CN107528804B - Demodulation method of SOQPSK (quadrature phase shift keying) signal - Google Patents
Demodulation method of SOQPSK (quadrature phase shift keying) signal Download PDFInfo
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Abstract
The invention discloses a demodulation method of an SOQPSK signal, wherein the SOQPSK signal is subjected to orthogonalization processing through a synchronous carrier, an I component and a Q component carrying information are stripped from a high-frequency signal, then signal similarity comparison is carried out by utilizing the phase characteristics of the SOQPSK signal to obtain information codes of the I component and the Q component, and the obtained two groups of information codes are input into a decoder to obtain an original code. The invention simplifies the complicated decoding mode in the traditional demodulation process and reduces the demodulation cost.
Description
Technical Field
The invention belongs to the technical field of SOQPSK signal demodulation, and particularly relates to a demodulation method of an SOQPSK signal.
Background
The SOQPSK signal is a function that changes a quadrature phase shift keyed frequency offset shaping pulse from a function with respect to an impulse to a continuous function. SOQPSK possesses the constant envelope of OQPSK and the continuous phase characteristics of CPM, making it more selective in the use of transmission devices (e.g., using nonlinear amplification devices), while saving bandwidth resources. Besides the modulation by combining the conventional precoding and frequency shaping pulse, the modulation mode also has an excellent 8-XTCQM mode. The maximum likelihood sequence detection is realized by aiming at a demodulation mode using a viterbi algorithm, and for a partial response SOQPSK signal, along with the increase of the frequency shaping pulse memory length, the number of required matched filters and the number of trellis states of Viterbi decoding are exponentially increased, so that the operation process is complex and the requirements of realizing devices are harsh.
Disclosure of Invention
The invention aims to: aiming at the problems of complex operation process and strict requirement for realizing devices of the existing demodulation mode, the demodulation method of the SOQPSK signal is provided, the phase characteristics of the SOQPSK signal are utilized, a simple decoding mode is obtained through theoretical derivation calculation, an expected experimental result is obtained through simulation, the complicated decoding mode in the traditional demodulation process is greatly simplified, and the demodulation cost is reduced.
In order to achieve the purpose, the invention adopts the technical scheme that:
a demodulation method of SOQPSK signal is disclosed, the SOQPSK signal is processed by orthogonalizing through synchronous carrier, the I component and Q component carrying information are stripped from the high frequency signal, then the signal similarity comparison is carried out by utilizing the phase characteristic of SOQPSK to obtain the information code of I component and Q component, and the obtained two groups of information codes are inputted into the decoder to obtain the original code.
Preferably, the signal similarity comparison includes integrating the I component or the Q component after being multiplied by the basic waveform, and comparing the integrated value with the integrated value of the product of the basic waveform, and the obtained difference value is used as a quantization value of the difference, and the information code corresponding to the basic waveform is locked by the minimum quantization value of the difference.
Preferably, the components I and Q after the orthogonalization processing enter two groups of signal similarity comparison modules for the signal similarity comparison respectively, each group of signal similarity comparison modules contains a basic waveform of a phase characteristic of a waveform derived from the SOQPSK signal, and the two groups of signal similarity comparison modules contain all representation forms of the SOQPSK signal;
and after the components I and Q respectively enter two groups of signal similarity comparison modules, performing signal similarity comparison to obtain an information code corresponding to the basic waveform of the minimum difference quantization value.
Preferably, each set of signal similarity comparison modules includes a plurality of channels, each channel is correspondingly inputted with one of the basic waveforms, and the two sets of signal similarity comparison modules include a plurality of basic waveforms covering all representations of the SOQPSK signal.
Preferably, each set of signal similarity contrast modules comprises 8 channels.
Preferably, each channel includes a multiplier, two integrators and a subtracter, the multiplier is used for multiplying the input component signal and the basic waveform, one integrator is used for integrating the output signal of the multiplier, the other integrator is used for integrating the square of the basic waveform, and the subtracter is used for subtracting the outputs of the two integrators and taking the difference value as the quantized value of the difference degree.
