CN117938601A

CN117938601A - Digital demodulation method, device, equipment and storage medium

Info

Publication number: CN117938601A
Application number: CN202410118671.1A
Authority: CN
Inventors: 魏急波; 辜方林; 凌碧海; 熊俊; 张晓瀛; 刘潇然; 赵海涛
Original assignee: National University of Defense Technology
Current assignee: National University of Defense Technology
Priority date: 2024-01-26
Filing date: 2024-01-26
Publication date: 2024-04-26

Abstract

The application discloses a digital demodulation method, a device, equipment and a storage medium, which relate to the field of digital communication and comprise the following steps: acquiring a filtered signal of a transmission signal passing through a filter, and carrying out phase difference on the filtered signal; extracting the obtained differential phase, and determining a signal to be demodulated according to the differential phase; determining a target differential phase of the filtered signal according to the current communication environment, and constructing a composite grid according to the target differential phase; determining a sub-grid based on the composite grid, and determining branch path metrics and total path metrics of signals to be demodulated according to the sub-grid; and carrying out Viterbi demodulation based on the total path metric, and carrying out backtracking of Viterbi demodulation according to the total path metric to obtain a demodulation result. The application builds a GMSK composite grid phase compensation model, provides a GMSK signal composite Viterbi demodulation algorithm based on differential phase, can overcome the influence of large Doppler frequency offset on demodulation performance, and can still maintain excellent performance under large frequency offset.

Description

Digital demodulation method, device, equipment and storage medium

Technical Field

The present invention relates to the field of digital communications, and in particular, to a digital demodulation method, apparatus, device, and storage medium.

Background

Modern communications are increasingly demanding in terms of modem technology, and in particular, when spectrum resources are increasingly scarce, the importance of small bandwidth and good performance modem technology is self-evident. The Gaussian Minimum-shift keying (Gaussian Minimum-SHIFT KEYING, GMSK) modulation mode has the advantages of constant envelope, good spectrum utilization rate and the like, is widely applied to modern communication, and is suitable for a communication system with adjacent channel interference and a nonlinear power amplifier.

The demodulation technique of GMSK signals can be classified into coherent demodulation and noncoherent demodulation. The coherent demodulation mode needs carrier recovery, requires carrier frequency deviation and timing error compensation and carrier phase synchronization, and has complex realization and weak anti-interference capability; the incoherent demodulation mode has a relatively simple structure and good robustness to the frequency deviation and the phase deviation of the carrier wave, so that the method is widely applied. For example, the movement speed of a bullet-bullet communication link and a star-bullet communication link may be up to mach 10, the acceleration may be up to 20g, etc., and the high-speed motorized communication environment determines that a significant doppler effect exists in the signal transmission process, and meanwhile, strict requirements are also put on the reliability of communication by the application scenes. Therefore, coherent demodulation is obviously difficult to adapt to the application requirements in such a high dynamic background, and research on a noncoherent demodulation algorithm with robustness and high reliability on doppler frequency offset is needed.

The demodulation performance of the current demodulation algorithm can be improved mostly, but the demodulation algorithm is difficult to adapt to large Doppler frequency offset in a high-dynamic communication environment, for example, the demodulation of GMSK is combined with machine learning, so that the performance is improved, but the demodulation algorithm needs a large amount of data to assist and has poor adaptability to the high-dynamic communication environment; the Viterbi algorithm based on the phase state grid diagram and the Viterbi algorithm assisted by amplitude limiting and frequency discrimination improve demodulation performance, but have weaker adaptability to frequency deviation; in addition, the performance of the Viterbi demodulation method based on differential phase detection of the GMSK signal is improved, but the capability of resisting frequency offset still has room for improvement. Therefore, how to maintain strong robustness to frequency offset to adapt to a high dynamic environment while ensuring good demodulation performance is a problem to be solved in the art.

Disclosure of Invention

In view of the above, the present invention aims to provide a digital demodulation method, apparatus, device and storage medium, which construct a GMSK composite grid phase compensation model, and propose a GMSK signal composite Viterbi demodulation algorithm based on differential phase, so as to overcome the influence of large doppler frequency offset on demodulation performance, and still maintain excellent performance under large frequency offset. The specific scheme is as follows:

In a first aspect, the present application provides a digital demodulation method, including:

acquiring a filtered signal of a transmission signal after being filtered by a Gaussian filter, and carrying out phase difference on the filtered signal by a differential phase detection network;

extracting a differential phase obtained after the filtered signals are subjected to differential, and determining a signal to be demodulated according to the differential phase;

determining a target differential phase corresponding to the filtered signal according to the current communication environment, and constructing a composite grid according to the target differential phase;

determining a sub-grid based on the composite grid, and determining branch path metrics and total path metrics of the signals to be demodulated according to the sub-grid;

and carrying out Viterbi demodulation based on the total path metric, and carrying out backtracking of the Viterbi demodulation according to the total path metric to obtain a demodulation result.

