I. Introduction
A spatially distributed network (SDN) consists of numerous devices/nodes with limited sensing, data processing, and communication capabilities. SDNs have been widely used to represent wireless sensor networks [1], [2] and robotic networks [3] for estimation, optimization, and control purposes. As SDNs may not have a control center, data processing/decision-making should be designed and implemented at the node level with direct data exchange between the neighboring nodes, also known as distributed estimation/optimization/control [4]. The communication network topology in SDNs is constructed based on the locations of the nodes and their communications range, as a node can only send information to the nodes within its communication range. Since the individual node may have different but limited communication range, the network topology in SDNs can then be modeled as a directed graph.