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Multiuser (MU) - multiple input multiple output (MIMO) techniques are attractive to increase the downlink spectrum efficiency since they allow a small number of antennas at each user station (STA). In MU-MIMO systems, the transmission performance is affected by the STA combination that is spatially multiplexed in the same frequency and same time slot. Thus, the AP needs to determine the optimum STA...
This paper proposes a space-time block coded (STBC) transmission with phase feedback for two-user multi-input multi-output multiple access channels (MIMO-MAC). In the proposed system, the phase feedback is transmitted to only one user, which reduces the overhead of the reverse link. We derive a closed-form solution for the proposed phase feedback, in order to maximize the overall received signal-to-interference-plus-noise...
Recently, there has been growing interest in secure communication via multi-antenna physical-layer designs. In this paper, we consider a transmit covariance design for a secrecy rate maximization problem under a multicast scenario, where a multi-antenna transmitter delivers a common confidential message to multiple single-antenna receivers in the presence of multiple multi-antenna eavesdroppers. This...
This paper investigates a network information flow problem for a multiple-input multiple-output (MIMO) Gaussian wireless network with K-users and a single intermediate relay having M antennas. In this network, each user intends to convey a multicast message to all other users while receiving K-1 independent messages from the other users via an intermediate relay. This network information flow is termed...
We consider several fading channel models for which we aim to maximize ergodic capacity assuming that channel state information (CSI) is available at both the receiver and the transmitter. We characterize the optimal power allocation structure in the single-input-single-output (SISO), multiple-input- single-output (MISO), and multiple-input-multiple-output (MIMO) models subject to both long-term and...
This paper addresses the linear processing issues for two way non-regenerative MIMO relay systems with multiple antennas at each node. Based on theoretical derivation, we first propose an optimal joint iterative linear processing scheme for the relay node and receiving source nodes, aiming to minimize the total mean squared error (MSE). The convergence of this iterative algorithm is proved in terms...
In this paper, we are interested in blind and semi-blind identification of multiple-input multiple-output (MIMO) channel for orthogonal frequency division multiplexing (OFDM) systems. Using the sparsity property of wireless channel impulse response, we propose an iterative method which minimizes a cost function to result from the combination of blind or semi-blind criterion and the lp norm. This norm...
This paper proposes a low-complexity signal detection algorithm for spatially correlated multiple-input multiple-output (MIMO) channels. The proposed algorithm sets a minimum mean-square error (MMSE) detection result to a starting point, and searches for signal candidates in multi-dimensions of the noise enhancement from which the MMSE detection suffers. The multi-dimensional search is needed because...
TDD multiuser downlink MIMO channels with delayed channel state information at the transmitter (CSIT) are considered. Block diagonalization is applied at the base station (BS). In order to cope with the inter-user interference caused by the delayed CSIT, we develop a novel capacity estimation method at first and then propose robust delayed CSIT aware multimode selection schemes based on the estimation...
The tree representation of the MIMO detection problem is illuminating for the development, interpretation, and classification of various detection methods. One method, based on the Dijkstra's search algorithm, pursues tree exploration according to a bounded, sorted list of tree nodes. Since sorting directly affects tree exploration and truncation in this tree-search method, it is critical to the performance...
It is well known that although the conventional sphere decoder (SD) achieves optimal maximum likelihood (ML) performance at a reduced complexity compared to the naive ML detector, the SD computational complexity varies with signal noise ratio (SNR) and is high in the low SNR region. This paper proposes a new idea to overcome these drawback that reduces the complexity significantly at a negligible...
The performance of an OFDM system can be improved by performing per-subcarrier antenna selection, which facilitates the exploitation of frequency and spatial diversity in the wireless channel. In this paper, we extend the concept of per-subcarrier antenna selection to a multiuser cognitive radio environment and present a practical subcarrier and antenna selection algorithm that exploits the multiuser,...
In wireless X networks where all transmitters send the independent messages to all receivers, the theoretical degrees of freedom (DOF) and interference alignment (IA) scheme for its achievability are given by Cadambe and Jafar. However, IA scheme for wireless X network may be infeasible in practice unless the transmitters have the perfect channel information. In addition, if the transmitter with single...
In this paper, we consider $K$-user MIMO Y channels where users simultaneously exchange messages with each other via an intermediate relay. Degrees of freedom (DOF) of this channel are not known in general. The investigation of the feasibility conditions of signal space alignment for network coding is an initial step for addressing this open problem. We verify that when user has antennas ($i=1,...
In MIMO-OFDM communications, the channel state information (CSI) of the forward link is needed for precoder design at the transmitter to achieve the maximal performance gains. In frequency division duplex (FDD) systems, the CSI estimated at the receivers needs to be fed back to the transmitters. Because of the limited network resources, there will be CSI feedback errors due to quantization, delay...
We consider a simple closed-loop spatial multiplexing architecture which can be incorporated into an outer system with off-the-shelf single-input single-output encoders/decoders. Instead of relying on transmitter-side channel state information for matching the layers of the multidimensional signal to the eigenmodes of the multiple-input multiple-output channel through a precoding, the eigenmodes with...
We investigate the source and relay precoding based on the minimum mean-square-error (MMSE) criterion for amplify-and-forward (AF) MIMO two-way relay systems. This joint design problem is shown to be a highly nonconvex optimization problem. In this work, we present two efficient design algorithms. The first one aims to minimize the total MSE of two users by alternatively solving three trackable sub-problems...
Block Diagonalization (BD) algorithm is a generalization of channel inversion scheme in multiuser multi-input multi-output (MIMO) broadcast channels. Although the BD algorithm is effective in removing interuser interference, it has a drawback that additional information should be delivered to the receiver. Recent work on BD with vector perturbation (VP) avoids the need for additional information and...
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