# CERP: Cooperative and Efficient Routing Protocol for Wireless Sensor Networks
## 4 Cooperative Efficient Routing Protocol Formulation
### CERP Description  
The prevailing research on cooperative transmission strategies predominantly emphasizes physical layer approaches. Thus, to fully maximize the available bandwidth and power efficiency, recognizing the cooperative benefits at elevated levels, such as routing and security, is imperative. In this study, we propose to explore cooperative efficiency at both the lower network and application layers, introducing an RPL-inspired routing protocol, grounded in bit-power-transmission and bit error probability (BEP) within a cooperative-aided framework. It is requisite for each node in the network to maintain a routing table throughout the topology discovery phase, which encompasses a list of potential nodes that may ultimately interface with the cluster head (CH), identifying a selected node as the preferred relay. Furthermore, as a node dispatches a packet towards the CH, the CH, upon recognizing the sender, engages its preferred relay selection process to ascertain the packet's subsequent destination. This suggests a prospect of enhanced reception reliability and reduced energy consumption with each transmission hop. The CH (or root node in the RPL procedure) instigates the network topology's establishment. During the topology creation process, each network node furnishes its positional information to the CH.  
Upon the integration of a new node, the CH deduces the most fitting relay selection technique for it, taking into account the particular characteristics of the identified node. The power transmission of each link between the sensor node and the CH is computed during the recommended relay selection procedure. According to the energy link and packet loss as interpreted by BEP, the node facilitating the lowest transmission power, if present, is designated as the preferred relay (comparable to the preferred parent in the RPL framework). Consequently, the CH undertakes the responsibility of determining the subsequent hop for the source node, as shown in Figure 4.  
Once the network has been discovered and its routing has been established, the CH should initiate a new topology creation process at regular intervals, an action denoted by the coherence interval, or \(I_{c}oh\). Like ContikiRPL, the proposed protocol includes a neighbor-finding stage, denoted by [41]. During the relay selection algorithm phase, nodes also refresh their database of nearest neighbors. UDP was employed as the transport layer protocol. The contikiRPL selects a route for RPL routing based on the expected number of transmissions (ETX) needed to successfully transmit a packet across the connection [42]. The path that minimizes ETX from the source to the DODAG root is the route from a given node to the DODAG root. The routes, however, are constructed in the proposed protocol following PRSA using the BEP optimization as formulated in Equation (9). A brief comparison between RPL and the proposed protocol is summarized in Table 2.  
To direct traffic upwards like that of an RPL DODAG, CERP simply requires the data acquired by PRSA. The PRSA reveals which relay the node prefers to use. When a node  
\begin{table}
\begin{tabular}{l l l} \hline
**Protocol** & **RPL** & **CERP** \\ \hline Next hop & Preferred parent & Preferred relay \\ Building routes initialized by & Root & CH \\ Transport layer protocol & UDP & UDP \\ Network layer protocol & IPv6 & IPv6 \\ Control message type & ICMP & ICMP \\ Metric and constraint & ETX & \(E_{d_{S}}^{b}+P_{cha}\) \\ \hline \end{tabular}
\end{table}
Table 2: Comparison between RPL and CERP.  
Figure 4: CERP construction steps.  
has to transmit data to the CH, it does so by first sending the data to the desired relay in the tree, which then forwards these to its preferred relay, and so on, until the data reaches the CH. In the case of a leak in the node, the paths leading to the CH are shown in Figure 5.