# Energy Efficient Routing in Wireless Sensor Networks: A Comprehensive Survey
## 3 Network Structure
### Hierarchical
#### 3.2.3 Fuzzy Logic Based
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Protocol** & **Advantages** & **Disadvantages** & **Scalability** & **Mobility** & **Routing** & **Robustness** \\ \hline \multirow{6}{*}{DREEM-ME} & \multirow{6}{*}{\begin{tabular}{c} It has extended \\ stability period and \\ lower number of \\ dropped packets. \\ \end{tabular} } & \multirow{6}{*}{\begin{tabular}{c} It has unbalanced \\ consumption. \\ \end{tabular} } & \multirow{6}{*}{Limited} & \multirow{6}{*}{None} & \multicolumn{2}{c}{The outer regions} \\  & & & & & inner regions and \\  & & & & & those send them to \\  & & & & & the BS white nodes \\  & & & & & nearby the BS use \\  & & & & & direct communication. \\  & & & & & In the first region, the \\  & & & & & closest one to the BS, \\  & & & & & nodes use direct \\ REECH-ME & \
\begin{tabular}{c} stability period, \\ increased network \\ lifetime and balanced \\ energy consumption. \\ \end{tabular} & \multirow{6}{*}{
\begin{tabular}{c} It has limited \\ scalability. \\ \end{tabular} } & \multirow{6}{*}{Limited} & \multirow{6}{*}{None} & \multicolumn{2}{c}{communication while} \\  & & & & in the other regions, \\  & & & & data are aggregated \\  & & & & and sent to the BS via \\  & & & & each region’s cluster \\  & & & & head. \\  & & & & Nodes in Zone 0 use \\ Z-SEP [105] & It provides increased & It has increased & & direct routing while \\  & stability period and & consumption during & & nodes in Zones 1 and \\  & great throughput. & direct transmission. & & 2 transmit data to the \\  & & & & BS via their cluster \\  & & & & heads. \\  & & & & The cluster node send \\ ZSEP-E [106] & It provides improved & Random deployment & & & data to their cluster \\  & network lifetime and & of the nodes and the & & heads, which \\  & evenly distribution of & BS is not considered. & & aggregated and \\  & advanced nodes. & & forwarded them to \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Synopsis of Hierarchical Protocols belonging to the Zone based subcategory. input variables and uses a \"competition radius\". The first Fuzzy input is the residual energy of the candidate cluster head while the second one is the distance between cluster head and base station. Sensor nodes which have more residual energy and are closer to the base station are more probable to become the next cluster head. In EAUCF, high energy nodes are more probable to be elected as cluster heads and network lifetime is extended. On the other hand, there is a lack of parameters for selection of data packets to be broadcasted. In addition, mobility of nodes is not supported. Energy-aware distributed dynamic Clustering Protocol in wireless sensor networks using Fuzzy logic (ECPF) [110] is a dynamic clustering protocol that utilizes fuzzy logic to divide the network in unequal clusters. ECPF operates in rounds with each one of them consisting of two phases:  
1. Setup phase, which forms network clusters and elects cluster heads and
2. Steady State phase that uses TDMA frames, where in each frame a node sends data to its cluster head and at the end of it the cluster head aggregates data collected and sends the outcome to the base station. In addition, cluster heads store their residual energy information in their memory at the end of every round, to reduce communication between nodes. In the case that the residual energy of a cluster head is below a threshold, this cluster head informs the base station with a small data packet in the current TDMA and the base station in its turn, informs the nodes to perform from the beginning both clustering and cluster head election. With the use of ECPF, both network lifetime is extended and scalability is attained. On the other hand, coverage preservation causes high energy consumption. Multi-Objective Fuzzy Clustering Algorithm for wireless sensor networks (MOFKA) [111] is an energy-balancing clustering protocol that utilizes fuzzy logic to address the hotspot problem but is also an independent distribution method for the wireless sensor network.