CN114465628A - Accurate sub-audio CTCSS frequency searching system and method - Google Patents

Accurate sub-audio CTCSS frequency searching system and method Download PDF

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CN114465628A
CN114465628A CN202210059804.3A CN202210059804A CN114465628A CN 114465628 A CN114465628 A CN 114465628A CN 202210059804 A CN202210059804 A CN 202210059804A CN 114465628 A CN114465628 A CN 114465628A
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ctcss
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CN114465628B (en
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刘泷
宋永刚
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NANJING SINOVATIO TECHNOLOGY CO LTD
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
    • H04B1/0014—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage using DSP [Digital Signal Processor] quadrature modulation and demodulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0007—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at radiofrequency or intermediate frequency stage
    • H04B1/0017—Digital filtering
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/0003—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain
    • H04B1/0028—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage
    • H04B1/0032—Software-defined radio [SDR] systems, i.e. systems wherein components typically implemented in hardware, e.g. filters or modulators/demodulators, are implented using software, e.g. by involving an AD or DA conversion stage such that at least part of the signal processing is performed in the digital domain wherein the AD/DA conversion occurs at baseband stage with analogue quadrature frequency conversion to and from the baseband
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
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Abstract

The invention discloses a subaudio CTCSS frequency searching system, which carries out four-order cyclic cumulant calculation on demodulated baseband data through a calculating module so that a subaudio CTCSS frequency value is accurate to one bit behind a decimal point for searching.

Description

Accurate sub-audio CTCSS frequency searching system and method
Technical Field
The invention relates to the related field of frequency identification of a sub-audio CTCSS of an FM analog interphone, and relates to a system and a method for searching the frequency of the precise sub-audio CTCSS.
Background
The minimum adjacent interval of the sub-audio CTCSS frequency is 2.3HZ, so the requirement on the identification precision of the CTCSS frequency is higher, the CTCSS frequency value is generally calculated by adopting a DFT method, the requirement on data volume is higher, the identification precision range is not easy to control and guarantee due to the spectrum leakage existing in the DFT calculation, and simultaneously, the frequency is easy to be influenced by noise, so the actual sub-audio CTCSS frequency identification precision is limited.
Therefore, a new technology is needed to solve the above problems.
Disclosure of Invention
The invention aims to: the invention aims to provide a system and a method for searching the frequency of a precise sub-audio CTCSS, which solve the problem of frequency identification precision of the sub-audio CTCSS.
The technical scheme is as follows: the invention provides a precise sub-audio CTCSS frequency searching system which comprises a sampling module, a digital down-conversion module, a first low-pass filtering module, an orthogonal demodulation module, a second low-pass filtering module, a calculating module, a query module, a comparison module and a judging module, wherein the sampling module is used for sampling a signal to be searched;
the sampling module is used for comparing a sampling rate fsSampling to obtain zero intermediate frequency sampling data;
the digital down-conversion module is used for carrying out digital down-conversion on zero intermediate frequency sampling data and sampling frequency corresponding to channel frequency interval of interphone on digital down-conversion
Figure RE-GDA0003586004960000011
Obtaining data after down-sampling;
the first low-pass filtering module is used for obtaining a sampling frequency according to an FM modulation signal bandwidth formula BW-2 ═ 2 × (baseband bandwidth + maximum modulation frequency offset)
Figure RE-GDA0003586004960000012
Generating a low-pass filter coefficient by means of a low-pass filter (1)1Further filtering the down-sampled data for the first time to obtain time domain data;
the orthogonal demodulation module is used for carrying out FM orthogonal demodulation on the time domain data to obtain demodulated baseband data;
the secondary low-pass filtering module is used for filtering the audio signal according to the fact that the subaudio frequency range is less than 300HZ, the voice data frequency range is 300-3400 HZ and the sampling frequency
Figure RE-GDA0003586004960000013
Generating a low-pass filter coefficient filter by means of a 300HZ low-pass filter (2)2Generating a band-pass filter coefficient filter by a 300-3400 HZ band-pass filter (3)3Respectively performing secondary filtering and low-pass filter on the demodulated baseband data2Obtaining sub-audio data, band-pass filter coefficient3Obtaining voice data;
the calculation module is used for calculating fourth-order circulation cumulant for the subaudio frequency data
Figure RE-GDA0003586004960000021
The query module is used for querying the fourth-order cycle cumulant
Figure RE-GDA0003586004960000022
The most important of the sequenceHigh value
Figure RE-GDA0003586004960000023
The comparison module is used for accumulating the fourth-order cycle
Figure RE-GDA0003586004960000024
Comparing the maximum value in the sequence with a threshold value if CmaxReturning to the sampling module when the threshold is not more than the threshold; otherwise, extracting the cyclic frequency value alpha corresponding to the maximum valuemax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxAnd is accurate to one digit after decimal point;
the judging module is used for judging the pre-configured subaudio frequency value CTCSS of the local machinelocalAnd the searched frequency value freqctcssIf the voice data are consistent, the voice data are played; otherwise, returning to the sampling module.
