The existing clustering algorithms are either static or dynamic depending on the frequency of clustering. In static clustering, clusters are formed once, which reduces the clustering overhead but leads to early energy drain of a few nodes in the network. The network lifetime can be improved by dynamic clustering in which clusters are reformed after every round, which increases the clustering overhead. To optimize the parameters, including clustering overhead, network lifetime, energy hole, FND (first node dies) and LND (last node dies) in WSN, a hybrid unequal clustering with layering protocol (HUCL) is proposed. The HUCL is a hybrid of static and dynamic clustering approaches. In HUCL, the network is divided into layers and clusters of various sizes. The cluster heads are selected based on available energy, the distance to the sink and the number of neighbors. Once the cluster is formed, the same structure is maintained for a few rounds. The data are forwarded to the sink through a multi-hop layer-based communication with an in-network data compression algorithm. In comparison with the existing protocols, the HUCL balances energy and achieves a good distribution of clusters, extends the lifetime of the network and avoid the energy hole problem. 
Energy efficient data collection through hybrid unequal clustering for wireless sensor networks