Skywave massive MIMO-OFDM beam structure signal detection method and system

Abstract

The present invention discloses a method and system for detecting a Tianbo massive MIMO-OFDM beam structure signal. The Tianbo massive MIMO-OFDM base station uses a beam structure detector to detect the uplink transmission signal of each user. The beam structure detector is composed of a beam transformation module, a beam extraction module and a low-dimensional beam domain detector for each user. The beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector, and the beam extraction module extracts the beam domain received signal vector according to the beam set of each user, and finally uses the beam domain detector of each user and the extracted beam domain received signal vector to perform signal detection on the transmission signal of each user. The present invention can effectively reduce the design and implementation complexity of the signal detector while ensuring the uplink signal detection performance of the Tianbo massive MIMO-OFDM.

Description

Technical Field

[0001] The present invention belongs to the field of communication technology, and in particular relates to a skywave large-scale MIMO-OFDM beam structure signal detection method and system. Background Art

[0002] Skywave communication usually occupies the working frequency band of 3-30MHz. It can achieve long-distance communication of thousands of kilometers through ionospheric reflection and achieve global network coverage with low deployment cost. However, due to limited spectrum resources and complex and changeable ionospheric conditions, the data transmission rate of traditional point-to-point skywave communication is usually low. Large-scale MIMO multiple-input multiple-output (MIMO) technology can serve a large number of users on the same time-frequency resources by configuring a large number of antennas on the base station side, thereby greatly improving spectrum efficiency and power efficiency. The combination of skywave communication and large-scale MIMO technology can effectively improve the system capacity and reliability of skywave communication.

[0003] Uplink signal detection plays a critical role in massive MIMO communications. However, as the dimensionality of massive MIMO systems increases, although the maximum likelihood detector can achieve optimal performance, it also has computational overhead that is unbearable in practical systems. Some nonlinear detection algorithms such as local search and spherical decoding also face high computational complexity. At the same time, as the number of antennas and users in massive MIMO systems increases, some linear signal detection algorithms such as zero-breaking detection and minimum mean square error detection also have huge computational complexity due to large-dimensional matrix inversion and matrix multiplication.

[0004] In Skywave massive MIMO orthogonal frequency division multiplexing (OFDM) communications, due to limited transmission paths and small angular spread, the channel has significant sparse characteristics in the beam domain. How to use the sparse characteristics of the beam domain channel to reduce the design and implementation complexity of signal detection while maintaining good detection performance is a problem that the Skywave massive MIMO-OFDM system needs to solve. Summary of the invention

[0005] Purpose of the invention: In view of the shortcomings of the prior art, the present invention proposes a skywave massive MIMO-OFDM beam structure signal detection method and system, which utilizes the sparse characteristics of the beam domain channel and significantly reduces the computational complexity of the design and implementation of the signal detector while ensuring the signal detection performance.

[0006] Technical solution: In order to achieve the above-mentioned purpose, the present invention provides the following technical solution:

[0007] The skywave massive MIMO-OFDM beam structure signal detection method comprises:

[0008] The base station uses a signal detector with a beam structure to detect the uplink transmission signal of each user;

[0009] The base station designs a beam structure detector in the space domain according to the space beam basis channel model and the space beam domain channel of each user, or designs a beam structure detector in the space-frequency domain according to the space-frequency beam basis channel model and the space-frequency beam domain channel of each user;

[0010] The beam structure detector consists of a beam transformation module, a beam extraction module and each user's beam domain detector; the beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector, the beam extraction module extracts the beam domain received signal vector according to each user's spatial beam set, and each user's beam domain detector processes the extracted beam domain received signal vector to obtain a detection result.

[0011] Furthermore, the spatial beam-based channel model is a spatial beam matrix multiplied by a spatial beam domain channel vector, and the space-frequency beam-based channel model is a space-frequency beam matrix multiplied by a space-frequency beam domain channel vector.

[0012] Furthermore, the spatial beam matrix is ​​a matrix composed of spatial domain direction vectors corresponding to a selected set of direction cosine sampling grid points, and each spatial domain direction vector is called a spatial beam; the space-frequency beam matrix is ​​a matrix composed of spatial-frequency domain direction vectors corresponding to a selected set of direction cosine and time delay sampling grid points, and each space-frequency domain direction vector is called a space-frequency beam.

