Generalized Signal Alignment For MIMO Two-Way X Relay Channels

Abstract

We study the degrees of freedom (DoF) of MIMO two-way X relay channels. Previous work studied the case $N<2M$, where $N$ and $M$ denote the number of antennas at the relay and each source, respectively, and showed that the maximum DoF of $2N$ is achievable when $N\le \lfloor \frac{8M}{5}\rfloor$ by applying signal alignment (SA) for network coding and interference cancelation. This work considers the case $N>2M$ where the performance is limited by the number of antennas at each source node and conventional SA is not feasible. We propose a \textit{generalized signal alignment} (GSA) based transmission scheme. The key is to let the signals to be exchanged between every source node align in a transformed subspace, rather than the direct subspace, at the relay so as to form network-coded signals. This is realized by jointly designing the precoding matrices at all source nodes and the processing matrix at the relay. Moreover, the aligned subspaces are orthogonal to each other. By applying the GSA, we show that the DoF upper bound $4M$ is achievable when $M\le \lfloor \frac{2N}{5}\rfloor$ ($M$ is even) or $M\le \lfloor \frac{2N-1}{5}\rfloor$ ($M$ is odd). Numerical results also demonstrate that our proposed transmission scheme is feasible and effective.

6 pages, 6 figures, to appear in IEEE ICC 2014

References in corpus (2)

• Physical Layer Network Coding
• Degrees of Freedom Region for the MIMO X Channel

Cited by in corpus (4)

• Generalized Signal Alignment: On the Achievable DoF for Multi-User MIMO Two-Way Relay Channels
• Generalized Signal Alignment For Arbitrary MIMO Two-Way Relay Channels
• A New DoF Upper Bound and Its Achievability for $K$-User MIMO Y Channels
• MIMO Multiway Distributed-Relay Channel with Full Data Exchange: An Achievable Rate Perspective