Preferably, each channel includes two multipliers, two integrators and an adder, wherein one of the multipliers is used for inputting the product of the component signal and the basic waveform, the one of the integrators is used for integrating the multiplied signal, the other multiplier is used for inverting the integrated signal, the other integrator is used for multiplying the square of the basic waveform, the adder is used for adding the inverted signal and the square of the basic waveform, and the added value is used as the quantized value of the difference.
Preferably, the decoder adopts a decoding mode of 8-XTCQM, and the information codes of the I component and the Q component are decoded by the 8-XTCQM to obtain an original code.
Due to the adoption of the technical scheme, the invention has the beneficial effects that:
the method of the invention carries out orthogonalization processing on the received SOQPSK signal by the synchronous carrier, then the orthogonalized signal is multiplied with the basic waveform and then integrated, then the product is compared with the product integral of the basic waveform, and the numerical value is used as the basis of decoding to obtain the decoding result.
Drawings
Fig. 1 is a flowchart of SOQPSK demodulation according to embodiment 1 of the present invention.
Fig. 2 is a flowchart of SOQPSK demodulation according to embodiment 2 of the present invention.
FIG. 3 is a precoding flow diagram of the 8-XTCQM of the present invention.
Detailed Description
Example 1:
referring to fig. 1, the SOQPSK signal demodulation method according to the present invention, according to the concept of 8-XTCQM during demodulation, means: the demodulation method can be based on the method called by 8-XTCQM basic waveform, and the received signal and the basic waveform are correlated to demodulate.
The received modulated signal: r (t) ═ i (t) sin (w)ct)+Q(t)sin(wct)；
Other interference factors such as noise, Doppler frequency shift and the like are ignored in the signal, and the method mainly focuses on a demodulation mode, so that the other interference factors are not analyzed too much. The expression form of the received signal is derived from the 8-XTCQM modulation mode, and the expression form can be regarded as a unified expression of SOQPSK modulation, and the expression form is more convenient to process when demodulation theory derivation is carried out, because the modulation effect realized by the expression form is consistent with that realized by the conventional mode.
The received waveform is subjected to orthogonalization processing for subsequent separation of information components I and Q, and the frequency of a mixing signal used for the orthogonalization processing is a synchronous carrier frequency.
The received signals are respectively passed through mixing signal as cos (w)ct) and the mixing signal is sin (w)ct) of the Q channel of the first transistor,
the received signal is fed to two mixers, the frequency used by the mixers being the carrier frequency and the two mixers being 90 ° out of phase, expressed as cos (w)ct) and sin (w)ct) expressed as cos (w) by mixingcthe signal of t) is denoted as RI (t); by mixing the expression sin (w)cthe signal of t) is denoted as RQ (t), and the signal expressions through the two channels are respectively:
and (3) channel I: ri (t) ═ i (t) cos2(wct)+Q(t)sin(wct)cos(wct)；
And (3) a Q channel: rq (t) ═ i (t) sin (w)ct)cos(wct)+Q(t)sin2(wct)。
RI (t) signals enter a basic waveform module corresponding to the I component, the module is 8 channels, and a basic waveform corresponding to the I component is adopted in each channel; RQ (t) signal enters a basic waveform module corresponding to Q component, the module is 8 channels, and a basic waveform corresponding to Q component is adopted in each channel
In each channel, the signal will go through a multiplier, an integrator and a subtracter, and the subtracter also includes another integrator for integrating the square of the basic waveform.
To avoid confusion, a channel in the basic waveform block corresponding to the I component is illustrated, and the corresponding basic waveform is I' (t).
The multiplier is targeted to ri (t) and the base waveform I' (t) corresponding to the channel. The signal through the multiplier is expressed as:
CI(t)＝I(t)I′(t)cos2(wct)+Q(t)I′(t)sin(wct)cos(wct)
the integrator is subject to C (t), and the integration period is two code element periods. The signal through the integrator is expressed as:
The similarity comparison is carried out in a difference mode, a comparison scale is an integral of a product of a basic waveform, and theoretical derivation and actual data are demonstrated.
