KR20180124501A - Apparatus and method for estimating hopping frequency - Google Patents

Abstract

The present invention relates to an apparatus for estimating hopping frequency of a signal communicating in an expansion spectrum manner and a method thereof. The apparatus with good performance comprises: a signal analyzing unit applying short-time Fourier transform (STFT) to an input signal and calculating spectrogram on the input signal based on the input signal applied with STFT; and a carrier frequency estimating unit estimating carrier frequency on the input signal using the spectrogram.

Description

[0001] APPARATUS AND METHOD FOR ESTIMATING HOPPING FREQUENCY [0002]

The present invention relates to an apparatus and method for estimating a hopping frequency, and more particularly, to an apparatus and method for estimating a hopping frequency of a signal communicated in a spread spectrum manner.

The spread spectrum method is used in various fields due to its strong advantages in noise, interference, and disturbance signals. Among them, the frequency hopping spread signal scheme shifts the carrier frequency to the hopping frequency according to the pseudorandom code sequence, and randomly hopes and transmits various frequency bands. In order to avoid interference with various signals, the commercial frequency-hop spread signal system utilizes a large number of frequency bands as a carrier frequency and quickly transitions.

Especially, the frequency hopping spreading signal is a signal suitable for military communication because it has a great resistance to the intentional disturbance signal of the enemy when it does not know the random leaping pattern, and it is also impossible to tap. Therefore, the problem of hop frequency estimation must be solved due to the characteristics of the military communication system which must intercept the enemy transmission signal.

In this regard, there is a " Hop-timing estimation for FH signals using a coarsely channelized receiver (IEEE) ", which was previously disclosed by Aydin, Levent and Andreas Polydoros. Here, the technique described in this document is a method of estimating the jump timing of the hopping frequency by dividing the entire frequency into bands of the same size. In such a case, there is a problem that it is difficult to realize the hopping frequency hopping timing in a real system because the amount of calculation is very large.

Therefore, a new estimation technique that is improved in terms of the amount of calculation compared with the prior art and that can be implemented in an actual system is also required.

Korean Patent No. 1290902 (Name: Interference signal avoiding apparatus and method for frequency hopping spreading system)

1. Aydin, Levent, and Andreas Polydoros. "Hop-timing estimation for FH signals using a coarsely channelized receiver.", IEEE transactions on communications 44.4 (1996): 516-526. 2. Simon, Marvin K., et al. "Hop timing estimation for noncoherent frequency-hopped M-FSK intercept receivers." IEEE transactions on communications 43.2 / 3/4 (1995): 1144-1154.

It is an object of the present invention to provide an apparatus and method for estimating a hopping frequency that can be implemented realistically by greatly improving the calculation amount from the prior art.

According to an aspect of the present invention, there is provided an apparatus for estimating a hopping frequency of a signal communicated by a spread spectrum method, the apparatus comprising: a receiver for applying a short-time Fourier transform (STFT) to an input signal, A signal analyzer for calculating a spectrogram of an input signal; And a carrier frequency estimator for estimating a carrier frequency of the input signal using the spectrogram.

Also, the hopping frequency estimation apparatus according to an embodiment of the present invention includes a power spectral density calculation unit for calculating a spectral density of a spectrogram with respect to an input signal; A noise eliminator for eliminating the influence caused by the non-orthogonal component and the noise signal in the input signal by performing threshold judgment on the power spectral density; And a filter unit for further removing the influence caused by the non-orthogonal component in the power spectral density by using the threshold determination result for the power spectral density as the input of the local maximum value filter.

The carrier frequency estimator may estimate the carrier frequency of the input signal based on the power spectral density at which the influence of the non-orthogonal component and the noise signal is removed.

The carrier frequency estimator may estimate the carrier frequency of the input signal by applying a local average to the power spectral density when the input signal is a signal employing the frequency modulation and modulation scheme.

According to another aspect of the present invention, there is provided a method of estimating a hopping frequency of a signal communicated by a spread spectrum method, comprising: applying a STFT to an input signal by a signal analyzing unit; Calculating a spectrogram of the input signal based on the input signal to which the STFT is applied by the signal analysis unit; And estimating a carrier frequency for the input signal using the spectrogram by a carrier frequency estimating unit.

