Multi-user non-orthogonal signal acquisition method based on interference-eliminated correlation peak difference

Abstract

The application discloses a multi-user non-orthogonal signal capture method based on interference deletion correlation peak difference, and belongs to the field of multi-user signal access detection.The application realizes the method as follows: in a multi-user signal power domain multiple access communication, the spread spectrum sequence of any user is correlated with the received mixed user signal; according to the periodicity of the cross-correlation of the spread spectrum sequences of different users, the cross-correlation results of the spread spectrum codes of different users are reconstructed in the mixed user signal correlation results, the cross-correlation interference between different users is removed, and only the autocorrelation of the current user sequence is left in the correlation results; the current user is captured and judged according to the peak value of the autocorrelation results; the change amount of the correlation results before and after the interference removal is used as a judgment basis, the point with the minimum change amount is taken as a judgment output, the current user and other user signals are judged and separated, the precision of the signal capture judgment in a multi-user communication scene is improved, and the time complexity of the capture method is reduced.

Description

Technical Field

[0001] The invention relates to a multi-user non-orthogonal signal capture method based on interference cancellation correlation peak difference, and belongs to the field of multi-user signal access detection. Technical Background

[0002] CDMA (Code Division Multiple Access) is a new and mature wireless communication technology developed from spread spectrum communication, a branch of digital communications. Based on spread spectrum technology, CDMA modulates information bits with a specific signal bandwidth using a high-speed pseudo-random code with a bandwidth far greater than the signal bandwidth. This increases the bandwidth of the original data signal, which is then modulated with a carrier and transmitted. The receiving end uses the same pseudo-random code to perform correlation processing with the received wideband signal, converting the wideband signal into a narrowband signal of the original information data, thereby completing the despreading process and enabling information communication. Due to its unique characteristics, such as strong anti-interference and multipath resistance, high spectral efficiency, convenient user access, simple frequency planning, and excellent confidentiality, CDMA is increasingly being adopted as a multiple access technology in communication systems.

[0003] In CDMA mobile communication systems, signal capture is the first step in signal access to the receiver and subsequent baseband information processing. Its purpose is to achieve coarse synchronization between the received signal and the local signal and detect the activity of user signals by performing a two-dimensional search of the received signal's code phase and carrier frequency in the time-frequency domain. The large number of randomly initiated device signals that alias and propagate within the channel requires satellite equipment to quickly and accurately capture and identify signals from different devices. This requires more efficient and less complex signal capture strategies. Therefore, research on capture technologies for scenarios with massive user device access is of both theoretical and practical significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for multi-user signal capture in a multi-user spread spectrum signal aliasing communication scenario, utilizing the difference between correlation peaks before and after interference cancellation. In multi-user signal power domain multiple access communication, the spread spectrum sequence of any user is correlated with the received aliased user signal, and the result is an aliasing of the autocorrelation of the spread spectrum sequence of the currently selected user and the cross-correlation of the spread spectrum sequence of the currently selected user and the spread spectrum sequences of other different users. Based on the periodicity of the cross-correlation between spread spectrum sequences of different users, the cross-correlation results of the spread spectrum codes of different users are reconstructed and deleted in the aliasing of the multi-user signal correlation results. After eliminating the cross-correlation interference between different users, only the autocorrelation of the current user sequence remains in the correlation result, and the capture decision of the current user is made based on the peak value of the autocorrelation result.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] The present invention discloses a multi-user non-orthogonal signal capture method based on interference cancellation and correlation peak difference. The method uses the difference in the change in correlation operation results before and after the correlation results as the basis for signal capture judgment. Before interference cancellation, the output of the current user's correlator is a mixture of the current user's autocorrelation result and the cross-correlation interference from other users. Due to the cross-correlation characteristics of pseudo-random codes, the cross-correlation interference is evenly distributed in the correlator output. If the current user's signal received power is stronger than that of other users' signals, the user's autocorrelation will occupy a major portion of the aliased output of the correlator. After interference cancellation, the autocorrelation peak is prominent, making capture easier. If the signal receiving power of the current user is weaker than that of other users, the cross-correlation interference of other users will still obscure the autocorrelation result of the current user after interference removal, and the correlation peak cannot be directly used for judgment. However, since the autocorrelation result of the current user has a peak, from the perspective of the entire correlation output result, after interference removal, the change at the point where the autocorrelation peak is located is the smallest. The change in the correlation results before and after interference removal is used as the basis for judgment, and the point with the smallest change is used as the judgment output. The signals of the current user and other users are judged and separated, thereby improving the accuracy of signal capture judgment in multi-user communication scenarios and reducing the time complexity of the multi-user non-orthogonal signal capture method.

