CN113270105B - Voice-like data transmission method based on hybrid modulation - Google Patents
Voice-like data transmission method based on hybrid modulation Download PDFInfo
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- CN113270105B CN113270105B CN202110548729.2A CN202110548729A CN113270105B CN 113270105 B CN113270105 B CN 113270105B CN 202110548729 A CN202110548729 A CN 202110548729A CN 113270105 B CN113270105 B CN 113270105B
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/16—Vocoder architecture
- G10L19/18—Vocoders using multiple modes
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10L—SPEECH ANALYSIS OR SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING; SPEECH OR AUDIO CODING OR DECODING
- G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
- G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
- G10L19/16—Vocoder architecture
- G10L19/18—Vocoders using multiple modes
- G10L19/20—Vocoders using multiple modes using sound class specific coding, hybrid encoders or object based coding
Abstract
The invention discloses a mixed modulation-based voice-like data transmission method, which comprises the following steps: carrying out serial-parallel conversion on an input data stream to obtain a segmented data stream with a fixed length; dividing frequency bands in the optimal transmission bandwidth of a voice channel of a vocoder, and adopting different modulation modes for different frequency bands to achieve the minimum transmission error rate, wherein the error rates of all the frequency bands are the same; obtaining data symbols through fast Fourier inverse transformation; framing the blank symbol, the synchronous head symbol and the data symbol together to obtain a voice signal frame; and receiving the voice signal frame at a receiving end and demodulating to obtain a data stream. The invention can modulate data on the amplitude or phase parameter of a plurality of frequency points of frequency division bands to generate a voice-like signal, has the time-frequency characteristic of common voice, can transmit through a voice channel with a vocoder, and can be widely used for the secret communication of an end-to-end voice channel.
Description
Technical Field
The invention belongs to the technical field of design-like voice modulation, and particularly relates to a mixed modulation-based voice-like data transmission method.
Background
Voice communication is an indispensable mode for daily information communication, and eavesdropping on mobile phones and telephones sometimes occurs. After the Trojan horse is installed on the mobile phone, the call of a user can be easily intercepted through a wireless network; the monitoring of the telephone voice can be achieved by combining the telephone lines. In VoIP services, which are internet telephony services, which have appeared in recent years, although secure transmission to some extent can be achieved by means of encryption of IP packets, voice is still in a clear text form in IP packets, and secure transmission from end to end cannot be achieved. Therefore, if the voice can be encrypted before voice transmission, the voice information leakage caused by interception of a third party in the subsequent voice processing and transmission process can be fundamentally avoided.
However, the data obtained by digitally encrypting the voice signal usually has no voice feature, which causes difficulty in transmitting the data through the voice channel. Since in most speech transmission systems, in order to save transmission channel bandwidth, the speech is compression coded; the vocoder used in the traditional voice channel usually uses the mixed parameter coding algorithm to process the voice and transmits the voice by extracting the model parameter of the voice. The encrypted voice data does not have the basic characteristics of the voice signal, so that the basic parameters of the voice signal cannot be extracted when the voice data passes through the vocoder, or the data is treated as noise, so that data information is lost, and a receiving end cannot decrypt the received encrypted data to obtain correct voice.
Therefore, data obtained by digitally encrypting a voice signal needs to be processed before transmission so as to have voice characteristics and to be able to smoothly pass through a voice channel. This is similar to the purpose of modulation, which is to convert a digital signal into a form to accommodate channel transmission. The general modulation method is to change a sinusoidal carrier signal, using the typical characteristics of the carrier: amplitude, frequency, phase, etc. to carry the digital data. However, most conventional data modems cannot be used in systems that use voice codec compression techniques. The main purpose of speech coding is to reduce the bits needed to represent the speech while still maintaining an acceptable speech quality at the time of decoding recovery, so that the human ear sounds almost the same as the original speech. Thus, the vocoder will limit the optimal band range of the voice data it transmits. Meanwhile, because human ears have non-linear perception to sound frequency and the vocoder channel has different responses to different frequency bands, the modulation mode of treating carrier frequency without difference may cause the frequency, phase and amplitude characteristics of the data-carrying output by the modem to be greatly distorted due to the difference before and after sampling waveform or the incompatibility of the carrier frequency and the vocoder channel. Therefore, most modems cannot be directly applied to channels using voice codecs, and a modem scheme needs to be redesigned to convert digital signals into voice signals with certain time-frequency characteristics, i.e., a voice-like modem scheme.
