  We generalize the system level synthesis framework to systems defined by
bounded causal linear operators, and use this parameterization to make
connections between robust system level synthesis and classical results from
the robust control literature. In particular, by leveraging results from L1
robust control, we show that necessary and sufficient conditions for robust
performance with respect to causal bounded linear uncertainty in the system
dynamics can be translated into convex constraints on the system responses. We
exploit this connection to show that these conditions naturally allow for the
incorporation of delay, sparsity, and locality constraints on the system
responses and resulting controller implementation, allowing these methods to be
applied to large-scale distributed control problems -- to the best of our
knowledge, these are the first such robust performance guarantees for
distributed control systems.
