  In this note, the coordination of linear discrete-time multi-agent systems
over digital networks is investigated with unmeasurable states in agents'
dynamics. The quantized-observer based communication protocols and Certainty
Equivalence principle based control protocols are proposed to characterize the
inter-agent communication and the cooperative control in an integrative
framework. By investigating the structural and asymptotic properties of the
equations of stabilization and estimation errors nonlinearly coupled by the
finite-level quantization scheme, some necessary conditions and sufficient
conditions are given for the existence of such communication and control
protocols to ensure the inter-agent state observation and cooperative
stabilization. It is shown that these conditions come down to the simultaneous
stabilizability and the detectability of the dynamics of agents and the
structure of the communication network.
