To increase reliability and fault tolerance in wireless sensor network, using spare nodes is a useful method. In this article, we survey the influence of using single-type and multi-type spare nodes on the fault tolerance in the low density. To achieve this, we use single-type and multi-type spare nodes and construct the network reliability graph for one, two and three-node densities. Then, we consider the mentioned spares from spare-less to three spares and construct Markov models. Afterwards, reliability function, the average failure rate and the entire network MTTF are calculated by solving Markov equations. The simulation results showed that the use of shared spare nodes leads to improving MTTF in the higher density. Moreover, we found that there is a limited number of spares to improve the MTTF so that we will no longer have more improvement by applying more spares.
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