Low-complexity broadband satellite communication multipath fading channel simulation system

Abstract

The invention relates to a low-complexity broadband satellite communication multipath fading channel simulation system, which comprises an upper computer parameter configuration module and an FPGA (Field Programmable Gate Array) processing module, and is characterized in that the upper computer parameter configuration module is used for generating and issuing multipath fading channel parameter information according to a preset path channel scene; the FPGA processing module is used for receiving the multipath fading channel parameter information and executing multipath fading channel simulation; the FPGA processing module comprises a parameter processing module, a channel coefficient generation module, a multipath time delay module and a multipath superposition module. According to the system, FPGA resource consumption is greatly reduced, and inter-path statistical independence and simulation fidelity are improved.

Description

Technical Field

[0001] This invention belongs to the field of broadband satellite communication technology, specifically relating to a low-complexity broadband satellite communication multipath fading channel simulation system. Background Technology

[0002] In satellite communication systems, communication quality is a core indicator of system performance, and the channel environment is a key factor affecting communication quality. Compared to terrestrial wireless channels, satellite communication channels exhibit greater complexity. During the design and optimization of satellite communication systems, multiple tests are necessary to verify their stability and reliability in real-world channel environments. However, testing methods relying on actual communication links are not only time-consuming but also costly. With the increasing demand for broadband satellite communication, developing high-performance broadband satellite channel simulators is particularly important, requiring continuous optimization of the simulation range and accuracy, and the design and implementation of modules rarely seen or unseen in other research or products.

[0003] In broadband satellite communication systems, signals often undergo complex multipath propagation and Doppler spread caused by high-speed relative motion, resulting in fading effects such as amplitude fluctuations, phase rotation, and time-varying spectral broadening at the receiver. To conduct system verification, link budget evaluation, and receiver algorithm and hardware system integration on the ground, it is typically necessary to construct a controllable, reproducible, and statistically reliable multipath fading channel simulator. Classical Jakes-type models and their improved forms often use the Sum of Sinusoids (SoS) method to generate Rayleigh fading processes. By rationally designing the angle of arrival and initial phase, the output satisfies the Rayleigh amplitude distribution and the desired autocorrelation / Doppler spectrum characteristics. Simultaneously, to obtain multiple uncorrelated (or low-correlation) fading waveforms, orthogonal weighted sequences can be introduced to orthogonally weight and combine the oscillator components, thereby expanding the scale of the multipath fading output without significantly increasing the multiplication complexity. However, in engineering scenarios oriented towards broadband and high Doppler, multipath-related peak increases may still occur in multipath waveforms within the dynamic delay window. Furthermore, traditional parallel implementations are prone to oscillator core duplication, matrix multiplication / multiply-accumulate array size expansion, and storage and routing pressures, making it difficult to meet the engineering requirements of compact FPGA resources, high throughput, and strong configurability. Therefore, there is an urgent need for a multipath fading channel simulation implementation scheme that balances statistical fidelity and low hardware complexity. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides a low-complexity broadband satellite communication multipath fading channel simulation system. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a low-complexity broadband satellite communication multipath fading channel simulation system, comprising: a host computer parameter configuration module and an FPGA processing module, wherein... The host computer parameter configuration module is used to generate and send multipath fading channel parameter information according to the preset path channel scenario; the multipath fading channel parameter information includes sine wave superposition method parameters, integer delay parameters of each multipath component, fractional delay parameters of each multipath component, gain parameters of each multipath component, and column permutation information. The FPGA processing module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core using a time-division multiplexing structure, based on the parameters of the sine wave superposition method. It then uses Walsh-Hadamard transform based on column permutation information to achieve multipath expansion, obtaining the complex fading coefficients of each multipath component. Interpolation of these complex fading coefficients yields the fading channel coefficients of each multipath component. Based on the fractional delay parameters of each multipath component, a Farrow structure fractional delay filter is used to obtain the fractional delay of each multipath component. Based on the integer delay parameters of each multipath component, the onboard storage resources of the FPGA are used to obtain the integer delay of each multipath component. Finally, the fading channel coefficients and integer delays of each multipath component are multiplied and summed to obtain the multipath fading channel output signal.

[0005] In one embodiment of the present invention, the FPGA processing module includes a parameter processing module, a channel coefficient generation module, a multipath delay module, and a multipath superposition module, wherein, The parameter processing module is used to parse and cache the multipath fading channel parameter information, and allocate the sine wave superposition method parameters, the gain parameters of each multipath component and the column permutation information to the channel coefficient generation module, and allocate the integer delay parameters of each multipath component and the fractional delay parameters of each multipath component to the multipath delay module. The channel coefficient generation module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core using a time-division multiplexing structure based on the parameters of the sine superposition method. Combined with the column permutation information, the module uses Walsh-Hadamard transform to obtain the complex fading coefficients of each multipath component. The module then multiplies the complex fading coefficients of each multipath component with the corresponding gain parameters and performs interpolation to output the fading channel coefficients of each multipath component. The multipath delay module is used to filter the input baseband signal using a four-branch FIR sub-filter bank shared by each path, obtaining four intermediate results; for each multipath component, the four intermediate results are weighted by a Farrow architecture polynomial according to the corresponding fractional delay parameter to obtain the fractional delay of each multipath component; the fractional delay is written into the memory and the integer delay of each multipath component is output according to the integer delay parameter of each multipath component; The multipath superposition module is used to multiply and sum the fading channel coefficients of each multipath component and the integer delay of each multipath component to obtain the multipath fading channel output signal.

