An interference signal cancellation method based on modulation interference accurate reconstruction

Abstract

The application discloses a kind of based on modulation interference accurate reconstruction interference signal cancellation method, belong to satellite communication technical field.It includes: the symbol estimation of interference signal to mixed signal, time delay estimation, carrier phase estimation and amplitude estimation;Carrier recovery is carried out to mixed signal, and the symbol is reconstructed, and the interference signal for cancellation is generated;Mixed signal is delayed, and the interference signal regenerated is time aligned;Interference signal in the mixed signal after delay is cancelled using channel response estimation method, and the remaining low-speed signal is output;Carrier phase is restored to the remaining low-speed signal, and interference signal cancellation is completed.The application can effectively reduce the power spectral density of low-speed signal in overlapping satellite communication system, under the condition that low-speed signal occupies total power of satellite about convention, improve the system capacity of low-speed signal.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of satellite communication technology, in particular to an interference signal cancellation method based on modulation interference accurate reconstruction. BACKGROUND

[0002] In the field of frequency band sharing satellite communication, low speed signals are directly sequence spread spectrum and transmitted in the same frequency band with other modulation signals, and the other modulation signals are regarded as interference signals of the low speed signals. The transmission of multiple users' signals in time domain and frequency domain completely or partially overlaps, which is called co-band transmission. The transmission mode of sharing frequency band can improve the spectrum utilization of the system, and to a certain extent, improve the anti-interference ability, anti-destruction ability and anti-interception ability of the communication signal. In satellite communication, low speed signals can be directly sequence spread spectrum and transmitted in the same frequency band with other modulation signals. At this time, the other modulation signals can be regarded as interference signals of the low speed spread spectrum signals, and the greater the power of the other modulation signals on the satellite, the greater the influence of the other modulation signals on the low speed spread spectrum signals. In order to reliably establish a communication link, it is necessary to increase the transmission power of the low speed spread spectrum signals. However, with the increase of the power of the low speed spread spectrum signals, the influence of the low speed spread spectrum signals on the other modulation signals will gradually appear, and the anti-interception performance of the low speed spread spectrum signals will gradually decrease. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies in the background art, and to provide an interference signal cancellation method based on modulation interference accurate reconstruction. The present application can effectively reduce the power spectral density of low speed signals in the overlapping satellite communication system, and improve the system capacity of low speed signals under the condition that low speed signals occupy about 70% of the total power of the satellite.

[0004] The technical scheme adopted by the present application is as follows:

[0005] An interference signal cancellation method based on modulation interference accurate reconstruction, comprising the following steps:

[0006] Step 1, receiving the mixed signal of the interference signal and the low speed signal, and sequentially performing symbol estimation, time delay estimation, carrier phase estimation and amplitude estimation of the interference signal;

[0007] Step 2, performing carrier recovery on the mixed signal, and then reconstructing the symbol after carrier recovery according to the amplitude obtained by amplitude estimation, to regenerate the interference signal for cancellation;

[0008] Step 3, delaying the mixed signal according to the time delay obtained by time delay estimation, and time aligning the mixed signal with the interference signal regenerated in step 2;

[0009] Step 4: Referring to the regenerated interference signal, use the channel response estimation method to cancel the interference signal in the delayed mixed signal and output the remaining low-speed signal.

[0010] Step 5: Perform carrier phase restoration on the remaining low-speed signal to complete the interference signal cancellation.

[0011] Furthermore, the specific method for symbol estimation is as follows:

[0012] When the signal-to-noise ratio of the modulated interference signal is greater than 10dB, the estimated transmitted bits are obtained through hard decision, and then the estimated modulation symbols are obtained through symbol mapping.

[0013] When the signal-to-noise ratio of the modulated interference signal is less than 10dB, the estimated transmitted bits are obtained through decoding and secondary encoding, and then the estimated modulation symbols are obtained through symbol mapping.

