## 4 Simulation Assessment of the ARounD Communication Scheme
### Simulation Environment  
In order to assess the ARounD communication scheme, it was defined a simulation environment with size 200 m \(\times\) 200 m, containing 503 sensor nodes (one PAN coordinator, one pair of source and destination nodes, plus 500 general purpose nodes). This assessment adopted the radio model CC2420 (Texas Instruments/Chipcon CC2420 Datasheet: [[http://www.ti.com/product/CC2420/technicaldocuments](http://www.ti.com/product/CC2420/technicaldocuments)]([http://www.ti.com/product/CC2420/technicaldocuments](http://www.ti.com/product/CC2420/technicaldocuments))), which is compliant with IEEE 802.15.4. Moreover, a linear energy model provided by Castalia was used for simulations. The initial energy for all nodes was set to 18,720 Joules, which is the typical energy for two AA batteries. As radio propagation model, we adopted the _unit disc_ model, where the range of the disk was defined to 55 m. In addition, it was used an interference model, where concurrent transmissions generate collisions at the receiver.  
For the nodes' deployment, node 0 was set as the PAN coordinator and nodes 1 and 2 as the source and destination nodes for the source-to-destination message stream, respectively. These nodes are statically deployed in the communication environment. The PAN coordinator is located in the central position of the field (100 m, 100 m). For nodes 1 and 2, two different scenarios were defined, in order to avoid biased assessments. Firstly, nodes 1 and 2 were deployed in positions (30 m, 30 m) and (170 m, 30 m), respectively, in adjacent quadrants (_Scenario 1_). This configuration was used to have a balanced deployment. Secondly, nodes 1 and 2 were deployed in positions (30 m, 30 m) and (170 m, 170 m), respectively, in opposite quadrants (Scenario 2). This configuration was used to configure a communication scenario, where the PAN coordinator is located between the source and destination nodes, forcing the peer-to-peer communication through nodes deployed in more congested areas of the network.  
The other 500 general-purpose nodes were randomly deployed in the environment. Basically, five different physical topologies were generated for setting-up the position of these nodes, which were used for the assessment of the ARounD communication mechanisms. Thus, we have 10 different deployments: five topologies for _Scenario 1_ and five topologies for _Scenario 2_. For each topology, 10 simulations were run with different sets of random variables. The results presented along this section correspond to the average of results from these set of simulations. Figure 17 illustrates one of 5 physical topologies considered for _Scenario 1_, while Figure 18 illustrates one of 5 physical topologies considered for _Scenario 2_.  
Figure 17: Scenario 1: nodes 1 and 2 in adjacent quadrants.  
The cluster-tree formation is based on the IEEE 802.15.4/ZigBee standard. The PAN coordinator performs the cluster-tree scheduling and checks if the current cluster-tree configuration is schedulable. Table 2 summarises the most important configuration parameters used in the simulations and pointed out in this section.