## 4 Simulation Works and Discussion
### Multiple Sink Multi-Radios  
In our previous scenarios we have simulated and analyzed the impact with:  
* Multiple sinks, each with single radio
* Single sink with multi radio
* Single sink with multi-radio in a round robin fashion  
Each scenario show some level improvement for MC-DCF when the sink node(s) obtain data from source nodes, compared to our previous work where the sink encountered severe degradation when receiving from sources by a single sink with single radio interface that has to constantly switching between sending node interfaces.  
In this scenario we will be analyzing the impact of data sending from sources to three sink nodes. Each sink will be equipped with three radio interfaces using the three non-overlapping channels in IEEE 802.11. Figure 15 shows a sensor network with multiple sink nodes each having three radio interfaces.  
Figure 14: Throughput impact comparison with one-many communications at sink node.  
Figure 16 show delay impact with the increase in sink nodes and radio interfaces. We have observed that with three channels there has been a 96% reduction in delay at the sink side comparing to our previous work where the source node transmitting directly to the sink experience high level due to channel switching by the single radio interface. With two channels sending data from sources, there has been an approximately 87.4% delay improvement. Single channel and 802.11 DCF show little improvements. As mention previously single channel performance does not improve with increasing sink nodes or radio interfaces as the decisions are based on the window size resetting, backing off, wait states and the fact that all nodes are contending for the same medium. MC-DCF with multiple channel switching and multiple radio interfaces have yield a better performance when using multiple sinks in contrast to single channel and 802.11 DCF which shows a better performance in previous work.  
Figure 16: Delay impact from source nodes when using multiple sinks with multiple radio interfaces.  
Figure 15: Multiple sink nodes with multiple radios.  
Figure 17 shows an improvement of over 90% for three channels with packet delivery ratio when the number of sink nodes and radio interfaces increase by three as compare to single sink node with single radio interface in our previous work. With two channels sending data from the sources to the sinks there has been improvement by over 81% compared to the poor performance experience with a single channel. Similarly, where the delay with a single channel shows no significant improvement, packet delivery ratio using single channel shows no major improvement.  
The aggregate throughput in Figure 18 of the overall system with source nodes sending to the sinks have shown that with multiple sink nodes, channels and radio interfaces 92% more data have been delivered to the sink compare to that of single sink with single radio and single channel. Single channel and 802.11 DCF in all instances has not shown any significant improvement with increasing of sink nodes receiving data from the source nodes.  
Figure 18: Throughput of overall system using multiple sink nodes with multiple radio interface.  
Figure 17: Delivery ratio impact from sources when using multiple sinks with multiple radio interfaces.