  This paper studies networked control systems closed over noiseless digital
channels. By focusing on noisy LTI plants with scalar-valued control inputs and
sensor outputs, we derive an absolute lower bound on the minimal average data
rate that allows one to achieve a prescribed level of stationary performance
under Gaussianity assumptions. We also present a simple coding scheme that
allows one to achieve average data rates that are at most 1.254 bits away from
the derived lower bound, while satisfying the performance constraint. Our
results are given in terms of the solution to a stationary signal-to-noise
ratio minimization problem and builds upon a recently proposed framework to
deal with average data rate constraints in feedback systems. A numerical
example is presented to illustrate our findings.
