractor 33 (step 140).

The symbol timing error extractor 33 extracts an error of symbol timing from the frequency to be obtained as shown in Equation 9 below (step 150), and when the extraction of the symbol timing error is completed, the determined signal 34 is determined. (Step 160).

At this time, the determiner 34 restores the data received from the extracted symbol timing error and the carrier frequency and outputs the restored data (step 170).

For example, when data is received through a wired or wireless communication line, the received data signal r (t) Suppose it is equal to the following equation (10).

r (t) = e ^{j (2 π f c t + ψ (t-εT s ) + θ)}

here, f _c Is the carrier frequency, ψ (t) Is a phase signal with a period of 2T, θ Is the initial phase.

Also, εT _s Is a time delay caused by channel filtering, i.e., the optimal time for a signal to be sampled due to timing error, it is generally assumed that there is no loss. εT _s The range of Limited to

Where carrier frequency f _c In order to extract the first, the received signal r (t) By using the second delay circuit section 21, that is, delay 2T by twice the symbol period of the signal. r (t-2T) Then form the complex conjugate through the third operator 22, r ^* (t-2T) Formed into a signal, and the received signal r (t) After multiplying using a multiplier and a fourth operator 23, the following equation 11 is applied to the carrier extracting unit 24 side.

here, e ^jθ = cosθ + jsinθ Because of, to be.

therefore, θ = 2 π f _c 2T Since the carrier extracting unit 24 is a carrier frequency from the above equation f _c Is extracted as in Equation 12 below.

In Equation 12, the molecular value is tan ^-1 Use the table to get accurate carrier frequency f _c Can be extracted.

In addition, the received data signal r (t) Is delayed by the symbol period T of the signal through the first delay circuit unit 11 r (t-T) Is formed and then applied to the first operator 12 is applied r (t-T) Signal is complex conjugate r ^* (t-T) It is formed into a signal, and this signal is applied to the second operator 13 side, which is a multiplier.

The second operator 13 is a complex conjugate r ^* (t-T) Signal and original signal received r (t) Is calculated as in Equation 13 below and the result is s (t) Is applied to the compensating circuit section 31 side.

At this time, the compensation circuit unit 31 is applied s (t) Carrier frequency extracted from f _c Using s (t) The phase component is compensated by removing the phase DC term due to the carrier frequency of the signal.

When the phase-compensated signal is applied to the DFT narrowband frequency extractor 32 as described above, the DFT narrowband frequency extractor 32 applies the applied data signal to the half of the symbol period using a discrete Fourier transform (DFT). The symbol timing error is extracted from the phase angle via a symbol timing error extractor 33 which is a differential detector after extracting the corresponding frequency components. εT _s Extracts and recovers the next received data before outputting.

For example, the presumed exercise value is, for example, 10101010... If the phase signal output from the timing error extractor 33, which is a differential detector ψ (t) Has a cycle 2T _b Will be a periodic function, the waveform of which is shown in FIG.

As can be seen in Figure 4, this waveform is 2 π f _c T DC value of 2 T _b It is composed of a period function waveform having a period, which is expressed by Equation 14 below.

here, g _T (t) As shown in Figure 4, the center is at the origin, and the period T = 2 T _b Is a waveform.

In Equation 14 2 π f _c T Is the carrier frequency in carrier recovery f _c Since the signal was found correctly through carrier recovery, s (t) Can be removed from.

if, L Output phase signal of timing error judgment circuit section 14 as a differential detector ψ (t) Can be expressed again by the following equation (15).

Phase signal in Equation 15 above ψ (t) To T _s Signal sampled every second ψ [n] Signal, sampled ψ [n] of N The discrete Fourier transformed signal at Ψ [k] If you say, g _T [n] The discrete Fourier transformed signal under the assumption that is a real function of Ψ [k] Is a timing error from the phase angle of the discrete Fourier transformed signal. εT _s Since it can be obtained, the point that can accurately sample the received data can be found by the following equation (16).

