Pilot Design Method, Channel Estimation Method and Device for OCDM Communication System

Abstract

A pilot design method, a channel estimation method and a device for an OCDM communication system belong to the field of communication technologies, and solve the problem of unstable frequency-domain channel estimation caused by improper pilot design in the existing OCDM communication system. The pilot design method of the present invention includes: selecting a block pilot structure in the modulation domain and pre-designing a pilot sequence for the current transmitted data block; obtaining a vector Γ after the pilot sequence is transformed into the frequency domain H Fx p , where Γ is a diagonal matrix composed of Zadoff-Chu root sequences, and F is a discrete Fourier transform matrix; checking whether the pilot sequence x p satisfies the constraint condition: there are no elements with a value of 0 in the vector Γ H Fx p ; if the constraint condition is not satisfied, the pilot sequence x p is reconstructed until the constraint condition is satisfied; if the constraint condition is satisfied, the pilot sequence is selected as the pilot sequence for the current transmitted data block. The present invention also realizes channel estimation based on the pilot design method. The present invention is applicable to OCDM communication systems.

Description

Technical Field

[0001] This application relates to the field of communication technologies, and particularly to pilot design and channel estimation for OCDM communication systems. Background Art

[0002] In recent years, as a new multi-carrier modulation technology, Orthogonal Chirp Division Multiplexing (OCDM) technology has begun to attract attention in the fields of wireless communication and underwater acoustic communication. This technology uses a group of mutually orthogonal chirp signals as carrier waves to modulate communication information, and can effectively combat adverse effects such as frequency-selective fading of the channel.

[0003] The transmitter of the OCDM communication system modulates information symbols in the chirp domain. At the receiver, in order to balance system complexity and be compatible with other communication systems, the received signal is usually subjected to a Fast Fourier Transform (FFT) and then channel estimation and equalization are performed in the frequency domain based on pre-inserted pilots. In this process, the modulation domain of the OCDM system is the chirp domain, while channel estimation is completed in the frequency domain. Therefore, when designing pilots, the results after the pilots are transformed from the chirp domain to the frequency domain should be fully considered. The transformation process includes operations such as multiplication and accumulation. If the pilot design is improper, there may be zero elements or extremely small values in the transformed sequence, resulting in the constructed observation matrix being non-invertible, which will cause conventional channel estimation algorithms, such as the Least Square (LS) channel estimation algorithm, to fail and unable to perform accurate channel estimation in the frequency domain, thereby causing difficulties in data decoding. Verified by Monte Carlo simulation experiments, when a random sequence obeying a discrete uniform distribution is selected as the pilot symbol, the frequency of this phenomenon is relatively high, so that conventional frequency-domain channel estimation methods cannot be directly applied to OCDM communication systems, seriously affecting the stability of OCDM communication systems. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of unstable frequency-domain channel estimation caused by improper pilot design in existing OCDM communication systems, and provide a pilot design method, a channel estimation method and a device for OCDM communication systems.

[0005] The present invention is realized through the following technical solutions. On the one hand, the present invention provides a pilot design method for an OCDM communication system, and the pilot design method includes:

[0006] Step 1: Select a block pilot structure in the modulation domain and pre-design the pilot sequence x of the current transmitted data block p = [x p,0 , x p,1,..., x p,N-1 T , where N is the number of chirp carriers in the OCDM signal;

[0007] Step 2: Obtain the vector Γ H Fx p , where Γ is a diagonal matrix composed of Zadoff-Chu root sequences, and F is a discrete Fourier transform matrix;

[0008] Step 3: Check the pilot sequence x p whether it satisfies the constraint condition: there are no elements with a value of 0 in the vector Γ H Fx p ;

[0009] If the constraint condition is not satisfied, reconstruct the pilot sequence x p until the constraint condition is satisfied;

[0010] If the constraint condition is satisfied, select this pilot sequence as the pilot sequence of the current transmitted data block.