Disclosure of Invention
The invention aims to provide a voice-like data transmission method based on hybrid modulation, which aims to solve the technical problems that the existing modem can not be directly applied to a channel using a voice coder-decoder, and digital signals can not be converted into voice signals with certain time-frequency characteristics.
In order to solve the technical problems, the specific technical scheme of the invention is as follows:
a voice-like data transmission method based on hybrid modulation comprises the following steps:
step 2, selecting the transmission frequency band [ f ] of the vocoder channelL，fH]Wherein f isLLowest frequency allowed by the vocoder, fHThe highest frequency allowed by the vocoder. Transmitting frequency band f of vocoder channel according to different modulation modesL，fH]Is divided into m frequency bands, and the number of frequency points contained in each frequency band is N l1, 2, the frequency interval between adjacent frequency points is delta f, and delta f is more than or equal to 1/T, wherein T is a data symbol period;
step 3, in each frequency band, mapping data into phase and amplitude parameters of frequency points according to the modulation mode of the frequency band, and constructing a frequency spectrum { X (p) } of a data symbol;
step 4, performing inverse fast fourier transform on the frequency domain data of the constructed data symbols to obtain time domain waveforms { x (q) } of the data symbols, framing n data symbols, blank symbols and synchronous symbols together to obtain a voice-like signal, wherein each group of the voice-like signal is called a frame of the voice-like signal, and the combination of the blank symbols, the synchronous symbols and the data symbols is completely contained;
and 5, receiving the voice-like signal at the demodulation end, and carrying out frame synchronization and voice-like demodulation operations to obtain a data stream.
Furthermore, the step of dividing the frequency bands is to select a modulation mode in each frequency band, so that the data carried by each frequency band obtains the same error rate after transmission;
the selection of the modulation mode of each frequency band is determined by the maximum phase number N of each frequency point modulation, and meets the following requirements:
N＜fs/(M·f(i))
wherein f issFor the signal sampling rate, f (i) is the frequency point frequency, i ═ 1, 2lM is the offset number of the sampling point;
when f issAnd M is fixed, the transmission frequency band is divided into M frequency bands, and the phase number of frequency point modulation in each frequency band is less than N.
Further, in step 3, if the phase of each frequency point can carry j bits of data, the phase can be mapped to 2jAn optional phase parameter; the mapping of data and amplitude adopts a relative amplitude modulation mode that every two frequency points in a frequency band are in a group, and the data volume borne by each frequency band through amplitude modulation is Nl2 bit, NlThe number of frequency points included for each frequency band, where l is 1, 2.
Further, in the step 4, the frame structure of the signal frame includes nbThe data transmission method comprises the following steps of (1) carrying k bits of data by using a blank symbol, a synchronous head symbol and n data symbols; when the secret communication is carried out, the signal frame also comprises the key sequence number of the corresponding key stream.
The invention relates to a similar voice data transmission method based on hybrid modulation, which has the following advantages:
1. the quasi-voice signal obtained based on the mixed modulation mode of the sub-band and the multi-parameter has the time-frequency characteristic of a common voice signal, the frequency range is in the optimal transmission frequency band range of the vocoder, the quasi-voice signal can smoothly pass through a channel of the vocoder, and the quasi-voice signal has good capability of resisting the voice compression and decompression nonlinear operation;
2. the invention divides the frequency spectrum space into a plurality of sections, and selects the optimal modulation mode in each section, so that each frequency band can obtain the same minimum bit error rate, and simultaneously, the bit quantity borne by the data symbol is maximized;
3. the invention has high framing and deframing speed, does not influence the transmission of low-speed data, has small modulation and demodulation delay and can realize real-time transmission.
Drawings
FIG. 1 is a flow chart of a voice-like data transmission method based on hybrid modulation according to the present invention;
FIG. 2 is a schematic diagram of a magnitude spectrum of a single data symbol of the present invention;
FIG. 3 is a schematic diagram of a phase spectrum of a single data symbol of the present invention;
FIG. 4 is a diagram illustrating a frame structure format of a signal frame according to the present invention;
fig. 5 is a diagram illustrating the autocorrelation characteristic of the synchronization symbol according to the present invention.
Detailed Description
In order to better understand the purpose, structure and function of the present invention, a voice-like data transmission method based on hybrid modulation according to the present invention is described in further detail below with reference to the accompanying drawings.
