KR20110070357A - FSS receiver for correction using zero crossing demodulation and its control method - Google Patents

Abstract

The present invention relates to an FSK receiver method based on zero crossing demodulation and an FSK receiver using the same. More specifically, after extracting a zero crossing point from an IF signal, the number of sampling between the zero crossing points is used. The present invention relates to a decoding method using a method of calculating a period and a frequency, and a receiver using the same.

The FSK receiver using the zero crossing demodulation according to the present invention for achieving the above object receives an RF signal and converts it into an IF signal and a first zero crossing point and a second zero crossing point in the IF signal. And extract the period of the frequency using the extracted time between the first zero crossing point and the second zero crossing point, and then extract the frequency using the period and demodulate the digital data by comparing with the boundary frequency. Contains wealth.

Description

Frequency Shift Keying Receiver for Error Correction based on Zero Crossing Demodulation and method approx.

The present invention relates to an FSK receiver method based on zero crossing demodulation and an FSK receiver using the same. More specifically, after extracting a zero crossing point from an IF signal, the number of sampling between the zero crossing points is used. The present invention relates to a decoding method using a method of calculating a period and a frequency, and a receiver using the same.

Frequency Shift Keying (FSK) is a modulation scheme that assigns two frequencies of a sine wave of a constant amplitude and sends the assigned frequency among two frequencies to the other side as the data changes to 1 or 0. It is more used for data transmission because it is more error-resistant than the amplitude shift method (ASK) and the circuit is relatively simple. This FSK is easy to configure and relatively strong in long-distance transmission, and thus is widely used in PSTN. FSK is mainly used for data transmission of relatively low speed (asynchronously less than 200 [BPS]).

The modulation scheme transmits carrier frequencies differently in response to digital signals (0 and 1 for binary FSK, 00,01, 10 and 11 for 4 FSK). In other words, the carrier frequency is changed with respect to 0 and 1 of the digital data, and the binary 1 and 0 correspond to two frequencies of the high frequency and the low frequency where the center frequency is inserted.

1 is a diagram illustrating an example of an FSK. As shown in the figure, this frequency varies corresponding to 0 and 1, but the amplitude is always constant. That is, the FSK transmitter modulates bit 1 to a high frequency and 0 to a low frequency. When the modulated radio wave is transmitted as an output signal, the FSK receiver receives the digital signal from the frequency in such a manner that the high frequency (frequency above the predetermined reference value) corresponds to 1 and the low frequency (frequency below the predetermined reference value) corresponds to 0. Demodulate the data.

As a result, it is of utmost importance in the FSK receiver how exactly and simply how to demodulate from the frequency into digital data. Accordingly, various demodulation methods exist in the FSK receiver.

On the other hand, zero crossing (hereinafter referred to as zero crossing) is a concept commonly used in stable control and soundforge programs in electronic circuits. In other words, in the electronic circuit, the AC voltage has a sinusoidal shape, which is used to detect a moment when the voltage passes Ov and to control on / off at this point to prevent a sudden change of current. In addition, when a waveform of a specific sound is called from the soundforge program, if the value of the waveform rises positive and negative according to the time axis, the point where the magnitude of the sound becomes 0 is called zero crossing. When editing, it is cut from this zero crossing point to another zero crossing point and used for pasting back and forth.

The present invention is to provide a method for designing a more efficient and economical FSK receiver using such a zero crossing.

The present invention is to provide a method for designing a more efficient and economical FSK receiver using such a zero crossing.

The FSK receiver using the zero crossing demodulation according to the present invention for achieving the above object receives an RF signal and converts it into an IF signal; Extracting a first zero crossing point and a second zero crossing point from the IF signal, extracting a period of frequency using the time between the extracted first zero crossing point and the second zero crossing point, and then using the period. A demodulator which extracts a frequency and compares it with a boundary frequency and demodulates the digital data, and a frequency correction unit for calculating a correction boundary frequency using an average of intervals between crossing points in the IF signal, and correcting it with a new boundary frequency.

