# Integrated Evaluation of Reliability and Power Consumption of Wireless Sensor Networks
## 6 Experimental Evaluation
### Sensitivity Analysis
#### 6.3.2 Results
When we increment 5 times (e.g., 50 kb to 250 kb) the _Packet Size_ (PaS), the sensor node will consume five times more to send a packet; and, when we change five times (e.g., 250 m to 1250 m) the value of the _Initial Radio Range_ (IRR), the sensor node should consume 25 times more to send a packet (based on _First Order Radio Model_). However, this behaviour did not happen when we increment the _Initial Radio Range_ (IRR), because the _Routing Protocol_ (RP) changes it at runtime. For example, the protocol DIRECT changes (in all experiments) the value of the factor _Initial Radio Range_ (IRR) to a value equal to the distance between the sensor node and the sink node. For that reason and because the sink node is in the centre of WSN, _Place Size_ (PIS) influences more the WSN power consumption than _Initial Radio Range_ (IRR). Besides _Packet Size_ (PS), _Sending Regular Rate_ (SRR) also has a strong impact on the WSN power consumption. If the sensor node frequently sends several small packets, this behaviour increases its power consumption. The reason is straightforward: it consumes the same energy in the same period if it sends a big packet once or if it sends a small packet frequently. For example, two sensor nodes (\(A\) and \(B\)) send a different packet at different periods: the sensor node A sends a packet of 50 kb every 2 s; while the sensor node B sends every 250 kb every 10 s. Their power consumption will be the same every 10 s because they will send 250 kb at this period. However, _Packet Size_ (PS) influences the WSN power consumption more than _Sending Regular Rate_ (SRR) because it directly affects the WSN power consumption. For that reason, it is more important to reduce _Package Size_ (PS) and increase _Sending Regular Rate_ (SRR). Additionally, the interaction between _Packet Size_ (PS) and _Sending Regular Rate_ (SRR) is the 8 th in the ranking (out of 36), which shows that there is a strong interaction between them. The _Place Algorithm_ (PA) also has a strong influence (less than the previous factors) on the WSN power consumption due to the selected routing protocols. The interaction between them is the 5 th in the ranking. For example, as mentioned before, the protocol DIRECT benefits the sensor nodes close to the sink node. Finally, _Node Number_ (NN) has little impact on the WSN power consumption because of two factors: (i) protocol DIRECT does not require any other node to send the data to a sink node; and (ii) the link layer protocol was considered as perfect, i.e., it does not account for power consumption to receive packets by mistake or collision. If the experiment would use other protocols of the Link Layer and Routing Layer, the number of sensor nodes and the distribution could have a more significant impact on the WSN power consumption. _Reliability._ WSN reliability was calculated at time 25 s because the most of the WSNs evaluated have the reliability greater than 0 at this time. Since the purpose of sensitivity analysis is to use the same factors and levels to assess the power consumption and reliability of WSNs, we evaluated the reliability of the _Region I_ and we only considered battery level as the reliability of the sensor node (see Section 4.4). Without this consideration (battery level as reliability), the reliability of the sensitivity analysis would have to be done using other factors and levels (e.g., the reliability of the communication link). The four factors that affected more the WSN reliability were _Routing Protocol_ (RP), _Place Size_ (PIS), _Packet Size_ (PaS) and _Initial Energy Level_ (IEL). As mentioned in [18], the WSN reliability varies according to the distance between the _Region I_ and the sink node, the routing protocol used and the number of sensor nodes inside of the region. As the _Path Model_ (see Section 4.4) is based on the routing algorithm, we expected that the routing protocol interferes on the WSN reliability.