A method for evaluating interference cancellation performance of a satellite communication system

Abstract

This invention discloses a method for evaluating the interference cancellation performance of a satellite communication system, belonging to the field of satellite communication technology. It includes: analyzing the parameters of the interfering signal; constructing a reconstructed signal based on the parameters of the interfering signal; calculating the average power of the interfering signal at the observation time; calculating the average power of the reconstructed signal at the observation time without channel estimation error; calculating the power of the residual interfering signal caused by the channel estimation error; calculating the average power of the residual interfering signal at the observation time after interference cancellation without channel estimation error; calculating the logarithmic average interference suppression ratio; and calculating the signal-to-noise ratio (SNR) loss of the useful signal caused by the residual interfering signal after interference cancellation. This invention can evaluate the degree of interference cancellation and the degradation of the SNR of the useful low-speed spread spectrum signal caused by the residual interfering signal after interference cancellation, and has reuse value for accurately controlling the transmission power of low-speed signals in overlapping satellite communication systems.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to a method for evaluating the interference cancellation performance of a satellite communication system. Background Technology

[0002] In the field of band-shared satellite communication, low-speed signals, after direct sequence spread spectrum (DSS), are transmitted in the same frequency band as other modulated signals. These other modulated signals are considered interference signals to the low-speed signal. Band-shared transmission refers to the complete or partial overlap of the transmitted signals from multiple users in both the time and frequency domains. Using a band-shared transmission method can improve the system's spectral efficiency and, to some extent, enhance its anti-interference, anti-destruction, and anti-interception capabilities. In satellite communication, low-speed signals can be directly sequence spread spectrum and then transmitted in the same frequency band as other modulated signals. In this case, the other modulated signals can be considered interference signals to the low-speed spread spectrum signal. The greater the power of the other modulated signals on the satellite, the greater their interference impact on the low-speed spread spectrum signal.

[0003] Interference cancellation technology can reduce the impact of interference signals on low-speed spread spectrum signals. However, after the interference signal is eliminated, the impact of the remaining interference signal on the signal-to-noise ratio of the low-speed spread spectrum signal cannot be accurately assessed, which makes it impossible to accurately adjust the transmission power of the low-speed spread spectrum signal and affects the stability of the system link. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the aforementioned background technology and provide a method for evaluating the interference cancellation performance of satellite communication systems. This invention can not only estimate the degree of interference signal cancellation, but also accurately estimate the impact of the remaining interference signal after cancellation on the signal-to-noise ratio of low-speed spread spectrum signals.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for evaluating the interference cancellation performance of a satellite communication system includes the following steps:

[0007] Step 1: Receive the interference signal, calculate the white noise N0 and the power spectral density of the interference signal. And analyze the parameters of the interference signal;

[0008] Step 2: Construct a reconstructed signal based on the parameters of the interference signal;

[0009] Step 3, calculate the interference signal at the observation time. average power ;

[0010] Step 4: Calculate the reconstructed signal at the observation time when there is no channel estimation error. average power ;

[0011] Step 5: Calculate the residual interference signal power caused by channel estimation error. ;

[0012] Step 6: Calculate the residual interference signal at the observation time after interference signal cancellation when there is no channel estimation error. average power ;

[0013] Step 7: Calculate the logarithmic representation of the average interference suppression ratio ρ;

[0014] Step 8: Calculate the signal-to-noise ratio loss χ of the useful signal caused by the residual interference signal after the interference signal is eliminated. χ is the performance evaluation index of interference elimination.

[0015] Furthermore, in step 1, the parameters of the interference signal include amplitude. Carrier instantaneous phase Transmission delay Symbolic sequence Channel impulse response .

[0016] Furthermore, in step 3, The calculation method is as follows:

[0017]

[0018] Where T is the symbol period and N is the window length for calculating the average power, with a value of 1024.

[0019] Furthermore, in step 4, The calculation method is as follows:

[0020]

[0021] in, To normalize the magnitude estimate of the variance, The normalized time delay estimate variance is given by T, where T is the symbol period and g(t) is... The first derivative of , where N is the window length for calculating the average power, with a value of 1024.

