Performance Analysis for Traffic Offloading with MU-MIMO Enabled AP in LTE-U Networks

Abstract

In this paper, we investigate the effect of Multiple- User Multiple-Input Multiple-Output (MU-MIMO) enabled WiFi Access Point (AP) on the performance of traffic offloading in LTE-Unlicensed (LTE-U) networks. We first derive closed-form expressions for the downlink rates of both cellular user and offloaded user under limited Channel State Information (CSI) feedback, and obtain the sum-rate of the system. Then, we validate our analysis by numerical simulations and evaluate the system performance under different number of offloaded users and various CSI feedback lengths. The evaluation illustrates that there is a trade-off between the number of users offloaded to WiFi AP and the sum-rate of the system, and performance inflection point lies on the SNR conditions. Meanwhile, increasing CSI feedback length for the cellular Base Station (BS) or the WiFi AP alone helps increase the sum-rate of the system and rate of corresponding users, while it sacrifices the rate of users in the other network. These results suggest that adaptive utilization of antenna numbers on the MU-MIMO enabled AP based on SNR, and deciding CSI feedback length according to practical traffic demand of corresponding users are critical to achieve high rate performance for traffic offloading in LTE-U networks.