[0007] The present invention discloses a multi-user signal non-orthogonal capture method based on interference cancellation correlation peak difference, comprising the following steps:

[0008] Step 1: Each user at the transmitting end uses a pre-assigned independent spreading sequence to send a signal. At the receiving end, correlation operations are performed on the multi-user aliasing signals using different user spreading sequences to obtain the cumulative correlation results between the aliasing signals and the spreading codes of each user, which are used for subsequent delay estimation.

[0009] Each user at the transmitting end uses a pre-assigned independent spreading sequence to send a signal. The number of users sending signals is N. The signal sent by the i-th user is expressed as

[0010] y i (t) = d i (t)c i (t)

[0011] where d i (t) is the data bit symbol sent by the i-th user, d i (t) takes the value of 1 or -1, d i The expression of (t) changing with time is

[0012] d i (t) = d i((a-1)T)=±1,t∈[(n-1)T,nT),n∈N +

[0013] c i (t) is a periodic function, which represents the spreading sequence selected by the i-th user, satisfying c i (T+t)=c i (t), where T is one symbol period. At the receiving end, the spreading sequence selected by each user is known, but the spread signals of all users are mixed together and cannot be distinguished.

[0014] The N user aliased signals arriving at the receiver are expressed as

[0015]

[0016] Among them A i represents the amplitude of the i-th user signal, τ i represents the absolute delay of the i-th user, n represents the Gaussian white noise generated by the receiving end, and f i represents the Doppler frequency deviation of the i-th user.

[0017] The aliased received signal and the spreading code selected by each user are integrated separately. The integrated detection result of the spreading code of the jth user in any kth symbol period is expressed as

[0018]

[0019] in Since the symbol period is much smaller than the coherence time of the frequency offset, the integration time

[0020]

[0021] Due to the pseudo-randomness of the spreading code design and the fact that the noise obeys Gaussian distribution, it is possible to not distinguish between users and symbol numbers, η j,k Still Gaussian noise, the Gaussian noise η j,k Simplified expression is η, the correlation result Cor between the received signal and the user correlator j,k (x) is simplified to

[0022]

[0023] Among them, τ' i =τ i mod T represents the relative delay of the accumulated symbols in one symbol period.

[0024] definition

[0025]

[0026] Indicates the result of correlation between the signal component of user i and the correlator of user j in the received signal. i (t) takes the value of 1 or -1 in a T symbol period, so the correlation result Cor between the received signal and the user correlator at the jth user is j,k (x) is expressed as

[0027]

[0028] The relevant results of user j are accumulated L times incoherently, and the noise term η does not increase with the increase of the accumulation number, that is,

[0029]

[0030] The correlation accumulation result between the aliased signal and each user's spreading code is calculated according to the above formula and used for subsequent delay estimation.

[0031] Step 2: The size of the correlation result between the received aliased signal and each user correlator is mainly determined by the correlation between the spreading codes. Due to the pseudo-random design of the spreading code, the correlation result will only show a most obvious peak when and only when the spreading code used by the user correlator is consistent with the spreading code used by the user component. Define the user who meets the preset correlation peak judgment threshold as a high-power user, and accurately capture the high-power user i according to the correlation peak judgment threshold formula. pm , accurately estimate the high-power user i pm Relative local latency Correlation results for low power users s (x), due to the serious interference of high-power user signals, it is impossible to correctly capture low-power users, so the relevant results of low-power users are directly stored Cor s (x) Standby.