As shown in fig. 1, an overall flow diagram of a speech-like data transmission method based on hybrid modulation provided by the present invention is shown, and the method specifically includes the following steps:
step 2, frequency band division: selecting the optimal transmission band [ f ] of the vocoder channelL，fH]Wherein f isLLowest frequency allowed by the vocoder, fHThe highest frequency allowed by the vocoder. Transmitting frequency band f of vocoder channel according to different selectable modulation modesL，fH]Is divided into m frequency bands, and the number of frequency points contained in each frequency band is N l1, 2.. times, m, the frequency interval between adjacent frequency points is Δ f, which is not less than the reciprocal of one data symbol period T, that is: delta f is more than or equal to 1/T;
in particular, common vocoder channel optimizationThe frequency band is [300Hz, 3400Hz]Selecting a plurality of effective frequency points in the frequency band range, wherein the number of the effective frequency points is N f30 with initial frequency fL300Hz with a maximum frequency of fH3400Hz and frequency interval Δ f 100Hz, then each frequency point has a frequency f (i):
f(i)＝f0+i*Δf，i＝0，1，2，...，30-1
wherein f is0For the starting frequency, generally equal to fL(ii) a i is the frequency point position and Δ f is the frequency interval of adjacent frequency points.
Each data frame comprises the sum of the sub-carriers corresponding to each frequency point after the voice-like modulation.
Further, the number of sampling points per period of the subcarrier corresponding to a single frequency point is set as nT＝fs/f(i)，fsRepresenting the sampling rate, the phase shift caused by the shift of a single sampling point is
If the sampling point offset of M points occurs when the receiving end performs frame synchronization, and the number of phases that can be modulated by the subcarrier corresponding to the frequency points f (i) is N, the conditions for demodulation without error code are as follows:
substituting the formula, the phase number N which can be modulated at each frequency point can be obtained to satisfy:
N＜fs/(M·f(i))
that is, the number of phases that can be modulated by the subcarrier corresponding to each frequency point is related to the frequency of the frequency point and the accuracy of frame synchronization, when the sampling rate fsAnd the sampling point offset number M is fixed, the frequency spectrum can be divided into a plurality of frequency bands according to the difference of f (i), and each frequency band selects different multilevel phase shifts according to the difference of the modulatable phase numbersWhen the Phase-adjustable bit number N is less than 2, the Phase modulation is no longer adopted, i.e., other modulation modes such as amplitude Shift Keying and the like are considered in a high frequency band.
When 2, the transmission frequency band can theoretically be divided into four frequency bands, and for reducing the algorithm complexity, the transmission effect is achieved at the same time, and in practical application, three frequency bands are divided: [300Hz, 1000Hz]、[1100Hz，1600Hz]、[1700Hz，3200Hz]. Fig. 2 and fig. 3 show schematic diagrams of amplitude frequency and phase frequency of a certain data symbol in this case, and a frequency band one contains the number of frequency points N1If Quadrature Phase Shift Keying (QPSK) modulation is adopted for 8 frequency points, the data volume S is carried in one frequency band1(f)＝2*N116 bits; frequency point number N contained in frequency band two2If the packet relative amplitude modulation and Binary Phase Shift Keying (BPSK) modulation are mixed for 6 frequency points, the data volume S is carried in the frequency band two2(f)＝N26 bits; frequency point number N contained in frequency band III3If only a packet relative amplitude modulation mode is adopted for 16 frequency points, the phase of each frequency point is kept to be 0, and the data volume S is borne in the frequency band III3(f)＝N3And/2 is 8 bits. The sum of the data volumes contained in the three frequency bands should satisfy:
S(f)＝S1(f)+S2(f)+S3(f)＝2*N1+N2+N330 (bit) =/2
Up to this point, the amount of data of k-30 bits contained in each segment of the data stream is allocated to the spectrum of the corresponding data symbol.
Step 3, data-spectrum parameter mapping: in each frequency band, mapping data into phase and amplitude parameters of frequency points according to a modulation mode of the frequency band, and constructing a frequency spectrum { X (p) } of a data symbol;
step 4, similar voice generation: performing inverse fast Fourier transform on the frequency domain data of the constructed data symbols to obtain time domain waveforms { x (q) } of the data symbols, framing n data symbols, blank symbols and synchronous symbols together to obtain a similar voice signal, wherein each group of the combination completely containing the blank symbols, the synchronous symbols and the data symbols is called a frame of the similar voice signal;
in particular, referring to the schematic diagram of FIG. 4, the frame structure format of each speech-like signal is shown by nb6 blank symbols, 1 synchronous head symbol and n 32 data symbols, each signal frame contains nbThe + n +1 symbol is 39 symbols, the time of each symbol is T10 ms except for the synchronization header, the synchronization header is 20 ms, and the frame time of each signal is Tall＝T*(nb+ n) +2 × T400 msec.
