RU2206179C2 - Broadband signal receiving device - Google Patents

Abstract

FIELD: radio engineering; broadband signal communication systems. SUBSTANCE: receiving device has protective unit, pseudorandom sequence generator, correlator and spectrum distortion evaluation unit, logic circuit, and delay unit. Cut in protective unit are noise-affected spectrum sections formed due to deflection of some of protective unit strips. Spectrum distortion evaluating unit functions to detect noise-affected sections. Logic circuit serves to determine amount of pseudorandom sequence shift by quantity and location of connected strips. Noise immunity of proposed device is higher by 3-5 dB in case 80% of protective-unit strips are disconnected. EFFECT: enhanced noise immunity, reduced signal detection time. 1 cl, 3 dwg

Description

 The invention relates to the field of radio engineering and can be used in communication systems with broadband signals.

 To increase the reliability of communication signals with large bases are widely used. The implementation of large bases is achieved by complicating the signal structure and introducing frequency redundancy.

 Under conditions of exposure to concentrated (narrow-band) interference spectrum, frequency redundancy increases the likelihood of interference from the receiver operating band.

 Given the current employment of the main ranges of radio frequencies, this circumstance sets the task of protecting the receivers of complex signals from the action of narrow-band interference. The task of combating narrow-band interference is successfully solved by the introduction of a protection unit (KB). An example of a receiving device with a protection unit can be the device described in the article by Malyshev II, Zinchuk V. M., Shestopalov V. I., Novikov V. A. "Questions of Radio Electronics", a series of "Radio Engineering", vol. 3, 1973, pp. 14-23.

 When notching narrowband or, what is also concentrated on the interference spectrum, distortion of the signal autocorrelation function occurs. These distortions are manifested in a decrease in the main “peak” of the correlation function and an increase in lateral “peaks”. In addition to reducing the main “peak” of the correlation function and increasing the lateral ones, the irregularity of the spectrum of complex signals leads to the expansion of the main “peak” of the correlation function when cutting out the extreme parts of the spectrum of the useful signal and to narrowing it when cutting the middle part of the spectrum of the useful signal.

 This issue is considered in detail in an article by Bokka O.F. "Analysis of changes in the correlation function of a broadband signal during rejection of narrowband interference." "Questions of Radio Electronics", a series of "Radio Engineering", issue 1, 1975, pp. 88-95.

 Analyzing the materials of this article, we can conclude that the correlation function of the signal expands as many times as the frequency band decreases. In such analog devices, a decision is made to detect a signal without taking into account the phenomena described above and they have a significant drawback: when the frequency band is reduced by a factor of d, the signal base decreases by a factor of d, and the device does not respond to this fact. The noise immunity in this case drops by d times (power). So when you turn off 80% of the rulers of the protection unit, the loss is 7 dB.

 Note again that the correlation function decreases in amplitude and expands in duration in direct proportion to the decrease in the frequency band. Thus, the noise immunity decreases in proportion to the decrease in the amplitude of the correlation “peak”. However, there is also a decrease in the signal base, an increase in the duration of the correlation outlier, which, in principle, allows to reduce the search time with a serial-parallel correlation detector. This feature is not implemented in known detectors.

 Closest to the claimed technical solution is the receiver described in the article by Bokka O.F. “Signal Detection Against the Background of Colored Noise”, part 3 (“Communication Technology”, series “Radio Communication Technology”, issue 7, 1989, pp. 87-95).

The prototype receiver circuit is shown in FIG. 1, where the following notation is introduced:
1 ¹ -1 ^p - band-pass filters (FP);
2 ¹ -2 ^p - quadratic detectors;
3 ¹ -3 ^p - integrators;
4 ¹ -4 ^p - adjustable amplifiers;
5 - adder;
6 is a diagram for selecting a minimum;
7 - band-pass filter (FP);
8 - quadratic detector;
9, 14 - integrators;
10 is a block of time intervals;
11 - pseudo-random sequence generator (GPSP);
12 - multiplier;
13 - subtractive device;
15 is a block for calculating the square root;
16 - a quadrator;
17 is a decision scheme;
18 is a block scaling.

 The prototype receiver has the following functional relationships.

