Uplink Downlink Rate Balancing and throughput scaling in FDD Massive MIMO Systems

摘要

In this work we extend the concept of uplink-downlink rate balancing tofrequency division duplex (FDD) massive MIMO systems. We consider a basestation with large number antennas serving many single antenna users. We firstshow that any unused capacity in the uplink can be traded off for higherthroughput in the downlink in a system that uses either dirty paper (DP) codingor linear zero-forcing (ZF) precoding. We then also study the scaling of thesystem throughput with the number of antennas in cases of linear Beamforming(BF) Precoding, ZF Precoding, and DP coding. We show that the downlinkthroughput is proportional to the logarithm of the number of antennas. While,this logarithmic scaling is lower than the linear scaling of the rate in theuplink, it can still bring significant throughput gains. For example, wedemonstrate through analysis and simulation that increasing the number ofantennas 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 ofthe number of receive antennas can be achieved even when the number of transmitantennas only increases logarithmically with the number of receive antennas.