# Adaptive Rate-Compatible Non-Binary LDPC Coding Scheme for the B5G Mobile System
## 4 Design and Performance Simulation of the Adaptive RC-NB-LDPC Coding Scheme
### Design and Performance Simulation of the Adaptive RC-LDPC Coding Scheme
#### 2.2.3 Reconstructed image quality simulation  
In this paper, we select the \"Lena\" 512 \(\times\) 512 grayscale image as the test image. The source-coding method is the SPIIHT algorithm, the channel-coding method is rate-compatible LDPC code, and the channel model is the AWGN channel. We select three different channel conditions as test conditions. The specific parameters of the channel are shown in Table 5.  
We performed a performance analysis comparison of the following three transmission schemes:  
* Scheme 1, the fixed-rate transmission scheme. That is, the channel coding uses a fixed code rate of 3/4 for three types of test channels in this paper. * Scheme 2, the adaptive-rate transmission scheme. That is, after channel clustering, the corresponding rate is selected for each type of test channel. Corresponding to three types of test channels, the coding rates used in this paper are 1/2, 4/5, and 7/8, respectively. * Scheme 3, the adaptive-rate transmission scheme with UEP. According to different parts of the code stream that have different effects on image recovery, we adopt different levels of the channel protection mechanism, that is, the high-level protection for the important code stream and the low-level protection for the secondary code stream. Corresponding to the three types of test channels, the coding rate groups in this paper are (1/2, 3/4), (2/3, 5/6) and (3/4, 7/8), respectively. The scheme affects the different degrees of the restored image according to different parts of the code stream, adopts different levels of channel protection mechanisms, protects the important code stream to a high degree, and protects the secondary code stream to a low degree to achieve different degrees of differentiation. In this paper, the PSNR of the reconstructed image is chosen as the criterion for evaluating image quality. The simulation results are shown in Table 6. The \"fail\" in the table indicates that the decoding is unsuccessful or the reconstructed image quality is extremely poor due to severe error. In order to ensure the correctness of the results, we repeat the transmission process 50 times and take the average result. As shown in Table 6, with the fixed bit rate scheme, in the case of poor channel conditions, a decoding failure occurs. This is because the fixed bit rate employed does not provide sufficient channel protection under poor conditions. For image compression streams, if the error occurs at a critical location and there is no error retransmission or other means of recovery, it will result in decoding failure or poor reconstructed image quality. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Compression Ratio**} & \multirow{2}{*}{**Test Schemes**} & \multicolumn{3}{c}{**PSNR (dB)**} \\ \cline{3-5}  & & **Class1** & **Class2** & **Class3** \\ \hline \multirow{4}{*}{1} & Scheme 1 & Fail & 33.53 & 35.94 \\  & Scheme 2 & 31.79 & 35.24 & 37.68 \\  & Scheme 3 & 32.38 & 35.75 & 38.23 \\ \hline \multirow{4}{*}{0.5} & Scheme 1 & Fail & 30.71 & 32.77 \\  & Scheme 2 & 28.86 & 32.47 & 34.64 \\  & Scheme 3 & 29.33 & 32.91 & 35.14 \\ \hline \multirow{4}{*}{0.1} & Scheme 1 & Fail & 27.82 & 29.24 \\  & Scheme 2 & 27.26 & 29.01 & 29.32 \\ \cline{1-1}  & Scheme 3 & 27.68 & 29.28 & 29.32 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Reconstructed image PSNR for different schemes. \begin{table}
\begin{tabular}{l l} \hline \hline \multirow{2}{*}{**Channel Types**} & \multicolumn{2}{c}{**Test Parameters**} \\  & \multicolumn{1}{c}{[\(\mathbf{E_{b}/N_{0}}\), Bandwidth]} \\ \hline Class 1 & [2.2, 2500 KHz] \\ Class 2 & [2.8, 4500 KHz] \\ Class 3 & [3.5, 6500 KHz] \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Test channel parameter. It can also be seen that compared to scheme 1, scheme 2 achieves an average gain of about 2 dB. The reason is that scheme 2 adopts different code rates according to different channel conditions. When the channel condition is poor, low code rate coding is used to enhance channel protection.