The input of the receiver is connected to the inputs of the bandpass filters of the rulers, each of which consists of a series-connected bandpass filter 1, a quadratic detector 2, an integrator 3, an adjustable amplifier 4. The outputs of the bandpass filters 1 ¹ -1 ^p , in addition, are connected to the second input of the adjustable amplifiers 4 ¹ -4 ^n, the third inputs of which are connected to the output selecting circuit 6, the minimum, the inputs of which are connected to the LF-outputs of integrators March ¹ -3 ^n. The outputs of the BZ rulers are connected to the adder 5, the HF output of which is connected to a series multiplier 12, an integrator 14, a decision circuit 17 and a series-connected bandpass filter 7, a quadratic detector 8, an integrator 9, a subtractor 13, a square root calculation unit 15 and a block scaling 18. The output of the scaling unit 18 is connected to the second input of the decision circuit 17, the output of the integrator 14 is connected to the input of the quadrator 16, the output of which is connected to the subtractor 13, the output of the decision circuit 17 with union of a block of time slots 10, a second input and whose output is connected to the pseudo-random sequence generator 11, second and third outputs of which are connected respectively to the multiplier 12 and the integrator 9 and 14.

 For a better understanding of the operation of the claimed technical solution, we enlarge the prototype receiver.

Combine in one block: a multiplier 12, a band-pass filter 7, a quadratic detector 8, integrators 9 and 14, a subtractor 13, a square root calculator 15, a quadrator 16, a decision circuit 17 and a scaler 18. We will call this block a correlator. The correlator performs the following functions:
1) signal search;
2) comparing it with a threshold;
3) develops a decision on the continuation of the search or its termination.

 Combine the N lines of the protection block, the adder 5 and the minimum 6 selection scheme into one block, which we will call the protection block in the future.

An enlarged diagram of the receiver of the prototype is presented in figure 2, where the following notation is introduced:
1 - protection unit (BZ);
2 - pseudo-random sequence generator (GPSP);
3 - correlator;
4 - block time intervals.

 The prototype receiver depicted in figure 2 has the following functional relationships.

 The input of the protection unit 1 is the input of the receiver. The RF output of the protection unit 1 is connected to the input of the correlator 3, the output of which is connected to the first input by the time interval unit 4, the other input and output of which is connected to the GPS 2, the first output of which is connected to the second input of the correlator 3.

 The prototype receiver of FIG. 2 as follows.

 The input signal plus interference passes through a protection unit (BZ), which determines the spectral density, in the frequency regions affected by noise, the BZ lines are turned off, which leads to a decrease in the frequency band and a change in the shape of the correlation function. There are various options for changing the correlation function: expansion, the appearance of side outliers, etc., depending on which part of the frequency range the BZ lines are turned off.

Then the signal is searched and compared with the threshold in the correlator 3, which, in addition, provides information on the block of time intervals about the continuation of the signal search or about the completion of the search when the signal is found. The block of time intervals generates a time stamp pulse after a predetermined time interval T equal to the correlator integration time. Until a signal is found, the block of time intervals generates a time stamp in the GPS, which shifts the SRP by τ ₀ . In the case of a multi-channel correlator (n is the number of channels), the bandwidth shift in the generator is made by the value nτ ₀ . When a signal is detected, the command from the correlator interrupts the generation of pulses by a block of time intervals and the signal is continuously received.

 But this prototype receiver has an advantage: a decrease in noise immunity due to a decrease in the frequency band caused by a distortion of the autocorrelation function in the protection unit. Especially large losses in noise immunity when turning off most of the BZ lines.

 The claimed technical solution is free from this drawback.

 This disadvantage is eliminated by the fact that in the device containing the protection unit, the input of which is the input of the receiving device, and the RF output is connected to the first input of the correlator, the output of which is connected to the input of the time interval unit, the second input of which is connected to the second output of the PSP generator, and its first output is connected to the second input of the correlator, a series-connected block for evaluating the distortion of the spectrum, a logic circuit, and a delay block are introduced. In this case, the input of the spectrum distortion assessment unit is connected to the low-frequency output of the protection unit, and the output of the delay unit is connected to the input of the SRP generator. In addition, the second input of the delay block is connected to the output of the block of time intervals.