[0006] In one embodiment of the present invention, the parameters of the sinusoidal superposition method are expressed as follows: , , and ,in, , , and They are independent of each other, and The distribution within the range is uniform. The number of oscillators. For the maximum Doppler frequency shift, The sampling period is Sampling rate, Index of the basic oscillator; The integer time delay parameters of each multipath component are expressed as follows: ,in, For integer delay parameters, , For the first Total delay of the multipath components, It is a set of non-negative integers; The fractional delay parameters of each multipath component are expressed as follows: ,in, For fractional delay parameters, ; The gain parameters of each multipath component are expressed as follows: ,in, These are the gain parameters for each multipath component. For the first The linear power of the multipath components, , For the first Path power parameters of the multipath components; The column permutation information is generated as follows: The column permutation vector P is constructed as follows: ,in, And each element is distinct. The order of the Walsh-Hadamard transform; Using the dynamic window as a constraint, establish the objective function for column permutation optimization: ,in, , For each path in the multipath, The relative time offset between two different paths. For window coefficients, For coherent time, The cross-correlation function measures the cross-correlation between two different paths with an offset of . The similarity between the two positions in the permutation vector is calculated; in each iteration, the column indices of two positions in the permutation vector are swapped or replaced, and the updated objective function is calculated. , and when If the value decreases, the update is accepted until the preset number of iterations or the convergence condition is met. The final column permutation vector obtained from the update is then used. This serves as the column replacement information.

[0007] In one embodiment of the present invention, the channel coefficient generation module includes a time-division multiplexing oscillator core module, a column permutation Walsh transform module, and a gain and linear interpolation module, wherein, The time-division multiplexing oscillator core module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core based on the parameters of the sine wave superposition method using a time-division multiplexing structure; The Walsh transform module of the column permutation is used to combine the column permutation information and use the Walsh Hadamard transform to obtain the complex fading coefficients of each multipath component; The gain and linear interpolation module is used to multiply the complex fading coefficient of each multipath component with the corresponding gain parameter and then interpolate to output the fading channel coefficient of each multipath component.

[0008] In one embodiment of the present invention, the time-division multiplexing oscillator core module is specifically used for: A time-division multiplexing structure is used to reuse the same oscillator core. The phase accumulator is updated sequentially using the oscillator index as the polling address. The accumulated phase is then input into the sine wave generation unit to generate the corresponding sine and cosine sequences. Finally, 64 basic oscillator components are generated serially in time sequence. The basic oscillator components include in-phase components and quadrature components.

[0009]

[0010]

[0011] in, These are components in the same direction. For orthogonal components, Indicates a discrete-time index; The Walsh transform module for column permutation is specifically used for: Based on the component index of each fundamental oscillator component The target column index is obtained using the column replacement information. ; Using the target column index and each path index As input, the Walsh symbol coefficients corresponding to each path are calculated in real time based on the Walsh-Hadamard code generation rules. ; The fundamental oscillator components are sign-selected according to the Walsh sign coefficients, and the results are accumulated into the corresponding multipath accumulators in either an additive or subtractive manner to obtain the complex fading coefficients of each multipath component. The gain and linear interpolation module is specifically used for: Multiplying the complex fading coefficients of each multipath component by their corresponding gain parameters yields the weighted complex fading coefficients:

[0012] in, The weighted complex fading coefficients are... The complex fading coefficients of each multipath component are given. This is an index for the update time of the fading coefficients. Index for multipath components; Based on the complex fading coefficient at the endpoint and Calculate the interpolation step size And perform recursion according to the baseband sampling time within the update interval. The fading channel coefficients of each multipath component are generated in sync with the baseband sampling. ,in, The interpolation factor. The fading channel coefficients generated by interpolation, for and The time index for interpolation between them This is the time index for the fading channel coefficients.

[0013] In one embodiment of the present invention, the multipath delay module includes a fractional delay module and an integer delay module, wherein, The fractional delay module is used to filter the input baseband signal by a four-way branch FIR sub-filter group shared by each path to obtain four intermediate results; for each path, the four intermediate results are combined by polynomial weighting according to the corresponding fractional delay parameters to obtain the fractional delay of each multipath component. The integer delay module is used to write the fractional delay into the memory and output the integer delay of each multipath component.

[0014] In one embodiment of the present invention, the fractional delay module is specifically used for: The input baseband signal is filtered by a four-path branch FIR sub-filter bank shared by all paths, resulting in four intermediate filtering results:

[0015] in, This is the intermediate filtering result. For the first Path filter tap coefficients This is the number of taps; Based on the corresponding fractional delay parameters, the four intermediate filtering results are subjected to Farrow polynomial weighted combination to generate the fractional delay of each multipath component:

[0016] in, For the first The fractional delay of each path, For fractional delay parameters polynomial weighting coefficients, Using Horner nested structure Perform the evaluation: , , , , To construct the polynomial coefficients of the Farrow filter interpolation function, Denotes the coefficient of the cubic term. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. Indicates the coefficient of the constant term; The integer delay module is specifically used for: The fractional delay is written into the memory, and based on the integer delay parameters... The input data is read out with a delay to obtain the integer delay of each multipath component. .

[0017] In one embodiment of the present invention, the multipath superposition module is specifically used for: For each path, calculate the fading channel coefficients for that path. and the integer delay of each corresponding multipath component Perform complex multiplication to obtain the weighted components of the path:

[0018] in, For the first The weighted components of the path, For discrete-time sampling index, The time index for the fading channel coefficients; The weighted components of each path are input into a hierarchical addition tree for summation, and the complex summation is completed level by level to obtain the multipath superimposed signal: Each adder performs addition operations on the weighted components of the in-phase components and the weighted components of the quadrature components respectively. Pipeline registers are set between each adder to store and synchronize the intermediate summation results step by step. The complex baseband signal is composed of the multipath superposition signals of in-phase components and the multipath superposition signals of quadrature components.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: In the simulation system of this invention, multipath fading channel parameter information is generated and distributed through the host computer parameter configuration module, allowing for flexible configuration of the relevant characteristics of the multipath fading channel. By employing a time-division multiplexing architecture, a Walsh-Hadamard transform implemented with only addition and subtraction, and a four-branch FIR sub-filter bank shared by each path in the Farrow architecture for filtering, FPGA resource consumption is greatly reduced. Without increasing the number of oscillators or filters, column permutation information is generated and distributed through offline search by the host computer, which reduces the worst cross-correlation peak of the multipath components within a preset dynamic window, improving the statistical independence between paths and the simulation fidelity. Attached Figure Description

