## 5 Simulation Study
### Performance Evaluation on Different Grid Cluster Sizes  
The performance of WMN responds differently to traffic characteristics such as packet generation rate and packet size. Similarly, the WMN responds differently to the number of nodes in the network topology and the position of the destination node. An evaluation of the performance of OLSR multiple metrics while increasing the number of smart meter nodes within the 400 \(\times\) 400 m\({}^{2}\) area is carried out. The proposed \(OLSR_{MM}\) is compared to the other OLSR versions. The network scenarios considered are as follows:  
* A grid topology with smart meter nodes increased from 25 to 36, 49 and 64 grid clusters. This results in the distance between each smart meter node reduced from 100 m to 80 m, 66 m and 57 m for each grid cluster, respectively.
* The grid topology network was also evaluated for the position of the data concentrator, which was positioned at the top right corner and the centre of the grid.  
The average PDR on grid clusters of 25, 36, 49 and 64 smart meter nodes with the data concentrator placed at the centre and at the top corner is presented in Figures 12 and 13. When the data concentrator is placed in the centre of the grid, the number of hops to the destination is reduced. However, the amount of data transmitted between the smart meter node and the data concentrator is not affected. It is observed in Figures 12 and 13 that the \(OLSR_{MM}\) outperforms the other OLSR versions. \(OLSR_{MM}\) also improves the overall PDR of the application traffic in both the central and top corner placement of the data concentrator. The reliability improvement of \(OLSR_{MM}\) when the data concentrator is placed at the top corner is higher than that of central placement. It can be further concluded that sending traffic across multiple paths from the source to the destination using \(OLSR_{MM}\) is more effective at reducing packet drops and congestion over a higher number hops to a destination.  
Overall, the grid clusters with the data concentrator placed at the centre of the grid achieved a higher reliability percentage than those with the data concentrator placed at the top corner. With respect to smart meter deployment in NAN, the placement of data concentrators closer to the smart meter nodes can improve reliability. Figures 14 and 15 show the average end-to-end delay for both scenarios. For the 64-grid cluster, when the data concentrator is placed at the centre, \(OLSR_{MM}\) achieved maximum latency of 4500 ms and 4700 ms when it was paced at the top corner. The average end-to-end delay for grid clusters with the data concentrator placed at the top corner recorded higher delay than the grid clusters with the data concentrator placed at the centre. This is because of the distance to the data concentrator. The main advantage of our routing approach is that it has a better reliability performance, even more than ETX that has the best PDR performance among the conventional OLSR versions. The \(OLSR_{MM}\) also recorded an average end-to-end delay that is as low as OLSR-ML.  
Figure 12: PDR for smart grid application on grid clusters with a central placement of the data concentrator.  
Figure 13: PDR for SG application on grid clusters with the data concentrator placed at the top corner.