The invention also provides a precise sub-audio CTCSS frequency searching method, which comprises the following steps:
(1) for the sampling rate fsSampling to obtain zero intermediate frequency sampling data;
(2) sampling frequency corresponding to digital down-conversion interphone channel frequency interval for zero intermediate frequency sampling data
Figure RE-GDA0003586004960000025
Obtaining data after down-sampling;
(3) according to the FM modulation signal bandwidth formula BW-2 (base band bandwidth + maximum modulation frequency deviation) and the sampling frequency
Figure RE-GDA0003586004960000026
Generating a low-pass filter coefficient filter by a low-pass filter 11Further filtering the down-sampled data for the first time to obtain time domain data;
(4) performing FM quadrature demodulation on the time domain data to obtain demodulated baseband data;
(5) according to the sub-audio frequency range being less than 300HZ and the voice data frequency range 3003400HZ and sampling frequency
Figure RE-GDA0003586004960000027
Generation of the Low-pass Filter coefficient Filter by the 300HZ Low-pass Filter 22Generating a band-pass filter coefficient filter by a 300-3400 HZ band-pass filter 33Respectively performing secondary filtering and low-pass filter on the demodulated baseband data2Obtaining sub-audio data, band-pass filter coefficient3Voice data;
(6) calculating fourth order cyclic cumulant for sub-audio data
Figure RE-GDA0003586004960000028
(7) Querying fourth order cycle cumulant
Figure RE-GDA0003586004960000029
Maximum value in sequence
Figure RE-GDA00035860049600000210
(8) Accumulating the fourth order cycle
Figure RE-GDA0003586004960000031
Comparing the maximum value in the sequence with a threshold value if CmaxIf not more than threshold, returning to the step (1), otherwise, extracting the cyclic frequency value alpha corresponding to the maximum valuemax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxAnd is accurate to one digit after decimal point;
(9) judging the pre-configured subaudio frequency value CTCSS of the local machinelocalAnd the searched frequency value freqctcssIf the two are consistent, playing the voice data if the two are consistent, otherwise returning to the step (1).
Has the advantages that: compared with the prior art, the method has the remarkable characteristic that the demodulated baseband data is subjected to fourth-order cyclic cumulant calculation through the calculation module, so that the sub-audio CTCSS frequency value is accurate to one bit behind a decimal point for searching.
Drawings
FIG. 1 is a flow chart of the frequency search for the accurate sub-audio CTCSS of the present invention;
FIG. 2 is time domain data digitally down-converted to a 25K sample rate in accordance with the present invention;
FIG. 3 shows the cyclic frequency and the fourth-order cyclic accumulation of the sub-audio data according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Example one
Referring to fig. 1, the present embodiment provides a precise sub-audio CTCSS frequency searching system, which includes a sampling module, a digital down-conversion module, a first low-pass filtering module, an orthogonal demodulation module, a second low-pass filtering module, a calculating module, a querying module, a comparing module, and a determining module;
the sampling module is used for comparing the sampling rate fsSampling to obtain zero intermediate frequency sampling data { x (t) }, wherein t is 1, 2;
the digital down-conversion module is used for carrying out digital down-conversion on sampling frequency corresponding to channel frequency intervals of the interphone on zero intermediate frequency sampling data { x (t), wherein t is 1,2
Figure RE-GDA0003586004960000032
Obtaining the down-sampled data { x1(n, n 1, 2.. once. }, since general acquisition equipment has a certain sampling bandwidth, and the bandwidth of the FM analog interphone is small, usually the channel interval is 25KHZ (or 12.5KHZ), digital down-conversion needs to be performed on the sampling data first, and the sampling rate is reduced to the frequency 25KHZ (or 12.5KHZ) corresponding to the actual interphone channel interval, so as to obtain down-sampled data { x }1(n),n＝1,2,......}；
The first low-pass filtering module is used for obtaining a sampling frequency according to an FM modulation signal bandwidth formula BW-2 ═ 2 × (baseband bandwidth + maximum modulation frequency offset)
Figure RE-GDA0003586004960000033
As known in the standard of interphone specification, the bandwidth of the audio baseband is 3KHZ, the maximum modulation frequency deviation is 5K, so a low-pass filter with a passband of 16K under a sampling rate of 25KHZ or a low-pass filter with a passband of 10.7K under a sampling rate of 12.5KHZ is designed to generate a low-pass filter coefficient1Further down-sampled data { x1(n), 1,2, the first filtering is carried out to n2(n),n＝1,2,......}；
The orthogonal demodulation module is used for time domain data { x2(n), n 1,2, the2(n), n ═ 1,2, … … } product x 'of conjugates of adjacent chips'2(n)＝x2(n+1)*conj(x2(n)), and then the phase sequence after product is calculated
Figure RE-GDA0003586004960000041
And a phase difference
Figure RE-GDA0003586004960000042
Wherein T issFor sampling chip duration, i.e.