[0011] Furthermore, the method for checking the constraint condition includes, but is not limited to, determinant check, norm check or rank check;

[0012] The determinant check is to determine whether the formula |diag(Γ H Fx p )|≠0 holds. If it holds, the pilot sequence x p satisfies the constraint condition;

[0013] The norm check is to determine whether the formula ||Γ H Fx p ||0 = N holds. If it holds, the pilot sequence x p satisfies the constraint condition;

[0014] The rank check is to determine whether the formula rank[diag(Γ H Fx p )] = N holds. If it holds, the pilot sequence xp satisfies the constraint condition;

[0015] where |·| represents the determinant of a matrix; ||·||0 represents the 0-norm of a vector, which is used to calculate the number of non-zero elements in the vector; diag(·) represents converting a vector into a diagonal matrix; rank[·] represents the rank of a matrix; the diagonal elements of Γ are

[0016]

[0017] where n ∈ [0, N - 1], j is the imaginary unit; F is a discrete Fourier transform matrix, and its form is​

[0018]

[0019] Among them, m ∈ [0, N - 1].

[0020] Furthermore, whether the pilot sequence x p satisfies the constraint conditions specifically includes:

[0021] Set a threshold ε. If the modulus values of all elements in the vector Γ H Fx p are all greater than the threshold ε, then the pilot sequence x p satisfies the constraint conditions; otherwise, it does not satisfy.

[0022] Furthermore, whether the pilot sequence x p satisfies the constraint conditions specifically includes:

[0023] Set a threshold ε. If abs{|diag(Γ H Fx p )|} > ε holds, then the pilot sequence x p satisfies the constraint conditions; otherwise, it does not satisfy, where abs represents calculating the modulus value of a complex number.

[0024] In a second aspect, the present invention provides a channel estimation method for an OCDM communication system. The channel estimation method includes:

[0025] Send the pilot sequence x designed based on a pilot design method for an OCDM communication system as described above p to the receiving end of the OCDM communication system, and after processing and calculating the received signal, obtain the frequency - domain response estimation value of the channel.

[0026] Furthermore, the channel estimation method specifically includes:

[0027] Send the pilot sequence x designed based on a pilot design method for an OCDM communication system as described above p to the receiving end of the OCDM communication system to obtain the OCDM received signal sequence r in the time domain, r ∈ C N ;

[0028] Perform a fast Fourier transform to transform it into a sequence y = Fr in the frequency domain; according to the least - squares principle, obtain the frequency - domain response estimation value of the channel:

[0029]

[0030] Among them, After being converted into a diagonal matrix, the channel frequency - domain response matrix is

[0031] Further, the OCDM received signal sequence r is expressed as:

[0032] r = HΦ H x p + n

[0033] where H represents the channel impulse response matrix, n is additive white Gaussian noise, and Φ is the Fresnel transform matrix.

[0034] In a third aspect, the present invention provides a computer device, including a memory and a processor. A computer program is stored in the memory. When the processor runs the computer program stored in the memory, it executes the steps of a pilot design method for an OCDM communication system as described above.

[0035] In a fourth aspect, the present invention provides a computer-readable storage medium. Multiple computer instructions are stored in the computer-readable storage medium. The multiple computer instructions are used to cause a computer to execute a pilot design method for an OCDM communication system as described above.

[0036] Advantages of the present invention:

[0037] The present invention proposes a pilot design and channel estimation technology applicable to an OCDM communication system. According to the structure of the OCDM communication system and the form of the OCDM signal, a channel estimation method applicable to the OCDM communication system is designed based on the least squares principle. By using a pilot design method based on constraint conditions, the instability problem in channel estimation in the frequency domain of the OCDM communication system is solved, providing technical support for the reliable communication of the OCDM communication system and promoting the practical application of the OCDM communication.