[0020] Figure 1 A schematic diagram of a low-complexity broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention; Figure 2 A flowchart illustrating a method in a low-complexity broadband satellite communication multipath fading channel simulation system provided in this embodiment of the invention; Figure 3 This is a structural diagram of the channel coefficient generation module in the broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention; Figure 4 This is a structural diagram of the time-division multiplexing shared oscillator in the channel coefficient generation module of the broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention; Figure 5 This is a structural diagram of the Walsh Hadamard transform in the channel coefficient generation module of the broadband satellite communication multipath fading channel simulation system provided in this embodiment of the invention. Figure 6 This is a structural diagram of the multipath delay module in the broadband satellite communication multipath fading channel simulation method provided in this embodiment of the invention; Figure 7 The Farrow structure diagram of the fractional delay filter Lagrange cubic interpolation filter in the simulation term of broadband satellite communication multipath fading channel provided in the embodiment of the present invention is shown. Figure 8 This is a hardware structure diagram of the multipath superposition module in a broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0022] Example 1 This invention proposes a low-complexity simulation system for multipath fading channels in broadband satellite communication. Based on an improved Sum of Sinusoids (SOS) model using the Zheng-Xiao method, the system generates multiple sets of sine / cosine sequences on a single oscillator core using Time Division Multiplexing (TDM). Multiple low-correlation multipath fading coefficients are constructed using a Walsh-Hadamard Transform involving only addition and subtraction operations. To address the issue that Walsh codes are only orthogonal at zero delay and prone to dynamic leakage under high Doppler or finite integration windows, an offline column permutation mapping generation mechanism is introduced. This significantly reduces the peak cross-correlation value across paths within the dynamic window without altering the single-path Rayleigh statistics, power spectrum, and coherence time characteristics. The column permutation parameters can be obtained offline via a host computer and then embedded in the hardware. This system eliminates the need for large-scale matrix multiplication, making it suitable for compact FPGA implementation and demonstrating the low cost and high stability of broadband satellite channel simulation.

[0023] Please see Figure 1 and Figure 2 , Figure 1 This is a block diagram illustrating the principle of a low-complexity broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention. Figure 2 A flowchart illustrating a method in a low-complexity broadband satellite communication multipath fading channel simulation system provided in this embodiment of the invention.

[0024] like Figure 1 As shown, the low-complexity broadband satellite communication multipath fading channel simulation system includes a host computer parameter configuration module and an FPGA processing module.

[0025] The host computer parameter configuration module generates and distributes multipath fading channel parameter information based on a preset multipath channel scenario. This multipath fading channel parameter information includes sine wave superposition parameters (parameters used to generate time-varying fading coefficients using the sine wave superposition method), integer delay parameters for each multipath component, fractional delay parameters for each multipath component, gain parameters for each multipath component, and column permutation information. The host computer parameter configuration module transmits the multipath fading channel parameter information to the FPGA processing module via an Ethernet interface using the TCP protocol.

[0026] The FPGA processing module receives multipath fading channel parameter information and performs multipath fading channel simulation. Specifically, the FPGA processing module uses a time-division multiplexing structure to generate multiple sets of sine and cosine sequences on a shared oscillator core based on the sine wave superposition method parameters. Based on column permutation information, it uses Walsh-Hadamard transform to achieve multipath expansion, obtaining the complex fading coefficients of each multipath component. Interpolation of the complex fading coefficients yields the fading channel coefficients of each multipath component. Based on the fractional delay parameters of each multipath component, a Farrow structure fractional delay filter is used to obtain the fractional delay of each multipath component. Based on the integer delay parameters of each multipath component, the onboard storage resources of the FPGA are used to obtain the integer delay of each multipath component. Finally, the fading channel coefficients and integer delays of each multipath component are multiplied and summed to obtain the multipath fading channel output signal.

[0027] In one specific embodiment, the FPGA processing module includes a parameter processing module, a channel coefficient generation module, a multipath delay module, and a multipath superposition module.

[0028] The parameter processing module receives multipath fading channel parameter information from the host computer parameter configuration module, parses and caches the multipath fading channel parameter information, and allocates the sine wave superposition method parameters, the gain parameters of each multipath component and the column permutation information to the channel coefficient generation module, and allocates the integer delay parameters and fractional delay parameters of each multipath component to the multipath delay module.

[0029] The channel coefficient generation module receives sine wave superposition parameters, gain parameters of each multipath component, and column permutation information, and generates fading channel coefficients corresponding to the satellite multipath fading channel. Specifically, the channel coefficient generation module uses a time-division multiplexing structure to generate multiple sets of sine and cosine sequences based on the sine wave superposition parameters on a shared oscillator core. Combined with column permutation information, it uses Walsh-Hadamard transform to achieve multipath expansion and obtain the complex fading coefficients of each multipath component, thereby reducing the resource consumption of multipliers and lookup tables. Then, the complex fading coefficients of each multipath component are multiplied by the corresponding gain parameters and linearly interpolated to match the data rate of the signal to be processed, outputting the fading channel coefficients of each multipath component.

[0030] The multipath delay module applies configurable multipath delays to each multipath component. These delays consist of integer multiples of sampling delay and fractional multiples of sampling delay. The fractional multiples of sampling delay are implemented using a Farrow-structured fractional delay filter. The Farrow fractional delay structure optimizes resource usage by employing the same set of FIR filter banks and a Horner polynomial evaluation structure. The integer multiples of sampling delay are implemented using onboard FPGA storage resources. Specifically, after receiving the integer delay parameters, fractional delay parameters, and input baseband signal for each multipath component, the multipath delay module filters the input baseband signal using a shared four-branch FIR sub-filter bank, obtaining four intermediate results. For each multipath component, the module performs a Farrow-structured polynomial weighted combination of the four intermediate results based on the corresponding fractional delay parameters to obtain the fractional delay for each multipath component. The fractional delays are written to memory and read out according to the integer delay parameters of each multipath component to achieve integer delays, thus obtaining the integer delay for each multipath component.

