RU2537972C1 - Method to transfer data in analogue tv frequency band - Google Patents

Abstract

FIELD: physics, communication.

SUBSTANCE: invention relates to communication equipment and may be used for transfer of data in an analogue TV frequency band. The method is based on selection of frequency windows in a TV band suitable for use by secondary operators, at the same time frequency windows are selected from a grid of sound bands of analogue TV, for such windows they determine an index of "being non-Gaussian" for a TV signal, and windows are selected with maximum index of "being non-Gaussian", levels of TV signals are measured in selected windows, and the secondary operator signal level is set in each window as 20 dB below the appropriate measured level, afterwards information is sent in selected windows simultaneously with transfer of TV signals, and on the receiving side of the secondary operator a mixture of a TV signal and a secondary operator signal is transferred to intermediate frequency, and its non-linear conversion is performed for suppression of a TV signal, afterwards the transmitted information is identified.

EFFECT: technical result consists in provision of magnetic compatibility of television operators in a single frequency band.

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Description

The invention relates to electronics and can be used to transmit data in the frequency band of analog TV.

A known method of transmitting data in the frequency band of an analogue TV, called teletext (GOST R 50861 - 96). Teletext signals are transmitted in unoccupied television lines. That is, the television channel is temporarily divided for image transmission and teletext transmission.

To receive teletext, the television receiver is complemented by a decoder.

The disadvantage of this method is that the teletext technology is built into television equipment and only TV operators can transmit data. Data transmission by other, independent operators in the frequency band of analogue TV is possible only by agreement with the TV operators.

A known method of transmitting signals in the VHF range, called RDS (Radio Data System) (ITU-R 643-2). This method is based on the transmission by VHF FM broadcast operators as part of the main signal of additional information using subcarriers. In this case, the spectrum of the RDS signal is placed in such a way as not to affect the main broadcast signal. This method can also be used by TV broadcast operators.

The disadvantage of this method is that RDS technology is built into the equipment of the primary operator and the use of this technology by independent secondary users is impossible without coordination with the main operator.

Closest to the claimed method is a prototype method of data transmission using the ECMA-392 standard (Guryanov I.O. Cognitive radio: new approaches to providing radio-frequency resources for promising radio technologies. Electrosvyaz Magazine, No. 8, 2012; Standard ECMA-392) . The method is based on searching in the analogue TV band for unoccupied frequency areas (frequency windows) suitable for data transmission, and using them for data transmission without coordination with the TV operators to which these frequency bands belong.

The disadvantage of this method is the possibility of using for secondary purposes only free frequency windows.

The proposed method provides data transmission in the analogue TV band without coordination with the TV operators in the selected frequency windows and differs from the prototype method in the transmission of data not in free windows, but in those engaged in transmitting TV programs.

The proposed method for transmitting data in the frequency band of analog TV by secondary operators without interfering with the main TV operator, based on the choice in the TV band of frequency windows suitable for use by secondary operators, characterized in that the frequency windows are selected from the grid of sound bands of analog TV for such windows determine the indicator of "non-Gaussianity" of the TV signal and select the window with the maximum indicator of "non-Gaussianity", measure the levels of TV signals in the selected windows and set the signal level of the secondary operator in each of the windows, it is 20 dB lower than the corresponding measured level, after which information is transmitted in the selected windows simultaneously with the transmission of TV signals, and on the receiving side of the secondary operator, the mixture of the TV signal and the signal of the secondary operator is transferred to the intermediate frequency and its non-linear conversion is performed to suppress TV signal, after which the transmitted information is isolated.

Thus, the proposed method is implemented under the following conditions:

1. From the grid of sound bands of analogue TV broadcasting, those bands are selected in which the temporary TV signal is minimally distorted by external noise. We call these bands frequency windows for secondary use. The bandwidth of such a frequency window is 200 kHz.

2. The secondary operator uses these windows to transmit digital data at a speed of v <10000 bits / sec.

3. The signal level of the secondary operator is set below the level of the analogue TV signal in the selected window by 20 dB in order to eliminate interfering actions with the primary user.