And (3) determining a scale:
and m is 1,2,3,4,5,6,7 and 8 and represents a channel number.
The subtractors are subject to DI (t) and SIm(t), the signal through the integrator is expressed as:
when I (t) and I '(t) are the same, WI' (t) is 0, that is, "when I (t) and I '(t) have high similarity," is a sufficient condition of "WI' (t) is 0".
By matlab
All possible assignment operations of (a) and (b), which are known from the data results to have a value of 0 if and only if I (t) and I ' (t), prove that "if I (t) and I ' (t) have a high degree of similarity" are "I (t) and I ' (t) ═ t0 "is a requirement.
The basic waveform corresponding to the current channel can be obtained from the minimum WI, and the basic waveform is closest to the I component information code of the received information, so the information code corresponding to the basic waveform can be regarded as the information code of the I component of the received information.
Similarly, the information code of the Q component of the received information can be obtained by performing the above-described procedure.
Thus, an information code of the received information I component and an information code of the received information I component are obtained; the two groups of code elements are input into the 8-XTCQM decoder matched with the invention in parallel to obtain the original code.
The demodulation decoding method provided by the invention replaces complex viterbi and other algorithms with simpler subtraction operation, proves the rationality of the method through operation derivation and actual verification, simplifies the demodulation process, saves the demodulation cost and reduces the demodulation difficulty.
Example 2:
the difference between this embodiment and embodiment 1 is that there are two multipliers, two integrators and one adder in each channel, and the following description is made by using a specific implementation method:
in conventional SOQPSK modulation and demodulation, the most primitive angle is usually processed, for example, precoding is performed to change an original code from a binary code into a ternary information code through a special conversion relationship, a frequency offset pulse shaping function is combined to obtain a phase function of SOQPSK, and then the phase function is put into a general function of a phase modulation signal to obtain a modulated signal of SOQPSK. This modulation concept makes the demodulation process exceptionally difficult.
After the 8-XTCQM modulation mode appears, the unique phase characteristic of the SOQPSK starts to be fully utilized in the modulation, the modulation efficiency is greatly improved by adopting a calling mode, the modulation difficulty is reduced, but a series of complex algorithms are still adopted for demodulation in the demodulation process, such as the most common viterbi algorithm, a huge operand is required, and a series of parameters such as the probability of state transition are required to be provided.
Although the conventional demodulation uses multiple channels and basic waveform calling, the phase specificity of the SOQPSK is not taken as a breakthrough point for demodulation.
Referring to fig. 2, the received signal to be processed is r (t), where external influences such as noise and frequency offset are not considered.
The received signal is fed to two mixers, the frequency used by the mixers being the carrier frequency and the two mixers being 90 ° out of phase, expressed as cos (w)ct) and sin (w)ct) expressed as cos (w) by mixingcthe signal of t) is denoted as RI (t); by mixing the expression sin (w)cthe signal of t) is marked as RQ (t), and two paths of signals passing through the mixer have respective tasks:
obtaining an information code corresponding to the I component from RI (t); and obtaining the information code corresponding to the Q component from RQ (t).
Referring to fig. 2, ri (t) is sent to 8 channels covering all possible basic waveforms of I component, where the 8 channels are used to complete similarity comparison with I component in ri (t), and the channel with the largest similarity (i.e. the smallest quantization value of the difference) indicates that the basic waveform in the channel is most similar to I component in ri (t), and the information code corresponding to the basic waveform can be used as the information code of I component in ri (t).
Sending the rq (t) into 8 channels covering all possible basic waveforms of the Q component, where the 8 channels are used to perform similarity comparison with the Q component in rq (t), and the channel with the largest similarity (i.e. the smallest variance quantization value) indicates that the basic waveform in the channel is most similar to the Q component in rq (t), and the information code corresponding to the basic waveform can be used as the information code of the Q component in rq (t).
