## 4 Simulation Works and Discussion
### Single Sink with Multiple Radios  
In our second set of simulations, we use a single sink node and increased the number of sink radio interfaces to three. Figure 6 shows a sink node with three radio interfaces. We then assign each interface to a channel and assign three sending nodes on each channel to create a one to one mapping with the interface. In this case no channel switching is required. Each sender to the sink remains on said channel throughout the simulation. This allows constant flow between sending node and the radio interface.  
Figure 5: Throughput of the overall system using multiple sink nodes with single radio interface.  
Figure 6: Single sink node with multiple radios.  
Figure 7 shows the delay impact when MC-DCF uses a single sink with three radio interfaces to receive packet data which creates a one-to-one mapping in receiving data from sending nodes. MC-DCF with single radio from previous work had to perform channel switching to receive data when two or more non-overlapping channels are sending data to the sink. The result in our previous work showed that when two or more channels were used there was poor performance; the repeat of this performance is shown in Figure 7, except that only three sources were assigned to send data to the three interfaces, where each interface and each node is assign to one of the non-overlapping channels. However, when the one-to-one assignment is used we have seen over 40% success in improvement for delays. This outcome indicates that if we eliminate radio switching between channels and receive data flowing constantly from senders to the receiving radio interfaces we can improve the performance at the sink. However this would not be practical when network size increases, as we would need to constantly increase the radio interfaces at the sink and in addition, the limitation of non-overlapping channels would not make it feasible as there would not be enough non-overlapping channel to assign to radio interfaces.  
The packet delivery ratio in Figure 8 shows a similar improvement of approximately 46% for MC-DCF operating with multi-radios when compared to MC-DCF operating with a single radio as in our previous work. Each interface on a sending node is assigned to different non-overlapping channels. 802.11 DCF showed little or no improvement as this protocol was only designed to operate with a single channel. As mentioned before, the one-to-one assignments situation is not ideal for a large network as it would not be practical to have each radio interface assign to a non-overlapping channel from a sending node. Figure 9 also showed a 53% improvement in the one-to-one assignment with three non-overlapping channels for aggregate throughput. However for small parks and building areas this kind of implementation can be considered.  
Figure 7: Delay impact with multichannel multi-radios communication at sink node.  
The one to one scenario demonstrated above is not practical in all instances, but will depend on the size of the network and the number of sending nodes directly to the sink. Ideally there will be more nodes sending to the sink that will create a one-to-many assignment, where many nodes are sending to the same radio interface. Sending nodes can be odd or even in numbers. We derived some equations to solve these scenarios for our next simulation. These equations are used when there are even transmitter (senders) to receiver (sink) and uneven transmitter to receiver ratios.