# An Integrated Cognitive Radio Network for Coastal Smart Cities
## 3 Simulation Results and Discussion
Similarly, for cognitive maritime networks, we simulated HSDV with the spectrum selection scheme proposed by [PERSON] et al. [26] and named it as the reference scheme for S2S. We analyzed our integrated coastal city with three different metrics:  
* packet delivery ratio
* end-to-end delay
* routing overhead ratio  
Figure 4 presents the packet delivery ratio with the number of nodes as an independent variable for different communications systems, and with different idle probabilities of the PU as a parameter. The packet delivery ratio is a measure of the number between the delivered generated packets. The delivery ratio increases for all the communications systems when the number of nodes (vehicles and ships) in the network increases. The pattern is similar for hybrid and pure communications--that is, the network shows better performance with an increasing number of nodes and increasing idle probability of the PU together. This is because increasing the number of nodes in the network increases the connectivity, and in the second case, the high probability means that the channel is free from the PU for a long time, which provides more common free channels in the network. Moreover, the fog cloud improves network performance in terms of packet delivery ratio, since all the functions and the network management are now centrally controlled by the controller that increases the network intelligence by globally dictating network behavior. The word _globally_ here means that the controller is responsible for keeping the global network view by interacting with LCs. This means that the controller manages the entire information about the status of channels and relays. As a result, by computing the maximum reward, the controller is responsible for providing the more stable paths from source to destination per inquiring node. When the network is sparse at a 70% idle probability for the PU, we achieved 69% successful delivery of packets for S2S, 79% for V2V, and 80% for V2S communications. The delivery ratio of V2S communications is high, compared to the other two communications systems when the number of nodes is high. This is because of the fog cloud that maintains stability between the two environments. The S2S performance is poor because of the constantly changing sea surface. Figure 4 also shows that when the idle probability is low, there is a performance degradation in the network. This is because with low probability, nodes face difficulty in reaching a consensus on a common free channel. Figure 4: Performance comparison between the proposed hybrid and pure communications in terms of packet delivery ratio. Figure 5 shows the end-to-end delay with the number of nodes as an independent variable for different communications systems, and with different idle probabilities of the PU as a parameter. End-to-end delay is a measure of the difference between the number of times a packet starts going from a source and ends at the destination. When the network is sparse between (6 and 12 nodes), the delay is high for all the communications. The independent variable, that is, the number of nodes in the network decreases the delay with an increase in its numeral. This pattern of improved performance in terms of delay with an increasing number of nodes and increasing idle probability of the PU, is again the same for both hybrid and pure communications. This is because increasing the number of nodes in the network increases the connectivity, and in the second case, the high probability means that the channel is free from the PU for a long time, which provides more common free channels in the network. The delay is high for S2S communications because of the environmental factor. This means that with the changing positions of ships in a marine environment, the sea surface is also changing constantly and, therefore, results in more fragile links than in terrestrial networks. Moreover, hybrid communications shows better performance due to its hybrid nature, that is, the path is divided into two types of networks.