There are only 8 possible waveforms for the I component in SOQPSK, I shown in FIG. 21，I2，I3,I4,I5,I6,I7,I8A similarity contrast channel is established for each base waveform, with two multipliers, two integrators, and an adder in each channel.
There are only 8 possible waveforms for the Q component in SOQPSK, Q shown in FIG. 21,Q2，Q3,Q4,Q5,Q6,Q7Q8A similarity contrast channel is established for each base waveform, with two multipliers, two integrators, and an adder in each channel.
Referring to fig. 2, ri (t) is obtained by respectively passing through multipliers in 8 channels:
CIm(t)＝I(t)Im(t)cos2(wct)+Q(t)Im(t)sin(wct)cos(wct), where m is 1,2,3,4,5,6,7, 8.
The formula of the double angle can be used to obtain:
referring to fig. 2, rq (t) shown is obtained after passing through multipliers in 8-way channels respectively:
CQn(t)＝I(t)Qn(t)sin(wct)cos(wct)+Q(t)Qn(t)sin2(wct), where n is 1,2,3,4,5,6,7, 8.
The formula of the double angle can be used to obtain:
the carrier frequency is an integer multiple of the symbol frequency and is much greater than the symbol frequency, and the product term carrying the carrier component can be eliminated in two symbol periods, so the use of two symbol periods is due to the fact that statistics are a function of the two symbol periods when setting the base waveform. The frequency of the signal is converted by a mixer, and then the frequency is integrated by an integrator to limit the signal so as to achieve the effect of low-pass filtering.
CIm(t) is obtained after passing through an integrator
Where m is 1,2,3,4,5,6,7,8, (note: coefficient 0.5 is omitted). CQn(t) is obtained after passing through an integrator
Wherein n is 1,2,3,4,5,6,7,8, (note: coefficient 0.5 is omitted).
The data of the basic waveform can be stored in a memory and called during demodulation, and the expression is
Wherein m is 1,2,3,4,5,6,7, 8;
wherein n is 1,2,3,4,5,6,7, 8.
8-way DIm(t) and 8 DQ pathsn(t) the signals respectively pass through the multiplier for negation and then are associated with the SI of the corresponding channelm(t)，SQn(t) performing addition operation to obtain 8
And 8
WT is derived by two sets of comparatorsmM and WQ corresponding to the maximum value in (t)nAnd (t) n corresponding to the maximum value.
Sending the obtained m, n into an 8-XTCQM decoder to obtain an original code, wherein the specific flow is as follows:
MI0＝[(m-1)/4]，MI1＝[((m-1)-MI0)/2]，MI2＝(m-1)-MI0-MI1；
MQ0＝[(n-1)/4]，MQ1＝[((n-1)-MQ0)/2]，MQ2＝(n-1)-MQ0-MQ1(ii) a Wherein]Represents rounding, [ x ]]Representing the largest integer not exceeding x.
KIn-1＝MI2，KQn-1＝MQ2，KIn＝(1-2KIn-1)KIn-1，KQn＝(1-2KQn-1)KQn-1，KInRepresenting the value of I, KI, of the original code at the current momentn-1I value representing source code of next last time；KQnRepresenting the Q value, KQ, of the original code at the current timen-1Representing the Q value of the original code at the last time.
KIn，KQnAnd performing serial-to-parallel conversion to obtain the original code.
The decoding method has error detection function and can be performed by MI1＝MQ1，MI0＝MQ0The principle of error detection is explained in detail in the precoding process of 8-XTCQM, see fig. 3, if it is established to do so.
The decoding mode has a proofreading function, KIn-1Representing the I value of the original code at the next previous moment, and performing error detection by comparing the I values in the previous original code; for the same reason, KQn-1And the Q value of the original code at the next previous moment is represented, and error detection is carried out by comparing the Q values in the previous original code.
