In order to enable frequency-division duplex (FDD) massive multiple-input-multiple-output (MIMO) systems, a beam-grouping, precoding and feedback scheme is proposed to reduce the downlink training overhead and channel state information (CSI) feedback overhead. When the number of transmit antennas on a base station (BS) is growing large, the downlink training overhead for CSI estimation and the CSI feedback overhead are growing tremendously. In addition to the downlink training overhead, simulation results show that the proposed method is able to reduce the feedback overhead without sacrificing the downlink achievable information rate (AIR). Furthermore, the proposed method has a lower computation complexity comparing with other methods in the recent literature.

One of the demands of the next-generation wireless communication systems is being supportive to asynchronous traffic types. In order to meet this demand, many waveform candidates for next-generation wireless communication systems have low out-of-subband emissions (OOSBE) of the transmitted signal, and the popular ones deploy either filtering or windowing at the transmitter. In this paper, a joint windowing and filtering multi-carrier waveform based on a generalized orthogonal frequency division multiplexing (OFDM) system is proposed. A joint window and filter optimization problem to minimize OOSBE is also formulated. The optimization problem is first divided into two solvable subproblems using interior-point methods, and then an iterative algorithm is proposed to obtain the optimal window and filter pair. Simulation results suggest that the proposed joint windowing and filtering waveform has an advantage in suppressing OOSBE or enhancing spectral efficiency, and is more robust to frequency asynchronism compared to waveforms deploying only either filtering or windowing.

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