Secure Transmission Using Angle Reciprocity for TDD/FDD Massive MIMO Systems

Massive multiple-input-multiple-output (MIMO) systems provide high spatial resolution of the antenna array and the angle reciprocity of the massive MIMO channel holds in both time division duplex (TDD) and frequency division duplex (FDD) systems. In this paper, we propose a new secure strategy towards transmissions in massive MIMO systems. Each coherent time is divided into two stages. The angle signature of the uplink (UL) channel is estimated in the first stage and the downlink (DL) angle signature can be obtained using angle reciprocity. In the second stage, the angle signature of the DL channel is adjusted by spatial rotation according to the data to be transformed. Using the independent distribution of angle signatures of different channels, security performance can be enhanced.