## 2 System Model  
We consider an MCR-MANET consisting of multiple cognitive users (CUs) and a primary user (PU), as shown in Figure 1. The PU operates on a licensed channel and switches randomly to ON mode or OFF mode. When the PU is in the ON mode, cognitive users can not transmit packets on the \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Paper** & **Clustering/CDS** & **Routing** & **Cognitive** & **Multi-** & **Node** & **Stability** & **Energy** \\  & **Algorithm** & **Algorithm** & **Network** & **Channel** & **Speed** & **of Route** & **Consumption** \\ \hline \hline Proposed CRD & Yes & Yes & Yes & Yes & Yes & Yes & Yes \\ [7] & Yes & - & - & - & - & Yes & Yes \\ [8] & Yes & - & - & - & Yes & Yes & - \\ [11] & Yes & - & - & - & - & - & - \\ [12] & Yes & - & - & - & - & - & - \\ [13] & Yes & - & - & - & - & - & - \\ [14] & Yes & - & - & - & - & - & Yes \\ [15] & - & Yes & - & - & - & - & Yes \\ [16] & Yes & Yes & - & - & Yes & Yes & - \\ [22] & - & Yes & Yes & Yes & - & - & - \\ [23] & - & Yes & Yes & Yes & - & - & - \\ [24] & - & Yes & Yes & Yes & Yes & - & - \\ [25] & - & Yes & Yes & - & Yes & - & - \\ [26] & - & Yes & Yes & Yes & Yes & - & - \\ [32] & - & Yes & - & - & Yes & - & Yes \\ [34] & - & Yes & - & - & Yes & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of proposed protocol (CRD) with other protocols. licensed channel in the affected region of PU. When the PU is in the OFF mode, cognitive users can use the licensed channel to transmit packets in the networks. This paper focuses on addressing the routing problems when the PU is in the ON mode to improve the spectrum utilization in cognitive environment. Moreover, the PU's mobility follows the random waypoint (RWP) model. In the secondary network, each user can be seen as a mobile node and its properties can be listed as follows:  
* All nodes move randomly in the two-dimension space based on the RWP model. * Each node can know the location of the destination and its own location through the global positioning system (GPS) [3; 36]. * The transmission range of nodes is fixed [9]. * Each node receives packets on a given channel (receiving channel) while it can switch to any channel to send packets. Moreover, mobile nodes in the secondary network can be classified into groups/clusters. Each cluster has three types of nodes including cluster head, gateway and cluster member, respectively [37]. Firstly, a cluster head (CH) is a representation of a cluster and its tasks are aggregating packets of all cluster members and transmitting the aggregated packet within a single hop. Moreover, CH can directly communicate with a gateway or other CHs. Secondly, a gateway (GW) is an intermediate node which can directly communicate with its CH or CHs/GWs of other clusters within a single hop. Finally, a node in a cluster is a member (CM) if it is neither a cluster head nor a gateway. It only communicates with its CH within a single hop. Figure 1 describes the operation of cluster head and gateway and cluster member in MCR-MANETs. As can be seen in Figure 1, source \(S\) generates a RREQ packet and sends it to CH\({}_{1}\) without switching channel. CH\({}_{1}\) chooses a focus region with sending channel 2 to forward the RREQ to GW\({}_{1}\) and GW\({}_{2}\). Because GW\({}_{2}\) is in the radio range of PU and PU uses channel 1 as licensed channel, GW\({}_{2}\) can not forward the RREQ packet on channel 1 to CH\({}_{3}\) while GW\({}_{1}\) can choose a focus region to forward the RREQ packet to GW\({}_{3}\) without switching channel. GW\({}_{3}\) continues to forward the RREQ packet to CH\({}_{2}\) without switching channel. CH\({}_{2}\) chooses a focus region with sending channel 3 to forward the RREQ packet to GW\({}_{4}\). GW\({}_{4}\) continues to forward the RREQ to CH\({}_{4}\) without switching channel. CH\({}_{4}\) switches to channel 2 and forwards the RREQ packet to destination \(D\).