Secure GDoF of the Z-channel with Finite Precision CSIT: How Robust are Structured Codes?

Abstract

Under the assumption of perfect channel state information at the transmitters (CSIT), it is known that structured codes offer significant advantages in an interference network, e.g., lattice alignment allows a receiver to directly decode the sum of aligned interfering codewords at higher power levels even though individual codewords are not resolvable, subtract the aggregate interference, and then proceed to decode desired codewords at lower power levels. To what extent are such benefits of structured codes fundamentally limited by uncertainty in CSIT? To answer this question, we explore what is perhaps the simplest setting where the question presents itself — a Z interference channel with secure communication. Using sum-set inequalities based on Aligned Images bounds we prove that the GDoF benefits of structured codes are lost completely under finite precision CSIT. The secure GDoF region of the Z interference channel is obtained as a byproduct of the analysis.