[0031] The multipath overlay module is used to multiply and accumulate the fading channel coefficients and integer delays of each multipath component received. For each path, the corresponding fading channel coefficients and integer delays are multiplied and accumulated to obtain the multipath fading channel output signal.

[0032] In a specific embodiment, the specific execution steps in the host computer parameter configuration module are as follows: Figure 2 S1 in the text includes: In the S11 model of the improved Sum of Sinusoids (SOS) model by the Zheng-Xiao method, the same-direction component... and orthogonal components It can be represented as: ; ; ; in, , and They are independent of each other, and The distribution within the range is uniform. For the maximum Doppler frequency shift, The number of oscillators. For continuous time variables, Index of the basic oscillator.

[0033] S12. During the implementation process, it is necessary to generate The multipath fading components with low cross-correlation are identified, and a Walsh Hadamard orthogonal hybrid structure is used to map the shared oscillator pool output to multipath fading coefficients. The Walsh Hadamard transformation matrix is ​​as follows: An orthogonal matrix whose order is In engineering implementation, the best option is selected. ( (where the integer is positive), and to generate at least 48 multipath components, the following condition must be met: Therefore, the minimum order that satisfies the condition is To ensure that the input dimension of the Walsh Hadamard mix matches the output dimension of the shared oscillator pool, this implementation sets the number of oscillators to a selected value. This configuration satisfies the output requirement of 48 paths while avoiding the additional multiply-accumulate and storage resource overhead of choosing a larger order, achieving a better trade-off between statistical approximation accuracy and FPGA implementation complexity. In the FPGA implementation, since the transmitted and processed data are discrete, the in-direction components can be... and orthogonal components The formula can be transformed into: ; ; ; in, The sampling period is The sampling rate is used in the hardware implementation. This represents one clock cycle; This represents a discrete-time index in digital signal processing. Represents the sequence number of the sampling sequence, i.e., the first... One sampling point.

[0034] Therefore, the parameters of the sinusoidal superposition method are expressed as: , , and .

[0035] S13, No. The total time delay of the multipath components is denoted as The sampling period is To facilitate FPGA implementation, It is divided into two parts: integer delay and fractional delay. ; in, The integer delay parameter represents the integer number of sampling points for the delay. , It is a set of non-negative integers; This is a fractional delay parameter, representing the delay amount less than one sampling period. .

[0036] The integer time delay parameters of each multipath component can be expressed as: The fractional delay parameters of each multipath component can be expressed as: .

[0037] S14. The host computer determines the first step based on the Power Delay Profile (PDP). Path power parameters of multipath components Convert it into linear power , can be represented as: ; Will Gain parameters converted to each multipath component It can be represented as: .

[0038] S15. The host computer obtains the Walsh-Hadamard transform order determined in step S12. and the required number of multipaths Then, the column permutation vector P is constructed as follows: ; in, Furthermore, each element is distinct and is used to output the first element from the shared oscillator pool. Each fundamental oscillator component index is mapped to the target Walsh code index. ; This is the order of the Walsh-Hadamard transform.

[0039] To reduce dynamic cross-correlation leakage between multipath components, the host computer uses... Using the dynamic window as a constraint, we establish the column permutation optimization objective function: among all P values ​​satisfying the permutation constraints, minimize the worst cross-correlation peak value of each multipath component within the dynamic window, denoted as: ; in, , For each path in the multipath, This represents two different paths out of 48. The relative time offset between two different paths. For window coefficients, For coherent time, The cross-correlation function measures the cross-correlation between two different paths with an offset of . The degree of similarity at the time.

[0040] The host computer uses a search algorithm to iteratively update the column permutation vector P; in each iteration, the column indices of two positions in the permutation vector are swapped or replaced, and the updated objective function is calculated. , and when If the value is reduced, an update is accepted until the preset number of iterations or the convergence condition is met, resulting in the final column permutation vector. The host computer uses the column permutation vector as column permutation information to provide an index mapping basis for the subsequent generation of Walsh symbol coefficients and completion of multipath expansion on the FPGA side.

[0041] S16: Using the Ethernet TCP protocol, the parameters of the sine wave superposition method, the integer delay parameters of each multipath component, the fractional delay parameters of each multipath component, the gain parameters of each multipath component, and the column permutation information in steps S12, S13, S14, and S15 are transmitted to the FPGA processing module through the network port.

[0042] Please see Figure 3 , Figure 3 This is a structural diagram of the channel coefficient generation module in a broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention. The channel coefficient generation module includes a time-division multiplexing oscillator core module, a column permutation Walsh transform module, and a gain and linear interpolation module. The time-division multiplexing oscillator core module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core using a time-division multiplexing structure based on sine wave superposition parameters. The column permutation Walsh transform module is used to combine column permutation information and use Walsh Hadamard transform to obtain the complex fading coefficients of each multipath component. The gain and linear interpolation module is used to multiply the complex fading coefficients of each multipath component with the corresponding gain parameters and perform interpolation to output the fading channel coefficients of each multipath component.

[0043] In a specific embodiment, the specific execution steps in the channel coefficient generation module are as follows: Figure 2 S22) includes: S221. Generate multiple sets of sine and cosine sequences based on the parameters of the sine wave superposition method.

[0044] Please see Figure 4 , Figure 4 This is a structural diagram of the time-division multiplexing shared oscillator in the channel coefficient generation module of the broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention.

