Feedback-Capacity of Degraded Gaussian Vector BC using Directed Information and Concave Envelopes

Viswanathan Ramachandran, Sibi Raj B. Pillai

Research output: Contribution to journalArticleAcademic

Abstract

It is known that the capacity region of a two user physically degraded discrete memoryless (DM) broadcast channel (BC) is not enlarged by feedback. An identical result holds true for a physically degraded Gaussian BC, established later using a variant of the Entropy Power Inequality (EPI). In this paper, we extend the latter result to a physically degraded Gaussian Vector BC (PD-GVBC). However, the extension is not EPI based, but employs a recent result on the factorization of concave envelopes. While the existing concave envelope factorization results do not hold in the presence of feedback, we show that factorizing the corresponding directed information quantities suffice to attain the feedback capacity region of a PD-GVBC. Our work demonstrates that factorizing concave envelopes of directed information can handle situations involving feedback. We further show that the capacity region of a discrete memoryless reversely physically degraded BC is not enlarged by feedback.
Original languageEnglish
Article number1704.05479
Number of pages16
JournalarXiv
Volume2017
Publication statusPublished - 2017
Externally publishedYes

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