CN117544457A - Combined time domain equalization method under CPM modulation - Google Patents
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Abstract
The application provides a joint time domain equalization method under CPM modulation, which comprises the steps of receiving an initial signal, sampling, obtaining first data in local storage, processing the first data to obtain a first head scattered pilot signal, respectively performing first processing and second processing on the first head scattered pilot signal to obtain a first processed signal and a second processed signal, respectively performing third processing on the first processed signal to obtain a third processed signal, performing fourth processing on the second processed signal to obtain a fourth processed signal, obtaining a channel estimation frequency response, performing signal-to-noise ratio estimation on the first processed signal to obtain a signal-to-noise ratio estimation value, obtaining a frequency domain equalization coefficient according to the channel estimation frequency response and the signal-to-noise ratio estimation value, obtaining second data and a tail scattered pilot signal, and processing the second data and the tail scattered pilot signal to obtain a fifth processed signal to obtain a time domain signal after single carrier equalization; by the method, the problem that the channel parameters cannot be estimated correctly due to insufficient signal-to-noise ratio detection in the traditional frequency domain single carrier equalization method under the condition of low signal-to-noise ratio can be solved.
Description
Technical Field
The application relates to the technical field of single carrier equalization, in particular to a joint time domain equalization method under CPM modulation.
Background
The single carrier equalization technology is an effective method for resisting frequency selective fading, when a signal is transmitted from a transmitting end to a receiving end, under the condition of low signal-to-noise ratio, particularly when the signal is transmitted after being processed by a CPM (Continue Phase Modulation) modulation mode, because some noise exists in a transmission environment, the signal can be interfered in the transmission process, namely, serious inter-code crosstalk problem exists, so that the single carrier equalization technology cannot work normally, and the signal received by the receiving end is inconsistent with the signal sent by the transmitting end.
Disclosure of Invention
The present application aims to solve the above problems, and provides a joint time domain equalization method under CPM modulation, including:
receiving an initial signal, wherein the initial signal is obtained after CPM modulation processing, and the initial signal comprises bit synchronization information which is used for representing a start mark and an end mark of a data bit in the initial signal;
sampling the initial signal according to the bit synchronization information in a first preset time length every interval;
acquiring first data stored locally according to the bit synchronization information, wherein the first data comprises an initial head scattered pilot signal, and performing CPM modulation processing on the initial head scattered pilot signal to obtain a first head scattered pilot signal;
performing first processing on the first head scattered pilot signals to obtain first processing signals so as to realize time domain cross correlation of the first head scattered pilot signals;
performing second processing on the first head scattered pilot signals to obtain second processing signals so as to realize time domain autocorrelation of the first head scattered pilot signals;
performing fast Fourier transform on the first processing signal to obtain a third processing signal, and performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
taking the third processing signal as a numerator and the fourth processing signal as a denominator, and calculating to obtain a channel estimation frequency response;
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio estimation value;
according to the channel estimation frequency response and the signal to noise ratio estimation value, calculating to obtain a frequency domain equalization coefficient;
the initial signal also comprises second data and tail scattered pilot frequency, and the second data and the tail scattered pilot frequency are subjected to fast Fourier change to obtain a fifth processing signal;
calculating the product of the fifth processing signal and the frequency domain equalization coefficient, performing fast Fourier inverse transformation to obtain a sixth processing signal, and intercepting the first N in the corresponding sequence length d Obtaining the time domain signal after single carrier equalization by a plurality of symbols, wherein N is as follows d Representing the total number of symbols in the second data.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
acquiring a filter coefficient of a receiving end;
the first head scattered pilot signal is subjected to first processing to obtain a first processing signal, which comprises the following steps:
convolving the filter coefficient with the first head scattered pilot signal to obtain a first signal; performing fast Fourier transform on the first signal to obtain a second signal;
the initial signal also comprises a head scattered pilot signal, and the head scattered pilot signal is obtained;
performing fast Fourier change on the head scattered pilot signals to obtain third signals;
performing conjugate multiplication on the second signal and the third signal to obtain a fourth signal;
and performing fast Fourier inverse change processing on the fourth signal to obtain the first processing signal.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
acquiring the second signal and the fourth signal;
performing second processing on the first head scattered pilot signals to obtain second processed signals, including:
multiplying the second signal by the fourth signal to obtain a fifth signal;
and performing fast Fourier inverse change processing on the fifth signal to obtain the second processing signal.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
acquiring a second sequence length of the first processing signal;