Figure RE-GDA0003586004960000043
Obtaining demodulated baseband data { y (n), wherein n is 1,2
Figure RE-GDA0003586004960000044
The real phase of the signal is continuously changed, and in order to ensure that the demodulated data is continuous data, the method avoids the possible existence of the conventional demodulation method when the instantaneous phase is calculated firstly and then the instantaneous phase difference is calculated
Figure RE-GDA0003586004960000045
Left and right steps, the invention adopts a method of firstly utilizing conjugate products of adjacent chips to calculate the phase difference, namely
Figure RE-GDA0003586004960000046
Recalculating the instantaneous phase of the product, i.e.
Figure RE-GDA0003586004960000047
And converting the real-time data into continuous instantaneous frequency, and calculating the difference value of the instantaneous frequency to obtain demodulated continuous baseband real-time data { y (n), wherein n is 1,2
Figure RE-GDA0003586004960000048
Wherein
Figure RE-GDA0003586004960000049
Because FM is analog modulation, instantaneous frequency and instantaneous frequency difference are continuous, and demodulated baseband data is continuous;
the secondary low-pass filtering module is used for controlling the range of 63-255 HZ according to the frequency of the subaudio frequency data and controlling the range of 300-3400 HZ according to the frequency of the voice data, and the sampling frequency of the baseband data is at the moment
Figure RE-GDA00035860049600000410
I.e. 25KHZ (or 12.5KHZ), respectively generates a 300HZ low-pass filter coefficient filter2And 300-3400 HZ band-pass filter coefficient filter3Secondary filtering is performed on the demodulated baseband data { y (n) }, wherein n is 1,22Obtain sub-audio data { yctcss(k) K is 1,2, 300-3400 HZ band-pass filter coefficient filter3Obtain the voice data yvoice(m),m＝1,2,......}；
The computing module is used for sub-audio data { yctcss(k) A.k.1, 2. calculate the fourth order cyclic cumulative amount
Figure RE-GDA0003586004960000051
The fourth-order circulation cumulant calculation formula is
Figure RE-GDA0003586004960000052
Wherein<·>tRepresents averaging the time series, s (t) is the original data, i.e. the demodulated filtered extracted sub-audio data { y }ctcss(k) 1,2And if the audio data is a monophonic signal, the fourth-order cyclic cumulant of the subaudio data is modulo:
Figure RE-GDA0003586004960000053
i.e. the fourth order cumulant fulfils the maximum value if and only if the cyclic frequency a is equal to the true subaudio frequency CTCSS; wherein the cyclic frequency range is set to be a subaudio frequency range of 63-255 HZ, and the minimum adjacent frequency interval is 2.3HZ, so that the cyclic frequency range to be searched is defined to be 63-255 HZ, the step length is 0.1HZ, namely { alpha [ [ alpha ] ]i63+0.1 i 0,1, 2.. 1920, for each cycle frequency αiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure RE-GDA0003586004960000054
The fourth order moment is calculated as
Figure RE-GDA0003586004960000055
Wherein N represents the length of the extracted frame data, and N is 2048 by default; then, the fourth order cumulant is obtained according to the second order moment calculation formula and the fourth order moment calculation formula
Figure RE-GDA0003586004960000056
Calculating the fourth-order cycle cumulant corresponding to each cycle frequency to obtain the fourth-order cycle cumulant sequence
Figure RE-GDA0003586004960000057
The query module is used for querying the fourth-order cycle cumulant
Figure RE-GDA0003586004960000058
Maximum value in the sequence according to each cycle frequency alphaiCorresponding fourth order cyclic cumulant sequences
Figure RE-GDA0003586004960000059
Find and compareMaximum value
Figure RE-GDA00035860049600000510
The comparison module is used for accumulating the fourth-order cycle
Figure RE-GDA00035860049600000511
Comparing the maximum value in the sequence with a threshold, and extracting a cyclic frequency value alpha corresponding to the maximum valuemax(ii) a Calculating the threshold of the cyclic cumulant sequence according to the formula
Figure RE-GDA0003586004960000061
I.e. the threshold is 100 times the mean value of the circulating cumulant, if CmaxReturning to the sampling module when the threshold is not more than the threshold; if Cmax>threshold shows that the cyclic frequency search is successful, and the cyclic frequency value alpha corresponding to the maximum value is extractedmax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxAnd is accurate to one digit after decimal point;
the judging module is used for judging the preset subaudio frequency value CTCSS of the local machine according to the use principle of the subaudio CTCSS configuration in the interphonelocalAnd the searched frequency value freqctcssIf the data are consistent, the voice data y is playedvoice(m), m ═ 1, 2.· a. }; otherwise, returning to the sampling module.
Referring to fig. 2 and fig. 3, taking an example that a 100HZ sub-audio frequency is set for a certain brand analog interphone, setting the transmitting frequency of the interphone to 173MHZ, pressing the PTT button of the interphone to trigger a call, setting the local oscillation frequency of the local acquisition device to 173MHZ, and acquiring time domain data within 2 seconds by using the acquisition device, where the sampling rate of the acquisition device for the known experiment is 3.84 MHZ.
