## 4 Lifetime Improvement Mechanisms in Routing
### Power Control Mechanism
The simulation [18] shows that ATPC conserves significantly more transmission power than other solutions. This algorithm only uses 53.6% of the transmission energy in comparison with the maximum transmission power scheme. [PERSON] _et al._[19] followed a similar concept as in previous algorithm but they tried to omit the initialization phase in order to reduce the overhead. This new algorithm, which could be applied in Directed Diffusion routing protocols, is named _On-Demand Transmission Power Control (ODTPC)_. It has two steps as follows: in the first step, a node which has data to be sent, searches in its neighbor table to find the best transmission power level. The data packet should be sent with the maximum transmission power level if there is no optimal transmission power level to the receiver. After that, the RSSI parameter related to the data packet is measured by receiver. Then the successful communication margin achieved upon the measured RSSI is returned to the sender by an ACK packet with the approximate transmission power level. Now, the sender can calculate the estimated transmission power level based on the RSSI and the margin field. In the second step, the sender gradually proceeds to adjust the transmission power level by increasing or decreasing it based on the lower and upper threshold of RSSI value over time. With the help of an analytical model, the RSSI threshold is calculated approximately. Equation (9) presents this value where: \(f=30\) bytes (the length of packet) and \(\mathrm{P_{N}}=-110\) dBm (the average noise floor). These parameters are achieved from experiments. \[\mathrm{RSSI_{THRE}(dB)}=10\mathrm{log}\left[-1.28\mathrm{ln}\left(2\left(1-0. 99^{\frac{1}{86}}\right)\right)\right]+\mathrm{P_{N}(dB)} \tag{9}\]  
Since the real-data and ACK packets have been exchanged with a beaconing mechanism, this algorithm has no throughput overhead. The experiments [19] in a real test-bed environment show that ODTPC consumes less than 53.48% of the energy consumption for the initialization phase in comparison with the maximum transmission power scheme. It also improves the transmission energy consumption on the entire network by rates of 50% and 120% in comparison with the ATPC and maximum transmission power schemes, respectively. Just like the ATPC protocol, this algorithm has an execution cost for calculating the RSSI parameters. The authors of the _Energy Efficient and Collision Aware (EECA)_ protocol [16] also used a power control mechanism in order to save more energy in their proposal. They exploited a node-disjoint multiple path method between the source and the destination with the aid of the nodes' location information. In order to avoid the interference among two routes, the minimum distance between them should be determined to be more than R, which it is the maximum radio transmission range for each node. As shown in Figure 7, the black nodes in the area between two dotted lines are not selected by multi-path routing mechanism due to collision among the nodes located on two paths. In the route construction phase, each relay node chooses the next hop based on the three following factors: residual energy, distance to the source-sink line and progress length. These factors are employed by each next-hop candidate to calculate a back-off timer. The node having minimum back-off time wins the contest and introduces itself as the next hop. With the help of the power control component of the protocol, it is possible to find two collision-free routes and transmit the data with minimum power in order to save the energy. The strategy of data transmission on each path is like the ODTPC algorithm. Figure 7(a) indicates the state in which node B uses the maximum transmission power level to reach the next hop C. This method wastes energy since it is not able to decrease the transmission power level to send data to node C. The usage of power control mechanism in EECA is shown in Figure 7(b), where nodes B and C use sufficient transmission power level to reach the next hop and conserve much more energy.