[0045] After receiving the parameters for the sine wave superposition method, the channel coefficient generation module reuses the same oscillator core in the time-division multiplexing oscillator core module using a time-division multiplexing structure. It updates the phase accumulator sequentially using the oscillator index as the polling address, and inputs the accumulated phase into the sine wave generation unit (i.e., the sine and cosine lookup table) to generate the corresponding sine and cosine sequences. Finally, it serially generates 64 fundamental oscillator components in a time sequence. That is, the fundamental oscillator component. It is a sine and cosine sequence, including in-phase and quadrature components:

[0046]

[0047] .

[0048] in, These are components in the same direction. For orthogonal components, This represents a discrete-time index.

[0049] S222. Based on column permutation information, Walsh-Hadamard transform is used to achieve multipath expansion and obtain the complex fading coefficients of each multipath component.

[0050] Please see Figure 5 , Figure 5 The diagram shows the structure of the Walsh-Hadamard transform in the channel coefficient generation module of the broadband satellite communication multipath fading channel simulation system provided in this embodiment of the invention.

[0051] After receiving the Walsh-Hadamard column permutation information, the channel coefficient generation module, in the Walsh transform module of column permutation, calculates the coefficients based on each fundamental oscillator component. Component index Find the target column index using column permutation information. Then index the target column and each path. As input, the Walsh symbol coefficients corresponding to each path are calculated in real time based on the Walsh-Hadamard code generation rules. Finally, the fundamental oscillator components are sign-selected (either kept or negative) based on the Walsh sign coefficients, and the results are accumulated into the corresponding multipath accumulators using either addition or subtraction methods to obtain the complex fading coefficients of each multipath component. .

[0052] Specifically, the core basis of the Walsh-Hadamard transform is: the elements of the Walsh-Hadamard matrix. Take only And it satisfies strict orthogonality. Therefore, using Linear mixing of a set of basic components essentially involves "orthogonal projection / expansion" of the components using a set of mutually orthogonal symbol sequences without introducing multipliers, thereby forming multiple mutually distinguishable combined outputs. Due to the "energy dispersion and mutual cancellation" characteristics brought about by orthogonality, the symbol patterns corresponding to different paths are less likely to exhibit consistent superposition in a statistical sense, thus helping to reduce the correlation between different paths; simultaneously, because the coefficients are only... In hardware, this is equivalent to "addition / subtraction selection plus accumulation," which can significantly reduce the multiplication resources and logic complexity of FPGAs. Furthermore, introducing column permutation is equivalent to changing the order of the symbol sequence while maintaining the orthogonal basis, which can further suppress cross-correlation peaks and improve engineering usability.

[0053] S223, The channel coefficient generation module receives the gain parameters of each multipath component. Then, in the gain and linear interpolation module, the complex fading coefficients of each multipath component are multiplied by the corresponding gain parameters to obtain the weighted complex fading coefficients: ; in, The weighted complex fading coefficients are... The complex fading coefficients of each multipath component This is an index for the update time of the fading coefficients. This is the index for the multipath components.

[0054] Subsequently, to match the baseband data rate, a linear interpolation recursive approach is used for each complex coefficient between two adjacent update times: obtaining the complex fading coefficients at the endpoints. and Then, calculate the interpolation step size. ,in The interpolation factor is used, and recursion is performed based on the baseband sampling time within the update interval. , The fading channel coefficients generated by interpolation, for and The time indexes of the interpolation are used to generate the complex fading channel coefficients for each path synchronized with the baseband sampling. , This is the time index for the fading channel coefficients.

[0055] It should be noted that the in-phase components and quadrature components are processed in steps S222 and S223 respectively.

[0056] Please see Figure 6 , Figure 6This diagram illustrates the structure of the multipath delay module in the broadband satellite communication multipath fading channel simulation method provided in this embodiment of the invention. The multipath delay module includes a fractional delay module and an integer delay module. The fractional delay module receives the input baseband signal and filters it using a shared four-branch FIR sub-filter bank to obtain four intermediate results. For each path, the module performs a polynomial weighted combination of the four intermediate results based on the corresponding fractional delay parameters to obtain the fractional delay of each multipath component. The integer delay module writes the fractional delay to a memory and outputs the integer delay of each multipath component.

[0057] In a specific embodiment, the specific execution steps in the multipath delay module are as follows: Figure 2 S23 in the text includes: S231. Based on the fractional delay parameters of each multipath component, the fractional delay of each multipath component is obtained through a Farrow structure fractional delay filter.

[0058] Please see Figure 7 , Figure 7 This is a Farrow structure diagram of the fractional delay filter (Lagrange-cubic interpolation filter) in the simulation of multipath fading channels for broadband satellite communication provided in this embodiment of the invention. The multipath delay module receives the fractional delay parameters of each multipath component. and the input baseband signal The input baseband signal is filtered by a four-way branch FIR sub-filter bank shared by all paths, resulting in four intermediate filtering results: ; in, This is the intermediate filtering result. For the first Path filter tap coefficients This is the number of taps. For discrete-time sampling index, For filter tap index, The input baseband signal sequence.

[0059] Subsequently, based on the corresponding fractional delay parameters, a Farrow polynomial weighted combination is performed on the obtained four intermediate filtering results to generate the fractional delay output for that path. The weighted combination satisfies: ; in, For the first The fractional delay of each path, For fractional delay parameters polynomial weighting coefficients, Using Horner nested structure Evaluate to reduce the number of multipliers.

[0060] Furthermore, this step is based on fractional time delay filtering theory, where any non-integer sampling delay... The time-domain shift can be represented as the shift of the input sequence. With a group of random Variational interpolation filter The convolution, i.e.: ; in, Indicates the coefficient number of the Finite Impulse Response (FIR) filter.

