Method for improving communication effect of plasma sheath channel based on fountain code soft decoding

Abstract

This invention relates to the field of channel communication technology, specifically disclosing a method for improving the communication performance of plasma sheath channels based on fountain code soft decoding. After establishing a plasma channel model, the amplitude attenuation function follows a log-normal distribution, and the phase shift function follows a Gaussian distribution. The probability densities of the amplitude attenuation function and the phase shift function are calculated respectively. Then, combined with the plasma channel model, the conditional probability density of the plasma sheath channel for matched filtering of the received signal is calculated. The log-likelihood ratio in the plasma sheath channel under BPSK modulation of ideal channel information is calculated, as well as the likelihood probability value and log-likelihood ratio of the received signal under unknown plasma sheath channel parameters. This determines the initial values ​​for iteration, which are then used for fountain code soft-decision decoding. This invention enables the reuse of usable information in discarded fountain code packets, thereby further improving the utilization rate of fountain code packets and enhancing the overall communication efficiency of the plasma sheath channel.

Description

Technical Field

[0001] This invention relates to the field of channel communication technology, and in particular to a method for improving the channel communication performance of plasma sheaths based on fountain code soft decoding. Background Technology

[0002] When a hypersonic vehicle is flying at high speed, its surface is covered with a plasma sheath. The plasma sheath interferes with the normal signal transmission between the vehicle and the ground base station, which seriously affects the communication quality of the telemetry and control link and is not conducive to ground control of the vehicle.

[0003] Currently, there are three main approaches to solving this problem: reducing the transmission rate, increasing the transmission frequency, and weakening the influence of the plasma sheath on the signal through intervention mechanisms. However, the dynamic nature of plasma parameters and the difficulty in establishing effective feedback loops in the link limit the application of these three methods in plasma sheath channels. Furthermore, the large transmission delay in plasma sheath channels results in low transmission efficiency for traditional feedback retransmission communication systems. While forward error correction codes such as fountain codes can be used to circumvent the drawbacks of feedback retransmission mechanisms, the harsh transmission environment of plasma sheath channels may cause errors in certain bits of the fountain code encoded packets during information transmission. If the traditional hard-decision method of fountain codes is used, these encoded packets will be discarded, which is a significant waste for plasma sheath channels where channel resources are extremely limited. Moreover, research has found that only part of the information in these encoded packets is erroneous, and the remaining information can actually be utilized.

[0004] Therefore, how to reuse available information to improve the communication efficiency of the entire plasma sheath channel is an urgent problem to be solved. Summary of the Invention

[0005] To address the technical problems in the prior art, this invention provides a method for improving the communication performance of plasma sheath channels based on fountain code soft decoding.

[0006] This invention discloses a method for improving the communication performance of plasma sheath channels based on fountain code soft decoding, comprising the following steps:

[0007] Establish a multiplicative channel using the plasma sheath channel, including the amplitude attenuation function r and the phase shift function. and Gaussian white noise n awgn Plasma channel model;

[0008] The amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Following a Gaussian distribution, calculate the amplitude attenuation function r and the phase shift function respectively. The probability density P(r) and

[0009] The conditional probability density P(y) of the plasma sheath channel for matched filtering of the received signal y is calculated using the amplitude attenuation function r and the plasma channel model. i |x i (,r); where x is the transmitted signal;

[0010] Based on the amplitude attenuation value and the conditional probability density P(y) i |x i ,r), calculate the log-likelihood ratio LLR(y) in the plasma sheath channel under the condition of ideal channel information modulated by BPSK. i );

[0011] Alternatively, based on the probability density P(r) of the amplitude decay function r and the conditional probability density P(y) i |x i ,r), calculate the likelihood probability value P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), and calculate the log-likelihood ratio LLR(y) in the plasma sheath channel. i );

[0012] According to the log-likelihood ratio LLR(y) i Determine the initial value for iteration, and perform soft-decision decoding of the fountain code based on the initial value for iteration.

[0013] Furthermore, using the plasma sheath channel as a multiplicative channel, an amplitude attenuation function r and a phase shift function are established. and Gaussian white noise n awgn The plasma channel model includes:

[0014] The plasma sheath channel is configured to satisfy:

[0015]

[0016] Where R(t) represents the received signal, S(t) represents the transmitted signal, j is the imaginary part of the complex signal, and θ0 is the initial angle between the incident electromagnetic wave and the plasma sheath channel.