Optionally, the determining the signal to be demodulated according to the differential phase includes:

Determining a normalized bandwidth of the Gaussian filter corresponding to the transmission signal, and determining the target symbol number of the Viterbi demodulation according to the normalized bandwidth; the target symbol number is the symbol number which causes at least inter-symbol interference when the Viterbi demodulation is performed;

and determining a delayer of the filtered signal based on the target symbol number, and obtaining the signal to be demodulated based on the delayer.

Optionally, the determining, according to the current communication environment, the target differential phase corresponding to the filtered signal includes:

determining the differential phase of the basic grid of the Viterbi demodulation, and determining the corresponding phase rotation unit degree and first phase rotation times of the filtered signal according to the current communication environment;

And calculating the target differential phase according to the differential phase of the basic grid, the phase rotation unit degree, the first phase rotation times and the normalized bandwidth.

Optionally, the determining the sub-grid based on the composite grid includes:

Giving an initial value of 1 to the second phase rotation times of the composite grid, dividing the second phase rotation times by two, and then rounding downwards to obtain a target parameter;

And determining the sub-grid according to the target parameter, the differential phase of the basic grid and the phase rotation unit degree.

Optionally, after the viterbi demodulation based on the total path metric, the method further includes:

Storing an initial minimum value in the total path metric in the Viterbi demodulation at this time;

Adding one to the second phase rotation times, and judging whether the new second phase rotation times are larger than the first phase rotation times or not;

If not, jumping to the step of determining a sub-grid based on the composite grid and determining the branch path metric and the total path metric of the signal to be demodulated according to the sub-grid.

Optionally, the performing backtracking of the viterbi demodulation according to the total path metric obtains a demodulation result, including:

And if the second phase rotation times are added by one, the obtained new second phase rotation times are larger than the first phase rotation times, determining a target minimum value from the initial minimum values in all the total path metrics, and carrying out backtracking of the Viterbi demodulation according to the target minimum value to obtain the demodulation result.

Optionally, after the performing the backtracking of the viterbi demodulation according to the total path metric to obtain a demodulation result, the method further includes:

Determining the data demodulation requirement of a preset back end, and converting the demodulation result into hard decision information or soft decision information according to the data demodulation requirement and outputting the hard decision information or soft decision information to the preset back end.

In a second aspect, the present application provides a digital demodulating apparatus comprising:

The phase difference module is used for acquiring a filtered signal of the transmission signal after being filtered by the Gaussian filter and carrying out phase difference on the filtered signal by the differential phase detection network;

The signal determining module is used for extracting a differential phase obtained after the filtered signals are subjected to differential, and determining a signal to be demodulated according to the differential phase;

The grid construction module is used for determining a target differential phase corresponding to the filtered signal according to the current communication environment and constructing a composite grid according to the target differential phase;

a metric determining module, configured to determine a sub-grid based on the composite grid, and determine a branch path metric and a total path metric of the signal to be demodulated according to the sub-grid;

And the digital demodulation module is used for carrying out Viterbi demodulation based on the total path metric and carrying out backtracking of the Viterbi demodulation according to the total path metric to obtain a demodulation result.

In a third aspect, the present application provides an electronic device comprising a processor and a memory; wherein the memory is configured to store a computer program that is loaded and executed by the processor to implement the aforementioned digital demodulation method.

In a fourth aspect, the present application provides a computer readable storage medium storing a computer program which, when executed by a processor, implements the aforementioned digital demodulation method.

In the application, firstly, a filtered signal of a transmission signal after being filtered by a Gaussian filter is obtained, the filtered signal is subjected to phase difference by a differential phase detection network, then, the differential phase obtained after the filtered signal is subjected to difference is extracted, a signal to be demodulated is determined according to the differential phase, a target differential phase corresponding to the filtered signal is determined according to the current communication environment, a composite grid is constructed according to the target differential phase, a sub-grid can be determined based on the composite grid, branch path measurement and total path measurement of the signal to be demodulated are determined according to the sub-grid, viterbi demodulation is performed based on the total path measurement, and backtracking of the viterbi demodulation is performed according to the total path measurement to obtain a demodulation result. In this way, the application builds a composite grid phase compensation model of GMSK, and provides a GMSK signal composite Viterbi demodulation algorithm based on differential phase, which can overcome the influence of large Doppler frequency offset on demodulation performance and still maintain excellent performance under large frequency offset.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flow chart of a digital demodulation method provided by the application;

FIG. 2 is a schematic diagram of a 2bit differential phase based composite Viterbi demodulation scheme according to the present application;

FIG. 3 is a flowchart of a specific digital demodulation method according to the present application;

Fig. 4 is a graph showing the performance of various incoherent demodulation algorithms of GMSK according to the present application;

