Cluster Head Node Energy Utilization:

compared the energy used by the cluster header nodes of the Optimised grids, Equal grids and COTS networks. I also examined the energy use of equivalent theoretical models of the three networks (the theoretical models depict an ideal situation where there are no packet collisions, re-transmission, overhearing and 100% message delivery).

Figure 4.15 shows the theoretical transmission energy consumption of the three networks. It can be seen that the energy use is balanced better among the cluster head nodes in the Optimised grids network compared to the COTS and Equal grids networks (where the cluster head nodes near the base station consume nearly twice the energy of the equivalent Optimised grids cluster head nodes). The COTS network consumes the most energy. The reason is that the COTS network has a fixed longer transmission distance as these products do not have variable transmission range and use more energy. Its transmission distance is not based on the grid size as compared to Equal grids and Optimised grids network. Thus if the grid size becomes smaller, they will still be spending the same amount of energy for a shorter distance. When the grid size is increased and becomes longer than their transmission range, they cannot be included in the simulation for comparison.

Figure 4.15: Theoretical transmission energy consumption.

The enhanced NS2 simulations generated an average transmission energy consumption results for the three networks, as shown in Figure 4.16. In the Optimised grids network the cluster head of grid 1 consumes 43.5 % and 32.4% less transmission energy than the

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equivalent nodes in the COTS network and Equal grids networks respectively. The transmit energy values for Optimised grids network (which averages 93% throughput) are very close to the theoretical values. However the results for the COTS and the Equal grids network (which average about 75% throughput) show lower consumption compared to the theoretical values, particularly for cluster head nodes nearer the base station. Fig 4.16 also show that small peaks for grid 5 and 7 for the Equal grids and COTS network. The peaks represent that these nodes are consuming a lot of energy, while they keep on transmitting messages and grids 4 and 6 spend more time receiving the messages, hence consume less energy. Simulation analysis shows that collisions are taking place at this point as the network is highly congested for both these networks. This also explains, beyond that point, the throughput for these grids is lower as compared to Optimised grids network as shown in Figure 4.12.

Figure 4.16: Simulated transmission energy consumption

Similarly, the enhanced NS2 simulations were used to derive the reception energy used by the cluster header nodes, as shown in Figure 4.17. This shows that the receive energy consumption in the Optimised grids network is up to 33% lower than that in the Equal grids and COTs networks. Recall that in the symmetric COTS and Equal grids networks, the cluster head node in grid (i+2) can overhear messages from cluster head node in grid (i). Note that the case of cluster header nodes near the base station (i.e. cluster header nodes 1 and 2) the reception energy is much reduced as the base station does not source or forward data.

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Figure 4.17: Receive energy consumption

Figure 4.18 shows the idle energy consumption for the three networks. It can be seen that as the traffic approaches the base station the nodes become more active and hence the idle energy consumption starts to decrease. The Optimised grids network has more idle energy consumption compared to the COTS and Equal grids as it is more efficient in transmitting and receiving data and hence has more times for the nodes to stay idle.

Figure 4.18: Idle energy consumption

The total cluster head energy consumption was also compared including idle, receive, and transmission energies. The enhanced NS2 simulations of the COTS, Equal grids and Optimised grids networks, Figure 4.19, show that in the COTS and Equal grids suffer from congestion in grids toward the base station is reflected in the total energy graphs, where the small peaks and troughs occur because some nodes are spending time re- transmitting messages, while their neighbouring nodes are too busy receiving useful as well as redundant messages.

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Figure 4.19: Actual total energy consumption

In contrast, the Optimised grids network, the cluster head energy use is better balanced due to energy efficient grid sizing (even though the receive energy saved by good spatial reuse was consumed by the increase idle state). Therefore in the Optimised grids network the lifetime of the cluster head nodes can be improved by at least 30% and 50% respectively compared with the best case where equal radio range and commercial off the shelf (COTS) systems are used. Implementing the Optimised grid spacing would further improve protocols such as SPAN, LEACH and SMAC.

Another important issue is to look at is the total time spent by the cluster head nodes in tranceiving data and remaining in idle state. This will allow me to see if the theory can be further improved to increase the cluster-head lifetime and also in general to improve the network lifetime.

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Figure 4.20 shows two graphs, the LHS graph shows that as the cluster head traffic approaches the base station, the clusters spend more time in transmitting and receiving data. This is also proven by the RHS graph that the idle time for the cluster head decreases as the traffic approached the base station. The cluster head nodes in all the three networks remain idle for average of 92% of the time in the furthest grid (19). In the Optimised grids network the cluster head node of grid (2) spends 36% of the total simulation time in idle state and 64% of the time transmitting and receiving data. The cluster head node of grid (3) of COTS and Equal grids network spend 23% of total simulation time in idle state and 77% of the simulation time in transmitting and receiving data.