the performing fast fourier transform on the first processed signal to obtain a third processed signal includes:
when judging that the second sequence length meets the fast Fourier transform rule, performing fast Fourier transform on the first processing signal to obtain the third processing signal;
and when the second sequence length is judged to not meet the fast Fourier transform rule, filling the second sequence length, and performing fast Fourier transform to obtain the third processing signal.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
acquiring a third sequence length of the second processing signal;
the fast fourier transform is performed on the second processed signal to obtain a fourth processed signal, including:
when the third sequence length is judged to meet the fast Fourier transform rule, performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
and when the third sequence length is judged to not meet the fast Fourier transform rule, filling the third sequence length, and performing fast Fourier transform to obtain the fourth processing signal.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio curve;
the signal-to-noise ratio estimating the first processing signal to obtain a signal-to-noise ratio estimated value includes:
obtaining the peak value of the signal-to-noise ratio curve;
calculating the data variance of other data except the peak value in the signal-to-noise ratio curve;
and solving the square of the peak value, taking the square of the peak value as a numerator and the data variance as a denominator, and calculating to obtain the signal-to-noise ratio estimated value.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
the step of calculating the frequency domain equalization coefficient according to the channel estimation frequency response and the signal to noise ratio estimation value specifically comprises the following steps:
performing conjugate multiplication on the channel estimation frequency response to obtain a first numerical value;
calculating the product of the first value and the channel estimation frequency response to obtain a second value;
calculating the sum of the second value and the signal-to-noise ratio estimated value to obtain a third value;
and taking the first numerical value as a numerator, taking the third numerical value as a denominator, and performing product division to obtain the frequency domain equalization coefficient.
According to the technical scheme provided by the embodiment of the application, the fourth sequence length of the second data is obtained, and the fifth sequence length of the tail scattered pilot frequency is obtained;
adding according to the fourth sequence length and the fifth sequence length to obtain a sixth sequence length;
and performing fast fourier transform on the second data and the tail scattered pilot frequency to obtain a fifth processing signal, including:
when judging that the length of the sixth sequence meets a fast Fourier transform rule, performing fast Fourier transform on the second data and the tail dispersion at the same time to obtain the fifth processing signal;
and when judging that the length of the sixth sequence does not meet the fast Fourier transform rule, filling the length of the sixth sequence, and performing fast Fourier transform to obtain the fifth processing signal.
According to the technical scheme provided by the embodiment of the application, the method further comprises the following steps:
acquiring a first sequence length of the first signal;
performing fast fourier transform on the first signal to obtain a second signal, including:
when judging that the length of the first sequence meets the rule of the fast Fourier transform, performing the fast Fourier transform on the first signal to obtain a second signal;
and when the first sequence length is judged to not meet the fast Fourier transform rule, filling the first sequence length, and performing fast Fourier transform to obtain the second signal.
According to the technical scheme provided by the embodiment of the application, the sequence length corresponding to the head scattered pilot frequency is obtained;
performing fast fourier transform on the head scattered pilot signal to obtain a third signal, including:
when judging that the sequence length of the head scattered pilot signals meets a fast Fourier change rule, performing fast Fourier change on the head scattered pilot signals to obtain the third signals;
and when judging that the sequence length of the head scattered pilot signals does not meet the rule of the fast Fourier change, filling the sequence length of the head scattered pilot signals, and carrying out the fast Fourier change to obtain the third signal.
Compared with the prior art, the beneficial effect of this application:
the method comprises the steps of carrying out CPM modulation processing on initial signals after CPM modulation processing is received, sampling the initial head scattered pilot signals in first data stored locally to obtain first head scattered pilot signals, carrying out first processing on the first head scattered pilot signals to achieve time domain cross correlation of the first head scattered pilot signals, carrying out second processing on the first head scattered pilot signals to achieve time domain self correlation of the first head scattered pilot signals, and carrying out fast Fourier change on the first processed signals to obtain third processed signals; performing fast Fourier change on the second processing signal to obtain a fourth processing signal, taking the third processing signal as a molecule, taking the fourth processing signal as a denominator, calculating to obtain a channel estimation frequency response, performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio estimation value, obtaining a frequency domain equalization coefficient according to the channel estimation frequency response and the signal-to-noise ratio estimation value, performing fast Fourier change on the second data in the initial signal and the tail scattered pilot frequency to obtain a fifth processing signal, and finally obtaining a time domain signal after single carrier equalization according to the fifth processing signal and the frequency domain equalization coefficient.
