KR100737810B1 - Method of timing recovery and tracking using correlation value estimation window and computer-readable medium having thereon program performing function embodying the same - Google Patents

Abstract

The present invention relates to a timing recovery and tracking method using a correlation result prediction window in a receiver using a DSRC communication method, comprising: (a) a lower position and an upper portion such that a correlation value includes a symbol position exceeding a threshold value based on a window of a preamble field; Constructing a correlation value result prediction window bounded by a position; and (b) obtaining a correlation value after reaching the lower position of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field. Determining whether the threshold value is exceeded, and (c) if the threshold value is exceeded, updating the lower position and the upper position of the correlation result prediction window and changing the position to the next window (b) It relates to a timing recovery and tracking method using a correlation value result prediction window comprising the step of jumping to a).

According to the present invention, a DSRC using Manchester coding, which is sensitive to timing by a channel, is applied by predicting a section in which a correlation value becomes the highest or lowest value in advance using a correlation result prediction window and then tracking the timing based on the correlation result prediction window. In the receiver using the method, accurate timing recovery is performed, and a correlation value result prediction window or a threshold value can be variably set according to channel characteristics, thereby enabling more accurate timing recovery and tracking.

DSRC, correlation, preamble, FSW, CSW, correlation result prediction window, variable setting, timing recovery, tracking, threshold, channel status, Manchester code

Description

FIELD OF TIMING RECOVERY AND TRACKING USING CORRELATION VALUE ESTIMATION WINDOW AND COMPUTER-READABLE MEDIUM HAVING THEREON PROGRAM PERFORMING FUNCTION EMBODYING THE SAME}

1 is a view showing the structure of a slot used in the DSRC scheme according to the prior art.

2 is a diagram showing a correlation in a preamble field in a DSRC scheme according to the prior art.

3 is a view showing a correlation between the FSW and CSW in the DSRC method according to the prior art.

4 is a flowchart of a timing recovery and tracking method using the correlation value result prediction window according to the present invention.

5 is a diagram showing an example of a correlation value result prediction window in the timing recovery and tracking method using the correlation value result prediction window according to the present invention;

<Description of the symbols for the main parts of the drawings>

The present invention relates to a timing recovery and tracking method using a correlation value prediction window, and a computer readable recording medium recording a program for realizing the same. More specifically, the correlation value result is a section in which the correlation value becomes the highest or lowest value. By predicting in advance with the prediction window and tracking the timing based on the correlation result prediction window, accurate timing recovery is performed in the receiver using the DSRC method, which is particularly sensitive to channel timing. Correlation value result prediction window can be set variably or threshold value can be set variably so that more accurate timing recovery and tracking is possible. It relates to a recording medium.

Dedicated Short Range Communication (DSRC) is a short-range wireless communications standard dedicated to Intelligent Transportation Systems (ITS) in the 5.8 GHz band to support Transport Information and Control System (TICS) services.

Dedicated Short Range Communication (DSRC) provides short-range wireless high-speed packet communication between roadside equipment (RSE) installed on the roadside and on-board equipment (OBE) installed in a vehicle. Through this DSRC method, various ITS services such as automatic toll collection service, roadside search, traffic information collection and provision, and traffic signal transmission are possible.

1 is a view showing a frame structure used in the DSRC scheme according to the prior art.

As shown in (a) of FIG. 1, a frame used in a DSRC scheme includes a frame control message slot (FCMS), a message data slot (MDS), and an activation slot. ACTS). Of these, the sum of the MDS slots and AS slots does not exceed eight.

FCMS is used to provide all information about channel usage from RSE to OBE and is located only once at the beginning of the frame. This frame control slot contains communication profile and slot assignment information and is dedicated to downlink, i.e., communication from RSE to OBE.

Figure 1 (b) shows the structure of the FCMS.

As shown, the FCMS includes a preamble (PR), a frame start word (FSW), and the like.

The preamble PR has a length of 16 bits and is defined as "10101010 10101010". PR is sent from the MSB.

The FSW is used to extract frame sync and has a length of 32 bits and is defined as "00011011 10101000 01001011 00111110". The FSW is sent from the MSB.

The MDS is used to provide uplink and downlink data channels, and consists of a message data channel (MDC) and an acknowledgment signal transmission channel (ACKC). The MDC is used for data transmission, and the ACKC is used for informing the transmitting side whether the MDC has been transmitted correctly at the receiving side. Channel protection periods t3 to t4 may be inserted before and after the ACKC.

Figure 1 (c) shows the structure of the MDS.

The preamble PR has a length of 16 bits and is defined as "10101010 10101010". PR is sent from the MSB.

