KR101648516B1 - Frequency Shift Keying Receiver for Error Correction based on Zero Crossing Demodulation and method thereof - Google Patents

Abstract

The present invention relates to an FSK receiving method based on zero crossing demodulation and an FSK receiver using the method. More specifically, the present invention extracts a zero crossing point from an IF signal, And a receiver using the method.

According to an aspect of the present invention, there is provided an FSK receiver using a zero crossing demodulation, the RF processor including an RF processor for receiving an RF signal and converting the RF signal into an IF signal, a first zero crossing point and a second zero crossing point, Extracting a frequency period using the time between the extracted first zero crossing point and the second zero crossing point, extracting a frequency using the period, and comparing the extracted frequency with a boundary frequency to demodulate the digital data into digital data .

Zero crossing, demodulation, FSK, receiver, ZigBee

Description

Technical Field [0001] The present invention relates to a correction FSK receiver using zero crossing demodulation and a control method thereof,

The present invention relates to an FSK receiving method based on zero crossing demodulation and an FSK receiver using the method. More specifically, the present invention extracts a zero crossing point from an IF signal, And a receiver using the method.

Frequency shift keying (FSK) is a modulation method in which a frequency of a sinusoidal wave having a constant amplitude is set to two, and the frequency assigned to one of the two frequencies is transmitted to the counterpart as the data changes to 1 or 0. It is more resistant to errors than the amplitude shift method (ASK) and is used in data transmission because of its relatively simple circuit. Such FSK is easy to construct and is strong in relatively long distance transmission, and is widely used in PSTN. FSK is mainly used for data transmission of relatively low speed (200 [BPS] or less asynchronously).

And is a modulation scheme in which the frequencies of the carrier waves are differently transmitted corresponding to digital signals (0 and 1 for binary FSK and 00, 01, 10, 11, etc. for 4FSK). In other words, binary 1 and 0 are transmitted in correspondence with two frequencies of a high frequency and a low frequency in which a center frequency is inserted, in such a manner that the frequency of a carrier wave is different for 0 and 1 of digital data.

1 is a diagram showing an example of FSK. As shown in the figure, these frequencies vary corresponding to 0 and 1, but the amplitude is always constant. That is, the FSK transmitter modulates bit 1 in correspondence with a high frequency and 0 with a low frequency. When the modulated radio wave is transmitted as an output signal, the FSK receiver that receives the modulated radio wave outputs a frequency to a digital (low frequency) frequency Demodulates the data.

As a result, it is most important for the FSK receiver to accurately and simply demodulate the frequency to digital data at this frequency. Therefore, there have been various demodulation schemes in the FSK receiver.

On the other hand, zero crossing (zero crossing) is a concept that is often used in a stable control and sound forge program mainly in electronic circuits. In other words, in an electronic circuit, an AC voltage has a sinusoidal shape. It is used to detect a moment when a voltage passes Ov and to control the ON / OFF at this point to prevent a sudden change in current. Also, when a waveform of a specific sound is loaded in a sound forge program, when the waveform of the negative waveform is shifted between positive and negative values according to the time axis, a point where the amplitude of the sound is zero is called a zero crossing , It is cut from this zero crossing point to another zero crossing point at the time of editing and is used for pasting back and forth.

In the present invention, a method for designing a more efficient and economical FSK receiver using the zero crossing is provided.

In the present invention, a method for designing a more efficient and economical FSK receiver using the zero crossing is provided.

According to an aspect of the present invention, there is provided an FSK receiver using a zero crossing demodulation, comprising: an RF processor for receiving an RF signal and converting the RF signal into an IF signal; Extracting a first zero crossing point and a second zero crossing point from the IF signal, extracting a frequency period using the time between the extracted first zero crossing point and the second zero crossing point, A demodulator for demodulating the IF signal by digital data after extracting the frequency, and a frequency corrector for calculating a correction boundary frequency using an average of intervals between the crossing points in the IF signal and correcting the corrected boundary frequency to a new boundary frequency.