[0013] Furthermore, the beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector using a spatial beam matrix.

[0014] Further, the spatial beam sets of each user are sets of spatial beams corresponding to non-zero elements of spatial beam domain channels in spatial beam-based channel models of each user or a selected set including the spatial beam sets.

[0015] Furthermore, when adding a new spatial beam to a set of spatial beams, the selected spatial beam should belong to a user that has a non-zero spatial beam selected to the existing set of spatial beams.

[0016] Furthermore, the beam structure detector design in the spatial domain has a specific process of first making each user's spatial domain detector have a spatial beam matrix multiplied by the beam structure of the beam domain detector, and using the spatial beam matrix, each user's spatial beam set, each user's spatial beam domain channel and each user's beam domain detector to update the signal detection mean square error expression, and obtain each user's beam domain detector expression by solving the optimization problem of minimizing this mean square error.

[0017] Furthermore, a beam structure detector design in the space-frequency domain is specifically a beam structure in which the space-frequency domain detector has a space-frequency beam matrix multiplied by a beam domain detector multiplied by the conjugate transpose of the frequency beam matrix, wherein the beam domain detector of each user is a scalar factor multiplied by the corresponding space-frequency beam domain channel matrix.

[0018] Furthermore, the frequency beam matrix is ​​a matrix composed of frequency domain direction vectors corresponding to a selected set of time-delay sampling grid points, and each frequency domain direction vector is called a frequency beam.

[0019] Furthermore, the detection of each user's uplink signal according to the designed beam structure detector includes the following steps:

[0020] (1) Using the beam transformation module, the spatial domain received signal vector on each subcarrier is transformed into a beam domain received signal vector;

[0021] (2) using the beam selection module to extract the beam domain received signal vector according to the spatial beam set of each user;

[0022] (3) Detect the uplink transmission signal of each user using the beam domain detector of each user and the extracted beam domain received signal vector.

[0023] Furthermore, all operations involving the spatial beam matrix or its conjugate transpose multiplied vector are effectively implemented via the chirp-z transform.

[0024] A skywave massive MIMO-OFDM beam structure signal detection system comprises a base station and a plurality of user terminals, wherein the base station implements the above-mentioned skywave massive MIMO-OFDM beam structure signal detection method.

[0025] Beneficial effect: Compared with the prior art, the present invention utilizes the sparse characteristics of the skywave massive MIMO-OFDM channel in the spatial beam domain and the space-frequency beam domain to design the detector. The base station utilizes the sparse spatial beam domain channels and space-frequency beam domain channels of each user to design the corresponding low-dimensional beam domain detector. While ensuring the signal detection performance, the design complexity is effectively reduced. The beam structure detector formed can significantly reduce the implementation complexity of signal detection on the base station side and improve the overall transmission efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a block diagram of a skywave massive MIMO-OFDM beam structure signal detection system according to an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of a beam structure signal detection process according to an embodiment of the present invention;

[0028] Figure 3 The performance comparison between the beam structure detector in the spatial domain and the minimum mean square error (MMSE) detector in the embodiment of the present invention is shown;

[0029] Figure 4 The performance comparison between the beam structure detector in the space-frequency domain and the MMSE detector in the embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION

[0030] The technical solution provided by the present invention will be described in detail below in conjunction with specific embodiments. It should be understood that the following specific implementation methods are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0031] The embodiment of the present invention discloses a skywave massive MIMO-OFDM beam structure signal detection method and system, such as Figure 1 Said, including:

[0032] The base station uses a signal detector with a beam structure to detect the uplink transmission signal of each user;

[0033] The base station designs a beam structure detector in the space domain according to the space beam basis channel model and the space beam domain channel of each user, or designs a beam structure detector in the space-frequency domain according to the space-frequency beam basis channel model and the space-frequency beam domain channel of each user;

[0034] The beam structure detector is composed of a beam transformation module, a beam extraction module and each user beam domain detector. The beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector. The beam extraction module extracts the beam domain received signal vector according to each user's spatial beam set. Each user beam domain detector processes the extracted beam domain received signal vector to obtain the detection result.

