CN113612714A - Multi-symbol detection demodulation method and telemetering PCM/FM signal demodulation method - Google Patents
Multi-symbol detection demodulation method and telemetering PCM/FM signal demodulation method Download PDFInfo
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Abstract
The invention provides a multi-symbol detection demodulation method, which comprises the steps of firstly obtaining a baseband complex signal to be demodulated and a plurality of groups of local reference wave signals, matching the number of sample points of the baseband complex signal with the number of sample points of the local reference wave signals to the same number, then carrying out maximum likelihood calculation, searching the waveform combination of the local reference wave signals corresponding to the maximum likelihood value, and then outputting the corresponding local code element information as demodulation code element information. The invention can realize MSD demodulation of a plurality of code rates by sample point number matching, optimizes the maximum likelihood calculation process and reduces the calculation difficulty and complexity by adopting a shift register to store a modular square value, so that the method can be realized in hardware such as FPGA/DSP and the like. The invention also provides a telemetering PCM/FM signal demodulation method adopting the multi-symbol detection demodulation method, and simultaneously, multi-level buffers are designed in each step of operation, comparison and the like, so that the operation speed of the system is improved, and the invention can realize stable and reliable demodulation under high code rate.
Description
Technical Field
The invention belongs to the field of digital communication, and relates to a multi-symbol detection demodulation method and a telemetering PCM/FM (pulse code modulation/frequency modulation) signal demodulation method adopting the multi-symbol detection demodulation method.
Background
The PCM/FM modulation and demodulation system is used as a main communication system in the telemetering system, after band-pass filtering and down-conversion processing are carried out on an intermediate frequency FM signal, cross-product frequency discrimination demodulation or MSD demodulation is carried out to obtain original information, and the cross-product frequency discrimination demodulation is mainly used in the traditional demodulation mode. However, the demodulation method of cross product frequency discrimination has threshold effect, that is, when the signal-to-noise ratio of the input signal of the demodulation end is low, the signal-to-noise ratio of the output end is sharply reduced. While in the field of telemetry, particular attention is paid to telemetry receiver sensitivity performance, it is desirable that the input signal-to-noise ratio at the demodulation threshold point be lower to improve the sensitivity of the telemetry receiver. And along with the continuous improvement of the telemetering data code rate, the telemetering action distance is continuously increased, and the problems of threshold effect, low power utilization rate and the like in the cross product frequency discrimination demodulation of the PCM/FM signals are increasingly prominent. It is therefore proposed to apply multi-symbol detection (MSD) techniques to the demodulation of PCM/FM signals, thereby overcoming the threshold effect of conventional cross product frequency demodulation at low signal-to-noise ratios.
The traditional multi-symbol detection demodulation method only adapts to a code rate, namely a bit rate, which represents the number of bits transmitted per second. In practical applications, the code rate is usually not fixed, and it is desirable to support configuration at any time, so how to improve the multi-symbol detection demodulation method to adapt to multiple code rates is also a problem that needs to be paid attention to in design.
In addition, when the traditional multi-symbol detection demodulation method is implemented, the calculated amount is increased sharply along with the increase of the length of the observed symbol, so that the implementation of the method in an FPGA (programmable logic array) is very difficult, and therefore, how to reduce the calculated amount of the multi-symbol detection demodulation method is one of the problems which need to be solved in hardware at present.
Disclosure of Invention
Aiming at the defect that the traditional multi-symbol detection demodulation method cannot be flexibly configured in practical application due to the fact that the traditional multi-symbol detection demodulation method cannot adapt to a plurality of code rates, the invention provides the multi-symbol detection demodulation method, and the adaptation to the plurality of code rates is realized by matching the number of sample points of a baseband complex signal with the number of sample points of a local reference wave signal.
In addition, based on the problem that the traditional multi-symbol detection demodulation method is difficult to realize on hardware due to large calculated amount, the multi-symbol detection demodulation method provided by the invention improves the maximum likelihood calculation process, obtains waveform correlation values corresponding to all waveform combinations of the local reference wave signal by designing a special mode square value sequencing addition mode, reduces the calculated amount and can be realized in an FPGA; and the multi-level buffer is designed to improve the operation speed of the system.
The technical scheme of the invention is as follows:
in a first aspect, the present invention provides a multi-symbol detection demodulation method, including the following steps:
a1, obtaining a baseband complex signal to be demodulated and a plurality of groups of local reference wave signals;
a2, matching the number of the sampling points of the baseband complex signal with the number of the sampling points of the local reference wave signal to the same number;
a3, performing maximum likelihood calculation on all waveform combinations of the baseband complex signals after matching the sample number and the local reference wave signals after matching the sample number, and searching the local reference wave signal waveform combination corresponding to the maximum likelihood value;
and A4, outputting the local symbol information of the local reference wave signal waveform combination corresponding to the maximum likelihood value as the demodulation symbol information.
