  We consider unsourced random access with MIMO receiver - a crucial
communication scenario for future 5G/6G wireless networks. We perform a
projection-based decoder analysis and derive energy efficiency achievability
bounds when channel state information is unknown at transmitters and the
receiver (no-CSI scenario). The comparison to the maximum-likelihood (ML)
achievability bounds by Gao et al. (2023) is performed. We show that there is a
region where the new bound outperforms the ML bound. The latter fact should not
surprise the reader as both decoding criteria are suboptimal when considering
per-user probability of error (PUPE). Moreover, transition to projection
decoding allows for significant dimensionality reduction, which greatly reduces
the computation time.