FIG. 5 is a graph showing the comparison of error code performance under different frequency bias without a composite grid according to the present application;

FIG. 6 is a graph showing the comparison of error code performance under different frequency bias when a composite grid is provided in the present application;

Fig. 7 is a schematic structural diagram of a digital demodulation device according to the present application;

fig. 8 is a block diagram of an electronic device according to the present application.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The Gaussian minimum frequency shift keying modulation mode in modern communication has the advantages of constant envelope, good spectrum utilization rate and the like, has wide application in the modern communication, and is suitable for a communication system with adjacent channel interference and a nonlinear power amplifier. However, the current high-speed mobile communication environment has a remarkable Doppler effect in the signal transmission process, and strict requirements are also put on the reliability of communication. Therefore, the current demodulation algorithm is difficult to adapt to the application requirement under the high dynamic background, and the GMSK composite grid phase compensation model constructed by the application can overcome the influence of large Doppler frequency offset on demodulation performance and still maintain excellent performance under large frequency offset through the GMSK signal composite Viterbi demodulation algorithm based on differential phase.

Referring to fig. 1, the embodiment of the invention discloses a digital demodulation method, which comprises the following steps:

And S11, acquiring a filtered signal of the transmission signal after filtering by a Gaussian filter, and carrying out phase difference on the filtered signal by a differential phase detection network.

In this embodiment, as shown in fig. 2, the receiving end is required to obtain a filtered signal of the transmission signal after filtering by the gaussian filter. Specifically, assuming that the transmission sequence is α=. A _-1,a₀,a₁...;a_i e { -1, +1}, the GMSK transmission signal corresponding thereto may be expressed as:

Where ωc is the carrier angular frequency, P _s is the power of the transmitted signal, T is the symbol period, g (T) is the baseband frequency pulse, h is the modulation index, 0.5 in GMSK, Is an additional phase corresponding to the transmitted sequence. For GMSK signals, g (t) is the impulse response of a rectangular pulse after passing through a gaussian filter:

g(t)＝Q(cB_tT(-t/T))-Q(cB_tT(1-t/T))；

where c=7.546, b _t T is the normalized bandwidth of the gaussian filter, and

Is a standard Q function.

After the GMSK signal passes through an AWGN (additive white Gaussian Noise) channel, ADDITIVE WHITE Gaussian Noise, the received signal is expressed as:

r(t,α)＝s(t,α)+n(t)；

n (t) is Gaussian white noise with double sideband power spectral density of N ₀/2.

At the receiving end, r (t, α) first filters out-of-band noise through a front-end filter, whose bandwidth is typically set to the 99% power bandwidth of the GMSK transmit signal. After passing through the filter, the phase signal for back-end detection can be expressed as:

Where ρ is the signal-to-noise ratio at the receiving end, and n _c (t) and n _s (t) are the in-phase and quadrature components of n (t), respectively. After the filtered signal is obtained, the filtered signal can be subjected to phase difference through a differential phase detection network.

And step S12, extracting a differential phase obtained after the filtered signals are subjected to differential, and determining a signal to be demodulated according to the differential phase.

As shown in fig. 2, in this embodiment, the filtered signal may pass through a 2bit differential phase detection network, where the network delays and differentiates the 2bit phase of the signal, and extracts the phase after the differentiation. And then determining the normalized bandwidth of a Gaussian filter corresponding to the transmitted signal, determining the target symbol number of Viterbi demodulation according to the normalized bandwidth, and determining a delay device of the filtered signal based on the target symbol number, so as to obtain the signal to be demodulated based on the delay device. The target symbol number is the symbol number causing at least inter-symbol interference when viterbi demodulation is performed.

It is noted that for GMSK signals, the network output at the end of the kth symbol interval (t=kt+t) can be represented by the following equation:

Where ζ _k =η (kt+t) - η (kT-T), the meaning of L is that the main inter-symbol crosstalk is caused by each L symbols around the current symbol, where all modulo 2pi operations satisfy-pi < Φ _k +.pi, and each value of θ _i at different B _t T is shown in the following table:

the values of θ _i and 99% power bandwidth of the signal at different B _t T are shown

The units of the values of θ _i in the above table are degrees.

In Viterbi demodulation, it is necessary to construct a likelihood of a difference between an ideal differential phase value and the output of the 2bit differential phase network at the receiving end. The ideal differential phase value corresponding to the transition from state S _k to state S _k+1 at the kth symbol interval is calculated as follows:

Where d= (d _k-2L'-1,d_k-2L',d_k-2L'+1,...,d_k) is a sequence corresponding to transition from state S _k to state S _k+1, state S _k is defined as S _k＝(a_k-2L'-1,a_k-2L',a_k-2L'+1,...,a_k-1), and L ' is the number of symbols of the inter-symbol interference between two sides considered during Viterbi demodulation, so that 1L ' is less than or equal to L '.

