# Efficient Opportunistic Routing Protocol for Sensor Network in Emergency Applications
## 4 Performance Evaluation
### Energy Efficiency  
In this section, we analyze the energy efficiency of the proposed ODCR protocol, well-known clustering protocols LEACH [18] and TEEN [19] and a very recent opportunistic routing protocol, called LORA [21].  
The cluster formation phase is initiated in LEACH and TEEN protocols after a certain number of rounds where all nodes participate in the cluster restoration or reformation. On the other hand, cluster restoration is initiated in the proposed ODCR protocol only when a node becomes a border node or becomes isolated. In addition, only the border nodes and two neighboring CHs participate in this cluster restoration process. Other nodes remain in their cluster and do not participate in the cluster formation process.  
Hence, the proposed ODCR protocol seems to be more energy efficient, lower packet loss ratio and higher throughput as compared to the existing LEACH and TEEN protocols. Let us assume that:  
The number of nodes in the network = \(n\)  
The number of clusters in the network = \(c\)  
Then, the average number of nodes in each cluster = \(\frac{n}{c}\)  
The number of messages each node transmits and receives for cluster formation = \(m\)  
\[\text{The average number of message transmission for cluster formation }=n\times m \tag{6}\]  
**For cluster restoration in the ODCR protocol:**  
The number of nodes participate in cluster restoration = 3, where 3 \(<n\)  
\[\text{The average number of message transmissions in ODCR for cluster restoration }=3\times m \tag{7}\]  
Hence, the number of transmitted messages for cluster restoration is \(\text{O}(n)\).  
Comparing Equations (6) and (7), we expect that the average number of message transmissions in the ODCR protocol is much lower than that of the LEACH and TEEN protocols.  
On the other hand, LORA [21] is a non-clustered multi-hop opportunistic routing protocol.  
Let us assume that the number of hops from source to destination in LORA  
\[=h\ f_{1}+f_{2}+f_{3}+\ldots\ldots\ldots\ldots\ldots\ldots+f_{h-1}\leq n \tag{8}\]  
where \(f_{i}\) represents the number of forwarder nodes at hop \(i\).  
The total number of message transmissions for selecting forwarder nodes will be about  
\[f_{1}\times m_{1}+f_{2}\times m_{2}+f_{3}\times m_{3}+\ldots+f_{h}\times m_{h} \tag{9}\]  
where \(m_{i}\) represents the number of message transmissions for selecting forwarder nodes at hop \(i\).  
If \(b_{1},\ b_{2}\ldots\ldots,\ b_{h}\) represent the number of message transmissions for selecting the best forwarder node at hops 1, 2, \(\ldots\ldots\), \(h\), respectively, the total number of message transmissions would be  
\[f_{1}\times(m_{1}+b_{1})+f_{2}\times(m_{2}+b_{2})+f_{3}\times(m_{3}+b_{3})+ \ldots+f_{h}\times(m_{h}+b_{h}). \tag{10}\]  
Hence, the selection of forwarder nodes for transmitting a data packet from the source to destination will be \(O(n^{2})\). The process of selecting such a path with forwarder nodes occurs every time a node transmits data to the destination. Hence, it is more likely that the total number of message transmissions in the LORA protocol is much more than that in the proposed ODCR protocol. We will perform an experimental simulation to verify this.  
As energy consumption of sensor nodes is directly proportional to the number of transmitted messages, the energy consumption of the ODCR protocol is expected to be much lower than that in the LEACH, TEEN and LORA protocols. Similarly, as the number of message transmissions is much morein LEACH, TEEN and LORA protocols, the probability of packet loss in these protocols will be higher than that of the proposed ODCR protocol.