J ul 2 01 5 1 Uplink Downlink Rate Balancing and throughput scaling in FDD Massive MIMO Systems

In this work we extend the concept of uplink-downlink rate ba lancing to frequency division duplex (FDD) massive MIMO systems. We consider a base station with l arge number antennas serving many single antenna users. We first show that any unused capacity i n the uplink can be traded off for higher throughput in the downlink in a system that uses either dirty paper (DP) coding or linear zero-forcing (ZF) precoding. We then also study the scaling of the system t hroughput with the number of antennas in cases of linear Beamforming (BF) Precoding, ZF Precoding, a d DP coding. We show that the downlink throughput is proportional to the logarithm of the number of antennas. While, this logarithmic scaling is lower than the linear scaling of the rate in the uplink, it can still bring significant throughput gains. For example, we demonstrate through analysis and simulation th at increasing the number of antennas from 4 to 128 will increase the throughput by more than a factor of 5. We also show that a logarithmic scaling of downlink throughput as a function of the number of receive antennas can be achieved even when the number of transmit antennas only increases logarithmic ally with the number of receive antennas. c © 2015 IEEE. Personal use of this material is permitted. Permi ssion from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishi ng this material for advertising or promotional purposes, c reating new collective works, for resale or redistribution to servers o lists, or reuse of any copyrighted component of this work in other works. I. Bergel is with Faculty of Engineering, Bar-Ilan Universi ty, 52900 Ramat-Gan, Israel; (e-mail: bergeli@biu.ac.il) . Y. Perets is with Marvell Semiconductor Israel, Azorim Park , Petach-Tikva, 49527, Israel; (e-mail: yoni@marvell.com ). S. Shamai (Shitz) is with the Department of Electrical Engin eering, TechnionIsrael Institute of Technology, Technio n City, Haifa 32000, Israel; (e-mail: sshlomo@ee.technion.ac.il ). Manuscript submitted July 9th, 2015. September 30, 2018 DRAFT 2