In the use process, firstly, an initial signal after CPM modulation processing is received, sampling is carried out on the initial signal according to synchronization in the initial signal as information every interval for a first preset time length, the first data stored locally is obtained, the same CPM modulation processing is carried out on the initial head scattered pilot signal in the first data, the first head scattered pilot signal is obtained, then the first processing is carried out, a first processing signal is obtained, the time domain cross-correlation of the first head scattered pilot signal can be realized, the second processing is carried out on the first head scattered pilot signal, a second processing signal is obtained, the time domain autocorrelation of the first head scattered pilot signal can be realized, the first processing signal is subjected to fast Fourier change, a third processing signal is obtained, the second processing signal is subjected to fast Fourier change, a fourth processing signal is obtained, channel estimation frequency response is obtained according to the fourth processing signal, the first processing signal is subjected to signal to noise ratio estimation, a frequency domain equalization coefficient is obtained according to the signal noise ratio estimation value and the channel estimation frequency, the second data in the initial signal and the tail scattered pilot signal are subjected to fast Fourier change, and the obtained signal is equalized according to a fifth carrier wave obtained after the time domain is subjected to the fast Fourier change;
the method can solve the problem that the traditional frequency domain single carrier equalization method cannot estimate the channel parameters correctly under the condition of low signal-to-noise ratio due to insufficient detection signal-to-noise ratio, and the method effectively improves the detection signal-to-noise ratio through correlation gain by performing time domain correlation, including time domain positive correlation and time domain autocorrelation, on the received signals, and ensures the accuracy of frequency domain single carrier equalization under the condition of low signal-to-noise ratio; the method can also solve the problem that under the CPM modulation mode, the channel parameter estimation effect is deteriorated under the multipath environment due to the inter-code crosstalk existing in the modulation mode, and ensure the accuracy of CPM modulation frequency domain single carrier equalization under the multipath environment.
Drawings
Fig. 1 is a flowchart of a joint time domain equalization method under CPM modulation provided in an embodiment of the present application;
FIG. 2 is a signal structure diagram provided in an embodiment of the present application;
fig. 3 is a constellation diagram before equalization under a multipath channel when GMSK modulation is performed by the method according to the embodiment of the present application;
fig. 4 is a constellation diagram after equalization under a multipath channel when GMSK modulation is performed by the method according to the embodiment of the present application;
fig. 5 is a comparison result of bit error rate simulation before and after equalization under a multipath channel during GMSK modulation according to an embodiment of the present application.
Detailed Description
In order that those skilled in the art may better understand the technical solutions of the present application, the following detailed description of the present application is provided by way of example and illustration only, and should not be construed to limit the scope of the present application in any way.
CPM is continuous phase modulation (Continue Phase Modulation), is a phase modulation technology, has the characteristic of continuous phase, has excellent spectrum characteristics, and has higher frequency band utilization rate compared with a PSK modulation mode (PSK modulation is a digital modulation technology and represents an input signal through carrier phase);
the single carrier equalization technology is an effective method for resisting frequency selective fading, when a signal is transmitted from a transmitting end to a receiving end, under the condition of low signal-to-noise ratio, particularly when the signal is transmitted after being processed by a CPM (Continue Phase Modulation) modulation mode, because some noise exists in a transmission environment, the signal can be interfered in the transmission process, namely, serious inter-code crosstalk problem exists, so that the single carrier equalization technology cannot work normally, and the signal received by the receiving end is inconsistent with the signal sent by the transmitting end.
The present application provides a joint time domain equalization method under CPM modulation, in which channel estimation is performed by combining time domain with frequency domain, so that a finally obtained single carrier equalized time domain signal is consistent with a signal sent by a transmitting end.
The method for joint time domain equalization under CPM modulation provided by the application is shown in fig. 1, and comprises the following steps:
s1, receiving an initial signal, wherein the initial signal is obtained after CPM modulation processing, the initial signal comprises bit synchronization information, and the bit synchronization information is used for representing a start mark and an end mark of a data bit in the initial signal;
s2, sampling the initial signal according to the bit synchronization information in a first preset time length at each interval;
s3, acquiring first data stored locally according to the bit synchronization information, wherein the first data comprises initial head scattered pilot signals, and performing CPM modulation processing on the initial head scattered pilot signals to obtain first head scattered pilot signals;
s4, performing first processing on the first head scattered pilot signals to obtain first processing signals so as to realize time domain cross correlation of the first head scattered pilot signals;
s5, performing second processing on the first head scattered pilot signals to obtain second processing signals so as to realize time domain autocorrelation of the first head scattered pilot signals;
s6, performing fast Fourier transform on the first processing signal to obtain a third processing signal, and performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
s7, calculating to obtain a channel estimation frequency response by taking the third processing signal as a molecule and the fourth processing signal as a denominator;
s8, performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio estimation value;
s9, calculating to obtain a frequency domain equalization coefficient according to the channel estimation frequency response and the signal-to-noise ratio estimation value;
s10, the initial signal also comprises second data and tail scattered pilot frequency, and fast Fourier change is carried out on the second data and the tail scattered pilot frequency to obtain a fifth processing signal;
s11, calculating a fifth processing signal and a frequency domainEqualizing the product of the coefficients, performing fast Fourier inverse transformation to obtain a sixth processing signal, and intercepting the first N in the corresponding sequence length d Obtaining the time domain signal after single carrier equalization by a plurality of symbols, wherein N is as follows d Representing the total number of symbols in the second data.