Also, a hopping frequency estimation method according to an embodiment of the present invention includes: calculating a power spectral density of a spectrogram with respect to an input signal by a power spectral density calculation unit; Removing the effects caused by the non-orthogonal component and the noise signal in the input signal by performing a threshold decision on the power spectral density by noise elimination; And further removing, by the filter unit, the influence caused by the non-orthogonal component in the power spectral density by using the threshold determination result for the power spectral density as an input of the local maximum value filter.

In addition, the step of estimating the carrier frequency for the input signal may be based on the power spectral density at which the effects of the non-orthogonal component and the noise signal are removed.

In addition, estimating the carrier frequency for the input signal may be accomplished by applying a local average to the power spectral density, where the input signal is a signal employing a frequency modulation transition scheme.

According to the apparatus and method for estimating the hopping frequency of the present invention, the complexity of the algorithms used for estimating the hopping frequency is not high based on the STFT and various filters and the calculation amount is small.

Further, according to the apparatus and method for estimating the hopping frequency of the present invention, since the estimation is performed based on the power density of the frequency, there is an advantage that the hopping period and the time synchronization are not met.

1 is a block diagram of a hopping frequency estimation apparatus according to an embodiment of the present invention.
2 is a conceptual diagram illustrating a hopping frequency estimation method according to the prior art.
FIG. 3 is a conceptual diagram for explaining an advantage of the hopping frequency estimation apparatus according to an embodiment of the present invention compared to the prior art.
4 is a flowchart illustrating a hopping frequency estimation method according to an embodiment of the present invention.

The present invention will now be described in detail with reference to the accompanying drawings. Hereinafter, a repeated description, a known function that may obscure the gist of the present invention, and a detailed description of the configuration will be omitted. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art. Accordingly, the shapes and sizes of the elements in the drawings and the like can be exaggerated for clarity.

Hereinafter, a hopping frequency estimation apparatus 100 according to an embodiment of the present invention will be described.

1 is a block diagram of a hopping frequency estimation apparatus 100 according to an embodiment of the present invention. As described above, the hopping frequency estimation apparatus 100 according to an embodiment of the present invention is characterized by estimating a hopping frequency of a signal communicated by a spread spectrum method with a small calculation amount. The hopping frequency estimation apparatus 100 according to an embodiment of the present invention includes a converter 110, a signal analysis unit 120, a power spectrum density calculation unit 130, a noise removing unit 140, a filter unit 150 and a carrier frequency estimating unit 160. [ Referring now to FIG. 1, a description will be given of each configuration included in the hopping frequency estimation apparatus 100 according to an embodiment of the present invention.

The converter 110 functions to convert an input signal into a digital signal. Generally, since the signal communicated in a spread spectrum manner is an analog signal, the converter 110 converts the input signal y (t), which is an analog signal, to a digital signal y [n] ). For this purpose, the converter 110 preferably comprises an ADC (analog-to-digital converter).

The signal analyzing unit 120 applies a short-time Fourier transform (STFT) to the input signal y [n] and outputs the input signal Y (t, f) (T, f) for the input signal Y (t, f). Here, t denotes time and f denotes a sampled frequency. In addition, the STFT (short-time Fourier transform) is a device for analyzing an input signal by time and frequency. For example, STFT is a method of arranging a windowed input signal by N tap Fast Fourier transform (FFT) on a single chip of one period.

Here, the reason why STFT is used without receiving FFT and receiving the entire signal is that STFT is better suited for different parameter estimation and frequency resolution. In STFT, the signal can be estimated with time and frequency, so it is possible to know the hop period, and it is easy to estimate the time related parameters such as the cycle of one bit.

Also, STFT has poor frequency resolution compared to FFT. However, this point is rather advantageous because a fast frequency hopping system is not a form in which a signal is spread over a wide band, but is energized at a hopping frequency in one hop. In addition, when noise is added, rather than expressing detailed changes due to noise, it is necessary to extract only a frequency component in a chip rather than a chip.

In other words, the signal analyzer 120 can analyze the input signal converted into the digital signal through the STFT instead of the FFT. Thereafter, the signal analyzer 120 calculates the spectrogram P (t, f) for the input signal by squaring the magnitude of the input signal y (t, f) indicating the result of applying the STFT.