Through the above detailed description of the present invention, the demodulation method utilizes the phase characteristics of the SOQPSK signal as much as possible in the aspects of the similarity comparison processing and the decoding processing, so that the difficulty of the demodulation process is greatly reduced, and the proposed demodulation method further includes an error detection function, which is not available in the conventional demodulation method.
By matlab
By obtaining a data result, such as the data shown in Table 1, the values in the x-th row and the y-th column represent
As a result of the operation of (3), the minimum value of 0 is obtained when x is equal to y among the 64 numerical values. That is, if and only if I (t) ═ I ' (t), the value thereof is 0, proving the requirement that "is" WI ' (t) ═ 0 "when I (t) and I ' (t) have a high degree of similarity; data shown in Table 2, values in x-th row and y-th column are shown as
The verification concept of the operation result of (1) is the same as that of the above, and therefore, the description thereof is omitted.
Table 1.
Result of the operation of
Table 2.
Result of the operation of
Claims (7)
1. A demodulation method of an SOQPSK signal is characterized in that the SOQPSK signal is subjected to orthogonalization processing through a synchronous carrier, an I component and a Q component which carry information are stripped from a high-frequency signal, then signal similarity comparison is carried out by utilizing the phase characteristics of the SOQPSK signal to obtain information codes of the I component and the Q component, and the obtained two groups of information codes are input into a decoder to obtain an original code;
the signal similarity comparison comprises the steps of multiplying the I component or the Q component with a basic waveform, integrating, comparing with the integral of the product of the basic waveform, taking the obtained difference value as a quantized value of the difference degree, and locking the information code corresponding to the basic waveform through the minimum quantized value of the difference degree.
2. The method of demodulating SOQPSK signal according to claim 1, wherein the orthogonalized I and Q components are respectively inputted into two sets of signal similarity comparison modules for comparing the signal similarities, each set of signal similarity comparison module contains a basic waveform of the waveform derived from the phase characteristics of the SOQPSK signal, and the two sets of signal similarity comparison modules contain all the representations of the SOQPSK signal;
and after the components I and Q respectively enter two groups of signal similarity comparison modules, performing signal similarity comparison to obtain an information code corresponding to the basic waveform of the minimum difference quantization value.
3. The method of demodulating an SOQPSK signal according to claim 2, wherein each group of signal similarity comparison modules includes a plurality of channels, each channel has one of the basic waveforms, and the plurality of basic waveforms included in the two groups of signal similarity comparison modules cover all representations of the SOQPSK signal.
4. The method of demodulating an SOQPSK signal according to claim 3, wherein each group of the signal similarity contrast modules includes 8 channels.
5. A method for demodulating an SOQPSK signal as claimed in claim 3 or 4, wherein each channel comprises a multiplier for multiplying the input component signal by the base waveform, two integrators for integrating the output signal of the multiplier, and a subtractor for subtracting the output of the two integrators and taking the difference as the quantized value of the difference.
6. The method of claim 3 or 4, wherein each channel comprises two multipliers, two integrators and an adder, wherein one of the multipliers is used for inputting the product of the component signal and the base waveform, one of the integrators is used for integrating the multiplied signal, the other multiplier is used for inverting the integrated signal, the other integrator is used for multiplying the square of the base waveform, the adder is used for adding the inverted signal and the square of the base waveform, and the added value is used as the quantized value of the difference.
7. The method of demodulating SOQPSK signal as claimed in any one of claims 1-3, wherein the decoder uses 8-XTCQM decoding method to decode the I and Q component information codes by 8-XTCQM to obtain the original code.
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Denomination of invention: A demodulation method of SOQPSK signal Effective date of registration: 20211215 Granted publication date: 20200424 Pledgee: Agricultural Bank of China Limited Chengdu Jincheng sub branch Pledgor: CHENGDU YERUAN TECHNOLOGY CO.,LTD. Registration number: Y2021980015176 |