RU2234810C1 - Method and device for extracting information about doppler shift of signal carrier frequency - Google Patents

Abstract

FIELD: communications engineering; information and measurement devices.

SUBSTANCE: proposed method that can be used for extracting information about Doppler shift of signal carrier frequency in information and measurement devices without a priori information about modulating message using two-position frequency keying due to quadrature separation of input signal relative to center frequency rating with low-frequency filtration of cophasal and quadrature components and generation of complex signal from filtered-off components includes signal division into two equal components, frequency conversion of both components followed by low-frequency filtration, multiplication of filtered-off signals, and calculation of Fourier transform with respect to signal; in the process frequency of one signal component is converted in phase relative to signal center frequency rating and that of other component, in quadrature relative to same frequency; each of converted-frequency signal components converted is filtered in low frequency band, complex signal with real part equal to filtered-off cophasal signal and imaginary part equal to filtered-off quadrature signal are generated; Fourier-transform image of generated complex signal is calculated; argument of maximum of Fourier-transform image of signal is found in region of negative frequencies and argument of maximum of Fourier-transform image of signal, in region of positive frequencies; Doppler signal carrier frequency shift is obtained as half-sum of found maxima of arguments. Device implementing proposed method has splitter, first mixer , first low-band filter, second mixer, second low-band filter, Fourier-transform processor, heterodyne, phase shifter, and arithmetic unit.

EFFECT: enlarged functional capabilities.

2 cl, 1 dwg

Description

The invention relates to communication technology and can be used to extract information about the Doppler frequency shift of the carrier signal in information-measuring devices without a priori information about the modulating message.

The extraction of information on the Doppler frequency shift of the carrier signal is very important in systems of long-distance space communications with spacecraft (SC) such as Mars Polarlander, Mars Pathfinder [1] or with SCs of the type Voyager and Galileo [2].

There are a number of methods for extracting information about the Doppler shift of the carrier frequency for signals with on-off phase shift keying based on a priori knowledge of the information contained in the modulating message [5, 6], which significantly complicates the processing process [7] and makes them unacceptable in emergency situations when such information may not be available. To overcome these drawbacks, a method and device for extracting information about the Doppler frequency shift of the carrier signal with on-off phase shift keying, which do not require a priori knowledge of the information contained in the modulating message [7], were created.

However, at present, in systems of long-distance space communication with spacecraft, in paging communication systems, signals with on-off frequency shift keying (2CHMn or FSK - Frequency Shift Keying) continue to be widely used [3, 4, 8-10], for which methods of extracting information about Doppler frequency shift of the carrier signal [5-7] is not applicable.

For signals using spectrally effective modulation methods in the presence of a priori knowledge of the modulating message, it is possible to accurately extract information about the Doppler frequency shift of the carrier signal using the method [11]. Known for signals with 2 FMN, if the separation is equal to the minimum shift, methods for extracting information about the Doppler frequency shift of the carrier signal [12] without a priori information about the modulating message, based on fourth-order nonlinear operations, leading to a decrease in estimation accuracy [15], since in such operations the ratio of the power of the carrier signal to the spectral density of the noise power decreases by about four times [8]. In addition, these methods of extracting information about the Doppler shift of the carrier frequency of the signal for signals with 2 FMN, when the separation between the manipulation frequencies is not equal to the minimum shift, is not applicable, since in non-linear operations with such a signal its carrier is not restored [8].

The closest to the proposed method of extracting information about the Doppler frequency shift of the carrier signal without a priori information about the modulating message, according to the totality of the actions used on the signal, is the method [7] based on a second-order nonlinear operation adopted as a prototype.

According to this method:

1. Divide the signal into two equal components.

2. The frequency of the first component of the signal is converted by mixing it with a heterodyne signal whose frequency is lower than the frequency of the carrier signal.

3. The second component of the signal is converted in frequency by mixing it with a second heterodyne signal, the frequency of which is higher than the frequency of the carrier signal.

4. Low-pass filter each of the frequency-converted signal components.

5. Multiply the filtered signals.

6. Low-pass filter the result of multiplication.

7. Find the Fourier transform of the filtered multiplication result.

The disadvantage of the prototype method is the impossibility of extracting information about the Doppler frequency shift of the carrier signal with on-off frequency manipulation, because when used in the prototype method of non-linear operations with such a signal, its carrier is not restored [8].

The prototype device [7] is connected to its first input through a splitter, a first mixer and a first low-pass filter (LPF) to the first input of the multiplier, the second input of which is connected to the second input of the splitter through a second mixer and a second LPF connected in series. Between the Fourier processor, the output of which is the output of the prototype device, and the output of the multiplier, the third low-pass filter is turned on. The first local oscillator is connected to the second input of the first mixer of the prototype device, and the second local oscillator is connected to the second input of the second mixer of the prototype device.

