A Phase-Assisted FCrSK Multi-User Interference Cancellation Method

Abstract

The present invention discloses a method for suppressing multi-user interference in FCrSK based on phase assistance. Under the premise of the folded Chirp in-band frequency division multiple access technology, in order to overcome the problem of inter-user spectrum interference occurring in the process of multi-access implementation, the present invention is proposed. By adding an auxiliary phase to each user, the energy superposition value at the decision point of the target user is maximized, which can improve the signal-to-interference ratio. The auxiliary phase is obtained by offline calculation, which aims to maximize the minimum value of all user decision points, and performs an auxiliary phase search to obtain the optimal auxiliary phase. This method introduces the optimal auxiliary phase into the transmit waveform module, and selects different auxiliary phases according to the user modulation symbols to optimize the transmit waveform (the modulation symbols of all users are completely known at the base station end of the downlink). This method can effectively reduce multi-access interference and improve the concurrent user access ability at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of in-band frequency division multiple access for multi-slope folded Chirp, and specifically to a method for suppressing FCrSK multi-user interference when implementing multi-slope folded Chirp multiple access by introducing phase assistance. Background Art

[0002] The multi-slope folded Chirp communication system can ensure the time-bandwidth consistency of signals with different slopes, and has good insensitivity to Doppler frequency offset. It can be used as a long-distance and highly reliable information transmission technology for high-speed rail communication and low-earth orbit satellite communication.

[0003] Utilize the idle part inside the bandwidth of the Chirp signal to provide multi-access channels for users. This method ensures in-band frequency division multiple access without the need for additional spectrum resources, providing high-capacity access for communication. After multi-user access, there is partial overlapping interference in the spectra of different users, and the interference from other users to this user is still a chirp signal. Its signal energy is dispersed in the frequency domain, so other mismatched users will interfere with the detection of the user itself. If this interference is not suppressed or eliminated, it will lead to errors in decision-making, thus greatly reducing the reliability of the communication system. Summary of the Invention

[0004] To overcome the problem of inter-user spectrum interference that occurs during the implementation of multiple access, the present invention provides a method for suppressing FCrSK multi-user interference based on phase assistance, by introducing appropriate auxiliary phases to different users to achieve the purpose of mutual interference cancellation.

[0005] The idea of multi-user interference suppression with auxiliary phases in the present invention: According to the interference structure introduced at the decision point of the target user by a specific user signal combination, an additional phase is added to the transmitted signal of each user to overcome the problem of signal energy loss at the decision point due to phase cancellation in the spectrum of the target user. At the same time, the signal energy of the target signal is maximized by the superposition of the signal phases at the decision points of all users.

[0006] A method for suppressing FCrSK multi-user interference based on phase assistance in the present invention includes the following steps:

[0007] S1. In the FCrSK system, the product of the time width and the bandwidth of the adopted folded Chirp signal must be a prime number N, and the slope difference during slope processing is an integer multiple of the symbol length T divided by the signal bandwidth B. In the case of slope mismatch, the energy of the mismatched signal at the receiving end is evenly distributed over the entire bandwidth B, so that the mutual interference between different slopes can be minimized in the entire frequency domain.

[0008] S2. Different users in the FCrSK system use different initial frequencies as the multi-user access method;

[0009] S3. When the slope mutual interference drops to the minimum value in the full frequency domain After that, aiming at maximizing the signal strength at the multi-user decision point, search for multi-user phase precoding. Through multiple phase traversals, obtain the optimal auxiliary phase;

[0010] S4. According to the modulation symbols of multiple users (the modulation symbols of all users are completely known at the downlink base station side), select the corresponding auxiliary phase in the phase table obtained in S3, and load this auxiliary phase on the transmit waveform of the corresponding user.

[0011] Furthermore, the reason for limiting the product of the time width and bandwidth of the signal to a prime number in S1 is as follows:

[0012] When the sampling rate f s = B, and the time-bandwidth product of the signal is set to a prime number N, the interference between slopes can be reduced to the minimum value The following explains the principle through discrete chirp Fourier transform:

[0013]

[0014] Among them, Z represents the set of integers, n is the sampling point sequence of the discrete Fourier transform, p is the chirp slope difference, and q represents the frequency offset;

[0015] Therefore, in the case of chirp-rate mismatch, the signal energy has a constant envelope in the frequency domain, that is:

[0016]

[0017] Among them, l represents the frequency point, and △m is the absolute value of the difference between the standard slope and the actual slope of the chirp signal.