[0035] Figure 2 A schematic diagram of the process of beam structure signal detection is given, including:

[0036] (1) Using the beam transformation module, the spatial domain received signal vector on each subcarrier is transformed into a beam domain received signal vector;

[0037] (2) using the beam selection module to extract the beam domain received signal vector according to the spatial beam set of each user;

[0038] (3) Utilize the beam domain detector of each user and the extracted beam domain received signal vector to perform signal detection on the uplink transmission signal of each user.

[0039] The method of the present invention is mainly applicable to a skywave massive MIMO-OFDM system in which a large-scale antenna array is equipped at the base station side to simultaneously serve multiple users. The specific implementation process of the channel information acquisition method involved in the present invention is described in detail below in conjunction with a specific communication system example. It should be noted that the method of the present invention is not only applicable to the specific system model exemplified below, but also to system models with other configurations.

[0040] 1. System Configuration

[0041] In this embodiment, a day-wave massive MIMO-OFDM system is considered. The base station is configured with a uniform linear array with M antennas to provide services for U single-antenna users. In OFDM modulation, the number of carriers is N. c , the length of the cyclic prefix is ​​N g , the subcarrier spacing is △f, and the sampling interval is T s =1 / N c △f. Where N v subcarriers are used to transmit data, and their index set is In skywave communication, due to the system's carrier frequency f c The antenna spacing d of the array needs to change with the ionospheric conditions, depending on the highest operating frequency f of the system. o To set, that is, d = λ o / 2, where λ o =c / f o , c is the speed of light.

[0042] 2. Channel Model

[0043] In uplink transmission, the analog baseband signal received on the nth OFDM symbol of the mth antenna is

[0044]

[0045] in is the analog baseband signal sent by user u on the nth OFDM symbol, m∈{0,1,…,M-1}, is additive white Gaussian noise, is the time-varying channel impulse response between user u and the mth antenna of the base station, which can be expressed as

[0046]

[0047] Where P u is the number of paths between user u and the base station. In (2) u,p , the complex gain of the pth path of user u, expressed as where β u,p and are the gain and initial phase respectively, and Uniformly distributed in [0,2π). ν u,p is the Doppler frequency, which is mainly caused by user movement and the ionosphere. are the direction cosines, where and are the arrival azimuth and arrival elevation respectively. τ u,p is the delay of the pth path between user u and the first antenna of the base station, △τ=d / c. And the present invention takes into account the transmission delay along the antenna array, that is, m△τΩ u,p .

[0048] After OFDM demodulation, the received data on the kth subcarrier of the nth OFDM symbol on the mth antenna can be expressed as

[0049]

[0050] in x m,n,k represents the data sent by user u on the kth subcarrier of the nth OFDM symbol, z m,n,k is additive white Gaussian noise, with a mean of 0 and a variance of A complex Gaussian random variable, is the channel frequency response on the kth subcarrier of the nth OFDM symbol between user u and the mth antenna of the base station, expressed as

[0051]

[0052] make The spatial channel vector of user u on the kth subcarrier of the nth OFDM symbol has the mth element: The space-frequency domain channel vector is defined as According to (4), the present invention has

[0053]

[0054] in represents the Hadamard product, 1 M represents a vector of all 1s with dimension M, and

[0055]

[0056] are the spatial domain direction vector and the frequency domain direction vector of the pointing direction cosine Ω and the time delay τ respectively. Due to the existence of the spatial broadband effect, the spatial domain direction vector varies with different subcarriers, and the present invention defines

[0057]

[0058] Since the parameters of each path of each user (Ω u,p ,τ u,p ) is restricted to the set and Among them is the maximum delay spread, and these sets are evenly divided into multiple subsets, namely

[0059]

[0060] in is the number of equivalent delay extension points, and the number of subsets divided by direction cosine and delay are and N de =F de N τ , where F an and F de is the refinement factor, Indicates rounding up. an and N de When the The spatial domain direction vector v(Ω u,p ) is approximately the sampling space domain direction vector in Will satisfy The frequency domain direction vector u(τ u,p ) is approximately the direction vector in the sampling frequency domain in Therefore, the definition Spatial Domain Channel Vector become

[0061]

[0062] in

[0063]

[0064] Similarly, define and Then the space-frequency domain channel vector It can be expressed as

[0065]

[0066] in

[0067]

[0068] The present invention refers to each sampling spatial domain direction vector as a spatial beam, and each sampling frequency domain direction vector as a frequency beam. It is called space-frequency beamforming. and They become the spatial beam domain channel coefficients and the space-frequency beam domain channel coefficients respectively. Then (12) and (14) are the spatial beam-based channel model and the space-frequency beam-based channel model respectively.

