RU2207721C2 - Facility for search with use of delay of signals with sudden frequency change - Google Patents

Abstract

FIELD: radio engineering, communication systems with sudden change of frequency. SUBSTANCE: given facility realizes method of search during which duration of pulses across output of mixer formed by narrow-band interference is markedly greater than that of pulses of legitimate signal which makes it feasible to suppress narrow-band noises practically without distortion of pulse of legitimate signal thanks to employment of limitation and procedures of direct and inverse Fourier transform. EFFECT: increased noise immunity to narrow-band noises and as result diminished probability of false alarms. 4 dwg

Description

 The invention relates to the field of radio engineering and can be used in communication systems with an abrupt change in frequency.

 Known devices for searching for the delay of signals with frequency hopping, described in the monographs of R. K. Dixon "Broadband Systems". M.: Communication, 1979, pp. 191-192, Fig. 6, 9, V.I. Borisova et al., “Interference immunity of radio communication systems with signal expansion using the pseudo-random tuning of the operating frequency”, M .: Radio and communications, 2000, p. 219, Fig. 6.4. , the disadvantage of which is low noise immunity to narrowband interference.

 The closest in technical essence to the proposed device is a device for searching for complex signals by delay, described in the monograph by G. I. Tuzov "Statistical theory of the reception of complex signals", M .: Sov. Radio, 1977, p. 326, Fig. 7, 2b, adopted as a prototype.

In FIG. 1 shows a prototype diagram, which introduced the following notation:
1 - mixer (multiplier);
2 - band-pass filter;
3 - amplitude detector;
4 - a crucial unit;
5 - controlled clock;
6 - tunable frequency synthesizer (code sequence generator).

 The prototype device contains a series-connected mixer 1, the signal input of which is the input of the device, a bandpass filter 2, an amplitude detector 3, a deciding unit 4, a controlled clock generator 5 and a tunable frequency synthesizer 6, the output connected to the reference input of the mixer 1.

 In the prototype device, a delay search is performed by a variable clock frequency method, which is as follows.

At the first stage, the clock frequency of block 5 is set equal to f ₁ = f _T ± Δf, Δf << f _T ; where f _T is the clock frequency used in the formation of the signal with a jump in the transmitter. Due to this, the reference signal with an abrupt change in frequency slides (ahead or lags) relative to the input signal with an abrupt change in frequency, while the input and reference signals coincide periodically in time.

In block 1, the input mixture is multiplied (mixed) with a delay-sliding reference signal generated by block 6, and the reference signal differs from the input signal by the frequency shift of each of the frequencies by ΔF equal to the intermediate frequency of the receiver f _PR . The result of multiplication is filtered at the difference (intermediate) frequency in block 2. The voltage filtered in block 2 is detected by block 3, the voltage envelope is compared with the threshold in block 4. If the threshold is exceeded, block 4 generates an “I” command, which is sent to block 5. Upon receipt command "I" in block 5 sets the clock frequency f _T , while ensuring the synchronism in time of the input and reference code sequence (input and reference signals with a frequency jump).

 The disadvantage of the prototype is the high likelihood of false alarms when exposed to narrowband interference.

 To eliminate this drawback, the device for searching for delayed signals with an abrupt frequency change, comprising a first amplitude detector, a series-connected mixer, the first signal input of which is the input of the device, and a band-pass filter, connected in series the first decision unit and the controlled clock generator, as well as tunable frequency synthesizer, the output of which is connected to the second reference input of the mixer, the first commutator is connected in series, the unit is direct the Fourier transform, the first limiter, the inverse Fourier transform block, the second amplitude detector, the first drive, the second decision block, the output of which is connected to the first input of the OR element, as well as the second limiter, second drive, the second switch and the clock divider, the input of which is connected to the output of a controlled clock generator and the third signal input of the second switch, the second signal input of which is connected to the output of the clock divider. In addition, the output of the second switch is connected to the input of the tunable frequency synthesizer and the second inputs of the direct and inverse Fourier transform blocks. The output of the bandpass filter is connected to the first signal input of the first switch, the first signal output of which is connected to the second limiter, the first amplitude detector, the second drive and the first decision unit, the output of which is connected to the second input of the OR element, the output of which is connected to the second control input of the first switch and the first control input of the second switch, respectively.