[0032] UnitCor i,j The size of (x) is mainly determined by the correlation between the spreading codes. Due to the pseudo-random design of the spreading codes, the correlation result will show a most obvious peak when and only when i=j, that is, the spreading code used is consistent with the spreading code used by the user component.

[0033] Define users that meet the preset correlation peak judgment threshold as high-power users. pm , and its capture result satisfies

[0034]

[0035] Therefore, according to the above formula, high-power user i can be accurately captured. pm , accurately estimate the high-power user i pm Relative local latency

[0036] Correlation results for low power users s (x), then store it directly for future use.

[0037] Step 3: Based on the interference of the high-power user's code phase reconstructed on the correlation results of other low-power users, interference is deleted, and the maximum correlation value of the low-power user before and after the interference is deleted is recorded respectively. Based on the correlation results before and after the low-power user is deleted, the maximum value of the correlation result of the low-power user before and after the deletion and the code phase coordinate corresponding to the maximum value are recorded respectively.

[0038] According to the captured high-power user delay Get the cross-correlation interference UnitCor of high-power users to low-power users b,s (x).

[0039] The results related to low-power users are expressed as Cor s (x), Correlation results for low-power users s (x) Perform interference removal, and the low-power user correlation result Cor after interference removal s (x) The result is

[0040] Cor s,IC (x) = Cor s (x)-max[Cor b (x)] / L·UnitCor b,s (x)

[0041] Among them, Cor b (x) represents the correlation result of the large user, and L is the length of the correlation code.

[0042] Due to the power advantage of high-power users, they occupy the largest proportion in the entire correlation result. Under the premise that the interference reconstruction of large users is correct, if they are eliminated from the correlation results of small users, the code phase coordinate point with a larger numerical change represents the greater the mutual interference it receives from high-power users, and the lower the probability that it is the peak point of the autocorrelation of small-power users.

[0043] Correlation results before removing small user interference s (x) performs a differential operation, if

[0044]

[0045] Cor s (x n ) is the maximum value of the correlation result before the small user interference is deleted. The entire correlation result is traversed and all the maximum values ​​of the correlation result before deletion and the code phase coordinates corresponding to the maximum values ​​are recorded. Correlation result after interference deletion Cor s,IC(x) and so on, we can get all the maximum values ​​of the correlation results after deletion and the code phase coordinates corresponding to the maximum values. s (x) and Cor s,IC The maximum value set of (x) is denoted as peak s (x) and peak s,IC (x).

[0046] Step 4: According to the maximum value of the correlation results of the low-power user before and after the interference is deleted, find the points with the same code phase, perform subtraction and comparison in sequence, and find the code element coordinates with the smallest maximum value change. The change in the correlation value before and after the low-power user is deleted is used as the decision quantity, and the threshold judgment is performed with the set change threshold. If the change result is greater than the set change threshold, it is determined that the low-power user is successfully captured, x s This is the code phase of the low-power user after deletion. If the change is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been found. The relevant results of the user after this deletion are retained, and the code phase of the successfully captured low-power user is used for interference removal again.

[0047] Comparison peak s (x) and peak s,IC (x) is the independent variable coordinate value, and its common part set X is taken c Then we make the difference between the maximum values ​​before and after deletion, and we have

[0048] Δpeak s (x) = peak s (x)-peak s,IC (x)

[0049] Where x∈X c .

[0050] Compare and get the peak value with the smallest change before and after deletion, and set its corresponding coordinate as x s .

[0051] x s =argmin|Δpeak s (x)|,x∈X c

[0052] If the change result min|Δpeak s (x)| is greater than the set change threshold, it is determined that the low-power user is successfully captured, x s This is the code phase of the low-power user after deletion. If the change is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been found. The relevant results of the user after this deletion are retained, and the code phase of the successfully captured low-power user is used for interference removal again.

[0053] Step 5: Repeat steps 3 and 4 to judge and separate the signals of different users until the code phases of all users are found, that is, the non-orthogonal capture of multi-user signals is achieved based on the interference cancellation correlation peak differential judgment.