Further, the specific implementation of step a2 includes: the number of sampling points of the local reference wave signal is N, the number of sampling points of the baseband complex signal is N, and both N and N are positive integers;
and when N is greater than N, extracting N sampling points from the N sampling points of the baseband complex signal, and taking the baseband complex signal of the extracted N sampling points as the baseband complex signal after the number of the matched sampling points.
Further, when N < N, the value of more than N samples of the local reference wave signal is set to zero.
In a second aspect, the present invention provides a telemetry PCM/FM signal demodulation method, comprising: sequentially carrying out analog-to-digital conversion and digital down-conversion on the telemetering PCM/FM signal to be demodulated to obtain a baseband complex signal to be demodulated; and acquiring a plurality of groups of local reference wave signals with different code rates, different sampling rates, different pre-modulation filters and different sequencing modes, and performing multi-symbol detection demodulation on the baseband complex signal to be demodulated according to the multi-symbol detection demodulation method.
Compared with the prior art, the invention has the following beneficial effects:
on one hand, the invention matches the number of the sampling points of the baseband complex signal with the number of the sampling points of the local reference wave signal to the same number and then carries out maximum likelihood calculation, thereby realizing MSD demodulation of a plurality of code rates and improving flexible configuration degree in practical application.
On the other hand, the invention combines the sorting mode of the local waveform and adopts the shift register to store the modulo square value, and provides optimized sorting addition to obtain 2m+2The method for combining the waveform correlation values corresponding to the local reference wave signal waveform combination optimizes the maximum likelihood calculation process, reduces the calculation difficulty and the calculation complexity, and can be realized in the FPGA; simultaneously, multi-level buffers are designed in each step of operation, comparison and the likeThe invention improves the system operation speed, and can realize stable and reliable demodulation under high code rate.
Drawings
Fig. 1 is an overall flowchart of a multi-symbol detection demodulation method proposed by the present invention.
Fig. 2 is a schematic diagram of an extraction method for extracting N samples from N samples of a baseband complex signal according to the second embodiment.
Fig. 3 is a detailed flowchart of a multi-symbol detection demodulation method in a fourth embodiment of the present invention.
Fig. 4 is a schematic diagram of a multi-symbol detection demodulation method according to a fifth embodiment of the present invention, in which 8 sets of calculated modulo-square values are stored in 5 × 8 shift registers, where the 8 sets of modulo-square values are numbered c1-c8, and correspond to the original symbols of the local reference waveform respectively as 000-111.
Fig. 5 is a schematic diagram of a multi-symbol detection demodulation method according to a fifth embodiment of the present invention, in which modulo-square values stored in 5 × 8 shift registers are sorted and added to obtain waveform correlation values corresponding to 128 groups of local reference wave signal waveform combinations.
Fig. 6 is a schematic diagram of a multi-symbol detection demodulation method according to a sixth embodiment of the present invention, in which a division comparison method is adopted, waveform correlation values corresponding to 128 groups of local reference wave signal waveform combinations are compared for 7 times, a maximum value is found, and corresponding local symbol information is output.
FIG. 7 is a schematic diagram showing the comparison of the bit error performance analysis between the conventional cross product frequency discrimination demodulation and the multi-symbol detection demodulation of the present invention for PCM/FM signals, wherein BER is the bit error rate and EBNO is the bit signal-to-noise ratio.
FIG. 8 is an overall flow chart of a telemetry PCM/FM signal demodulation method in accordance with the present invention.
FIG. 9 is a flow chart of a telemetry PCM/FM signal demodulation method according to a seventh embodiment of the invention for generating a local reference waveform.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
In a first aspect, the present invention provides a multi-symbol detection demodulation method, which specifically includes the following embodiments:
example one
In the telemetering system, the multi-symbol detection demodulation method utilizes the characteristic that the phases of adjacent code elements of a PCM/FM signal are continuous, and reduces the correlation operation in an observation symbol interval to the sum of the correlation operation in each symbol interval from the viewpoint of reducing the correlation length, namely, the sum of segmented correlation results is equivalent to the longer correlation of the whole, thereby effectively reducing the operation amount of the FPGA.