[0018] Furthermore, the specific steps of S3 are as follows:

[0019] S3.1. Let the number of users be N user , and the modulus value of the user decision point be I q . First, randomly generate N user random phases, start setting q = 1, and then add the generated random phases to the transmit signal;

[0020] S3.2. According to N and P, calculate the modulus value I q(x) of the decision point of each user after adding the auxiliary phase;

[0021] S3.3. Obtain the minimum value of I q(x) ,

[0022] I min (q) = min{Iq (1), I q (2),..., I q (N user )}, at this time, let q = q + 1;

[0023] S3.4. Determine whether q is equal to the total number of tests L. If it is less than L, repeat steps S3.1, S3.2, and S3.3 until q = L, complete the optimal auxiliary phase search process, and take the phase combination corresponding to the maximum modulus value among the L times as the optimal phase combination;

[0024]

[0025] In the implementation of the FCrSK system, the auxiliary phase table can be generated offline according to the above steps first. At the transmitter, find the phase vector in the corresponding phase table according to the data sent by different users, and finally multiply each user signal by the corresponding phase.

[0026] The method of the present invention is based on the in-band frequency division multiple access technology of folded Chirp, and uses the phase assistance method to suppress the interference between users. By searching for the optimal auxiliary phase, it overcomes the cancellation problem at the decision point, maximizes the minimum value of the interference at the decision point, and then demodulates the processed user spectrum at the receiver, so that the reliability of the system demodulation can be greatly improved. Description of the Drawings

[0027] Figure 1 It is the time-frequency structure diagram of the folded Chirp of the k-th user in the embodiment;

[0028] Among them, B is the signal bandwidth, T is the symbol length, f max , f min correspond to the highest and lowest frequencies of the signal, and k is the starting frequency point of the signal;

[0029] Figure 2 It is the search flow chart of the auxiliary phase for the multi-user interference suppression method in the embodiment;

[0030] Figure 3 It is the spectrogram of matching and mismatch when N is a prime number in the embodiment;

[0031] Figure 4 It is the signal processing flow block diagram of the system with the phase assistance function in the embodiment. Detailed Embodiment

[0032] The following further elaborates on the content of the present invention in detail in combination with the embodiments and the drawings, but it is not a limitation to the present invention.

[0033] Embodiment

[0034] S1. In the FCrSK system, the product of the time width and the bandwidth of the folded Chirp signal adopted must be a prime number N, and the slope difference during slope processing must be an integer multiple of the symbol length T divided by the signal bandwidth B. In the case of slope mismatch, the energy of the mismatched signal at the receiving end is evenly distributed over the entire bandwidth B, so that the cross-interference between different slopes can be minimized in the entire frequency domain.

[0035] S2. Different users in the FCrSK system use different initial frequencies as the multi-user access method.

[0036] S3. When the cross-interference between slopes is minimized in the entire frequency domain after that, aiming at maximizing the signal strength at the multi-user decision point, search for multi-user phase precoding is carried out. Through multiple phase traversals, the optimal auxiliary phase is obtained.

[0037] S4. According to the modulation symbols of multiple users (the modulation symbols of all users are completely known at the base station end of the downlink), select the corresponding auxiliary phase in the phase table obtained in S3, and load this auxiliary phase on the transmission waveform of the corresponding user.

[0038] Refer to Figure 1 , the time-frequency structure diagram of the folded Chirp of the k-th user. The black box corresponds to the frequency domain space of each user. Different starting frequencies can be assigned to different users to achieve multi-user access. That is, the FCrSK system can achieve in-band frequency division multiple access function without additional spectrum resources. However, due to the spectrum interference problem between different users in the FCrSK in-band frequency division multiple access, this will lead to that when demodulating and making a decision on the signal, there is not only the spectrum signal of this user at the decision point, but also the influence of interference from other users, resulting in misjudgment. At the same time, if the interference between multiple users is not suppressed and the signal with a large amount of interference is used for decision-making, it may lead to not only failure to demodulate the useful signal, but also the introduction of a large number of consecutive errors, thus deteriorating the system performance.

