## 5 Experimental Results
Moreover, for the memory usage in a clusterhead [Figure 23 (right)], due to the centralized operation, the clusterhead using the CASA scheme consumes more memory, compared with the clusterhead using the DASA with only local information. However, when measuring the memory utilization in a sensing round, the memory usage performance of the proposed approaches are comparable since the number of active nodes in a round \(M_{RG}\) is considered to be close in each approach as demonstrated in Figure 7:2 Accordingly, the current wireless sensor networking products (e.g. Crossbow's IRIS Note with 8K bytes RAM and 512K bytes Flash or Tmote Sky with 10K bytes RAM and 48K bytes Flash) are capable of running the proposed scheduling schemes. Figure 7:3 The network connectivity using the CASA scheme in round 1 (left) and round 2 (right). The last set of experiments depicts the energy consumption of the proposed algorithms and compare the results with those of other cluster-based scheduling protocols. Assume that clusters are formed in a random network of 100 sensors with side length \(l=100\) m. A simple model [10] where the radio dissipates \(E_{elec}=\) 50 nJ/bit to run the transmitter or receiver circuitry and \(E_{amp}\) = 100 pJ/bit\(\rm{m}^{2}\) for the transmit amplifier is applied in order to achieve an acceptable SNR. Suppose an \(r^{2}\) energy loss due to channel transmission. Thus, to transmit a \(K\)-bit message a distance \(R\) using the radio model, the radio  
Figure 7:4 Memory usage of sensor nodes in a cluster versus number of sensors \(N_{S}\) (left); memory usage of a clusterhead versus number of sensors \(N_{S}\) (right). Figure 7:5 The network connectivity using the DASA scheme in round 1 (left) and round 2 (right). expends: \(E_{T}=E_{elec}\cdot K+E_{amp}\cdot K\cdot R^{2}\) and to receive this message, the radio expends: \(E_{R}=E_{elec}\cdot K\) (Figure 24). For data dissemination, the cluster-based hierarchical routing protocol [36] may be used for inter-cluster routing. The intra-cluster routing is built upon the node-level topology of cluster, which is obtained by the CAWT mechanism. Thus, data traffic between two clusters will be relayed through the gateway nodes. Assuming that each node has a 36-byte data packet to transmit, Figure 25 (left) illustrates the average energy consumption per round under different transmission range with varying the number of sensors in the network. Furthermore, with varying the size of data packet in each sensor node, Figure 25 (right) presents the number of sensing rounds given the energy constraint. As expected, due to an increasing packet size and a higher energy dissipation rate, the number of sensing rounds decreases given a fixed initial energy (\(0.5\) J). On the other hand, with an appropriate transmission ranges according to the network density (with \(l=100\) m, \(N_{s}=100\), and \(R\approx 14.14\) m; with \(l=100\) m, \(N_{s}=200\), and \(R\approx 10.0\) m; with \(l=100\) m, \(N_{s}=300\), and \(R\approx 8.17\) m; with \(l=100\) m, \(N_{s}=400\), and \(R\approx 7.07\) m) and varying the packet size, the number of sensing rounds in the network with different network densities suffers only small variations, which suggests that the proposed schemes may achieve high scalability for sensor scheduling. Figure 26 shows the number of rounds when the first node dies in the network using the LEACH [10], the MECH [11], the CASA, and the DASA with varying the initial energy of each node from 0.25 J to 1.0 J. The LEACH and the MECH are clustering-based protocols that tries to minimize the energy dissipation in sensor networks. Observe that the proposed approaches are superior to the LEACH and the MECH approaches, while the number of sensing rounds grows nearly linearly as the initial energy increases. The simulation results demonstrate that the proposed schemes are more energy efficient than the LEACH and the MECH schemes.