Fig. 1 is a general flowchart of a multi-symbol detection demodulation method according to the present invention, which first obtains a baseband complex signal to be demodulated and a plurality of groups of local reference wave signals. The number of samples in the baseband complex signal to be demodulated is not matched with the number of samples in the local reference wave signal generally, and based on the method, the number of samples in the baseband complex signal and the number of samples in the local reference wave signal are matched to be the same, and then the maximum likelihood calculation is carried out, so that the matching of each code rate is realized, and the MSD demodulation of a plurality of code rates is realized. The maximum likelihood calculation is to calculate the correlation operation of all waveform combinations of the baseband complex signal after the matching of the sample points and the local reference wave signal after the matching of the sample points, perform the modulo square calculation on the correlation operation result, sort and add the correlation values according to a certain mode to obtain the waveform correlation values corresponding to all waveform combinations of the local reference wave signal, and finally compare and find the maximum likelihood value, wherein the local code element information of the local reference wave signal waveform combination corresponding to the maximum likelihood value is the demodulation code element information. Wherein the correlation operation is a mathematical operation of similarity comparison of two sequences; when the specific local modulation sequence is matched with the received data sequence, each element in the sequence has the same conjugate product, otherwise, the conjugate product of each element is random, so that when the received sequence is matched with the specific traversal sequence, the modulus value after the conjugate point multiplication operation is maximum, and the maximum likelihood demodulation basis of the sequence is used.
Example two
On the basis of the first embodiment, the number of samples of the local reference wave signal is N, and the number of samples of the baseband complex signal is N, where N and N are positive integers. In general, N and N are not equal, and when N > N, N samples may be extracted from N samples of the baseband complex signal, and the baseband complex signal from which N samples are extracted may be used as the baseband complex signal after matching the number of samples and the local reference wave signal of the N samples to perform maximum likelihood calculation.
In this embodiment, an extraction method is provided, as shown in fig. 2, assuming that N sample values of the baseband complex signal are b respectively0、b1、b2、……、bN-1The subscripts are the position numbers 0, 1, 2, … … N-1 of the N sample values of the baseband complex signal, respectively. To extract N samples from the N samples of the baseband complex signal, a formula may be used
To obtain the sampling positions of n sampling points, specifically: firstly, performing N times of analog up-sampling on position numbers of N sample values of a baseband complex signal, for example, obtaining the position numbers of 0, 1, 2, … … and Nx (N-1) after up-sampling by adopting an accumulation mode; then, sampling the position numbers 0, 1, 2, … … and Nx (N-1) after the up-sampling by N times, namely, sampling from the first position number 0 in the position numbers after the up-sampling, and extracting a sampling point every N position numbers to obtain the position numbers after the sampling which are respectively 0, N, 2N, … … and (N-1) xN, wherein N sampling position numbers are obtained after the sampling; then dividing the N sampled position numbers 0, N, 2N, … …, (N-1) xN by N respectively and rounding the calculation result to obtain N position numbers to be extracted, wherein the N position numbers to be extracted are 0, round (N/N), round (2N/N), … … and round ((N-1) xN/N), and the round symbol indicates that four rounds are performedFifthly, adding; and finally, extracting the position numbers corresponding to the N sampling points of the baseband complex signal according to the N position numbers to be extracted, namely 0, round (N/N), round (2N/N), … … and round ((N-1) multiplied by N/N), which are obtained through calculation, wherein the extracted N sampling points of the baseband complex signal are a0、a1、a2、……、an-1Wherein a is0＝b0，a1＝bround(N/n)，a2＝bround(2N/n)，……、an-1＝bround((n-1)×N/n)。
Wherein the value of n is preferably an integer power of 2, so that multiplication and division of the decimation method in the FPGA can be realized through simple shift operation.
This embodiment provides a feasible extraction method, but is not limited to the present invention, and other extraction methods capable of extracting N samples from N samples are also applicable to the present invention, for example, other methods that calculate an extraction multiple according to an information transmission code rate in a multi-symbol detection demodulation process, and then extract the N samples of the baseband complex signal according to the calculated extraction multiple to obtain the N samples of the baseband complex signal.
EXAMPLE III
On the basis of the second embodiment, when N < N, the number of samples of the baseband complex signal and the local reference wave signal may be matched in a manner of setting a value of more than N samples of the number of N samples of the local reference wave signal to zero. The sampling points of each position have values in the dynamic generation process of the local reference wave signal, in order to realize the sampling point number matching, the sampling point values exceeding N of the local reference wave signal are set to be zero, and the exceeding N-N sampling points have no influence on the calculation result because the sampling point values are zero.
Similarly, this embodiment provides a feasible sampling point number matching method, but is not limited to the present invention, and other methods that can match sampling points of N baseband complex signals with sampling points of N local reference wave signals are also applicable to the present invention, for example, an interpolation method may be used to process the baseband complex signals, calculate an interpolation multiple according to an information transmission code rate in a multi-symbol detection and demodulation process, and then interpolate the N sampling point numbers of the baseband complex signals according to the calculated interpolation multiple to obtain the N sampling point numbers of the baseband complex signals, thereby implementing the matching of the N sampling point numbers of the baseband complex signals and the local reference wave signals.
Example four
The present embodiment further describes generation and calculation of a local reference wave signal on the basis of the first to third embodiments. After receiving a group of baseband complex signals to be demodulated, maximum likelihood calculation needs to be carried out on the baseband complex signals and a plurality of groups of local reference wave signals, and each group of local reference wave signals have different code rates, different sampling rates, different pre-modulation filters and different sequencing modes.