The scheme of the claimed receiver is shown in figure 3, where the following notation is introduced:
1 - protection unit (BZ);
2 - pseudo-random sequence generator (GPSP);
3 - correlator;
4 - block time intervals;
5 - block distortion spectrum;
6 is a logical diagram;
7 - delay unit.

 The receiver depicted in figure 3, has the following functional relationships.

 The proposed receiving device comprises a protection unit 1, the input of which is the input of the receiver, and the high-frequency output (RF) of the protection unit 1 is connected to the first input of the correlator 3, the output of which, through a block of time intervals 4, is connected to the second input of the delay unit 7, the output of which is connected to the input generator PSP 2. In this case, the first output of the generator 2 is connected to the second input of the correlator 3. The second output of the generator 2 is connected to the second input of the block of time intervals 4. The low-frequency output (LF) of the protection unit 1 is connected in series nnye distortion spectrum estimation unit 5 and the logic circuit 6 is connected to the first input of the delay unit 7.

 The proposed receiver of FIG. 3 as follows.

 The mixture of signal and noise coming to the input of the receiver passes through the protection unit, in which sections of the spectrum affected by interference are cut out by disconnecting part of the lines of the protection unit. From the low-frequency output of the protection unit, the signal is supplied to the spectrum distortion assessment unit, which compares the voltage at the low-frequency output of the protection unit with a minimum value and determines the parts of the spectrum affected by interference.

The signal from the spectrum distortion estimator is fed to a logic circuit that determines the amount of shift in the memory bandwidth by the number and location of the disabled rulers of the protection unit. In the delay unit, a delay value is generated by which the SRP is shifted in the pseudo-random sequence generator. And if in the prototype the shift of the SRP was carried out by a command from the block of time intervals, it was fixed and equal to τ ₀ (nτ ₀ for the multi-channel correlator), now the magnitude of the shift of the SRP is determined by the number and location of the disabled KB lines. And the more disabled the rulers, the greater the gain in the proposed receiver in relation to the prototype. In the case of a small number of disabled rulers, the claimed receiver works as a prototype. The gain in the case of disconnection of 80% of the extreme lines is 3-5 dB.

Here is a numerical example:
We increase the SRP shift step from τ ₀ to (4-5) τ ₀ , then for the same search time T 4-5 cycles will be carried out instead of one.

величина сигнала U_сиг = 4,6σ+0,7σ = 5,3σ. Вместо 8,0 σ величина сигнала получается в 1,5 раза меньше или на 4 дБ. Таким образом, получаем выигрыш на 4 дБ по сигналу и, кроме того, уменьшается время обнаружения за одну попытку: Т/5•0,6+2Т/5•0,24+3Т/5•0,084+4Т/5•0,03=0,3.Consider the calculation for one attempt. If you set B = 1023, the probability of a false alarm R _lt = 10 ^-3 , the probability of skipping the signal R _ps = 10 ^-3 , then with the normal law of the distribution of the amplitude, we obtain the threshold value U _pop = 4.9Ω, the value of the signal U _sig = 4.9Ω + 3.1Ω = 8Ω.
In five attempts, the value of the signal base (B) can be reduced to 200 and the threshold value U _pop = 4.6σ, the probability of missing the signal in one attempt out of five

the signal value U _sig = 4.6σ + 0.7σ = 5.3σ. Instead of 8.0 σ, the signal value is 1.5 times smaller or 4 dB. Thus, we get a gain of 4 dB on the signal and, in addition, the detection time is reduced in one attempt: T / 5 • 0.6 + 2T / 5 • 0.24 + 3T / 5 • 0.084 + 4T / 5 • 0, 03 = 0.3.

Claims (1)

 A broadband signal receiver comprising a protection unit, the input of which is the input of the device, and a high-frequency (RF) output is connected to the first input of the correlator, the output of which is connected to the input of the time interval unit, the second input of which is connected to the second output of the pseudo-random sequence generator (PSP), the first output of which is connected to the second input of the correlator, characterized in that a series-connected spectrum distortion assessment unit, a logic circuit and a delay unit, the output of which is connected to union of the generator with the input PSP, the second input of the delay unit is coupled to the output of timeslots distortion estimator spectrum input coupled to the low frequency (LF) output protection unit.

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