[0054] Beneficial effects:

[0055] 1. The non-orthogonal capture method for multi-user signals based on interference cancellation correlation peak difference disclosed in the present invention utilizes the pseudo-random characteristics of spread spectrum codes and uses the idea of ​​interference cancellation to capture each user signal, greatly improving the access detection capability of aliased signals and realizing the detection and separation of multi-user aliased signals.

[0056] 2. The non-orthogonal capture method for multi-user signals based on interference cancellation correlation peak difference disclosed in the present invention utilizes the differences in the proportions of users with different power in the correlation results, fully utilizes the information contained in the correlation results before and after interference cancellation, and effectively improves the probability of successful capture of weak-power user signals.

[0057] 3. Existing multi-user aliased signal capture methods based on interference cancellation require repeated interference cancellation of user correlation results to find the autocorrelation peak of the user signal for judgment, which incurs time overhead. The multi-user signal non-orthogonal capture method based on interference cancellation correlation peak difference proposed in this invention takes into account the dominant position of the user autocorrelation result in the overall correlation result and uses the change in the correlation result before and after a single interference cancellation as a new judgment basis, effectively reducing the time complexity of the capture algorithm and improving capture accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 The figure is a flow chart of the non-orthogonal capture method of multi-user signals based on interference cancellation correlation peak difference of the present invention.

[0059] Figure 2 These are the relevant results for high-power users in the implementation example.

[0060] Figure 3 The following are the relevant results for small power users in the implementation example.

[0061] Figure 4 This is the correlation result of the low-power user after interference cancellation in the implementation example.

[0062] Figure 5 The figure is a comparison chart of the capture success rate performance between the traditional capture decision strategy and the capture strategy proposed by the present invention in the implementation example. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to have a deeper understanding of the implementation ideas of the solutions of the present invention, the technical solutions in the embodiments of the present invention will be described in detail and clearly in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0064] The specific steps of the embodiment of the present invention are described below with reference to specific scenarios:

[0065] The multi-user signal non-orthogonal capture method based on simplified interference cancellation disclosed in this embodiment is for an 8-user large dynamic random asynchronous access system. Each user uses a GOLD sequence with a code length of 128 for spread spectrum communication. The same root raised cosine sequence is used for shaping and matching. The upsampling multiple is 8. It is assumed that user 5 is a high-power interference user with a power 14dB higher than that of other users. The capture decision flow chart of the entire invention is as follows: Figure 1 shown.

[0066] The non-orthogonal capture method for multi-user signals based on interference cancellation correlation peak difference disclosed in this embodiment is specifically implemented in the following steps:

[0067] Step 1: Each user at the transmitting end uses a pre-assigned independent spreading sequence to send a signal. At the receiving end, a correlation operation is performed on the multi-user mixed signal using different user spreading sequences to perform multi-user access detection.

[0068] Assuming that the number of users sending signals simultaneously is N=8, the signal sent by the i-th user can be expressed as

[0069] y i (t) = d i (t)c i (t)

[0070] where d i (t) is the data bit symbol sent by the i-th user, which takes the value of 1 or -1. Its expression of time variation is:

[0071] d i (t) = d i ((a-1)T)=±1,t∈[(n-1)T,nT),n∈N +

[0072] c i (t) is a periodic function, which represents the spreading sequence selected by the i-th user, satisfying c i (T+t)=c i(t), where T is one symbol period. At the receiver, we assume that the spreading sequence selected by each user is known, but the spread signals of all users are mixed together and cannot be distinguished.

[0073] The N user aliased signals arriving at the receiving end can be expressed as

[0074]

[0075] Among them A i represents the amplitude of the i-th user signal, τ i represents the absolute delay of the i-th user, n represents the Gaussian white noise generated by the receiving end, and f i represents the Doppler frequency deviation of the i-th user.

