# Comparative Study of Energy Efficient Routing Techniques in Wireless Sensor Networks
## 3 The Proposed Taxonomy
### Network Topology (Structure)
#### 3.6.3 Heterogeneity-Based  
HHetrogeneity-based routing protocols are destined to a specific network topology in which there are several types of sensors, e.g., some sensor nodes can be battery-powered, and therefore it has a limited lifetime (battery-powered sensors), but others can have no energy constraint (line-powered sensors). Heterogeneity-based protocols manage to route  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Protocol**} & \multicolumn{4}{c}{**Network Topology: Hierarchical**} & \multirow{2}{*}{**Cluster**} \\  & **Block** & **Grid** & **Chain** \\  & **Cluster-Based** & **Cluster-Based** & **Scalability** & **Scalability** & **Delay** & **Energy Efficiency** \\ \hline
**LEACH** & ✓ & & & Medium & Very low & Very small & Very low \\ \hline
**CCM** & ✓ & & & High & Very low & Small & Very low \\ \hline
**LEACH-VF** & ✓ & & & High & Very low & Very small & Medium \\ \hline
**HCTE** & ✓ & & & Medium & Very low & Very small & Very low \\ \hline
**SLGC** & & ✓ & & Medium & Very low & Very small & Medium \\ \hline
**HGMR** & & ✓ & & High & Very high & Moderate & Medium \\ \hline
**CCS** & & & ✓ & Low & Low & Large & Low \\ \hline
**PEGASIS** & & ✓ & Low & Very low & Very large & Low \\ \hline \hline \end{tabular}
\end{table}
Table 5: Routing protocols for WSNs.  
and take advantage of unlimited or highest energy of some nodes to extend the network lifetime. When some sensors in the network are at one energy level while others nodes are at another, we talk about two levels of heterogeneity in the same way; WSNs can have three or more levels of heterogeneity if the network contains three or more categories of sensors with different energy levels. Some of the representative protocols in this category are:  
* **Developed Distributed Energy-Efficient Clustering (DDEEC)** This protocol is designed as a heterogeneity-based routing protocol and works at two levels of energy [72]. It presents an enhancement of the DEEC [73] protocol and uses some election probability functions to alternate the election of CHs between advance and normal nodes in order to remove the drawbacks of the DEEC election method. Research such as [74] shows that DDEEC outperforms DEEC in terms of network and stability period, but it presents some delays.
* **Threshold-Sensitive Stable Election Routing Protocol (TSEP) Protocol** TSEP is designed as a three-level heterogeneity-based routing protocol [75]. In fact, it divides nodes into three categories based on their energies, which are: normal, intermediate and advance nodes and acts as a reactive routing protocol. Simulations in [76] prove that TSEP increases stability, network lifetime and network throughput but causes some delays.
* **Enhanced Developed Distributed Energy Efficient Clustering (EDDEEC)** EDDEEC is designed as a three-level heterogeneity-based routing protocol [77]. It works in hierarchical networks and defines three types of sensors classified according to their energy levels into normal, advance and super nodes. Authors in [78] show that the scalability and the network lifetime is more efficient by using this protocol as compare to DEEC, but it presents some delays.
* **Balanced Energy Efficient Network Integrated Super Heterogeneous (BEENISH) Protocol** This protocol is designed as a four-level heterogeneity-based routing protocol [79]. It defines four types of nodes, namely normal, advance, super and ultra-super nodes, based on their energy levels. This protocol also works in a hierarchical context and uses some election probability functions in CH election. Simulations show that this protocol enhances the stability period, the throughput and the network lifetime as compare to DDEEC, TSEP and EDDEEC.  
Table 6 establishes a comparison between heterogeneity-based routing protocols [80].