The power spectral density calculation unit 130 calculates the power spectral density of the spectrogram with respect to the input signal. That is, the power spectral density calculation unit 130 obtains the power spectral density S (f) for the spectrogram P (t, f). As an example, there is a method in which the spectrogram (P (t, f)) obtained previously is averaged over time. In this process, it is possible to know which frequency component has a signal.

The noise eliminator 140 performs a threshold determination on the power spectral density S (f) to eliminate the influence caused by the non-orthogonal component and the noise signal in the input signal. Here, when the threshold determination function used in the threshold determination is T, T can be expressed by the following equation (1).

In Equation (1), M represents the maximum value of S (f), and p represents a real number between 0 and 1. For example, if p is 0.1, values less than or equal to 0.1 of the maximum value of S (f) are set to 0, and larger values are retained.

)를 국부 최댓값 필터(Local maximum filter)의 입력으로 이용함으로써 전력 스펙트럼 밀도(S(f))에서 비직교 성분에 의해 발생하는 영향을 제거하는 기능을 한다. 국부최댓값필터는 중간값을 기준으로 좌우 M(M은 자연수)개의 값과 비교해 중간값이 가장 클 경우 값을 유지하고, 아닐 경우 0으로 만들어 주는 필터이다. 예시로 3탭 국부최댓값 필터는 피크 검출기이다. 이는 문턱판정에서 지워지지 않는 큰 비직교 성분을 제거하는 역할과 정확한 도약 주파수를 검출하기 위함이다.The filter unit 150 outputs a threshold determination result (S (f)) for the power spectral density S

) As an input to the local maximum filter to eliminate the influence caused by the non-orthogonal component in the power spectral density S (f). The local maximum filter is a filter that compares the value with the left and right M (M is a natural number) value based on the median value and keeps the value when the median value is largest, and makes the value zero. For example, the 3-tap local maximum filter is a peak detector. This is to detect a large non-orthogonal component that is not erased in the threshold judgment and an accurate hopping frequency.

The carrier frequency estimator 160 estimates the carrier frequency of the input signal using the spectrogram. That is, the carrier frequency estimator 160 may estimate the carrier frequency of the input signal based on the power spectral density at which the influence of the non-orthogonal component and the noise signal is removed.

When the input signal is a signal employing a frequency modulation transition method, there is a need to estimate the hopping frequency in detail. In this case, the carrier frequency estimator 160 may estimate the carrier frequency for the input signal by applying a local average to the power spectral density described above, because the carrier frequency estimator 160 often symmetrically modulates the center frequency of the hopping frequency.

As described above, the hopping frequency estimation apparatus 100 according to an embodiment of the present invention is based on STFT and various filters. The complexity of the algorithms used is not high and the amount of computation is small. And it estimates based on the power density of the frequency, so it does not need time synchronization and does good performance without hop cycle estimation. As described above, in the conventional art, it is difficult to implement in an actual system because the calculation amount of the optimal algorithm for estimating the hop-timing is very large.

Therefore, the prior art has proposed a method of estimating hop-timing by dividing the entire frequency into bands of the same size. However, if an estimation algorithm using the hopping frequency estimation apparatus 100 according to an embodiment of the present invention is used instead of dividing all the frequencies into bands having the same size (see FIG. 2) in the estimation algorithm according to this method, The performance can be greatly improved in terms of the calculation amount since it is necessary to calculate only the hopping frequency without dividing the whole frequency as shown in Fig. And because the divided bands can be divided more precisely and narrowly, the noise can be reduced.

4 is a flowchart illustrating a hopping frequency estimation method according to an embodiment of the present invention. As described above, the hopping frequency estimation method according to an embodiment of the present invention is characterized by estimating a hopping frequency of a signal communicated by a spread spectrum method. A description will now be made of a hopping frequency estimation method according to an embodiment of the present invention with reference to FIG. Further, in the following description, the redundant description is omitted.

Step S110 is a step of converting the input signal into a digital signal by the converter. As described above, since the input signal is generally composed of an analog signal, step S110 may be performed by converting an analog signal into a digital signal for the estimation process described below.