Next, the maximum likelihood calculation is performed on a group of baseband complex signals to be demodulated and 8 groups of local reference wave signals, and the calculation flow is shown in fig. 3.
Configuring and receiving 8 groups of local reference wave signals, receiving baseband complex signals (namely IQ data) and performing sampling point number matching with the local reference wave signals, and then performing complex correlation operation on the 8 groups of local reference wave signals subjected to sampling point number matching and baseband complex signals to be demodulated respectively to obtain 8 groups of waveform correlation values.
And then 8 groups of operation modules can be called simultaneously to realize the simultaneous operation of 8 types of local waveforms, specifically, 8 groups of operation modules simultaneously carry out square operation after the real parts and the imaginary parts of the obtained 8 groups of waveform correlation values are summed respectively, and then carry out square operation after the imaginary parts are summed respectively, and then add the square value of the sum of the real parts and the square value of the sum of the imaginary parts of each group of waveform correlation values to obtain 8 groups of module square values.
And then sequencing and adding the obtained 8 groups of module square values in different modes to obtain waveform correlation values corresponding to all waveform combinations of the local reference wave signals, wherein the waveform combination number of the local reference wave signals is determined by the length of the observation symbol. Order observation symbolThe length is m, because one code element is expanded into the width of three code elements, m code elements are expanded into m +2, and all waveform combinations of the local reference wave signals are 2 in totalm+2In digital communications, one-bit binary digits are often represented by symbols having the same time interval, and the signal in such a time interval is called a binary symbol, and this interval is called a symbol length. m is typically an odd number not greater than 7, i.e. m may be 1, 3, 5 or 7. In consideration of performance and resource balance, in the embodiment, m is taken as 5 as an example for explanation, and the observation symbol length is 5, so that the calculation amount can be greatly reduced, and the method can be implemented in an FPGA.
Because the observation symbol length is 5, 8 groups of obtained module square values are sorted and added in different modes to obtain 2 combinations of all waveforms of the local reference wave signal5+2And finally, comparing waveform correlation values corresponding to the 128 groups of local reference wave signal waveform combinations, and finding out the maximum value, namely the maximum likelihood value. The local symbol information of the local reference wave signal waveform combination corresponding to the maximum likelihood value is the demodulation symbol information finally required by the multi-symbol detection demodulation method, and the middle one-bit symbol of the local symbol combination corresponding to the maximum likelihood value is usually used as the demodulation output.
EXAMPLE five
On the basis of the fourth embodiment, this embodiment provides a way of sorting and adding 8 sets of calculated modulo-square values in a special way, so as to obtain 128 sets of local reference wave signal waveform combinations.
As shown in fig. 4, 8 groups of memory cells are provided, each group of memory cells includes m shift registers, where m is 5 in this embodiment, and each group of memory cells includes 5 shift registers, and it is assumed in fig. 4 that the shift registers with position numbers 1 to 5 are the first group of memory cells, the shift registers with position numbers 6 to 10 are the second group of memory cells, and so on.
After each observation of 1 symbol waveform, a group of baseband complex signals and 8 groups of local reference wave signals are subjected to complex correlation operation according to the calculation method of the fourth embodiment to generate 8 groups of module square values c1-c 8. 8 sets of the modulo-square values c1-c8 are stored in the first to eighth sets of the storage units, respectively, and 8 sets of the modulo-square values c1-c8 generated by the complex correlation operation are stored in the same set of the storage units corresponding to the local symbols 000-111, respectively. As shown in fig. 4, it is assumed that data originally stored in 5 shift registers in the first group of memory cells with position numbers 1-5 are d1, d2, d3, d4, and d5, data originally stored after the modulo-square value c1 is stored in the first group of memory cells are sequentially shifted, data stored in 5 shift registers after the modulo-square value c1 is stored in the first group of memory cells are updated to d2, d3, d4, d5, and c1, and storage manners of the remaining memory cells are similar and will not be described again. The originally stored d1-d40 in the eight groups of memory cells are also the previously generated modulo-squared values c1-c 8.
After observing 1 code element waveform, updating the modulus square values stored in 5 multiplied by 8 shift registers in 8 groups of storage units, and enabling the first group of storage units to store the modulus square values with binary codes of 000, wherein the values stored in the 5 shift registers of the first group of storage units are s1-s5 respectively; the second group of memory cells stores the modulo-square value of which the binary code is 001, and the values stored in the 5 shift registers of the second group of memory cells are s6-s10 respectively; the third group of memory cells stores the modulo-square value of the binary code 010, and the values stored in the 5 shift registers of the third group of memory cells are s11-s15 respectively; … …, respectively; the eighth group of memory cells stores the modulo-squared value of binary 111, with values stored in the 5 shift registers of the eighth group of memory cells being s36-s40, respectively. The shift register is adopted to store the modular square value, and 8 groups of shift registers obtained by calculation can be subjected to proper shift sequence according to the arrangement sequence of local waveforms, so that the purposes of reducing the use of LUT (Look-Up-Table) and saving internal resources are achieved.