[0038] The present invention is applicable to an OCDM communication system. Description of the Drawings

[0039] To more clearly illustrate the technical solutions of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0040] Figure 1 is the process of pilot constraint condition verification and reconstruction;

[0041] Figure 2 is the working flowchart of the OCDM communication system;

[0042] Figure 3 is the channel impulse response model applied in the current embodiment;

[0043] Figure 4Schematic diagram of the element values in the sequence after random pilot transformation and the sequence after pilot transformation designed based on the constraint conditions;

[0044] Figure 5 Schematic diagram of the failed channel estimation result and the effective channel estimation result;

[0045] Figure 6 Schematic diagram of the symbol phase compensation and equalization process;

[0046] Figure 7 Schematic diagram of the symbol output result obtained by using the zero-forcing equalizer and the symbol output result obtained by using the minimum mean square error equalizer;

[0047] Figure 8 BER performance curve of the OCDM communication system in the current embodiment. Detailed implementation manners

[0048] The following details the implementation manners of the present invention. Examples of the implementation manners are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The implementation manners described below with reference to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0049] Embodiment 1. A pilot design method for an OCDM communication system, the pilot design method includes:

[0050] Step 1: Select a block pilot structure in the modulation domain (chirp domain). Before symbol modulation at the transmitter, pre-design the pilot sequence x p =[x p,0 ,x p,1 ,...,x p,N-1 T , where N is the number of chirp carriers in the OCDM signal. Define the constraint condition for pilot design as that there are no elements with a value of 0 in the vector Γ H Fx p transformed from the pilot sequence, and check whether the designed pilot x p satisfies the constraint condition.

[0051] Specifically, in addition to directly judging the element values in Γ H Fx p , some mathematical discriminants can also be used to check the constraint condition. One checking method is the determinant check: judge whether the following formula holds. If it holds, the pilot sequence x p satisfies the constraint condition;

[0052] |diag(Γ​H Fx p )|≠0

[0053] Among them, |·| represents the determinant of a matrix; diag(·) represents converting a vector into a diagonal matrix, and this diagonal matrix serves as the observation matrix in subsequent channel estimation; Γ is a diagonal matrix composed of Zadoff-Chu root sequences, and its diagonal elements are

[0054]

[0055] where n ∈ [0, N - 1], j is the imaginary unit; F is the discrete Fourier transform matrix, and its form is

[0056]

[0057] This discriminant can also be further expanded mathematically and expressed as

[0058]

[0059] or

[0060]

[0061] where x p,n is the nth element in the pilot sequence x p .

[0062] Since and hold for any m ∈ [0, N - 1] all the time, it can be simplified to

[0063]

[0064] Furthermore, the test method for the above-mentioned constraint conditions also includes but is not limited to norm test or rank test;

[0065] Specifically,

[0066] The norm test is to determine whether the discriminant ||Γ H Fx p ||0 = N holds. If it holds, the pilot sequence x p satisfies the constraint conditions;

[0067] The rank test is to determine whether the discriminant rank[diag(Γ H Fx p )] = N holds. If it holds, the pilot sequence xp satisfies the constraint conditions;

[0068] Among them, |·| represents the determinant of a matrix; ||·||0 represents the 0-norm of a vector, which is used to calculate the number of non-zero elements in the vector; rank[·] represents the rank of a matrix.

[0069] Step 2: If the pilot sequence x p satisfies the constraint conditions in step (1), directly select this pilot sequence as the pilot sequence of the current transmitted data block. If x p does not satisfy the constraint conditions, then reconstruct x p Reconstruction means redesigning the current pilot sequence x p The method is not unique and can be adjusted according to modulation parameters and system characteristics. Take the constraint conditions as the termination conditions of the reconstruction process. When x p reaches the termination conditions after reconstruction, use the current x p as the pilot sequence of the current transmitted data block. The above process is as Figure 1 shown.

[0070] It should be noted that the test method of the constraint conditions is not limited to the test method described in this embodiment. Any method that can test whether the vector Γ H Fx p contains zero elements can be used as the test method of the constraint conditions. The pilot reconstruction process can also be carried out in a variety of ways.

