## 6 Numerical Results
### Performance in the Symmetric Networks
Error rate is not the only performance measure of the system, and we also evaluate the schemes from the perspective of minimal received SINR, which represents the performance of the worst data stream. If the minimal received SINR is too low, the communications of some users might be terminated. Therefore, it is important to guarantee the minimal received SINR so that all the users in the network can transmit data normally. The average minimal received SINR of different schemes are compared in Figures 7 and 8 for the (4 \(\times\) 4, 1)\({}^{20}\) and (6 \(\times\) 6, 2)\({}^{18}\) symmetric networks, respectively. For the (4 \(\times\) 4, 1)\({}^{20}\) network in Figure 7, the minimal received SINR of the conventional IA system increases slowly with the raise in \(E_{b}/N_{0}\), and ranges only from \(-\)6 to \(-\)3 dB, implying that the worst data stream is suffering from strong interference and the communication of the corresponding user is likely to be terminated. On the contrary, the JSCC-IA scheme with identical propagation delay can achieve much higher minimal received SINR, and can reach the value of 17 dB at \(E_{b}/N_{0}\) = 14 dB. When different propagation delays are considered, the JSCC-IA scheme might be degraded in the high \(E_{b}/N_{0}\) regimes, and cannot reach such a high level as the one with the same delay. In spite of this, it still exhibits much better minimal received SINR than the conventional IA system, with as much as 9 dB higher minimal received SINR than the traditional IA system at \(E_{b}/N_{0}\) = 14 dB. For the multi-data-stream scenario of (6 \(\times\) 6, 2)\({}^{18}\) in Figure 8, similar performances can be observed. Considering the \(E_{b}/N_{0}\) of 14 dB, the JSCC-IA scheme shows implicit advantage over the conventional IA system, with 23 and 10 dB higher minimal SINR than the traditional one in the cases of identical and different propagation delays, respectively. Therefore, the JSCC-IA scheme can enhance the minimal SINR, and thus reduce the outage probability in the large-scale WSNs. Figure 6: The average experimental BER performances of the conventional IA scheme and the JSCC-IA schemes with identical/different propagation delays in the (6 \(\times\) 6, 2)\({}^{18}\) symmetric networks. Although the minimal received SINR provides us the measure of the performance of the worst data stream, it does not present further details on the other streams. Therefore, we introduce the average received SINR among all the data streams to further evaluate the overall performance thoroughly in Figures 9 and 10. For the (4 \(\times\) 4, 1)\({}^{20}\) network in Figure 9, the performance of the conventional IA scheme is poor, only ranging from the value of \(-\)3 to 0 dB from the _Eb/N\({}_{0}\)_ of \(-\)10 to 14 dB. Therefore, most of the users in the traditional IA system are suffering from strong interference, and might fail to communicate normally under such a low received SINR level. Figure 8: The average minimal received SINR of the conventional IA scheme and the JSCC-IA schemes with identical/different propagation delays in the (6 \(\times\) 6, 2)\({}^{18}\) symmetric networks. Figure 7: The average minimal received SINR of the conventional IA scheme and the JSCC-IA schemes with identical/different propagation delays in the (4 \(\times\) 4, 1)\({}^{20}\) symmetric networks. However, the JSCC-IA scheme can achieve higher average received SINR, especially in the high \(E_{b}\)/\(N_{0}\) regimes. For instance, given \(E_{b}\)/\(N_{0}\) = 14 dB, the average received SINR of the conventional IA scheme, the JSCC-IA scheme with identical propagation delay and the JSCC-IA scheme with different propagation delays is 0 dB, 21 dB and 11 dB, respectively. For the (6 \(\times\) 6, 2)\({}^{18}\) network in Figure 10, the performance of the conventional IA system becomes even poorer due to the larger number of total data streams, and the best average received SINR is only \(-\)1 dB at \(E_{b}\)/\(N_{0}\) = 14 dB, indicating that the communication might be terminated.