The following detailed description will proceed to sort and add the modulo-square values stored by the respective shift registers in 8 groups of memory cells in a specific manner to obtain 2m+2The method for combining the waveform correlation values of local reference wave signal waveform combination includes the first step of 2m+2The waveform correlation values corresponding to the waveform combination of the group local reference wave signals are respectively 0 to 2m+2-1 corresponding m +2 bit binaryRepresenting, then grouping m +2 bit binary representations of waveform correlation values corresponding to each group of local reference wave signal waveform combinations according to every adjacent 3 bit binary number, dividing into m groups of 3 bit binary numbers, and finally selecting m modulus square values from a shift register at a corresponding position in a storage unit for storing corresponding numbering modulus square values according to the obtained m groups of 3 bit binary numbers to form a group of waveform correlation values corresponding to the local reference wave signal waveform combinations, namely determining a storage unit for storing the corresponding numbering modulus square values according to the m groups of 3 bit binary numbers obtained after grouping, wherein if the 3 bit binary number is 000, the corresponding storage unit is a first group of storage units for storing binary codes of 000; if the 3-bit binary number is 111, the corresponding storage unit is an eighth group of storage units for storing binary codes of 111; and simultaneously determining and extracting the register in the storage unit at the corresponding position according to the position of the 3-bit binary number, if the 1 st group of 3-bit binary numbers are grouped later, extracting the value stored in the first shift register in the corresponding storage unit, and if the m group of 3-bit binary numbers are grouped later, extracting the value stored in the m-th shift register in the corresponding storage unit. In more detail, if the first group of 3-bit binary numbers is 000, the corresponding stored value s1 is extracted from the first shift register storing the first group of memory cells modulo-square binary coding to 000; if the third set of 3-bit binary numbers is 001, the corresponding stored value s8 is extracted from the third shift register storing the second set of memory cells modulo-squared binary coded as 001.
For example, when m is 5, since one symbol is spread into 3, 5 symbols m1-m5 are spread into 7 symbols o1-o7, as shown in fig. 5, 128 groups of local reference wave signal waveform combinations are provided, and the corresponding waveform correlation values are 7-bit binary representations corresponding to 0-127, i.e., 0000000, 0000001, 0000010, … …, 1111101, 1111110, and 1111111, respectively. And grouping 7-bit binary representations of waveform correlation values corresponding to each group of local reference wave signal waveform combinations according to each adjacent 3-bit binary number, wherein the binary representations are 3-bit binary numbers which are divided into 5 groups in total, and selecting 5 stored modular square values corresponding to numbers from 40 shift registers according to the obtained 3-bit binary numbers of the 5 groups to form a group of waveform correlation values corresponding to the local reference wave signal waveform combinations.
A waveform correlation value represented as 0000000 in 7-bit binary, dividing 0000000 into 000, and extracting correspondingly stored values s1, s2, s3, s4, s5 from the first to fifth shift registers in the first group of memory cells storing modulo-square binary coding of 000 to form the waveform correlation value, as shown in fig. 5; 0000001 is divided into 000, 001, and the corresponding stored values s1, s2, s3, s4 are extracted from the first to fourth shift registers of the first group of memory cells storing the modulo-square binary code of 000, and the corresponding stored values s10 are extracted from the fifth shift register of the second group of memory cells storing the modulo-square binary code of 001, which collectively constitute the waveform correlation value, as shown in fig. 5; similarly, 0000010 is divided into 000, 001, 010, and extracts the corresponding stored values s1, s2, s3 from the first to third shift registers in the first group of memory cells storing the modulo-square binary code of 000, extracts the corresponding stored value s9 from the fourth shift register in the second group of memory cells storing the modulo-square binary code of 001, and extracts the corresponding stored value s15 from the fifth shift register in the third group of memory cells storing the modulo-square binary code of 010, which collectively constitute the waveform correlation value; 0000011 is divided into 000, 001, 011, and correspondingly stored values s1, s2, s3 are extracted from the first to third shift registers in the first group of memory cells storing modulo-square binary coding of 000, correspondingly stored value s9 is extracted from the fourth shift register in the second group of memory cells storing modulo-square binary coding of 001, and correspondingly stored value s20 is extracted from the fifth shift register in the fourth group of memory cells storing modulo-square binary coding of 011, together forming waveform correlation values; 0000100 is divided into 000, 001, 010, 100, extracting correspondingly stored values s1, s2 from a first shift register to a second shift register in a first group of memory cells storing a modulo-square value binary code of 000, extracting correspondingly stored value s8 from a third shift register in a second group of memory cells storing a modulo-square value binary code of 001, extracting correspondingly stored value s14 from a fourth shift register in a third group of memory cells storing a modulo-square value binary code of 010, extracting correspondingly stored value s25 from a fifth shift register in a fifth group of memory cells storing a modulo-square value binary code of 100, and jointly forming a waveform correlation value; … …, respectively; 111111 are divided into 111, and the waveform correlation values are extracted from the first to fifth shift registers of the eighth group of memory cells storing the modulo-square binary code 111, and the corresponding stored values s36, s37, s38, s39, s40 are extracted.
