# Energy Efficient Routing in Wireless Sensor Networks: A Comprehensive Survey
## 3 Network Structure
### Hierarchical
#### 3.2.1 Hierarchy Based
However, the algorithm complexity causes overhead. _Grid Based Data Dissemination_ (GBDD) [70] is a protocol in which the BS expresses an interest in data communication, and constructs a grid of squared cells. The sides of the cell have of a size a, containing a node. The size a is determined by two radio ranges that every node is capable of high power range (RH) and low power range (RL). The BS uses its geographical coordinates \((x,y)\) as the starting point of grid cell formation and sets itself as the crossing point of the grid. In GBDD,continuous data delivery from source to the BS is achieved. Another advantage of GBDD is that only the BS constructs the grid. A disadvantage of GBDD is that, at high speeds, more energy is consumed. _Extending Lifetime of Cluster Head_ (ELCH) [71] protocol uses an election scheme, where cluster nodes vote their cluster heads and multi-hop routing between cluster head and the BS communication. ELCH operation consists of two phases:  
1. Election phase. The neighboring nodes form clusters and elect a cluster head using a voting scheme. 2. Network preparation phase. The cluster consists of neighboring nodes and one cluster head. Afterwards, cluster head uses the TDMA mechanism to transmit the time slot of every cluster node and maintains a maximum power table each round for every node. Then, data communication begins, data flow from cluster nodes directly to cluster head while each cluster head communicates with each other and the BS using multi-hop routing. In ELCH, energy consumption is kept low and thus the network life is prolonged. However, in the case that the number of cluster nodes exceeds a specific amount, network operation faces a negative effect. _Novel Hierarchical Routing Protocol Algorithm_ (NHRPA) [72] performs only one initialization node process during sensor node network deployment. NHRPA mainly uses loop, judgment, and assignment operations to deal with nodes and considers node distribution density, nodes residual energy, and node to the BS distance to adopt a suitable routing technology. The use of NHRPA achieves balanced energy consumption and can adopt suitable routing technology. However, packet latency is caused. _Scaling Hierarchical Power Efficient Routing_ (SHPER) [73] is a hierarchical energy efficient protocol which aims to extend the network lifetime as much as possible by both using the optimal routing paths and keeping alive the weakest network nodes. The operation of SHPER consists of two phases:  
1. Initialization phase: In this phase, the BS transmits a TDMA schedule and requests of the nodes to advertise themselves. Then, the nodes transmit their advertisements and their in-between distances are identified. After that, the BS elects a predefined number of high and low level cluster heads, based on their residual energy, then it broadcasts new cluster head IDs and threshold values. High level cluster head is closer to the BS and communicates with it via single-hop routing, while low level cluster heads are the distant ones and need to route data to the BS via the high level cluster heads. 2. Steady state phase: Each cluster head defines the most energy efficient path to route its messages to the BS by taking into account both the residual energy of sensor nodes and the energy cost of data transmission. Thus, weak nodes are preserved. Nodes transmit sensed data if their sensed value is above the hard threshold and changed from their previous value by the soft threshold. SHPER attains high energy efficiency because it both achieves even energy depletion of nodes and performs routing via the most energy efficient paths. In addition, due to its hierarchical architecture, it attains high scalability. When the energy reserves of nodes are unequal and the BS is far away from the network field, the use of SHPER protocol becomes even more beneficial. However, mobility is not considered. _Power Efficient Multimedia Routing_ (PEMuR) [74] is based on SHPER protocol and combines hierarchical energy efficient routing and video packet scheduling models.