In Equation 16, the transmitted signal is r (t) Assuming r (t) A certain time t ₀ When delayed by, the signal in the frequency domain of the delayed signal is expressed by Equation 17 below.

r (t-t ₀ ) = R (f) e- ^{j 2 π ft 0}

here, r (t) Is a real function with DC equal to 0, the spectrum of the right function becomes a real number, so the frequency term related to the delay of time is simply e ^{-j 2 π ft o} Becomes

therefore, g _T [n] Is a real function with DC equal to zero and a time delay εT _s Speaking of time delay, e ^{-j 2 π f εT s} Becomes

Also, -j 2 π f εT _s As can be seen in Equation 18 below Φ [K] of L Same as the second variable.

-j 2 π f εT _s = Φ [L]

here, Because of, f Is substituted into Equation 16, and the following Equation 19 is obtained.

Therefore, the above equation (19) εT _s In summary, the timing error can be extracted as shown in Equation 16 above.

As described above, the present invention uses a differential detector that multiplies a received signal by a signal delayed by a set symbol period of the received signal, thereby generating a high frequency generated by performing a derivative in a conventional method using a frequency discriminator. Since the noise of the band is increased, the reliability of the received data is provided, and the calculation amount can be reduced because only the DFT component corresponding to half of the symbol rate is calculated instead of the DFT process, which requires a large amount of calculation.

Claims (8)

A data signal recovery apparatus comprising: first delay means for delaying received data by a symbol period T; First calculation means for taking plural conjugates to the delayed signal; Second calculating means for multiplying the signal from which the plural conjugate is taken and the received original data; Second delay means for delaying the received data by two times (2T) of a symbol period; Third operation means for taking a plural conjugate to the signal delayed by 2T; Fourth computing means for multiplying the signal from which the plural conjugate is taken and the received original data; Carrier extracting means for extracting a carrier frequency from a signal input from said fourth calculating means; Compensating means for compensating a phase component by a carrier frequency using a carrier frequency extracted from a signal input from said second calculating means; Narrowband frequency extracting means for extracting only a discrete Fourier transform (DFT) component corresponding to half of a symbol rate by removing the phase component by the carrier frequency; Symbol timing error extraction means for extracting a symbol timing error from an input signal extracted with a frequency component corresponding to half of the symbol transmission rate; And a reconstruction unit for recovering reliable data by compensating for a signal received from the extracted symbol timing error and a carrier frequency, wherein the symbol timing and carrier frequency are simultaneously extracted. The apparatus of claim 1, wherein the carrier extracting unit extracts a carrier frequency using periodic characteristics of the phase signal and a differential detection unit. The apparatus of claim 1, wherein the phase delay of the periodic signal by differential detection is used. 2. The symbol timing and carrier frequency using delay combining according to claim 1, wherein the phase delay of a periodic signal by differential detection for determining a time delay by comparing phase values of frequency components corresponding to half of the symbol frequency is used. Simultaneous extraction device. The method according to claim 2, wherein the differential detection means is a symbol conjugate using the delay combination and the carrier frequency at the same time, characterized in that for multiplying the complex signal of the signal delayed the received signal by a predetermined symbol period and the original signal received Extractor. 5. The apparatus of claim 4, wherein the narrowband frequency extraction unit calculates only a DFT component corresponding to half of a symbol frequency. A data restoration method, comprising: delaying a received signal by symbol periods T and 2T through respective delay means; Taking a complex conjugate to each of the delayed signals and multiplying each of the received original signals; Extracting a carrier frequency by averaging a signal delayed by a symbol period 2T multiplied by the original received signal after the complex conjugate is taken; Compensating for a phase DC component by a carrier frequency using the extracted carrier frequency to a signal multiplied by the complex conjugate and then multiplied with an original received signal; Extracting a symbol timing error by extracting only the discrete Fourier transform (DFT) component corresponding to half of a symbol rate of the phase compensated signal; And recovering received data in consideration of the extracted symbol timing error. 2. 8. The method of claim 7, wherein the symbol timing and the carrier frequency are extracted from the same data.