[0069] definition is the scaled spatial beam domain channel, and its nth an The elements are definition is the spatial beam matrix, then (12) becomes

[0070]

[0071] Similarly, define is the scaled space-frequency beam domain channel, whose (n de N an +n an ) elements are definition is the frequency beam matrix and Indicates The block diagonal matrix is ​​formed. Then (14) becomes

[0072]

[0073] in is the space-frequency beam matrix.

[0074] Skywave massive MIMO-OFDM channels are usually sparse in the beam domain. The set of non-zero locations of the spatial beam domain channel vector for user u is defined as and Indicates the number of elements in a collection. express The nth an elements. Define a set in definition in Indicates that according to the set Extract matrix V k The corresponding columns.

[0075] Then (16) can be expressed as

[0076]

[0077] Defining a Collection in Then (17) can be expressed as

[0078]

[0079] in

[0080] 3. Beam Structure Detector in Spatial Domain

[0081] Consider the uplink transmission on the kth subcarrier of the nth OFDM symbol. For simplicity, the subscript n is omitted in the following. The received signal model in (3) can be expressed as

[0082]

[0083] in is additive white Gaussian noise with a mean of 0 and a covariance matrix of Complex Gaussian distribution, where 0 is the all-zero vector, I M For the unit array.

[0084] Considering the linear detector in the spatial domain of user u Then the mean square error (MSE) of signal detection can be expressed as

[0085]

[0086] Then for the detector w u,k The design can be expressed as

[0087]

[0088] According to the spatial beam-based channel model of each user and the spatial beam domain channel, MSE u,k It can be expressed as

[0089]

[0090] in The optimal solution to the optimization problem (22) can be obtained as

[0091]

[0092] in

[0093]

[0094] The superscript + represents a pseudo-inverse operator. Further, the present invention assumes that the number of users is finite and the direction cosines of the users are discrete and finite. When M tends to infinity, the present invention has At this time, the optimal solution (24) becomes

[0095]

[0096] in

[0097]

[0098] Expression (26) gives an asymptotically optimal detector structure. Since there are only spatial beam domain channels in the optimization problem (27), and the structure (26) is very similar to the spatial beam-based channel model (18), the present invention will It is called beam domain detector, and the corresponding spatial domain detector It is called a beam structure detector in the spatial domain.

[0099] It can be proved that when The optimal solution to the optimization problem (27) has the following structure

[0100]

[0101] This result shows that when the direction cosine sets of any two users do not overlap, the elements in the optimal beam domain detector are non-zero only on the beam occupied by the user. Since the angular spread of the skywave massive MIMO channel is very small and has a very significant sparse characteristic, the present invention can only focus on optimizing the non-zero elements in the beam domain detector, thereby transforming problem (26) into a low-dimensional beam domain detector optimization problem as shown below:

[0102]

[0103] in

[0104]

[0105] and is the beam extraction matrix, expressed as

[0106]

[0107] and is corresponding to For the sake of simplicity in the following description, the present invention uses the spatial beam set in (31) The beam structure detector is defined as

[0108] When the number of users increases, the condition that the user's angular cosine sets do not overlap may not be well met. Therefore, it is necessary to consider using more beams in addition to the beams occupied by the user itself to further improve the performance of the detector. It can be proved that for a given spatial beam set Define a new set of spatial beams in When M approaches infinity,

[0109]

[0110] The equation holds true when the following conditions are met

[0111]

[0112] The above results show that when the present invention needs to select more beams to further improve the performance of the beam structure detector, it should choose to meet The beams satisfying condition (33) should not be selected because they do not change the detector performance. In other words, the added beam should belong to a user that already has a non-zero beam selected into the existing spatial beam set.

[0113] Although the number of antennas in an actual system is limited, according to the above discussion, the present invention can assume that the spatial domain detector still has a beam structure. The beam selection matrix Definition and S u Similar, except beam set Replaced by and The present invention then turns to optimize The optimal solution that minimizes MSE is

[0114]

[0115] in and is the beam set corresponding to The corresponding spatial domain detector is

[0116]

[0117] The corresponding signal detection result can be expressed as

[0118]

[0119] From (36), it can be seen that the implementation of beam structure detection mainly consists of the following steps:

[0120] (1) Using the beam transformation module, the spatial domain received signal vector on each subcarrier is transformed into a beam domain received signal vector;

[0121] (2) using the beam selection module to extract the beam domain received signal vector according to the spatial beam set of each user;

[0122] (3) Utilize the beam domain detector of each user and the extracted beam domain received signal vector to perform signal detection on the uplink transmission signal of each user.