[0014] Furthermore, the time delay estimation employs a frequency domain nonlinear estimation algorithm, and the estimation result is as follows:

[0015]

[0016] In the formula:

[0017]

[0018] in, Let m be the number of observed symbols, T be the ordinal number of the symbol, and T be the symbol period. For signal transmission delay, It is a mixed signal in the form of a complex digital signal. for The complex conjugate, Number of sampling points per symbol It is a complex argument function; This is a correction factor, adjusted according to the signal characteristics, with a value ranging from 0.01 to 1.

[0019] Furthermore, the specific method for carrier phase estimation is as follows:

[0020] Matched filtering is applied to the mixed signal, and unsigned crosstalk points are selected to obtain statistically independent samples. Carrier phase estimation is performed using sample data:

[0021]

[0022]

[0023] In the formula, The number of symbols observed before and after the estimated symbol; For the estimated modulation symbol, is the complex conjugate of the mixed signal, is the mixed signal in the form of complex digital signal, is the carrier phase, is the estimated carrier phase, is the correction factor, which is adjusted according to the signal characteristics, and the value range is 0.01 to 1.

[0024] Further, the specific way of amplitude estimation is:

[0025] The mixed signal is matched filtered, and the un-signed inter-symbol interference point is taken to obtain the statistically independent sample The sample data is used to estimate the interference amplitude:

[0026]

[0027] In the formula, is the number of observed symbols; is the estimated modulation symbol, is the conjugate of the modulation symbol, is the mixed signal in the form of complex digital signal, is the signal amplitude estimation value; Re is the real part, is the correction factor, which is adjusted according to the signal characteristics, and the value range is 0.01 to 1.

[0028] Further, in step 4, the filter coefficient stops updating the filter coefficient when the filter coefficient reaches the optimal value, and the criterion for judging whether the filter coefficient reaches the optimal value is that the power ratio of the residual interference signal after the interference signal is cancelled to the input original interference signal is less than 0.1; wherein, The calculation method of is:

[0029]

[0030] In the formula, is the normalized amplitude estimation variance; is the carrier phase estimation variance, is related to the size of is the normalized time delay estimation variance, is a constant related to the roll-off factor; is the normalized channel estimation variance; is the modulation order, that is, the number of bits transmitted per modulation interference symbol, for QPSK modulation, for 16APSK modulation, for BPSK modulation, ; is the corresponding bit error rate.​​

[0031] The present application has the following advantages over the background art:

[0032] 1. The present application uses interference signal cancellation technology to reduce the power spectral density of low-speed signals and reduce the impact of low-speed signals on modulated signals.

[0033] 2. The present application uses interference signal cancellation technology to improve the system capacity of low-speed communication systems under the same satellite capacity conditions.

[0034] 3. Since the impact of modulated signals on low-speed signals is eliminated, low-speed signals can transmit very small power to establish a reliable link, and the spectral density of low-speed signals is much lower than the spectral density of noise, so the impact of low-speed signals on other modulated signals can be ignored. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is a schematic diagram of co-band transmission.

[0036] Figure 2 is a schematic diagram of interference signal cancellation implementation principle.

[0037] Figure 3 is a schematic diagram of channel response estimation. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with the accompanying drawings.

[0039] An interference signal cancellation method based on modulation interference precise reconstruction, Figure 1 is a schematic diagram of co-band transmission, which describes the spectral relationship between low-speed spread spectrum signals and other modulated signals. The flow of the method is shown in Figure 2 , which specifically includes the following steps:

[0040] Step 1, interference signal modulation symbol estimation. The mixed signal of the interference signal and the low-speed signal is subjected to symbol estimation by the symbol estimation module to complete the symbol estimation of the interference signal. When the signal-to-noise ratio of the modulated interference signal is high, the transmitted bits can be estimated by hard decision, and then the estimated modulation symbols are obtained by symbol mapping; when the signal-to-noise ratio of the modulated interference signal is low, the transmitted bits need to be estimated by decoding and secondary encoding, and then the estimated modulation symbols are obtained by symbol mapping.