[0022] Furthermore, in step 5, The calculation method is as follows:

[0023]

[0024] Where E represents the calculated signal power, To reconstruct the transmission delay of the signal, The superscript represents the estimation error of the channel impulse response. This indicates complex conjugate, and N is the window length for calculating the average power, with a value of 1024.

[0025] Furthermore, in step 6, The calculation method is as follows:

[0026]

[0027] in, Bit error rate, The modulation order is the number of bits transmitted per modulation symbol. For QPSK modulation, For 16APSK modulation, For BPSK modulation, ; To estimate the variance of the carrier phase, is a coefficient, and N is the window length for calculating the average power, with a value of 1024.

[0028] Furthermore, step 7 is specifically implemented as follows:

[0029] Calculate the interference suppression ratio :

[0030]

[0031] Calculate the logarithmic representation of the average interference suppression ratio ρ:

[0032]

[0033] Where N is the window length for calculating the average power, with a value of 1024, and T is the symbol period.

[0034] Furthermore, in step 8, χ is calculated as follows:

[0035]

[0036] in, Let N be the power spectral density of the interference signal, and N0 be the power spectral density of the white noise.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] 1. This invention provides an accurate estimation method for the degree of interference signal elimination.

[0039] 2. This invention provides quantitative indicators for the impact of the remaining interference signal on the low-speed spread spectrum signal after the interference signal is eliminated. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of co-band transmission.

[0041] Figure 2 This is a schematic diagram comparing the interference signal before and after its elimination. Detailed Implementation

[0042] The invention will now be further described with reference to the accompanying drawings.

[0043] A method for evaluating the interference cancellation performance of a satellite communication system. Figure 1 This diagram illustrates the spectral overlap between the low-speed spread spectrum signal and the interference signal, representing a common-band transmission method. The method specifically includes the following steps:

[0044] Step 1: Receive the interference signal, calculate the white noise N0 and the power spectral density of the interference signal. And analyze the parameters of the interference signal, including amplitude. Carrier instantaneous phase Transmission delay Symbolic sequence Channel impulse response ;

[0045] When the interference is an amplitude-phase modulated signal of type PSK, APSK, QAM, etc., the interference signal can be represented as:

[0046]

[0047] N takes the value 1024;

[0048] Step 2: Based on the parameters of the interference signal, construct a reconstructed signal; the reconstructed interference signal can be represented as:

[0049]

[0050] In the formula, , , , as well as The amplitude, carrier phase, transmitted symbol sequence, signal transmission delay, and channel impulse response of the interference signal are estimated, with N taking the value of 1024.

[0051] Step 3, calculate the interference signal at the observation time. average power :

[0052]

[0053] Where T is the symbol period and N is 1024;

[0054] Step 4: Calculate the reconstructed signal at the observation time when there is no channel estimation error. average power :

[0055]

[0056] Where T is the symbol period and N is 1024;

[0057] Cross-correlation terms at observation time The average power is:

[0058]

[0059] In the formula This indicates taking the real part.

[0060]

[0061] In the formula Bit error rate; It is related to the carrier modulation method and can be calculated using the following formula:

[0062]

[0063] therefore:

[0064]

[0065] In the formula for The real part of . Assume the modulation order is . That is, each modulation symbol carry For bit information, when the bit error rate is low, the following formula approximately holds:

[0066]

[0067] In the formula This represents the symbol error rate. For BPSK modulation, when the bit error rate is low, it is calculated as follows:

[0068]

[0069] For QPSK modulation, the following can be calculated:

[0070]

[0071] For other higher-order modulations, the following can be calculated:

[0072]

[0073] Step 5, calculate the residual interference signal caused by the channel estimation error, such as... Figure 2 As shown, the residual interference signal power :

[0074]

[0075] Where E represents the calculated signal power, To reconstruct the transmission delay of the signal, The superscript represents the estimation error of the channel impulse response. This represents complex conjugate, where N takes the value 1024;

[0076] Step 6: Calculate the residual interference signal at the observation time after interference signal cancellation when there is no channel estimation error. average power :

[0077]

[0078] in, Bit error rate, The modulation order is the number of bits transmitted per modulation symbol. For QPSK modulation, For 16APSK modulation, For BPSK modulation, ; To estimate the variance of the carrier phase, and The magnitude is related to the value of N. Under small error conditions, it can be approximated as 1. T is the symbol period, and N is a value of 1024.

