KR20080051003A - Apparatus and method for recovery a symbol timing using distance accumulation - Google Patents

Abstract

A method and an apparatus for recovering a symbol timing using distance accumulation are provided to improve a reception performance of a digital communication device by simply recovering the symbol timing based on accumulated distance values between oversampled data. A symbol timing recovery apparatus includes a folding unit(310), a distance accumulating unit(320), and a timing acknowledging unit(330). The folding unit folds oversampled data in plural symbol periods into one symbol period, so that a distance accumulated value represents a timing error performance. The distance accumulating unit calculates a distance accumulated value between oversampled data and measures a distance in respective timings. The timing acknowledging unit compares the calculated distance accumulated values with each other and detects a timing, when the distance accumulated value is the smallest.

Description

Apparatus and method for recovery a symbol timing using distance accumulation}

The present invention relates to an apparatus and method for recovering a symbol timing using distance accumulation. More particularly, the present invention relates to a method for recovering a symbol timing, and more particularly, to accumulate over-sampled data and to compare distance accumulated values between the over-sampled data calculated according to the timing. The present invention relates to a symbol timing recovery apparatus using distance accumulation and a method thereof for use in symbol timing recovery by checking a timing corresponding to the timing.

The present invention is derived from a study conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication [Task management number: 2005-S-046-02, Task name: Radio resource utilization base technology].

In a digital communication system, reception performance is directly affected by the frequency and phase of a given signal-to-noise ratio (SNR). In particular, in the digital communication system, a difference may occur between a phase of a transmission signal and a phase of an input signal due to various radio wave environments. Therefore, in the digital communication system, the above-described phase difference must be compensated for (in particular, correct symbol timing at the receiving end) to have optimum performance in a changing radio wave environment.

For the above reason, a symbol timing recovery process is required in a digital communication system.

To date, much research has been done on the timing recovery process. The purpose of the timing recovery process is to find the correct symbol timing synchronization. Thus, representative conventional methods related to timing synchronization include NSL (Nonlinear Spectral Line) and Gardner.

1 is an explanatory diagram showing a conventional NSL method, and FIG. 2 is an explanatory diagram showing a conventional Gardner method.

First, the NSL method will be described with reference to FIG. 1. In the conventional NSL method, a squared received signal has a characteristic of having a symbol period of an original signal. The conventional NSL method is a method of obtaining a timing tone through a band pass filter by squaring a received signal.

Meanwhile, referring to FIG. 2, the conventional Gardner method has been developed to be suitable for Binary Phase Shift Keying (BPSK) or Quadrature Phase Shift Keying (QPSK). The conventional Gardner method detects a zero crossing point of a symbol, and corrects a slope by using values of adjacent samples.

In addition, the conventional Gardner method uses a timing error detector (TED). Here, the timing error detector is represented by Equation 1 below using a probability distribution function (PDF) of a received signal.

"은 추정할 타이밍 위상(phase)을 나타낸다.Here, "y (n)" is an input of the timing recovery block, and "

Represents the timing phase to be estimated.

The conventional Gardner method performs recursion in a direction to reduce timing error and recovers the timing tone through the convergence value for timing recovery. However, the conventional NSL method or Gardner method used for symbol synchronization is not suitable for a wireless communication environment such as a digital radio which has a good performance in a multi fading environment but requires a simple method due to its complicated structure.

That is, since a digital communication system such as a digital radio is easily exposed to various propagation environments, the timing recovery process as described above is important, but in a low-cost model such as a digital radio, reception performance must be improved in a simple manner.

Therefore, in a low-cost digital radio system such as a digital radio, there is a need for a timing recovery scheme with a particularly simple structure in performing timing recovery to improve reception performance.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problem, and symbol timing by folding over-sampled data and comparing the accumulated value between the oversampled data calculated according to the corresponding timing to check the timing corresponding to the minimum accumulated value. An object of the present invention is to provide an apparatus and method for recovering symbol timing using distance accumulation, for use in recovery.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a symbol timing recovery apparatus, comprising: folding means for folding “over sampled data” existing in a plurality of symbol intervals into one symbol interval such that a distance accumulated value indicates a timing error performance; Distance accumulation means for calculating a distance accumulation value between 'over sampled data' folded by the folding means and measuring the distance at each timing; And timing checking means for comparing the distance accumulation values calculated by the distance accumulation means and confirming the timing at which the distance accumulation value is minimum.