[0123] Next, the present invention discusses the design complexity and implementation complexity of the beam structure detector in the spatial domain. Definition The design complexity mainly comes from (34), noting that P u,u′,k It is only related to the non-zero beam position, that is, it is related to the slowly varying statistical channel information, which can be calculated in advance. Therefore, the design complexity is The implementation complexity mainly comes from (36), where according to the chirp-z transform, V k can be rewritten as

[0124]

[0125] Among them, F N represents the unitary discrete Fourier transform matrix of N points, F N×G Indicated by F N The matrix composed of the first G (G ≤ N) columns, N (S) is greater than or equal to M+N an An integer of -1.

[0126] but can be implemented quickly and only needs to be calculated once for all users, so the implementation complexity is

[0127] 4. Beam Structure Detector in Space-Frequency Domain

[0128] Considering the uplink transmission on the nth OFDM symbol, the received signal in (3) can be rewritten as

[0129] y=H SF x+z (38)

[0130] in Its ((k-k0)M+m)th element is y m,k , and is subject to the mean of 0, and the covariance matrix is The complex Gaussian distribution of is a vector-valued diagonal matrix. Then the traditional spatial-frequency domain detector design for user u can be expressed as

[0131]

[0132] in

[0133]

[0134] According to the space-frequency beam-based channel model (19), the channel matrix can be rewritten as

[0135]

[0136] in is the space-frequency beam-domain channel matrix, definition It can also be proved It can be expressed as In the form of, the optimal solution of the optimization problem (39) is

[0137]

[0138] in

[0139]

[0140] When M approaches infinity, due to At this time, the optimal solution (42) becomes

[0141]

[0142] in

[0143]

[0144] Expression (44) gives an asymptotically optimal detector structure. Since there is only the space-frequency beam domain channel matrix in the optimization problem (45), and the structure (44) is very similar to the structure in (41), which is constructed based on the space-frequency beam-based channel model (19), the present invention also It is called a beam-domain detector, and the corresponding space-frequency domain detector It is called a beam structure detector in the space-frequency domain.

[0145] It can be proved that when and When , the optimal solution of problem (45) is

[0146]

[0147] From the above results, it can be seen that when there are no two paths with direction cosines but different delays, and the direction cosine sets between users do not overlap, the asymptotically optimal beam domain detector is the energy of the space-frequency beam domain channel vector of each user multiplied by the corresponding space-frequency beam domain channel matrix. According to (44), the space-frequency domain detector can be expressed as

[0148]

[0149] The test results can be expressed as

[0150]

[0151] According to (18) and (19), we have

[0152]

[0153] Substituting (49) into (48), we can obtain

[0154]

[0155] definition The design complexity of the beam structure detector in the space-frequency domain mainly comes from (46), which only requires the calculation of the scalar factor Therefore, the design complexity is The implementation complexity mainly comes from (50), which can be calculated by To achieve It can also be calculated by Then extract the corresponding position to achieve it, so the implementation complexity is

[0156] VII. Implementation Effect

[0157] In order to enable those skilled in the art to better understand the solution of the present invention, the performance results of the beam structure detection method in this embodiment under specific configuration are given below.

[0158] Considering the skywave massive MIMO-OFDM communication system, the system parameters are configured as follows: carrier frequency f c =16MHz, subcarrier spacing △f = 250Hz, number of subcarriers N c =2048, the number of effective subcarriers N v =1536, cyclic prefix length N g =512, base station antenna spacing d = 9m, 16-QAM modulation, refinement factor F an =F de =F do = 2. For the convenience of description, the beam structure detector in the spatial domain is abbreviated as BSD-SD, the beam structure detector in the spatial-frequency domain is abbreviated as BSD-SFD, and the minimum mean square error detector is abbreviated as MMSE.