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

F ' _if is the correction boundary frequency

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

Further comprising a feedback frequency correction unit for calculating an average of the intervals between the respective crossing points for each of the decoded digital data values and then calculating an average of the calculated average values to extract a feedback boundary frequency and then calculating the average value of the feedback frequency, .

The feedback frequency correction unit may calculate the feedback boundary frequency using the following equation.

The demodulation unit may further include a function of sampling the IF signal at sampling intervals of a predetermined interval, wherein the frequency period extraction is performed by calculating a sampling number between the first and second zero crossing points, It is preferable to extract it using the sampling unit time.

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

The demodulator demodulates the extracted frequency to 1 when the extracted frequency is larger than the boundary frequency, and demodulates it to 0 otherwise.

And the FSK receiver is a Zigbee receiver.

According to another aspect of the present invention, there is provided a method of demodulating an FSK receiver using a zero crossing function, the method comprising: receiving a modulated RF signal from an FSK receiver and converting the modulated RF signal into an IF signal; A frequency correction step of calculating a correction boundary frequency using an average of intervals between the crossing points in the IF signal and correcting the correction boundary frequency to a new boundary frequency and extracting each frequency period using the interval between the crossing points in the IF signal, And demodulating the digital data into digital data by comparing the extracted frequency with the boundary frequency.

And the demodulating step includes a first zero crossing extracting step of extracting a first zero crossing point which is a zero crossing point detected first in the IF signal; A second zero crossing extracting step of extracting a second zero crossing point which is a zero crossing point found first after the first zero crossing point; A frequency cycle extracting step of extracting a frequency cycle 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 demodulating step of demodulating the extracted frequency and the boundary frequency by using digital data.

It is also preferable that the frequency correction step calculates the correction boundary frequency using the following equation.

F ' _if is the correction boundary frequency

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

And a feedback frequency correction step of calculating an average of the intervals between the respective crossing points according to the decoded digital data values and then calculating an average of the calculated average values to extract a feedback boundary frequency and then calculating a new boundary frequency .

In addition, it is preferable that the feedback frequency correction step calculates the feedback boundary frequency using the following equation.

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

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

And the frequency extracting step is an inverse number of the extracted frequency period.

Preferably, the digital data demodulating step demodulates the digital data to 1 when the extracted frequency is larger than the boundary frequency, and demodulates the digital data to 0 otherwise.

And the FSK receiver is a Zigbee receiver.

As described in detail above, by using the FSK demodulation method using zero crossing and the FSK receiver using the zero crossing, it is possible to provide a receiver with less cost and size by providing a simpler demodulation algorithm than the conventional FSK demodulation method and FSK receiver .

2 is a diagram for explaining a demodulating 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 sampling the s (t) signal is shown. The first zero crossing point is t _n , and then the next zero crossing point is t _{n + 1} .

The zero crossing point has a magnitude of the signal at the n-th sampling time at each sampling. If the magnitude of the signal at the (n + 1) th sampling is +, the zero crossing point is included between the sampling times.

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

There are various methods for obtaining? n, but in this embodiment, the number of sampling between the zero crossings is used. First, the number of samples 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 12. The number of times of sampling may be multiplied by a unit sampling time which is one sampling time. That is, Tclk * 12 becomes? N.

Thereafter, the calculated delta n is a period, so that taking the reciprocal of this value, the frequency Fn is calculated. The calculated frequency Fn is compared with the boundary frequency to demodulate to a high frequency plane 1 larger than the boundary frequency, and demodulated to 0 when the frequency is smaller than the boundary frequency.

3 is a block diagram of an FSK receiver in accordance with an embodiment of the present invention.

The FSK receiver includes an RF processor 110, a demodulator 120, a controller 130, a memory 140, a frequency corrector 150, and a feedback frequency corrector 160. Of course, many other components are required, but components that are not directly related to the embodiments of the present invention or that are not problematic for a person skilled in the art to understand the present invention are omitted.