The structural diagram of the proposed device is shown in figure 2, where indicated:
1 - mixer;
2 - band-pass filter;
3, 12 - the first and second amplitude detectors;
4, 7 - the first and second decision blocks;
5 - controlled clock;
6 - tunable frequency synthesizer;
8, 15 - the first and second switches;
9 - block direct Fourier transform;
10, 16 - the first and second limiters;
11 - block inverse Fourier transform;
13, 17 - the first and second drives;
14 - clock divider;
18 is an OR element.

 The proposed device contains a series-connected mixer 1, the first signal input of which is the input of the device, and a bandpass filter 2, the output of which is connected to the first signal input of the first switch 8, the first signal output of which is connected to the second limiter 16, the first amplitude detector 3, and the second drive 17 and the first crucial unit 4, the output of which is connected to the first input of the OR element 18 and the control input of the controlled clock 5. 5. The second the channel output of the first switch 8 is connected to the direct Fourier transform unit 9, the first limiter 10, the inverse Fourier transform unit 11, the second amplitude detector 12, the first drive 13 and the second decision unit 7, the output of which is connected to the second input of the OR element 18, the output which is connected to the second control input of the first switch 8 and the first control input of the second switch 15, the second signal input of which is connected to the output of the clock divider And, the input of which it is single with the output of the controlled clock frequency generator 5 and the third signal input of the second switch 15, the output of which is connected to the second inputs of the direct Fourier transform unit 9 and the inverse Fourier transform unit 11 and through the tunable frequency synthesizer 6 to the second reference input of the mixer 1.

 The proposed device operates as follows.

The signal input of block 1, which is the input of the device, receives an input mixture containing a narrow-band interference and a periodic signal with a frequency hopping, which is a periodic sequence of N radio pulses of duration τ _o whose frequencies vary in accordance with a given pseudo-random code that is the same for the transmitter and receiver of this radio link.

 A signal with an abrupt change in frequency is supplied to the reference input of block 1, which differs from the input signal by shifting all frequencies of the tuning program by an amount equal to the intermediate frequency of the receiver.

 In the initial mode of operation, when the device is not in synchronism with the input signal, “0” commands are generated at the output of blocks 4 and 7, which are sent to block 18, the output of which also generates a “0” command, which is fed to the control inputs of blocks 8 and fifteen.

By this command, the output of block 2 through block 8 is connected to the first signal input of block 9, and the output of block 14 through block 15 is connected to the input of block 6, while clock pulses from block 14 are fed to block 6, whose clock frequency is (N + 1 ) times lower than the clock frequency f _{T of} block 5, which is achieved by dividing in block 14 the clock frequency of block 5 by (N + 1) times, where N is the number of frequencies in the tuning program of the transmitter and receiver.

In this mode of operation, scanning is performed on the delay of the reference signal with an abrupt change in the frequency generated by block 6, due to the fact that block 6 at each frequency of the tuning program stands for time τ ₁ = (N + 1) τ _o . During time τ _{1, the} transmitter manages to be tuned to all N frequencies of the tuning program, therefore, at the output of block 1, as a result of multiplying the input and reference signals at each of the N frequencies of the tuning program, a coincidence pulse of tuning programs of full duration τ _o , which occupies the same time position at all intervals τ ₁ corresponding to various frequencies generated by block 6.

The distance between the coincidence pulses at adjacent frequencies is τ ₁ = (N + 1) τ _o , the temporal position of the coincidence pulse in the interval τ ₁ relative to the start of the jump (moment of frequency change) carries information about the initial phase (delay) of the input signal with a frequency change reference signal.

 The foregoing is illustrated in Fig. 3, where Fig. 3a shows an input signal with a frequency-hopping (input code sequence), while for the sake of simplicity and clarity, the number of frequencies in the transmitter tuning program is selected to be three.

 Figure 3b shows the receiver tuning program and the matching pulses of the receiver and transmitter tuning programs at the output of block 1.