The sampling module firstly records the stored sampling data as { x (t), wherein t is 1,2, the sampling rate is 3.84MHz, and the channel interval of the interphone for testing is known to be 25 KHZ; the local oscillation frequency of the acquisition equipment is the same as the transmission frequency of the interphone, so that the data stored by the acquisition equipment is zero intermediate frequency data;
the digital down-conversion module carries out digital down-conversion processing on the sampled data to reduce the sampling rate to 25KHZ so as to meet the requirement of the channel sampling rate, thereby recording the down-sampled data as { x }1(n),n＝1,2,......}；
The first low-pass filtering module can know the maximum frequency deviation +/-5 KHZ of the interphone at the 25KHZ channel interval according to the national test specification of the analog interphone, the audio bandwidth is 3KHZ, an FM modulation bandwidth calculation formula BW (2) (baseband bandwidth + maximum modulation frequency deviation) ═ 2 (3+5) KHZ (16 KHZ) is substituted, namely the actual effective bandwidth of the interphone is 16KHZ, and therefore the data { x after down-sampling is carried out1(n), n ═ 1, 2. } low pass filter1Filtering out the out-of-band interference outside the 16KHZ, and obtaining time domain data after filtering and recording as { x2(n),n＝1,2,......}；
Orthogonal demodulation module for time domain data { x2(n), n is 1,2, the said. } to extract baseband data, wherein, the FM quadrature demodulation is optimized, namely, the phase angle and frequency are firstly calculated by arc tangent, then the frequency difference is calculated, the angle difference is firstly calculated by complex division, then the angle and frequency are calculated by arc tangent, thus obtaining continuous demodulation data by calculation, and the arc tangent function is avoided in the method of extracting baseband data
Figure RE-GDA0003586004960000071
The problem of left and right step discontinuity, further complex division is equivalent to complex conjugate multiplication. The specific calculation process is that firstly, the calculation is carried out
Figure RE-GDA0003586004960000072
Post-calculation
Figure RE-GDA0003586004960000073
Final calculation
Figure RE-GDA0003586004960000074
Wherein
Figure RE-GDA0003586004960000075
Thereby obtaining continuous baseband data y (n),n＝1,2,......}；
the secondary low-pass filtering module separates sub-audio data and voice data from the demodulated baseband data { y (n), n is 1,2, 1.. the. }, according to the generation process of the analog interphone signal, the sub-audio data and the voice data are completely overlapped and transmitted in the time domain, and the sub-audio data and the voice data in the frequency domain use different frequency ranges, so that the separation of the sub-audio data is convenient for the interphone to receive, namely the frequency range of the sub-audio data is 63-255 HZ, the frequency range of the voice data is 300-3400 HZ, the sampling rate of the demodulated baseband data is 25KHZ, and therefore a 300HZ low-pass filter can be directly designed2And a band-pass filter of 300-3400 HZ3Then, the baseband data { y (n) }, n ═ 1, 2. } is secondarily filtered, and the 300HZ low-pass filter coefficient filter2Obtain sub-audio data { yctcss(k) K is 1,2, 300-3400 HZ band-pass filter coefficient filter3Obtain the voice data yvoice(m),m＝1,2,......}；
The calculation module uses the fourth order cyclic cumulant on the sub-audio data yctcss(k) The frequency of k is 1,2, the frequency of the sub-audio CTCSS is accurately searched until one digit after a decimal point, the frequency range of the sub-audio CTCSS is 63-255 HZ, the minimum CTCSS frequency interval is 2.3HZ, so that the cyclic frequency range to be searched is also defined to be 63-255 HZ, the step length is 0.1HZ, namely the cyclic frequency is { alpha }i63+0.1 i 0,1, 2.. 1920, for each cycle frequency αiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure RE-GDA0003586004960000076
The fourth order moment is calculated as
Figure RE-GDA0003586004960000077
Wherein the number of N is 2048,
Figure RE-GDA0003586004960000078
then, the fourth-order cumulant is obtained by calculation, and the calculation formula is
Figure RE-GDA0003586004960000079
Finally, obtaining a fourth-order circulation cumulant sequence
Figure RE-GDA0003586004960000081
The query module analyzes the four-order circulation cumulant obtained by calculation, respectively searches for the maximum value, and compares the maximum value with the maximum value to obtain the result
Figure RE-GDA0003586004960000082
The comparison module extracts the cyclic frequency value alpha corresponding to the maximum value at the momentmaxFind the maximum value Cmax＝6.1*106Corresponding to a cycle frequency of alpha max100 HZ; by calculation formula
Figure RE-GDA0003586004960000083
Obtaining threshold of 1.7 x 106(ii) a Fourth order cycle accumulation magnitude Cmax＝6.1*106Greater than threshold value of 1.7 x 106So that the precise frequency of the obtained sub-audio CTCSS frequency is the cycle frequency alphamaxI.e. freqctcss＝αmax＝100HZ；
The judgment module is used according to the using principle of the sub-audio CTCSS configuration in the interphone, and the four-order circulation accumulates the quantity value Cmax＝6.1*106Greater than a threshold of 1.7 x 106So that the precise frequency of the obtained sub-audio CTCSS frequency is the cycle frequency alphamaxI.e. freqctcss＝αmax100HZ, at which time the baseband data samples at a frequency
Figure RE-GDA0003586004960000084
Then the native configuration sub-audio frequency value CTCSSlocalAnd the searched frequency value freqctcssConsistently, the voice data y is played directly through the playervoice(m), m 1,2, the clear sound can be heard.