And extracting the phase of the filtered signal, carrying out 2bit difference, determining L 'according to B _t T of the transmitted signal, and obtaining a signal phi _k-L' for demodulation after the difference phase passes through an L' T delayer. The determined signal to be demodulated is:

And step S13, determining a target differential phase corresponding to the filtered signal according to the current communication environment, and constructing a composite grid according to the target differential phase.

It should be noted that, considering the frequency offset effect in 2bit differential Viterbi demodulation, if there is a doppler effect in an AWGN channel, the received signal may be expressed as:

Wherein Δf (T) is doppler frequency offset, and after front-end filtering and 2bit differential phase network, the output at the end of the kth symbol interval (t=kt+t) is expressed as:

Wherein phi _k is the output of the 2bit differential phase network without the influence of frequency offset, and delta theta _d is the accumulated phase offset caused by the frequency offset caused by Doppler effect in 2T time.

Then in back-end Viterbi demodulation, the calculation of the branch path metrics becomes:

B_M(S_k,S_k+1)＝{mod[(Φ_k-L'+Δθ_d,k-L'-P(S_k,S_k+1)),2π]}²;

As can be seen from the above equation, when there is a frequency offset, an error is introduced in the calculation of the branch path metric value and the total path metric value, and the greater the accumulated phase offset due to the doppler effect, the greater the calculation error of the path metric, the more serious the demodulation performance is degraded.

Therefore, in this embodiment, for the influence of the frequency offset on the output of the 2bit differential phase network, a composite grid is constructed on the basis of Viterbi demodulation to compensate for the accumulated phase error, and a composite Viterbi algorithm is provided and applied to the rear end of the receiver to improve the adaptability to the frequency offset. The method comprises the steps of firstly determining the differential phase of a basic grid of Viterbi demodulation, determining the corresponding phase rotation unit degree and first phase rotation frequency of a filtered signal according to the current communication environment, calculating a target differential phase according to the differential phase, the phase rotation unit degree, the first phase rotation frequency and the normalized bandwidth of the basic grid, and constructing a composite grid according to the target differential phase. It can be understood that in specific engineering application, in combination with specific communication systems and communication environments, when parameters such as carrier frequency and frame structure are determined, the range of the doppler frequency offset and the accumulated phase error caused by the doppler frequency offset can be analyzed, and accordingly, a suitable value of the first phase rotation number M and the phase rotation unit degree delta theta is selected, so that the phase error can be compensated in a relatively matched manner, and a relatively accurate judgment result can be obtained.

Step S14, determining a sub-grid based on the composite grid, and determining branch path metrics and total path metrics of the signals to be demodulated according to the sub-grid.

In this embodiment, appropriate values of M and Δθ are selected, and values of P (S _k,S_k+1) are calculated according to B _t T, so as to construct a composite grid, where initial assignment j=1. Order theThe sub-trellis p= { P ₁+xΔθ,P₂+xΔθ,...,P_N +xΔθ }, can be selected, and the branch path metric and the total path metric at the state transition time corresponding to each symbol can be calculated according to M (S _k+1)＝M(S_k)+B_M(S_k,S_k+1) and B_M(S_k,S_k+1)＝{mod[(Φ_k-L'+Δθ_d,k-L'-P(S_k,S_k+1)-xΔθ),2π]}², and Viterbi demodulation is performed (no trace back is performed at this time).

And step S15, carrying out Viterbi demodulation based on the total path metric, and carrying out backtracking of the Viterbi demodulation according to the total path metric to obtain a demodulation result.

In this embodiment, viterbi demodulation may be performed based on the total path metric obtained in the previous step, and the demodulation result may be obtained by performing back tracking of viterbi demodulation according to the total path metric. After the demodulation result is obtained, determining the data demodulation requirement of the preset back end, converting the demodulation result into hard decision information or soft decision information according to the data demodulation requirement, and outputting the hard decision information or soft decision information to the preset system back end to complete the whole demodulation process.

According to the embodiment, firstly, a filtered signal of a transmission signal after being filtered by a Gaussian filter is obtained, the filtered signal is subjected to phase difference through a differential phase detection network, then, a differential phase obtained after the filtered signal is subjected to difference is extracted, a signal to be demodulated is determined according to the differential phase, a target differential phase corresponding to the filtered signal is determined according to a current communication environment, a composite grid is constructed according to the target differential phase, a sub-grid can be determined based on the composite grid, branch path measurement and total path measurement of the signal to be demodulated are determined according to the sub-grid, viterbi demodulation is performed based on the total path measurement, and a back trace of the viterbi demodulation is performed according to the total path measurement, so that a demodulation result is obtained. By means of the technical scheme, the method and the device for demodulating the 2-bit differential phase Viterbi based on the digital signal processing aim at the challenge that the existing GMSK demodulation method is difficult to adapt to the large Doppler frequency offset in the high dynamic communication environment, analyze the influence of accumulated phase errors caused by the Doppler frequency offset on the existing 2-bit differential phase Viterbi demodulation algorithm, construct a composite grid phase compensation model of the GMSK, and provide a brand new 2-bit differential phase composite Viterbi demodulation algorithm, so that the influence of the large Doppler frequency offset on demodulation performance is overcome at the cost of increasing smaller complexity.

