## 8 Simulation Assessment
### Performance Metrics  
The aim of this simulation assessment is to evaluate the network behaviour according to well-defined metrics, both for the unconditioned and conditioned scenarios. In a first set of experiments, the behaviour of Load-SDA and Nodes-SDA allocation schemes are compared against both a state-of-the-art allocation scheme, and a standard allocation scheme. In a second set of experiments, the behaviour of the Load-SDA allocation scheme is compared just against the proposed Nodes-SDA allocation, in order to highlight the differences between these two schemes. The following acronyms were used to identify the allocation schemes. * _Load-SDA_: Allocation scheme based on the message load (Load-SDA), where the X parameter value (Equation (27)) was considered to be 2 (two) messages, and the main CSMA-CA parameters were defined according to their default values (\(SD_{min}\) corresponds to 15.36 ms, assuming a network with bit rate of 250 kbps, frequency band of 2.4 GHz, and one symbol as 4 bits). * _Nodes-SDA_: Allocation scheme based on the number of nodes (Nodes-SDA). In this case, similar rules as defined for Load-SDA scheme were considered. \begin{table}
\begin{tabular}{c c} \hline \hline
**Definition** & **Standard Value** \\ \hline Radio model & Chipcon CC2420 \\ Initial energy (per node) & 18.720 Joules \\ Simulation time (each experiment) & 110.000 s \\ _aBaseSlotDuration_ & 60 \\ _aNumSuperframeSlots_ & 16 \\ _aInitBackoffPeriod_ & 20 \\ _macMinBE_ & 3 \\ _macMaxBE_ & 5 \\ _macMaxCSMABackoffs_ & 4 \\ _macMaxFrameRetries_ & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation Configuration. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Features** & **Unconditioned Scenario** & **Conditioned Scenario** \\ \hline Maximum number of child nodes (per cluster) & 6 nodes & 6 nodes \\ Maximum number of CCH for PAN coordinator & 2 nodes & 2 nodes \\ Maximum number of CCH (other CHs) & 2 nodes & 3 nodes \\ Set of data rates & 0.05 and 0.01 pkts/s & 0.05 and 0.01 pkts/s \\ Data rate distribution in the environment & randomly distributed & two well-defined zones \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summarising the different Simulation Scenarios. * _SOA-SDA_: State-of-the-art Allocation scheme based on the work proposed by [13], considering a similar beacon interval (BI) value for all the clusters. For this scheme, leaf cluster-heads were configured with the minimum SD (considering SO = 0) and all other cluster-heads were configured according to the rules defined in [13]. The BI value was defined according to the same constraints imposed by the Load-SDA allocation scheme, according to Equation (10). * _STD-SDA_: Similar-Duration Allocation scheme. For this scheme, all clusters in the network share the same Superframe Duration and Beacon Interval. The BI value was defined according to Equation (10). The SD value was defined as the upper average of the SOs (SuperframeOrder), as defined by the _Load-SDA_ scheme for all clusters (respecting the constraint defined by Equation (5)). In order to analyse the network behaviour, the following performance metrics were used:
* _Message Discard Rate_: percentage of discarded messages due to buffer overflows in the cluster-heads, considering the number of discarded messages vs. the number of messages that arrived to the cluster-head. * _Message Loss Rate_: percentage of messages lost during the communication, considering the number of messages successfully received at the destination node and the number of messages generated by the source node (encompasses both discarded messages and messages lost due to collisions). * _Average End-to-end Delay_: time interval between data frame generation at the application layer of the source node and its reception at the application layer of sink node. * _Energy Consumption_: average energy consumption of the overall network. For each of the allocation schemes, 10 different simulations were performed for each scenario (unconditioned and conditioned) with different sets of random variables.