Nonlinear MIMO Communications under pi-Periodic Phase Measurements

Abstract

This paper proposes a halved-phase only multipleinput- multiple-output (HPO-MIMO) whose base station (BS) acquires pi-periodic phases of complex envelope signals by phase detectors. Because phases are directly extracted from the received radio frequency (RF) signals, the RF receivers of HPO-MIMO are simplified significantly, and enjoy much lower power consumption and fabrication cost in comparison to their correspondences in MIMO. However, existing MIMO baseband algorithms will not work in HPO-MIMO because the latter losses magnitude information completely and its phase observations suffer from pi-ambiguities. Practical baseband algorithms are developed for HPO-MIMO by firstly categorizing the multiuser detection (MUD) and channel estimation (CE) problems as generalized linear mixing ones under pi-periodic phase measurements, and then resolving the latter by a modified generalized approximate message passing (GAMP). In GAMP, the mean-variance messages involving phase observations are numerically updated by the importance sampling technique. Scale-and-polarity ambiguities among the CE and MUD results are removed based on the measurements from a conventional RF chain. Simulation results validate the effectiveness of the proposed algorithms, and compare HPO-MIMO with existing MIMO schemes thoroughly.