KR101203721B1 - Apparatus and method of frame detection and automatic gain control for burst mode communication systems - Google Patents

Abstract

The present invention relates to a frame synchronization device and method of a burst communication receiving system.

The present invention can stably perform accurate frame synchronization in a situation where the signal size is not constant for each burst received from another user in a burst communication communication system, by using a burst signal having a constant size after frame synchronization is performed. Accurate automatic gain control can be performed per burst.

Burst, Frame Sync, Correlation Relative, Automatic Gain Control

Description

Apparatus and method of frame detection and automatic gain control for burst mode communication systems

The present invention relates to a communication receiving system in a burst environment, and more particularly, to a frame synchronization device of a burst communication receiving system and a frame synchronization acquisition and automatic gain control method using the same.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy and the Ministry of Information and Telecommunications Research and Development. Development of Multimedia Transmission Technology].

In burst type communication, a frame is transmitted by attaching a short preamble to the beginning of a burst transmission at a transmitter. The receiver performs frame synchronization, timing synchronization, frequency / phase synchronization, demodulation / decoding, etc. on a burst basis using the preamble.

In such a burst communication mode, there may be a section in which no noise exists in the frame and a frame may be received from another user for each burst. Therefore, the size of the received signal may vary from frame to frame. In particular, the magnitude of the received signal in the ranging period may be different.

Therefore, in order to properly perform synchronization and demodulation on a signal, it is necessary to be able to perform frame synchronization regardless of the signal level of the burst signal. To this end, conventionally, in order to obtain frame synchronization, a correlation between an input signal and a known signal sequence is obtained, and when this value exceeds a threshold, it is set as a start point of a frame. However, when the input signal level changes, it is difficult to set the threshold.

Therefore, placing Automatic Gain Control (AGC) after the match filter and before frame synchronization in burst communication mode results in amplifying the noise section to the desired reference level. This makes the boundary between the burst signal and the noise section unclear, increasing the likelihood of error in subsequent operations, including frame synchronization.

Accordingly, the present invention provides a frame synchronization device and method capable of performing stable frame synchronization and accurate automatic gain control in a situation in which the magnitude of a received signal is not constant for each burst received.

An apparatus for synchronizing a frame of a received signal input to a receiving system in a burst type communication environment which is one feature of the present invention for achieving the technical problem of the present invention,

A correlation calculator which calculates a plurality of correlation values between the received signal and the sequence of the sample unit inputted in a sample unit after being oversampled by a preset multiple; A correlation relative value calculator that calculates a plurality of correlation relative values using the plurality of correlation values, respectively; A threshold exceeding signal extractor which compares the plurality of correlation relative values with a preset reference threshold and extracts signals for a plurality of correlation relative values representing a value greater than the reference threshold; A maximum sample signal searcher for searching for a signal having the largest value among the extracted signals; And a signal selector that selects a frame synchronization start point of the received signal based on the signal searched by the maximum sample signal searcher, synchronizes the received signal in the sample unit, and outputs the synchronized signal.

In another aspect of the present invention, a method of synchronizing a frame of a signal input to a receiving system in a burst type communication environment for achieving the technical problem of the present invention,

Calculating a plurality of correlation values between a received signal and a sequence of a sample unit inputted in a sample unit after being oversampled by a preset multiple; Calculating a plurality of correlation relative values using the plurality of correlation values; Extracting a signal for a plurality of correlation relative values exceeding a preset reference threshold value among the plurality of correlation relative values; And extracting a sample signal for a correlation relative value representing a maximum value among the correlation relative values of the complement exceeding a reference threshold value, and synchronizing the received signal using the extracted sample signal.

Accordingly, the present invention can stably and accurately perform frame synchronization in a situation where a signal size is not constant for each burst in a receiver of a burst communication system. In addition, accurate automatic gain control per burst can be performed using a burst signal having a constant magnitude after frame synchronization is performed.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, parts irrelevant to the description are omitted for simplicity of explanation, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise. Also, the terms " part, "" module," and " module ", etc. in the specification mean a unit for processing at least one function or operation and may be implemented by hardware or software or a combination of hardware and software have.

Hereinafter, a reception system and a frame synchronization and gain control method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a structural diagram of a burst communication receiving system according to an embodiment of the present invention.

As shown in FIG. 1, the reception system has a structure of all digital feedforward, and includes an RF receiver 100, an analog-digital converter 200, a match filter unit 300, and a frame synchronizer. 400, an automatic gain controller 500, a symbol timing synchronizer 600, a frequency / phase compensator 700, and a demodulator / decoder 800.

The RF receiver 100 down-converts a high frequency signal of a band desired by the reception system to a baseband signal from an analog high frequency signal transmitted from a transmission system. In this case, the analog high frequency signal transmitted from the transmission system is received by the reception system in burst units, hereinafter, the received signal is also referred to as a burst signal.

