# Semantic Communication on Digital Wireless Communication Systems
## 4 Optimization for the Bit-Conversion JSCC Scheme
### Hybrid JSCC/SSCC Transmission Scheme
At the same time, the JSCC/SSCC hybrid transmission scheme demonstrates approximately twice the spectrum efficiency of the SSCC-QPSK scheme, comparable to the SSCC-16 QAM scheme, as shown in Figure 17d. **Simulation verification-2. **  
The simulation configurations comparing the hybrid JSCC-SSCC transmission scheme with the bit-conversion JSCC scheme are shown in Table 5. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Case** & **Modulation** & **Binary Codec** & **Channel Coding** \\ \hline Hybrid JSCC/SSCC transmission &
\begin{tabular}{c} QPSK \\ (1/3 data) \\ \end{tabular} & natural binary coding & LDPC (CR = 0.5) \\ \cline{2-4} (QPSK + 16 QAM) & 16 QAM & Manhattan distance & NO \\ \cline{2-4} SSCC-QPSK & QPSK & natural binary coding & LDPC (CR = 0.5) \\ \hline SSCC-16 QAM & 16 QAM & natural binary coding & LDPC (CR = 0.5) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation configurations for hybrid scheme vs. SSCC scheme. Figure 17: Simulation result of hybrid JSCC/SSCC vs. SSCC. (**a**) BER vs. SNR; (**b**) IER vs. SNR; (**c**) PSNR vs. SNR; (**d**) spectrum efficiency. The simulation result is shown in Figure 18. It can be observed that the BER of the hybrid JSCC/SSCC transmission scheme is better than the JSCC 16 qam and worse than the JSCC-QPSK. In terms of IER metrics, the hybrid JSCC/SSCC transmission scheme demonstrates a great improvement and performs better than the JSCC-QPSK scheme. Finally, the hybrid JSCC/SSCC transmission scheme outperforms the JSCC-QPSK scheme in terms of the PSNR, with a performance gain of 3-5 dB in an SNR range of [0; 0; 10; 5], as shown in Figure 18c. At same time, the hybrid JSCC/SSCC transmission scheme has the same spectrum efficiency as the JSCC-QPSK scheme, as shown in Figure 18d. Based on the simulation above, it is evident that the hybrid JSCC/SSCC transmission scheme can resolve the issue that the quantization output range of semantic encoding has to be bound to the modulation order. Additionally, within the SNR range of [0; 0; 10; 5], the semantic transmission performance is comparable to the SSCC-QPSK scheme, and the spectrum efficiency of this hybrid JSCC/SSCC scheme is twice that of the SSCC-QPSK scheme. It still maintains the advantage of the JSCC scheme in terms of bandwidth conservation. This  
Figure 18: Simulation result of hybrid JSCC/SSCC vs. JSCC. (**a**) BER vs. SNR; (**b**) IER vs. SNR; (**c**) PSNR vs. SNR; (**d**) spectrum efficiency. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Test Case** & **Modulation** & **Binary Codec** & \
\begin{tabular}{c} **Channel** \\ **Coding** \\ \end{tabular} \\ \hline Hybrid JSCC/SSCC transmission (QPSK + 16 QAM) &
\begin{tabular}{c} QPSK \\ (1/3 data) \\ \end{tabular} & natural binary coding & LDPC(CR = 0.5) \\ \cline{2-4}  & 16 QAM & Manhattan distance & NO \\ \cline{2-4}  & (2/3 data) & binary coding & NO \\ \hline JSCC-QPSK & QPSK & natural binary coding & NO \\ \hline JSCC-16 QAM & 16 QAM & natural binary coding & NO \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Simulation configurations for hybrid scheme vs. JSCC scheme. indicates that this hybrid JSCC/SSCC scheme has specific application scenarios, especially for semantic imaging transmission in lower SNR scenarios.