From Feedback Capacity to Tight Achievable Rates without Feedback for AGN Channels with Stable and Unstable Autoregressive Noise

In this paper we employ the information structures of optimal channel inputs of feedback capacity of additive Gaussian noise (AGN) channels, driven by stable and unstable autoregressive noise, to derive achievable rates for nofeedback capacity, and the corresponding channel input processes. The expressions of rates are derived using time-domain methods, they hold for stable and unstable noise, for all values of transmit power. The method avoids power spectral techniques and their limitations. The lower bounds are evaluated against the classical nonfeedback capacity obtained via water-filling frequency-domain techniques.