[MATLAB] RFID ASK modulation based on S-function

Table of contents

Call user-defined S-Function.m file in MATLAB code

Write S-function to realize ASK modulation

Write S-function source files using MATLAB language

Calling S-functions in Simulink

---

Call user-defined S-Function.m file in MATLAB code

1. Add the S-Function.m file to the MATLAB search path.

a. Use the addpath function in the MATLAB command window to add the directory where the S-Function.m file is located to the MATLAB search path. For example: addpath('C:\MySfuncFolder')

b. Folder paths can be added to the MATLAB search path. Under the MATLAB window, click Set Path, then select Add Folder to add the folder where the S-Function.m file is located to the search path.

2. Use the s-function constructor in MATLAB code to create an S-function object and set the input, output, and parameter properties. For example:

s = sfunction('mySfunc');
s.InputPortWidth = 1;
s.InputPort(1).DatatypeID = 0;
s.OutputPortWidth = 1;
s.OutputPort(1).DatatypeID = 0;
s.NumDialogPrms = 0;

This will create an S-function object called "mySfunc" and set the datatype and width properties for the input and output ports.

3. Call the set function to set the input port data of the S-Function object. For example:

set(s, 'Inputs', {1});

This will set an input port data of the S-function object to 1.

4. Call the evaluate function to run the S-Function object and obtain the output result. For example:

y = evaluate(s);
disp(y);

This will run the S-function object and get the output y, and print the output in the command window.

It should be noted that the S-Function.m file needs to follow a specific S-Function interface specification, including input and output parameters and execution functions. Developers need to understand how to write or use S-function codes, and implement S-function interfaces according to the specifications. When calling S-Function.m in MATLAB, you need to create an S-Function object and set related properties, and then run the evaluate function to obtain the output result.

Write S-function to realize ASK modulation

1. Create an S-function template. S-functions can be created using the S-function template provided by MATLAB. Enter the following code in the MATLAB command window to create a basic S-function template:

sfcn_template

2. Write the S-function function.

a. Open the generated S-function source file (sfun_template.c), and ASK modulation can be implemented in the S-function function.

b. Define the input, output, and parameters in the S-function function to get the input data from the Simulink model, execute the ASK modulation algorithm, and return the output data to the model.

c. Realize the output function of the S-function function, where ASK modulation can be performed. For example:

static void mdlOutputs(SimStruct *S, int_T tid) {
    double *y = (double *)ssGetOutputPortSignal(S, 0);
    double *u = (double *)ssGetInputPortSignal(S, 0);
    double fc = *mxGetPr(ssGetSFcnParam(S,0));
    double f = 2.0*M_PI*fc;
    int_T i;
    for (i=0; i < ssGetOutputPortWidth(S,0); i++) {
        if (u[i] == 0) {
            y[i] = sin(0);
        } else {
            y[i] = sin(f*(double)tid*u[i]);
        }
    }
}

In the above code, the carrier frequency (fc) is first obtained from the S-function parameter, and then the frequency (f) of the modulating wave is calculated. Next, use a for loop to iterate through each sample, and apply the ASK modulation algorithm.

3. Compile the S-function file into a binary file. In the MATLAB command window, use the mex command to compile the S-function file. For example: mex sfun_template.c This will generate a binary file sfun_template.mexw64 or sfun_template.mexa64 (depending on your system architecture) in the current working directory.

4. Use S-functions in Simulink models. In the Simulink model, drag and drop the S-Function block into the model, and set the required parameters such as carrier frequency in the parameters.

5. Connect the input, output and parameter signals. Use the Connector tool to connect the required signals to the S-Function block.

6. Model run and validation. Start a model simulation and verify the output.

It should be noted that writing S-function requires basic knowledge of MATLAB-Simulink and C programming, as well as the interface specifications required by S-function. You can refer to the official documentation and examples of MATLAB to learn how to write S-function. This example is just a simple example and cannot be fully applied to all ASK modulation requirements.

Write S-function source files using MATLAB language

1. Create an S-function template.

a. In the command line window, type the following command to create a basic S-function template:

sfcnnew

b. Select the "MATLAB S-Function" template, and enter the S-function name and path. Then click the "Create" button to generate the S-function template.

