# An Energy-Aware Method for Selecting Cluster Heads in Wireless Sensor Networks
### The Concept of Routing in Wireless Sensor Networks  
Routing is a considerable challenge due to several features in WSNs. The first feature is that there are many sensor nodes in WSNs. Based on this feature, it is impractical to build an addressing scheme for considerable sensor nodes because the ID maintenance overhead is too high. Therefore, the traditional IP-based protocol cannot be utilized in WSNs, and sensor nodes placed by the ad hoc method in the environment must be self-organized because sensor network operations need to be monitored. Consequently, these sensors require systems that establish communication and manage the distribution process. Moreover, in WSNs, received data are more critical than recognizing the ID of the data that should be sent. Second, unlike conventional communication networks, all WSN applications are required to transfer the sensed data from various sources to a specific base station. Third, sensor nodes have severe limitations in storage capability, energy, and processing. Thus, it is necessary to manage resources accurately. Forth, in most WSN scenarios, sensor nodes do not move after placing sensor nodes in the environment. By contrast, in a traditional wireless network, the sensor nodes can move everywhere, and the topology in this network changes constantly and unpredictably. However, in several applications, some sensor nodes may be able to move. Fifth, the requirements for the design of WSNs are determined by their applications. Sixth, for WSNs, it is indispensable to realize the status of sensor nodes because gathering data is based on their location, and GPS may provide this status. However, there are some methods by which we can find the location without GPS. Finally, gathering data in WSNs is performed by several sensor nodes. Therefore, the occurrence of redundancy in these data is tremendously high. This redundancy should be extracted by the routing protocol to increase the energy consumption and bandwidth. It is worth mentioning that WSNs are usually data-driven because data are requested according to several specific features. In the following, we express several considerable issues in the routing protocol:  
1. Coverage: In WSNs, each sensor node can obtain some information about the area, and this information relies on the accuracy and range of sensor nodes. Furthermore, the information  
Figure 2: Power consumption of sensor node subsystems [7].  
collected by the sensor node belongs to a specific part of the environment. Hence, area coverage is a significant issue that is used in WSNs' design.
2. Data aggregation: Since sensor nodes likely produce several redundant data, similar data packets generated from several nodes can be integrated to reduce the number of transfers. This method is used in several routing protocols to optimize energy consumption and data transfer.
3. Quality of Service (QoS): Data should be sent in several applications at a particular time; otherwise, the data will be useless. Therefore, the limited delay in data transfer is a condition for other time-consuming applications. On the other hand, in other applications, storing energy is more essential than the quality of service. However, to save energy in sensor nodes and increase the lifetime, it is indispensable to diminish the quality of the result. Thus, the routing protocol usually ignores the QoS.