In addition, the present invention provides a method for recovering a symbol timing, the method comprising: folding a 'oversampled data' present in a plurality of symbol intervals into one symbol interval such that a distance accumulated value indicates a timing error performance; A distance measurement step of calculating a distance accumulation value between the folded “over sampled data” and measuring a distance at each timing; And a symbol timing recovery step of recovering the symbol timing by comparing the calculated distance accumulation values to check timing of the minimum distance accumulation value.

The present invention as described above has the effect of improving the reception performance by performing a timing recovery of a simple structure in a simple digital communication system.

In addition, the present invention has an effect that is suitable for the timing recovery method by a simple structure that can improve the reception performance by performing the timing recovery in a low-cost digital wireless system such as a digital radio.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, whereby those skilled in the art may easily implement the technical idea of the present invention. There will be. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Prior to describing the present invention, the digital communication system to which the present invention is applied performs sampling at a speed faster than the symbol rate in order to perform digital filtering and the like. The present invention performs symbol timing recovery using the oversampled data as described above.

3 is a diagram illustrating an embodiment of a symbol timing recovery apparatus using distance accumulation according to the present invention.

As shown in FIG. 3, a symbol timing recovery apparatus (hereinafter, referred to as a "timing recovery apparatus") using distance accumulation according to the present invention includes a folding unit 310, a distance accumulation unit 320, and an interpolator unit. (interpolator, 330).

The folding unit 310 moves the oversampled data to one section of the constellation (that is, a predetermined quadrant) when the digital signal is determined. For example, the folding unit 310 folds over-sampled data located in 2, 3, and 4 quadrants on the coordinate plane of the constellation into one quadrant.

Specifically, in the case of QPSK, the constellations before folding and after folding may be shown as shown in FIGS. 4 to 6 according to timing errors. That is, FIG. 4 is an embodiment constellation diagram before and after folding when the timing error of QPSK to which the present invention is applied is zero, and FIG. 5 is before and after folding when timing error 1/8 of the QPSK to which the present invention is applied. 6 is an embodiment constellation diagram before and after folding when the timing error 1/4 of the QPSK to which the present invention is applied.

In FIGS. 4 to 6, "(a)" and "(b)" are shown after folding, respectively, before folding.

4 to 6, it can be seen that the greater the timing error, the greater the dispersion in the constellation.

Meanwhile, as illustrated in FIGS. 4 to 6, the folding unit 310 moves oversampled data in quadrants 2, 3, and 4 on the coordinate plane of the constellation diagram to one quadrant.

That is, the folding unit 310 moves the oversampled data to one section of the constellation, so that the value accumulated by the distance by the distance accumulator 320 is necessary to indicate the timing error degree regardless of the modulation method. . That is, since the value of the oversampled data is different when the distance is accumulated according to the modulation method, the value accumulated by the distance between the unfolded oversampled data cannot represent the degree of timing error. Thus, regardless of the modulation method, the oversampled data is folded so that the distance value accumulated by the distance accumulator 320 may indicate a timing error degree.

)은 하기 [수학식 2]와 같이 나타낸다.In the conventional modulation scheme, the larger the timing error of the oversampled data, the larger the dispersion of constellations. The distance accumulator 320 is over-sampled to measure the dispersion of the constellations corresponding to the timing errors. Use the sum of the distances between the data. That is, the distance accumulator 320 accumulates the value of the distance between the oversampled data folded from the folding unit 310. At this time, the square of the value accumulated the distance between each oversampled data (

) Is represented by the following [Equation 2].

Here, "I" and "Q" represent "I-channel component" and "Q-channel component (Quadrature-phase)" when the complex signal is represented by polar coordinates, respectively. In addition, "k" represents the order of sampling. That is, "I _k " represents data sampled one sampling period after "I _{k -1} ".

)이 최소인 경우에 타이밍을 계산한다. 만약 오버 샘플링된 데이터 간의 최소 거리누적값이 다수인 경우에, 인터폴레이터부(330)는 최소 거리누적값에 대응된 타이밍 중간값으로 타이밍을 계산한다.When the interpolator 330 receives a distance accumulation value between the oversampled data calculated by the distance accumulation unit 320, the interpolator unit 330 receives a distance accumulation value between the respective oversampled data (

If) is the minimum, the timing is calculated. If the minimum distance accumulation value between the oversampled data is plural, the interpolator 330 calculates the timing using a timing intermediate value corresponding to the minimum distance accumulation value.

