Accurate channel state information at the transmitter (CSIT) is essential to achieve multiplexing gains in multi-user (MU) MIMO systems through precoding at the base station (BS). In conventional frequency division duplexing (FDD) systems, CSIT is obtained through downlink pilot-aided channel estimation and limited uplink feedback. However, the resources consumed by training and feedback become unacceptable in FDD massive MIMO systems due to the large number of BS antennas. In this paper, a one-bit feedback scheme is proposed to deal with this problem and realize massive MIMO gains in FDD systems. In contrary to the conventional scheme, estimation of instantaneous CSIT is no longer required in the proposed scheme. Instead, a number of predefined precoding vectors are probed in the training phase. Based on the received signal strength, each user feeds back one bit for each precoding vector indicating whether or not this precoding vector is suitable. In this case, the overhead used for training and feedback only depends on the number of predefined precoding vectors and the number of users. A low-complex user scheduling algorithm is further proposed at the BS based on the feedback bits. Numerical results have illustrated the superiority and effectiveness of our proposed scheme.
['Yingjie Zhang', 'Wei Feng', 'Ning Ge']
Dealing with large overhead in FDD massive MIMO systems: A one-bit feedback scheme