A multi-antenna, greedy, iterative, and quantized (MAGIQ) precoding algorithm is proposed for downlink channels. MAGIQ allows a straightforward integration with orthogonal frequency-division multiplexing (OFDM) for frequency selective channels. MAGIQ is compared to three existing algorithms in terms of information rates and complexity: quantized linear precoding (QLP), SQUID, and an ADMM-based algorithm. The information rate is measured by using a lower bound for finite modulation sets, and the complexity is measured by the number of multiplications and comparisons. MAGIQ and ADMM achieve similar information rates for Rayleigh flat-fading channels and one-bit quantization per real dimension, and they outperform QLP and SQUID for higher order modulation formats.

A low cost solution for constructing receiver signal points is investigated that combines a large number of constrained radio frequency (RF) frontends with a limited number of full RF chains. The constrained RF front ends have low cost and are limited to on/off switching of antenna elements and a small number of phases. Severe degradations are typically observed for multi-user MIMO for these simple on/off antenna arrays. A few full RF frontends are shown to compensate for the signal errors of the high number of constrained RF frontends for various scenarios. An algorithm for such a hybrid RF (HRF) system is developed that achieves performance close to that of exhaustive search with respect to the mean square error of the constructed receiver signals for Rayleigh fading and the WINNER 2 Urban Macro channel model.

Abstract-This paper presents a practical implementation of Noisy Network Coding (NNC) for half-duplex Two-Way Relay channels (TWRC). With Noisy Network Coding, the relay quantizes the incoming signals and forwards them digitally. The receivers do not try to recover the relay quantization index but the codewords that are embedded in the quantized signal. Our approach uses irregular repeat-accumulate low-density parity check (LDPC) codes to implement NNC. We derive the joint factor graph and the message passing rules for the corresponding joint iterative decoding scheme. Our simulation results confirm the performance advantages predicted by random coding arguments.