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

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

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

The frequency corrector 150 calculates a correction boundary frequency using the average of the intervals between the crossing points in the IF signal and corrects the corrected boundary frequency 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 digital data. That is, an average of the intervals between the crossing points in the IF signal corresponding to the digital data restored to 1 and an average of the intervals between the crossing points in the IF signal corresponding to the digital data restored to 0, And performs a function of correcting the corrected boundary frequency again by the frequency correction unit 150. [

The control unit 150 controls the overall components of the RF processor 110, the demodulator 120, the frequency corrector 150, the feedback frequency corrector 160, and other components of the FSK receiver .

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

The FSK receiver receives the modulated RF signal and converts it into an IF signal (S210).

Thereafter, sampling is performed for more than a predetermined number of the IF signals (S220). 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 that is the first detected zero crossing point in the IF signal is extracted (S230). The zero crossing point has a magnitude of the signal at the n-th sampling time at each sampling. If the magnitude of the signal at the (n + 1) th sampling is +, the zero crossing point is included between the sampling times. Therefore, the first zero crossing point is determined as a point at which the magnitude of the signal changes from - to +.

A second zero crossing point, which is a zero crossing point found first after the first zero crossing point, is extracted (S240). As before, the point where the magnitude of the signal changes from - to + after the first zero crossing is determined as the second zero crossing point.

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

Thereafter, when the sampling number is multiplied by the unit sampling time, the cycle value of the corresponding frequency is calculated (S260).

If the period is calculated as a reciprocal, the frequency of the signal is calculated (S270).

If the calculated frequency value is higher than the boundary frequency (S270-Y), the demodulation process is completed (S280).

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

The above-described demodulation process is an explanation in the case of 5a. Suppose that F _L means low frequency and F _H means high frequency. In other words, the transmitter demodulates the low frequency F _L when 0 is input and the high frequency F _H when 1 is input. On the other hand, the receiver calculates the frequency as described above and then demodulates it to 0 or 1 in comparison with the boundary frequency 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 are received as they are. At this time, as shown in FIG. 5B, the actual low frequency F ' _L actually received by the receiver becomes F _L +? F _if , and the actual high frequency F' _H becomes F _H +? F _if . That is, the closer the boundary frequency is to the intermediate value between the low frequency and the high frequency, the more accurate decoding is achieved.

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

However, the error value ΔF _if can not be obtained immediately, and the following method is used.

First, the corrected boundary frequency F ' _if according to the present invention is a value obtained by adding the error value (ΔF _if ) to the initial boundary frequency (F _if ) as shown in the following equation.

F ' _if = F _if +? F _if

In this case, F _L is the low frequency and F _H is the high frequency. The actual low frequency F ' _L received by the receiver becomes F _L + DELTA F _if , and the actual high frequency F' _H becomes F _H + DELTA F _if .

For convenience of calculation, it is assumed that the deviation value between the boundary frequency and the low frequency and the high frequency is F _mod . That is, the low frequency is F _if -F _mod and the high frequency is F _if + F _mod . If based on IEEE 802.15.4, the actual F _mod will be 500KHZ.

Meanwhile, the actual deviation value F ' _mod becomes + -F _mod + ΔF _if .

On the other hand, in the case of the receiver, as the accumulated data increases, the number of demodulated zeros becomes almost equal to the number of demodulated zeros. That is, P ₀ , which is the probability of _0, and P _{1, which} is _1, are almost similar. In this case, the average of the actual deviation values becomes equal to the error value as follows.

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

On the other hand, as described above, the actual frequency is calculated by the reciprocal of delta _n . Therefore, as in the following equation, the corrected boundary frequency F ' _if is an inverse number of the average value of the entire delta _n .

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

These feedback boundary frequencies are obtained by averaging the decoded frequencies of 1 and 0 as follows, and then averaging the two.