[0041] Step 2, interference signal transmission delay estimation. The symbol-estimated signal is subjected to transmission delay estimation by the transmission delay estimation module to complete the time delay estimation of the interference signal. The transmission delay error estimation uses a frequency domain nonlinear estimation algorithm, which obtains the estimation of the symbol timing error by calculating the phase of the Fourier transform of at The estimation result is:

[0042]

[0043] In the formula:

[0044]

[0045] is the number of observation symbols, is the mixed signal in the form of complex analog signal, is the complex conjugate of , m is the ordinal number of the symbol, and T is the symbol period, is the signal transmission delay, is the mixed signal in the form of complex digital signal, is the complex conjugate of , is the number of sampling points per symbol, is the complex argument function; is a correction factor, which is adjusted according to the signal characteristics and has a value range of 0.01 to 1.

[0046] The value is 1024 symbols, which can meet the interference cancellation performance requirements, and the performance loss caused by the corrected delay error is less than 0.01 dB.

[0047] Step 3, interference signal carrier phase estimation. Match filtering is performed on the interference signal after transmission delay estimation, and the inter-symbol crosstalk point is taken to obtain statistically independent samples:

[0048]

[0049] Carrier phase estimation is performed using sample data:

[0050]

[0051]

[0052] In the formula, is the number of observation symbols before and after the estimated symbol; is the estimated modulation symbol, is the complex conjugate of ; is the mixed signal in the form of complex digital signal, is the carrier phase, is the estimated carrier phase; is a correction factor, is white noise, which is adjusted according to the signal characteristics and has a value range of 0.01 to 1.

[0053] The value of 127 symbols can meet the interference cancellation performance requirements, and the performance loss caused by the corrected carrier phase error is less than 0.02 dB.

[0054] Step 4, interference signal amplitude estimation. The interference signal after symbol estimation is matched filtered, and the intersymbol interference point is taken to obtain statistically independent samples:

[0055]

[0056] The sample data is used for interference amplitude estimation:

[0057]

[0058] In the formula, is the number of observation symbols; is the estimated modulation symbol, is the conjugate of the modulation symbol, is the mixed signal in the form of a complex digital signal, is the signal amplitude, is the signal amplitude estimate; Re is the real part, is the correction factor, is white noise, which is adjusted according to the signal characteristics and has a value range of 0.01 to 1.

[0059] The value of 127 symbols can meet the interference cancellation performance requirements, and the performance loss caused by the corrected amplitude error is less than 0.02 dB.

[0060] Step 5, interference signal reconstruction. The symbol after carrier recovery is reconstructed according to the amplitude output by the amplitude estimation, and the interference signal used for cancellation is regenerated.

[0061] Step 6, mixed signal delay. The mixed signal of the interference signal after symbol estimation and the low-speed signal is time-delayed and time-aligned with the regenerated interference signal.

[0062] Step 7, channel response estimation. The delayed mixed signal is used to realize interference signal cancellation by using channel response estimation method with the regenerated interference signal, and the remaining low-speed signal is output. The channel response estimation is realized by using a least mean square algorithm adaptive filter, as shown in Figure 3 The least mean square algorithm is described as follows:

[0063]

[0064]

[0065]

[0066] In the formula is the order of the filter; is the coefficient of the filter; the input of the filter is the symbol shaped waveform sequence after local filtering ; the output is the reconstructed interference signal . The error signal is the output after cancellation, i.e.

[0067]

[0068] is the correction factor, is the mixed signal, which is adjusted according to the characteristics of the channel response, and the value range is 0.5 to 1. The filter coefficient is updated according to the following formula:

[0069]

[0070] is the step size, and in order to ensure the convergence of the algorithm, the following requirements are required:

[0071]

[0072] wherein is the maximum eigenvalue of the input signal autocorrelation matrix.

[0073] Step 8, low-speed signal carrier phase restoration. The low-speed signal remaining after the interference signal is cancelled is subjected to carrier phase restoration.

[0074] Step 9, interference cancellation performance evaluation. The power ratio of the residual interference signal after the interference signal is cancelled to the original input interference signal in the remaining signal output by the channel response estimation can be expressed as:

[0075]

[0076] wherein is the normalized amplitude estimation variance; is the carrier phase estimation variance, and are related to the size of is the normalized time delay estimation variance, is a constant related to the roll-off factor; is the normalized channel estimation variance; is the modulation order, i.e. the number of bits transmitted per modulated interference symbol, for QPSK modulation, take , for 16APSK modulation, take , and for BPSK modulation, take ; is the corresponding bit error rate.