4. At the receiving side of the secondary operator, algorithms are used that are designed to optimally receive the secondary signal against the background of the primary analogue TV signal.

The possibility of the secondary use of the occupied frequency band is based on the stable statistical properties of the primary signal: the primary signal in the audio band of an analogue TV is an essentially non-Gaussian process with the distribution of the envelope according to the Rais law, as it is formed by frequency modulation (Tikhonov V.I. Statistical radio engineering. - 2- E ed. - M.: Radio and Communications, 1982. - 624 p.). Moreover, its one-dimensional envelope probability density W (A) is practically independent of the content of the sound program. This greatly facilitates the reception of the secondary signal against the background of the primary when applying the optimal reception algorithm in the receiver of the secondary user. External electromagnetic interference can distort the primary signals, reducing their "non-Gaussian". Therefore, the choice of frequency windows for secondary use is carried out according to the criterion of maximum “non-Gaussianity” of the signal in this window.

The choice of frequency windows for secondary use is carried out from the grid of sound bands of analog TV broadcasting as follows. The envelope of the signal A (t) in the selected frequency window is analyzed. The analysis consists in comparing the mean signal power A (t) in different parts of its spectrum. Two sections are distinguished: adjacent to the zero frequency with the F _H band (section with the LF band) and the area outside the LF band (section with the HF band). In the transmitting equipment of the secondary user, the power values P _LF and P _{HF of the} primary signal A (t) are measured in both sections. Based on the measured values, the parameter value is calculated

α = P _LF / P _HF

The parameter α characterizes the degree of non-Gaussianity of the primary signal in the analyzed frequency window. Next, the windows with the highest values of the parameter α are selected. These windows are used for data transfer by the secondary user.

The signal reception in the secondary network, close to optimal in these conditions, is implemented by the receiver shown in figure 1. Here 1 is an input circuit, 2 is a radio frequency amplifier, 3 is a frequency converter, 4 is an intermediate frequency amplifier, 5 is a nonlinear processing unit, 6 is a multiplier, 7 is a reference signal generation circuit, 8 is an integrator with a reset, 9 is a clock synchronization block , 10 - threshold device. The receiver circuitry before the BNO is part of a typical superheterodyne receiver circuit. The justification of the receiver circuitry following the BNO is given in (Kamnev V.E., Cherkasov V.V., Chechin G.V. Satellite communication networks. Textbook. - M.: Alpina Publisher, 2004. - 536 p. .). The presence of BNO is due to the "non-Gaussian" interference (Valeev V.G., Kornilov I.N. Non-linear signal processing to suppress interference in the receiving path of electronic systems / Journal of Radio Engineering, 2010. No. 6. P.37-42).

An additive mixture of the useful signal of the secondary network S ₂ (t), the signal of the primary user S ₁ (t) and third-party interference n2 (t) acts at the input of the BNO:

x (t) = A _x (t) cos [ω ₀ t-φ _x (t)],

where A _x (t) is the envelope of the mixture, ω ₀ is the carrier frequency, φ _x (t) is the law of variation of the phase of the mixture.

The optimal signal processing algorithm in the secondary user receiver (Fig. 1) is substantiated in (Valeev V.G., Kornilov I.N. On the possibilities of recycling the occupied frequency resource. VI All-Russian Scientific and Technical Conference "Radar and Radio Communication": Proceedings of the conference Moscow: IRE named after V.A. Kotelnikov RAS, 2012. Volume 1, p.272-275) and has the following form:

$$Z={\displaystyle \underset{0}{\overset{T}{\int }}f\left[x(t)\right]S_{\mathrm{ABOUT}P}\left(t\right)}\text{dt, (2)}$$

$$f(x)=g(A_x(t)\cos \left[{\omega }_{0}t-{\varphi }_x(t)\right],g(A_x(t))\approx (A_x(t)-(A_0(t))/P_{\mathrm{AT}H},\text{(3)}$$

where Z is the process at the output of the integrator; f (x) is the characteristic of NLS; g (A _x (t)) is the amplitude characteristic of the NLS in the first harmonic; A ₀ (t) is the average value of the envelope; T is the integration time; S _OP (t) is the reference oscillation formed by the block SFOS.