While forming the waveform correlation values corresponding to 128 groups of local reference wave signal waveform combinations, local symbol information corresponding to each local reference wave signal waveform combination of each group can be added, and the local symbol information is usually the middle one-bit symbol of the local symbol combination (in the embodiment, the middle one of o1-o7 is o4), so that the local symbol information corresponding to the maximum likelihood value can be directly output as demodulation symbol information after the maximum likelihood value is found. Of course, the local symbol information may not be added to the waveform correlation value corresponding to the local reference wave signal waveform combination, but the local symbol information corresponding to the local reference wave signal waveform combination is searched after the maximum likelihood value is found and is output as the demodulated symbol information.
EXAMPLE six
The present embodiment provides a pair 2 based on the fourth and fifth embodimentsm+2And comparing waveform correlation values corresponding to the local reference wave signal waveform combinations to find out a comparison method of the maximum value.
In this embodiment, the method of segmentation comparison is adopted, 2m+2And comparing waveform correlation values corresponding to the local reference wave signal waveform combination according to a pairwise group at the same time, and comparing the comparison result of each time for m +2 times according to a pairwise group at the same time to obtain a maximum likelihood value.
Taking m as an example and taking 5 as an example, as shown in fig. 6, in the first comparison, every two waveform correlation values corresponding to 128 groups of local reference wave signal waveform combinations are simultaneously compared in a group to obtain 64 groups of comparison results, and the 64 groups of comparison results can be respectively stored in 64 registers; during the second comparison, 64 groups of comparison results obtained by the first comparison are compared pairwise and simultaneously to obtain 32 groups of comparison results, and the 32 groups of comparison results are stored in 32 registers; by analogy, as shown in fig. 6, a final comparison result can be obtained by performing comparison for 7 times, a waveform correlation value of a local reference wave signal waveform combination corresponding to the comparison result is a maximum likelihood value, and symbol information and soft information corresponding to a maximum waveform group are output after the maximum waveform group is obtained.
In 7 comparisons, the result generated by each comparison is stored in a register, so that the operation speed and the stability of the system can be improved. In addition, the invention can be provided with a multi-level buffer to buffer the result after each operation, thereby improving the operation speed of the system and ensuring that the invention can realize stable and reliable demodulation under high code rate.
When the observed symbol length is 5, a performance comparison graph of the multi-symbol detection demodulation method adopting the invention and the cross product frequency discrimination demodulation method adopting the cross product frequency discrimination demodulation method shown in fig. 7 is obtained through simulation tests, and it can be seen that the demodulation performance of the multi-symbol detection demodulation method adopting the invention has the error rate of 10-5The time is 2.9dB better than the traditional cross product frequency discrimination demodulation.
In a second aspect, the present invention provides a telemetry PCM/FM signal demodulation method, which specifically includes the following embodiments:
EXAMPLE seven
The PCM/FM modulation firstly carries out PCM coding on data information, baseband PCM code elements are formed through pre-modulation and filtering, and then the baseband PCM signals are subjected to FM modulation to obtain PCM/FM signals. Generally, as shown in fig. 8, a mode is adopted for demodulating PCM/FM signals, firstly, telemetry PCM/FM signals subjected to pulse code modulation/frequency modulation in a telemetry system are received as telemetry PCM/FM signals to be demodulated, then analog-Digital conversion is performed on the telemetry PCM/FM signals to be demodulated, and then the telemetry PCM/FM signals to be demodulated are shifted to a baseband through Digital Down Converters (DDCs) to obtain baseband complex signals to be demodulated; next, the multi-symbol detection demodulation method of the first to sixth embodiments is applied to process the baseband complex signal to be demodulated to obtain demodulation information.
