2013/09/03 by Sina Lashgari, Lashgari, Sina, A. Salman Avestimehr +3
Computer Science · Engineering · Mathematics · #Advanced MIMO Systems Optimization #Channel (broadcasting) #Combinatorics #Computer network #Computer science #Converse #Cooperative Communication and Network Coding #Degrees of freedom (physics and chemistry) #FOS: Computer and information sciences #Information Theory (cs.IT) #Interference alignment #Lemma (botany) #Linear network coding #Linear subspace #MIMO #Mathematical analysis #Mathematics #Physics #Pure mathematics #Telecommunications #Topology (electrical circuits) #Upper and lower bounds #Wireless Communication Security Techniques #cs.IT #math.IT
paper · pdf · doi:10.48550/arxiv.1309.0799
To appear in the IEEE Transactions on Information Theory
openalex publication_date 2013/09/03 · arxiv created 2014/02/01 · arxiv updated 2014/02/04 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We establish the degrees of freedom of the two-user X-channel with delayed channel knowledge at transmitters (i.e., delayed CSIT), assuming linear coding strategies at the transmitters. We derive a new upper bound and characterize the linear degrees of freedom of this network to be 6/5. The converse builds upon our development of a general lemma that shows that, if two distributed transmitters employ linear strategies, the ratio of the dimensions of received linear subspaces at the two receivers cannot exceed 3/2, due to delayed CSIT. As a byproduct, we also apply this general lemma to the three-user interference channel with delayed CSIT, thereby deriving a new upper bound of 9/7 on its linear degrees of freedom. This is the first bound that captures the impact of delayed CSIT on the degrees of freedom of this network, under the assumption of linear encoding strategies.