Multi-user non-orthogonal signal capturing method based on interference deletion correlation peak difference

Abstract

The invention discloses a multi-user non-orthogonal signal capturing method based on interference deletion correlation peak difference, and belongs to the field of multi-user signal access detection. The implementation method comprises the following steps of: correlating a spread spectrum sequence of any user with a received aliasing user signal in multi-user signal power domain multiple access communication; according to the characteristic that spread spectrum sequence cross-correlation among different users has periodicity, in aliasing of multi-user signal correlation results, cross-correlation results of spread spectrum codes of the different users are reconstructed, after cross-correlation interference among the different users is eliminated, only self-correlation of a current user sequence is left in the correlation results, and the self-correlation interference among the current user sequence is eliminated. Performing capture judgment on the current user according to the peak value of the self-correlation result; according to the method, the variation of related results before and after interference deletion is used as a judgment basis, a point with the minimum variation is used as judgment output, and signals of a current user and other users are judged and separated, so that the precision of 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 deletion 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 on the branch of digital communication technology - spread spectrum communication technology. The principle of CDMA technology is based on spread spectrum technology. The information bits with a certain signal bandwidth to be transmitted are modulated with a high-speed pseudo-random code with a bandwidth much larger than the signal bandwidth, so that the bandwidth of the original data signal is expanded, and then modulated and sent out through carrier wave modulation. The receiving end uses exactly the same pseudo-random code to correlate with the received bandwidth signal, and replaces the broadband signal with the narrowband signal of the original information data to complete the despreading work and realize information communication. Due to its unique characteristics such as strong anti-interference ability, strong anti-multipath ability, high spectrum efficiency, convenient user access, simple frequency planning and good confidentiality, more and more communication systems use CDMA technology as multiple access technology.

[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 to detect the activity of the user signal by completing a two-dimensional search of the code phase and carrier frequency of the received signal in the time-frequency domain. A large number of randomly initiated device signals are aliased and propagated in the channel, requiring satellite equipment to quickly and accurately capture and identify signals from different devices, which requires a more efficient signal capture strategy with a more streamlined complexity. Therefore, the research on capture technology in the scenario of massive user device access has theoretical and practical significance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for capturing multi-user signals by using the difference of correlation peaks before and after interference deletion in a multi-user spread spectrum signal aliasing communication scenario. In the 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 will be the 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 cross-correlation of the spread spectrum sequence of other different users. According to the periodicity of the cross-correlation of spread spectrum sequences between different users, in the aliasing of multi-user signal correlation results, the cross-correlation results of different user spread spectrum codes are reconstructed and deleted. After eliminating the cross-correlation interference between different users, only the autocorrelation of the current user sequence remains in the correlation result, and the current user is captured and judged according to the peak value of the autocorrelation result.

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

[0006] The invention discloses a multi-user non-orthogonal signal capture method based on interference-elimination correlation peak difference, and uses the difference in the change value of the correlation operation result before and after the correlation result as the basis for signal capture judgment. Before interference elimination, the output result of the current user correlator is the aliasing of the autocorrelation result of the current user and the cross-correlation interference from other users. Due to the cross-correlation characteristics of the pseudo-random code, the cross-correlation interference is evenly distributed in the output result of the correlator. If the signal receiving power of the current user is stronger than that of other users, the autocorrelation of the user will occupy a major part in the aliasing output result of the correlator. After interference elimination, the autocorrelation peak is obvious and easy to be captured. 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 deletion, and the correlation peak cannot be used directly 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 deletion, the change at the point where the autocorrelation peak is located is the smallest. The change in the correlation results before and after interference deletion is used as the basis for judgment, and the point with the smallest change is used as the judgment output. The current user and other user signals are judged and separated, thereby improving the accuracy of signal capture judgment in multi-user communication scenarios and reducing the time complexity of multi-user non-orthogonal signal capture methods.

[0007] The 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 spread spectrum sequence to send a signal. At the receiving end, a correlation operation is performed on the multi-user aliased signal using different user spread spectrum sequences to obtain the correlation accumulation result between the aliased signal and each user's spread code 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), T is a 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 signal arriving at the receiving end is 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, and 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,

[0020]

[0021] Due to the pseudo-randomness of the spreading code design and the fact that the noise follows a 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 as 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] It represents the result of correlation between the signal component of the i-th user and the correlator of user j in the received signal. i (t) takes a value of 1 or -1 in a T symbol period, so for the jth user, the correlation result Cor between the received signal and the user correlator 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 times, 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 characteristic 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 users who meet the preset correlation peak judgment threshold as high-power users, and accurately capture high-power users i according to the correlation peak judgment threshold formula pm , accurately estimate the high-power user i pm Relative local delay 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) Reserved.

