We derive inner and outer bounds on the capacity region for a class of three-user partially connected interference channels. We focus on the impact of topology, interference alignment, and interplay between interference and noise. The representative channels we consider are the ones that have clear interference alignment gain. For these channels, Z-channel type outer bounds are tight to within a constant gap from capacity. We present near-optimal achievable schemes based on rate-splitting and lattice alignment.
The idea of sending multiple copies of the same sub-message at different signal levels, so-called Zigzag decoding, appeared in @cite_13 where receivers collect side information and use them for interference cancellation.
@cite_13
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We characterize the generalized degrees of freedom of the K user symmetric Gaussian interference channel where all desired links have the same signal-to-noise ratio (SNR) and all undesired links carrying interference have the same interference-to-noise ratio, INR = SNRα. We find that the number of generalized degrees of freedom per user, d(α), does not depend on the number of users, so that the characterization is identical to the 2 user interference channel with the exception of a singularity at α = 1 where d(1) = 1 K. The achievable schemes use multilevel coding with a nested lattice structure that opens the possibility that the sum of interfering signals can be decoded at a receiver even though the messages carried by the interfering signals are not decodable.