# A Survey on Node Clustering in Cognitive Radio Wireless Sensor Networks
## 6 Survey of Some of the Existing Node Clustering Techniques
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Clustering Scheme** & **Objectives** & **Metrics** & **Performance Enhancement** & **CH Selection** & **Special Node** \\ \hline
**KoN-MAC** & MAC protocol & Similar to WSNs & Added channel weight & Elected & Gateway node \\ \hline
**MQ-MAC** & MAC protocol & Similar to LEACH & Modified for CRNs & Predetermined probability (similar to LEACH) & Gateway node \\ \hline
**CSS** & Energy efficiency & Similarity between & Energy consumption & No CH, but selects a node for & \\  & Cooperative task & sensor nodes & Energy consumption & spectrum sensing & NA \\ \hline
**ECS** & Cooperative spectrum sensing & Spectrum-aware & Energy consumption (compared with & Predetermined probability (similar to LEACH) & \\  & node-grouping & DEC algorithm [6] for WSNs & Only nodes in awake mode engage in the & NA \\ \hline
**SCEM** & Cross-layer routing protocol & Higher spectrum rank & Optimal number of clusters & Based on highest spectrum energy rank & NA \\ \hline
**CENTRE** & Energy efficiency & Distance to the CH & \
\begin{tabular}{c} Clustering overhead \\ (compared with DSAC) \\ \end{tabular} & Self-declared &
\begin{tabular}{c} Temporary support \\ (TS) node \\ \end{tabular} \\ \hline
**ESSA-RIC** & Energy efficient & Optimal number of & Cooperative probability of detection & Number of vacant channels (similar to HEED [57]) & NA \\ \hline
**BECIR** & Spectrum sensing & NA & Energy consumption & Iterative (based on energy level) & No, but all nodes \\  & & & & \\ \hline
**CogLEACH** & Clustering evaluation in three & Number of vacant & & Number of vacant channels as a weight in the & NA \\  & different similarity models & channels & Extension of LEACH & probability of each node becoming a CH & \\ \hline
**DSAC** & Energy efficiency &
\begin{tabular}{c} Optimal number \\ of clusters \\ \end{tabular} & Energy consumption & Iterative (each node has equal probability to & Only certain nodes \\  & & of clusters & Scalability & become CH) & can be CHs \\ \hline
**EAC** & Energy efficiency & \
\begin{tabular}{c} Optimal number \\ of clusters \\ \end{tabular} & NA &
\begin{tabular}{c} Residual energy and number of \\ neighbor nodes \\ \end{tabular} & NA \\ \hline
**ESAC/mESAC** & Event-driven clustering & Spectrum availabilities & \
\begin{tabular}{c} Energy consumption \\ (with a cost of delay) \\ \end{tabular} &
\begin{tabular}{c} Node degree, available channels, \\ and distance to the sink \\ \end{tabular} & NA \\ \hline
**LEAUCH** & Energy efficiency & \begin{tabular}{c} Number of channels \\ available \\ Uneven-sized clustering \\ \end{tabular} & \
\begin{tabular}{c} Energy consumption \\ Network load balance \\ \end{tabular} &
\begin{tabular}{c} Number of idle channels \\ Distance from the sink \\ \end{tabular} & NA \\ \hline
**Virtual clustering** & Control channel establishment & \begin{tabular}{c} Similarities of spectrum \\ MC protocol \\ \end{tabular} & \
\begin{tabular}{c} Conflict migration \\ computation \\ Geographic location \\ \end{tabular} &
\begin{tabular}{c} \\ Control packet success rate \\ Delay \\ \end{tabular} & NA & NA \\ \hline
**SCR** & Routing & Spectrum measurements & Mean packet delay & Spectrum energy rank & NA \\  & Residual energy & Energy consumption & & \\ \hline
**CR-HDC** & Energy efficiency & \
\begin{tabular}{c} Geographic location \\ Optimal transmission \\ range \\ \end{tabular} & NA &
\begin{tabular}{c} Iterative (based on residual energy and \\ average one-hop distance to all other nodes) \\ \end{tabular} & NA \\ \hline \hline \end{tabular}
**NA: Not applicable or information not available.**  
\end{table} 
Table 2: Comparison of the existing clustering schemes for CR-WSNs.