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 Effect of Imperfect Channel Knowledge on a MIMO System with Interference

Abstract: A common model for transmission over wireless links is that of a multiantenna system affected by an additive interfering signal. In some scenarios of interest, such as when the interferer is located close to the transmitter and performs retransmission, interference may be learned by the transmitter, but remain unknown at the receiver. In this case, it is well known that, if transmitter and receiver have perfect channel state information (CSI), then a technique called Dirty Paper Coding (DPC) is able to fully mitigate the interference. This paper studies the impact of imperfect CSI on a multiple-input multiple-output (MIMO) system with interference and compares the performance of DPC with that of a scheme where interference is decoded at the receiver, which we refer to as beamforming with joint decoding (BF-JD). Unlike DPC, which models the interference as an "unstructured" random process, BF-JD exploits the fact that the interfering signal is a codeword of the interferer's codebook. It is demonstrated by analysis and numerical results that BF-JD provides advantages over DPC when CSI is imperfect at the transmitter but perfect at the receiver, whereas this is not true for the case of imperfect CSI at both transmitter and receiver.

Energy Efficient Pilot and Link Adaptation for Mobile Users in TDD Multi-User MIMO Systems

Abstract: In this paper, we develop an uplink pilot and downlink link adaptation approach to improve the energy efficiency (EE) of mobile users in time division duplexing (TDD) multi-user multiple input and multiple output (MU-MIMO) systems. Assuming reciprocity between uplink and downlink channels, the downlink transmission is based on uplink channel estimation. While more uplink pilot power ensures more accurate channel estimation and better downlink performance, it incurs higher energy consumption of mobile users. This paper reveals the relationship and tradeoff among pilot power, channel estimation, and downlink link adaptation that achieves the highest energy efficiency for mobile users. We show that the energy efficiency of different users can be decoupled because the downlink average throughput of each user is independent of the pilot powers of other users and energy-efficient design can be done on a per-user basis. Based on the analysis, we propose an uplink pilot and downlink link adaptation algorithm to improve the EE of mobile users. Simulation results are finally provided to demonstrate the significant gain in energy efficiency for mobile users.

Digital Predistortion for Multiuser Hybrid MIMO at mmWaves

Abstract: Efficient mitigation of power amplifier (PA) nonlinear distortion in multi-user hybrid precoding based broadband mmWave systems is an open research problem. In this article, we carry out detailed signal and distortion modeling in broadband multi-user hybrid MIMO systems, with a bank of nonlinear PAs in each subarray, while also take the inevitable crosstalk between the antenna/PA branches into account. Building on the derived models, we adopt and describe an efficient closed-loop (CL) digital predistortion (DPD) solution that utilizes only a single-input DPD unit per transmit chain or subarray, despite crosstalk, providing thus substantial complexity-benefit compared to the state-of-the art multi-dimensional DPD solutions. We show that under spatially correlated multipath propagation, each single-input DPD unit can provide linearization towards every intended user, or more generally, towards all spatial directions where coherent propagation is taking place, and that the adopted CL DPD system is robust against crosstalk. Extensive numerical results building on practical measurement-based mmWave PA models are provided, demonstrating and verifying the excellent linearization performance of the overall DPD system in different evaluation scenarios.

Open-loop beamforming MIMO communications in frequency division duplex systems

Abstract: Techniques are provided for wireless communication between a first wireless communication device and a second wireless communication device. At a plurality of antennas of the first wireless communication device, one or more signals transmitted by a second wireless communication device in a first frequency band are received. Beamforming weights are computed from information derived from the signals received at the plurality of antennas using one or more of a plurality of methods without feedback information from the second wireless communication device about a wireless link from the first wireless communication device to the second wireless communication device. The beamforming weights are applied to at least one transmit signal to beamform the at least one transmit signal for transmission to the second wireless communication device in a second frequency band.

Four-shaped 2 3 2 multi-standard compact multiple-input-multiple-output antenna system for long-term evolution mobile handsets

Abstract: The use of multiple-input-multiple-output (MIMO) antenna systems will be required by next generation wireless systems to achieve their high throughput data transmissions. In this work, the authors present the design and fabrication of a 2 - 2 MIMO antenna system for the 700-MHz band of the long-term evolution (LTE) wireless standard. The MIMO antenna system is based on a novel 4-shaped antenna geometry that is compact in size and covers two bands of operation. The dual-band 2 - 2 MIMO antenna system covers the 734-790-MHz and the 2307-2475-MHz LTE and industrial, scientific and medical (ISM) bands. It occupies an FR-4 material substrate size of 58-110-1.56-mm 3 . The antenna has frequency tuning capabilities without changing the over all size of the MIMO system substrate. Several isolation enhancements methods were investigated, and the values of the correlation coefficient (|ρ| max ) were within the LTE requirements. The maximum obtained gain for a single operating antenna at 770 and 2380 MHz was 5 and 4.5 dBi, respectively.