Wireless smart sensor networks (WSSN) have many advances compared with traditional structural health monitoring (SHM) such as wireless process, real-time calculation and low cost. However power consumption is considered as one of the most limitations in this field. The unique features offered by decentralized data aggregation (DDA) technique with the potential to overcome power consumption enable implementation of the dense array of WSSN on large structures. This paper presents a system identification of a simply supported plate based on the random decrement technique (RDT) and natural excitation technique (NExT) in combination with eigensystem realization algorithm (ERA) using Illinois Structural Health Monitoring Project (ISHMP) Services Toolsuite. Finally the system parameters including natural frequency and mode shapes are in accordance with numerical simulation showing efficacy and feasibility of decentralized NExT/ERA and RDT/ERA system identification.