[0017] Furthermore, the amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Following a Gaussian distribution, calculate the amplitude attenuation function r and the phase shift function respectively. The probability density P(r) and include:

[0018] Calculate the probability density P(r) of the amplitude decay function r:

[0019]

[0020] Where, μ r Let σ be the mean of the amplitude decay function r. r Let be the variance of the amplitude decay function r;

[0021] And, calculate the phase shift function. probability density

[0022]

[0023] in, Phase shift function The mean, Phase shift function The variance.

[0024] Furthermore, the conditional probability density P(y) of the plasma sheath channel for matched filtering of the received signal y is calculated using the amplitude attenuation function r and the plasma channel model. i |x i ,r), including:

[0025] Calculate conditional probability density Where σ is Gaussian white noise n awgn The variance.

[0026] Furthermore, the step of calculating the amplitude attenuation value and the conditional probability density P(y) i |x i ,r), calculate the log-likelihood ratio LLR(y) in the plasma sheath channel under the condition of ideal channel information modulated by BPSK. i ),include:

[0027] Since the codeword of the transmitted signal modulated by BPSK is x i =-1,+1, then the log-likelihood ratio in the plasma sheath channel under the condition of ideal channel information modulated by BPSK is...

[0028] Furthermore, the log-likelihood ratio LLR(y) i Simplified to

[0029] Furthermore, the probability density P(r) based on the amplitude decay function r and the conditional probability density P(y) i |x i ,r), calculate the likelihood probability value P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), including:

[0030]

[0031] Furthermore, the calculation of the plasma sheath

[0032] Log-likelihood ratio (LLR) in the channel i ),include:

[0033] Calculate the mean of the amplitude decay function r.

[0034] Calculate the log-likelihood ratio

[0035] Furthermore, calculating the probability density P(r) of the amplitude decay function r includes:

[0036]

[0037] Where F(Inr) represents the cumulative probability function of Inr, and

[0038] The present invention provides a method for improving the communication performance of plasma sheath channels based on fountain code soft decoding. After establishing a plasma channel model, the amplitude attenuation function follows a log-normal distribution, and the phase shift function follows a Gaussian distribution. The probability densities of the amplitude attenuation function and the phase shift function are calculated respectively. Then, the conditional probability density of the plasma sheath channel for matched filtering of the received signal is calculated in conjunction with the plasma channel model. Furthermore, the log-likelihood ratio in the plasma sheath channel under the condition of ideal channel information modulated by BPSK, and the likelihood probability value and log-likelihood ratio of the received signal under the condition of unknown plasma sheath channel parameters are calculated. The initial value of the iteration is then determined, and fountain code soft decision decoding is performed accordingly. This achieves the purpose of applying fountain code soft decoding to plasma sheath channel communication, enabling the reuse of usable information in discarded fountain code encoded packets, thereby further improving the utilization rate of fountain code encoded packets and improving the overall communication efficiency of the plasma sheath channel. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a flowchart illustrating the steps of a method for improving plasma sheath channel communication based on fountain code soft decoding according to an embodiment of the present invention.

[0041] Figure 2This is an experimental simulation diagram (I) of the method for improving the communication effect of plasma sheath channel based on fountain code soft decoding according to an embodiment of the present invention;

[0042] Figure 3 This is an experimental simulation diagram (II) of the method for improving the communication effect of plasma sheath channel based on fountain code soft decoding according to an embodiment of the present invention. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0044] Fountain codes possess rate-free characteristics, enabling efficient data transmission even when channel conditions are unknown, making them suitable for complex environments in wireless communication. This invention provides a method for improving plasma sheath channel communication performance based on fountain code soft decoding, such as... Figure 1 As shown, the steps include:

[0045] Step S10: Establish a multiplicative channel using the plasma sheath channel, including the amplitude attenuation function r and the phase shift function. and Gaussian white noise n awgn The plasma channel model.

[0046] Specifically, this step includes: setting the plasma sheath channel to meet the following requirements:

[0047]

[0048] Where R(t) represents the received signal, S(t) represents the transmitted signal, j is the imaginary part of the complex signal, and θ0 is the initial angle between the incident electromagnetic wave and the plasma sheath channel.

[0049] Step S20: The amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Calculate the amplitude attenuation function r and the phase shift function, respectively, following a Gaussian distribution. The probability density P(r) and

[0050] In small-scale variations of the plasma sheath channel, the amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Calculate the amplitude attenuation function r and the phase shift function, respectively, following a Gaussian distribution. The probability density P(r) and as follows:

[0051] First, calculate the probability density P(r) of the amplitude decay function r:

[0052]

[0053] Where F(Inr) represents the cumulative probability function of Inr, and μ r Let σ be the mean of the amplitude decay function r. r Let be the variance of the amplitude decay function r.

