# A Biologically Inspired Self-Organizing Underwater Sensor Network
## 6 Experiment
### Performance of the Slot Distributor  
We first check the performance of the slot distributor. Two sets of experiments are carried out. In the first experiment, we exhibit the performance of a relatively small network in detail, showing readers how the coordinator works. In the network, 25 nodes are deployed as a grid formation, with the edge length of 200 m. The communication range is set to 300 m, satisfying the situation of high-frequency acoustic communication devices. The deployment is shown in Figure 7.  
The performance of the method is shown in Figure 8, which shows the communication results in each frame with the number of successes and failures shown. The pulse in the figure indicates nodes trying to occupy slots, which may introduce collisions into the network. However, as time goes on, most nodes have already occupied optimum slots, and the deployment of pheromone clues prohibits nodes from occupying more slots. Finally, the network converges to the state without communication collision. Figure 9 shows the average occupation of slots by nodes. The available slots are those slots not occupied by a first-order or second-order neighbor, and the occupied slots are those slots actually occupied by nodes. From this figure, we can see that nodes are trying to occupy more available slots, and finally, almost all valid slots are occupied by nodes in the network. Figure 8: Communication results in each frame. “sent messages” denotes the total number of message packets sent by sensor nodes in the whole network in a frame. “successful messages” indicates message packets successfully received by all nodes within the communication range, and “failed messages” indicates message packets not successfully received by all nodes within the communication range because of communication collisions. Note that there is a case where a message packet is received successfully by some neighbors, while a collision happens with other neighbors; we treat this message packet as failed to be sent. Figure 7: Node distribution in a sensor network consisting of 25 nodes. Dots denote sensor nodes, and the number beside indicates the ID of the sensor node. The ring around a dot is the communication range of the node. The edge of each grid is 200 m, and the communication range for each node is 300 m.  
As a result, from Figure 10, we notice that the average expected wait keeps dropping and finally converges to a relatively small value. In Figure 11, we show the final slots occupied by a sub-network consisting of Node 19 and its neighbors. We see that Node 19 has does not have all of its slots occupied by either its first-order neighbors or by its second-order neighbors. There are no slots occupied by more than one of its first-order neighbors, so collision will not occur among the first-order neighbors. In some cases, a slot is occupied by a first-order neighbor or more than one second-order neighbor. For example, Slot 7 is occupied by Node 7 (i.e., a second-order neighbor of Node 19) and Node 24 (i.e., a first-order neighbor of Node 19) at the same time. This is reasonable because Node 7 and Node 24 are neither first-order neighbors nor second-order neighbors, and this will not cause communication collision. Figure 10: The average expected wait over time, i.e., the average value of expected wait of all nodes in the sensor network in each slot. Figure 9: The average number of slots occupied by nodes over time. For each node, its available slots denote the communication slots not occupied by any of the node’s first-order or second-order neighbors. The average available slots represent the average number of all nodes’ available slots, and the average occupied slots denote the average number of available slots occupied by nodes. To verify that our method still works on large networks, we test a network containing 100 nodes, with nodes deployed randomly in the area of interest, as displayed in Figure 12. The communication result in each frame along time is shown in Figure 13. Apparently, the network still converges and our method works.