Further, the data frame transmits data in s (t) ═ n × k ═ 960 bits, so that the total data transmission rate v (t) is:
furthermore, the synchronization symbol should be a fixed-length time sequence with strong autocorrelation, such as chirp signal, whose time length is 2 × T ═ 20 msec, and whose instantaneous frequency varies with time within the range of [300Hz, 3400Hz ]. Referring to the schematic diagram of fig. 5, that is, a schematic diagram of the autocorrelation characteristic of the synchronization symbol, only at the non-late and non-early time "0", the synchronization symbol exhibits strong correlation, and the correlation at other times is weak; according to the characteristic, the receiving end can utilize the same synchronous symbol sampling data to carry out sliding correlation, and accurately position the position of the data symbol in the received voice-like signal according to the set correlation threshold.
Step 5, similar voice demodulation: and receiving the voice-like signal at a demodulation end, and carrying out frame synchronization and voice-like demodulation operations to obtain a low-speed data stream.
Specifically, the bit error rate of data transmission in each frequency band measured at the demodulation end is as follows: the frequency band is one 5 per mill, the frequency band is two 5 per mill and the frequency band is three 5 per mill, and the three frequency bands reach the same minimum error rate, so that the overall error rate is minimum and is 5 per mill.
The voice data transmission method based on mixed modulation can be used for transmitting encrypted voice data, so that intelligible voice is changed into unintelligible voice, and simultaneously, the voice characteristic is kept, and the encrypted voice data can be smoothly transmitted through a voice compression coding channel.
It is to be understood that the present invention has been described with reference to certain embodiments, and that various changes in the features and embodiments, or equivalent substitutions may be made therein by those skilled in the art without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (4)
1. A voice-like data transmission method based on hybrid modulation is characterized by comprising the following steps:
step 1, performing serial-to-parallel conversion on the input low-speed data stream to obtain n segments of fixed-length segmented data stream { d1，1，d1，2，...，d1，k；d2，1，d2，2，...，d2，k；......；dn，1，dn，2，...，dn，kThe data bit quantity contained in each data stream is represented by k;
step 2, selecting the transmission frequency band [ f ] of the vocoder channelL，fH]Wherein f isLLowest frequency allowed by the vocoder, fHThe highest frequency allowed by the vocoder; transmitting frequency band f of vocoder channel according to different modulation modesL，fH]Is divided into m frequency bands, and the number of frequency points contained in each frequency band is Nl1, 2, r, m, wherein the frequency interval between adjacent frequency points is Δ f, Δ f is greater than or equal to 1/T, and T is a data symbol period;
step 3, in each frequency band, mapping data into phase and amplitude parameters of frequency points according to the modulation mode of the frequency band, and constructing a frequency spectrum { X (p) } of a data symbol;
step 4, performing fast Fourier inversion on the frequency domain data of the constructed data symbol to obtain a time domain waveform { x (q) } of the data symbol; framing the n data symbols, the blank symbols and the synchronous symbols together to obtain a voice-like signal; each group integrally including a combination of a blank symbol, a sync symbol and a data symbol is called a frame of a frame-like speech signal;
and 5, receiving the voice-like signal at the demodulation end, and carrying out frame synchronization and voice-like demodulation operations to obtain a data stream.
2. The transmission method of claim 1, wherein in step 2, the step of dividing the frequency bands is to select a modulation method for each frequency band, so that the data carried by each frequency band has the same error rate after transmission;
the selection of the modulation mode of each frequency band is determined by the maximum phase number N of each frequency point modulation, and meets the following requirements:
N＜fs/(M·f(i))
wherein f issFor the signal sampling rate, f (i) is the frequency point frequency, i ═ 1, 2lM is the offset number of the sampling point;
when f issAnd M is fixed, the transmission frequency band is divided into M frequency bands, and the phase number of frequency point modulation in each frequency band is less than N.
3. The transmission method of voice-like data based on hybrid modulation as claimed in claim 1, wherein in step 3, if the phase of each frequency point can carry j bits of data, it can be mapped to 2jAn optional phase parameter; the mapping of data and amplitude adopts a relative amplitude modulation mode that every two frequency points in a frequency band are in a group, and the data volume borne by each frequency band through amplitude modulation is NlA/2 bit.
4. The method according to claim 1, wherein in step 4, the frame structure of the signal frame comprises nbA blank symbol of oneThe synchronous head symbol and n data symbols, each data symbol bears k bits of data; when the secret communication is carried out, the signal frame also comprises the key sequence number of the corresponding key stream.
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