 In FIG. 3c, it is shown that the temporal position of the coincidence pulse determines the initial phase of the input signal with an abrupt change in frequency (input code sequence).

On fig.3g it is shown that the effect on the input of the device of narrow-band interference at a frequency f ₂ leads to the appearance on the second time interval τ ₁ of an interference pulse of duration τ ₁ = (N + 1) τ _o .
On figa and 3b, the numbers indicate the sequence numbers of the frequencies of the tuning program of the receiver and transmitter, respectively.

Отфильтрованная смесь через блок 8 поступает на блок 9, где на интервале τ₁ с использованием тактовых импульсов, поступающих на второй опорный вход блока 9 от блока 14 через блок 15, осуществляется процедура прямого преобразования Фурье, в результате чего на выходе блока 9 выделяется напряжение, характеризующее спектр сигнала и узкополосной помехи на его первом сигнальном входе.The result of multiplying the input mixture with the reference frequency signal is filtered in block 2 in the passband Δf, which ensures the passage of a coincidence pulse of duration

The filtered mixture through block 8 enters block 9, where, on the interval τ ₁ , using the clock pulses supplied to the second reference input of block 9 from block 14 through block 15, the direct Fourier transform procedure is performed, as a result of which the voltage is released at the output of block 9, characterizing the spectrum of the signal and narrowband interference at its first signal input.

Narrow-band interference at a frequency of f ₂ is allocated at the output of block 2 in the form of a radio pulse of duration τ ₁ , and the radio pulse of a useful signal has a duration of τ _o (Fig. 3d), while τ ₁ ≫τ _o , therefore, at the output of block 9 (Fig. 3d) the interference is highlighted in the form of a narrow and high pulse, and the useful signal is in the form of a low and wide pulse, since the spectrum of the interference pulse at the output of block 2 is (N + 1) times narrower than the spectrum of the signal pulse.

 In block 10, due to the limitation, the interference level is normalized, and at the output of block 10, the amplitude of the narrow interference pulse becomes equal to the amplitude of the wide signal pulse (Fig. 3f). From the output of block 10, the voltage is supplied to block 11, where, using the clock pulses from block 14 through block 15, the inverse Fypie transform procedure is performed, which transfers the process to the time domain.

At the output of block 11, the voltage at a frequency f ₂ is shown in FIG. 3g, where it is shown that the interference is a pulse of duration τ ₁ = (N + 1) τ _{o of} small amplitude due to its suppression due to the restriction in block 10, and the signal has a duration of τ _o .
From the output of block 11, voltage is supplied to block 12, where, due to detection, the envelopes of the interference pulses and the signal are extracted. In block 13, voltage is accumulated, and comparison of the accumulated voltage with the threshold is made in block 7. If the threshold is exceeded, block 7 generates an “I” command, transmitted through block 18 to block 15, which, by this command, connects the output of block 5 to the input of block 6.

At the same time, the “I” command from the output of block 7 through block 18 is fed to the control input of block 8, while the output of block 2 through block 8 is connected to series-connected blocks 16, 3, 17 and 4, after which the device enters the tuning mode with the duration of standing at each frequency equal to τ _o . The temporary position of the pulse of the useful signal in the interval τ ₁ determines the initial phase of the input signal (figb, c).

Therefore, when switching to an operating mode from clock pulses of duration τ _o generated by block 5, the input and reference signals with a frequency-like jump arriving at the first signal and second reference inputs of block 1 turn out to be synchronous.

 In this operating mode, the voltage from the output of block 2 is supplied through block 8 to block 16, where the amplitude of the pulses is normalized due to their limitation (in order to attenuate the influence of pulses from narrow-band interference). From the output of block 16, the level-normalized pulses are sent to block 3, where, due to their amplitude detection, the envelopes of the pulses are accumulated, which accumulate in block 17, the accumulated voltage is compared with a threshold (fixed) in block 4, the excess of which means the end of the search procedure. After the search for the delay is completed, the device, by a command from block 4 to the control input of block 5, enters the delay tracking mode. At the same time, the command from block 4 is sent to block 18, while the passage of the “I” command to the control inputs of blocks 8 and 15 is ensured.