The analog-to-digital conversion unit (ADC) 200 is down-converted to the baseband signal by the RF receiver 100 to sample the output analog signal at regular intervals and convert the analog signal into a digital signal. Here, a certain period may be applied differently every time the system is designed. In the embodiment of the present invention, a predetermined period is assumed to be four times the symbol period. That is, four sample values exist in one symbol, and this is called a signal in a sample unit, that is, a sample signal.

The match filter unit 300 receives the digital signal converted by the analog-to-digital converter 200 to reduce adjacent symbol interference (ISI) to improve the signal-to-noise ratio (SNR) of the signal. Output the signal.

The frame synchronizer 400 receives a digital signal in burst units having an improved signal-to-noise ratio output from the match filter unit 300, and finds a start position of the burst signal based on this. To this end, the frame synchronizer 400 calculates a correlation relative value from a digital signal in burst units. This will be described later in detail.

In addition, the automatic gain controller 500 maintains a constant magnitude of the received signal in burst units output from the frame synchronizer 400.

The symbol timing synchronizer 600 finds the starting point of the received signal through the frame synchronizer 400 and the automatic gain controller 500 and finds the exact timing of the received signal whose magnitude is maintained at a constant level.

The frequency / phase compensator 700 estimates and compensates a transmission / reception frequency / phase offset using a preamble data sequence included in burst data and known to the reception system.

The demodulation / decoder unit 800 demodulates a symbol of a received signal in units of bursts, and obtains final data in which errors are corrected through a decoding process by forward error correction (FEC) on a result including an error. .

Next, the structure of the frame synchronizer 400 described above will be described in detail with reference to FIG. 2. Before describing FIG. 2, in the embodiment of the present invention, in order to frame synchronization of a signal transmitted from a transmission system, the transmission system transmits a preamble in front of the transmission signal.

In this case, it is assumed that the preamble sends the same as a constant amplitude zero auto-correlation (CAZAC) sequence already stored in the receiving system. In the embodiment of the present invention, a CAZAC sequence is used as an example, but any sequence having a property similar to that of the CAZAC sequence (for example, M-Sequence) may be used. In this case, since the burst signal is sampled at four times the symbol period in the analog-to-digital converter 200, the burst signal is oversampled four times per symbol to become an input sample signal.

2 is a structural diagram of a frame synchronizer according to an embodiment of the present invention.

As shown in FIG. 2, the frame synchronizer 400 includes a correlation calculator 410, a correlation relative value calculator 420, an over-threshold signal extractor 430, a maximum sample signal searcher 440, and a signal selector ( 450).

The correlation calculator 410 calculates a correlation value between the burst signal input in the sample unit and the CAZAC sequence. Then, the correlation value in the unit of sample is obtained using the obtained correlation value. Then, the correlation relative value and the reference threshold value are compared, and signals for correlation relative values showing a threshold value larger than a preset threshold value are detected.

When the largest signal among the detected signals is obtained, a time point at which the obtained signal occurs is a frame synchronization time point in samples. The correlation calculator 410 will be described in detail with reference to FIG. 3.

3 is an exemplary diagram of a correlation calculator according to an embodiment of the present invention.

As shown in FIG. 3, the correlation calculator 410 includes a plurality of multipliers 411-1 to 411-16, an adder 412, and an absolute value calculator 413.

The multipliers 411-1 to 411-16 multiply the burst signal (hereinafter, referred to as an input sample signal) input in units of samples with each CAZAC sequence already stored. The input sample signal is a four times oversampled signal, denoted by x. The multipliers 411-1 to 411-16 exist as many as the number of elements of the CAZAC sequence (eg, 16), and the first multiplier 411-1 multiplies the input sample signal x _k by the CAZAC sequence C ₁₅ , The second multiplier 411-2 multiplies the input sample signal x _{k -4} with the CAZAC sequence C ₁₄ .

The adder 412 adds 16 values output by multiplying the input sample signal and the CAZAC sequence by the multipliers 411-1 to 411-16, respectively, and the absolute value calculator 413 is added by the adder 412 to output the result. The absolute value of the calculated value is calculated and output as a correlation value for the input sample signal. In this case, a value output as a correlation value may be expressed as in Equation 1 below, and is a sample unit.

The correlation value output from the absolute value calculator 413 is input to the correlation relative value calculator 420 of FIG. 2. The correlation relative value calculator 420 calculates a correlation relative value using the correlation value calculated by the correlation calculator 410 and calculates the value using Equation 2 below.

 Where k means any sample time point and N means any time period. And Window means the window size. Here, the N value and the Window value may be variously changed by the system designer, and in the embodiment of the present invention, it is assumed that N is 3.