Specifically, in this embodiment, an initial signal sent by a transmitting end is first received, where the initial signal is obtained after CPM modulation processing, the initial signal includes bit synchronization information, where the bit synchronization information is used to characterize a flag of start and end of a data bit in the initial signal, and the initial signal further includes a head scattered pilot, a second data and a tail scattered pilot; sampling second data and tail scattered pilot frequency in the initial signal according to the bit synchronization information in the initial signal at each interval for a first preset time length, wherein the expression of the sampled signal is as follows:
r(n)＝[C(n c1 t s -τ 0 ) D(n d t s ) C(n c2 t s -τ 0 )],n＝0,1,...,N-1
wherein: r (n) represents the sampled signal;
C(n c1 t s ) Represents n c1 t s Head scattered pilot frequency of sampling time, n c1 ＝0,1,......,N c -1，N c Representing the length of the tail scattered pilot;
t s taking the time domain sampling interval as the duration of one symbol, namely a first preset duration;
τ 0 representing an initial phase of the head scattered pilot;
D(n d t s ) Represents n d t s Third data of sampling time, which is data except for head scattered pilot and tail scattered pilot, namely useful data, n d ＝N c ,N c +1,...,N c +N d -1，N d Representing the length of the third data;
n represents a sampling point;
C(n c2 t s ) Substitution ofTable n c2 t s Tail scattered pilot frequency of sampling time, n c2 ＝Nc+Nd,Nc+Nd-1,....,N-1。
Acquiring first data stored locally according to the bit synchronization information, wherein the first data also stores the bit synchronization information, acquiring the bit synchronization information in the first data according to the bit synchronization information in the initial signal so as to enable the signal obtained by sampling to be consistent with the signal stored locally, wherein the first data comprises an initial head scattered pilot signal, and performing CPM modulation processing on the initial head scattered pilot signal, which is the same as that of the initial signal, to obtain a first head scattered pilot signal;
the expression of the first head scattered pilot signal is:
wherein: s is(s) mod Representing a first head scattered pilot signal;
exp (·) represents an exponentiation exponent operation;
e represents the energy of each symbol in the first head scattered pilot signal;
is the initial phase;
t s taking the time domain sampling interval as the duration of one symbol, namely a first preset duration;
a i a transmitted symbol sequence representing M-ary, the range of values of the sequence being { ±1, ±3.+ -. M-1};
h is the modulation index;
j represents a complex number;
representing the phase of the modulated signal;
i represents the phase accumulation sampling point of the modulated signal;
t represents time, for example, t is 0 to 1s and ts is 1ms;
n represents a sampling point;
q (t) is the integral of the gaussian minimum shift keying pulse g (t), i.e.:
g(t)＝Q[2πB(t-t s /2)/(ln2) 0.5 ]-Q[2πB(t+t s /2)/(ln2) 0.5 ]
where B represents the channel bandwidth.
Further, the method further comprises:
acquiring a filter coefficient of a receiving end;
the first head scattered pilot signal is subjected to first processing to obtain a first processing signal, which comprises the following steps:
performing convolution operation on the filter coefficient and the first head scattered pilot signal to obtain a first signal, and performing fast Fourier change processing on the first signal to obtain a second signal;
the initial signal also comprises a head scattered pilot signal, the head scattered pilot signal is obtained, and fast Fourier change processing is carried out on the head scattered pilot signal to obtain a third signal;
performing conjugate multiplication on the second signal and the third signal to obtain a fourth signal;
and performing fast Fourier inverse change processing on the fourth signal to obtain the first processing signal.