Based on the above embodiment, the present application builds a composite grid phase compensation model of GMSK, and proposes a new 2bit differential phase composite Viterbi demodulation algorithm, and in this embodiment, the process of demodulating according to the composite grid will be described in detail. Referring to fig. 3, the embodiment of the application discloses a specific digital demodulation method, which comprises the following steps:

and S21, determining a target differential phase corresponding to the filtered signal according to the current communication environment, and constructing a composite grid according to the target differential phase.

Step S22, determining a sub-grid based on the composite grid, and determining branch path metrics and total path metrics of signals to be demodulated according to the sub-grid.

When determining the sub-grid based on the composite grid, firstly, the second phase rotation frequency j of the composite grid is given an=initial value of 1, the second phase rotation frequency is divided by two and then is rounded downwards to obtain a target parameter, and then the sub-grid is determined according to the target parameter, the differential phase of the basic grid and the unit degree of phase rotation. After constructing the composite grid, initially assigning j=1, letThe sub-grid p= { P ₁+xΔθ,P₂+xΔθ,...,P_N +xΔθ }, can be selected.

Then, according to M (S _k+1)＝M(S_k)+B_M(S_k,S_k+1) and B_M(S_k,S_k+1)＝{mod[(Φ_k-L'+Δθ_d,k-L'-P(S_k,S_k+1)-xΔθ),2π]}², the branch path metric and the total path metric at the state transition corresponding to each symbol can be calculated.

In this embodiment, when the B _t T of the transmitting end and the Viterbi detection of the receiving end determine the selected L ', all the P (S _k,S_k+1) values can be determined, N P (S _k,S_k+1) values corresponding to all possible sequences with a length of 2L' +2 are set, and p= { P ₁,P₂,...,P_N }, which is the differential phase of the basic grid, are obtained by rotating the differential phase of the basic grid by Δθ, and are expressed as:

P＝{P_ix}＝{P_i+xΔθ},x＝0,±1,...,i＝1,2,...,N；

if the value of x is M, x is taken from 0 to Representing a rounding down.

After the composite grid construction is completed, the values of x and Δθ are selected, i.e., a set of sub-grids p= { P ₁+xΔθ,P₂+xΔθ,...,P_N + xΔθ }, is selected. At this time, the calculation of the corrected branch path metric value becomes:

B_M(S_k,S_k+1)＝{mod[(Φ_k-L'+Δθ_d,k-L'-P(S_k,S_k+1)-xΔθ),2π]}²;

In this way, the accumulated phase error Δθ _d caused by the doppler frequency offset is compensated by the phase rotation xΔθ in the composite grid, if the x value satisfies that |xΔθ|is greater than |Δθ _d |, that is, if a sub-grid exists in the composite grid so that the phase rotation of a certain path is greater than the accumulated phase error caused by the doppler effect, then a sub-grid must exist in the composite grid, the accumulated phase error after the 2bit differential phase is compensated is necessarily smaller than Δθ/2, that is, the x value satisfies that |Δθ _d +xΔθ|is less than or equal to Δθ/2, so that the calculation error of the branch path metric and the total path metric after the composite grid is compensated is reduced.

In an actual differential demodulation system, if jitter or interference Δθ _e exists in the differential phase, when Δθ _e is less than or equal to 0.03 pi, the error code curve at this time almost coincides with the error code curve when Δθ _e =0, and the error code rate of the system is not affected by phase error. Therefore, if Δθ is less than or equal to 0.06 pi, by selecting the M value, the x value can exist so that |Δθ _d +xΔθ| is less than or equal to 0.03 pi, the demodulation performance of the corresponding path is hardly affected by the doppler frequency offset. If the static doppler frequency offset of 32KHz is considered at the symbol rate R _s =500 KHz, Δθ _d =0.256 pi is calculated, Δθ=0.06 pi is selected, m=9, and x= -4 satisfies |Δθ _d +xΔθ|=0.016pi and is less than or equal to 0.03 pi, the calculation error of the branch path metric and the total path metric is small under the corresponding path, and demodulation can be performed correctly.

And step S23, carrying out Viterbi demodulation based on the total path metric, and carrying out backtracking of the Viterbi demodulation according to the total path metric to obtain a demodulation result.

