In 1-D linear networks, the energy consumption was only concerned with cluster heads, and the network lifetime was based on the rotation of cluster heads in each grid. This section looks into a lot more detail with the energy consumptions of single wireless sensor node, total wireless sensor nodes, cluster head and total grid consumption for the three 2- D networks with full idle energy and also Sleep Mode. In Sleep Mode, the idle energy consumption for all the nodes is reduced to 10% of the original value. This means that the nodes are only awake for 10% of the idle time.
Figure 6.6 (a,b,c) gives a complete breakdown of energy consumptions for all the three 2- D networks with full idle energy consumption. Figure 6.6 (a) represents the 2-D
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Optimised grids network, while Figure 6.6 (b&c) represents the 2-D Equal grids and 2-D COTS networks, respectively.
Figure 6.6 Sensor node, cluster head and grid energy consumption for 2-D networks with 100% idle Energy.
The individual wireless sensor node energy consumption per second for the 2-D Optimised grids network is 2% & 3 % lower as compared with the other two networks. This might not seem as a big value, but over a couple of days and the number of nodes, these values can produce significant savings in energy costs and hence an increase the network lifetime. Also realising that these wireless sensor nodes transmit very little data and normally remain idle for long periods of time. e.g. one message every 2.67 seconds. The most important factor is the total cluster head energy consumption. The 2-D Optimised grids network uses 30% and 47% less energy compared with the 2-D Equal and 2-D COTS network. The blue line of Figure 6.6(a) indicates how the network energy consumption is balanced throughout all the cluster head nodes in the 2-D Optimised grids network. The total grid energy consumption (black line) includes the total consumption for all the sensor nodes and the cluster head for the three 2-D networks. The 2-D Optimised grids network has 55% and 63% less energy consumption as compared with 2-D Equal grids and 2-D COTS network. Near to the base station, the 2-D Equal grids and 2-D COTS network have bigger grid size compared to the 2-D Optimised grids network. This bigger size worked out in their advantage in the 1-D linear networks where they had more nodes to rotate to become cluster heads and hence have a longer network lifetime.
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Figure 6.7 Sensor node, cluster head and grid energy consumption with 10% idle energy.
It has been learnt from Chapter 4.0 that idle energy becomes dominant when the traffic is low. This also means that apart from the cluster heads nearest to the base station, all the other wireless sensors nodes spend a lot of their time in idle state and therefore consume large amounts of idle energy. The next stage involved in adding the Sleep mode to the three 2-D networks. The Sleep mode is explained in Chapter 5.0 section 5.1. In Sleep mode the nodes only stay awake for 10% of the total idle time. For 90% of the time it is assumed that the node goes to sleep and does not consume any energy at all.
Figure 6.7 (a,b,c) reflects the energy consumptions for the wireless sensor nodes, cluster heads, and total grid for the three 2-D networks with the Sleep Mode. By introducing the Sleep mode, the total grid consumption for the first grid of the 2-D Optimised grids networks is 40% and 59% lower as compared with the 2-D Equal grids & COTS network.
Figure 6.8 Total grid lifetimes for 2-D sensor networks with 100% idle and Sleep mode.
The total network lifetime for the three 2-D networks was compared with the Idle and Sleep Mode as shown in Figure 6.8 (a,b) In both the cases, the 2-D Optimised grids network showed much better network lifetime performance. Without the Sleep Mode
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(Figure 6.8a) the 2-D Optimised grids network has 4.5% and 10.1% more network lifetime as compared with the 2-D Equal grids and 2-D COTS network. With the Sleep Mode (Figure 6.8b), grid (4) in the Sleep 2-D Optimised network has the lowest grid life of 242 hours. This still has 18% more lifetime compared with lowest grid (7) of Sleep 2-D Equal grids network and 31% more than lowest grid (5) of Sleep 2-D COTS network.
A key point is that the 2-D Optimised grids network has 25% higher throughput and much lower latency and jitter. It is using more energy to forward these extra packets to the base station to achieve a 25% higher throughput and still has higher network lifetime.
Figure 6.9 Theoretical Network lifetime expectancy for 2-D networks.
A theoretical calculation for the grid lifetimes were carried out to see if the simulated models had any correlation with theoretical values. Figure 6.9 shows that in an ideal network where there are no delays, collisions or any other overhead, the 2-D Optimised grids network has 12 % and 20% more lifetime compared to the other two 2-D networks. Another key point is to compare the theoretical values of Figure 6.9 with simulated values of Figure 6.8(a) from grid 13 to 19. The theoretical and simulated values for all the three networks are very close. This is due to the reason that at the lower end of these networks, the traffic is very low and the three networks behave ideally. But from grids 1 to 12, the 2-D Optimised grids deviates a lot less compared to the other two 2-D networks.
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