The frequency correction unit preferably calculates a correction boundary frequency using the following equation.

F ' _if is the calibration boundary frequency

δ _n is the time between the nth zero crossing point and the n + 1 zero crossing point.

In addition, after calculating the average of the interval between the crossing points for each of the decoded digital data value, the average of the calculated average value to extract the feedback boundary frequency, and further comprising a feedback frequency correction for calculating this as a new boundary frequency It is preferable.

The feedback frequency correction unit preferably calculates a feedback boundary frequency using the following equation.

The demodulation unit may further include a function of sampling the IF signal at sampling intervals at regular intervals, and extracting the frequency period calculates the number of samplings between the first and second zero crossing points, and calculates the number of samplings. It is preferable to extract using the sampling unit time.

The zero crossing point is preferably a point where the magnitude of the IF signal changes from-to +.

In addition, the demodulation unit demodulates to 1 when the extracted frequency is greater than the boundary frequency, and demodulates to 0 otherwise.

The FSK receiver is preferably a Zigbee receiver.

A demodulation method of an FSK receiver using a zero crossing function according to the present invention for achieving the above object comprises a radio wave reception step of receiving an RF signal modulated by the FSK receiver and converting it into an IF signal; Compensation boundary frequency is calculated using an average of intervals between crossing points in the IF signal, and a frequency correction step of correcting this to a new boundary frequency and each frequency period are extracted using the interval between crossing points in the IF signal. And a demodulation step of extracting a frequency using the same, and demodulating the digital data by comparing the frequency with the boundary frequency.

The demodulation step may include a first zero crossing extraction step of extracting a first zero crossing point that is a first zero crossing point detected from the IF signal; A second zero crossing extraction step of extracting a second zero crossing point, which is a zero crossing point first found again after the first zero crossing point; A frequency period extracting step of extracting a period of frequency by using the time between the first zero crossing point and the second zero crossing point; Preferably, the method includes a frequency extracting step of extracting a frequency using the extracted frequency period, and a digital data demodulating step of comparing the extracted frequency with a boundary frequency and demodulating the digital data.

In the frequency correction step, it is preferable to calculate a correction boundary frequency using the following equation.

F ' _if is the calibration boundary frequency

δ _n is the time between the nth zero crossing point and the n + 1 zero crossing point

And calculating a mean of the intervals between the crossing points for each of the decoded digital data values, extracting a feedback boundary frequency by obtaining the average of the calculated average values, and then calculating the feedback boundary frequency as a new boundary frequency. It is desirable to.

In addition, in the feedback frequency correction step, it is preferable to calculate a feedback boundary frequency using the following equation.

And a sampling step of sampling the IF signal at sampling intervals at regular intervals, and the frequency period extracting step calculates the number of samplings between the first and second zero crossing points, and calculates the number of samplings and the sampling units. It is preferable to extract using time.

In addition, the zero crossing point is preferably a point where the magnitude of the IF signal changes from-to +.

The frequency extracting step may be an inverse of the extracted frequency period.

In the digital data demodulating step, it is preferable to demodulate to 1 if the extracted frequency is greater than the boundary frequency, and to demodulate to 0 otherwise.

The FSK receiver is preferably a Zigbee receiver.

As described in detail above, the FSK demodulation method using zero crossing and the FSK receiver using the same can provide a receiver having a lower cost and size by providing a simpler demodulation algorithm than the conventional FSK demodulation method and the FSK receiver. Will be.

2 is a diagram illustrating a demodulation method of an FSK receiver using a zero crossing function according to an embodiment of the present invention.

S (t) shown in the figure is an example of an IF domain signal, and an example of the case where the s (t) signal is sampled is shown. The first zero crossing point is t _n , and the next zero crossing point is t _{n + 1} .

It is understood that the zero crossing point has the magnitude of the signal at the nth sampling time at each sampling time, and the zero crossing point is included between the sampling times if the magnitude of the signal at the n + 1th sampling time is +.

delta n is the time between tn and tn + 1, which is the first period of the s (t) signal.

