  Identifiability conditions for single or multiple modules in a dynamic
network specify under which conditions the considered modules can be uniquely
recovered from the second-order statistical properties of the measured signals.
Conditions for generic identifiability of multiple modules, i.e. a subnetwork,
are developed for the situation that all node signals are measured and
excitation of the network is provided by both measured excitation signals and
unmeasured disturbance inputs. Additionally, the network model set is allowed
to contain non-parametrized modules that are fixed, and e.g. reflect modules of
which the dynamics are known to the user. The conditions take the form of
path-based conditions on the graph of the network model set. Based on these
conditions, synthesis results are formulated for allocating external excitation
signals to achieve generic identifiability of particular subnetworks. If there
are a sufficient number of measured external excitation signals, the formulated
results give rise to a generalized indirect type of identification algorithm
that requires only the measurement of a subset of the node signals in the
network.