Example two
Referring to fig. 1, according to a first embodiment, the present embodiment provides a method for searching a frequency of a precise sub-audio CTCSS, including the following steps:
(1) for the sampling rate fsSampling to obtain zero intermediate frequency sampling data { x (t) }, wherein t is 1, 2;
(2) sampling frequency corresponding to channel frequency interval of digital down-conversion interphone is carried out on zero intermediate frequency sampling data { x (t), t ═ 1,2
Figure RE-GDA0003586004960000085
Obtaining the down-sampled data { x1(n), n ═ 1, 2.· a. }; since general acquisition equipment has a certain sampling bandwidth, the bandwidth of an FM analog interphone is smaller, and the channel interval is usually 25KHZ (or 12.5KHZ), digital down-conversion is firstly required to be performed on the sampled data, and the sampling rate is reduced to the frequency 25KHZ (or 12.5KHZ) corresponding to the channel interval of the actual interphone, so that the down-sampled data { x } is obtained1(n),n＝1,2,......}。
(3) According to the FM modulation signal bandwidth formula BW-2 (base band bandwidth + maximum modulation frequency deviation) and the sampling frequency
Figure RE-GDA0003586004960000091
As known in the standard of interphone specification, the bandwidth of the audio baseband is 3KHZ, the maximum modulation frequency deviation is 5K, so a low-pass filter with a passband of 16K under a sampling rate of 25KHZ or a low-pass filter with a passband of 10.7K under a sampling rate of 12.5KHZ is designed to generate a low-pass filter coefficient1Further down-sampled data { x1(n), 1,2, the time domain data { x2(n),n＝1,2,......}；
(4) Time domain data { x2(n), n 1,2, the2(n), n ═ 1,2, … … } product x 'of conjugates of adjacent chips'2(n)＝x2(n+1)*conj(x2(n)), and then the phase sequence after product is calculated
Figure RE-GDA0003586004960000092
And a phase difference
Figure RE-GDA0003586004960000093
Wherein T issFor sampling chip duration, i.e.
Figure RE-GDA0003586004960000094
Obtaining demodulated baseband data { y (n), wherein n is 1,2
Figure RE-GDA0003586004960000095
The real phase of the signal is continuously changed, and in order to ensure that the demodulated data is continuous data, the method avoids the possible existence of the conventional demodulation method when the instantaneous phase is calculated firstly and then the instantaneous phase difference is calculated
Figure RE-GDA0003586004960000096
Left and right steps, the invention adopts a method of firstly utilizing conjugate products of adjacent chips to calculate the phase difference, namely
Figure RE-GDA0003586004960000097
Recalculating the instantaneous phase of the product, i.e.
Figure RE-GDA0003586004960000098
And converting the real-time data into continuous instantaneous frequency, and calculating the difference value of the instantaneous frequency to obtain demodulated continuous baseband real-time data { y (n), wherein n is 1,2
Figure RE-GDA0003586004960000099
Wherein
Figure RE-GDA00035860049600000910
Because FM is analog modulation, instantaneous frequency and instantaneous frequency difference are continuous, and demodulated baseband data is continuous;
(5) according to the frequency of the subaudio frequency data, the range is 63-255 HZ, and according to the frequency of the voice data, the range is 300-3400 HZ, and at the moment, the sampling frequency of the baseband data is
Figure RE-GDA00035860049600000911
Namely 25KHZ (or 12.5KHZ), respectively generate 300HZ low-pass filter coefficients2And 300-3400 HZ band-pass filter coefficient filter3Secondary filtering is performed on the demodulated baseband data { y (n) }, wherein n is 1,22Obtain sub-audio data { yctcss(k) K is 1,2, 300-3400 HZ band-pass filter coefficient filter3Obtain the voice data yvoice(m),m＝1,2,......}；
(6) For sub-audio data { yctcss(k) A.k.1, 2. calculate the fourth order cyclic cumulative amount
Figure RE-GDA00035860049600000912
The fourth-order circulation cumulant calculation formula is
Figure RE-GDA0003586004960000101
Wherein<·>tRepresents averaging the time series, s (t) is the original data, i.e. the demodulated filtered extracted sub-audio data { y }ctcss(k) K 1, 2.. the. fourth order cyclic accumulation of the sub-audio data is modulo:
Figure RE-GDA0003586004960000102
i.e. the fourth order cumulant fulfils the maximum value if and only if the cyclic frequency a is equal to the true subaudio frequency CTCSS; wherein the cyclic frequency range is set to be a subaudio frequency range of 63-255 HZ, and the minimum adjacent frequency interval is 2.3HZ, so that the cyclic frequency range to be searched is defined to be 63-255 HZ, the step length is 0.1HZ, namely { alpha [ [ alpha ] ]i63+0.1 i 0,1, 2.. 1920, for each cycle frequency αiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure RE-GDA0003586004960000103
The fourth order moment is calculated as
Figure RE-GDA0003586004960000104
Wherein N represents the length of the extracted frame data, and N is 2048 by default; then four-order cumulant is obtained by calculation, the calculation formula is
Figure RE-GDA0003586004960000105
Calculating the fourth-order cycle cumulant corresponding to each cycle frequency to obtain the fourth-order cycle cumulant sequence
