Comments on "Diversity ALOHA"

In a recent paper, a generalization of the slotted ALOHA random access scheme is considered in which a user transmits multiple copies of the same packet. In frequency diversity ALOHA, multiple copies of the same packet are simultaneously transmitted on different channels. We found the analysis for one of the proposed schemes, namely, channel selection without replacement, to be incorrect. These comments contain a counterexample to the published results and a corrected version of the analysis.