It should be noted that, in the conventional Viterbi demodulation based on 2bit differential, the calculation formula of the state transition time division branch path metric value is:

B_M(S_k,S_k+1)＝{mod[(Φ_k-L'-P(S_k,S_k+1)),2π]}²；

The total path metric corresponding to the end of the kth symbol interval is:

M(S_k+1)＝M(S_k)+B_M(S_k,S_k+1)；

When demodulation, branch path measurement and total path measurement are calculated according to the formula, forward state transition is carried out, when a plurality of branch paths reach the same state node by the maximum likelihood idea, the path with the minimum total path measurement is reserved as a surviving path, and the rest paths are competing paths and are deleted, so that complexity is simplified. And when the demodulation length of the Viterbi reaches the backtracking length, performing backward backtracking judgment, selecting the minimum value in the final total path measurement, backtracking the state corresponding to the minimum value to obtain a maximum likelihood path, and judging the corresponding transmission sequence according to the state transition condition in the maximum likelihood path so as to finish demodulation.

In the present embodiment, after the construction of the composite trellis is completed in the composite Viterbi demodulation, for each group of sub-trellis, forward state transition is performed according to the corrected branch path metric calculation formula and the total path metric calculation formula, and at the same time, the absolute value of the difference between the surviving path metric value and the competing path metric value is calculated and stored, and when the system has channel coding, the absolute value can be used as a reliability measure of soft information, and the greater the value, the more reliable the bit correctness judged by the surviving path. When the demodulation length of the sub-trellis Viterbi reaches the traceback length, the minimum value in the final total path metric is selected for storage. And after all the sub-grids finish forward calculation, comparing the saved calculation results, selecting a minimum value, and backtracking the sub-grid corresponding to the minimum value to obtain a demodulation result. And storing an initial minimum value in a final total path metric in the viterbi demodulation after the viterbi demodulation is performed based on the total path metric, adding one to the second phase rotation number, judging whether the new second phase rotation number is larger than the first phase rotation number, namely j=j+1, if j is smaller than or equal to M, jumping to the step of determining a sub-grid based on the composite grid, and determining the branch path metric and the total path metric of the signal to be demodulated according to the sub-grid. Otherwise, comparing the minimum value of the total path metrics stored in the M times of Viterbi demodulation, selecting the minimum value, and backtracking according to the Viterbi demodulation process corresponding to the minimum value, namely if the number of second phase rotations is increased by one and the obtained new number of second phase rotations is larger than the number of first phase rotations, determining a target minimum value from the initial minimum values in all the total path metrics, and backtracking according to the target minimum value to obtain a demodulation result.

For more specific processing in step S21, reference may be made to the corresponding content disclosed in the foregoing embodiment, and no further description is given here.

In this embodiment, assuming that the data length of a frame is K, according to the Viterbi algorithm, 1 multiplication and 2 additions are required for each state transition calculation, 2 ^2L'+1 states are shared at the end of each symbol interval, and two branches are shared for each state node to perform state transition, so that the calculation complexity is O (3k.2 2 ^2L'+2) when there is no composite grid. When a composite grid is present, the added complexity depends on the added number of sub-grids, i.e., the value of M, and the final algorithm complexity is O (3MK.2 ^2L'+2). It should be noted that, the forward computation process of each sub-grid is independent, so that the composite Viterbi detection can be processed in parallel, and compared with the conventional algorithm, the performance degradation is avoided in terms of processing delay.

According to the above steps, the simulation experiment is performed according to the above disclosed algorithm process in combination with the above embodiment, and the result is as follows:

And establishing a GMSK modulation and demodulation system model by utilizing Matlab, and simulating error code performance and adaptability to frequency offset of an algorithm provided by the embodiment. The transmitting end adopts a GMSK modulation mode with the B _t T value of 0.5, the parameters selected by the receiving end are L' =1, M=9, delta theta=0.06 pi and 16-point sampling according to the frame structure set by the transmitting end, and the channel is set as an additive Gaussian white noise channel. The method comprises the steps of carrying out 99% signal bandwidth filtering, 2bit differential phase detection, L' T delay and compound Viterbi demodulation on a received signal in sequence, and adding Turbo coding and decoding with parameters of (2, 1 and 3) at two ends of a system so as to utilize soft information constructed during compound Viterbi demodulation.

The demodulation performance of the algorithm provided herein and the traditional classical algorithm are simulated and compared and analyzed, and then the Doppler effect resistance performance analysis is performed on the conditions of no composite grid and composite grid.

FIG. 4 compares the error performance of "2bit differential demodulation", "2bit differential+Viterbi demodulation" and "2bit differential+composite Viterbi demodulation" without frequency offset, and it can be seen that the performance of "2bit differential+Viterbi demodulation" is superior to "2bit differential demodulation", the former has an obvious error rate drop amplitude along with the increase of signal-to-noise ratio, and can be rapidly dropped by one order of magnitude under high signal-to-noise ratio, and can reach 1×10 ^-5 orders of magnitude under 7 dB; the performance of the 2bit difference and the composite Viterbi demodulation is basically consistent with that of the 2bit difference and the Viterbi demodulation, which indicates that the structure of the composite grid does not cause the reduction of error code performance and still keeps good performance.