Specifically, in this embodiment, the coefficient of the filter in the receiving end is obtained, and the coefficient of the filter and the first header are scatteredConvolving the frequency to obtain a first signalFor the first signal->Performing fast Fourier change processing to obtain a second signal, when the first signal is subjected to fast Fourier change, acquiring a first sequence length corresponding to the first signal, and when the first sequence length is judged to meet a fast Fourier change rule, performing fast Fourier change on the first signal to obtain the second signal; when judging that the first sequence length does not meet the fast Fourier transform rule, filling the first sequence length, performing fast Fourier transform on the filled first signal to obtain the second signal, performing Fast Fourier Transform (FFT) on the head scattered pilot frequency in the initial signal to obtain a third signal, when performing fast Fourier transform on the head scattered pilot frequency, acquiring the sequence length corresponding to the head scattered pilot frequency, and when judging that the sequence length corresponding to the head scattered pilot frequency meets the fast Fourier transform rule, performing fast Fourier transform on the head scattered pilot frequency to obtain the third signal; when judging that the sequence length corresponding to the head scattered pilot frequency does not meet the fast Fourier change rule, filling the sequence length corresponding to the head scattered pilot frequency, and performing fast Fourier change on the filled head scattered pilot frequency to obtain the third signal;
performing conjugate multiplication on the second signal and the third signal to obtain a fourth signal, and performing Inverse Fast Fourier Transform (IFFT) processing on the fourth signal to obtain a first processed signal, so as to implement time domain cross correlation of the first scattered pilot signal, thereby improving the signal ratio of the first scattered pilot, where the specific expression of the processing is as follows:
wherein: FFT (·) representation pairThe time domain signal is subjected to FFT processing, the length of the FFT processing is an integer power value of least 2 greater than Nc (for example, the length of the first signal is 10, the processing length of the FFT is 2 4 I.e. 16);
IFFT (·) means IFFT processing the frequency domain signal;
(·) represents performing conjugate processing on the signal;
representing a first signal;
C(n c1 t s ) Represents n c1 t s Head scattered pilot frequency of sampling time, n c1 ＝0,1,......,N c -1，N c Representing the length of the tail scattered pilot;
r sx representing the time domain cross correlation result of the scattered pilot frequency of the received signal;
further, the method further comprises:
acquiring the second signal and the fourth signal;
performing second processing on the first head scattered pilot signals to obtain second processed signals, including:
multiplying the second signal by the fourth signal to obtain a fifth signal;
and performing fast Fourier inverse change processing on the fifth signal to obtain the second processing signal.
Specifically, in this embodiment, the second signal and the fourth signal are obtained, the product of the second signal and the fourth signal is obtained, and then the fifth signal is subjected to Inverse Fast Fourier Transform (IFFT) processing, so as to obtain a second processed signal, thereby implementing time-domain autocorrelation of the first head scattered pilot signal;
the specific expression of the above process is:
r xx representing the autocorrelation result.
Further, the method further comprises:
acquiring a second sequence length of the first processing signal;
the performing fast fourier transform on the first processed signal to obtain a third processed signal includes:
when judging that the second sequence length meets the fast Fourier transform rule, performing fast Fourier transform on the first processing signal to obtain the third processing signal;
and when the second sequence length is judged to not meet the fast Fourier transform rule, filling the second sequence length, and performing fast Fourier transform to obtain the third processing signal.
Specifically, in this embodiment, a second sequence length of the first processing signal is obtained, and when the second sequence length is determined to satisfy a fast fourier transform rule, a fast fourier transform is directly performed on the first processing signal to obtain the third processing signal;
judging whether the second sequence length meets a fast Fourier change rule, wherein the fast Fourier change rule is an integer power value larger than the minimum 2 of the second sequence length, if not, the second sequence length of the first processing signal needs to be filled, for example, the second sequence length is 10, and the FFT processing length is 2 4 Namely 16, 6 0 are required to be filled on the basis of the second sequence length so as to meet FFT processing rules, and after the filling is finished, the first processing signals after filling are subjected to fast Fourier change to obtain third processing signals;
the method can be concretely represented as follows:
R sx ＝FFT([r sx z i1 ])
wherein z is i1 R represents sx I.e. the number of 0 s filled by the second sequence length.
Further, the method further comprises:
acquiring a third sequence length of the second processing signal;
the fast fourier transform is performed on the second processed signal to obtain a fourth processed signal, including:
when the third sequence length is judged to meet the fast Fourier transform rule, performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
and when the third sequence length is judged to not meet the fast Fourier transform rule, filling the third sequence length, and performing fast Fourier transform to obtain the fourth processing signal.