The correlation relative value for any sample time point k is obtained by dividing the correlation value at this time point by the average of the correlation values of the sample signals coming in a certain window after a certain period N after the sample at this time point. In this case, the reason for obtaining the correlation relative value in the embodiment of the present invention is because it is difficult to directly compare the correlation value of the CAZAC sequence with the reference threshold value.

That is, since the absolute value of the correlation of the CAZAC sequence changes greatly according to the signal level of the burst input from another user, it is impossible to obtain an appropriate threshold value. However, the correlation relative value is almost independent of the signal level of the burst input. Here, the value of N is selected in consideration of the time point to start to stabilize the small value avoiding the transition region of the autocorrelation value of the CAZAC sequence.

The window size is set to reduce the noise effect and to select an area where the autocorrelation value of the CAZAC sequence continues. This takes into account the CAZAC sequence correlation characteristics.

The threshold exceeded signal extractor 430 sets a threshold in consideration of characteristics of autocorrelation values of the CAZAC sequence. Here, the method for setting the threshold value in consideration of the characteristics of the autocorrelation value is already known, and detailed descriptions thereof will be omitted in the embodiments of the present invention. In addition, since the threshold is set so that the frame detection rate is sufficiently high, some samples may cross the threshold during the symbol period.

The maximum sample signal searcher 440 finds the sample having the maximum value among the correlation relative values of the interval interval samples (eg, two samples before and after the threshold value) of the sample point above the threshold. This is for frame synchronization with sample accuracy. In this case, the two samples are searched in a predetermined interval because the four-fold over sampling is taken as an example of the present invention.

The signal selector 450 selects the start point of the frame of the input sample signal in consideration of the length of the CAZAC signal and the like based on the synchronization point corresponding to the maximum correlation relative value found by the maximum sample signal searcher 440. That is, the start point of the burst signal is found and the subsequent samples are output to the automatic gain controller 500 from this start point.

Next, the automatic gain control unit 500 according to the embodiment of the present invention will be described in detail with reference to FIG. 4.

4 is an exemplary view of an automatic gain control unit according to an embodiment of the present invention.

As shown in FIG. 4, the automatic gain control unit 500 includes a sample signal average magnitude value output unit 510, a gain calculator 520, and a multiplier 530.

The sample signal average magnitude value output unit 510 calculates a level value, that is, a sample signal average magnitude value at a point in time, and outputs it to the gain calculator 520. Here, the level value output from the sample signal average magnitude output unit 510 may be obtained as shown in Equation 3 below. In addition, the method of operating the components of the sample signal average magnitude value output unit 510 shown in FIG. 4 is already known, and a detailed description thereof will be omitted in the exemplary embodiment of the present invention.

The gain calculator 520 calculates the gain of the automatic gain control (hereinafter referred to as 'AGC_gain') as shown in Equation 4 below.

Equation 4 means that the desired reference power value (ref_power) is the result of dividing the average power of the signals in the predetermined window to be input after the time of applying the AGC.

In this case, the reason for using the average power value of the signals in the predetermined window to be input after the time of applying the AGC is to not use the signal before frame synchronization. That is, the same interval as the noise section before the start of the frame is not used for calculating the average level of the signal. This is advantageous when there is little change in signal level in one burst.

The calculation for automatic gain control may be calculated in units of window size used to obtain AGC_gain according to the nature of the communication channel. In addition, when there is no fading within one burst, the AGC_gain obtained first may be used until the burst end.

The multiplier 530 multiplies (x _k * AGC_gain) the input sample signal output from the frame synchronizer 400 with the AGC_gain value calculated by the gain calculator 520, and shows the input sample signal having a predetermined magnitude as the result. The signal is transmitted to the symbol timing synchronizer 600 of 1.

Next, a method of synchronizing frames and controlling automatic gain using the frame synchronizer 400 and the automatic gain controller 500 described with reference to FIGS. 3 and 4 will be described with reference to FIG. 5.

5 is a flowchart illustrating a frame synchronization and automatic gain control method in a burst communication receiving system according to an embodiment of the present invention.

As illustrated in FIG. 5, when a digital signal (hereinafter, referred to as a “sample signal”) in units of samples is input to the frame synchronizer 400 (S100), the correlation calculator 410 may input the input sample signal and the CAZAC sequence. Calculate liver correlation. At this time, it is assumed that the sample signal is a four times oversampled signal, and the process until the sample signal input to the frame synchronizer 400 is generated is already known, and detailed description thereof will be omitted. ..

When the correlation calculator 410 calculates a correlation between the input sample signal and the CAZAC sequence (S110), the correlation relative value calculator 420 calculates a correlation relative value of a sample unit using the calculated correlation result. (S120). When the correlation relative value calculator 420 obtains the correlation relative value, the threshold exceeded signal extractor 430 extracts all signals exceeding a predetermined threshold (S130).