The Doppler frequency offset is considered, the system error code curves without the composite grid and with the composite grid under the conditions of no frequency offset, 16KHz frequency offset and 32KHz frequency offset are respectively simulated and analyzed, and simulation results are shown in fig. 5 and 6. As can be seen by comparison, when no composite grid exists, the capability of the algorithm for resisting Doppler shift is limited, the performance is obviously reduced under the frequency offset of 16KHz, and the algorithm has lost demodulation effect under the frequency offset of 32 KHz; and when the composite grid exists, the algorithm has stronger adaptability to Doppler frequency shift, and even under the frequency shift of 32KHz, the algorithm can still keep the demodulation performance basically consistent with that of no frequency shift. Therefore, the algorithm provided by the embodiment has good performance and stronger Doppler frequency shift resistance.

Through the technical scheme, the embodiment provides a GMSK signal composite Viterbi demodulation algorithm based on a 2-bit differential phase, analyzes a mechanism of Viterbi demodulation by utilizing the 2-bit differential phase and a composite grid, and carries out theoretical deduction on Doppler frequency offset resistance; a Matlab system simulation model is established, the feasibility and the stability of the algorithm are verified by simulation results, the error rate of the algorithm can reach 10 ^-5 orders of magnitude under 7dB, the performance is not degraded under the condition of not exceeding 32KHz Doppler frequency offset, and the excellent performance can be maintained. The algorithm has good performance, moderate implementation complexity, good robustness to carrier frequency offset and phase error, and good applicability and application prospect in a high dynamic communication environment.

Referring to fig. 7, the embodiment of the application also discloses a digital demodulation device, which comprises:

The phase difference module 11 is configured to obtain a filtered signal of the transmission signal after being filtered by the gaussian filter, and perform phase difference on the filtered signal by using a differential phase detection network;

A signal determining module 12, configured to extract a differential phase obtained by differentiating the filtered signal, and determine a signal to be demodulated according to the differential phase;

the grid construction module 13 is used for determining a target differential phase corresponding to the filtered signal according to the current communication environment and constructing a composite grid according to the target differential phase;

a metric determining module 14, configured to determine a sub-grid based on the composite grid, and determine a branch path metric and a total path metric of the signal to be demodulated according to the sub-grid;

And the digital demodulation module 15 is used for carrying out viterbi demodulation based on the total path metric and carrying out backtracking of the viterbi demodulation according to the total path metric to obtain a demodulation result.

According to the embodiment, firstly, a filtered signal of a transmission signal after being filtered by a Gaussian filter is obtained, the filtered signal is subjected to phase difference through a differential phase detection network, then, a differential phase obtained after the filtered signal is subjected to difference is extracted, a signal to be demodulated is determined according to the differential phase, a target differential phase corresponding to the filtered signal is determined according to a current communication environment, a composite grid is constructed according to the target differential phase, a sub-grid can be determined based on the composite grid, branch path measurement and total path measurement of the signal to be demodulated are determined according to the sub-grid, viterbi demodulation is performed based on the total path measurement, and a back trace of the viterbi demodulation is performed according to the total path measurement, so that a demodulation result is obtained. In this way, by constructing the composite grid phase compensation model of the GMSK, the embodiment provides a GMSK signal composite Viterbi demodulation algorithm based on the differential phase, which can overcome the influence of large Doppler frequency offset on demodulation performance and still can maintain excellent performance under large frequency offset.

In some embodiments, the signal determination module 12 specifically includes:

The symbol determining unit is used for determining the normalized bandwidth of the Gaussian filter corresponding to the sending signal and determining the target symbol number of the Viterbi demodulation according to the normalized bandwidth; the target symbol number is the symbol number which causes at least inter-symbol interference when the Viterbi demodulation is performed;

And the signal delay unit is used for determining a delay device of the filtered signal based on the target symbol number and obtaining the signal to be demodulated based on the delay device.

In some embodiments, the grid construction module 13 specifically includes:

The phase determining unit is used for determining the differential phase of the basic grid of the Viterbi demodulation and determining the corresponding phase rotation unit degree and the first phase rotation times of the filtered signal according to the current communication environment;

And the phase calculation unit is used for calculating the target differential phase according to the differential phase of the basic grid, the phase rotation unit degree, the first phase rotation times and the normalized bandwidth.