[0071] In this embodiment, if the designed pilot satisfies the constraint conditions, the estimated value of the channel frequency response can be stably obtained; if the designed pilot does not satisfy the constraint conditions, the transformed vector Γ H Fx p may contain 0 elements, which will cause the observation matrix in the conventional least squares channel estimation algorithm to be irreversible, and the estimated value of the channel frequency response cannot be obtained, and stable channel estimation cannot be achieved.

[0072] Therefore, this embodiment solves the problem of the failure of the least squares method in channel estimation in the frequency domain of the OCDM communication system through the pilot design method based on constraint conditions, and provides technical support for the OCDM communication system to achieve reliable communication.

[0073] Embodiment 2 is a further limitation on the pilot design method of an OCDM communication system described in Embodiment 1. In this embodiment, the further limitation on whether the pilot sequence x p satisfies the constraint conditions is as follows: Set a suitable threshold ε. If the modulus values of all elements in the vector Γ H Fx p are greater than the threshold ε, then the pilot sequence x p satisfies the constraint conditions, otherwise it does not.

[0074] If a computer is used for the test operation, due to the floating-point operation error of the computer, sometimes the vector Γ H Fxp The zero elements in it may be calculated as complex numbers with a very small modulus value. Therefore, in this case, in this embodiment, the condition for determining whether the modulus value of the element is zero is not directly used as the judgment condition for the test, but a smaller threshold ε should be selected for judgment. Usually, ε can be taken as 10 -5 or so.

[0075] Embodiment 3 further limits a pilot design method for an OCDM communication system described in Embodiment 1. In this embodiment, for verifying whether the pilot sequence x p satisfies the constraint conditions, further limitations are made, specifically including: setting an appropriate threshold ε. If the formula abs{|diag(Γ H Fx p )|} > ε holds, then the pilot sequence x p satisfies the said constraint conditions; otherwise, it does not satisfy, where the symbol "abs" represents calculating the modulus value of a complex number. That is, when using a computer device to perform the verification operation, an appropriate threshold ε is set to replace the 0 value in the said constraint conditions for verification to adapt to the computer floating-point operation error: when using element-by-element numerical verification, it is judged whether the modulus values of the elements in the vector Γ H Fx p are all greater than the threshold ε; when using determinant verification, it is judged whether the value of abs{|diag(Γ H Fx p )|} is greater than the threshold ε.

[0076] If a computer is used for the verification operation, limited by the computer floating-point operation error, sometimes the zero elements in the vector Γ H Fx p may be calculated as complex numbers with a very small modulus value. Therefore, in this case, in this embodiment, the condition for determining whether the determinant value of the observation matrix diag(Γ H Fx p ) is zero is not directly used as the judgment condition for the test, but whether its modulus value is greater than a smaller threshold ε is tested.

[0077] Embodiment 4, a channel estimation method for an OCDM communication system, the said channel estimation method includes:

[0078] Sending the pilot sequence x designed by a pilot design method for an OCDM communication system as described above p to the receiving end of the OCDM communication system. At the receiving end of the OCDM communication system, the OCDM received signal sequence r in the time domain is obtained, and then a fast Fourier transform is performed to transform it into a sequence y = Fr in the frequency domain. Then, according to the principle of least squares estimation, the frequency domain response estimation value of the channel is obtained as

[0079]

[0080] Among them, Since the design of the pilot x p satisfies the constraint conditions, the observation matrix diag(Γ H Fx p ) is invertible, and the channel estimation method of this embodiment can be stably realized. The OCDM received signal sequence r ∈ C N , after being converted into a diagonal matrix, the channel frequency-domain response matrix

[0081] This embodiment can be converted into a diagonal matrix to obtain the channel frequency-domain response matrix which can be used for the implementation of subsequent equalization algorithms; performing an inverse Fourier transform on can obtain the channel time-domain impulse response.

