# On Applicability of Network Coding Technique for 6 LoWPAN-based Sensor Networks
## 4 Performance of NC6 LoWPAN Mechanism
Supporting by reference about the energy that is consumed by the Tmote Sky motes from [41], we can receive energy that is required for sending \(n\)-byte packets: \(E(send)=0.12n+3.54\) [J], and for receiving \(n\)-byte packets: \(E(receive)=0.12n+4.03\) [J]. By collecting all of the packets transmitted and received in the network presented in Figure 11 (with mean 28 Bytes: encoded and native data packets, including headers), we can assess the NC efficiency in terms of the total energy consumed in the network (\(E(send)+E(receive)\)). Figure 13 shows this assessment. Figure 6:2 Packet lose ratio (extended testing scenario). The highest energy consumption gain was observed when six streams were transmitted simultaneously in the network. Using the NC6 LoWPAN, about 7% of the total energy was saved. It should be emphasized that the experiments were performed with a relatively high traffic volume generated during more than 1 hour, by each node of the networks (high total energy consumed). We can expect that the traffic will be much lower in many cases of the WSN. Thus, coding opportunities can also be decreased, and consequently, the energy consumption efficiency can be lower. Nevertheless, the results confirm that the NC6 LoWPAN can be effectively used in the 6 LoWPAN-based networks. Total energy consumption, as shown in Figure 13, is directly reflected in a WSN lifetime. Assuming that each node is powered by a battery with 1200 mAh capacity and 1.5 V nominal voltage, we have estimated the lifetime of the extended network shown in Figure 6:3 Thus, a node can use maximum energy equal to 6480 J. Since the experiments lasted for 67 min., we can linearly estimate the lifetime of the network that is composed of seven nodes. Figure 14 shows this estimation. A relatively low value of the network lifetime is a result of high traffic sent in the network during each experiment. In real WSNs, such traffic typically appears occasionally, thus the network lifetime is incomparably better. Nevertheless, an activation of the NC during higher traffic periods brings an increase in the lifetime. For example, for seven streams that were sent over the network, we can observe that estimated network lifetime is increased by about 60% if the NC is applied (with five native packets buffered in the NC buffers), when comparing to the network without the NC. Since the  
Figure 6:4 Estimated network lifetime (extended testing scenario). Figure 6:5 Total energy consumed in the network for packets transmission and reception (extended testing scenario). NC6 LoWPAN mechanism is applied in real sensor motes and the results come from the experiments conducted in the real network, we mainly focused on the confirmation that the NC can bring benefits in overall traffic sent in the 6 LoWPAN-based network, and in consequence, we can achieve lower overall energy consumption and a longer network lifetime. Moreover, the better benefits can be reached if the network is highly loaded. The NC6 LoWPAN optimisation and its adaptation to specific applications used in the WSNs is left for further investigations.