# Energy Saving in Wireless Sensor Networks via LEACH-Based, Energy-Efficient Routing Protocols
## 3 LEACH-Based Energy-Efficient Routing Protocols  
It is noteworthy that, although LEACH was introduced in the beginning of 21 st century, numerous energy-efficient protocols keep on being proposed every year since then, as modifications and optimizations of LEACH [29; 33; 34; 35; 36; 37; 38; 39]. Many of these LEACH descendants have proven to enhance the operation of their predecessor. Yet, these protocols have different pros and cons when compared in terms of not only their energy efficiency but also many other features, such as scalability, overhead, load balance, latency, complexity, cluster formation, location information, fault tolerance modulation techniques, communication model, and channel encoding [31]. Also, in order to perform the communication among each cluster head and the base station, some of these protocols utilize single-hop routing, while other ones use the multi-hop routing, which is necessitated in large-scale WSNs. Consequently, based on the above considerations, it is obvious that the selection of the most suitable hierarchical routing protocol is application-dependent. In what follows in this section, various descending protocols of LEACH are indicatively referred to as examples of reference. Threshold LEACH (T-LEACH) [40] is a single-hop routing protocol. Similarly to LEACH, T-LEACH also strives to extend the lifetime of a WSN by decreasing the energy consumption that is associated with data transmission and aggregation. Yet, contrary to LEACH, where cluster heads are selected according to a specific probability in each round, in T-LEACH, new cluster heads are selected only when the residual energy of the existing cluster heads becomes lower than a specific energy threshold, which is dynamically calculated based on various network parameters. In this way, in T-LEACH, the frequency of cluster head changes is reduced. Consequently, the transmission of advertisement messages, which takes places among the cluster head and its cluster nodes every time that a new cluster head is selected, becomes less frequent too. The reduction in data transmissions results to corresponding energy saving. Indeed, it has experimentally been demonstrated that T-LEACH achieves higher energy efficiency than LEACH. On the other hand, the configuration and utilization of the appropriate threshold value can be challenging, and it may be associated with additional communication overhead. LEACH balanced (LEACH-B) [41] is a single-hop routing protocol. It aims to balance the formation of clusters by taking into consideration both the residual energy of the sensor nodes and the desired proportion of cluster heads in the whole network. The total number of cluster heads is defined by the product \(n\cdot p\), where \(n\) represents the total number of network nodes, and \(p\) symbolizes the desired percentage of the cluster heads. The first cluster heads are selected randomly by a procedure similar to that adopted by LEACH. All cluster heads are sorted according to their residual energy. If the number of the randomly nominated cluster heads is lower than the product \(n\cdot p\), then some normal network nodes are selected as cluster heads. If this number is larger than the product \(n\cdot p\), then cluster heads with lower energy are one by one converted to normal network nodes until the number of cluster heads becomes equal to the product \(n\cdot p\). LEACH-B achieves energy balance in cluster head selection and cluster formation. Yet, it suffers from high complexity, high overhead, and low scalability. Centralized LEACH (LEACH-C) [42] is a single-hop routing protocol. It has a steady phase, which is like that in LEACH, and a setup phase, which differs from that of LEACH, since the cluster heads are selected by the base station. Specifically, all nodes report to the base station both their location and the quantity of their residual energy.