Multi-user MIMO

About: Multi-user MIMO is a research topic. Over the lifetime, 10265 publications have been published within this topic receiving 227206 citations. The topic is also known as: multi user mimo & MU-MIMO.

The Capacity of Gaussian MIMO Channels Under Total and Per-Antenna Power Constraints

Abstract: The capacity of a fixed Gaussian multiple-input multiple-output (MIMO) channel and the optimal transmission strategy under the total power (TP) constraint and full channel state information are well known. This problem remains open in the general case under individual per-antenna (PA) power constraints, while some special cases have been solved. These include a full-rank solution for the MIMO channel and a general solution for the multiple-input single-output (MISO) channel. In this paper, the fixed Gaussian MISO channel is considered and its capacity and optimal transmission strategies are determined in a closed form under the joint total and PA power constraints in the general case. In particular, the optimal strategy is hybrid and includes two parts: first is equal-gain transmission and second is maximum-ratio transmission, which are responsible for the PA and TP constraints, respectively. The optimal beamforming vector is given in a closed form and an accurate yet simple approximation to the capacity is proposed. Finally, the above results are extended to the MIMO case by establishing the ergodic capacity of fading MIMO channels under the joint power constraints when the fading distribution is right unitary-invariant (of which i.i.d. and semi-correlated Rayleigh fading are special cases). Unlike the fixed MISO case, the optimal signaling is shown to be isotropic in this case.

Dynamic subchannel and bit allocation in multiuser MIMO/OFDMA systems

Abstract: An adaptive subchannel allocation and modulation scheme is developed for multiuser multiple-input multiple-output (MIMO)/orthogonal frequency division multiple access (OFDMA) systems through some modification of the approach for OFDMA systems. In the multiuser MIMO/OFDMA system, there are SDMA subchannels, in which each user occupies a single-user MIMO subchannel, for each OFDM subcarrier. An optimal procedure for allocating the SDMA subchannels to users and loading bits to single-user MIMO subchannels is formulated as an integer programming (IP) problem. Then, a suboptimal algorithm that separately performs subchannel allocation and bit loading is proposed. Computer simulation results indicate that the performance of the suboptimal algorithm is reasonably close to that of the optimal IP.

Efficient Positioning in MIMO Radars With Widely Separated Antennas

Abstract: An algebraic closed-form solution for locating a moving target using a distributed multiple-input multiple-output radar system is proposed. The position and velocity of the target are estimated by presenting a two-stage weighted least squares algorithm. In contrast to existing research, the proposed estimator is shown analytically to be approximately unbiased and its variance is equal to the Cramer-Rao lower bound. Numerical simulations corroborate the theoretical studies and demonstrate the superiority of this algorithm over the existing methods.

Spatial decomposition of MIMO wireless channels

Abstract: In this paper a novel decomposition of spatial channels is developed to provide insight into spatial aspects of multiple antenna communication systems. The underlying physics of the free space propagation is used to model the channel in scatterer free regions around the transmitter and the receiver, and the rest of the complex scattering media is represented by a parametric model. The channel matrix is separated into a product of known and random matrices where the known portion shows the effects of the physical configuration of antenna elements. We use the model to show the intrinsic degrees of freedom in a multiantenna system. Potential applications of the model are briefly discussed.

Some Analysis in Distributed MIMO Systems

Abstract: The predicted capacity gain of a traditional co- located MIMO system is often severely limited in realistic propagation scenarios, especially when the number of antennas becomes large. Recently, a generalized paradigm for multiple-antenna communications, distributed MIMO, is proposed as a remedy. In this paper, through asymptotic large-system analysis, we provide solid justifications on the advantages of distributed MIMO over co-located MIMO when communication channels are subject to spatial correlation and shadow fading. We also exploit inherent macrodiversity in distributed MIMO to devise a cost- effective link adaptation scheme that achieves significant performance gain.