[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 value 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 delay

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

[0037] Step 3: According to the interference to the correlation results of other small users reconstructed from the code phase of the high-power user, the interference is deleted, and the maximum correlation value of the small-power user before and after the interference deletion is recorded respectively. According to the correlation results before and after the deletion of the small-power user, the maximum correlation results of the small-power user before and after the deletion and the code phase coordinates corresponding to the maximum 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 relevant results of 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 account for the largest proportion in the entire correlation results. 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 suffers 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 small user interference deletion s (x) performs a difference 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) Similarly, all the maximum values ​​of the correlation results after deletion and the code phase coordinates corresponding to the maximum values ​​are obtained. 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 corresponding code phase, make differences in turn for comparison, and find the code element coordinates with the smallest maximum value change. The change in the correlation value before and after the deletion of the low-power user is used as the amount to be determined, and the threshold determination 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 result is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been searched. The relevant results of the user after this deletion are retained, and the code phase of the successfully captured low-power user is used to perform interference deletion again.

[0047] Compare with 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 a 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] By comparing the peak value with the smallest change before and after deletion, its corresponding coordinate is set 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 That is, the code phase of the low-power user after deletion; if the change result is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been searched. The relevant results of the user after this deletion are retained, and the code phase of the successfully captured low-power user is used to perform interference deletion again.

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

[0054] Beneficial effects:

[0055] 1. The non-orthogonal capture method of 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, thereby 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 of multi-user signals based on interference deletion correlation peak difference disclosed in the present invention utilizes the difference in the proportion of different power users in the correlation results, fully utilizes the information contained in the correlation results before and after interference deletion, and effectively improves the probability of successful capture of weak power user signals.

[0057] 3. In the existing multi-user aliasing signal capture method based on interference deletion, in order to find the autocorrelation peak of the user signal for judgment, it is necessary to repeatedly perform interference deletion on the user correlation results, which generates time overhead. The multi-user signal non-orthogonal capture method based on interference deletion correlation peak difference proposed in the present invention uses the change in the correlation results before and after a single interference deletion as a new basis for judgment, based on the dominant position of the user autocorrelation results in the entire correlation results, to effectively reduce the time complexity of the capture algorithm and improve the capture accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0061] Figure 4 The results are related to the low-power user after interference removal 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 combination with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a 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 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 in conjunction with specific scenarios:

[0065] The multi-user signal non-orthogonal capture method based on simplified interference cancellation disclosed in this embodiment is aimed at 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, and its power is 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 acquisition 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: At the transmitting end, each user uses a pre-assigned independent spread spectrum sequence to send a signal. At the receiving end, different user spread spectrum sequences are used to perform correlation operations on multi-user mixed signals 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 changing with time 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), T is a symbol period. At the receiving end, 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 signal 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 follows a Gaussian distribution, it is possible to not distinguish between the user and the symbol number. 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] It represents the result of correlation between the signal component of the i-th user and the correlator of user j in the received signal. i (t) is either 1 or -1 in 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 incoherently, and the noise term η does not increase with the increase of the accumulation number, 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: The correlation peak of user 5 is more obvious and can be accurately captured to complete the code phase offset estimation, 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, but the correlation results of the small user can be stored for backup.

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

[0094]

[0095] Therefore, the user can accurately capture and precisely 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), it is directly stored for future use. Taking user 2 as an example, the relevant results at this time are as follows Figure 3 Shown

[0097] Step 3: According to the interference to the correlation results of other small users reconstructed by the code phase of user 5, interference is deleted, and the maximum correlation value of the small-power user before and after the interference deletion is recorded respectively. According to the correlation results before and after the small user is deleted, the maximum value and the corresponding code phase coordinate are recorded respectively.

[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 account for the largest proportion in the entire correlation results. Under the premise that the large user interference is reconstructed correctly, 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 suffers 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 result before small user interference deletion is Cor 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. s,IC (x)And so on.