Expanding a symbol to a width of 3 symbols, taking into account the effect of the pre-modulation filter, will yield 23According to the code rate, the sampling rate, the filter parameter and the modulation degree parameter, and the continuous characteristic of the PCM/FM code element phase, a local reference waveform generation tool can be designed by using a matlab tool, and is used for generating local reference waveforms with different code rates, different sampling rates, different preset filters and different sequencing modes. In this embodiment, a method for generating a local reference wave signal is provided, as shown in fig. 9, a plurality of groups of local reference waveform symbols are generated according to different local symbol information and are subjected to code pattern conversion, in the embodiment of the present invention, maximum likelihood calculation is performed on a group of baseband complex signals and 8 groups of local reference wave signals, then 8 groups of local reference waveform symbols are generated according to 8 groups of local symbols 000-111 and are subjected to code pattern conversion, usually, return-to-zero codes (RZ) are converted into non-return-to-zero codes (NRZ); then sampling a plurality of groups of local reference waveform code elements after code pattern conversion according to the actual sampling frequency, then performing pre-modulation filtering, finally performing PCM/FM modulation on the result after the pre-modulation filtering according to the frequency modulation sensitivity to obtain a plurality of groups of parameters of local reference wave signals, wherein the calculation of the frequency modulation sensitivity can firstly obtain a plurality of test source data, convert the test source data into the same code pattern, namely a non-return-to-zero code (NRZ), then perform sampling and pre-modulation filtering on the test source data after the code pattern conversion according to the actual sampling frequency and the pre-modulation filter parameters which are the same as those in the generation of the local reference wave, and calculate the frequency modulation sensitivity k by combining the modulation degree parameters. The coe file is produced by carrying out 16-system quantization on the parameters of multiple groups of local reference wave signals, and the parameters can be conveniently stored in the FPGA.
After the local reference waveform is produced, the local reference waveform can be input into a local reference waveform receiving module through an AXIS interface and a configuration protocol, the local reference waveform receiving module is used for receiving and storing the local reference waveform, and after the local reference waveform is received, the local reference waveform group is updated to be used in subsequent multi-symbol detection and demodulation.
The baseband complex signal to be demodulated can be received by adopting a shift register mode, the input sequence of the shift register is designed according to the generation sequence of the local reference waveform, the length of the shift register can be set to be 3 multiplied by the number of sampling points of the local reference waveform (namely 3n, because one code element is expanded into 3 code element lengths), and meanwhile, the value of the shift register is latched according to the bit synchronization signal and the code rate parameter.
When the maximum likelihood calculation is carried out, the complex correlation and square operation can adopt Xilinx official IP core (the IP core is similar to a function library in programming and can be directly called), and the Xilinx official IP core is appropriately packaged, so that the correlation operation of 8 groups of local reference waveforms and the received baseband complex signal can be simultaneously carried out, the square operation is realized, 8 groups of module square values are simultaneously called for 8 times when the 8 groups of module square values are solved, and the stability and the highest operation rate of the system are improved.
Finally, it is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (14)
1. A multi-symbol detection demodulation method, comprising the steps of:
a1, obtaining a baseband complex signal to be demodulated and a plurality of groups of local reference wave signals;
a2, matching the number of the sampling points of the baseband complex signal with the number of the sampling points of the local reference wave signal to the same number;
a3, performing maximum likelihood calculation on all waveform combinations of the baseband complex signals after matching the sample number and the local reference wave signals after matching the sample number, and searching the local reference wave signal waveform combination corresponding to the maximum likelihood value;
and A4, outputting the local symbol information of the local reference wave signal waveform combination corresponding to the maximum likelihood value as the demodulation symbol information.
2. The method according to claim 1, wherein the step a2 comprises:
the number of sampling points of the local reference wave signal is N, the number of sampling points of the baseband complex signal is N, and both N and N are positive integers;
and when N is greater than N, extracting N sampling points from the N sampling points of the baseband complex signal, and taking the baseband complex signal of which the N sampling points are extracted as the baseband complex signal after the number of the matched sampling points.
3. The multi-symbol detection demodulation method according to claim 2, wherein the specific method of extracting N samples from the N samples of the baseband complex signal comprises:
b1, respectively setting the position numbers of N sample points of the baseband complex signal as 0, 1, 2, … … and N-1, and carrying out N times of analog up-sampling on the position numbers of the N sample points of the baseband complex signal to obtain the position numbers of 0, 1, 2, … … and N x (N-1) after up-sampling;
b2, sampling from the first position number in the position numbers after up-sampling, and extracting a sampling point every N position numbers to obtain the position numbers after sampling which are respectively 0, N, 2N, … …, (N-1) xN;
b3, dividing the n sampled position numbers by n respectively and rounding the calculation result to obtain n position numbers to be extracted;
and B4, extracting the position numbers corresponding to the N sampling points of the baseband complex signal according to the N position numbers to be extracted calculated in the step B3.
4. The multi-symbol detection demodulation method according to claim 2 wherein when N < N, the value of more than N samples among N samples of the local reference wave signal is set to zero.
5. The multi-symbol detection demodulation method of any of claims 2 through 4 wherein n is an integer power of 2.
6. The method according to claim 1, wherein 8 groups of local reference wave signals with different code rates, different sampling rates, different pre-modulation filters and different sequencing modes are obtained in step a 1.
