I. Introduction
At present, every industry requires rotating machinery which increases the demand for rolling-element bearings, making it an important element for a machine [1] - [3]. It is worth noting that the failure of a machine leads to sudden and unexpected stoppage of production, creating safety issues as well as even economic losses [4]. Therefore, monitoring the condition of rolling element bearing has a significant impact on lowering equipment damages and maintenance costs as well as improving sustainability as a result; maintenance costs make up more than 60% of total cost [5]. Effective and reliable machinery fault diagnosis offers the scientific foundation for an appropriate maintenance strategy, reducing unforeseen maintenance costs and production downtime and eventually enhancing operating performance, reducing energy use, and enhancing industrial sustainability [6].