Figure RE-GDA0003586004960000106
(7) Querying fourth order cycle cumulant
Figure RE-GDA0003586004960000107
Maximum value in the sequence according to each cycle frequency alphaiCorresponding fourth order cyclic cumulant sequences
Figure RE-GDA0003586004960000108
Finding and comparing the maximum value
Figure RE-GDA0003586004960000109
(8) Accumulating the fourth order circulation
Figure RE-GDA00035860049600001010
Comparing the maximum value in the sequence with a threshold, and extracting a cyclic frequency value alpha corresponding to the maximum valuemax(ii) a Calculating the threshold of the cyclic cumulant sequence according to the formula
Figure RE-GDA00035860049600001011
I.e. the threshold is 100 times of the mean value of the circulating cumulant, if CmaxReturning to the step (1) when the threshold is less than or equal to; if Cmax>threshold shows that the cyclic frequency search is successful, and the cyclic frequency value alpha corresponding to the maximum value is extractedmax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxThe accuracy can be one digit after a decimal point;
(9) according to the sub-audio CTCSS configuration in the interphoneThe use principle is arranged, and the local configuration subaudio frequency value CTCSS is judgedlocalAnd the searched frequency value freqctcssIf the data are consistent, the voice data y is playedvoice(m), m ═ 1, 2.· a. }; otherwise, returning to the step (1).
Referring to fig. 2 and fig. 3, taking an example that a 100HZ sub-audio frequency is set for a certain brand analog interphone, setting the transmitting frequency of the interphone to 173MHZ, pressing a PTT button of the interphone to trigger a call, setting the local oscillation frequency of a local acquisition device to 173MHZ, and acquiring time domain data within 2 seconds by using the acquisition device, where the sampling rate of the acquisition device for an experiment is known to be 3.84MHZ, the specific implementation steps are as follows:
(1) firstly, recording stored sampling data as { x (t), wherein t is 1,2, the sampling rate is 3.84MHz, and the channel interval of an interphone for testing is known to be 25 KHZ; the local oscillation frequency of the acquisition equipment is the same as the transmission frequency of the interphone, so that the data stored by the acquisition equipment is zero intermediate frequency data;
(2) carrying out digital down-conversion processing on the sampled data, reducing the sampling rate to 25KHZ to meet the requirement of the channel sampling rate, and recording the down-sampled data as { x1(n),n＝1,2,......}；
(3) According to the national test specification of analog interphones, the maximum frequency deviation +/-5 KHZ of the interphone under the 25KHZ channel interval is known, the audio bandwidth is 3KHZ, an FM modulation bandwidth calculation formula BW (base band bandwidth + maximum modulation frequency deviation) ═ 2 (3+5) KHZ ═ 16KHZ is substituted, namely the actual effective bandwidth of the interphone is 16KHZ, and therefore the data { x after down sampling is carried out1(n), n ═ 1, 2. } low pass filter1Filtering out the out-of-band interference outside the 16KHZ, and obtaining time domain data after filtering and recording as { x2(n),n＝1,2,......}；
(4) Time domain data { x2(n), n 1,2, the right. } to extract baseband data by performing optimized FM quadrature demodulation, i.e. calculating phase angle and frequency by means of arc tangent first, then calculating frequency difference, optimizing the calculation of angle difference by means of complex division first, then calculating angle and frequency by means of arc tangent calculation, and thus calculating continuous demodulation dataThe arctan-tangent function is
Figure RE-GDA0003586004960000111
The problem of left and right step discontinuity, further complex division is equivalent to complex conjugate multiplication. The specific calculation process is that firstly, the calculation is carried out
Figure RE-GDA0003586004960000112
Post-calculation
Figure RE-GDA0003586004960000113
Final calculation
Figure RE-GDA0003586004960000114
Wherein
Figure RE-GDA0003586004960000115
Thus, continuous baseband data { y (n) }, n ═ 1, 2.· is obtained;
(5) the sub-audio data and the voice data are separated from the demodulated baseband data { y (n), wherein n is 1,2, the. is 1.6.6 } and are completely overlapped and transmitted in the time domain, and the frequency domain use different frequency ranges, so that the separation of the sub-audio data is convenient when the interphone receives the signals, namely, the frequency range of the sub-audio data is 63-255 HZ, the frequency range of the voice data is 300-3400 HZ, the sampling rate of the demodulated baseband data is 25KHZ, and a 300HZ low-pass filter can be directly designed2And a band-pass filter of 300-3400 HZ3Then, the baseband data { y (n) }, n ═ 1, 2. } is secondarily filtered, and the 300HZ low-pass filter coefficient filter2Obtain sub-audio data { yctcss(k) K is 1,2, 300-3400 HZ band-pass filter coefficient filter3Obtain the voice data yvoice(m),m＝1,2,......}；
