In this paper, an iterative distributed approach is studied for the signal amplitude optimization when the distributed detection is carried out with a symmetric signaling constraint in a wireless sensor network (WSN) consisting of a fusion center (FC) and multiple sensors. In the conventional distributed detection, if sensors'' characteristics change due to aging problems or varying operating conditions, they have to be available at the FC for a best combining result. On the other hand, in the proposed approach, each sensor can adjust its signal amplitude using a type-based multiple access (TBMA) technique to provide a best performance at the FC through an iterative approach without sending their individual characteristics.