There are various methods for obtaining δ n, but in this embodiment, the number of samplings between the zero crossings is used. First, the number of sampling between the first zero crossing point and the second zero crossing point is calculated. In the case of Fig. 2, the number of sampling is twelve. The number of samplings is multiplied by the unit sampling time, which is the sampling end time. That is, Tclk * 12 becomes delta n.

Since the calculated δ n becomes a period after this, taking the inverse of this value yields a frequency F n. The frequency Fn thus calculated is demodulated to a high frequency plane 1 larger than the boundary frequency, and is demodulated to 0 when smaller than the boundary frequency.

3 is a block diagram of an FSK receiver according to an embodiment of the present invention.

The FSK receiver largely includes an RF processor 110, a demodulator 120, a controller 130, a memory 140, a frequency compensator 150, and a feedback frequency compensator 160. Of course, many other components are required, but the components which are not directly related to the embodiments of the present invention or are omitted even if omitted by those skilled in the art will understand the present invention.

First, the RF processor 110 receives a received RF signal and converts it into an IF signal.

The demodulator 120 performs a function of demodulating the IF signal into digital data of 0 or 1. In the present invention, the demodulation unit 120 demodulates by applying a method of detecting a zero crossing point. The demodulation method of the demodulator 120 will be described in more detail later with reference to FIG. 4.

The memory 140 stores a firmware and other necessary data for controlling transmission and reception of the FSK signal.

The frequency compensator 150 calculates a correction boundary frequency using an average of intervals between crossing points in the IF signal, and performs a function of correcting it to a new boundary frequency.

The feedback frequency correction unit 160 performs a function of correcting the boundary frequency again based on the data demodulated into the digital data. That is, the average of the intervals between the crossing points in the IF signal corresponding to the digital data restored to 1 and the interval between the crossing points in the IF signal corresponding to the digital data restored to 0 are averaged again. The frequency correction unit 150 performs a function of correcting the boundary frequency corrected again.

The controller 150 controls the RF processor 110, the demodulator 120, the frequency compensator 150, the feedback frequency compensator 160, and other components of the FSK receiver as a whole. .

4 is a flowchart illustrating a demodulation method according to an embodiment of the present invention.

The modulated RF signal is received by the FSK receiver and converted into an IF signal (S210).

Thereafter, sampling is performed for a predetermined number or more for the IF signal (S220). At this time, it is assumed that each sampling is performed every T _clk time. Hereinafter, the T _clk time is referred to as unit sampling time.

A first zero crossing point, which is a first zero crossing point detected from the IF signal, is extracted (S230). It is understood that the zero crossing point has the magnitude of the signal at the nth sampling time at each sampling time, and the zero crossing point is included between the sampling times if the magnitude of the signal at the n + 1th sampling time is +. Therefore, the first point at which the magnitude of the signal changes from-to + is determined as the first zero crossing point.

The second zero crossing point, which is the first zero crossing point found again after the first zero crossing point, is extracted (S240). As before, the second zero crossing point is determined after the first zero crossing where the signal size changes from-to + again.

Thereafter, the number of sampling between the first zero crossing point and the second zero crossing point is calculated (S250).

Subsequently, multiplying the number of sampling times by the unit sampling time results in calculating a period value of the corresponding frequency (S260).

Taking the reciprocal of the calculated period results in the calculation of the frequency of the corresponding signal (S270).

If the calculated frequency value is greater than the boundary frequency (S270-Y), it is demodulated to 1 because it is a high frequency (S280), and if it is the opposite (S270-N), it is demodulated to 0 because it is a low frequency (S285).

5A to 5C are diagrams showing examples in the frequency domain for explanation of the present invention.

The demodulation process as described above is an explanation of a case like 5a. That is, assume that F _L means low frequency and F _H means high frequency. In other words, if 0 is inputted, low frequency F _L is input, and if 1 is inputted, high frequency F _H is demodulated and transmitted. Meanwhile, the receiver demodulates 0 or 1 after calculating the frequency as described above and comparing the boundary frequency with F _if .