Step S120 is a step of applying STFT to the input signal by the signal analysis unit. As described above, STFT represents a device for analyzing an input signal by time and frequency, and can estimate a signal by time and frequency. Thus, using the STFT, the signal can be estimated with time and frequency, so that the hop period can be known and it is easy to estimate the parameters related to the time, such as the cycle of one bit.

In step S130, the spectrogram of the input signal is calculated based on the input signal to which the STFT is applied by the signal analysis unit. As described above, in step S130, the spectrogram can be derived by squaring the magnitude of the signal to which the STFT is applied.

Step S140 is a step of calculating the power spectral density of the spectrogram with respect to the input signal by the power spectral density calculating unit. Step S140 may be performed, for example, by taking an average of the spectrogram over time, and it may be determined through step S140 which frequency component the signal is present.

Step S150 is a step of removing the influence caused by the non-orthogonal component and the noise signal in the input signal by performing the threshold determination on the power spectral density by the noise elimination. Here, the step S150 may be performed based on Equation (1), and a description thereof will be described in detail above, and redundant description will be omitted.

Step S160 is a step of removing, by the filter unit, the influence caused by the non-orthogonal component in the power spectral density by using the threshold determination result on the power spectral density as the input of the local maximum value filter.

In step S170, the carrier frequency estimating unit estimates the carrier frequency of the input signal using the spectrogram. Here, step S170 may be performed based on the power spectral density at which the influence of the non-orthogonal component and the noise signal is removed. Also, the step S170 may be performed by applying a local average to the power spectral density when the input signal is a signal employing a frequency modulation transition scheme.

As described above, an optimal embodiment has been disclosed in the drawings and specification. Although specific terms have been employed herein, they are used for purposes of illustration only and are not intended to limit the scope of the invention as defined in the claims or the claims. Therefore, those skilled in the art will appreciate that various modifications and equivalent embodiments are possible without departing from the scope of the present invention. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: Hopping frequency estimation device
110: converter 120: signal analysis unit
130: Power spectral density calculation unit 140: Noise removing unit
150: filter unit 160: carrier frequency estimator

Claims (8)

An apparatus for estimating a hopping frequency of a signal communicated in a spread spectrum manner,
A signal analyzer for applying a short-time Fourier transform (STFT) to an input signal and calculating a spectrogram of the input signal based on the input signal to which the STFT is applied; And
And a carrier frequency estimator for estimating a carrier frequency of the input signal using the spectrogram. The method according to claim 1,
A power spectral density calculation unit for calculating a power spectral density of the spectrogram with respect to the input signal;
A noise eliminator for eliminating the influence caused by the non-orthogonal component and the noise signal in the input signal by performing a threshold decision on the power spectral density; And
Further comprising a filter unit that further removes an influence caused by non-orthogonal components in the power spectral density by using a threshold determination result for the power spectral density as an input of a local maximum value filter. 3. The method of claim 2,
Wherein the carrier frequency estimator estimates a carrier frequency for the input signal based on the power spectrum density in which the influence of the non-orthogonal component and the noise signal is removed. The method of claim 3,
Wherein the carrier frequency estimator estimates a carrier frequency for the input signal by applying a local average to the power spectral density when the input signal is a signal employing a frequency modulation shift scheme. A method for estimating a hopping frequency of a signal communicated in a spread spectrum manner,
Applying a STFT to an input signal by a signal analysis unit;
Calculating a spectrogram for the input signal based on the input signal to which the STFT is applied by the signal analyzing unit; And
And estimating a carrier frequency for the input signal using the spectrogram by a carrier frequency estimator. 6. The method of claim 5,
Calculating a power spectral density of the spectrogram for the input signal by a power spectral density calculation unit;
Performing a threshold determination on the power spectral density by noise cancellation to remove effects caused by non-quadrature components and noise signals in the input signal; And
Further comprising removing, by the filter unit, the influence caused by the non-orthogonal component in the power spectral density by using a threshold determination result for the power spectral density as an input to the local maximum value filter. Frequency estimation method. The method according to claim 6,
Wherein the step of estimating the carrier frequency for the input signal is based on the power spectral density at which the effects of the non-orthogonal component and the noise signal are removed. 8. The method of claim 7,
Wherein estimating the carrier frequency for the input signal is performed by applying a local average to the power spectral density when the input signal is a signal employing a frequency modulation shift scheme.

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