[0082] Embodiment 5, this embodiment is a specific example based on the pilot design method of an OCDM communication system and a channel estimation method of an OCDM communication system as described above, including:

[0083] This embodiment provides a pilot design and channel estimation method for an OCDM communication system. This embodiment mainly considers the underwater acoustic communication scenario and does not consider the Doppler effect between the transmitter and the receiver. The communication frequency band is selected as 10 - 12 kHz, the number of carriers is selected as 512, the modulation method is selected as QPSK, the pilot insertion method is block pilots, the system sampling rate is 48 kHz, and the implementation process of the OCDM communication system is as Figure 2 shown.

[0084] The channel of this embodiment is obtained through the Bellhop ray acoustics calculation tool, and the impulse response of the channel is as Figure 3 shown, which is obtained by simulating and calculating a set of sound speed profile data measured in a certain sea area. The pilot symbols are obtained by mapping a set of randomly generated binary numbers.

[0085] The generated pilot sequence is symbol-modulated through the inverse discrete Fresnel transform (IDFnT), and after being transmitted and passing through the channel, the OCDM received signal sequence in the time domain can be obtained at the receiving end, which can be expressed as:

[0086] r = HΦ H x p + n

[0087] Among them, H represents the channel impulse response matrix; n is additive white Gaussian noise; Φ is the Fresnel transform matrix. H is a cyclic matrix, and its form is

[0088]

[0089] The form of Φ is

[0090]

[0091] To reduce the complexity of channel estimation and equalizer, the OCDM signal in the time domain is transformed to the frequency domain for processing. The transformed signal sequence can be expressed as

[0092] y = Fr = FHΦ H x p + Fn

[0093] Decompose the matrix in the above formula to further obtain

[0094] y = FHF H FΦ H F H Fx p + w

[0095] = ΛΓ H Fx p + w

[0096] where Λ = FHF H is the channel frequency response matrix and is a diagonal matrix; Γ H = FΦ H F H is the coefficient matrix; Γ H Fx p is an N-dimensional column vector; w = Fn is the frequency-domain Gaussian white noise.

[0097] To obtain the estimated value of the channel frequency response matrix Λ, diagonalize Γ H Fx p as the observation matrix, denoted by diag(Γ H Fx p ); convert the channel frequency response matrix Λ into a column vector, denoted as as the estimator, then the cost function of its least squares estimation can be expressed as

[0098]

[0099] According to the principle of minimum cost, the estimated value of the channel frequency response vector is

[0100]

[0101] where, if the constraint conditions described above are satisfied when designing the pilot, the observation matrix diag(Γ H Fx p) It is reversible and can stably obtain the estimated value of the channel frequency response; if it is not checked whether the constraint conditions are met when designing the pilot, there may be 0 elements on the diagonal of the observation matrix. In this case, the observation matrix is irreversible, and the estimated value of the channel frequency response cannot be obtained, and stable channel estimation cannot be achieved.

[0102] Finally, the channel frequency response matrix Λ can be obtained by diagonalization

[0103]

[0104] If the impulse response of the channel is to be obtained, the inverse Fourier transform needs to be performed on the frequency response.

[0105] To clearly show the situation where 0 elements may appear in the sequence after the pilot transformation, this embodiment conducts simulation experiments twice and reduces the OCDM carrier number to 32 to present a clear diagram. In the first simulation experiment, a set of transmitted data is randomly generated and all of it is regarded as a pilot, and a total of 50 OCDM symbols are transmitted. When designing the pilot, no constraints are imposed on it, such as Figure 4 where a is the vector Γ after the random pilot transformation H Fx p In the case where there are zero elements in p each column in the figure represents the pilot sequence x corresponding to the current OCDM symbol H Fx p after being transformed into the frequency domain. The black block part represents that the element value is 0, and the white block part represents that the element value is not 0. The symbols with black blocks cannot perform correct channel estimation in the frequency domain, while the symbols without black blocks can perform correct channel estimation. In the second simulation experiment, the pilot is designed based on the above-mentioned constraint conditions, such as Figure 4 where b is the situation after the transformation of the pilot designed under the constraint conditions. There are no white blocks in the figure, which means that there are no longer zero elements in the transformed sequence, so the observation matrix is reversible, and the effectiveness of the subsequent channel estimation algorithm can be guaranteed.