[0061] Directly for each Generate a set of filter coefficients The cost is high, therefore adopting the Farrow structure will be more costly. The changing filter is decomposed into a fixed filter plus polynomial weights. Specifically, the variable filter is decomposed into a fixed filter plus polynomial weights. exist Used Polynomial approximation of order: ; in, To and Unrelated fixed coefficient sequences (i.e., the first) (tap coefficients of the FIR filter). These are polynomial weights that depend only on the fractional delay parameter. Substituting this expression into the convolution and swapping the order of summation yields the equivalent implementation of Farrow: ; ; Put The problem of updating the changed filter coefficients is transformed into updating with fixed FIR convolutions plus a small number of scalar weights, thus significantly reducing the complexity of real-time implementation. To further reduce the multiplication overhead of weight computation, the weights... It is usually expressed as The polynomial is evaluated using a Horner nested structure: ; in, , , , To construct the polynomial coefficients of the Farrow filter interpolation function, Denotes the coefficient of the cubic term. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. This represents the coefficient of the constant term.

[0062] This structure minimizes the number of multipliers required for polynomial computation to a linear minimum, facilitating pipelining and fixed-point implementation. Since the input is a complex baseband signal, the actual hardware requires performing the same sub-filtering and weighted combination (shared) on both the in-phase and quadrature components. and The calculation results ensure consistency between the two interpolation paths, preventing amplitude and phase mismatch from affecting subsequent multipath superposition and demodulation performance. Overall, the Farrow structure is theoretically equivalent to implementing an adjustable fractional delay filter. In engineering, a "fixed 4-channel FIR plus configurable weights" approach is used to balance interpolation accuracy and FPGA resource consumption.

[0063] The design and implementation process of the Farrow structure filter is as follows: For digital signals, fractional time delay requires the use of a fractional time delay filter, i.e., by obtaining an approximation. It is implemented using the unit impulse response function.

[0064] To obtain a continuous time signal Delay The ideal delay can be viewed as a linear function. The output of this function can be set to , can be represented as: ; After that exist Sampling is performed at all times, among which It is an integer. Given the sampling interval, the formula for continuous signal sampling can be obtained as follows: ; Here, D is a positive real number, which can be decomposed into an integer part and a fractional part. The fractional part needs to be implemented using a fractional delay filter: ; It can be seen that the ideal time-delay linear function can be regarded as an ideal digital filter. Input signal The signal is delayed by D after passing through this filter, thus obtaining the output signal. Digital filters It is also known as an ideal fractional delay filter. Its impulse response can be expressed as: ; Therefore, the frequency response expression of the system can be obtained as follows: ; in, It is the normalized angular frequency. From the integer part and fractional part composition, Therefore, the amplitude-frequency response and phase-frequency response of an ideal fractional delay filter can be expressed as follows: ; ; in, This represents the desired phase frequency response of an ideal fractional delay filter. The phase delay of an ideal fractional delay filter can be expressed as: ; The group delay function of an ideal fractional delay filter can be expressed as: ; When the system delay D is an integer, the impulse response function behaves as follows: For a single pulse at a given point, when D is not an integer, the impulse response function length becomes infinite. An ideal fractional delay filter is infinitely long and non-causal, making it impractical. Therefore, the design should consider using a realizable filter to approximate the characteristics of the ideal filter. That is, designing a realizable FIR filter... The approximation criterion is given.

[0065] Let the frequency response function of the actual designed fractional delay filter be... This makes it infinitely close to the frequency response function of an ideal fractional delay filter. Then the error function can be expressed as: ; The essence of Lagrange interpolation is to make the error function as flat as possible at a certain frequency point. Therefore, it is possible to perform frequency domain error interpolation. Find the derivative and locate a frequency point that makes it... If the first derivative is 0, the error function achieves optimal frequency approximation at that frequency point, thus ensuring maximum flatness within a certain range around that point. For the above error function at a certain frequency point... conduct The derivative of the first order is given by the following formula: ; This is generally set In other words, the goal is to maintain maximum flatness within the frequency range of 0. At this point, in... Seeking The second derivative yields... The set of linear equations, expressed in the form of impulse responses, are as follows: ; Expressed in matrix form as follows: ; in, , Indicates that the solution is yet to be found. First-order FIR filter impulse response coefficient vector , Indicates that the delay amount is included. Power-order constraint vector .

[0066] Given a set of numerical values, the coefficients of V can be obtained using polynomial interpolation. The solution process is the same as solving the classical Lagrange interpolation formula. In the z-domain, we have... ; For a fixed integer time delay, the error function tends to zero, and the obtained filter coefficients... for: .

[0067] These coefficients are the filter coefficients obtained using the Lagrange interpolation method.

[0068] The transfer function of a filter is defined as: ; in, Describe the complex variable of the Z-transform. This represents the fractional time delay parameter (corresponding to the delay variable in the Lagrange interpolation formula). ), This represents the nth filter tap coefficient, calculated using the Lagrange interpolation formula. Using of Using polynomials of order 1 to approximate filter coefficients ,Right now ; coefficients Bring into We can obtain: ; in, It can be viewed as the transfer function of a sub-filter. .

[0069] Analyzing the above equation, we can obtain the filter's transfer function. It can be regarded as Each filter bank output and a fractional delay The weighted sum. This is generally referred to as a weighted sum. Group Sub-filter and The structure consisting of fractional time-delay multipliers is called the Farrow structure. Each coefficient in the Farrow structure is... The polynomial is constructed, and the polynomial depends on the time delay parameter. .

[0070] Farrow structure as follows Figure 7 As shown, Figure 7 middle The coefficient matrix of the Farrow structure, representing the delay at one sampling point, is set as follows: .

[0071] S232, The multipath delay module receives the integer delay parameters of each multipath component. and fractional delay Then, in the integer delay module, based on the integer delay parameters of each multipath component... Delay the score Write to RAM and according to integer delay parameters Input data is read out with a delay to achieve integer time delay, thus obtaining the integer time delay of each multipath component. .

[0072] It should be noted that the in-phase and quadrature components of the logarithmic baseband signal are processed using steps S231 and S232, respectively.