[0159] Figure 3 The estimation performance comparison between BSD-SD and MMSE estimation in the embodiment is given, where the number of base station antennas M = 256 and the number of users U = 96. It can be seen that the proposed low-complexity BSD-SD is very close to the performance of the MMSE detector. At the same time, as the number of selected beams increases, the performance of BSD-SD can be further improved, and the performance gap between it and the MMSE detector is further narrowed.

[0160] Figure 4 The estimation performance comparison between BSD-SFD and MMSE estimation in the embodiment is given, where the number of users U=16. It can be seen that the proposed low-complexity BSD-SFD is also very close to the performance of the MMSE detector. At the same time, as the number of antennas increases, the performance of BSD-SFD can be further improved, and the performance gap between it and the MMSE detector is further narrowed.

[0161] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

[0162] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A skywave massive MIMO-OFDM beam structure signal detection method, characterized in that: include: The base station uses a signal detector with a beam structure to detect the uplink transmission signal of each user; The base station designs a beam structure detector in the space domain according to the space beam basis channel model and the space beam domain channel of each user, or designs a beam structure detector in the space-frequency domain according to the space-frequency beam basis channel model and the space-frequency beam domain channel of each user; The beam structure detector consists of a beam transformation module, a beam extraction module and each user's beam domain detector; the beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector, the beam extraction module extracts the beam domain received signal vector according to each user's spatial beam set, and each user's beam domain detector processes the extracted beam domain received signal vector to obtain a detection result.

2. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The spatial beam-based channel model is a spatial beam matrix multiplied by a spatial beam domain channel vector, and the space-frequency beam-based channel model is a space-frequency beam matrix multiplied by a space-frequency beam domain channel vector.

3. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 2, characterized in that: The spatial beam matrix is ​​a matrix composed of spatial domain direction vectors corresponding to a selected set of direction cosine sampling grid points, and each spatial domain direction vector is called a spatial beam; the space-frequency beam matrix is ​​a matrix composed of spatial-frequency domain direction vectors corresponding to a selected set of direction cosine and time delay sampling grid points, and each space-frequency domain direction vector is called a space-frequency beam.

4. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The beam transformation module converts the spatial domain received signal vector on each subcarrier into a beam domain received signal vector using a spatial beam matrix.

5. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The spatial beam sets of each user are the set of spatial beams corresponding to the non-zero elements of the spatial beam domain channel in the spatial beam-based channel model of each user or a selected set including the spatial beam set.

6. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 5, characterized in that: When adding a new spatial beam to a spatial beam set, the selected spatial beam should belong to a user that already has a non-zero spatial beam selected to the existing spatial beam set.

7. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The design of the beam structure detector in the spatial domain, the specific process is to first make each user's spatial domain detector have a spatial beam matrix multiplied by the beam structure of the beam domain detector, and use the spatial beam matrix, each user's spatial beam set, each user's spatial beam domain channel and each user's beam domain detector to update the signal detection mean square error expression, and obtain each user's beam domain detector expression by solving the optimization problem of minimizing this mean square error.

8. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The beam structure detector design in the space-frequency domain is specifically that the space-frequency domain detector has a beam structure of the conjugate transpose of the space-frequency beam matrix multiplied by the beam domain detector and then multiplied by the frequency beam matrix, wherein the beam domain detector of each user is a scalar factor multiplied by the corresponding space-frequency beam domain channel matrix.

9. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 8, characterized in that: The frequency beam matrix is ​​a matrix composed of frequency domain direction vectors corresponding to a selected set of time-delay sampling grid points, and each frequency domain direction vector is called a frequency beam.

10. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: The detection of each user's uplink signal by the designed beam structure detector includes the following steps: (1) Using the beam transformation module, the spatial domain received signal vector on each subcarrier is transformed into a beam domain received signal vector; (2) using the beam selection module to extract the beam domain received signal vector according to the spatial beam set of each user; (3) Detect the uplink transmission signal of each user using the beam domain detector of each user and the extracted beam domain received signal vector.

11. The skywave massive MIMO-OFDM beam structure signal detection method according to claim 1, characterized in that: All operations involving the spatial beam matrix or its conjugate transpose multiplied by a vector are efficiently implemented via the chirp-z transform.

12. A skywave massive MIMO-OFDM beam structure signal detection system, comprising a base station and a plurality of user terminals, characterized in that: The base station implements the skywave massive MIMO-OFDM beam structure signal detection method according to any one of claims 1-11.

Images