[0054] Secondly, calculate the phase shift function. probability density

[0055] in, Phase shift function The mean, Phase shift function The variance.

[0056] Step S30: Calculate the conditional probability density P(y) of the plasma sheath channel for matched filtering of the received signal y using the amplitude attenuation function r and the plasma channel model. i |x i ,r).

[0057] Conditional probability density P(y) i |x i In the equation (r), x represents the transmitted signal. The distribution between the codewords of the received signal and the codewords of the transmitted signal follows a Gaussian process. A Gaussian process is a normal distribution function with the received codeword as the variable, the transmitted codeword as the mean, and the variance as σ, where σ is the Gaussian white noise n. awgn The variance of is a known quantity.

[0058] Assuming matched filtering is applied to the received signal y, the conditional probability density is:

[0059] Conditional probability density

[0060] Step S40: Based on the amplitude attenuation value and the conditional probability density P(y) i |x i ,r), calculate the log-likelihood ratio LLR(y) in the plasma sheath channel under the condition of ideal channel information modulated by BPSK. i ).

[0061] Fountain code soft information is expressed using the log-likelihood ratio (LLR), which is the posterior probability of the received codeword. The LLR is defined as:

[0062]

[0063] As can be seen from the above definition, when the LLR approaches +∞, the probability of receiving a symbol as 0 is greater, and when the LLR approaches -∞, the probability of receiving a symbol as 1 is greater.

[0064] Since the codeword of the transmitted signal modulated by BPSK is x i =-1,+1, This step is under the condition of an ideal channel, that is, the specific value of the amplitude attenuation is known. Then, under the condition of ideal channel information modulated by BPSK, the log-likelihood ratio in the plasma sheath channel is...

[0065] The specific calculation is as follows:

[0066]

[0067] Alternatively, step S50: based on the probability density P(r) of the amplitude decay function r and the conditional probability density P(y) i |x i ,r), calculate the likelihood probability value P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), and calculate the log-likelihood ratio LLR(y) in the plasma sheath channel. i ).

[0068] In this step, the channel parameters are unknown. If the channel fading factor in the plasma sheath channel is 'a', then the likelihood probability density is redefined as: P(y i |x i )=P(a)×P(y i |x i In a plasma sheath channel, the channel fading factor α follows a log-normal distribution. In this embodiment, the channel fading factor α is the amplitude attenuation function r, therefore, it is necessary to determine the probability density P(r) and conditional probability density P(y) of the amplitude attenuation function r. i |x i Calculate the likelihood probability P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), including:

[0069]

[0070] To further simplify the above calculation, we can calculate the log-likelihood ratio LLR(y) in the plasma sheath channel when the channel parameters are unknown. i ),include:

[0071] Calculate the mean of the amplitude decay function r.

[0072] Then calculate the log-likelihood ratio Step S60: Based on the log-likelihood ratio LLR(y) i Determine the initial value for iteration and perform soft-decision decoding of the fountain code based on the initial value for iteration.

[0073] The application of the fountain code soft-decision decoding algorithm in the plasma sheath can be realized by performing fountain soft-decision decoding based on the initial iterative value of the obtained fountain code in the soft-decision decoding algorithm in the plasma sheath channel.

[0074] like Figure 2 and Figure 3 The following is a simulation example:

[0075] The Raptor code from the fountain code is used. The LDPC precoding in the Raptor code has a code rate of 0.95. The degree distribution function of the Raptor code adopts the Poisson distribution function. The decoding algorithm is a soft-decision decoding algorithm with 40 decoding iterations. The information bit length is 1000 bits, and the signal-to-noise ratio is 5dB. The LT code has 1000 information bits, 100 encoded packets, and uses BP decoding with a signal-to-noise ratio of 15dB. The mean distribution of the plasma sheath channel is 5.74 × 10⁻⁶. -5 The variance was 0.65. Monte Carlo simulation was used, and the number of simulations was 1000. The results were as follows: Figure 2 and Figure 3 The results are shown below. The horizontal axis represents transmission redundancy, the vertical axis represents the bit error rate, soft decode represents soft-decision decoding, and hard decode represents hard-decision decoding.

[0076] from Figure 2 and Figure 3 As can be seen, in the transmission environment of the plasma sheath channel, the soft-decision decoding algorithm of the fountain code performs significantly better than the hard-decision decoding algorithm. The soft-decision decoding algorithm can successfully complete the decoding with low redundancy and low signal-to-noise ratio, while the hard-decision decoding requires high redundancy to decode.