(6) Using fourth order cyclic cumulant on sub-audio data yctcss(k) And accurately searching the frequency of k & lt1 & gt, 2 & ltthe & gt. & ltthe & gt, accurately searching the frequency one bit behind a decimal point, wherein the frequency range of the known sub-audio CTCSS is 63-255 HZ, and the minimum frequency range isThe CTCSS frequency interval is 2.3HZ, so the cycle frequency range to be searched is defined to be 63-255 HZ, the step length is 0.1HZ, namely the cycle frequency is { alpha [ + ]i63+0.1 i 0,1, 2.. 1920, for each cycle frequency αiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure RE-GDA0003586004960000121
The fourth order moment is calculated as
Figure RE-GDA0003586004960000122
Wherein the number of N is 2048,
Figure RE-GDA0003586004960000123
then, the fourth-order cumulant is obtained by calculation, and the calculation formula is
Figure RE-GDA0003586004960000124
Finally, obtaining a fourth-order circulation cumulant sequence
Figure RE-GDA0003586004960000125
(7) Analyzing the four-order circulation cumulant obtained by calculation, respectively searching for the maximum value, and comparing and searching to obtain
Figure RE-GDA0003586004960000126
(8) At this time, the cyclic frequency value alpha corresponding to the maximum value is extractedmaxFind the maximum value Cmax＝6.1*106Corresponding to a cycle frequency of alpha max100 HZ; by calculation formula
Figure RE-GDA0003586004960000127
Obtaining threshold of 1.7 x 106(ii) a Fourth order cyclic accumulated quantity value Cmax＝6.1*106Greater than threshold value of 1.7 x 106So that the precise frequency of the obtained sub-audio CTCSS frequency is the cycle frequency alphamaxI.e. freqctcss＝αmax＝100HZ；
(9) According to the using principle of the sub-audio CTCSS configuration in the interphone, the value C is accumulated due to the fourth-order circulationmax＝6.1*106Greater than threshold value of 1.7 x 106So that the precise frequency of the obtained sub-audio CTCSS frequency is the cycle frequency alphamaxI.e. freqctcss＝αmax100HZ, at which time the baseband data samples at a frequency
Figure RE-GDA0003586004960000131
Then the local configuration sub-audio frequency value CTCSSlocalAnd the searched frequency value freqctcssConsistently, the voice data y is played directly through the playervoice(m), m 1,2, the clear sound can be heard.

Claims (8)

1. A precise sub-audio CTCSS frequency search system is characterized by comprising a sampling module, a digital down-conversion module, a first low-pass filtering module, an orthogonal demodulation module, a second low-pass filtering module, a calculation module, a query module, a comparison module and a judgment module;
the sampling module is used for comparing a sampling rate fsSampling to obtain zero intermediate frequency sampling data;
the digital down-conversion module is used for carrying out digital down-conversion on zero intermediate frequency sampling data and sampling frequency corresponding to channel frequency interval of interphone on digital down-conversion
Figure FDA0003477790070000011
Obtaining data after down-sampling;
the first low-pass filtering module is used for obtaining a sampling frequency according to an FM modulation signal bandwidth formula BW-2 ═ 2 × (baseband bandwidth + maximum modulation frequency offset)
Figure FDA0003477790070000012
Generating a low-pass filter coefficient by means of a low-pass filter (1)1Further filtering the down-sampled data for the first time to obtain time domain data;
the orthogonal demodulation module is used for carrying out FM orthogonal demodulation on the time domain data to obtain demodulated baseband data;
the secondary low-pass filtering module is used for filtering the audio signal according to the fact that the subaudio frequency range is less than 300HZ, the voice data frequency range is 300-3400 HZ and the sampling frequency
Figure FDA0003477790070000013
Generating a low-pass filter coefficient filter by means of a 300HZ low-pass filter (2)2Generating a band-pass filter coefficient filter by a 300-3400 HZ band-pass filter (3)3Respectively performing secondary filtering and low-pass filter on the demodulated baseband data2Obtaining sub-audio data, band-pass filter coefficient3Obtaining voice data;
the calculation module is used for calculating fourth-order circulation cumulant for the subaudio frequency data
Figure FDA0003477790070000014
The query module is used for querying the fourth-order cycle cumulant
Figure FDA0003477790070000015
Maximum value in sequence
Figure FDA0003477790070000016
The comparison module is used for accumulating the fourth-order cycle
Figure FDA0003477790070000017
Comparing the maximum value in the sequence with a threshold value if CmaxReturning to the sampling module when the threshold is not more than the threshold; otherwise, extracting the cyclic frequency value alpha corresponding to the maximum valuemax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxAnd is accurate to one digit after decimal point;
the judging module is used for judging the pre-configured subaudio frequency value CTCSS of the local machinelocalAnd the searched frequency value freqctcssIf the voice data are consistent, the voice data are played; otherwise return toAnd a back sampling module.