Acquiring a third sequence length of the second processing signal, judging whether the third sequence length meets a fast Fourier change rule, wherein the fast Fourier change rule is an integer power value which is more than the minimum 2 of the third sequence length, and when the third sequence length meets the fast Fourier change rule, directly performing fast Fourier change on the second processing signal to obtain a fourth processing signal;
if not, the third sequence length of the second processed signal needs to be padded, for example, the third sequence length is 10, and the processing length of the FFT is 2 4 Namely 16, 6 0 are required to be filled on the basis of the third sequence length so as to meet FFT processing rules, and after filling, the filled second processing signals are subjected to fast Fourier change to obtain fourth processing signals;
the method can be concretely represented as follows:
R xx ＝FFT([r xx z i2 ])
wherein z is i2 R represents xx I.e. the number of 0 s filled by the third sequence length.
Further, the method further comprises:
the specific step of obtaining the channel estimation frequency response according to the third processing signal and the fourth processing signal includes:
and taking the third processing signal as a molecule, taking the fourth processing signal as a denominator, and performing product removal to obtain the channel estimation frequency response.
Specifically, in this embodiment, the channel estimation frequency response Λ is obtained by taking the third processing signal as a numerator and the fourth processing signal as a denominator and by dividing the product, and may specifically be represented by the following formula:
Λ＝R sx /R xx 。
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio estimation value;
further, the method further comprises:
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio curve;
the signal-to-noise ratio estimating the first processing signal to obtain a signal-to-noise ratio estimated value includes:
obtaining the peak value of the signal-to-noise ratio curve;
calculating the data variance of other data except the peak value in the signal-to-noise ratio curve;
and solving the square of the peak value, taking the square of the peak value as a numerator and the data variance as a denominator, and calculating to obtain the signal-to-noise ratio estimated value.
Specifically, in this embodiment, the snr of the first processed signal is estimated to obtain an snr curve, and a peak value of the snr curve is obtained from the snr curve and recorded as a sx At the same time, it is necessary to calculate the signal-to-noise ratio curve except for peak value A sx Data variance of all data except for, and recording the result as sigma sx Solving the square of the peak value, taking the square of the peak value as a numerator and the data variance as a denominator, and calculating to obtain the signal-to-noise ratio estimation value, wherein the expression of the signal-to-noise ratio estimation value SNR is as follows:
further, the step of calculating the frequency domain equalization coefficient according to the channel estimation frequency response and the signal to noise ratio estimation value specifically includes:
performing conjugate multiplication on the channel estimation frequency response to obtain a first numerical value;
calculating the product of the first value and the channel estimation frequency response to obtain a second value;
calculating the sum of the second value and the signal-to-noise ratio estimated value to obtain a third value;
and taking the first numerical value as a numerator, taking the third numerical value as a denominator, and performing product division to obtain the frequency domain equalization coefficient.
Specifically, in this embodiment, conjugate multiplication is performed on the channel estimation frequency response to obtain a first value after the conjugate multiplication is performed, a product of the first value and the channel estimation frequency response is calculated to obtain a second value, a sum of the second value and the signal-to-noise ratio estimation value is solved to obtain a third value, the first value is used as a numerator, the third value is used as a denominator, and a product is made to obtain the frequency domain equalization coefficient H;
according to the channel estimation frequency response lambda and the signal-to-noise ratio estimation value SNR, a specific expression for calculating the frequency domain equalization coefficient H is as follows:
Λ * representing the conjugate multiplication of the channel estimate frequency response Λ.
Further, the method further comprises:
acquiring a fourth sequence length of the second data and a fifth sequence length of the tail scattered pilot frequency;
adding according to the fourth sequence length and the fifth sequence length to obtain a sixth sequence length;
and performing fast fourier transform on the second data and the tail scattered pilot frequency to obtain a fifth processing signal, including:
when judging that the length of the sixth sequence meets a fast Fourier transform rule, performing fast Fourier transform on the second data and the tail dispersion at the same time to obtain the fifth processing signal;
and when judging that the length of the sixth sequence does not meet the fast Fourier transform rule, filling the length of the sixth sequence, and performing fast Fourier transform to obtain the fifth processing signal.
Specifically, in this embodiment, a fourth sequence length of the second data is obtained, a fifth sequence length of the tail scattered pilot is obtained, a sixth sequence length is obtained by adding the fourth sequence length and the fifth sequence length, and when the sixth sequence length is determined to satisfy the fourier transform rule, a fast fourier transform is performed on the second data and the tail scattered pilot after being combined together to obtain a fifth processing signal;
when judging that the length of the sixth sequence does not meet the fast Fourier transform rule, filling the length of the sixth sequence to enable the length of the sixth sequence to meet the fast Fourier transform rule, and performing fast Fourier transform on the second data after filling and the tail scattered pilot frequency to obtain a fifth processing signal; the specific formula is as follows:
R＝FFT([r z k ])
wherein: r represents the combined second data and tail scattered pilots in the sampled signal r (n);
z k representing the number of 0 s filled by the sixth sequence length.