[0106] To verify whether the effectiveness of the channel estimation algorithm conforms to the above theory, the channel estimation results before and after applying the constraint conditions are compared (in order to clearly present the channel estimation results in this figure, the OCDM carrier number is restored to 512 at this time. If the carrier number is too small, the estimation accuracy will be very poor). First, a channel estimation simulation experiment is conducted on the situation where the constraint conditions are not applied and there are zero elements in the transformed sequence. After performing the inverse Fourier transform on the obtained estimated value of the frequency response, the estimated result of the channel impulse response in the time domain is obtained, such as Figure 5In this case, a is the channel estimation result that fails when there are zero elements in the transformed sequence. Since the channel estimation algorithm needs to invert the observation matrix, the estimated values of the frequency responses at the frequencies corresponding to these zero elements are theoretically infinite, and they appear as singular values with very large numerical values during computer operations. Therefore, after the inverse Fourier transform, the obtained impulse response is the superposition of the time-domain waveforms corresponding to these frequencies. After applying the constraint conditions for pilot design, effective channel impulse response estimation results are obtained through simulation experiments, as shown in Figure 5 as shown in b of

[0107] After testing with pilots that meet the constraint conditions in this embodiment, normal communication data x is added, and OCDM underwater acoustic communication experiments are carried out in the same channel environment, and different load rates are selected for performance testing. At the receiving end, after using the coefficient matrix Γ to perform phase compensation on y, the obtained channel frequency response estimator is substituted into the zero-forcing equalizer or the minimum mean square error equalizer, and then the inverse Fourier transform is performed. The recovered symbol sequence is

[0108]

[0109] where x′ ZF represents the symbol recovery result of the zero-forcing equalizer, and x′ MMSE represents the symbol recovery result of the minimum mean square error equalizer, and ρ is the signal-to-noise ratio. The above symbol recovery process is as shown in Figure 6 as shown. Under the condition that the signal-to-noise ratio in the frequency band is 25 dB, the obtained equalized output results are as shown in Figure 7 a and b of Figure 7 where a in Figure 7 is the symbol output result obtained using the zero-forcing equalizer, and

[0110] b in

[0110] is the symbol output result obtained using the minimum mean square error equalizer.

[0110] In this embodiment, the above method is applied to carry out performance simulation analysis of the bit error rate curve in the OCDM communication system. The load rates of the carrier are successively changed to 128 / 512 (25%), 256 / 512 (50%), and 512 / 512 (100%). The performance curves under the two equalizers are as shown in Figure 8 as shown.

[0111] In summary, the present application provides a pilot design and channel estimation method for an OCDM communication system, belonging to the field of wireless communication. In combination with the structural characteristics of OCDM signals, the present invention provides a pilot design method under constraint conditions and a corresponding channel estimation method. The pilot that meets the constraint conditions no longer contains zero elements in the sequence after being transformed into the frequency domain, avoiding the irreversible problem of the observation matrix and ensuring the stability of the frequency-domain channel estimation algorithm. The OCDM communication system adopting this method can recover the transmitted data without error under high signal-to-noise ratio.