In some embodiments, the metric determination module 14 specifically includes:

The parameter determining unit is used for giving an initial value of 1 to the second phase rotation times of the composite grid, dividing the second phase rotation times by two and then rounding downwards to obtain a target parameter;

And the sub-grid determining unit is used for determining the sub-grid according to the target parameter, the differential phase of the basic grid and the phase rotation unit degree.

In some embodiments, the digital demodulation module 15 further includes:

The metric value storage unit is used for storing an initial minimum value in the total path metric in the Viterbi demodulation at this time;

the frequency judging unit is used for adding one to the second phase rotation frequency and judging whether the new second phase rotation frequency is larger than the first phase rotation frequency or not; if not, jumping to the step of determining a sub-grid based on the composite grid and determining the branch path metric and the total path metric of the signal to be demodulated according to the sub-grid.

In some embodiments, the digital demodulation module 15 specifically includes:

And the signal demodulation unit is used for determining a target minimum value from the initial minimum values in all the total path metrics if the obtained new second phase rotation times are greater than the first phase rotation times after the second phase rotation times are added by one, and carrying out back tracking of the Viterbi demodulation according to the target minimum value to obtain the demodulation result.

In some embodiments, the digital demodulation module 15 further includes:

And the result output unit is used for determining the data demodulation requirement of the preset back end, converting the demodulation result into hard decision information or soft decision information according to the data demodulation requirement and outputting the hard decision information or soft decision information to the preset back end.

Further, the embodiment of the present application further discloses an electronic device, and fig. 8 is a block diagram of an electronic device 20 according to an exemplary embodiment, where the content of the diagram is not to be considered as any limitation on the scope of use of the present application.

Fig. 8 is a schematic structural diagram of an electronic device 20 according to an embodiment of the present application. The electronic device 20 may specifically include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input output interface 25, and a communication bus 26. Wherein the memory 22 is configured to store a computer program that is loaded and executed by the processor 21 to implement the relevant steps of the digital demodulation method disclosed in any of the foregoing embodiments. In addition, the electronic device 20 in the present embodiment may be specifically an electronic computer.

In this embodiment, the power supply 23 is configured to provide an operating voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and an external device, and the communication protocol to be followed is any communication protocol applicable to the technical solution of the present application, which is not specifically limited herein; the input/output interface 25 is used for acquiring external input data or outputting external output data, and the specific interface type thereof may be selected according to the specific application requirement, which is not limited herein.

The memory 22 may be a carrier for storing resources, such as a read-only memory, a random access memory, a magnetic disk, or an optical disk, and the resources stored thereon may include an operating system 221, a computer program 222, and the like, and the storage may be temporary storage or permanent storage.

The operating system 221 is used for managing and controlling various hardware devices on the electronic device 20 and the computer program 222, which may be Windows Server, netware, unix, linux, etc. The computer program 222 may further include a computer program that can be used to perform other specific tasks in addition to the computer program that can be used to perform the digital demodulation method performed by the electronic device 20 as disclosed in any of the previous embodiments.

Further, the application also discloses a computer readable storage medium for storing a computer program; wherein the computer program, when executed by a processor, implements the digital demodulation method disclosed previously. For specific steps of the method, reference may be made to the corresponding contents disclosed in the foregoing embodiments, and no further description is given here.

In this specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, so that the same or similar parts between the embodiments are referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.

Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative elements and steps are described above generally in terms of functionality in order to clearly illustrate the interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software modules may be disposed in Random Access Memory (RAM), memory, read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

Finally, it is further noted that relational terms such as first and second, and the like are 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. Moreover, 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 one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.

The foregoing has outlined rather broadly the more detailed description of the application in order that the detailed description of the application that follows may be better understood, and in order that the present principles and embodiments may be better understood; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present application, the present description should not be construed as limiting the present application in view of the above.

Claims

1. A digital demodulation method, comprising:

2. The digital demodulation method according to claim 1, wherein said determining a signal to be demodulated from said differential phase comprises:

3. The digital demodulation method according to claim 2, wherein the determining the target differential phase corresponding to the filtered signal according to the current communication environment includes:

4. The digital demodulation method according to claim 3, wherein said determining a sub-grid based on said composite grid comprises:

5. The digital demodulation method according to claim 4, wherein after said viterbi demodulation based on said total path metric, further comprising:

6. The digital demodulation method according to claim 5, wherein said backtracking of said viterbi demodulation according to said total path metric results in a demodulation result, comprising:

7. The digital demodulation method according to any one of claims 1 to 6, wherein after the backtracking of the viterbi demodulation according to the total path metric obtains a demodulation result, further comprising:

8. A digital demodulating apparatus, comprising:

9. An electronic device comprising a processor and a memory; wherein the memory is for storing a computer program that is loaded and executed by the processor to implement the digital demodulation method of any one of claims 1 to 7.

10. A computer readable storage medium for storing a computer program which, when executed by a processor, implements the digital demodulation method according to any one of claims 1 to 7.