# SPACNet: A Simulation Platform of an Acoustic Cognitive Network
## 3 Multinode UAC Module
### Simplified Collision Model  
In a large multinode UACNs simulation, to reduce the computing complexity and improve the simulation efficiency of SPACNet, the data transmission results should be calculated in advance based on the simplified model and fed back to the node model in the form of a table lookup. The actual process of signal conflict in the UACNs can be restored to the greatest extent by using the above method; however, it was found that the computation workload is large and the simulation runs slowly. To improve simulation efficiency further, the underwater acoustic signal transmission module was simplified to reduce invalid and repetitive calculations. To avoid invalid calculations, a simplified model is used to distinguish the valid transmission range and interference range of nodes. In Figure 6, notation \(R_{1}\) denotes the valid transmission range, and the destination node can receive the data packet successfully and recover the data information accurately within the \(R_{1}\) range. The black full line denotes the connection between two nodes. Notation \(R_{2}\) denotes the interference range, which may affect the normal communication of other nodes during data transmission. The black dashed line denotes the connection between two nodes. Further, the interference interval is the nonoverlapping part of the interference range and the valid transmission range, which is the teal area in Figure 6. Nodes within this range can receive signals from the transmitting node and have the opportunity to successfully demodulate data information, and signals from transmitting nodes will cause interference to the communication of nodes within this area. Hence, for a received node, there is no need to consider the transmitted node if the distance between the transmitted node and the received node is far enough  
Figure 5: Collision model of SPACNet. to exceed \(R_{2}\). For example, in Figure 6, nodes four and five do not need to be considered when dealing with the received signals of node one. As we know, in the P2P model, the data can be successfully demodulated if the minimum signal-to-noise (SNR) of the received signals is higher than the detection threshold, which is satisfied by Equation (10):  
\[DT>SL-TL-NL\, \tag{10}\]  
where \(DT\), \(SL\), \(TL\), and \(NL\) are the detection threshold, sound level, transmission loss, and noise level, respectively. Notation \(DT\) is based on the physical layer. To account for other node interference in the network, Equation (10) can be rewritten as:  
\[DT>SL-TL-NL-IL\, \tag{11}\]  
where \(IL\) is the interference level, which is the sum of the interference levels of all nodes. Notation \(IL\) can be defined as:  
\[IL_{i}=\sum_{j=1,j\
eq i}^{N}IL_{j}\, \tag{12}\]  
where the interference level of one node can be defined as:  
\[IL_{j}(r)=SL_{j}-TL_{j}(r)-NL. \tag{13}\]  
According to the P2P transmitted model [35], \(TL\) can be written as:  
\[TL(r)=n\times 10\lg(r)+\alpha r\, \tag{14}\]  
where \(r\) is the propagation distance and the value \(n\) is determined by extended propagation conditions. And \(\alpha\) is the absorptivity, which can be written as:  
\[\alpha\simeq 3.3\times 10^{-3}+\frac{0.11f^{2}}{1+f^{2}}+\frac{44f^{2}}{4100 +f^{2}}+3.0\times 10^{-4}f^{2}(dB/km)\, \tag{15}\]  
To obtain the farthest interference distance \(R_{2}\), the farthest from \(R_{2}\) interference is considered \(NL\), which means \(IL=0\). It is obtained by Equation (13) as:  
\[TL(R_{2})=SL-NL. \tag{16}\]  
Figure 6: Schematic diagram of node transmission range and interference range. By combining Equation (14) and Equation (16), the value of \(R_{2}\) is obtained by Equation (17):  
Figure 5:0  
Then, considering the value of \(R_{1}\), \(TL(R_{1})\) can be defined by:  
Figure 5:1  
By combining Equation (14) and Equation (18), the value of \(R_{1}\) is obtained by Equation (19):  
Figure 5:2  
It is worth noting that, although the values of \(R_{1}\) and \(R_{2}\) can be calculated, the reservation value is essential due to the dynamic underwater environment.