For example, suppose that 4 times oversampling data is used. In this case, it is assumed that the timings of the oversampling data are t1, t2, t3, and t4, and the distance accumulation values corresponding to the respective timings are 2, 1, 1, and 2, respectively. Then, the timing having the minimum accumulated value between the oversampled data is present in the middle of t2 and t3, so that the interpolator 330 calculates the timing using the intermediate value of t2 and t3. That is, the interpolator unit 330 calculates the timing as "(t2 + t3) / 2".

As described above, the interpolator 330 checks timing information for extracting a symbol when the timing error is minimal as described above.

7 is a diagram illustrating another embodiment of a symbol timing recovery apparatus using distance accumulation according to the present invention.

As shown in FIG. 7, the timing recovery apparatus according to the present invention may use the comparator 730 instead of the interpolator 330 of FIG. 3. That is, in the timing recovery apparatus according to the present invention, the cumulative distance between the oversampled data is minimized by using the comparator 730 having a simple operation instead of the interpolator 330 having a relatively complicated operation according to a predetermined number of oversampling. Find the timing. Here, in the timing recovery apparatus according to the present invention, since the timing error is determined as "symbol period / (oversampling number x 2)", the timing becomes finer as the "oversampling number" increases. Preferably, the timing recovery apparatus according to the present invention may use the comparator 730 in place of the interpolator 330 in the case of "over 8 oversampling".

On the other hand, the comparison unit 730 can obtain a timing of the minimum distance accumulation value by simply comparing the distance accumulation value. For example, when the cumulative distance is 1, 5, 7, 10, the comparator 730 obtains the timing of the cumulative distance "1" as the minimum timing.

8 is a flowchart illustrating a symbol timing recovery method using distance accumulation according to the present invention.

As shown in FIG. 8, the timing recovery apparatus according to the present invention moves the oversampled data to one section of the constellation (S801). That is, the timing recovery device folds data upon oversampling at each timing.

Thereafter, the timing recovery apparatus calculates a distance accumulation value between the folded oversampled data (S802). That is, the timing recovery apparatus calculates a distance accumulation value between the oversampled data folded for each timing.

Then, the timing recovery apparatus recovers the symbol timing by using the timing when the distance accumulation value calculated as described above is the minimum (this is timing information for extracting the symbol when the timing error is minimum) (S803). ). The timing recovery apparatus extracts a symbol by using the timing calculated as described above.

FIG. 9A is an embodiment constellation diagram after folding of oversampled data in case of QPSK to which the present invention is applied, and FIG. 9B is an embodiment graph of the distance accumulation value and timing of FIG. 9A.

As shown in FIG. 9A, in the case of the QPSK, the timing recovery apparatus collects all points into one constellation section through folding of the oversampled data.

Thereafter, the timing recovery apparatus calculates a distance accumulation value at each timing (that is, t1, t2, t3, and t4) of the points collected in one constellation section, as shown in Table 1 below.

timing Cumulative distance t1 10 t2 3 t3 7 t4 12

When the timing recovery apparatus performs normal interpolation, it appears as shown in FIG. 9B. Here, the timing recovery apparatus uses a 'quadratic interpolation' method.

The timing recovery apparatus uses the interpolation unit 330 of FIG. 3 or the comparison unit 730 of FIG. 7 to confirm timing and recover symbol timing when the distance accumulation value is minimum.

FIG. 9B shows a graph for the interpolation result of the distance accumulation value (hereinafter referred to as "first graph") and a graph for a simple display of the distance accumulation value (hereinafter referred to as "second graph").

As shown in FIG. 9B, the first graph shows that the timing is at “t2.4” when the distance accumulation value is the minimum as a result of interpolation. Therefore, when the interpolation unit 330 is used, the timing recovery apparatus determines, as timing, "t2.4" which is the timing when the distance accumulation value is minimum.

On the other hand, the second graph shows that the timing is at "t2" when the distance accumulation value is the minimum as a result of simply displaying the distance accumulation value. Accordingly, the timing recovery apparatus determines, as the timing, "t2" which is a timing when the distance accumulation value is minimum when the comparison unit 730 is used.

As described above, the timing recovery apparatus of the present invention is complex in the case of using the interpolation unit 330 but checks the relatively accurate timing even at low oversampling, thereby recovering more accurate timing than using the comparator 730. .