[0039] Refer to Figure 3 When the sampling rate f s = B, and the time-bandwidth product of the signal is set to a prime number N, the interference between its slopes can be minimized The principle is illustrated below through discrete chirp Fourier transform:

[0040]

[0041] Among them, Z represents the set of integers, n is the sampling point sequence of the discrete Fourier transform, p is the chirp slope difference, and q represents the frequency offset;

[0042] Therefore, in the case of chirp-rate mismatch, the signal energy has a constant envelope in the frequency domain, that is:

[0043]

[0044] Among them, \(l\) represents the frequency point, and \(\Delta m\) is the absolute value of the difference between the standard slope and the actual slope of the chirp signal.

[0045] Refer to Figure 2 , the specific steps of S3 are as follows:

[0046] S3.1: Let the number of users be \(N\) user , and the modulus value of the user decision point be \(I\) q . First, randomly generate \(N\) user random phases, start setting \(q = 1\), and then add the generated random phases to the transmitted signal;

[0047] S3.2: According to \(N\) and \(P\), calculate the modulus value \(I\) of the decision point of each user under the added auxiliary phase q(x) ;

[0048] S3.3: Obtain the minimum value of \(I\) q(x) ,

[0049] \(I\) min(q) =\(\min\{I\) q (1), \(I\) q (2), \(\cdots\), \(I\) q (N user )\}, at this time, let \(q = q + 1\);

[0050] S3.4: Judge whether \(q\) is equal to the total number of tests \(L\). If it is less than \(L\), repeat steps S3.1, S3.2, and S3.3 until \(q = L\) to complete the optimal auxiliary phase search process. Take the phase combination corresponding to the maximum modulus value among the \(L\) times as the optimal phase combination;

[0051]

[0052] In the implementation of the FCrSK system, the auxiliary phase table can be generated offline according to the above steps first. At the transmitter, find the phase vector in the corresponding phase table according to the data sent by different users, and finally multiply the signal of each user by the corresponding phase. The signal processing flow chart is as Figure 4 shown.

Claims

1. A phase-assisted FCrSK multi-user interference suppression method, characterized in that The method includes the following steps: S1. In the FCrSK system, the product of the time width and the bandwidth of the folded Chirp signal used must be a prime number N, and the slope difference during slope processing must be an integer multiple of the symbol length T divided by the signal bandwidth B. In the case of slope mismatch, the energy of the mismatched signal at the receiving end is evenly distributed over the entire bandwidth B, so that the mutual interference of different slopes can be minimized in the entire frequency domain. S2. Different users of the FCrSK system use different initial frequencies as the multi-user access method; S3. When the slope mutual interference drops to the minimum value in the full frequency domain After that, aiming at maximizing the signal strength at the multi-user decision point, search for multi-user phase precoding. Through multiple phase traversals, obtain the optimal auxiliary phase. The specific steps are as follows: S3.

1. Set the number of users as N user , and the modulus value of the user decision point is I q . First, randomly generate N user random phases. Start by setting q = 1, and then add the generated random phases to the transmitted signal; S3.

2. Calculate the modulus value I of the decision point for each user under the added auxiliary phase according to N and P q(x) ; S3.

3. Obtain the minimum value of I q(x) of I min(q) = min{I q (1), I q (2),..., I q (N user )}, at this time, let q = q + 1; S3.

4. Determine whether q is equal to the total number of tests L. If it is less than L, repeat steps S3.1, S3.2, and S3.3 until q = L, complete the optimal auxiliary phase search process, and take the phase combination corresponding to the maximum modulus value among the L times as the optimal phase combination; In the implementation of the FCrSK system, the auxiliary phase table can be generated offline according to the above steps first. At the transmitter, find the phase vector in the corresponding phase table according to the data sent by different users, and finally multiply each user signal by the corresponding phase; S4. According to the modulation symbols of multiple users, select the corresponding auxiliary phase in the phase table obtained in S3, and load the auxiliary phase on the transmitted waveform of the corresponding user.

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