Further, the step of obtaining the time domain signal after single carrier equalization according to the fifth processing signal and the frequency domain equalization coefficient specifically includes:
solving the product of the fifth processing signal and the frequency domain equalization coefficient, and performing fast Fourier inverse transformation processing to obtain a sixth processing signal;
acquiring a sixth sequence length of a sixth processing signal, and intercepting N before d Obtaining the time domain signal after single carrier equalization by a plurality of symbols, wherein N is as follows d Representing the total number of symbols in the second data.
Multiplying the fifth processing signal with the frequency domain equalization coefficient, performing fast Fourier inverse change to obtain a sixth processing signal, obtaining a sixth sequence length in the sixth processing signal, and intercepting the previous N d Obtaining the time domain signal after single carrier equalization
The specific expression is as follows:
r h ＝IFFT(R×H)
wherein: r is (r) h Representing the result obtained by the inverse fast Fourier transform of the product of the fifth processing signal and the frequency domain equalization coefficient;
n h representing the number of bits of the symbol in the second data.
As shown in fig. 3 and 4: fig. 3 shows a constellation diagram before equalization under a multipath channel in GMSK modulation according to the method described in the present application;
fig. 4 shows a constellation diagram after equalization under a multipath channel in GMSK modulation (minimum shift keying of gaussian filtering before modulation), and the constellation diagram after equalization is corrected to a correct position after equalization as can be seen by comparison;
fig. 5 shows the simulation comparison result of the bit error rate before and after equalization under the multipath channel in GMSK modulation in the method described in the present application, and the bit error rate before equalization is extremely high, the bit error rate after equalization is obviously reduced, and the demodulation threshold is about 10dB back than the theoretical bit error rate.
Specific examples are set forth herein to illustrate the principles and embodiments of the present application, and the description of the examples above is only intended to assist in understanding the methods of the present application and their core ideas. The foregoing is merely a preferred embodiment of the present application, and it should be noted that, due to the limited nature of text, there is an objectively infinite number of specific structures, and that, to those skilled in the art, several improvements, modifications or changes can be made, and the above technical features can be combined in a suitable manner, without departing from the principles of the present invention; such modifications, variations and combinations, or the direct application of the concepts and aspects of the invention in other applications without modification, are intended to be within the scope of this application.
Claims (10)
1. A joint time domain equalization method under CPM modulation, comprising:
receiving an initial signal, wherein the initial signal is obtained after CPM modulation processing, and the initial signal comprises bit synchronization information which is used for representing a start mark and an end mark of a data bit in the initial signal;
sampling the initial signal according to the bit synchronization information in a first preset time length every interval;
acquiring first data stored locally according to the bit synchronization information, wherein the first data comprises an initial head scattered pilot signal, and performing CPM modulation processing on the initial head scattered pilot signal to obtain a first head scattered pilot signal;
performing first processing on the first head scattered pilot signals to obtain first processing signals so as to realize time domain cross correlation of the first head scattered pilot signals;
performing second processing on the first head scattered pilot signals to obtain second processing signals so as to realize time domain autocorrelation of the first head scattered pilot signals;
performing fast Fourier transform on the first processing signal to obtain a third processing signal, and performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
taking the third processing signal as a numerator and the fourth processing signal as a denominator, and calculating to obtain a channel estimation frequency response;
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio estimation value;
according to the channel estimation frequency response and the signal to noise ratio estimation value, calculating to obtain a frequency domain equalization coefficient;
the initial signal also comprises second data and tail scattered pilot frequency, and the second data and the tail scattered pilot frequency are subjected to fast Fourier change to obtain a fifth processing signal;
calculating the product of the fifth processing signal and the frequency domain equalization coefficient, and performing fastFourier inverse transformation is carried out to obtain a sixth processing signal, and the first N in the corresponding sequence length is intercepted d Obtaining the time domain signal after single carrier equalization by a plurality of symbols, wherein N is as follows d Representing the total number of symbols in the second data.
2. The method of joint time domain equalization under CPM modulation of claim 1, further comprising:
acquiring a filter coefficient of a receiving end;
the first head scattered pilot signal is subjected to first processing to obtain a first processing signal, which comprises the following steps:
convolving the filter coefficient with the first head scattered pilot signal to obtain a first signal; performing fast Fourier transform on the first signal to obtain a second signal;
the initial signal also comprises a head scattered pilot signal, and the head scattered pilot signal is obtained;
performing fast Fourier change on the head scattered pilot signals to obtain third signals;
performing conjugate multiplication on the second signal and the third signal to obtain a fourth signal;
and performing fast Fourier inverse change processing on the fourth signal to obtain the first processing signal.
