On the Degrees of Freedom of the Symmetric Multi-Relay MIMO Y Channel
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AbstractIn this paper, we study the degrees of freedom (DoF) of the symmetric multi-relay multiple-input multipleoutput (MIMO) Y channel, where three user nodes, each with M antennas, communicate via K geographically separated relay nodes, each with N antennas. For this model, we establish a general DoF achievability framework based on linear precoding and post-processing methods. The framework poses a nonlinear problem with respect to user precoders, user post-processors and relay precoders. To solve this problem, we adopt an uplinkdownlink asymmetric strategy, where the user precoders are designed for signal alignment and the user post-processors are used for interference neutralization. With the user precoder and post-processor designs fixed as such, the original problem then reduces to a problem of relay precoder design. To address the solvability of the system, we propose a general method for solving matrix equations. Together with the techniques of antenna disablement and symbol extension, an achievable DoF of the considered model is derived for an arbitrary setup of (K,M,N). We show that for K≥2, the optimal DoF is achieved for MN∈[0,max{3K√3,1})∪[3k+9K2−12k√6,∞). We also show that the uplink-downlink asymmetric design proposed in this paper considerably outperforms the conventional approach based on uplink-downlink symmetry.
Acceptance Date01/05/2017
All Author(s) ListT. Ding, X. Yuan, S. C. Liew
Journal nameIEEE Transactions on Wireless Communications
Detailed descriptionAvailable as early access in IEEE Xplore
Volume Number16
Issue Number9
LanguagesEnglish-United States

Last updated on 2021-17-06 at 00:43