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily implemented by those skilled in the art will not be described in more detail.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

1 is an explanatory diagram showing a conventional NSL method;

2 is an explanatory diagram showing a conventional Gardner method,

3 is a block diagram of an embodiment of a symbol timing recovery apparatus using distance accumulation according to the present invention;

Figure 4 is an embodiment constellation diagram before and after folding when the timing error 0 of the QPSK to which the present invention is applied,

FIG. 5 is a diagram illustrating an embodiment of before and after folding when the timing error 1/8 of the QPSK to which the present invention is applied; FIG.

Figure 6 is an embodiment constellation diagram before and after folding when the timing error 1/4 of the QPSK to which the present invention is applied.

7 is a block diagram of another embodiment of a symbol timing recovery apparatus using distance accumulation according to the present invention;

8 is a flowchart illustrating a symbol timing recovery method using distance accumulation according to the present invention;

9A is an embodiment constellation diagram after folding of oversampled data in case of QPSK to which the present invention is applied;

FIG. 9B is a graph of one embodiment of the distance accumulation value and the timing of FIG. 9A.

* Explanation of symbols on the main parts of the drawing

310: folding unit

320: street accumulation

330: interpolation unit

730: comparison unit

Claims (14)

In the symbol timing recovery apparatus, Folding means for folding "over sampled data" present in a plurality of symbol intervals into one symbol interval so that a value accumulated in distance can indicate timing error performance; Distance accumulation means for calculating a distance accumulation value between 'over sampled data' folded by the folding means and measuring the distance at each timing; And Timing checking means for confirming a timing at which the distance accumulation value is minimum by comparing the distance accumulation values calculated by the distance accumulation means; Symbol timing recovery apparatus using a distance accumulation including a. According to claim 1, The folding means, And 'folding over-sampled data' in the first to fourth quadrants of the digital signal constellation into one of the first to fourth quadrants. The method according to claim 1 or 2, The timing is An apparatus for recovering symbol timing using distance accumulation, wherein the symbol information can be extracted when a timing error is minimal, and the symbol timing is recovered using the symbol information. The method of claim 3, wherein The timing checking means, In the case of a predetermined number of oversampling, symbol timing recovery apparatus using distance accumulation, characterized in that the distance accumulation value is determined by simply comparing the distance accumulation values calculated by the distance accumulation means numerically. The method of claim 4, wherein The oversampling number is Symbol timing recovery apparatus using distance accumulation, characterized in that the case of more than 8. The method of claim 3, wherein The timing checking means, And determining the timing at which the distance accumulation value is minimum according to a result of performing a quadratic interpolation method on the distance accumulation values calculated by the distance accumulation means. The method of claim 6, The timing checking means, Symbol timing recovery apparatus using distance accumulation, characterized in that the timing is calculated as an intermediate value of the timing corresponding to the at least two minimum distance accumulation value when the minimum distance accumulation value calculated by the distance accumulation means is at least two. . In the symbol timing recovery method, Folding the 'over sampled data' present in the plurality of symbol intervals into one symbol interval so that the accumulated value of the distance may indicate timing error performance; A distance measurement step of calculating a distance accumulation value between the folded “over sampled data” and measuring a distance at each timing; And A symbol timing recovery step of recovering symbol timing by comparing the calculated distance accumulation values to check timing of minimum distance accumulation values. Symbol timing recovery method using a distance accumulation including a. The method of claim 8, The folding step, A method for recovering symbol timing using distance accumulation, characterized by folding 'over sampled data' in the first to fourth quadrants of the digital signal constellation into one of the first to fourth quadrants. The method according to claim 8 or 9, The timing is Symbol timing recovery method using distance accumulation, characterized in that the timing information to extract the symbol when the timing error is minimal. The method of claim 10, The symbol timing recovery step, In the case of a predetermined number of oversampling, symbol timing recovery method using distance accumulation, characterized in that by comparing the calculated distance cumulative values numerically simply to determine the timing of the minimum distance cumulative value. The method of claim 10, The oversampling number is Symbol timing recovery method using distance accumulation, characterized in that the case of more than 8. The method of claim 10, The symbol timing recovery step, And determining the timing of the minimum distance accumulation value according to a result of performing the quadratic interpolation method on the calculated distance accumulation values. The method of claim 13, The symbol timing recovery step, And calculating the timing as an intermediate value of the timings corresponding to the at least two minimum distance accumulation values when the calculated minimum distance accumulation values are at least two.

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