The disadvantage of the prototype device is also the impossibility of extracting information about the Doppler frequency shift of the carrier signal with on-off frequency manipulation.

The technical result of the invention is the ability to extract information about the Doppler frequency shift of the carrier signal with on-off frequency manipulation due to the quadrature decomposition of the input signal relative to the nominal frequency of the central frequency (with low-frequency filtering in-phase and quadrature components), the formation of a complex signal from the filtered components and through the use of discrete components in the Fourier transform of the complex signal.

The technical result is achieved in that in a method for extracting information about the Doppler frequency shift of the carrier signal, including dividing the signal into two equal components, frequency conversion of both components, followed by low-pass filtering of each of the frequency-converted signal components, and calculating the Fourier transform of the signal, according to the invention one signal component is converted in frequency in phase with respect to the nominal center frequency of the signal, the other is quadrature, with respect to the same frequency you filter each of the frequency-converted signal components in the low-frequency band equal to the half-width of the signal spectrum band, form a complex signal with the real part equal to the filtered in-phase signal and the imaginary part equal to the filtered quadrature signal, the Fourier transform is calculated from the generated complex signal , determine the maximum argument of the Fourier transform of the signal in the region of negative frequencies and the maximum argument of the Fourier transform of the signal in the region of positive frequencies, and the Doppler shift the carrier frequencies of the signal are obtained as half the sum of the maximum arguments found.

The method is implemented by a device for extracting information about the Doppler frequency shift of the carrier signal, its input connected through a series-coupled splitter and a first mixer to the first low-pass filter (LPF), while the second low-pass filter is connected to the second input of the splitter through a second mixer containing a Fourier processor and the local oscillator connected to the second input of the first mixer, according to the invention, the Fourier processor is integrated, in which the input of the actual signal component is connected to the output the first low-pass filter, and the input of the imaginary component of the Fourier processor signal is connected to the output of the second low-pass filter, the second input of the second mixer is connected to the local oscillator output through a phase shifter, and an arithmetic device is connected to the output of the Fourier processor, the output of which is the output of the device.

The drawing shows a structural diagram of a device in which the proposed method is implemented.

According to the proposed method:

1. Divide the signal into two equal components.

2. One component of the signal is converted in frequency in phase with respect to the nominal center frequency of the signal.

3. The other component of the signal is converted in frequency quadrature relative to the nominal center frequency of the signal.

4. Filter each of the frequency-converted signal components in the low-frequency band equal to the half-width of the signal spectrum band.

5. A complex signal is formed with the real part equal to the filtered in-phase component of the signal and the imaginary part equal to the filtered quadrature component of the signal.

6. The Fourier transform of the generated complex signal is calculated.

7. Determine the maximum argument of the Fourier transform of the signal in the region of negative frequencies and the maximum argument of the Fourier transform of the signal in the region of positive frequencies.

8. Get the Doppler frequency shift of the carrier signal as half the sum of the found maximum arguments.

As is known [13, 14], a signal with on-off frequency manipulation can be represented as

where φ (t) is the phase and ƒ _m (t) is the frequency deviation of the carrier frequency ƒ ₀ = ω ₀ / 2π. The signal alphabet h ₁ , h _{2 of} expression (1) in the general case can have an arbitrary shape on an interval equal to or greater than the duration of the transmitted symbol T = 1 / ƒ _m = 2π / ω _m , where ƒ _m is the frequency of signal manipulation, and ω _m - cyclic frequency of signal manipulation, respectively [14]. In the case under consideration, a signal with two-position frequency manipulation, we can restrict ourselves to the rectangular shape of the pulses of the alphabet h ₁ , h ₂ . In this case, a signal model s (t) that is simpler and more convenient for analysis of the particular case under consideration can be used

s _k (t) = Acos (ω _k t + Θ _k ), k = 1,2

where ω _k = ω ₁ or ω _{2 the} frequency of pressing and wrung out at the frequency separation ω _s , respectively equal

a Θ _k = Θ ₁ or Θ ₂ is the random initial phase of the signals s ₁ (t) and s ₂ (t), respectively.

The selection of signals s _k (t) is carried out independently on each time interval of duration T. The signal s (t) represented by expression (2) can be identically transformed to the following form

Where

a

In expression (6), random variables {m _n }, equally likely to take the values {± 1}, represent bits of transmitted information, and the function p (t) expresses the shape of a rectangular modulating pulse. By direct substitution of s ₁ (t) and s ₂ (t) from (2) into expressions (4) - (6), it is easy to verify that the signal s (t) in expression (4) takes the values A cos (ω ₁ t + Θ ₁ ) for m _n = 1 and, accordingly, A cos (ω ₂ t + Θ ₂ ) for m _n = -1.