2. The system for precise sub-audio CTCSS frequency search according to claim 1, wherein the calculating module further comprises the steps of:
1) defining a cyclic frequency sequence alphai＝63+0.1*i|i＝0,1,2,......,1920}；
2) Value α for each cycle frequencyiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure FDA0003477790070000021
The fourth order moment is calculated as
Figure FDA0003477790070000022
Wherein N represents the length of the extracted frame data, and N is 2048 by default;
3) according to the fourth-order circulation cumulant calculation formula
Figure FDA0003477790070000023
Calculating the fourth-order cycle cumulant corresponding to each cycle frequency to obtain a fourth-order cycle cumulant sequence
Figure FDA0003477790070000024
3. The system for accurate sub-audio CTCSS frequency search according to claim 1, wherein the threshold is calculated as
Figure FDA0003477790070000025
If Cmax>When threshold is reached, the frequency value freq of the sub-audio CTCSS is accurately searchedctcss＝αmax(ii) a Otherwise, returning to the sampling module.
4. A method for searching the frequency of a precise sub-audio CTCSS is characterized by comprising the following steps:
(1) for the sampling rate fsSampling to obtain zero intermediate frequency sampling data;
(2) sampling frequency corresponding to digital down-conversion interphone channel frequency interval for zero intermediate frequency sampling data
Figure FDA0003477790070000026
Obtaining data after down-sampling;
(3) according to the FM modulation signal bandwidth formula BW-2 (base band bandwidth + maximum modulation frequency deviation) and the sampling frequency
Figure FDA0003477790070000027
Generating a low-pass filter coefficient filter by a low-pass filter 11Further filtering the down-sampled data for the first time to obtain time domain data;
(4) performing FM quadrature demodulation on the time domain data to obtain demodulated baseband data;
(5) according to the condition that the subaudio frequency range is less than 300HZ, the voice data frequency range is 300-3400 HZ and the sampling frequency
Figure FDA0003477790070000028
Generation of the Low-pass Filter coefficient Filter by the 300HZ Low-pass Filter 22Generating a band-pass filter coefficient filter by a 300-3400 HZ band-pass filter 33Respectively performing secondary filtering and low-pass filter on the demodulated baseband data2Obtaining sub-audio data, band-pass filter coefficient3Voice data;
(6) calculating fourth order cyclic cumulant for sub-audio data
Figure FDA0003477790070000031
(7) Querying fourth order cycle cumulant
Figure FDA0003477790070000032
Maximum value in sequence
Figure FDA0003477790070000033
(8) Accumulating the fourth order circulation
Figure FDA0003477790070000034
Comparing the maximum value in the sequence with a threshold value if CmaxIf not more than threshold, returning to the step (1), otherwise, extracting the cyclic frequency value alpha corresponding to the maximum valuemax，αmaxNamely the accurately searched sub-audio CTCSS frequency value freqctcss＝αmaxAnd is accurate to one digit after decimal point;
(9) judging the pre-configured subaudio frequency value CTCSS of the local machinelocalAnd the searched frequency value freqctcssIf the two are consistent, playing the voice data if the two are consistent, otherwise returning to the step (1).
5. The method for searching for the frequency of a CTCSS according to claim 4, wherein the step (6) comprises the steps of:
1) defining a cyclic frequency sequence alphai＝63+0.1*i|i＝0,1,2,......,1920}；
2) Value α for each cycle frequencyiRespectively calculating corresponding values according to a second moment calculation formula and a fourth moment calculation formula, wherein the second moment calculation formula is
Figure FDA0003477790070000035
The fourth order moment is calculated as
Figure FDA0003477790070000036
Wherein N represents the length of the extracted frame data, and N is 2048 by default;
3) according to the fourth-order circulation cumulant calculation formula
Figure FDA0003477790070000037
Calculating the fourth-order cycle cumulant corresponding to each cycle frequency to obtain a fourth-order cycle cumulant sequence
Figure FDA0003477790070000038
6. The method for searching the frequency of a CTCSS according to claim 4, wherein the threshold is calculated as
Figure FDA0003477790070000039
If Cmax>When threshold is reached, the frequency value freq of the sub-audio CTCSS is accurately searchedctcss＝αmax(ii) a Otherwise, returning to the step (1).
7. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, characterized in that the steps of the method as claimed in claims 4 to 6 are implemented by the processor when executing the computer program.
8. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of claims 4 to 6.
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