CSW (Channel Start Word) is used to extract channel synchronization, has a length of 16 bits, and is defined as "01001011 00111110".

ACTS is used to request data slots and to provide only uplink. In order for the OBE to contact the communication link, it first requests the RSE to assign an MDS using an access request channel (ACTC). The allocation request of the MDS is possible by connecting to the ACTC in a slotted Aloha manner. There are six ACTCs in one ACTS, and the structure of the ACTS is as shown in FIG. A channel guard period t5 is set between each window, and a channel guard period t6 is set before and after the last window.

The preamble or channel identifier of ACTS is the same as that of MDS, and the channel identifier of ACTS and MDS is the same as LSB 16 bit of FSW of FCMS.

Hereinafter, a synchronization circuit for receiving and transmitting a signal transmitted from an RSE to an OBE to find and track timing will be described.

In order to operate a synchronization circuit in an OBE, that is, a DSRC receiver, synchronization is attempted using a known pattern of a PR field, an FSW field, and a PR field, and a CSW field of an FCMS slot.

That is, the initial timing is found using the preamble (PR) field at the beginning of each slot, and then the timing is tracked to restore the transmission data.

The modulation scheme of DSRC uses ASK based Manchester coding. The transmission rate is approximately 1.024 Mbps and is received at 2.048 Mbaud after Manchester coding. The clock supplied to the DSRC receiver is 32.768 MHz, which is exactly 32 times the received data. That is, to receive one bit, 32 symbols must be received. The correlation coefficients of the 32 symbols are then found and the timing is found.

2 is a diagram illustrating a correlation in a preamble field in a DSRC scheme according to the prior art. In the initial preamble field section, data is received in a predetermined pattern. In this interval, the correlation coefficient is calculated for all 64 symbols, and the initial timing pointer is found to start tracking.

The correlation of the preamble section will be described in more detail as follows.

The Manchester code used in the DSRC is composed of two symbols ('0' corresponds to '01' and '1' corresponds to '10') for one bit. Therefore, when the correlation coefficient is calculated for 32 symbols, two highest correlation values appear for one bit. This characteristic is an obstacle to extracting timing. Computation of the correlation value for 32 symbols results in the highest value between bits rather than the highest value in the middle of the bit, and when timing is extracted based on the highest value between the bits, the wrong data is received. .

Since the preamble field section is arranged at the beginning of every slot and has a constant pattern ("10101010_10101010"), a pattern of "10" appears continuously. Correlation values are calculated for 64 symbols corresponding to 64 symbols, that is, 2 bits, to match the characteristics of the preamble field section.

The value of the window for calculating the correlation value of the preamble field interval is 64'h0000ffff_ffff0000, for example, as shown in the window at the bottom of FIG. 2 (a), and the method of calculating the correlation uses an exclusive OR (XOR) operation. .

The correlation value in the ideal reception state is shown in the form of sawtooth as shown in (b) of FIG. 2, and the highest value appears exactly at the bit section. After calculating the correlation value, the timing of the bit section is extracted by detecting the location having a value greater than or lower than the correlation upper limit threshold and comparing with the correlation upper limit threshold and the correlation lower limit threshold. .

Since the preamble has a pattern of "10101010_10101010", the patterns of "10" and "01" appear alternately. When the pattern of the preamble is found 8 times, it is determined that the preamble is found and the timing is traced.

3 is a view showing a correlation between the FSW and CSW in the DSRC method according to the prior art.

The value of the correlation window used in the preamble (PR) field in the frame start word (FSW) field of the frame control slot (FCMS) and the channel start word (CSW) field of the message data slot (MDS) and the connection request slot (ACTS). Is calculated from 64 symbols to 32 symbols. That is, since the pattern of "10" is not repeated like the preamp field, the correlation value is calculated by changing the value of the correlation window to 32 symbols to correspond to one bit.

The CSW field of the message data slot and the connection request slot has the same contents as the lower two bytes of the FSW field of the frame control slot.

As shown in (a) of FIG. 3, the correlation value is calculated for the Manchester coded received signal using 32 symbols. As shown in (b) of FIG. Correlation values exist.

This phenomenon is a characteristic of Split Phase Code, or Manchester code, which hinders timing tracking.

The timing information extracted from the preamble section must be tracked in the FSW and CSW fields, so that proper data can be restored.

In the graph of the correlation coefficient in the ideal reception state illustrated in FIG. 3B, the correlation value always exceeds the threshold value at the bit boundary, and the correlation value randomly occurs in the middle of the bit.