[0079] Step 7, Calculate Interference suppression ratio at time .

[0080] Assume the estimation error of the channel impulse response is Then the estimation result of the channel impulse response can be expressed as:

[0081]

[0082] The reconstructed interference signal can be represented as:

[0083]

[0084] In the formula, For interference reconstructed based on the actual channel impulse response, N is taken as 1024. In engineering practice, it is generally assumed that the estimation error approximately follows a Gaussian distribution; therefore:

[0085]

[0086] get:

[0087]

[0088] The estimates of each parameter are unbiased and independent of each other.

[0089] therefore, The calculation method is as follows:

[0090]

[0091] Calculate the logarithmic representation of the average interference suppression ratio ρ:

[0092]

[0093] Where T is the symbol period and N is 1024;

[0094] Step 8, Define To receive the power spectral density of the interference signal, The power spectral density of the residual interference signal after the interference signal is eliminated can be expressed as:

[0095]

[0096] Therefore, the signal-to-noise ratio loss χ of the useful signal caused by the residual interference signal after interference signal elimination can be expressed as:

[0097]

[0098] Where N0 is the power spectral density of white noise.

[0099] In summary, this invention estimates the degree of interference signal cancellation by using the ratio of the average power of the residual interference signal after cancellation to the average power of the received interference signal. Based on this, the amount of signal-to-noise ratio loss in low-speed spread spectrum signals caused by the residual interference signal after cancellation can be further estimated.

[0100] This invention can assess the degree of interference signal elimination and the degradation of the signal-to-noise ratio (SNR) of the useful low-speed spread spectrum signal caused by the remaining interference signal after elimination. The system can adjust the earth station's transmit power and establish a stable link by referring to the SNR loss of the low-speed spread spectrum signal and the SNR of the low-speed spread spectrum signal under interference-free conditions. Therefore, this invention is of great significance for accurately controlling the transmit power of low-speed signals in overlapping satellite communication systems.

Claims

1. A method for evaluating the interference cancellation performance of a satellite communication system, characterized in that, Includes the following steps: Step 1: Receive the interference signal, calculate the white noise N0 and the power spectral density of the interference signal. And analyze the parameters of the interference signal; the parameters of the interference signal include amplitude. Instantaneous phase of carrier Transmission delay Symbolic sequence Channel impulse response ; Step 2: Construct a reconstructed signal based on the parameters of the interference signal; Step 3, calculate the interference signal at the observation time. average power ; The calculation method is as follows: Where T is the symbol period and N is the window length for calculating the average power, with a value of 1024; Step 4: Calculate the reconstructed signal at the observation time when there is no channel estimation error. average power ; The calculation method is as follows: in, To normalize the magnitude estimate of the variance, The normalized time delay estimate variance is given by T, where T is the symbol period and g(t) is... The first derivative of , where N is the window length for calculating the average power, and its value is 1024; Step 5: Calculate the residual interference signal power caused by channel estimation error. ; The calculation method is as follows: Where E represents the calculated signal power, To reconstruct the transmission delay of the signal, The channel impulse response estimation error is represented by the superscript *, which indicates the complex conjugate, and N is the window length for calculating the average power, with a value of 1024. Step 6: Calculate the residual interference signal at the observation time after interference signal cancellation when there is no channel estimation error. average power ; The calculation method is as follows: in, Bit error rate, The modulation order is the number of bits transmitted per modulation symbol. For QPSK modulation, For 16APSK modulation, For BPSK modulation, ; To estimate the variance of the carrier phase, is a coefficient, and N is the window length for calculating the average power, with a value of 1024; Step 7, calculate the logarithmic representation of the average interference suppression ratio ρ; the specific method is as follows: Calculate the interference rejection ratio : Calculate the logarithmic representation of the average interference suppression ratio ρ: Where N is the window length for calculating the average power, with a value of 1024, and T is the symbol period; Step 8: Calculate the signal-to-noise ratio loss χ of the useful signal caused by the residual interference signal after interference signal cancellation. χ is the performance evaluation index of interference cancellation. The calculation method of χ is as follows: in, Let N be the power spectral density of the interference signal, and N0 be the power spectral density of the white noise.

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