[0106] Use the above method to 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).

[0107] 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 corresponding code phase, make differences in turn for comparison, and find the code element coordinates with the smallest change in the maximum value. The change in the correlation value before and after its deletion is used as the amount to be determined, and the threshold judgment is performed with the set threshold to find the code phase offset of the small user.

[0108] Compare with 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 a 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] By comparing the peak value with the smallest change before and after deletion, its corresponding coordinate is set 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 That is the code phase of the small 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 it is considered that the signal has not been searched. The relevant results of the user after this deletion are retained, and the code phase of the small-power user that has been successfully captured is used to perform interference deletion again. Repeat steps three and four until the code phases of all users are found.

[0114] Figure 5 The figure shows the performance comparison of the capture success rate between the traditional capture decision strategy and the capture strategy proposed in the present invention. The traditional strategy directly uses the small user correlation result obtained after deleting the cross-correlation interference of the high-power user signal for decision, and the decision object is the ratio of the secondary peak-to-peak value to the main peak-to-peak value of the small user correlation result after deletion. The variable strategy method used for comparison is the decision method proposed in the present invention.

[0115] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above 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 multi-user signal non-orthogonal acquisition method based on interference cancellation correlation peak difference, characterized in that: The following steps are included: Step 1: Each user at the transmitting end uses a pre-assigned independent spread spectrum sequence to send a signal. At the receiving end, a correlation operation is performed on the multi-user aliased signal using different user spread spectrum sequences to obtain the correlation accumulation result between the aliased signal and each user's spread code 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 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 delay 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: perform interference deletion based on the interference to the correlation results of other low-power users reconstructed from the code phase of the high-power user, and record the maximum values ​​of the correlation values ​​of the low-power users before and after the interference deletion respectively; based on the correlation results before and after the deletion of the low-power users, record the maximum values ​​of the correlation results of the low-power users before and after the deletion and the code phase coordinates corresponding to the maximum values ​​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 corresponding code phase, make differences in turn for comparison, and find the code element coordinates with the smallest maximum value change. The change in the correlation value before and after the deletion of the low-power user is used as the amount to be determined, and the threshold determination 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 amount result is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been searched. The relevant results of the user after this deletion are retained, and the interference is deleted again using the code phase of the successfully captured low-power user; Step 5: Repeat steps 3 and 4 to judge and separate signals of different users until the code phases of all users are found, that is, non-orthogonal capture of multi-user signals is achieved based on differential judgment of interference-cancelled correlation peaks.

2. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 1, characterized in that: The implementation method of step one is: Each user at the transmitting end uses a pre-assigned independent spread spectrum 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), T is a 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 signal arriving at the receiving end is 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, and 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, Due to the pseudo-randomness of the spreading code design and the fact that the noise follows a Gaussian distribution, it is possible to not distinguish between users and symbol numbers, η j,k Still Gaussian noise, change the Gaussian noise η j,k Simplified as 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 mod T represents the relative delay of the accumulated symbols in one symbol period; definition It represents the result of correlation between the signal component of the i-th user and the correlator of user j in the received signal. i (t) takes a value of 1 or -1 in a T symbol period, so for the jth user, the correlation result Cor between the received signal and the user correlator 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 times, 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, characterized in that: The implementation method of step 2 is: 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 code, the correlation result will show a most obvious peak value 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 delay Correlation results for low power users s (x), it is directly stored for future use.

4. The non-orthogonal acquisition method for multi-user signals based on interference cancellation correlation peak difference according to claim 3, characterized in that: The implementation method of step three is: According to the captured high-power user delay τ ipm Get the cross-correlation interference UnitCor of high-power users to low-power users b,s (x); The relevant results of 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 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 value change represents the greater the mutual interference from high-power users, and the lower the probability that it is the peak point of the autocorrelation of small-power users; Correlation results before small user interference deletion s (x) performs a difference 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 to record all the maximum values ​​of the correlation result before deletion and the code phase coordinates corresponding to the maximum values; 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: Compare with 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 find the peak with the smallest value 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 That is, the code phase of the low-power user after deletion; if the change result is less than the set change threshold, it is determined that the capture has failed and the low-power user has not been searched. The relevant results of the user after this deletion are retained, and the code phase of the small-power user that has been successfully captured is used for interference deletion again.

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