The maximum sample signal searcher 440 searches for the maximum sample signal representing the largest value among all the signals exceeding the extracted threshold (S140). The sample signal found in step S140 is used as a reference time point for frame synchronization. The signal selector 450 selects a burst start point of the input sample signal input to the frame synchronizer 400 based on the synchronization point corresponding to the maximum correlation relative value searched by the maximum value sample signal searcher 440, thereby At step S150, the input sample signal is output to the automatic gain control unit 500 as a starting point. Then, the automatic gain control unit 500 performs automatic gain control on the signal output by performing frame synchronization in step S150 and outputs it (S160).

The embodiments of the present invention described above are not only implemented by the apparatus and method but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded, The embodiments can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

1 is a structural diagram of a burst communication receiving system according to an embodiment of the present invention.

2 is a structural diagram of a frame synchronizer according to an embodiment of the present invention.

3 is an exemplary diagram of a correlation calculator according to an embodiment of the present invention.

4 is an exemplary view of an automatic gain control unit according to an embodiment of the present invention.

5 is a flowchart illustrating a frame synchronization and automatic gain control method in a burst communication receiving system according to an embodiment of the present invention.

Claims (11)

An apparatus for synchronizing a frame of a received signal input to a receiving system in a burst communication environment, A correlation calculator for calculating a plurality of correlation values between a received signal and a sequence input after being oversampled by a preset multiple and input in a sample unit; A correlation relative value calculator that calculates a plurality of correlation relative values using the plurality of correlation values, respectively; A threshold exceeding signal extractor which compares the plurality of correlation relative values with a preset reference threshold and extracts signals for a plurality of correlation relative values representing a value greater than the reference threshold; A maximum sample signal searcher for searching for a signal having the largest value among the extracted signals; And A signal selector which selects a frame synchronization start point of the received signal based on the signal searched by the maximum sample signal searcher and synchronizes the received signal in the sample unit Frame synchronization device comprising a. The method of claim 1, The correlation calculator, A multiplier for multiplying a received signal by the sample unit and a sequence and outputting a value equal to the number of elements of the sequence; An adder for adding and outputting values equal to the number of sequence elements output from the multiplier; And Absolute value calculator that calculates an absolute value to the value output from the adder and outputs it as the correlation value Frame synchronization device comprising a. The method of claim 1, The correlation relative value calculator divides the correlation value at a preset time point by the average of the correlation values of sample signals included in a set value after a preset time period from a sample signal for the preset time point. Frame synchronizer for calculating relation relative values. The method of claim 3, The predetermined period is a period set in consideration of a time point at which the transition of the autocorrelation value of the sequence is avoided and starts to stabilize to a preset value. Frame synchronizer which is the value set in consideration. The method of claim 1, Automatic gain control device for receiving the burst signal synchronized with the frame output from the signal selector, so that the magnitude of the burst signal is maintained at a constant size Frame synchronization device further comprising. The method of claim 5, The automatic gain control device, A sample signal average magnitude value output unit for calculating a sample signal average magnitude value; A gain calculator for calculating a gain value using the calculated sample signal average magnitude and a preset reference power value; And A multiplier for multiplying the received signal in the sample unit and the gain value calculated by the gain calculator and outputting the sample signal having a predetermined size. Frame synchronization device comprising a. In a method of synchronizing frames of a signal input to a receiving system in a burst communication environment, Calculating a plurality of correlation values between a received signal and a sequence input after being oversampled by a preset multiple and input in a sample unit; Calculating a plurality of correlation relative values using the plurality of correlation values; Extracting a signal for a plurality of correlation relative values exceeding a preset reference threshold value among the plurality of correlation relative values; And Extracting a sample signal for a correlation relative value representing a maximum value among the plurality of correlation relative values exceeding a reference threshold value and synchronizing a received signal using the extracted sample signal; Synchronization method comprising a. The method of claim 7, wherein And a time point of the sample signal with respect to the correlation relative value indicating the maximum value is a reference time point for frame synchronization with respect to the received signal. The method of claim 7, wherein Performing automatic gain control so that the size of the synchronized received signal maintains a predetermined predetermined size Synchronization method comprising a. 10. The method of claim 9, Performing the automatic gain control, Calculating and outputting an average magnitude value of the received signal by using the synchronized received signal; Calculating and outputting a gain value using the outputted average magnitude value and the reference power value; And Performing automatic gain control by multiplying the received gain by the output gain value; Synchronization method comprising a. The method of claim 10, The gain value is a value calculated by dividing a preset reference power value by the average power of signals in a set value to be input after a time to apply automatic gain control.

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