Up to now, a method for correcting a border frequency in FSK using zero crossing according to a preferred embodiment and an FSK receiver using the method 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 demodulating method using the zero crossing according to the present invention and the FSK receiver using the zero crossing according to the present invention can provide a receiver with less cost and size by providing a simpler demodulation algorithm than the conventional FSK demodulating method and FSK receiver, It is an invention that is industrially applicable because it has enough possibilities of business and can be implemented practically and clearly.

1 is a diagram showing an example of FSK,

2 is a diagram for explaining 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 in accordance with 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 explaining the present invention.

Description of the Related Art

110: RF processor 120: demodulator

130: control unit 140: memory unit

150: Frequency correction unit 160: Feedback frequency correction unit

Claims (17)

An RF processor for receiving an RF signal and converting the RF signal into an IF signal; Extracting a first zero crossing point and a second zero crossing point from the IF signal, extracting a frequency using a time between the extracted first zero crossing point and a second zero crossing point, comparing the frequency with a boundary frequency A demodulating unit for demodulating the digital data into digital data, and And a frequency correction unit for calculating a correction boundary frequency using an average of intervals between the crossing points in the IF signal and correcting the correction boundary frequency to a new boundary frequency. Claim 2 has been abandoned due to the setting registration fee. The method of claim 1, wherein The frequency correction unit Wherein the corrected boundary frequency is calculated by using the following equation.

F ' _if is the correction boundary frequency δ _n is the time between the nth zero crossing point and the (n + 1) th zero crossing point The method of claim 1, wherein Further comprising a feedback frequency correcting unit for calculating an average of the intervals between the respective crossing points for each of the decoded digital data values and then calculating an average of the calculated average values to extract a feedback boundary frequency and then calculating the average of the intervals, FSK receiver using zero crossing demodulation. Claim 4 has been abandoned due to the setting registration fee. The method of claim 3, wherein The feedback frequency correction unit Wherein the feedback boundary frequency is calculated using the following equation.

The method of claim 1, wherein The demodulator Further comprising the step of sampling the IF signal at sampling intervals of a predetermined interval, The period of the frequency is Wherein the number of sampling times between the first zero crossing point and the second zero crossing point is calculated and extracted using the calculated sampling number and the sampling unit time. delete delete delete Receiving a modulated RF signal from the FSK receiver and converting the received RF signal into an IF signal; A frequency correction step of calculating a correction boundary frequency by using an average of intervals between zero crossing points in the IF signal and correcting the correction boundary frequency to a new boundary frequency, And a demodulating step of demodulating the IF signal by using an interval between zero crossing points and comparing the frequency with the boundary frequency and demodulating the digital data into digital data. . The method of claim 9, wherein The demodulating step A first zero crossing extracting step of extracting a first zero crossing point that is the first detected zero crossing point in the IF signal; A second zero crossing extracting step of extracting a second zero crossing point which is a zero crossing point found first after the first zero crossing point; A frequency cycle extracting step of extracting a frequency cycle 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 And a digital data demodulating step of demodulating the extracted frequency by comparing the boundary frequency with digital data. Claim 11 has been abandoned due to the set registration fee. The frequency correction step Wherein the corrected boundary frequency is calculated by using the following equation.

F ' _if is the correction boundary frequency δ _n is the time between the nth zero crossing point and the (n + 1) th zero crossing point The method of claim 9, wherein Further comprising a feedback frequency correction step of calculating an average of the intervals between the respective crossing points for each of the decoded digital data values, calculating an average of the calculated average values to extract a feedback boundary frequency, And demodulating the FSK receiver using the zero crossing function. The method of claim 12, wherein The feedback frequency correction step Wherein the feedback boundary frequency is calculated using the following equation.

The method of claim 10, wherein Further comprising a sampling step of sampling the IF signal at sampling intervals of a predetermined interval, The frequency period extraction step Calculating a sampling number between the first and second zero crossing points, and extracting the sampling number using the calculated sampling number and the sampling unit time. delete delete delete

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