2. Write the S-function function.

a. Open the generated S-function source file (such as mySfunc.m) in MATLAB Editor, and define the input, output and parameters in the S-function function.

b. Implement ASK modulation in the S-Function. For example:

function mySfunc(block) 
    setup(block);

function setup(block) 
    block.NumInputPorts = 1;
    block.NumOutputPorts = 1;
    block.InputPort(1).Dimensions = 1;
    block.InputPort(1).DirectFeedthrough = false;
    block.OutputPort(1).Dimensions = 1;
    block.OutputPort(1).SamplingMode = 'sample';
    block.SampleTimes = [-1 0];
    block.NumDialogPrms = 1; %载波频率
    fc = block.DialogPrm(1).Data; assignin('base', 'fc', fc);
    block.RegBlockMethod('Outputs', @Outputs);

function Outputs(block) 
    u = block.InputPort(1).Data;
    time = block.CurrentTime;
    f = 2.0 * pi * evalin('base', 'fc');
    if (u == 0) { 
        y = sin(0); 
    } else { 
        y = sin(f * time * u); 
    }
    block.OutputPort(1).Data = y;

In the above code, we set the properties of the input, output and parameters in the setup method function of the S-function, and read the carrier frequency in the template parameters. In the Outputs method function, we read the binary input from the input port u, calculate the output of the ASK modulation, and write the output result to the output port y.

The following is a basic ASK S-function written in MATLAB. It has three input parameters, namely digital signal, high-level sine and low-level sine.

function [sys,x0,str,ts] = ask_sfun(t,x,u,flag)
% ASK S-Function函数
% 输入参数：
% t: 时间向量
% x: 状态向量（这里为空）
% u: 输入向量，包含数字信号，高电平正弦和低电平正弦
% flag: 状态标识符，用于指定函数的操作模式

switch flag,
    case 0 % 初始化
        [sys,x0,str,ts] = mdlInitializeSizes();
    case 2 % 更新状态
        sys = mdlUpdate(t,x,u);
    case 3 % 输出结果
        sys = mdlOutputs(t,x,u);
    case {1,4,9} % 不使用的标识符
        sys = [];
    otherwise % 错误处理
        error(['Unhandled flag = ',num2str(flag)]);
end

function [sys,x0,str,ts] = mdlInitializeSizes()
% 初始化函数
% 设置函数的输入和输出数量、样本时间等信息

% 设置结构体
sizes = simsizes;
sizes.NumContStates  = 0; % 连续状态数量为0
sizes.NumDiscStates  = 0; % 离散状态数量为0
sizes.NumOutputs     = 1; % 输出数量为1
sizes.NumInputs      = 3; % 输入数量为3
sizes.DirFeedthrough = 1; % 有直接通道
sizes.NumSampleTimes = 1; % 样本时间数量为1

% 指定样本时间
ts = [0 0];

% 初始化状态向量
x0 = [];

% 设置函数名
str = ['ask_sfun'];

% 返回结构体
sys = simsizes(sizes);

function sys = mdlUpdate(t,x,u)
% 更新函数
% 这里不需要进行状态更新，直接返回空向量

% 返回空向量
sys = [];

function sys = mdlOutputs(t,x,u)
% 输出函数
% 计算ASK信号

% 获取输入参数
f_high = u(2); % 高电平正弦频率
f_low = u(3); % 低电平正弦频率
digital_signal = u(1); % 数字信号
t_sample = t(1); % 当前样本时间
t_symbol = t_sample:1/f_high:t_sample+1/f_high; % 符号时间

% 根据数字信号选择高电平正弦或低电平正弦
if digital_signal == 1 % 数字信号为1，选择高电平正弦
    output_signal = sin(2*pi*f_high*t_symbol);
else % 数字信号为0，选择低电平正弦
    output_signal = sin(2*pi*f_low*t_symbol);
end

% 返回ASK信号
sys = output_signal;

Calling S-functions in Simulink

1. Open the Simulink model, click the "Library Browser" button in the "Model Navigator".

2. In the "Library Browser", find the "S-Function" library under the "Simulink" directory on the left, and expand it.

3. Select an S-function block in the "S-Function" library and drag it into the editor window.

4. Enter the parameters of the S-function in the "S-Function Builder" dialog box, and click the "OK" button.

5. Set the input and output ports of the S-function in the module parameters.

6. Realize the calculation logic and interface of the S-function in the S-function code file.

7. Click the Simulate button in the Model Navigator to run the model. In this way, Simulink can call the S-function and complete the simulation task according to the defined calculation logic.

Note that the S-function may need to be written in C or C++ language, and you need to be familiar with the use of related programming languages ​​and Simulink.