[0073] In one specific embodiment, please refer to Figure 8 , Figure 8 This is a hardware structure diagram of the multipath overlay module in a broadband satellite communication multipath fading channel simulation system provided in an embodiment of the present invention. Specific execution steps within the multipath overlay module ( Figure 2 S24 in the text specifically includes the following steps: S241, The complex fading channel coefficients of each path received by the multipath superposition module during baseband sampling synchronization. Baseband signal delay output of each multipath component For each path The baseband signal delay output of this path is multiplied by the corresponding complex fading coefficient to obtain the weighted component of this path, as follows: ; in, For the first The weighted components of the path.

[0074] S242. Input the weighted components of each path component into a hierarchical addition tree for summation, and perform complex accumulation level by level to obtain the multipath superimposed signal: ; Each adder performs addition operations on the weighted components of the in-phase components and the weighted components of the quadrature components. Pipeline registers are set between each adder stage to store and synchronize the intermediate summation results step by step to meet the timing requirements of the target clock frequency.

[0075] It is understandable that S241 and S242 are executed on the in-phase component and the quadrature component respectively, and finally the complex baseband signal after multipath superposition is composed of the multipath superposition signal of the in-phase component and the multipath superposition signal of the quadrature component.

[0076] The working principle of the low-complexity broadband satellite communication multipath fading channel simulation system in this embodiment is as follows: The host computer parameter configuration module transmits the parameters used to generate time-varying fading coefficients using the sine wave superposition method, the integer delay parameters of each multipath component, the fractional delay parameters of each multipath component, the gain parameters of each multipath component, and column permutation information to the parameter processing module. The parameter processing module then distributes these parameters to each functional module. The channel coefficient generation module generates time-varying channel coefficients corresponding to the satellite multipath fading channel. The channel coefficient generation module uses a time-division multiplexing structure to generate multiple sets of sine / cosine sequences based on the sine wave superposition method parameters on a shared oscillator core, and utilizes Walsh... The Hadamard transform is used to extend the multipath to obtain the complex fading coefficients of each multipath component, thereby reducing the resource consumption of multipliers and lookup tables. The complex fading coefficients are interpolated to match the data rate of the signal to be processed. The multipath delay module is used to apply configurable multipath delays to each multipath component, where the multipath delay consists of integer multiple sampling delays and fractional multiple sampling delays. The fractional multiple sampling delay is implemented through a Farrow structure fractional delay filter. The Farrow fractional delay structure uses the same set of FIR filter banks and Horner polynomial evaluation structure to optimize resource consumption. The integer multiple sampling delay is implemented through FPGA on-board storage resources. The multipath superposition module is used to multiply and accumulate the delay signals of each path output by the multipath delay module with the corresponding complex fading coefficients output by the channel coefficient generation module to synthesize the final multipath fading channel output signal.

[0077] This invention innovatively introduces an offline column permutation mapping mechanism based on the Walsh transform. By globally optimizing and fixing the optimal column permutation parameters, it effectively suppresses the cross-correlation peak under dynamic windows, compensating for the shortcomings of the standard Walsh transform in non-steady-state scenarios. This invention abandons the traditional multi-oscillator parallel architecture, adopting a time-division multiplexing (TDM) structure with a single oscillator core. Combined with the mathematical characteristic of the Walsh-Hadamard transform, which only requires addition and subtraction operations, it eliminates the need for large-scale matrix multiplication hardware. Compared with existing technologies, the number of independent fading paths that can be simulated with the same FPGA resources is significantly increased, meeting the high channel density requirements of broadband satellite channel simulation.

[0078] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A low-complexity broadband satellite communication multipath fading channel simulation system, characterized in that, include: The host computer parameter configuration module and the FPGA processing module, among which, The host computer parameter configuration module is used to generate and send multipath fading channel parameter information according to the preset path channel scenario; the multipath fading channel parameter information includes sine wave superposition method parameters, integer delay parameters of each multipath component, fractional delay parameters of each multipath component, gain parameters of each multipath component, and column permutation information. The FPGA processing module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core using a time-division multiplexing structure based on the parameters of the sine wave superposition method. It then uses the Walsh-Hadamard transform based on column permutation information to achieve multipath expansion and obtain the complex fading coefficients of each multipath component. Interpolation is performed on the complex fading coefficients to obtain the fading channel coefficients of each multipath component. Finally, based on the fractional delay parameters of each multipath component, the fractional delay of each multipath component is obtained through a Farrow structure fractional delay filter. Based on the integer delay parameters of each multipath component, the integer delay of each multipath component is obtained through the onboard storage resources of the FPGA; the fading channel coefficient of each multipath component and the integer delay of each multipath component are multiplied and accumulated to obtain the multipath fading channel output signal.

2. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 1, characterized in that, The FPGA processing module includes a parameter processing module, a channel coefficient generation module, a multipath delay module, and a multipath superposition module. The parameter processing module is used to parse and cache the multipath fading channel parameter information, and allocate the sine wave superposition method parameters, the gain parameters of each multipath component and the column permutation information to the channel coefficient generation module, and allocate the integer delay parameters of each multipath component and the fractional delay parameters of each multipath component to the multipath delay module. The channel coefficient generation module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core using a time-division multiplexing structure based on the parameters of the sine superposition method. Combined with the column permutation information, the module uses Walsh-Hadamard transform to obtain the complex fading coefficients of each multipath component. The module then multiplies the complex fading coefficients of each multipath component with the corresponding gain parameters and performs interpolation to output the fading channel coefficients of each multipath component. The multipath delay module is used to filter the input baseband signal using a four-branch FIR sub-filter bank shared by each path, obtaining four intermediate results; for each multipath component, the four intermediate results are weighted by a Farrow architecture polynomial according to the corresponding fractional delay parameter to obtain the fractional delay of each multipath component; the fractional delay is written into the memory and the integer delay of each multipath component is output according to the integer delay parameter of each multipath component; The multipath superposition module is used to multiply and sum the fading channel coefficients of each multipath component and the integer delay of each multipath component to obtain the multipath fading channel output signal.

3. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 2, characterized in that, The parameters of the sinusoidal superposition method are expressed as follows: , , and ,in, , , and They are independent of each other, and The distribution within the range is uniform. The number of oscillators. For the maximum Doppler frequency shift, The sampling period is Sampling rate, Index of the basic oscillator; The integer time delay parameters of each multipath component are expressed as follows: ,in, For integer delay parameters, , For the first Total delay of the multipath components, It is a set of non-negative integers; The fractional delay parameters of each multipath component are expressed as follows: ,in, For fractional delay parameters, ; The gain parameters of each multipath component are expressed as follows: ,in, These are the gain parameters for each multipath component. For the first The linear power of the multipath components, , For the first Path power parameters of the multipath components; The column permutation information is generated as follows: The column permutation vector P is constructed as follows: ,in, And each element is distinct. The order of the Walsh-Hadamard transform; Using the dynamic window as a constraint, establish the objective function for column permutation optimization: ,in, , For each path in the multipath, The relative time offset between two different paths. For window coefficients, For coherent time, The cross-correlation function measures the cross-correlation between two different paths with an offset of . The similarity between the two positions in the permutation vector is calculated; in each iteration, the column indices of two positions in the permutation vector are swapped or replaced, and the updated objective function is calculated. , and when If the value decreases, the update is accepted until the preset number of iterations or the convergence condition is met. The final column permutation vector obtained from the update is then processed. This serves as the column replacement information.

4. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 3, characterized in that, The channel coefficient generation module includes a time-division multiplexing oscillator core module, a column permutation Walsh transform module, and a gain and linear interpolation module, wherein... The time-division multiplexing oscillator core module is used to generate multiple sets of sine and cosine sequences on a shared oscillator core based on the parameters of the sine wave superposition method using a time-division multiplexing structure; The Walsh transform module of the column permutation is used to combine the column permutation information and use the Walsh Hadamard transform to obtain the complex fading coefficients of each multipath component; The gain and linear interpolation module is used to multiply the complex fading coefficient of each multipath component with the corresponding gain parameter and then interpolate to output the fading channel coefficient of each multipath component.

5. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 4, characterized in that, The time-division multiplexing oscillator core module is specifically used for: A time-division multiplexing structure is used to reuse the same oscillator core. The phase accumulator is updated sequentially using the oscillator index as the polling address. The accumulated phase is then input into the sine wave generation unit to generate the corresponding sine and cosine sequences. Finally, 64 basic oscillator components are generated serially in time sequence. The basic oscillator components include in-phase components and quadrature components. in, These are components in the same direction. For orthogonal components, Indicates a discrete-time index; The Walsh transform module for column permutation is specifically used for: Based on the component index of each fundamental oscillator component The target column index is obtained using the column replacement information. ; Using the target column index and each path index As input, the Walsh symbol coefficients corresponding to each path are calculated in real time based on the Walsh-Hadamard code generation rules. ; The fundamental oscillator components are sign-selected according to the Walsh sign coefficients, and the results are accumulated into the corresponding multipath accumulators in either an additive or subtractive manner to obtain the complex fading coefficients of each multipath component. The gain and linear interpolation module is specifically used for: Multiplying the complex fading coefficients of each multipath component by their corresponding gain parameters yields the weighted complex fading coefficients: in, The weighted complex fading coefficient is... Here are the complex fading coefficients for each multipath component. This is an index for the update time of the fading coefficients. Index for multipath components; Based on the complex fading coefficient at the endpoint and Calculate the interpolation step size And perform recursion according to the baseband sampling time within the update interval. The fading channel coefficients of each multipath component are generated in sync with the baseband sampling. ,in, The interpolation factor. The fading channel coefficients generated by interpolation, for and The time index for interpolation between them This is the time index for the fading channel coefficients.

6. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 2, characterized in that, The multipath delay module includes a fractional delay module and an integer delay module, wherein, The fractional delay module is used to filter the input baseband signal by a four-way branch FIR sub-filter group shared by each path to obtain four intermediate results; for each path, the four intermediate results are combined by polynomial weighting according to the corresponding fractional delay parameters to obtain the fractional delay of each multipath component. The integer delay module is used to write the fractional delay into the memory and output the integer delay of each multipath component.

7. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 6, characterized in that, The fractional delay module is specifically used for: The input baseband signal is filtered by a four-path branch FIR sub-filter bank shared by all paths, resulting in four intermediate filtering results: in, This is the intermediate filtering result. For the first Path filter tap coefficients This is the number of taps. For discrete-time sampling index, For filter tap index, The input baseband signal sequence; Based on the corresponding fractional delay parameters, the four intermediate filtering results are subjected to Farrow polynomial weighted combination to generate the fractional delay of each multipath component: in, For the first The fractional delay of each path, For fractional delay parameters The polynomial weighting coefficients, Using Horner nested structure Evaluate: , , , , To construct the polynomial coefficients of the Farrow filter interpolation function, Denotes the coefficient of the cubic term. Denotes the coefficient of the quadratic term. Denotes the coefficient of the linear term. Indicates the coefficient of the constant term; The integer delay module is specifically used for: The fractional delay is written into the memory, and based on the integer delay parameters... The input data is read out with a delay to obtain the integer delay of each multipath component. .

8. The low-complexity broadband satellite communication multipath fading channel simulation system according to claim 2, characterized in that, The multipath superposition module is specifically used for: For each path, calculate the fading channel coefficients for that path. and the integer delay of each corresponding multipath component Perform complex multiplication to obtain the weighted components of the path: in, For the first The weighted components of the path, For discrete-time sampling index, The time index for the fading channel coefficients; The weighted components of each path are input into a hierarchical addition tree for summation, and the complex summation is completed level by level to obtain the multipath superimposed signal: Each adder performs addition operations on the weighted components of the in-phase components and the weighted components of the quadrature components respectively. Pipeline registers are set between each adder to store and synchronize the intermediate summation results step by step. The complex baseband signal is composed of the multipath superposition signals of in-phase components and the multipath superposition signals of quadrature components.

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