[0076] Next, the aliased received signal and the spreading code selected by each user are integrated separately. The integrated detection result of the spreading code of the jth user in any kth symbol period can be expressed as

[0077]

[0078] in Since the symbol period is much smaller than the coherence time of the frequency offset, it can be considered that

[0079]

[0080] Due to the pseudo-randomness of the spreading code design and the fact that the noise obeys Gaussian distribution, it is not possible to distinguish between users and symbol numbers. j,k It is still Gaussian noise, so we can simplify it to η.

[0081] and then

[0082]

[0083] Among them, τ' i =τ i mod T represents the relative delay of the accumulated symbols in one symbol period.

[0084] Let's define

[0085]

[0086] Indicates the result of correlation between the signal component of user i and the correlator of user j in the received signal. i (t) takes a value of either 1 or -1 within a T symbol period.

[0087] Therefore, at the jth user, the correlation result between the received signal and the user correlator can be expressed as

[0088]

[0089] The relevant results of user j are accumulated L = 8 times in a non-coherent manner. The noise term η does not increase with the increase of the accumulation times, that is,

[0090]

[0091] The correlation accumulation result between the aliased signal and each user's spreading code is calculated according to the above formula and used for subsequent delay estimation.

[0092] Step 2: User 5 has a more obvious correlation peak and can be accurately captured. The code phase offset estimation is completed, so the first judgment is made on it and the symbol delay is estimated. The corresponding low-power user is seriously interfered by the high-power signal and cannot be correctly captured. However, the correlation results of the small user can be stored for future use.

[0093] For high power users pm , and its capture result obviously satisfies

[0094]

[0095] Therefore, the user can accurately capture and accurately estimate the relative local delay The simulation preset high-power user code phase offset is 8, which is consistent with the deletion result, such as Figure 2 shown

[0096] Correlation results for low power users s (x), then directly store it for future use. Taking user 2 as an example, the relevant results at this time are as follows Figure 3 shown

[0097] Step 3: Based on the interference of user 5's code phase reconstructed on the correlation results of other small users, perform interference cancellation, record the maximum correlation value of the small-power user before and after interference cancellation, and record the maximum value and corresponding code phase coordinate based on the correlation results before and after the small user cancellation.

[0098] According to the captured large user delay i pm You can get the interference of large users on small users UnitCor b,s (x)

[0099] The results related to small users can be expressed as Cor s (x), the result of removing its interference is shown below

[0100] Cor s,IC (x) = Cor s (x)-max[Cor b (x)] / L·UnitCor b,s (x)

[0101] Among them, Cor b (x) represents the correlation result of the large user, and L is the length of the correlation code. Taking user 2 as an example, after the interference removes the cross-correlation interference of user 5, the correlation result of user 2 is as follows Figure 4 shown

[0102] Due to the power advantage of large users, they occupy the largest proportion in the entire correlation result. Under the premise that the large user interference reconstruction is correct, if they are eliminated from the correlation results of small users, the code phase coordinate point with a larger numerical change represents the greater the mutual interference it receives from the large-power user, and the lower the probability that it is the peak point of the autocorrelation of the small-power user.

[0103] Therefore, based on the difference idea, the correlation results before small user interference deletion are firstly s (x) as an example, if

[0104]

[0105] It can be considered that Cor s (x n ) is the maximum value of the correlation result before the small user interference is deleted. The entire correlation result is traversed and all its maximum values ​​are recorded. The correlation result after interference deletion AuCo s,IC (x)And so on.

[0106] Cor s (x) and Cor s,IC The maximum value set of (x) is denoted as peak s (x) and peak s,IC (x).

[0107] Step 4: Based on the maximum value of the correlation results of the low-power user before and after interference deletion, find the points with the same corresponding code phase, perform subtraction and comparison in sequence, and find the code element coordinates with the smallest maximum value change. The change in the correlation value before and after deletion is used as the decision quantity, and the threshold judgment is performed with the set threshold to find the code phase offset of the low-power user.

[0108] Comparison peak s (x) and peak s,IC (x) is the independent variable coordinate value, and its common part set X is taken c Then we make the difference between the maximum values ​​before and after deletion, and we have

[0109] Δpeak s (x) = peak s (x)-peak s,IC (x)

[0110] Where x∈X c .