[0077] The method for improving the communication effect of plasma sheath channel based on fountain code soft decoding in this invention embodiment establishes a plasma channel model. The amplitude attenuation function follows a log-normal distribution, and the phase shift function follows a Gaussian distribution. The probability densities of the amplitude attenuation function and the phase shift function are calculated respectively. Then, the conditional probability density of the plasma sheath channel for matched filtering of the received signal is calculated in conjunction with the plasma channel model. Furthermore, the log-likelihood ratio in the plasma sheath channel under BPSK modulation of ideal channel information, and the likelihood probability value and log-likelihood ratio of the received signal under unknown plasma sheath channel parameters are calculated. This determines the initial value for iteration, which is then used for fountain code soft decision decoding. This achieves the goal of applying fountain code soft decoding to plasma sheath channel communication, enabling the reuse of usable information in discarded fountain code packets, thereby further improving the utilization rate of fountain code packets and enhancing the overall communication efficiency of the plasma sheath channel.

[0078] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A method for improving the communication performance of a plasma sheath channel based on fountain code soft decoding, characterized in that, Including the following steps: Establish a multiplicative channel using the plasma sheath channel, including the amplitude attenuation function r and the phase shift function. and Gaussian white noise n awgn Plasma channel model; The amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Following a Gaussian distribution, calculate the amplitude attenuation function r and the phase shift function respectively. The probability density P(r) and The conditional probability density P(y) of the plasma sheath channel for matched filtering of the received signal y is calculated using the amplitude attenuation function r and the plasma channel model. i |x i (,r); where x is the transmitted signal; Based on the amplitude attenuation value and the conditional probability density P(y) i |x i ,r), calculate the log-likelihood ratio LLR(y) in the plasma sheath channel under the condition of ideal channel information modulated by BPSK. i ); Alternatively, based on the probability density P(r) of the amplitude decay function r and the conditional probability density P(y) i |x i ,r), calculate the likelihood probability value P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), and calculate the log-likelihood ratio LLR(y) in the plasma sheath channel. i ); According to the log-likelihood ratio LLR(y) i Determine the initial value for iteration, and perform soft-decision decoding of the fountain code based on the initial value for iteration.

2. The method for improving the communication effect of plasma sheath channel based on fountain code soft decoding as described in claim 1, characterized in that, Establish a multiplicative channel using the plasma sheath channel, including the amplitude attenuation function r and the phase shift function. and Gaussian white noise n awgn The plasma channel model includes: The plasma sheath channel is configured to satisfy: Where R(t) represents the received signal, S(t) represents the transmitted signal, j is the imaginary part of the complex signal, and θ0 is the initial angle between the incident electromagnetic wave and the plasma sheath channel.

3. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 2, characterized in that, The amplitude attenuation function r follows a log-normal distribution, and the phase shift function... Following a Gaussian distribution, calculate the amplitude attenuation function r and the phase shift function respectively. The probability density P(r) and include: Calculate the probability density P(r) of the amplitude decay function r: Where, μ r Let σ be the mean of the amplitude decay function r. r Let be the variance of the amplitude decay function r; And, calculate the phase shift function. probability density in, Phase shift function The mean, Phase shift function The variance.

4. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 3, characterized in that, The conditional probability density P(y) of the plasma sheath channel for matched filtering of the received signal y is calculated using the amplitude attenuation function r and the plasma channel model. i |x i ,r), including: Calculate conditional probability density Where σ is Gaussian white noise n awgn The variance.

5. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 4, characterized in that, The data is based on the amplitude attenuation value and the conditional probability density P(y). i |x i ,r), calculate the log-likelihood ratio LLR(y) in the plasma sheath channel under the condition of ideal channel information modulated by BPSK. i ),include: Since the codeword of the transmitted signal modulated by BPSK is x i =-1,+1, then the log-likelihood ratio in the plasma sheath channel under the condition of ideal channel information modulated by BPSK is...

6. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 5, characterized in that, The log-likelihood ratio LLR(y) i Simplified to 7. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 6, characterized in that, The probability density P(r) based on the amplitude decay function r and the conditional probability density P(y) i |x i ,r), calculate the likelihood probability value P(y) of the received signal y when the plasma sheath channel parameters are unknown. i |x i =±1), including:

8. The method for improving plasma sheath channel communication performance based on fountain code soft decoding as described in claim 7, characterized in that, The calculation of the log-likelihood ratio LLR(y) in the plasma sheath channel i ),include: Calculate the mean of the amplitude decay function r. Calculate the log-likelihood ratio 9. The method for improving the communication effect of a plasma sheath channel based on fountain code soft decoding as described in claim 3, characterized in that, Calculating the probability density P(r) of the amplitude decay function r includes: Where F(Inr) represents the cumulative probability function of Inr, and

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