To confirm the effectiveness of the proposed method was performed semi-simulation of the receiver in figure 1. As a primary user signal S ₁ (t), we considered a real signal in the frequency band of the sound accompaniment of the selected analogue TV program. This signal also contains a component n ₂ (t), which corresponds to environmental noise. Figure 2 shows the temporal implementation of the envelope of such a signal for one of the TV channels (the signal is recorded in the band 83.65 ... 83.85 MHz) over an interval of 20 seconds, and figure 3 is a histogram of the envelope constructed from the recorded fragment. By the appearance of the histogram, we can conclude that this process is close to Rice.

The signal S ₂ (t) was modeled as

S ₂ (t) = A _S2 cos (2πf ₀ t + φ),

where the phase shift φ during the transition from transmission “1” to transmission “0” is taken to be π, and the carrier frequency f _{0 is} selected in the center of the band (83.65 ... 83, 85) MHz. The reference oscillation in the synchronous detector is taken in the form

S _OD (t) = cos2πf ₀ t,

clock synchronization is considered established. The threshold value is taken equal to Z ₀ = 0.

Block BNO was implemented according to the scheme of figure 4. Here 11 is an envelope detector, 12 is a compensator, 13 is an average estimation block, 14 is a subtraction block, 15 is a limiter, 6 is a multiplier. This scheme corresponds to processing by algorithms (2) and (3).

To select the amplitude of the signal S ₂ (t), the power level P _{1 of the} signal S ₁ (t) was measured. The amplitude A _{s2 of the} secondary signal S ₂ (t) was set 20 dB less than the amplitude of the primary signal.

The dependence of the probability of the error R _ОH per symbol in the secondary network on the data transfer rate V = 1 / T was investigated. The transmission rate was set by choosing the duration of the signal T S ₂ (t). The probability of error per character was estimated by an array of transmitted characters of size N = 20V.

The simulation results are shown in Fig. 5 as a function of the probability of error per symbol on the data rate in the secondary network. Graph 1 is obtained for a receiver with a linear correlator (without NLS), and graph 2 for a receiver with a NLS. If the compensator in the BNO is replaced with a high-pass filter with a cut-off frequency of 10 Hz, we get graph 3. The results show that the frequency bands of the TV soundtrack can be used simultaneously for their main purpose and for data transmission by secondary users.

The technical result is the electromagnetic compatibility of the functioning of the TV operator and the secondary operator in the same frequency band, allowing you to use the occupied sound bands of the TV to transmit data simultaneously for the main purpose and for data transfer by secondary users. Electromagnetic compatibility is achieved due to the fact that the interfering effect of secondary signals on the reception of TV programs is practically absent. The level of secondary signals with respect to TV signals in the TV soundtrack is minus 20 dB. With this level of interference at the input of the frequency detector of the TV receiver, the signal-to-noise ratio at the output of the frequency detector will be 30-40 dB (Zyuko A.G., Klovsky D.D., V.I. Korzhik, Nazarov M.V. Theory of electrical communications: Textbook for universities / under the editorship of Klovsky DD - M .: Radio and communications, 1999. - 432 p.). Such an attitude is enough for high-quality sound transmission.

Claims (1)

A method of transmitting data in the frequency band of analog TV by secondary operators without interfering with the main TV operator, based on the choice of frequency windows in the TV band suitable for use by secondary operators, characterized in that the frequency windows are selected from the grid of sound bands of analog TV, for such windows the indicator of the “non-Gaussianity" of the TV signal and select the window with the maximum indicator of “non-Gaussianity”, measure the levels of TV signals in the selected windows and set the signal level of the secondary operator in each it is 20 dB lower than the corresponding measured level, after which information is transmitted in the selected windows simultaneously with the transmission of TV signals, and on the receiving side of the secondary operator, the mixture of the TV signal and the signal of the secondary operator is transferred to the intermediate frequency and its nonlinear conversion is performed to suppress the TV signal, after which emit transmitted information.

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