[0111] Compare and get the peak value with the smallest change before and after deletion, and set its corresponding coordinate as x s .

[0112] x s =argmin|Δpeak s (x)|,x∈X c

[0113] If the change result min|Δpeak s (x)| is greater than the set threshold value, then the capture is determined to be successful, x s This is the code phase of the small-power user after deletion, and the system enters the subsequent tracking link. If the change result is less than the threshold value, it is determined that the capture has failed and the signal has not been found. The relevant results after the user is deleted are retained, and the interference is deleted again using the code phase of the small-power user that has been successfully captured. Steps three and four are repeated until the code phases of all users are found.

[0114] Figure 5 The following figure compares the capture success rate performance between a traditional capture decision strategy and the capture strategy proposed in this invention. The traditional strategy directly uses the correlation results of small users after removing the cross-correlation interference of high-power user signals for decision making. The decision factor is the ratio of the secondary peak-to-peak value to the primary peak-to-peak value of the small user correlation results after removal. The alternative strategy used for comparison is the decision method proposed in this invention.

[0115] The above specific description further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference, characterized by: The following steps are included: Step 1: Each user at the transmitting end uses a pre-assigned independent spreading sequence to send a signal. At the receiving end, a correlation operation is performed on the multi-user aliased signal using different user spreading sequences. The accumulated correlation result between the aliased signal and each user's spreading code is obtained for subsequent delay estimation. Step 2: The size of the correlation result between the received aliased signal and each user correlator is mainly determined by the correlation between the spreading codes. Due to the pseudo-random characteristic of the spreading code, the correlation result will only show a most obvious peak when and only when the spreading code used by the user correlator is consistent with the spreading code used by the user component; define the user who meets the preset correlation peak judgment threshold as a high-power user, and accurately capture the high-power user i according to the correlation peak judgment threshold formula pm , accurately estimate the high-power user i pm Relative local latency Correlation results for low power users s (x), due to the serious interference of high-power user signals, it is impossible to correctly capture low-power users, so the relevant results of low-power users are directly stored Cor s (x) standby; Step 3: Based on the interference of the high-power user on the correlation results of other low-power users reconstructed from the code phase, interference is removed, and the maximum correlation value of the low-power user before and after the interference removal is recorded. Based on the correlation results before and after the low-power user is removed, the maximum correlation value of the low-power user before and after the removal and the code phase coordinate corresponding to the maximum value are recorded respectively; Step 4: According to the maximum value of the correlation results of the low-power user before and after the interference is deleted, find the points with the same code phase, perform subtraction and comparison in sequence, and find the code element coordinates with the smallest maximum value change. The change in the correlation value before and after the low-power user is deleted is used as the decision quantity, and the threshold judgment is performed with the set change threshold. If the change result is greater than the set change threshold, it is determined that the low-power user is successfully captured, x s That is the code phase of the low-power user after deletion; If the change is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been found. The relevant results after the user is deleted are retained, and the interference is removed again using the code phase of the successfully captured low-power user. Step 5: Repeat steps 3 and 4 to judge and separate the signals of different users until the code phases of all users are found, that is, the non-orthogonal capture of multi-user signals is achieved based on the interference cancellation correlation peak differential judgment.

2. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 1, wherein: The implementation method of step one is: Each user at the transmitting end uses a pre-assigned independent spreading sequence to send a signal. The number of users sending signals is N. The signal sent by the i-th user is expressed as y i (t)=d i (t)c i (t) where d i (t) is the data bit symbol sent by the i-th user, d i (t) takes the value of 1 or -1, d i The expression of (t) changing with time is d i (t)=d i ((a-1)T)=±1,t∈[(n-1)T,nT),n∈N + c i (t) is a periodic function, which represents the spreading sequence selected by the i-th user, satisfying c i (T+t)=c i (t), where T is one symbol period. At the receiving end, the spreading sequence selected by each user is known, but the spread signals of all users are mixed together and cannot be distinguished. The N user aliased signals arriving at the receiver are expressed as Among them A i represents the amplitude of the i-th user signal, τ i represents the absolute delay of the i-th user, n represents the Gaussian white noise generated by the receiving end, and f i represents the Doppler frequency deviation of the i-th user; The aliased received signal and the spreading code selected by each user are integrated separately. The integrated detection result of the spreading code of the jth user in any kth symbol period is expressed as in Since the symbol period is much smaller than the coherence time of the frequency offset, the integration time Due to the pseudo-randomness of the spreading code design and the fact that the noise obeys Gaussian distribution, it is possible to not distinguish between users and symbol numbers, η j,k Still Gaussian noise, the Gaussian noise η j,k Simplified expression is η, the correlation result Cor between the received signal and the user correlator j,k (x) is simplified to Among them, τ' i =τ i modT represents the relative delay of the accumulated symbols within a symbol period; definition Indicates the result of correlation between the signal component of user i and the correlator of user j in the received signal. i (t) takes the value of 1 or -1 in a T symbol period, so the correlation result Cor between the received signal and the user correlator at the jth user is j,k (x) is expressed as The relevant results of user j are accumulated L times incoherently, and the noise term η does not increase with the increase of the accumulation number, that is, The correlation accumulation result between the aliased signal and each user's spreading code is calculated according to the above formula and used for subsequent delay estimation.

3. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 2, wherein: The implementation method of step 2 is: UnitCor i,j The size of (x) is mainly determined by the correlation between spreading codes. Due to the pseudo-random design of spreading codes, the correlation result will show a most obvious peak when and only when i = j, that is, the spreading code used is consistent with the spreading code used by the user component; Define users that meet the preset correlation peak judgment threshold as high-power users. pm , and its capture result satisfies Therefore, according to the above formula, high-power user i can be accurately captured. pm , accurately estimate the high-power user i pm Relative local latency Correlation results for low power users s (x), then store it directly for future use.

4. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 3, wherein: The implementation method of step three is: According to the captured high-power user delay Get the cross-correlation interference UnitCor of high-power users to low-power users b,s (x); The results related to low-power users are expressed as Cor s (x), Correlation results for low-power users s (x) Perform interference removal, and the low-power user correlation result Cor after interference removal s (x) The result is Cor s,IC (x)=Cor s (x)-max[Cor b (x)] / L·UnitCor b,s (x) Among them, Cor b (x) represents the correlation result of the large user, and L is the length of the correlation code; Due to the power advantage of high-power users, they account for the largest proportion in the entire correlation result. Under the premise of correct reconstruction of the interference of high-power users, if they are eliminated from the correlation results of small users, the code phase coordinate point with a larger value change indicates that it has suffered greater mutual interference from high-power users, and the probability of it being the peak point of the autocorrelation of small-power users is lower. Correlation results before removing small user interference s (x) performs a differential operation, if Cor s (x n ) is the maximum value of the correlation result before the small user interference is deleted, and the entire correlation result is traversed, and all the maximum values ​​of the correlation result before deletion and the code phase coordinates corresponding to the maximum values ​​are recorded; the correlation result Cor after interference deletion s,IC (x) and so on, obtain all the maximum values ​​of the correlation results after deletion and the code phase coordinates corresponding to the maximum values; record Cor s (x) and Cor s,IC The maximum value set of (x) is denoted as peak s (x) and peak s,IC (x).

5. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 4, characterized in that: The implementation method of step 4 is: Comparison peak s (x) and peak s,IC (x) is the independent variable coordinate value, and its common part set X is taken c ; Then make the difference between the maximum values ​​before and after deletion, and we have Δpeak s (x)=peak s (x)-peak s,IC (x) Where x∈X c ; Compare and get the peak value with the smallest change before and after deletion, and set its corresponding coordinate as x s ; x s =argmin|Δpeak s (x)|,x∈X c If the change result min|Δpeak s (x)| is greater than the set change threshold, it is determined that the low-power user is successfully captured, x s This is the code phase of the low-power user after deletion. If the change is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been found. The relevant results of the user after this deletion are retained, and the code phase of the successfully captured low-power user is used for interference removal again.

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