  This paper characterizes the performance of massive multiuser spatial
modulation MIMO systems, when a regularized form of the least-squares method is
used for detection. For a generic distortion function and right unitarily
invariant channel matrices, the per-antenna transmit rate and the asymptotic
distortion achieved by this class of detectors is derived. Invoking an
asymptotic characterization, we address two particular applications. Namely, we
derive the error rate achieved by the computationally-intractable optimal
Bayesian detector, and we propose an efficient approach to tune a LASSO-type
detector. We further validate our derivations through various numerical
experiments.