[0077] Filter coefficient The filter coefficient is stopped updating after reaching the best value, and the criterion for judging whether the filter coefficient reaches the best value is the power ratio of the residual interference signal after the interference signal is cancelled to the input original interference signal Less than 0.1.

[0078] In summary, the present application uses modulation symbol estimation, transmission delay estimation, carrier phase estimation, interference amplitude estimation, channel response estimation and other methods to realize accurate reconstruction of the interference signal. By subtracting the reconstructed signal from the interference signal, the interference signal is cancelled. In the process of cancelling the interference signal, the useful signal is not damaged, and the performance is good. In the case of the signal-to-noise ratio of the interference signal being higher than 10dB, the performance loss of the low-speed signal is less than 0.5dB after the interference signal is cancelled. Since the influence of the modulation signal on the low-speed signal is eliminated, the low-speed signal can transmit very small power to establish a reliable link. The spectral density of the low-speed signal is much lower than the spectral density of the noise, and the influence of the low-speed signal on other modulation signals is negligible.

Claims

1. A method for interference signal cancellation based on modulation interference accurate reconstruction, characterized in that, The method comprises the following steps: Step 1, receiving a mixed signal of an interference signal and a low-speed signal, and sequentially performing symbol estimation, time delay estimation, carrier phase estimation and amplitude estimation of the interference signal; the time delay estimation adopts a frequency domain nonlinear estimation algorithm, and the estimation result is: In the formula: wherein, is the number of observed symbols, m is the ordinal number of the symbol, T is the symbol period, is the signal transmission delay, is the mixed signal in the form of a complex digital signal, is is the complex conjugate of is the number of sampling points per symbol, is the complex argument function; is the correction factor, which is adjusted according to the signal characteristics, and the value range is 0.01 to 1; Step 2, performing carrier recovery on the mixed signal, and then reconstructing the symbol after carrier recovery according to the amplitude size obtained by amplitude estimation, and regenerating the interference signal used for offset; Step 3, performing time delay on the mixed signal according to the time delay obtained by time delay estimation, and time-aligning with the regenerated interference signal in step 2; Step 4, referring to the regenerated interference signal, using a channel response estimation method to offset the interference signal in the delayed mixed signal, and outputting the remaining low-speed signal; Step 5, performing carrier phase restoration on the remaining low-speed signal, and completing the interference signal offset.

2. The method of claim 1, wherein, The specific mode of symbol estimation is: When the signal-to-noise ratio of the modulated interference signal is greater than 10 dB, the estimation of the transmission bit is obtained by hard decision, and then the estimated modulation symbol is obtained by symbol mapping; When the signal-to-noise ratio of the modulated interference signal is less than 10 dB, the estimation of the transmission bit is obtained by decoding and twice encoding, and then the estimated modulation symbol is obtained by symbol mapping.

3. The method of claim 1, wherein, The specific mode of carrier phase estimation is: The mixed signal is matched filtered to obtain a mixed signal sample in the form of a statistically independent complex digital signal with the point of the uncorrected inter-symbol interference Carrier phase estimation is performed using the sample data: wherein is the number of observed symbols before and after the estimated symbol; is the estimated modulation symbol, is the complex conjugate of is the carrier phase, is the estimated carrier phase; is the correction factor, which is adjusted according to the signal characteristics, and the value range is 0.01 to 1.​ 4. The method of claim 1, wherein, The specific mode of amplitude estimation is: The mixed signal is matched filtered to obtain a mixed signal sample in the form of a statistically independent complex digital signal with the taking of the unsigned inter-symbol interference point Interference amplitude estimation is performed using the sample data: In the formula, is the number of observation symbols; is the estimated modulation symbol, is the modulation symbol is the complex conjugate of the modulation symbol, is the signal amplitude estimate value; Re is the real part, is the correction factor, which is adjusted according to the signal characteristics, and the value range is 0.01 to 1.

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