As described above, in calculating a correlation value such as a preamble or an FSW or CSW, a timing error according to characteristics of a Manchester code becomes a problem when transmitting and receiving data through a DSRC communication method.

An object of the present invention relates to a timing recovery and tracking method using a correlation value prediction window and a computer-readable recording medium recording a program for realizing the same. More specifically, the correlation value correlates a section where the correlation value becomes the highest or lowest value. By predicting in advance with the value result prediction window and tracking the timing based on the correlation result result prediction window, accurate timing recovery is performed in the receiver using the DSRC method, which is particularly sensitive to channel timing. According to the present invention, a correlation value result prediction window can be variably set or a threshold value can be variably set, thereby providing a timing recovery and tracking method using a correlation value result prediction window capable of more accurate timing recovery and tracking.

Another object of the present invention is to provide a computer-readable recording medium having recorded thereon a program for realizing the timing recovery and tracking method using the correlation value result prediction window.

In order to achieve the above technical problem, the present invention is a timing recovery and tracking method using a correlation value prediction window in a receiver using a DSRC communication method, (a) a symbol whose correlation value exceeds a threshold based on a window of a preamble field Constructing a correlation value result prediction window that is bounded to a lower position and an upper position to include a position; (b) the lower portion of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field; Determining whether the threshold value is exceeded by reaching a position after reaching a position; and (c) updating the lower position and the upper position of the correlation result prediction window when the threshold value is exceeded, and proceeding to the next window. Timing recovery and tracking using the correlation result prediction window including the step of jumping to step (b) after repositioning Provide a method.

In addition, the present invention is a timing recovery and tracking method using the correlation result prediction window in the receiver using the DSRC communication method, (a) based on the window of the preamble field so that the correlation value includes a symbol position that exceeds the threshold value and the lower position and the; Constructing a correlation value result prediction window bounded to an upper position; and (d) calculating a correlation value within a range of the correlation value result prediction window in a window corresponding to a preamble field, an FSW field, or a CSW field to determine timing. The present invention provides a timing recovery and tracking method using a correlation result prediction prediction step including recovering.

In the timing recovery and tracking method using the correlation value result prediction window according to the present invention, the lower position is defined as the symbol position-3 at the point of time indicated by the correlation value exceeding the threshold value, and the upper position is determined from the lower position. It may be defined as a symbol position + 1 when the correlation value falls.

In the timing recovery and tracking method using the correlation value result prediction window according to the present invention, the step (c) is based on the change of the correlation value result prediction window based on the change in the lower position or the upper position. The method may further include variably setting the lower position or the upper position when the prediction window is updated.

In the timing recovery and tracking method using the correlation value result prediction window according to the present invention, the step (c) is based on whether or not a correlation value exceeding the threshold value appears in the correlation value result prediction window. The method may further include setting the value variably.

In the timing recovery and tracking method using the correlation value result prediction window according to the present invention, the step of variably setting the threshold value includes a correlation value exceeding the threshold value within a predetermined number of correlation value result prediction windows. If not shown may further comprise the step of jumping to step (a).

In addition, the present invention is a computer-readable recording medium recording a program for realizing the timing recovery and tracking function using the correlation value result prediction window in the receiver using the DSRC communication method, (a) the correlation value based on the window of the preamble field A function of configuring a correlation value result prediction window delimited by a lower position and an upper position to include a symbol position exceeding this threshold, and (b) the correlation value in a window corresponding to a preamble field or an FSW field or a CSW field. Determining whether the threshold value is exceeded by reaching a correlation value after reaching the lower position of the result prediction window; and (c) if the threshold value is exceeded, the lower position and the upper position of the result prediction window. Program to realize the function to update the function, change the position to the next window, and jump to the function (b). Provided is a computer readable recording medium having recorded thereon.

In addition, the present invention is a computer-readable recording medium recording a program for realizing the timing recovery and tracking function using the predicted correlation value result window in the receiver using the DSRC communication method, (a) the correlation value based on the window of the preamble field A function of configuring a correlation value result prediction window delimited by a lower position and an upper position to include symbol positions exceeding this threshold, and (d) the correlation value in a window corresponding to a preamble field or an FSW field or a CSW field. A computer-readable recording medium having recorded thereon a program for realizing a function of restoring timing by calculating correlation values within a result prediction window range is provided.

Hereinafter, a timing recovery and tracking method using the correlation value result prediction window of the present invention and a computer-readable recording medium recording a program for realizing the same will be described in more detail with reference to the accompanying drawings.

4 is a flowchart of a timing recovery and tracking method using the correlation value result prediction window according to the present invention.

First, a correlation result prediction window is configured based on the preamble field (S110).

