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.

Massive MU-MIMO-OFDM Downlink with One-Bit DACs and Linear Precoding

Abstract: Massive multiuser (MU) multiple-input multiple- output (MIMO) is foreseen to be a key technology in future wireless communication systems. In this paper, we analyze the downlink performance of an orthogonal frequency division multiplexing (OFDM)-based massive MU-MIMO system in which the base station (BS) is equipped with 1- bit digital-to-analog converters (DACs). Using Bussgang's theorem, we characterize the performance achievable with linear precoders (such as maximal-ratio transmission and zero forcing) in terms of bit error rate (BER). Our analysis accounts for the possibility of oversampling the time-domain transmit signal before the DACs. We further develop a lower bound on the information-theoretic sum-rate throughput achievable with Gaussian inputs. Our results suggest that the performance achievable with 1-bit DACs in a massive MU-MIMO- OFDM downlink are satisfactory provided that the number of BS antennas is sufficiently large.

MIMO-OFDM Wireless Channel Prediction by Exploiting Spatial-Temporal Correlation

Abstract: Channel prediction is an appealing technique to mitigate the performance degradation due to the inevitable feedback delay of the channel state information (CSI) in modern wireless systems. We first propose a general MIMO-OFDM channel prediction framework, which exploits both the spatial and temporal correlations among antennas. Then we derive two predictors which select data for auto-regressive (AR) predictors in different ways based on the proposed framework. The first predictor chooses the data set via minimizing the mean square error (MSE) of prediction model. The second predictor chooses the data in a heuristic way, which aims to reduce the computational complexity. Our algorithms can be applied to improve the precoding performance in multi-user MIMO-OFDM systems. Simulation results show that the proposed methods can overcome the feedback delay effectively, even when the channel changes rapidly.

Intrinsic capacity of the MIMO wireless channel

Abstract: This paper presents a new framework for the information-theoretic analysis of multipath multiple-input multiple-output (MIMO) wireless communications channels. The approach defines an upper bound on transmission that depends on the physical propagation scenario and transmit/receive antenna apertures but is otherwise independent of antenna properties. Transmit sources and receive sensors are abstracted in terms of spatial basis functions. The "intrinsic capacity" of the channel is defined as the maximum mutual information of the transmit and receive vectors over all possible modulations as well as transmit and receive basis functions and constrained by fixed average radiated power, limited transmit and receive volumes, and sensor noise. Definition of a "coherence matrix" allows a closed-form solution for the capacity under a new radiated power constraint.

Millimeter-Wave MIMO Radio Channel Sounder

Abstract: Nowadays, the need for high-data-rate-communication channels is increasing and will ineluctably continue to increase in the future. From a theoretical point of view, the multiple input multiple output (MIMO) approach seems to be one of the best solutions to provide such a high capacity. This paper presents a millimeter-wave MIMO channel measurement system developed in the Radio Laboratory of Helsinki University of Technology. The system is based on a sounder and virtual antenna arrays: The antenna arrays are obtained by two 2-D scanners which shift a single transmit antenna and a single receive antenna. Measurements in line of sight (LOS) and non-LOS are reported from what the MIMO channel capacity is calculated for various antenna array sizes. Furthermore, from the same measurements, the direction of departure and direction of arrival are estimated

Performance Study on a CSMA/CA-Based MAC Protocol for Multi-User MIMO Wireless LANs

Abstract: A multi-antenna access point (AP) can communicate simultaneously with multiple clients, however, this multi-user MIMO (MU-MIMO) capability is underutilized in conventional 802.11 wireless LANs (WLANs). To address this problem, researchers have recently developed a CSMA/CA-based MAC protocol to support concurrent transmissions from different clients. In this paper, we propose an analytical model to characterize the saturation throughput and mean access delay of this CSMA/CA-based MAC protocol operating in an MU-MIMO WLAN. We also consider and model a distributed opportunistic transmission scheme, where clients are able to contend for the concurrent transmission opportunities only when their concurrent rates exceed a threshold. Comparisons with simulation results show that our analytical model provides a close estimation of the network performance. By means of the developed model, we evaluate the throughput and delay performance with respect to different network parameters, including the backoff window sizes, the number of AP's antennas, the network size, and the threshold of the opportunistic transmission scheme. Performance optimization over key parameters is also conducted for the transmission schemes.