The problem is that when receiving at the receiver, the error value ΔF _if is added rather than when F _L or F _H is received as it is. In this case, as shown in FIG. 5B, the actual low frequency F ′ _L actually received by the receiver becomes F _L + ΔF _if , and the measured high frequency F ′ _H becomes F _H + ΔF _if . In other words, as the boundary frequency is closer to the middle value between the low frequency and the high frequency, accurate decoding is performed. However, the boundary frequency is not intermediate due to the error value. As a result, the accuracy decreases during decoding.

Accordingly, it is necessary to correct the boundary frequency by the error value. 5C is a diagram in the frequency domain when the boundary frequency is corrected.

However, it is not possible to directly obtain the error value △ F _if .

First, the boundary frequency (F _'if) corrected in accordance with the present invention is a value acquired by adding the error value (△ F _if) the first boundary frequency (F _if) as the expression below.

F ' _if = F _if + ΔF _if

F _L is low frequency and F _H is high frequency. The measured low frequency F ' _L received by the receiver becomes F _L + ΔF _if , and the measured high frequency F' _H becomes F _H + ΔF _if .

On the other hand, for convenience of calculation, suppose that the deviation value between the boundary frequency and the low frequency and the high frequency is F _mod . That is, the low frequency becomes F _if -F _mod and the high frequency becomes F _if + F _mod . If based on IEEE 802.15.4, the actual F _mod will be 500KHZ.

On the other hand, the measured deviation F ' _mod is + -F _mod + ΔF _if .

On the other hand, in the case of a receiver, as the accumulated data increases, the number of demodulated zeros and the number of 1s become almost equal. That is, P ₀ , the probability of _0, and P ₁ , the probability of _1, are almost similar. In this case, the average of the measured deviation values is equal to the error value as follows.

As a result, the average of the measured high and low frequencies coincides with the median modified by the error, and we use this modified median as the new boundary frequency. Therefore, the new boundary frequency F ' _if is the average of the measured frequencies.

On the other hand, as mentioned above, the measured frequency was calculated by the inverse of δ _n . Thus, as shown in the following equation, the correction boundary frequency F ' _if is the inverse of the average value of the entire δ _n .

On the other hand, after demodulating the correction boundary frequency using the algorithm described above, the feedback boundary frequency may be newly obtained and corrected using the number of 1's and 0's.

The feedback boundary frequency is obtained by averaging the decoded frequencies of 1 and 0 as follows, and then averaging the two again.

So far, the boundary frequency correction method and the FSK receiver using the same in FSK using zero crossing have been described.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limiting the scope of the invention as defined by the appended claims. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

The FSK demodulation method using the zero crossing and the FSK receiver using the same according to the present invention are commercially available in that a receiver having a lower cost and size can be provided by providing a simpler demodulation algorithm than the conventional FSK demodulation method and the FSK receiver. It is an invention with industrial applicability, since the possibility of business is not only sufficient but also practically obvious.

1 is a diagram illustrating an example of an FSK;

2 is a diagram illustrating a demodulation method of an FSK receiver using a zero crossing function according to an embodiment of the present invention;

3 is a block diagram of an FSK receiver according to an embodiment of the present invention;

4 is a flowchart illustrating a demodulation method according to an embodiment of the present invention;

5A to 5C are diagrams showing examples in the frequency domain for explanation of the present invention.

<Description of Symbols for Main Parts of Drawings>

110: RF processing unit 120: demodulation unit

130: control unit 140: memory unit

150: frequency correction 160: feedback frequency correction

Claims (17)

An RF processor for receiving a RF signal and converting the signal into an IF signal; Extracting a first zero crossing point and a second zero crossing point from the IF signal, extracting a period of frequency using the time between the extracted first zero crossing point and the second zero crossing point, and then using the period. A demodulation unit which extracts a frequency and demodulates the digital data by comparing with a boundary frequency; And a frequency correction unit for calculating a correction boundary frequency using an average of intervals between crossing points in the IF signal, and correcting the correction boundary frequency with a new boundary frequency. The method of claim 1 The frequency correction A FSK receiver using zero crossing demodulation, characterized in that the correction boundary frequency is calculated using the following equation.