5 is a diagram illustrating an example of a correlation value result prediction window in the timing recovery and tracking method using the correlation value result prediction window according to the present invention.

In this case, the 64 symbols in the window used for synchronization of the preamble field are divided into two, each having a number from 0 to 31, and then the position of the correlation value exceeds the threshold value and the correlation value exceeds the threshold value. The lower position (sample_window_low) and the upper position (sample_window_high) of the correlation value result prediction window are determined by giving some margin at the position.

Through this process, the correlation result prediction window is configured to include a section in which the correlation value exceeds a threshold.

For example, if the lower position (sample_window_low) is defined as the symbol position-3 at the point of time indicated by the correlation value exceeding the threshold value, and the upper position (sample_window_high) is defined as the symbol position + 1 when the correlation value falls from the lower position (sample_window_low), The correlation value result prediction window may be configured to include a section in which the correlation value exceeds a threshold and have a margin of two clocks on both sides.

Subsequently, the correlation value result prediction window may be predicted for the window of the preamble described with reference to FIG. 2 or the FSW and CSW windows described with reference to FIG. In other words, in the case of the window of the preamble described with reference to FIG.

Once the correlation result prediction window is configured, when the lower position (sample_window_low) of the correlation result prediction window is reached in the next window, the correlation value is checked to find a place exceeding the threshold (S120).

If the correlation value is found above the threshold value, the correlation value result prediction window is updated (S130).

Similarly, referring to FIG. 5, it can be seen that the correlation value result prediction window is updated.

In this case, set the symbol position -3 where the correlation value exceeds the threshold as the new lower position value, and similarly set the upper position to the symbol position + 1 when the correlation value falls from the set lower position, and then set the correlation result prediction window. Can be updated.

Thereafter, the correlation value check in the next window is performed based on the updated-correlation correlation result prediction window.

The timing can be known by updating the correlation value result prediction window. For example, when the correlation value is smaller than the previous correlation value, the timing is faster, and when the correlation value is larger, the timing is slower.

The correlation data can be used to predict timing to obtain accurate data. That is, the timing error according to the characteristics of the Manchester code described with reference to FIG. 3 may be eliminated by limiting the timing to be tracked in the correlation result prediction window.

The method may further include a direction setting step in order to efficiently perform timing tracking in the timing recovery and tracking method using the correlation value result prediction window according to the present invention.

The direction setting step tracks the movement of the correlation result prediction window and checks whether the correlation result prediction window moves in the direction of decreasing timing or direction of increase, so that a correlation value exceeding the threshold value appears in the correlation result prediction window. If not, the window was widened in that direction to predict the next correlation value.

Table 1 below shows an example of setting the direction.

direction Direction determination Update result according to direction setting 01 (New lower position-previous lower position)> 3 Lower position + 2'h1 upper position + 2'h2 00 (New lower position-previous lower position) <= 2 Lower position Upper position + 2'h1 11 (Old lower position-new lower position) <= 2 Lower position-2'h2 upper position 10 (Old lower position-new lower position)> 3 Lower position-2'h3 upper position-2'h1

As shown, the previous lower position is compared with the new lower position to extend the range of the correlation result prediction window in one direction or to move the correlation result prediction window in either direction and then within the correlation result prediction window. This increases the probability of a correlation exceeding the threshold.

The method may further include a threshold adjustment step in order to efficiently perform timing tracking in the timing recovery and tracking method using the correlation result prediction window according to the present invention.

Slowing the timing does not change the maximum value of the correlation, but as timing gets faster, the overall value of the correlation decreases. In addition, the channel may deteriorate so that the correlation value may not exceed the threshold.

In such a case, the threshold can be changed according to the channel situation to adjust the threshold to track the data.

First, the correlation value over a threshold value is counted when a correlation value exceeding a threshold appears at least once. For example, a good_counter is defined as a counter that is incremented one by one if a correlation value exceeding a threshold is found in the correlation result prediction window, and resets if it does not appear.

It also counts the cases where the correlation value does not appear above the threshold in the correlation result prediction window. For example, define a bad-counter as a counter that resets when a correlation value exceeding a threshold is found in the correlation result prediction window and increments by one when it does not appear.

If the bad-counter value is greater than or equal to a certain number, it may be considered that the correlation value does not exceed the threshold value because the channel characteristics are poor. Therefore, lower the threshold value to configure the timing.

In addition, if the good-counter value is more than a certain number, the channel characteristics are in good condition, so the threshold value is increased to configure more accurate timing.

As such, the range of the correlation result prediction window may be adjusted by adjusting the threshold.

