The purpose of this paper is to present ongoing PhD work that investigates both the cooperative diversity and techniques of network coding needed to improve communication reliability in wireless sensor networks. In this context, we propose a relay selection technique. It aims to select the smallest number of relay nodes under certain constraints. One of the main innovations is that this approach is formulated as an optimisation problem. In addition, we analyse the best approach for solving the proposed optimisation problem. The assessment results highlight that the proposed technique significantly improves the communication reliability of the network in comparison with the state-of-the-art techniques for selection of relay nodes. Network coding techniques will be tackled in the second stage of development of this research.