Large-Scale MIMO Communications With Low-Resolution ADCs Using 16-ary QAM and Protograph LDPC Codes

In this paper, a new coded modulation model of the large-scale multiple-input multiple-output (LS-MIMO) system with low-resolution ADCs in conjunction with the superposed 16-ary QAM modulation is proposed to achieve high bandwidth efficiency. We derive the formulas to convert the channel model of the 16-ary QAM communication systems into an equivalent channel model of the binary phase-shift keying (BPSK) communication system so that the standard double-layer Tanner graph, whose complexity level is the second order of the number transmit only, can be employed to jointly detect and decode the information bit. Furthermore, we perform extensive computer simulation works to discover that the equal-weight superposition constellation is the best choice in the coded system as the system can enjoy the power gain of the constellation and exploit the error-correcting power of the protograph low-density parity-check codes (LDPC) previously designed for LS-MIMO channels. This constellation offers approximately about 1 dB coding gain over the conventional equal-distance constellation in all considered few-bit ADCs.