## 2 Related Works  
Due to its outstanding success, LEACH protocol has gained much popularity in the WSN research field. Accordingly, one can find many studies which have proposed new techniques for the data routing in WSN, by modifying the LEACH protocol in order to mitigate its drawbacks. This section presents some of these approaches as related work to the approaches developed by us. In this context, it would be useful to mention that all of these approaches have succeeded to upgrade the WSN performance in comparison with conventional LEACH protocol. A part of these protocols has modified the set-up phase of the LEACH protocol, while the remaining part was interested in enhancing the steady-state phase. The LEACH-Centralized (LEACH-C) protocol was proposed in [14]. It is described as a centralized protocol due to all decisions being issued by the BS and then forwarded to the sensor nodes. For instance, electing the CHs of the network and managing the clusters are accomplished by the BS. The expected result of the LEACH-C protocol is to have an excellent distribution of nodes among the clusters. The LEACH-Deterministic Cluster Head Selection (LEACH-DCHS) protocol, which is presented in [15], aims to prolong the network lifetime. Accordingly, two modifications have been proposed. The first one is adjusting the threshold equation, which is used in electing the CHs of the network by taking into account the residual energy in the sensor nodes. The second modification is introducing a new definition for the network lifetime. The main idea of the Threshold-LEACH (T-LEACH) protocol was analyzed in [16]. In this protocol, the CHs of the network are chosen based on a threshold energy scheme. Moreover, the CHs are used for a fixed number of rounds. This situation is continued until the remaining energy of the CH becomes less than the threshold energy. If this happens, a new CH will be elected. The Unequal Clustering LEACH (U-LEACH) protocol was proposed in [17] and aims to reduce the energy consumption in a single hop communication, such as the LEACH protocol. In single-hop fashion, the CHs data is transmitted directly into the BS. The previous approach increases the energy consumption in the CHs, which are located far from the BS. For this reason, the U-LEACH supposes that the clusters size will be unequal and that it will be smaller as we move away from the BS. To solve the unbalanced clusters in the conventional LEACH protocol, the LEACH-Balanced (LEACH-B) protocol was proposed in [18]. This protocol takes into consideration the desired percentage of the nodes within the clusters, as well as it takes into account the residual energy of the nodes for electing the CHs and forming balanced clusters. For minimizing the transmissions distances over the network, the MHT-LEACH protocol was proposed in [11]. It splits all CHs into two levels. The first one is the internal level that includes all the CHs whose distances to the BS are less than a specific threshold. The second one is the external level which includes the CHs whose distances to the BS are equal or larger than the threshold. The data from any CH of the external level are routed to the BS by means of an appropriate CH from the internal level. A solution, Solar Aware-LEACH (s-LEACH), for adding an external energy source for the sensor nodes was discussed in [19]. The solution is based on using the solar power. All sensor nodes transmit their solar power status and residual energy to the BS, which, in turn, chooses the nodes that have a good power status and higher residual energy to become CHs. A new protocol for selecting the CHs of the network, the Advanced-LEACH (ALEACH) protocol, was suggested in [20]. According to this protocol, the threshold value is based on two terms: a general state probability and a current state probability. Thus, their combination provides the threshold value for each round. The DMHT-LEACH protocol developed and analyzed in [13] for enhancing the CHs data routing in the IMHT-LEACH protocol.