[0112] The explanations of the special terms and English abbreviations in the present application are given below, as shown in Table 1:

[0113] Table 1 Explanations of Special Terms and English Abbreviations

[0114]

Claims

1. A pilot design method for an OCDM communication system, characterized in that: The pilot design method comprises: Step 1: Select a block pilot structure in the modulation domain and pre-design the pilot sequence x of the current transmitted data block p =[x p,0 ,x p,1 ,...,x p,N-1 ] T , where N is the number of chirp carriers in the OCDM signal; Step 2: Obtain the vector Γ after the pilot sequence is transformed into the frequency domain H Fx p , where Γ is the diagonal matrix composed of Zadoff-Chu root sequences, and F is the discrete Fourier transform matrix; Step 3: Check the pilot sequence x p Whether the constraint condition is satisfied: vector Γ H Fx p There is no element with value 0 in ; If the constraint condition is not met, the pilot sequence x p Reconstructing until the constraint condition is satisfied; If the constraint condition is met, the pilot sequence is selected as the pilot sequence of the currently transmitted data block; The diagonal elements of Γ are Where n∈[0,N-1], j is the imaginary unit; F is the discrete Fourier transform matrix, which is in the form of Among them, m∈[0,N-1].

2. The pilot design method of an OCDM communication system according to claim 1, characterized in that: The constraint condition test method includes but is not limited to determinant test, norm test or rank test; The determinant test is the judgment formula |diag(Γ H Fx p )|≠0 is true, if true, then the pilot sequence x p Satisfy constraints; The norm test is the judgment formula ||Γ H Fx p ||0=N whether it is true, if it is true, then the pilot sequence x p Satisfy constraints; The rank test is the judgment formula rank[diag(Γ H Fx p )]=N, if yes, then the pilot sequence x p Satisfy constraints; Among them, |·| represents the determinant of the matrix; ||·||0 represents the zero norm of the vector, which is used to calculate the number of nonzero elements in the vector; diag(·) means converting the vector into a diagonal matrix; rank[·] represents the rank of the matrix.

3. The pilot design method of an OCDM communication system according to claim 1, characterized in that: The test pilot sequence x p Whether the constraints are met, including: Set the threshold ε, if the vector Γ H Fx p If the modulus of each element in is greater than the threshold ε, then the pilot sequence x p The constraints are satisfied, otherwise they are not satisfied.

4. The pilot design method of an OCDM communication system according to claim 1, characterized in that: The test pilot sequence x p Whether the constraints are met, including: Set the threshold ε, if abs{|diag(Γ H Fx p )|}>ε holds, then the pilot sequence x p The constraint condition is satisfied, otherwise it is not satisfied, wherein abs{·} represents the calculation of the modulus value of the complex number.

5. A channel estimation method for an OCDM communication system, characterized in that: The channel estimation method comprises: The pilot sequence x designed based on the method according to any one of claims 1 to 4 p It is sent to the receiving end of the OCDM communication system, and the received signal is processed and calculated to obtain the frequency domain response estimation value of the channel.

6. The channel estimation method of an OCDM communication system according to claim 5, characterized in that: The channel estimation method specifically comprises: The pilot sequence x designed based on the method according to any one of claims 1 to 4 p Send it to the receiving end of the OCDM communication system to obtain the OCDM receiving signal sequence r in the time domain, r∈C N ; Perform a fast Fourier transform to transform it into a sequence y=Fr in the frequency domain; according to the least squares principle, the frequency domain response estimate of the channel is obtained: in, After being converted into a diagonal matrix, the channel frequency domain response matrix is Channel Frequency Response Matrix Depend on Diagonalization gives:

7. The channel estimation method of an OCDM communication system according to claim 6, characterized in that: The OCDM received signal sequence r is expressed as: r=HΦ H x p +n Where H represents the channel impulse response matrix, n is the additive white Gaussian noise, and Φ is the Fresnel transform matrix.

8. A computer device comprising a memory and a processor, wherein a computer program is stored in the memory, wherein: When the processor runs the computer program stored in the memory, the steps of the method according to any one of claims 5 to 7 are performed.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a plurality of computer instructions, and the plurality of computer instructions are used to enable a computer to execute the method according to any one of claims 5 to 7.

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