3. The method of joint time domain equalization under CPM modulation of claim 2, further comprising:
acquiring the second signal and the fourth signal;
performing second processing on the first head scattered pilot signals to obtain second processed signals, including:
multiplying the second signal by the fourth signal to obtain a fifth signal;
and performing fast Fourier inverse change processing on the fifth signal to obtain the second processing signal.
4. The method of joint time domain equalization under CPM modulation of claim 1, further comprising:
acquiring a second sequence length of the first processing signal;
the performing fast fourier transform on the first processed signal to obtain a third processed signal includes:
when judging that the second sequence length meets the fast Fourier transform rule, performing fast Fourier transform on the first processing signal to obtain the third processing signal;
and when the second sequence length is judged to not meet the fast Fourier transform rule, filling the second sequence length, and performing fast Fourier transform to obtain the third processing signal.
5. The method of joint time domain equalization under CPM modulation of claim 1, further comprising:
acquiring a third sequence length of the second processing signal;
the fast fourier transform is performed on the second processed signal to obtain a fourth processed signal, including:
when the third sequence length is judged to meet the fast Fourier transform rule, performing fast Fourier transform on the second processing signal to obtain a fourth processing signal;
and when the third sequence length is judged to not meet the fast Fourier transform rule, filling the third sequence length, and performing fast Fourier transform to obtain the fourth processing signal.
6. The method of joint time domain equalization under CPM modulation of claim 1, further comprising:
performing signal-to-noise ratio estimation on the first processing signal to obtain a signal-to-noise ratio curve;
the signal-to-noise ratio estimating the first processing signal to obtain a signal-to-noise ratio estimated value includes:
obtaining the peak value of the signal-to-noise ratio curve;
calculating the data variance of other data except the peak value in the signal-to-noise ratio curve;
and solving the square of the peak value, taking the square of the peak value as a numerator and the data variance as a denominator, and calculating to obtain the signal-to-noise ratio estimated value.
7. The method for joint time domain equalization under CPM modulation as claimed in claim 1, wherein said step of calculating a frequency domain equalization coefficient according to a channel estimation frequency response and a signal to noise ratio estimation value specifically comprises:
performing conjugate multiplication on the channel estimation frequency response to obtain a first numerical value;
calculating the product of the first value and the channel estimation frequency response to obtain a second value;
calculating the sum of the second value and the signal-to-noise ratio estimated value to obtain a third value;
and taking the first numerical value as a numerator, taking the third numerical value as a denominator, and performing product division to obtain the frequency domain equalization coefficient.
8. The method of joint time domain equalization under CPM modulation of claim 1, further comprising:
acquiring a fourth sequence length of the second data and a fifth sequence length of the tail scattered pilot frequency;
adding according to the fourth sequence length and the fifth sequence length to obtain a sixth sequence length;
and performing fast fourier transform on the second data and the tail scattered pilot frequency to obtain a fifth processing signal, including:
when judging that the length of the sixth sequence meets a fast Fourier transform rule, performing fast Fourier transform on the second data and the tail dispersion at the same time to obtain the fifth processing signal;
and when judging that the length of the sixth sequence does not meet the fast Fourier transform rule, filling the length of the sixth sequence, and performing fast Fourier transform to obtain the fifth processing signal.
9. The method of joint time domain equalization under CPM modulation of claim 2, further comprising:
acquiring a first sequence length of the first signal;
performing fast fourier transform on the first signal to obtain a second signal, including:
when judging that the length of the first sequence meets the rule of the fast Fourier transform, performing the fast Fourier transform on the first signal to obtain a second signal;
and when the first sequence length is judged to not meet the fast Fourier transform rule, filling the first sequence length, and performing fast Fourier transform to obtain the second signal.
10. The method of joint time domain equalization under CPM modulation of claim 2, further comprising:
acquiring a sequence length corresponding to the head scattered pilot frequency;
performing fast fourier transform on the head scattered pilot signal to obtain a third signal, including:
when judging that the sequence length of the head scattered pilot signals meets a fast Fourier change rule, performing fast Fourier change on the head scattered pilot signals to obtain the third signals;
and when judging that the sequence length of the head scattered pilot signals does not meet the rule of the fast Fourier change, filling the sequence length of the head scattered pilot signals, and carrying out the fast Fourier change to obtain the third signal.
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