After exceeding the threshold in block 7, the "I" command at the control inputs of blocks 8 and 15 is held by storing this command in block 7 for a time t _о equal to the signal processing time in blocks 16, 3, 17 and 4. After the time interval t _about , in case of exceeding the threshold in block 4, the command "I" is remembered by him for a time t _about . If after t _about the threshold is not exceeded in block 4, the command "0" is generated at its output, which puts the device into search (scan) mode by delay.

The block diagram of block 8 is shown in figure 4, where indicated:
81 ₁ and 81 ₂ - the first and second keys;
82 - inverter,
Block 8 contains the first key 81 ₁ and the second key 81 ₂ , the combined signal inputs of which are the signal input of the block. At the control input of block 81 ₁ , the control command is supplied through the inverter 82, and at the control input of block 81 ₂ it arrives directly.

 Block 6 can be performed as presented in the aforementioned monograph Tuzova G.I. "The statistical theory of complex signals", Moscow: Sov. radio, 1977, p. 67, Fig. 2, 8 (provided that the clock generator is outside the block).

 Blocks 4 and 7 can be made in the form of a series-connected comparison circuit with a threshold and a storage device (for example, a trigger with a reset).

 Blocks 9 and 11 can be made in the form of series-connected ADCs, processor, and DACs (see Vodyako A.I., Gornets N.N., Puzankov D.V. "High-performance data processing systems", Moscow: Vysshaya Shkola, 1997 G., p. 58-63, as well as the monograph by Shirman Y.D., Manzhosa VK "Theory and technique of processing radar information against the background of interference", M .: Sov. radio, 1981, p. 154- 160 and B. Gold, C. Rabder, “Digital Signal Processing,” Moscow: Sov. Radio, 1973, pp. 203-204).

Block 13 can be made in the form of a matched filter implemented on the delay line, between adjacent taps of which it is chosen equal to τ ₁ = (N + 1) τ _o , N taps of the delay line are combined in the adder.

Block 17 can be made either in the form of a matched filter on the delay line with a delay between adjacent taps equal to τ _o and with the union of N taps in the adder, or in the form of an integrator (low-pass filter).

In the prototype device, narrow-band noise at the output of the mixer is converted into pulses, the duration of which is equal to the pulse duration of the useful signal τ _o . The impact of narrow-band interference of a large level leads to a false threshold exceeding, while the noise immunity of the device is reduced due to the high probability of false alarms.

 In the claimed device, the duration of pulses from narrow-band interference at the output of the mixer is (N + 1) times longer than the duration of pulses of a useful signal, which allows the use of methods for suppressing pulses from narrow-band interference, based on the difference between their duration and pulse duration of a useful signal. Using the direct Fourier transform procedure allows you to convert a long pulse from narrow-band noise into a narrow and high pulse, when suppressed, the pulse of the useful signal is practically not distorted.

 Thus, by suppressing narrow-band interference in the inventive device, the probability of false alarms is reduced.

Claims (1)

 1. A search device for the delay of signals with frequency hopping, comprising a first amplitude detector, a serially connected mixer, the first signal input of which is the input of the device, and a bandpass filter, serially connected to the first decision unit and the controlled clock generator, as well as a tunable frequency synthesizer, the output of which is connected to the second reference input of the mixer, characterized in that the first switch is connected in series, the direct conversion unit Fourier, the first limiter, the inverse Fourier transform unit, the second amplitude detector, the first drive, the second decision block, the output of which is connected to the first input of the OR element, as well as the second limiter, the second drive, the second switch and the clock divider, the input of which is connected to the output a controlled clock generator and a third signal input of the second switch, the second signal input of which is connected to the output of the clock divider, in addition, the output of the second switch is connected to the input tunable frequency synthesizer and second inputs of the direct and inverse Fourier transform blocks, the output of the bandpass filter is connected to the first signal input of the first switch, the first signal input of which is connected to the second limiter, the first amplitude detector, the second drive and the first decision block, the output of which is connected to the second input of the OR element, the output of which is connected to the second control input of the first switch and the first control input of the second switch with Responsibly.

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