7. The multi-symbol detection demodulation method according to claim 6 wherein the observation symbol length is m, m is an odd number not greater than 7, one symbol is expanded to a width of three symbols, and all waveform combinations of the local reference wave signal are 2 in totalm+2Seed growing;
the specific method for finding the maximum likelihood value in the step a3 includes:
c1, respectively carrying out correlation operation after sample point matching on the 8 groups of local reference wave signals acquired in the step A1 and the baseband complex signals to obtain 8 groups of waveform correlation values;
c2, respectively summing the real parts and the imaginary parts of the 8 groups of waveform correlation values obtained in the step C1, then performing square operation, respectively summing the imaginary parts, then performing square operation, and adding the square value of the sum of the real parts and the square value of the sum of the imaginary parts of each group of waveform correlation values to obtain 8 groups of module square values;
c3, carrying out the steps8 groups of module square values obtained by C2 are sorted and added in different modes to obtain 2m+2Combining the waveform correlation values corresponding to the local reference wave signal waveform combinations;
c4 for 2 obtained in the step C3m+2And comparing waveform correlation values corresponding to the waveform combinations of the local reference wave signals to find out the maximum value, namely the maximum likelihood value.
8. The method according to claim 7, wherein the step C3 comprises:
setting 8 groups of storage units, wherein each group of storage units comprises m shift registers; respectively storing 8 groups of generated modular square values into 8 groups of storage units after observing 1 code element waveform, updating the modular square values stored in m multiplied by 8 shift registers in the 8 groups of storage units, sequencing and adding the modular square values stored in each shift register in the 8 groups of storage units in different modes to obtain 2m+2And combining the waveforms of the local reference wave signals with the corresponding waveform correlation values.
9. The multi-symbol detection demodulation method according to claim 8 wherein 8 sets of the modulo-square values obtained in said step C2 are respectively assigned to 3-bit binary representations corresponding to 0 to 7, each set of said storage units storing the same numbered modulo-square values;
said step C3 yields 2m+2The method for combining the waveform correlation values corresponding to the local reference wave signal waveform combination comprises the following steps: order 2m+2The waveform correlation values corresponding to the waveform combination of the group local reference wave signals are respectively 0 to 2m+2-1 corresponding m +2 bit binary representations, grouping the m +2 bit binary representations of the waveform correlation values corresponding to each group of local reference wave signal waveform combinations according to each adjacent 3 bit binary representation, dividing the m groups of 3 bit binary representations into m groups of 3 bit binary representations, and selecting m modulo-square values from a shift register at a corresponding position in a storage unit storing corresponding numbered modulo-square values according to the obtained m groups of 3 bit binary representations to form a group of waveform correlation values corresponding to the local reference wave signal waveform combinations.
10. The multi-symbol detection demodulation method according to claim 7, wherein the specific way of finding the local symbol information of the local reference wave signal waveform combination corresponding to the maximum likelihood value and outputting the local symbol information as the demodulated symbol information in step a4 includes: 2 obtained in said step C3m+2And adding the local code element information corresponding to each local reference wave signal waveform combination into the waveform correlation value corresponding to the local reference wave signal waveform combination, and directly outputting the local code element information corresponding to the maximum likelihood value as demodulation code element information after finding the maximum likelihood value.
11. The multi-symbol detection demodulation method according to claim 7 wherein in said step C4, 2 is addedm+2And comparing waveform correlation values corresponding to the local reference wave signal waveform combinations in pairs and groups at the same time, and comparing the comparison result of each time for m +2 times to obtain the maximum likelihood value in a manner of comparing the comparison result of each pair and group at the same time.
12. The method according to claim 11, wherein said step C4 further comprises setting a plurality of registers, and storing each comparison result in a corresponding register.
13. A telemetry PCM/FM signal demodulation method comprising: sequentially carrying out analog-to-digital conversion and digital down-conversion on the telemetering PCM/FM signal to be demodulated to obtain a baseband complex signal to be demodulated; it is characterized by also comprising: obtaining a plurality of groups of local reference wave signals with different code rates, different sampling rates, different pre-modulation filters and different sequencing modes, and performing multi-symbol detection demodulation on the baseband complex signal to be demodulated according to the multi-symbol detection demodulation method of any one of claims 1 to 12.
14. The telemetry PCM/FM signal demodulation method according to claim 13 wherein the method of generating a plurality of sets of local reference wave signals includes: generating a plurality of groups of local reference waveform code elements according to different local code element information, carrying out code pattern conversion, sampling the plurality of groups of local reference waveform code elements after code pattern conversion according to actual sampling frequency, then carrying out pre-modulation filtering, carrying out PCM/FM modulation on the result after pre-modulation filtering according to frequency modulation sensitivity to obtain parameters of a plurality of groups of local reference wave signals, carrying out 16-system quantization on the parameters of the plurality of groups of local reference wave signals, and storing the parameters.
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