Obtained, in the form of expressions (4) - (6), the representation of the signal s (t) with two-position frequency manipulation allows us to conclude that it contains the deterministic component s ₊ (t), which is the sum of two cosines with frequencies ω ₁ , and ω ₂ symmetrically located relative to the nominal frequency of the carrier frequency ω ₀ , and the random component s _r (t) equal to

In this case, the signal (4) can be rewritten in the form

Due to the linearity of the direct Fourier transform (Fourier transform of the signal in the time domain to the frequency domain), the spectrum of the sum of the two terms of the signal (8) is equal to the sum of the spectra of the terms [16], while the first component of the signal (8), due to the determinants s ₁ (t) and s ₂ (t), create a discrete (linear) S ₁ (ƒ) component of the signal spectrum S (ƒ), and the second, due to the randomness of the modulating function m (t), a noise, continuous S _c (ƒ) component signal spectrum

For the sum of two cosines s ₊ (t) in accordance with expressions (2) - (5), the spectrum of S ₁ (ƒ) is [16]

The result can be used to extract information about the Doppler frequency shift of the carrier signal with on-off frequency shift keying. To simplify the analysis, we consider below only the most informative relative to the Doppler frequency shift of the carrier component of the signal s ₊ (t).

Let the carrier frequency of the signal, due to the Doppler shift, be ω _D = ω ₀ + Δ ω _D , then after quadrature decomposition of the signal s ₊ (t), as components of the signal s (t), relative to the nominal frequency of the signal

и, соответственно, квадратурный

сигналы (волнистая черта над сигналом обозначает применение к нему операции фильтрации) можно представить в видеAfter low-pass filtering, components with double carrier frequency are suppressed; the resulting filtered in-phase

and, accordingly, quadrature

signals (a wavy line above the signal indicates the application of filtering operations to it) can be represented as

₁₊(t) и

_Q+(t) в комплексный сигнал s_c+(t)After combining the signals

₁₊ (t) and

_{Q +} (t) to the complex signal s _{c +} (t)

when using the Euler formula for representing complex numbers, we can obtain the complex signal s _{c +} (t) in the following form

From the expression (16) it obviously follows that, for Δ ω _D = 0, the spectrum of the complex signal s _{c +} (t) is

and has a maximum in the region of negative frequencies at a frequency equal to -ƒ _s / 2, and a maximum in the region of positive frequencies at a frequency equal to ƒ _s / 2, and for Δ ω _D ≠ 0, the spectrum of the complex signal s _{c +} (t) is

and has a maximum in the region of negative frequencies at a frequency equal to -ƒ _c / 2 + Δ ƒ _D , and a maximum in the region of positive frequencies at a frequency equal to ƒ _s / 2 + Δ ƒ _D , so the half-sum of these maximum arguments will exactly give the Doppler value frequency shift of the carrier signal.

A device that implements the proposed method for extracting information about the Doppler frequency shift of the carrier signal (see the drawing) is connected through its successively connected splitter 1 and the first mixer 2 to the input of the first low-pass filter 3. The second low-pass filter 4 is connected to the second input of the splitter 1 through the second mixer 5 The local oscillator 6 is connected to the second input of the first mixer 2. The Fourier processor 7 is integrated. The input of the real component of the signal of the Fourier processor 7 is connected to the output of the first low-pass filter 3. The input of the imaginary component of the signal of the Fourier processor 7 is connected to the output of the second low-pass filter 4. The second input of the second mixer 5 is connected to the output of the local oscillator 6 through the phase shifter 8. To the output of the Fourier processor 7 connected arithmetic device 9, the output of which is the output of the device.

The proposed device operates as follows.

The modulated signal in a mixture with noise is fed through a device input to a splitter 1. One of the branched signal components goes to the first mixer 2, the other to the second mixer 3. In the first mixer 2, the branched signal component is in phase mixed with the local oscillator 4. In the second mixer 3 another branched component of the signal — through the phase shifter 5 — is quadrature mixed with the signal of the local oscillator 4. The conversion products from the outputs of the first 2 and second 3 mixers are filtered through the first 6 and second 7, respectively Low-pass filter. The signal from the output of the first low-pass filter 6 is fed to the input of the real component of the signal of the Fourier processor 8. The signal from the output of the second low-pass filter 7 is fed to the input of the imaginary component of the signal of the Fourier processor 8. The Fourier processor 8 calculates the Fourier transform of the complex signal received in the device as the result of the above actions on the input signal. From the output of the Fourier processor 8, the Fourier image of the complex signal is supplied to the arithmetic device 9, where the argument of the maximum Fourier image of the signal in the region of negative frequencies and the argument of the maximum Fourier image of the signal in the region of positive frequencies are first determined, and then the Doppler frequency shift of the carrier signal is obtained as half the sum of the maximum arguments found.

