## 5 Analysis of Prominent Clustering Routing Protocols in WSNs
### Cluster-Construction Based Clustering Routing Protocols
#### 5.1.10 Bcdcp  
Base-Station Controlled Dynamic Clustering Protocol (BCDCP), introduced by [PERSON] _et al._[25], is a centralized clustering routing protocol with the BS being capable of complex computation. The main idea of BCDCP is the cluster formation where each CH serves an almost equal number of MNs to balance CH overload and uniform CH placement throughout the network.  
At the beginning of cluster setup, the BS receives information on the residual energy from all the nodes in the network. Based on this information, the BS first computes the average energy level of all the nodes in the network, and then chooses a set of nodes whose energy levels are above the average value. Only the nodes from the chosen set, _i.e._, those with sufficient energy, can be elected CHs for the current round, while those with low energy can prolong their lifetime by performing the task of ONs. Based on the chosen set, the BS computes the number of clusters and performs the task of clustering, which is accomplished in terms of an iterative cluster splitting algorithm. This algorithm first splits the network into two sub-clusters, and proceeds further by splitting the sub-clusters into smaller clusters. This process will be repeated until the desired number of clusters is achieved. At each iteration of cluster splitting, two nodes that have the maximum separation distance are chosen for CHs from the chosen set where all the nodes are eligible to become CHs. Then, each of the remaining nodes in the current cluster is grouped with one CH or the other, whichever is closest. After balancing the two groups which have approximately the same number of nodes, the two sub-clusters are formed.  
In BCDCP, a multi-hop routing scheme is adopted to transfer the sensed data to the BS. Once the clusters and the CHs have been identified, the BS chooses the lowest-energy routing path and transfer information to the nodes along with the details on cluster groupings and selected CHs. The routing paths are selected by first connecting all the CHs by means of the Minimum Spanning Tree (MST) approach [69], which minimizes the energy consumption for each CH, and then randomly choosing one CH to forward the data to the BS. By randomizing the CH transmissions to the BS, the transmission burden is distributed almost evenly among all CHs in BCDCP. Figure 7 is the topology of the network in BCDCP.  
BCDCP utilizes a high-energy BS to set up clusters and uses MST [69] to connect CHs and randomly chooses a leader to send data to the BS. The advantages of BCDCP include the following [63]: (1) Clusters and transmission paths are constructed by the BS, thus BCDCP resolves the problem of CH distribution and ensures similar power dissipation of CHs; (2) TDMA is employed to schedule the time slots of cluster members; this allows sensor nodes to open communication interfaces only if data transmissions are required, which means energy can be saved at the same time.  
However, there exist a few disadvantages in BCDCP as follows: (1) BCDCP is a centralized algorithm which brings worse scalability and robust to large networks than distributed algorithms; (2) Each node needs to transmit information regarding its location and energy level to the BS during the process of cluster formation. Accordingly it increases the design complexity and the energy consumption of the nodes to some extent; (3) Due to the single-hop routing scheme, it is not appropriate for long-distance communications, which result in much energy consumption. Therefore, BCDCP is not adaptive to applications in large-range networks; (4) BCDCP is not suitable for reactive  
Figure 7: The Topology of the Network in BCDCP.  
networks where the user is not interested in periodic data retrieval, while the nodes only need to respond to events of certain significance in reactive networks.