F ' _if is the calibration boundary frequency δ _n is the time between the nth zero crossing point and the n + 1 zero crossing point The method of claim 1 After calculating the average of the interval between the crossing points for each of the decoded digital data value, extracting the feedback boundary frequency by calculating the average of the calculated average value, and further comprising a feedback frequency correction for calculating this as a new boundary frequency An FSK receiver using zero crossing demodulation. The method of claim 3, The feedback frequency correction FSK receiver using zero crossing demodulation, characterized in that to calculate the feedback boundary frequency using the following equation.

The method of claim 1 The demodulation unit And sampling the IF signal at sampling intervals at regular intervals. The frequency period extraction is And calculating the number of samplings between the first and second zero crossing points, and extracting the number of samplings using the calculated number of samplings and the sampling unit time. The method of claim 1 The zero crossing point is The FSK receiver using zero crossing demodulation, characterized in that the size of the IF signal is changed from-to +. The method of claim 1 The demodulation unit If the extracted frequency is greater than the boundary frequency demodulated to 1, otherwise it is demodulated to 0 FSK receiver using a zero crossing demodulation. The method of claim 1 The FSK receiver using a zero crossing demodulation, characterized in that the ZigBee receiver. A radio wave reception step of receiving an RF signal modulated by the FSK receiver and converting the RF signal into an IF signal; A frequency correction step of calculating a correction boundary frequency using an average of intervals between crossing points in the IF signal, and correcting it to a new boundary frequency; And a demodulating step of extracting each frequency period using the interval between the crossing points in the IF signal, extracting a frequency using the same, and demodulating the digital data by comparing the boundary frequency with the boundary frequency. Demodulation method of FSK receiver using The method of claim 9 The demodulation step A first zero crossing extraction step of extracting a first zero crossing point that is a first zero crossing point detected from the IF signal; A second zero crossing extraction step of extracting a second zero crossing point, which is a zero crossing point first found again after the first zero crossing point; A frequency period extracting step of extracting a period of frequency by using the time between the first zero crossing point and the second zero crossing point; A frequency extracting step of extracting a frequency using the extracted frequency period; And a digital data demodulation step of demodulating the extracted frequency and the boundary frequency into digital data. The method of claim 9 The frequency correction step A demodulation method of an FSK receiver using a zero crossing function, characterized in that the correction boundary frequency is calculated using the following equation.

F ' _if is the calibration boundary frequency δ _n is the time between the nth zero crossing point and the n + 1 zero crossing point The method of claim 9 After calculating the average of the interval between the crossing points for each of the decoded digital data value, the feedback frequency correction step of calculating the average of the calculated average value to extract the feedback boundary frequency, and then calculates the feedback boundary frequency as a new boundary frequency; Demodulation method of the FSK receiver using a zero crossing function, characterized in that. The method of claim 12, The feedback frequency correction step A demodulation method of an FSK receiver using a zero crossing function, characterized in that the feedback boundary frequency is calculated using the following equation.

The method of claim 10 The method further includes a sampling step of sampling the IF signal with a sampling unit time at regular intervals. Frequency period extraction step And demodulating the number of samplings between the first and second zero crossing points, and extracting the number of samplings using the calculated number of samplings and the sampling unit time. The method of claim 9 The zero crossing point is Demodulation method of the FSK receiver using a zero crossing function, characterized in that the size of the IF signal is changed from-to +. The method of claim 9 The digital data demodulation step If the extracted frequency is greater than the boundary frequency, demodulates to 1; otherwise, demodulates to 0; demodulating a FSK receiver using a zero crossing function. The method of claim 9 The FSK receiver demodulation method of the FSK receiver using a zero crossing function, characterized in that the Zigbee receiver.

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