  We focus on the signal detection for large quasi-symmetric (LQS)
multiple-input multiple-output (MIMO) systems, where the numbers of both
service (M) and user (N) antennas are large and N/M tends to 1. It is
challenging to achieve maximum-likelihood detection (MLD) performance with
square-order complexity due to the ill-conditioned channel matrix. In the
emerging MIMO paradigm termed with an extremely large aperture array, the
channel matrix can be more ill-conditioned due to spatial non-stationarity. In
this paper, projected-Jacobi (PJ) is proposed for signal detection in (non-)
stationary LQS-MIMO systems. It is theoretically and empirically demonstrated
that PJ can achieve MLD performance, even when N/M = 1. Moreover, PJ has
square-order complexity of N and supports parallel computation. The main idea
of PJ is to add a projection step and to set a (quasi-) orthogonal
initialization for the classical Jacobi iteration. Moreover, the symbol error
rate (SER) of PJ is mathematically derived and it is tight to the simulation
results.
