## Performance Evaluation  
### Environments and Measured Parameters  
In this subsection, we evaluate the performance of the proposed CRD routing protocol under different _max-speeds_ of mobile nodes (20 km/h, 40 km/h, 60 km/h and 80 km/h). The simulation environments and parameters are listed in Table 2. The simulation of the proposed CRD routing protocol is implemented in OMNET++ platform. At the beginning, the location of the nodes is deployed randomly in a region of 1000 \(\times\) 1000 m\({}^{2}\). The coverage range of PU is 250 m and the transmission range of all cognitive users is 250 m. The random waypoint model is used for the node mobility and the channel switching time is 5 ms [42]. The initial energy of each node is set up randomly from 17,280 Joules (3 V, 1600 mhA) to 28,800 Joules (5 V, 1600 mhA). To balance the effects of functions stability (_ST_), remaining energy ratio (_RE_) and speed ratio (_SP_) in the process of connected dominating set selection and cluster head election, the parameters \(w_{1},w_{2}\) and \(w_{3}\) in Equation (8) are chosen so that their value are nearly equal \(1/3\). To prioritize the stability of the connected dominating set, we choose \(w_{1}=0.4\) which is higher than the other parameters (\(w_{2}=0.3,\ w_{3}=0.3\)). The time of the simulation is 1500 s.  
The performance metrics of the proposed CRD protocol can be defined as follows  
* The number of cluster heads: the sum of CHs over the sum sessions.
* The number of new cluster heads: the average number of new CHs between two consecutive sessions.
* The reuse number of a cluster: the average number of sessions which a cluster is reused.
* The number of control packets, called the control overheads: the total number of control packets over the total of finished sessions which are used for route establishment from a source to a destination.
* The delay: the average time to establish a route for one session.
* The packet delivery ratio: the average ratio of the number of received packets at a destination to the number sent packets at a source for each finished session.
* The energy consumption: the average dissipated energy of a node for each session.
* The number of switched channels: the average number of times that nodes must switch channel when sending data from a source to a destination for one session.  
We also implement the AODV routing protocol [43] in MCR-MANET, called CR-AODV, for comparison purpose. The energy model and multi-channel models used in this paper are also applied for the CR-AODV protocol. The CR-AODV protocol is presented in each session as follows. First, PU sends a notice of its presence to the neighbors. Second, in the same way as the original AODV protocol, a source generates and sends RREQ packets on all available channels which are unoccupied by PU to find a destination. If a CU receives a RREQ packet, it will forward the RREQ packet on all channels. If the destination receives a RREQ, it will generate the RREP to reply to the source in the  
\begin{table}
\begin{tabular}{l l} \hline \hline Network size & 1000 \(\times\) 1000 m\({}^{2}\) \\ Number of nodes & 50 \\ Session length & 5 s \\ Number of PU & 1 \\ PU status & ON-OFF \\ Coverage range of PU & 250 m \\ Transmission range of nodes & 250 m \\ Number of channels & 5 \\ Initial energy & 17,280\(\sim\)28,800 Joules \\ Max speed of nodes & 20, 40, 60 and 80 km/h \\ Mobility model & Random waypoint \\ Channel switching time & 5 ms \\ Control packet size & 1024 bits \\ Data packet size & 2048 bits \\ Transmission energy & \(E_{TX}=(330\times 5\times PacketSize)/(2\times 10^{6})\) \\ Receiving energy & \(E_{RX}=(230\times 5\times PacketSize)/(2\times 10^{6})\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation Environments and Parameters.  
same way as the AODV protocol does. Finally, if the source receives a RREP, it will use the routing table to send data to the destination.