The good-counter is a counter that counts from 0 to 15, and when it reaches 15, the good-counter is incremented by one if the threshold-high is less than the threshold_limit, and likewise the threshold-low. Decreases one. Here, the highest-threshold value means the maximum value of the currently set threshold value, and similarly the current lowest-threshold value means the minimum value of the currently set threshold value. In addition, the threshold-limit value (threshold_limit) means a limit that can be set as a threshold.

Bad-counter is a counter that can count from 0 to 15. If the bad-counter value is 3 or more, the high-threshold value is decreased by one, and the low-threshold value is increased by one. When the bad counter reaches 8 or more, it may be determined that the timing tracking has failed, and the correlation value result prediction window may be configured based on the preamble.

The present invention also provides a computer-readable recording medium having recorded thereon a program for realizing a timing recovery and tracking function using a correlation value result prediction window in a receiver using a DSRC communication method.

However, the description of the computer-readable recording medium is omitted since it overlaps with the timing recovery and tracking method using the correlation result prediction window described with reference to FIGS. 4 to 5.

Although the present invention has been described in detail, this is for illustrative purposes only, and the protection scope of the present invention is not limited thereto, and the protection scope of the present invention is defined through the description of the claims.

As described above, according to the present invention, a timing value is tracked based on the correlation value result prediction window after predicting a section in which the correlation value becomes the highest or lowest value in advance using the correlation value result prediction window. In the receiver using the DSRC method to which the coding is applied, accurate timing recovery is performed, and the correlation value result prediction window or the threshold value can be set variably according to the channel characteristics, thereby enabling more accurate timing recovery and tracking. .

Claims (8)

A method for timing recovery and tracking using a correlation value prediction window in a receiver using a DSRC communication method, (a) constructing a correlation value result prediction window bounded to a lower position and an upper position such that the correlation value includes symbol positions above a threshold based on a window of the preamble field; (b) determining whether or not the threshold is exceeded by checking a correlation value after reaching the lower position of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field; (c) updating the lower position and upper position of the correlation result prediction window when the threshold value is exceeded, changing the position to the next window, and then jumping to step (b). Timing recovery and tracking method using a correlation value result prediction window comprising a. A method for timing recovery and tracking using a correlation value prediction window in a receiver using a DSRC communication method, (a) constructing a correlation value result prediction window bounded to a lower position and an upper position such that the correlation value includes symbol positions above a threshold based on a window of the preamble field; (d) restoring timing by calculating a correlation value within a range of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field; Timing recovery and tracking method using a correlation value result prediction window comprising a. The method according to claim 1 or 2, The lower position is defined as the symbol position-3 at the point of time represented by the correlation value above the threshold, And the upper position is defined as a symbol position + 1 when the correlation value falls from the lower position. The method of claim 1, In the step (c), the lower position or the upper position is variably set when the correlation value result prediction window is updated based on a change in the lower position or the upper position of the correlation value result prediction window. Timing recovery and tracking method using a correlation value result prediction window further comprising. The method of claim 1, In the step (c), the threshold value is variably set based on whether a correlation value exceeding the threshold value is present in the correlation result prediction window. Timing recovery and tracking method using a correlation value result prediction window further comprising. The method of claim 4, wherein The step of variably setting the threshold value, Jumping to step (a) when a correlation value exceeding the threshold value does not appear in the correlation value result prediction window of a predetermined number or more Timing recovery and tracking method using a correlation value result prediction window further comprising. A computer-readable recording medium having recorded thereon a program for realizing a timing recovery and tracking function using a predicted correlation value result window in a receiver using a DSRC communication method. (a) a function of configuring a correlation value result prediction window that is bounded to a lower position and an upper position such that the correlation value includes symbol positions that exceed a threshold based on the window of the preamble field; (b) determining whether or not the threshold value is exceeded by checking a correlation value after reaching the lower position of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field; (c) a function of updating the lower position and the upper position of the correlation result prediction window when the threshold value is exceeded, changing the position to the next window, and then jumping to the function (b). A computer-readable recording medium having recorded thereon a program for realizing this. A computer-readable recording medium having recorded thereon a program for realizing a timing recovery and tracking function using a predicted correlation value result window in a receiver using a DSRC communication method. (a) a function of configuring a correlation value result prediction window that is bounded to a lower position and an upper position such that the correlation value includes symbol positions that exceed a threshold based on the window of the preamble field; (d) a function of restoring timing by calculating a correlation value within a range of the correlation value result prediction window in a window corresponding to a preamble field or an FSW field or a CSW field; A computer-readable recording medium having recorded thereon a program for realizing this.

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