Joint Modulation and Beamforming for MIMO Systems With 1-b DACs

To realize multiple-input multiple-output (MIMO) with low cost and low power consumption, the use of low-resolution digital-to-analog converters (DAC) is drawing significant interest. While previous studies on low-resolution DAC MIMO have focused on optimizing precoding for massive MIMO, this approach faces the limitation that the coarse resolution at the transmitter makes it difficult to construct a transmit signal close enough to the desired one when a small scale MIMO transmitter is considered as in IoT networks. To address this problem, we propose a new transmission framework that jointly performs modulation and beamforming. With the proposed scheme, a message symbol is directly mapped into a feasible transmit vector. We also develop a channel-adaptive mapping function within the proposed framework that minimizes error probability. Simulation results show that the proposed scheme can significantly improve the error performance.