Krishna Sayana

Full-dimension MIMO (FD-MIMO) for next generation cellular technology

This article considers a practical implementation of massive MIMO systems [1]. Although the best performance can be achieved when a large number of active antennas are placed only in the horizontal domain, BS form factor limitation often makes horizontal array placement infeasible. To cope with this limitation, this article introduces full-dimension MIMO (FD-MIMO) cellular wireless communication system, where active antennas are placed in a 2D grid at BSs. For analysis of the FD-MIMO systems, a 3D spatial channel model is introduced, on which system-level simulations are conducted. The simulation results show that the proposed FD-MIMO system with 32 antenna ports achieves 2-3.6 times cell average throughput gain and 1.5-5 times cell edge throughput gain compared to the 4G LTE system of two antenna ports at the BS.

Fulfilling the promise of massive MIMO with 2D active antenna array

In this paper, we study practical 2-Dimensional (2D) active antenna array configurations for Massive MIMO systems and evaluate the system-level performance with the form factor at the base stations operating in cellular frequency band. To this end, we develop a 3-Dimensional Spatial Channel Model (3D SCM) to facilitate accurate performance evaluation and to build insights for system design. System-level simulation is conducted for various 2D antenna array configurations (8Hx8V, 8Hx4V) by using the 3D SCM developed. Simulation results show that 2-5 times cell average throughput gain and 1.5-9 times cell edge throughput gain can be achieved compared to the 4G LTE system.

DoA estimation and capacity analysis for 2D active massive MIMO systems

Mobile data traffic is expected to have an exponential growth in the future. In order to meet the challenge as well as the form factor limitation on the base station, two-dimensional (2D) “massive MIMO” has been proposed as one of the enabling technologies for future wireless systems. In 2D “massive MIMO” systems, a base station will rely on the uplink sounding signals to figure out the downlink spatial channel information to perform MIMO precoding. Accordingly, direction-of-arrival (DoA) estimation of the underlying three-dimensional (3D) channel at the base station becomes essential for 2D “massive MIMO” systems to realize the predicted capacity gains. In this paper, we will analyze the performance of DoA estimation based on ESPRIT methods and study its impact on the capacity of 2D “massive MIMO” systems. To be specific, for ESPRIT-type algorithms, we will derive the closed-form expressions for the mean square errors of the elevation and azimuth angle estimations. These results will be used to obtain design intuitions for 2D antenna arrays at the base station as well as the capacity of the underlying 2D “massive MIMO” systems.

Energy-Efficient Wireless Communications with Future Networks and Diverse Devices

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