Open AccessMinimum number of antennas and degrees of freedom of multiple‐input–multiple‐output multi‐user two‐way relay X channels
Author(s) -
Kim TaeHoon,
Jin DongSup,
Kim Jaehong,
No JongSeon,
Chung Habong
Publication year - 2015
Publication title -
iet communications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.355
H-Index - 62
eISSN - 1751-8636
pISSN - 1751-8628
DOI - 10.1049/iet-com.2014.0714
Subject(s) - relay , mimo , beamforming , degrees of freedom (physics and chemistry) , computer science , scheme (mathematics) , topology (electrical circuits) , mathematics , telecommunications , physics , power (physics) , mathematical analysis , quantum mechanics , combinatorics
In this study, the minimum number of antennas at each user is derived to obtain 2 M 2 degrees of freedom (DOF) in the M × 1 × M multiple‐input–multiple‐output (MIMO) multi‐user two‐way relay X channels. Based on the design of beamforming vectors for the conventional signal space alignment scheme, it is shown that each user needs at least ⌈ M 2 − ( M /2)⌉ antennas to obtain DOF 2 M 2 with the relay having M 2 antennas. As the number of users increases, the number of antennas also increases, which makes the implementation difficult. In an effort to reduce the number of antennas, the authors propose a new beamforming scheme of MIMO multi‐user two‐way relay X channels using the time extension. Through the numerical analysis, it is confirmed that the proposed scheme with time extension is a good alternative scheme to replace the conventional scheme.