I. Introduction
Distributed detection based on wireless sensor networks (WSN) is a topic which has attracted great interest in recent years (see [2] and references therein). A typical WSN has a large number of sensor nodes which are generally low-cost battery-powered devices with limited sensing, computing, and communication capabilities. Sensors acquire noisy measurements, perform simple data processing and propagate the information into the WSN to reach a decision about a physical phenomenon occurring in the coverage area. The data processing at each node and the propagation of the information within the network are key aspects to be considered to achieve the required performance level.