Sources of information

l. Harcke, L., and G. Wood, Laboratory and Flight Performance of the Mars Pathfinder (15.1 / 6) Convolutionally Encoded Telemetry Link, TDA PR 42-129, January-March 1997, pp. 1-11, May 15, 1997.

2. Rebold, T.A., M. Tinto, S.W. Asmar and E.R. Kursinski, Neptune Revisited: Synthesizing Coherent Doppler From Voyager’s Noncoherent Downlink, TDA PR 42-131, July-September 1997, pp. 1-19, November 15, 1997.

3. On-board devices of satellite radio navigation. / Ed. B.C. Shebshaevich, M., Transport, 1988, 201 p.

4. BROADCAST STANDARD FOR THE USCG DGPS NAVIGATION SERVICE COMDTINST M16577.1, U.S. Department of Transportation United States Coast Guard, Washington, DC, April, 1993.

5. US Patent No. 4490829, Dec. 1984, Van Etten 375/1.

6. Great Britain Patent No. 2120489B, Feb 1986 GB.

7. US Patent No. 4,706,286, Sturza; Mark A., Method and circuit for extraction of Doppler information from a pseudonoise modulated carrier, November 10, 1987 (prototype method and device).

8. Spilker J. Digital satellite communications, M., Communications, 1979, 592 S.

9. Feher K. Digital communications: Satellite / Earth stations Engineering N-Y., Prentice-Hall, 1983.

10. DOCUMENT 705-98, SPECTRUM EFFICIENT MODULATION, Prepared by Frequency Management Group Range Commanders Council, Published by Secretariat Range Commanders Council U.S. Army White Sands Missile Range, New Mexico 88002-5110, December 1998.

11. US Patent No. 5535249, Miyashita Toshikazu, Precise detection of frequency error for bursts modulated by predetermined symbol sequence, July 9, 1996.

12. United States Patent No. 4384357, deBuda, et al. Self-synchronization circuit for a FFSK or MSK demodulator, May 17, 1983.

13. Aulin T. And Sundberg C.-E. "Calculating Digital FM Spectra by Means of Autocorrelation," IEEE Trans. Comm., COM-30, No. 5 (May 1982), pp. 1199-1208.

14. Rowe H.E. And Prabhu V.K. "Power Spectrum of a Digital FM signal," Bell System Technical Journal, vol. 54, No. 6 (July-August 1975), pp. 1095-1125.

15. Kay S. M., Fundamentals of Statistical Signal Processing: Estimation Theory, NJ, Prentice-Hall, 1993.

16. Radio engineering circuits and signals. / Ed. K.A. Samoilo. - M.: Radio and Communications, 1982, 528 p.

Claims (2)

1. The method of extracting information about the Doppler frequency shift of the carrier signal, including dividing the signal into two equal components, the frequency conversion of both components, followed by low-pass filtering of each of the frequency-converted signal components, multiplying the filtered signals and finding the Fourier transform from the signal, characterized in that one component of the signal is converted in frequency in phase with respect to the nominal center frequency of the signal, the other is quadrature relative to the same frequency, filter each of the frequency-converted signal components in the low-frequency band equal to the half-width of the signal spectrum band, form a complex signal with the real part equal to the filtered in-phase signal and the imaginary part equal to the filtered quadrature signal, find the Fourier transform from the generated complex signal, find the argument of the maximum of the Fourier transform of the signal in the region of negative frequencies and the argument of the maximum of the Fourier transform of the signal in the region of positive frequencies, and the Doppler frequency shift Signal noise can be obtained as half the sum of the maximum arguments found. 2. A device for extracting information about the Doppler frequency shift of the carrier signal, containing a series-connected splitter that is the input of the device, the first mixer and the first low-pass filter (LPF), while the input of the second LPF is connected to the second output of the splitter through the second mixer, as well as the Fourier a processor and a local oscillator connected to the second input of the first mixer, characterized in that the input of the real component of the Fourier processor signal that forms the complex signal and calculates the Fourier image of a multiplex signal is connected to the output of the first low-pass filter, and the input of the imaginary component of the Fourier processor signal is connected to the output of the second low-pass filter, the second input of the second mixer is connected to the local oscillator output through a phase shifter, and an arithmetic device is connected to the output of the Fourier processor, the output of which is the output of the device.