837 research outputs found

    From Multi-Keyholes to Measure of Correlation and Power Imbalance in MIMO Channels: Outage Capacity Analysis

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    An information-theoretic analysis of a multi-keyhole channel, which includes a number of statistically independent keyholes with possibly different correlation matrices, is given. When the number of keyholes or/and the number of Tx/Rx antennas is large, there is an equivalent Rayleigh-fading channel such that the outage capacities of both channels are asymptotically equal. In the case of a large number of antennas and for a broad class of fading distributions, the instantaneous capacity is shown to be asymptotically Gaussian in distribution, and compact, closed-form expressions for the mean and variance are given. Motivated by the asymptotic analysis, a simple, full-ordering scalar measure of spatial correlation and power imbalance in MIMO channels is introduced, which quantifies the negative impact of these two factors on the outage capacity in a simple and well-tractable way. It does not require the eigenvalue decomposition, and has the full-ordering property. The size-asymptotic results are used to prove Telatar's conjecture for semi-correlated multi-keyhole and Rayleigh channels. Since the keyhole channel model approximates well the relay channel in the amplify-and-forward mode in certain scenarios, these results also apply to the latterComment: accepted by IEEE IT Trans., 201

    MIMO Multiway Relaying with Pairwise Data Exchange: A Degrees of Freedom Perspective

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    In this paper, we study achievable degrees of freedom (DoF) of a multiple-input multiple-output (MIMO) multiway relay channel (mRC) where KK users, each equipped with MM antennas, exchange messages in a pairwise manner via a common NN-antenna relay node. % A novel and systematic way of joint beamforming design at the users and at the relay is proposed to align signals for efficient implementation of physical-layer network coding (PNC). It is shown that, when the user number K=3K=3, the proposed beamforming design can achieve the DoF capacity of the considered mRC for any (M,N)(M,N) setups. % For the scenarios with K>3K>3, we show that the proposed signaling scheme can be improved by disabling a portion of relay antennas so as to align signals more efficiently. Our analysis reveals that the obtained achievable DoF is always piecewise linear, and is bounded either by the number of user antennas MM or by the number of relay antennas NN. Further, we show that the DoF capacity can be achieved for MN∈(0,Kβˆ’1K(Kβˆ’2)]\frac{M}{N} \in \left(0,\frac{K-1}{K(K-2)} \right] and MN∈[1K(Kβˆ’1)+12,∞)\frac{M}{N} \in \left[\frac{1}{K(K-1)}+\frac{1}{2},\infty \right), which provides a broader range of the DoF capacity than the existing results. Asymptotic DoF as Kβ†’βˆžK\rightarrow \infty is also derived based on the proposed signaling scheme.Comment: 13 pages, 7 figure

    MIMO Multiway Relaying with Clustered Full Data Exchange: Signal Space Alignment and Degrees of Freedom

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    We investigate achievable degrees of freedom (DoF) for a multiple-input multiple-output (MIMO) multiway relay channel (mRC) with LL clusters and KK users per cluster. Each user is equipped with MM antennas and the relay with NN antennas. We assume a new data exchange model, termed \emph{clustered full data exchange}, i.e., each user in a cluster wants to learn the messages of all the other users in the same cluster. Novel signal alignment techniques are developed to systematically construct the beamforming matrices at the users and the relay for efficient physical-layer network coding. Based on that, we derive an achievable DoF of the MIMO mRC with an arbitrary network configuration of LL and KK, as well as with an arbitrary antenna configuration of MM and NN. We show that our proposed scheme achieves the DoF capacity when MN≀1LKβˆ’1\frac{M}{N} \leq \frac{1}{LK-1} and MNβ‰₯(Kβˆ’1)L+1KL\frac{M}{N} \geq \frac{(K-1)L+1}{KL}.Comment: 13 pages, 4 figure
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