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Propagation-Delay Based Cyclic Interference Alignment with One Extra Time-Slot for Three-User X Channel
Feng LIU Shuping WANG Shengming JIANG Yanli XU
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences
Publication Date: 2019/06/01
Online ISSN: 1745-1337
Type of Manuscript: LETTER
Category: Coding Theory
interference alignment, three-user X channel, propagation delay, time-slot, degree of freedom,
Full Text: FreePDF(977.4KB)
For the three-user X channel, its degree of freedom (DoF) 9/5 has been shown achievable theoretically through asymptotic model with infinite resources, which is impractical. In this article, we explore the propagation delay (PD) feature among different links to maximize the achievable DoF with the minimum cost. Since perfect interference alignment (IA) is impossible for 9 messages within 5 time-slots, at least one extra time-slot should be utilized. By the cyclic polynomial approach, we propose a scheme with the maximum achievable DoF of 5/3 for 10 messages within 6 time-slots. Feasibility conditions in the Euclidean space are also deduced, which demonstrates a quite wide range of node arrangements.